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THE CARRYING CAPACITY OF THE ICHETUCKNE2 SPRINGS AND RIVER
CHARLES H. DUTOIT
A THESIS -PFESENTED TO THE GRADUATE COUNCIL OF THE
UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
I would like to thank my committee members, Dr. Frank
Nordlie and Dr. Ariel Lugo, for their help and interest in
the research, as well as Dr. Gordon Godshalk, who reviewed
This research was a result of the concern and prelimi-
nary wcrk of Dr. John Ewel, my chairman. Dr. Ewel's guidance
was fundamental to the design of the study, its implementa-
tion, and write-up.
The Florida Department cf Natural Resources, the agency
which administers Ichetucknee Springs State Park, not only
provided a comfortable working atmosphere, but also directly
assisted in the study by constructing fenced exclosures and
cages. I greatly appreciate Major Hardee's cooperation, and
am grate-ful to Captain Krause and CaDtain Barret, as well as
the entire staff, for installing the underwater structures
and helping me in innumerable ways. T thank Lt. Don Younker
for arranging and participating in visits by university and
A number of University of Florida students assisted in
the research. I thank Joe Vargo and Bob Rice for the hours
they spent in the water, and Ellen Kane for the hours she
spent at the planimetry table. I was also ably assisted in
both the field and lab by the following students: Charner
Benz, Karen Hokkanen, Doran Pace, David Sample, Barbara
Harris, John Goelz, Patty Kohnke, Robert Somes, and Brian
I was short of help on several occasions. I am grate-
ful to those individuals who assisted at such times; Dennis
Ojima, a fellow graduate student, and the following members
of the Gainesville chapter of the Sierra Club: Ken Watson,
Steve Dalton, Kathy Haseman, William Girnat, Otho Peterman,
and Tim Pollack.
Alma Lugo and Gary Daught drafted the figures, Joan
Crisman typed the manuscript, and Marilyn DuToit prepared
the plant communities mnap.
The research contained in this thesis was supported
by a research grant to the University of Florida: "Carrying
Capacity of the Ichetucknee Springs and River System,"
P. 0. 10638, J. Ewel, Principal Investigator.
ACKNOWLEDGE:IMETS . . . . . .
LIST OF TABLES . . . . . . .
LIST OF FIGURES . . . ......
. . . . vii
* . . v L
LIST OF COLOR PLATES.
ABSTRACT . . ..
* . . . . . . x
. . xi
INTRODUCTION . . . . . . ..
Geology . . . . . . ..
Hydrology . . . . . . ..
Water Quality . . . ...
Morpholigy of the Ichetucknee
Vegetation . . . . .
Natural History. . . . ..
Cultural History . ......
History of Recreational Use. .
Profile of Park Users . ....
The Carrying Capacity Concept.
METHODS . . . . . . .
Base Map . . . . .
Standing Crop. . . . ..
Plant Damage Survey. ......
Plant Resistance . . .
Changes in Plant Cover . .
Plant Recovery . . . .
Response to Repeated Cutting
Fauna Survey . . . .
RESULTS . . . . . .. .....
Base Map ...... ...............
Types and Amounts of Recreational Use
Plant Damage Survey . . . ..
Plant Resistance . . . . .
C-hanes in Plant Cover . . . ..
Experimental Plots ... ..........
EXciosures . . . . . . .
Blue Hole Cages. ..............
Response to Repeated Cuting .
Fauna Survey . . . . . .
S. . . 34
S. . . 34
S. . . 35
. . . 37
. . . 31 /
DISCUSSION . . . . . . . .. .
Impact of Recreation on the Plant Communities
of the Headsprings Reach . . . ..
Impact of Recreation on the Plant Ccmmunities
of the Rice Marsh and Floodplain Reach .
Impact of Recreation on the Animals of
the River . . . . . . . .
The Carrying Capacity for Recreation . ....
* . 112
* ]--4 -
APPEND I CES
A. METHODS OF INDIRECT MEAL 7F_: Z;fT . . . .. .142
A-i. PERCENTAGE DRY WE- .. OF
NETTED PLANTS, PLANT DAMAGE SURVEY,
SUMMER, 1973. . ....
. . . . 2
A-2. RELATIO;;3-HI? OF CLUMP BIOHASS AND
LENGTH OF LONGEST LEAF,
Sagittaria kurziana . . . .
A-3. RELATIONSHIP OF LEAF WEIGHT
2AND LEAF LENGTH,
Sagittaria kurziana . . . .
A- NDRPECT AND DIPECT MEA SUREMENT
OF PLANT 3IOLASS IN
EXPERIMENTAL PLOTS . . . ..
B. AMOUNTS OF HOURLY USE AND DAMAGE,
BY SPECIES, PLANT DAMAGE SURVEY,
SUMMER, 1978 . . . . . . .
C. BIOMASS O ACUATIC PLANTS OF THE
ICHETUCKNEE RIVER . . . . . .
D. STA.IDING CROP OF AQUATIC PLANTS IN THREE
REACHES OF THE ICHETUCKNEE RIVER. . .
LANT COMMUNITIES OF THE ICHETUCKNEE RIVER.
BIOGRAPHICAL SKETCH. . . . . I . . . .
. . 1 4
. .. 145
I li 7
S. .156 -
. 156 -
* 157 -
LIST OF TABLES
1. Water quality of the Ichetucknee Springs ..... 6
2. Common species of the plant communities
of the Ichetucknee Springs State Park . . . 8
3. Regrowth of aquatic plants following
cutting or uprooting . . . . . . ... 57
4. Plant biomass and the number and weight
of invertebrates sampled in three areas
subject to varying degrees of recreational
disturbance . . . . . . . . .. 82
5. Types and numbers of fish in disturbed
(First Dock area) and undisturbed
(Headsprings Exclosure) sections of the
Headsprings Reach . . . . . . . .. 35
6. Recommended carrying capacities . . . .. .128
LIST OF FIGURES
1. Map of Ichetucknee Springs State Park ..... 2
2. Annual park attendance, 1973-74 to 1977-78 . 12
3. Location of netting stations and
experimental plots . . . . . . . 23
4. Location of fenced exclosures, map-remap
sections, and fauna survey sites . . . .. .25
5. Location of cages in the Blue Hole . . .. 29
6. Types and amounts of recreational use,
January-August, 1978 . . . . . . . 3
7. Winter plant damage related to total number
of users and to number of divers .. . . .. .. 8
8. Damage, by species, related to number of
divers, Winter, 1977-78 . . . . .... 40
9. Percent total damage and percent of total
standing crop of species netted in
Winter, 1977-78 . . . . .. . . . 43
10. Amounts of daily plant damage and daily use
in three reaches, Summer, 1978 . . . .. 45
Ii. Amounts of hourly plant damage and use in
three reaches, Summer, 197'S. . . . .... 47
12. Number of users and fractional loss
of standing crop, for three reaches.
Summer, 1978... . . . . . . . 48
13. Percent total damage and percent total
standing crop for plant species in
three reaches, Summer, 1978. . .......... .50,
LIST OF FIGURES
14. Resistance to tearing and uprooting . .
15. Seasonal changes in plant cover in three
sections of the Headsprings Run . . ..
16. Standing crop and recovery of Sagittaria
leaves following cutting . . . . .
17. Standing crop and clump recovery of
Sagittaria following uprooting . . .
18. Number of Sagittaria clumps counted in
quadrats following uprooring, and standing
crop (no. of clumps) in undisturbed quad-
rats sampled in February and June, 1978.
19. Standing crop and regrowth of Mvyriophylum
following cutting . . . . . ..
20. Change in plant cover, Site A, Headsprings
Exclosure, 6-12-78 to 8-24-78 . . . ..
21. Change in channel profile, Site B, Headsprings
Exclosure, 8-3-78 to 10-12-78 . ......... .
22. Change in plant cover, Second Dock
Exclc3ure '7-25-78 to 10-26-78 . . . .
23. Growth of Zizania and Chara, Second
Dock Exclosure . . . . . . . .
24. Characteristics of Sagittaria leaves sampled
both inside and outside of Jug Cage . . ..
25. Sagittaria colonization and characteristics
of leaves sampled inside and outside of
the Run Cage . . . . . . . . .
26. Sagittaria leaf recovery in plots
subjected to repeated cutting .
27. Amounts of daily use and plant damage,
Headsprings Reach, Summner, 1978 . . . ..
. 1 52
. . 80
LIST OF FIGURES
28. .Amounts of hourly use and plant damage
for five survey days, Headsprings
Reach, Summer, 1978 . . . . . . . 91
29. Species damage in the Headsprings
Reach, April to August, 1973 . . .. . . 98
30. Amounts of Sagittaria torn and uprooted
over varying levels of diving activity
and amounts recovered in plots experimentally
subjected to tearing and uprooting . . .. .103
31. Size distribution of Sagittaria clumps
uprooted by divers compared to the size
distribution of clumps sampled from the
Devil's Eye Exclosure, which receives no use .i0
32. Damage Index for three reaches cf the
Ichetucknee River . . . . . ... . . 115
33. Damage Index related to physical
characteristics of the river and
behavioral characteristics of use . . ... .117
34. Fractional loss and fractional recovery
rate of Sagittaria, Myriophyllum, and
Vallisneria . . . . . . . . . 121
LIST OF COLOR PLATES
1. Headsprings Exclosure, July and
November . . . . . . . . . . .7
2. Tuber impact on thel Blue Hole . . . . 95
3. Sagittaria bed, April and August, 1973 .... . 97
4. Channel erosion in the Second Dock Area ... .. .11i
Abstract of Thesis Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Master of Science
CARRYING CAPACITY OF THE ICHETUCKNEE SPRINGS AND RIVER
Chairman: John Ewel
Major Department: Botany
A study was conducted in 1977-78 to determine the types and
amounts of recreational use that the communities of Ichetucknee Springs
and River can sustain without causing irreversible damage. I measured
the kinds and amounts of damage which result from swimming, canoeing,
diving and tubing, and monitored the recovery of aquatic communities.
A carrying capacity, defined as the rate of use at which damage is
equal to the natural ability of each plant community to recover, was
recommended for each type of use.
Tubing is, numerically, the most important form of recreation at
the Ichetucknee Springs; 3000 people per day (the present limit)
regularly float down the River on tubes on summer weekends, and week-
day use generally exceeds 1000. The reach between the Headsprings and
the Blue Hole sustains the greatest impact, both in terms oi channel
and bank erosion and in terms of percentage loss of vegetation. Tram-
pled plant beds support less shrimp and crayfish than healthy beds,
and disturbed areas contain fewer types and numbers of fish than un-
disturbed areas. The middle and lower reaches lose proportionally less
vegetation and, with some local exceptions, are not eroded by recre-
national use. Channel width and depth do not directly account for these
differences, but changes in the behavior of users, who become more
passive as they progress downstream, may be the most important factor.
A limit of 100 tubers per hour is recommended.
In winter, diving groups (2 to > 50 individuals) visit the Park
to snorkel in the River and dive in the Blue Hole. Plant damage in-
creases exponentially as diving activity in the Blue Hole increases.
Crowding in the pool, poor group control, and trampling along the edge
of the Blue Hole run account for this accelerated impact. The Sagit-
taria community, which comprises 75% of the total cover in the Blue
Hole, sustains the greatest damage. Recolonization of disturbed areas
by Sagittaria is very slow in winter; the amount of regrowth in a day
is about equal to the amount of damage caused by 50 divers in four
hours. On busy days, when as many as 100 divers visit the Park, dam-
age may exceed recovery by an order of magnitude. To save the natural
ecosystems in Blue Hole, a limit of 12 divers per hour should be en-
Swimming and canoeing are minor components of recreational use at
the Park. Although swimming, and the trampling that accompanies it,
result in loss of cover and bottom erosion, this activity is largely
confined to the Blue Hole and Headsprings pool. Canoeing appears to
have little impact onr submerged plant communities; paddles cause little
stem and leaf breakage and practically no -iprccting. If the mount of
swimming and canoeing does not increase substantially, no limit need be
placed on these activities.
Ch. ai i i'
../ Chai r -an
The Ichetucknee Springs State Park, located in norTh-
central Florida, is one of the State's most unique resources:
a clear, spring-fed river which winds through hammock, open
marsh, and floodplain forest. The Park, comprising an area
of 910 hectares (2,250 acres), straddles southeast Columbia
County and southwest Suwanee County; the Ichetucknee Piver
forms a natural boundary between the two counties. The
land for the Park was Durchased in 1970 by the State of
Florida from a British mining firm, the Lcncala Phoschate
The Ichetucknee Sorings State Park (Fig. 1) lies in the
Coastal Lowlands, a physiographic region defined by surface
elevations less than 30 meters (100 feet) above mean sea
level and locally characterized by karst topography, evi-
dent in the numerous springs, sinkholes, and limestone out-
crops in the area. A geologic section in the area of the
Park would show a surface mantle of sand and clay overlying
a thick bed of limestone, about 915 meters (300] feet) deep,
which rests unconformabiv over Paleozoic basemen- rock. The
up-er layers of limestone seCiment. of la-te Eocene ace, are
ccl --cLively called the OcalA group, which, being highly
ICHETUCKNEE SPRINGS ~
STATE PARK 0 ETU"KE a N
Entry Do IC HE HAD
_1._ 16 KILOMETERS 2.1
0 I/2 I MILE HEADSPRINGS .
-= = ROADS 0 U S. ROUTE @ STATE ROUTE B LUAC. BUE HOLE
\POWER LINE CUT ---PARK BOUNDARY S( f H
PLANT COMMUNITY KEY ISSION S,
I/EVILS EE SPRIN
H AMMOCK _i _(/
MARSH -- -- MSH-
ES SWAMP FOREST I I I
PINE PLANTATION I i.p Ns
i-, UPo( P ,'nt L /"Pze',Mon
j__ ^ i-~~and.ng ^ 3 '
Figure 1. Ma of ch-ietucknee Springs State Park.
Map was prepared frcnm aeria! photcgra-hs
i.S.D.A., a3-3)-ag ) and 'J.S.G.S. zopo-
graphic quadrangle (Hildreth, FL, !968).
permeable, forms the dominant water-bearing formation in
north-central Florida. This acuifer is overlain by Miocene
deposits, the Hawthorn and Alachua formations, which con-
sist of clay, phosphatic sand, and discontinuous beds of
limestone. A surface deposit, predominantly consisting of
unconsolidated sand, was laid down over Miocene sediment
during the interglacial periods of the Pleistocene when sea
level ranged 7.5-30 meters (25-100 feet) higher than ar
present (,Meyer 1962).
The major geologic features of the Coastal Lowlands
can be observed at the ichetucknee Springs State Park.
Ocala limestone outcrops in bluffs along the river; Miocene
deposits containing phosphatic ore are exposed in mining
pits in the hammock; and Pleistocene sands are everywhere
evident in the Sandhill community at higher Park elevations.
The Ichetucknee River lies in an ancient basin, he
Tchetucknee Trace, which is roughly defined by the 50 foot
contour level on U.S.G.S. topographic maps of south
Columbia County. Rose Creek and Clay Hole Creek, in the
vicinity of Lake City, form the headwaters of the basin.
Surface flow from these creeks is intercepted by sinkholes
near the town of Columbia which is located about 16 kilo-
meters (10 miles) southwest of Lake City. Here, the cap-
tured surface flow mingles with groundwater and eventua.ll.-.
emerges at the Ichetucknee Springs.
Geologists believe that the Ichetucknee Trace developed
along fracture lines associated with the uplift of the
Peninsular and/or Ocala arch (Meyer 1962).
Ocala limestone outcrops, or lies at or just below the
surface, in the Ichetucknee Trace. Ground water is dis-
charged in areas such as the Ichetucknee Springs where the
piezometric surface, or hydraulic head of the aquifer, is
higher than the topographic surface. Geologists recognize
two sources of discharge in the Ichetucknee Springs:
1. ground water from regions of higher artesian head in
northern Columbia County and surrounding areas, and 2.
local rainfall which enters the aquifer through sinkholes,
limestone outcrops, or permeable sand deposits (Meyer 1962).
The discharge of the major springs of The Park is shown
in Figure I. The average discharge of the Ichetucknee River,
measured at the Highway 27 Bridge, is 10.1 m 3/sec. (353
c.f.s.), which ranks sixth in magnitude among Florida springs.
The minimum discharge recorded over a period extending frcm
1917 to 1972 was 6.8 .3/sec. (241 c.f.s.), which is 33%
below average discharge. The maximum discharge during this
period was 16.4 m, sec. (578 c.f.s.), 611 above the average
flow (Rosenau and Faulkner 1974).
In Columbia County, groundwater rise generally lags
five months behind the period of maximum rainfall, which
occurs during the summer months (Meyer 1962). Small dis-
charge increases, of shcrT duration, result from local
recharge by rainstorms.
The water temperature of the Ichetucknee River remains,
year round, about 220C, which is approximately equal to the
mean annual air temperature of the region. Table i shows
the chemical characteristics of the water from a 1946
analysis (Ferguson et al. 1947). Inspection of this figure
shows that the river water is alkaline (pH 7.7) and that
calcium and bicarbonate are the two most important dissolved
mineral ions. Color was measured to be 0, indicative of the
remarkable clarity of the spring water.
Morphology of the Ichetucknee River
Three reaches can be distinguished in the Ichetucknee
River. The Headsprings, or Ichetucknee Springs, with a
discharge of 1.3 m /sec. (45 c.f.s.), is the source of the
"Headsprings Run,"1 defined as that portion of the river
between the Headsprings and the Blue Hole (Fig. 1), This
reach is relatively narrow and shallow, with an average
width of about 10 meters and depth of 1 meter, and is par-
tially shaded by hammock vegetation growing on the banks.
The section of the river between the Blue Hole and
Mill Springs, about 1.6 kilometers (1 mile) in length, is
called the "Rice Marsh." Discharge from the Jug Springs at
Blue Hole (about 2.4 m i/sec.), Mission Springs ,(1. mii/sec.),
and Devil's Eye Spring considerably strengthens the river
1 The ''Heasprings Reach," a term used throughout this
report, includes the "Headsprings Run" and the
Headsprings an:d Blue -ole.
Table 1. ',ater quality of the Ichetucknimee Springs. Data
are from Ferguson et al. (1947).
May 17, 1946
Parts Per Million
Silica (SiO2) 9.1
Iron (Fe) .03
Calcium (ca) 58
.Mai-nes iuLm (Mg) 6.6
Sodium (Na) 3.1
Potassium (K) 3
Bicarbonate (HCO3) 200
Sulfate (SO4) 8.
Chloride (Cl) 3.6
Fluoride (F) .1
Nitrate (NO3) 1.0
Dissolved Solidsa 1 88
Total Hardness as CaC0 172
Carbn Dioxide (CC2) 6
Color ) 0
Specific Conductance KxlO5 at 25C) 32.9
a. In a l.92-7, analysis by U.S. Geological Survey, dissolved solids
measured 170 -g/1 (Rosenau and Faulz:er 1974).
b. Color units are not specified by Ferguson at al. Their measurement
is based on a graduated scale of colored disks and is presented here
to indicate the relative clarity of the water. Some swamp water
measures 200C or more on the colored diask scale.
flow in this reach. A short distance below Blue Hole the
river widens to about 60 meters with an extensive marsh of
wild rice Zizania auatica, bordering an open channel, which
is 15 to 20 meters wide and about 2 to 3 meters deep.
The "Floodplain Reach" is that portion of the river
between Mill Springs and the point of discharge of the
Ichetucknee River into the Santa Fe River. In this reach
the river is 15 to 20 meters wide and 1-2 meters deeD and
is bordered by floodplain forest and limestone bluffs.
Three life forms of vascular plants are common in che
open channel and floodplain of the Ichetucknee River:
submerged macrophytes in the open channel, emergent macro-
phytes in the marsh, and arboreal vegetation in the flood-
plain swamp. Table 2 shows the common species of the river
and the upland communities. Sandhill vegetation occupies
about 273 hectares (675 acres), or 30% of the Park area, and
grows on Pleistocene sand deposits at higher elevations o
the Park. Hammock trees grow in the rich calcareous soil of
river banks and cover about 590 hectares (1460 acres), or
65% of the total area. River plants and floodDlain forest
occupy about 5% of the Park.
The Indian word ?T chetucknee" means "beaver ocnd."
Ironically, beaver are rarely observed in the Park, and in
fact, had not been seen for decades until the fall of 1977
Table 2. Common species of the plant communities of the
Ichetucknee Springs State Park.
when one was observed in the Headsprings Run during the
early days of our research. The long absence and recent
return of the beaver is only one of the interesting features
of the natural history of the Ichetucknee Springs. A monkey
has been reported; wild turkey, bobcat, and deer are common-
ly seen in the woodlands, and a great variety of birds and
fish, as well as otter, inhabit the marshes and river.
Less conspicuous features of the Springs are Eocene
fossils of mollusks, echinoderms, and foraminifera that are
embedded in submerged limestone banks and emergent bluffs.
The bones of terrestrial vertebrates of the Pleistocene
have been found in alluvial deposits along the Ichetucknee
River. The remains of an extinct bison were unearthed
during the construction of a canoe ramp in 1973, and the
bones of mammoths, mastodons, and a Pleistocene lion, Felix
atrox, have been recovered at the Park.
Anthropologists believe that the Utina Indians, a tribe
of the Western Timucuans, lived in the area of the Park in
prehistoric times. In 1950, John Goggin of the Florida
State Museum, excavating a refuse mound, unearthed evidence
of a Spanish-Indian contact on the banks of Ichetucknee
River. The recovery of both European and Indian artifacts.
including a lead cross and ceramic vessels, suggested that
a Spanish church formerly occupied this site, now known as
Mission Springs UDeagan 1972). The remains cf a grist mill
and earthworks at Mill Springs indicates more recent
occupation of the riverbanks.
History of Recreational Use
The type and amounts of use of the Ichetucknee River
and woodland has changed considerably from pre-Park days to
the present. Ferguson et al., in a 1947 publication, The
Springs of Florida, relate that the Headsprings was used
for watering stock, as well as for swimming and picnicking.
Fishermen and hunters frequented the river and uplands and
camped on the wooded river banks. The river was additional-
ly subject to unregulated use by local residents and college
students, whose beer cans were conspicuously evident prior
to a cleanup by the State. Under the administration of the
Department of Natural Resources, the Park has instituted a
number of regulations designed to limit environmental abuse,
and has developed facilities to increase access and visitor
comfort. A user now pays a 25 admission charge; parking
for cars and buses is provided at the Headsprings area, and
trails and docks provide easy access to the river. Camping
is prohibited, and visitors are not allowed to carry food
or beverages on the Ichetucknee River. A shuttle bus,
operating from the Wayside Park on Highway 27, transports
users back to the Headsprings area at the end of a run.
The Ichetucknee Springs under State ownership has
become an extremely popular resource; its facilities, clean-
liness, and recreational opportunities appeal to family
groups, community organizations, tourists, dive clubs, and
the general public. As shown in Figure 2, the amount of
Park use has increased considerably during this decade. The
amount of annual use remained fairly constant until 1976,
when there was a 35% increase (about 50,000 users) over the
previous year's attendance. On July 4, 1977, nearly 5000
tickets were sold at the main gate. This was the largest
amount of daily use ever recorded.
Profile of Park Users
In 1974 and 1975 a survey was conducted by the Florida
Department of Natural Resources at the Ichetucknee Springs
State Park to investigate the impact of crowding on a user's
enjoyment of the experience. In addition to providing infor-
mation on its primary objective, the survey furnished a
sociological sketch of Park users.
Male visitors outnumber female visitors by a factor of
two or more. Approximately 45% of the Park users are
between the ages of 19 and 26; 10% are under 18, and about
25% between 26 and 35. The city of Gainesville, which has
grown rapidly during this decade, is the largest single
source of users (35% of total), followed by Jacksonville
(about 20%), and the Fort White area (about 10%). An inter-
esting survey statistic shows that, on the average, there
are nearly nine individuals per tubing party. This fact is
likely accounted for by the large family groups, college
fraternities, and community organizations which regularly
visit the Park.
1973-74 1974-75 1975-76 1976-77 1977-78
Annual park attendance, 1973-74 to
1977-78. Data are from annual attendance
records which are based on monthly use
totals from July through the following
The Carrying Capacity Concept
The signs of environmental deterioration that have
accompanied increased use of the Park in recent years have
prompted the Department of Natural Resources to impose a
limit of 3000 users per day, as well as to sponsor research
on the "carrying capacity" of the Ichetucknee Springs and
River. The concept of a recreational carrying capacity has
become increasingly popular with resource managers; however,
it is not always clearly defined, and has been difficult to
apply. Lime and Stanky (1971, p. 175), in a review of the
development of the concept, provide a good definition:
The recreational carrying capacity is the
character of use that can be supported over a
specified time by an area developed at a certain
level without causing excessive damage to either
the physical environment or the experience of
In their definition, the authors emphasize the need for a
multi-dimensional concept which includes three basic consid-
erations: 1. user satisfaction, 2. environmental impact,
and 3. the objectives of resource managers. The theoretical
sources and applications of research in each of these three
areas is summarized in the following discussion.
The most comprehensive study to date on user satisfac-
tion is the nation-wide survey conducted by the Outdoor
Recreation Resources Review Commission (ORRRC 1962) on the
preferences and perceptions of users of State anrd National
Parks. A number of other studies on visitor attitudes have
been conducted on a regional or local scale, such as the
study by Lucas (1963) on the perception of "wilderness" by
different types of users of the Boundary Water Canoe Area in
northeast Minnesota, and locally, the survey conducted at
the Ichetucknee Springs State Park in 1974-75. Briefly sum-
marized, the results from these surveys demonstrate that
Park users vary greatly in their recreational preferences, in
their perception of environmental quality, and in their
tolerance to interaction with other recreationists.
The recreational carrying capacity, from the viewpoint
of user satisfaction, has been defined as "the maximum num-
ber of use-units (people, vehicles, etc.) that can utilize
the available recreational space at one time for some
activity while providing a 'satisfactory' experience for the
user" (Lime and Stanky 1971, p. 174). The most popular
application of this definition is the "space standard," a
concept developed by the U.S. Forest Service which defines
the amount of topographic space that a wilderness user
needs in order to have a satisfactory day of recreation.
The "space standard" for wilderness areas of National
Forests is 3 acres per person per day (Douglas 1975).
The assumptions implicit in the concept of a "space
standard" are similar to those inherent in the theory of
the carrying capacity of natural populations. According to
this theory, introduced by Verhuist in the 18th century,
and mathematically formalized by Lotka, there is a limit
to the growth of natural populations due to density depen-
dent interactions and shortages of available resources
(Krebs 1972). The concept of a carrying capacity for user
satisfaction is analogous to the concept of a growth limit
on natural populations in the sense that a "space standard"
ideally defines a level of use that an area can sustain
above which density-dependent interactions (user-user
contact) or environmental deterioration (recreational con-
sumption of the resource) strongly detract from the enjoy-
ment of the recreational experience. Although a "space
standard" based on user satisfaction is a useful concept,
it has a fundamental weakness. Lime and Stanky comment:
"space standards based on user satisfaction have generally
failed to incorporate the level of use the physical environ-
ment can tolerate over a given time before serious damage
results" (Lime and Stanky 1971, p. 175).
Recreational Impnact on the Resource
The majority of research on impact of recreational use
on natural ecosystems has been concerned with the effect of
hikers, campers, and picnickers on the vegetation and soils
of State and National Parks. Investigations of recreational
impact on lakes and rivers have been primarily limited to
studies on the environmental effect of outboard motor dis-
charge and watershed pollution (Stanky and Lime 1973).
Basically, two approaches are used in research on recreational
impact. One approach involves monitoring use levels and
measuring environmental damage in actual recreational
situations. The other measures environmental damage under
controlled levels of simulated impact, such as Wagar's
(1964) use of a tamp to simulate trampling on foot paths.
Recreational studies may be short term, such as Burden and
Randerson's (1972) study on the effect of seven days of
recreational use on a newly developed trail, or long term,
as exemplified by Lapage's (1967) three-year study on plant
cover changes at a New Hampshire campground. Historical
investigations, such as Gibbensand Heady's (1964) work at
Yosemite, use time-series photographs, naturalist writings,
survey reports, and interviews to determine environmental
change over extended periods of time.
The results of recreational impact studies have been
used by the U.S. Forest Service to formulate a Ground Cover
Index, which equates ground cover at a campsite with:
1. the amount of recreational use in the area, and 2. site
characteristics, such as slope and depth of B horizon.
A problem with recreational impact studies is the
element of uncertainty about the level of damage that a
resource can tolerate without causing irreversible deterio-
ration of a site. The consideration of this problem in*
other fields of ecology has led to the development of such
concepts as ecosystem stability, resistance, and resilience
(Bishop et al. 1974). Simply stated, these concepts are
concerned with: 1. the ability of an ecosystem to resist
perturbation, 2. the rate and direction of recovery follow-
ing disturbance (resilience), and 3. the threshold limit,
or carrying capacity, beyond which the system is unable Tc
return to its original condition.
Concepts of this nature underlie a great deal of carry-
ing capacity research and are implicitly acknowledged, if
not openly recognized, in many resource management decisions.
Wagar (1964), in his tamp experiments, found that the
"resistance" of terrestrial vegetation to trampling was
partially a function of life form; grasses and woody vines
are generally less vulnerable to trampling than dicotyledo-
nous herbs. Resource managers commonly use a variety of
techniques, such as paving heavily-used walkways and ferti-
lizing and irrigating, to increase the "resistance" of a
site (Lime and Stanky 1971). In England, Schoefield (1967)
determined the "carrying capacity" of a dune walk to be 7500
users per season. Increasing the amount of use beyond this
threshold limit resulted in soil exposure and dune erosion.
Schoefield also considered the "resilience" of this dune
system when he estimated that an eroded footpath would
recover in four years if protected from further use.
Objectives for the Management of Recreational Resources
The management objectives for a recreational area
should be ideally based on 1. user demands and preferences,
2. park philosophy, and 3. the durability of the resource.
The park manager's problem of balancing recreation with
preservation is similar to that of fisheries or agricultural
enterprises where overexploitation may deplete the resource.
The concept of "optimum sustained yield" as a management
objective for the fisheries and agricultural industries may
be just as applicable to the management of recreational
areas. The "sustained yield" concept is implicit in the
following statement by the Outdoor Recreation Resources
Review Commission (1962, p. 1) on the goal of maintaining
"site quality" in recreational areas.
site quality. .the extent to which an area
provides its intended amounts and kinds of
recreation opportunities while being main-
tained in a long term productive condition.
The objective of this research was to determine the
amount of environmental change that results from varying
types and amounts of recreational use. Information of this
nature should greatly aid Park management in defining a
carrying capacity that is consistent with their objectives
of preserving the resource and meeting the public demand for
recreation. To fulfill the stated goal of this research,
answers to the following questions are provided.
1. What is the relationship of plant damage to:
--the number of users?
--the type of use?
--the distribution of use, both daily and
2. What areas of the spring system and river, and
which plant communities, are most disturbed by
3. What is the rate and kind of vegetation
recovery following disturbance?
4. What impact does recreational use have on the
animals of the springs and river?
5. Is the damage to plant and animal communities
reversible or irreversible?
The Ichetucknee River was mapped to determine the
distribution of aquatic macrophytes. The method of mapping
varied over the river, depending on the width and deoth of
the major reaches. The Headsprings Run, about 500 meters in
length, was mapped in 10-meter sections using two fiberglass
meter tapes and a meterstick. One meter tape was stretched
across the run, perpendicular to the main channel. A second
tape was stretched parallel to the first, 10 meters down-
stream. The plant beds in each section were mapped by a
wading observer who used the tapes to chart bed position and
the meterstick to measure the dimensions of the bed. Depth
was also measured in each section and the type of bot-com
sediment noted. The Blue Hole pool and run were mapped in
a similar fashion, except the tapes were 5 rather than 10
The portion of the river extending from the Blue Hole
outlet to the Wayside Park Landing was mapped using a boat,
as the channel was too deep to wade. A 20-meter anchor
rope, marked at 5-meter intervals, served as a position
reference by which an underwater observer charred the major
plant beds. An assistant working from the boat 7ock deozh
soundings, measured river width with extension poles, and
recorded the compass direction of the main channel in each
Samples of each of the major plant species were clipped
or uprooted from quadrats of varying sizes. The samples
were returned to the lab, oven dried (three days at 70C),
and weighed. The standing crop for each species was esti-
mated by multiplying its sample weight/m by its cover value
(m ), which was measured by planimetry of the base map.
Plant Damage Survey
The one-way flow of a river provides a researcher with
an opportunity to directly measure the impact of trampling
on aquatic vegetation. The relationship of plant damage to
the amount of use can be estimated by counting users and
collecting river drift simultaneously. This method was used
throughout the study to measure the amount of damage to
river plants over varying types and levels of recreational
The impact of winter recreation was measured by sampling
plant damage both on busy weekends and quiet winter weekdays
over a period extending from December, 1977, to March, 1978.
On sampling days, the researcher and his assistant collected
drift for a four-hour period from a point in the river
located just below the Blue Hole outlet (Station 1, Fig. 3).
Handnets were used to retrieve plant clumps and fragments,
and recreationists entering Blue Hole or passing the collec-
tion station were counted and categorized according to type
of use (scuba diver, snorkler, cancer, tuber, or swimmer).
The netted material was returned to the lab, sorted accord-
ing to species and type of damage (torn or uprooted), oven
dried (three days at 70C), and weighed.
During the summer (April through August), when recre-
ationists range over the entire springs system and river,
plant damage was sampled one day each month from three
different stations situated at the downstream end of each
major reach. At Station 1, located just below Blue Hcie Run
(same station used in winter survey), plant material was
netted by two wading assistants, while a third counted and
categorized users. At Stations 2 and 3, located at Mill
Springs and just below Wayside Park Landing respectively,
drift was netted from either canoe or raft, as the depth of
the channel prohibited wading. To assess the impact of rate
of use (number of users per unit time), plant material was
netted and the number of users recorded on an hourly basis
throughout a sampling day.
At the end of a survey day, all the collected plant
material was returned to the lab, and, as was done in the
Cedar Head Spring
Blue Hole Spring
Ceviis Eye Soring
Figure 3. Location of netting stations and
experimental plots. The three netting
stations are identified by number, the
experimental plots by genus name.
winter survey, sorted according to species and type of
damage. As the available drying ovens could not accommodate
the large volume of vegetation, the sorted plants were
spread on screens and drained for an hour before taking a
fresh weight. Several small samples (a handful) of each
species were oven dried (three days at 70C) to determine
a dry weight equivalent for the fresh weight measurements.
A simple experiment was devised to test the ability of
a species to resist tearing or uprooting. One end of a
nylon string was tied to a plant stem just above the soil
surface. The other end was secured to a spring aligned with
a meterstick. Resistance was measured as the maximum amount
of spring stretch (in cm) at the point of tearing or
Changes in Plant Cover
To determine seasonal changes in plant cover, three
sections of the Headsprings Run (Fig. 4) were mapped in
November-December, 1977, remapped in April, 1978, and mapped
again in August, 1978. The method was the same as was used
in preparing the base map of the Headsprings Run: tapes,
10 meters apart, were stretched across the run, and plant
bed positions and dimensions charted on graph paper.
Several methods were used to assess the rate of vege-
tation recovery following disturbance. One method involved
M.S.Q M SR
0 5 10
Location of fenced exclosures, map-remap sections, and fauna survey sites.
The exclosures are indicated by dashed lines (---), and the map-remap areas
by solid lines (--), with M.S. H, M.S. Q, and M.S. R identifying the
specific map sections. The fish survey sites are indicated by lines with
terminal bars ([--- ), and the invertebrate survey sites by the letters
X, Y, and Z. Also included are the location of the i2 quadrats in the
Second Dock Exclosure, and the areas in the Hleadsprings Exclosure (sites
A and B) where channel closure was measured.
monitoring the recovery of sample plots which were experi-
mentally subjected to injuries similar to the kinds of
damage (tearing, uprooting) caused by recreational use. A
second method involved the measurement of plant regrowth in
trampled beds, which were protected from further disturbance
by fenced exclosures. A third way was to monitor plant
growth in cages situated in areas of heavy recreational use.
Basically, two types of treatment were used to simulate
the types of injury which result from trampling: 1. Plant
stems and leaves lying in the water column above a quadrat
were cut back to the substrate level. 2. All rooted Dlanr-s
lying within the boundaries of a staked quadrat were pulled
from the substrate. Appendix A-4 describes the methods used
to measure the regrowth of a number of plant species used in
The Park staff constructed two fenced exclosures in the
Headsprings Run (Fig. 4). One exclosure, situated between
the Headsprings pool outlet and the First Dock, protected
an area that had been previously subjected to a moderate
degree of trampling. A second exclosure was erected on the
eastern side of the run opposite the Second Dock. Prior to
fencing, the riverbed in this area had been extensively
trampled by wading tubers.
Headsprings Exclosure. Vegetation recovery was moni-
tored in two sections of the reach protected by the Head-
springs Exciosure. At Site A (Fig. 4), a 5-meter-long
section of the run lying immediately above the downstream
fence, the dominant plant beds were mapped on June 12, 1978,
and on August 24, 1978. An open grid was laid out to provide
a fixed reference for measurement of the beds. Nylon strings,
marked at meter intervals, were stretched above the channel
between pipes which were aligned in opposite pairs, one
meter apart, along the banks. The position of plant beds
was measured by running a plumb bob perpendicularly from the
marked strings down to the submerged beds.
A second section of the Exclosure, Site B (Fig. L.) was
used to measure channel closure. A meter tape was stretched
underwater from a pipe sunk in the channel floor to a second
pipe sunk 10 meters downstream. Channel width was measured
with a marked rod, which was held perpendicularly to the tape
at each meter interval over this section. Measurements were
taken on August 3, 1978, and October 12, 1978.
Second Cock Exclcsure. A heavily-trampled river bed,
protected from further disturbance by the Second Dock
Exclosure, was sectioned into eight I m units to facilitate
detailed measurement of plant cover changes (Fig. 4). In
each unit, stakes were fitted tightly into the corners of
a 1 m quadrat and sunk permanently in the underlying
substrate. Cover was measured on July 25, September 6, and
October 26, 1978, by positioning the quadrat, which was sub-
divided into one hundred 0.01 m units, over the stakes and
mapping the areas occupied by the constituent species in
In a separate section of the exclosure, the same method
was used to monitor the recovery of Zizania plants in a 1 m2
quadrat (Fig. 4). In addition to mapping cover, plant size
was noted by measuring the length of the three longest leaves
of each Zizania plant in the quadrat.
Two cages were installed in the Blue Hole (Fig. 5).
One cage, secured to the bottom in late May, was situated
in the channel 10 meters downstream from the Jug, the spring
water outlet in the Blue Hole. A second cage, installed in
June, was situated about 5 meters from the Jug, on the sou-cth
side of the Blue Hole pool. Both cages were made of hurri-
cane fencing and had the same dimensions: 1 x 1 x 1.75
Run Cage. The cage in the channel, designated Run Cage,
enclosed an area that was vegetated in part by Sagittaria,
the remainder being open sand. On May 29, shortly after
installation, the channel-ward edge of the Sagittaria bed'
was marked with stakes to provide a reference for future
measurement of vegetation outgrowth. Substrate level was
measured on the stakes, which had been marked off at
THE BLUE HOLE
Figure 5. Location of cages in the Blue Hole.
On July 6, about five weeks after installation, the
bottom of the Run Cage was photographed to determine changes
in plant cover. The substrate level was also measured to
determine how much sediment was deposited during this period.
At the end of the summer, the Sagittaria growth that
had colonized the open sand area during the recovery period
(May 29 to September 12) was mapped and then harvested
(whole plants) to determine the net increment of Sagittaria
cover and biomass in the Run Cage. Additionally, samples
of Sagittaria leaf blades were clipped from two quadrats,
one placed inside, the other outside the Run Cage.
In the lab, the harvested Sagittaria plants were
measured and oven dried (70C) to constant weight. The
leaves from the inside-outside samples were counted, measured,
and then oven dried.
Jug Cage. The cage situated on the south side of the
Blue Hole Pool, called Jug Cage, covered a portion of a
Sagittaria bed that had been subject to heavy disturbance
prior to protection. On July 6, about a week after the cage
was installed, leaf blades were clipped from quadrats placed
inside and outside the cage. Two months later (September
11), two new quadrats were cut to determine changes in commu-
nity structure (plant height and biomass) in both disturbed
and caged sections of the Sagittaria bed. Leaves sampled in
July were oven dried (70 0C) to constant weight. Leaves from
the September samples were counted and measured prior to dry
Response to Repeated Cutting
Sagittaria kurziana, the most abundant plant in the
Ichetucknee River, was used for an experiment on the effect
of repeated disturbance on plant growth. Three replicate
plots were used for each of three treatments applied to
Sagittaria plants growing in a protected bed within the
Devil's Eye Exclosure. All nine plots were subjected to the
same kind of disturbance: the blades of all Sagittaria
plants rooted within a quadrat (0.125 m ) were cut back to
the substrate level. The variable treatment factor was the
number of times a set of plots was cut during a four-month
interval extending from February 20 to June 13, 1978. One
set was cut every two to three weeks, a second set was cut
every four to six weeks, and the third was cut only once,
at the start of the experiment. On June 13, all nine sample
plots, representing three treatments, were recut. The
subsequent regrowth was harvested approximately five weeks
later on July 21 and oven dried (70C) to constant weight.
On August 5, 1978, a survey was conducted to determine
the numbers and biomass of invertebrates inhabiting both
disturbed and undisturbed plant beds. Figure 4 shows the
location of three sampling sites in the headwaters area of
the Headsprings Run. The first site, located inside the
Headsprings Exclosure, had been protected from trampDling for
more than two months prior to sampling. The second site,
in the Second Dock Exclosure, had been undisturbed for about
three weeks prior to sampling. The third site, located just
downstream from the Third Dock, was an area that had been
subjected to trampling right up to the time of sampling.
To minimize environmental variability, other than the
degree of recreational disturbance, all sampling was done
in Chara beds growing at shallow depths (less than 1 meter)
along the edge of the channel. A stove pipe (diameter =
15.8 cm) was used to extract two sample plugs of plant
material at each of the three sites. The pipe, sharpened
before use, was thrust down through a Chara bed into the
sediment below. The sample plug, containing plants, animals,
and sediment, was lifted from the substrate with a flat-
bottomed shovel and transferred to a fine-mesh net. The net
was agitated in the water to remove fine silt and debris,
then inverted into a plastic bag and returned to the lab.
In the lab, the sample material was placed in white
enamel pans, and all animals visible to the naked eye were
picked out and sorted into species. The animals were pre-
served in 5% Formalin, and the plant material was refriger-
ated until the sorting of all sample material was complete.
The plant material was then oven dried (700C) to constant
weight, and the animals drained and air dried ( hour)
prior to counting and weighing.
To assess the impact of recreational trampling on the
fish populations of the Headsprings Run, a survey was con-
ducted on August 10, 1978, and October 13, 1978, to deter-
mine the types and numbers of fish in: 1. a disturbed area,
the reach below the first dock; and 2. a protected area, the
Headsprings Exclosure (Fig. 4). At each study site, a 20-
meter rope was secured to an immovable object (dock piling
or fence) and floated downstream. An observer, with face
mask and underwater slate, slowly pulled himself upstream
along the rope, recording in his progress all fish seen
along the run. Both the protected area and disturbed area
were surveyed twice, in alternate runs, on each survey day.
The presence of other conspicuous organisms, such as cray-
fish or turtles, was also noted.
The Base Map (Appendix E) shows the plant cover in each
of the three reaches of the Ichetucknee River. Although
an average of 25% of the channel in the Headsprings Run
is vegetated, there is great variation in the amount of
cover over the course of this reach. In areas subject to
heavy recreational trampling and/or shading, plant cover may
be as low as 1%. In open, less disturbed sections, cover
values measured as high as 80%. Chara sp. and Zizania
aquatica are the dominant plans in the Headsprings Run,
each comprising about 25% of the total plant cover in this
Aquatic plants cover approximately 40% of the bottom in
the Blue Hole pool and run. Sagittaria kurziana is the
dominant species in this area, accounting for S0% of the
extant cover. Sagittaria is notably absent at Ichetucknee
Spring and comprises only 3% of the plant cover in the
In the Rice Marsh, about 60% of the channel bottom is
vegetated. Over small stretches of this reach, however,
cover may vary from 25% to G0%. Sagittaria is the dominant
plant in the Rice Marsh, accounting for 55% of the total
plant cover. Zizania and Chara cover less area, each com-
prising about 15% of total cover. The remaining vegetated
areas are comprised of Myriophyllum and Vallisneria, each of
which accounts for 5% of plant cover, and Ludwigia and
Nasturtium, which form small patches along the edge of this
The average amount of plant cover in the Floodplain
Reach, measured over 66 map sections, is 22%, which is simi-
lar to the average for the Headsprings Reach. The varia-
bility of cover in this lower reach is, however, much less
than that of the Headsprings Reach. In the Floodplain Reach,
the lowest cover in one section is 14% (lowest cover in the
Headsprings Reach is 1%). The maximum amount of cover is
32% (maximum cover in the Headsprings Reach is 80%).
Myriophyllum and Chara are the two most common plants of the
Floodplain Reach, accounting for 37% and 30% of total cover,
respectively. As the Base Map shows, Sagittaria (20% cover)
and Vallisneria (10% cover) grow along the edge of the chan-
nel in this reach.
Types and Amounts of Recreational Use
Figure 6 shows the types and amounts of monthly recre-
ational use from January-August, 1978. It is evident that:
1. weekend use is much greater than weekday use, usually by
a factor of three or more and 2. the number of visitors
increases substantially during the warm summer months. On
the average, about 150 people visited the Springs on a
 Weekend use L0 Weekdoy use
3000 A 1
 oi., ']o. .:. !~me.DT
S10 0O 1 '' .
,n 40 V:^
Fiue6 ye n aont of reretin l use Jur-uut
JanuAory I Februory I March I April I I Moy June Jul Augusi
Dier  -Canoe s E Swmmr In Tuer
Fiur 6. Tye an amut of reratoa use daur-u
1978. A. Amounts of use based on park attendance
I8 0- s,
records. a B. Percent of -total use foJ each type of
recreational activity. Data are based on user counts
from the plant damage survey, o.
winter weekend day in January. By April, average weekend
use had risen to nearly 1000 visitors per day. By midsummer,
the number of weekend visitors consistently reached 3000 per
day, the present Park limit on recreational use.
Figure 6B shows that divers constitute about 85% of the
total number of winter users. Canoes account for about 10%,
and swimmers and tubers comprise 5% of the total winter use.
The onset of warm weather in April signals the start of
the tubing season. The proportion of tubers jumped from 10%
of total use in March to 60% in April, and continued to
increase during the spring. By June tubers accounted for
95% of total recreational use. This level of tubing activity
was sustained throughout the summer months.
Plant Damage Survey
The relationship of winter plant damage to: 1. total
number of users (includes all types of recreationists) and
to 2. number of divers (includes only scuba divers and
snorklers) is shown in Figure 7. Examination of this figure
shows that the relationship of damage to rotal number of
users is not consistent. This lack of relationship, in
effect, is best explained by the observation that canoeists,
who were included in the determination of total amounts of
use, generally have very little impact on the submerged
plant communities of the river. Underwater assistants on
DIVERS (no./day )
. Figure 7.
Winter plant damage related to total number of
users and to number of divers. Relationship of
plant damage (y) to number of divers (x) is
described by the exponential equation,
y = 4.4e004x (r2 = 0.39).
The notation "J.7" indicates the data point
for January 7 which is mentioned in the text.
40 60 80
ALL USERS (no./day)
a number of occasions, watched canoes pass over plant beds.
Although paddling stirs the surface of the beds, it results
in very little stem or leaf breakage, and practically no
uprooting. On days when canoeists constitute a large pro-
portion of total use, as occurred on January 7 (66 canoeists,
24 divers, 15 tubers, and 4 swimmers) plant damage was expec-
tedly very light.
The relationship of damage to number of divers (Fig.
7), shows that plant damage predictably increases as winter
diving activity increases. As the number of divers increases,
the amount of tearing and uprooting increases exponentially.
Less than 50 dry grams of plant material was netted on days
when less than 40 divers were counted. On busier sampling
days, when the number of divers ranged from 60 to 100, the
weight of the netted material ranged from 200 to 500 dry
grams, a disproportionate increase relative to the amount
Species damage. Figure 8 shows the amounts of species
damage over varying levels of diving activity. One species,
Sagittaria kurziana, accounted for 40% of the total weight
of plant material collected during the winter survey. The
relationship of Sagittaria damage tc the number of divers is
similar to that of total plant damage and divers in that
impact accelerates when more than S0 divers use the resource.
Damage to the other species is less predictable over varying
levels of diving activity. WThen the amounts of damage to
Soagietanro nu anO
* Totalo damag(--)
0 Torn t-)
A Uprooted --)
0 20 40 60 80 100
Damage by species, related to number of divers,
Winter, 1977-78. For Sagittaria kurziana, the
relationship of damage (y) to number of divers
(x) is described by an exponential equation:
number of clumps uprooted, y = 50.7e 03x (r2 =0.83);
torn fragments, y = i.5e 006x (r =0.74); uprooted
clumps, y = 2.7eO0.4x (r2=0.86).
120 LJqwiqmgio repeni
100 ---- -- C mauoro
100 ----- Cicufa moculolda
40 50 60 70 80 90
0 10 20 30 40 50 60 70 80 90
Figure 8. Damage by species, related zo number of
divers, Winter, 1977-73 (continued).
0 10 20 30
- Nsturtium otficinoal
- - Myrirpayllum heterophyllum
.- \ -
,I \ v '
these species is considered collectively, however, it is
again evident that when the number of divers exceeds 60,
there is a marked increase in the amount of tearing and
uprooting of river plants.
Figure 9 shows, for each species, the percentage of
total damage and the percentage of total standing crop. It
is important to note that both damage and standing crop
values are estimates. The amount of plant drift netted is
undoubtedly less than the amount of plant material actually
torn or uprooted, and standing crop estimates are based on
a limited number of samples. The figure suggests that for
most species the amount of damage is proportional to
Chara appears to be an outstanding exception to this
assumption, in that the small amount netted is not propor-
tional to its large standing crop. This disproportion is
likely due to the difficulty of collecting this species.
Unlike other plants, Chara rolls on the bottom of the
channel, making it especially difficult to spot and retrieve
on busy days when the water turns nearly opaque with sus-
Ludwigia and Myriophyllum also appear to be exceptions
to the assumption that damage is proportional to standing
crop. As both Ludwigia and Myriophyllum could be netted
fairly efficiently, it appears that they may be selectively
damaged. Ludwigia accounted for 15% of the total weight of
0 o 1 1
E] Percent of Standing Crop
E] Percent of Total Netted In Winter
- I ...i .1 ~ ..& I I -~ I 4-4
Chra Cicuta ZzanMyriophyllumNsturtum
Chara Zinania Nasturtium
Percent total damage and percent of total standing crop (total
weight of plants in the Headsprings Reach) of species netted in
plant material netted during the winter damage survey.
However, the standing crop of Ludwigia comprises less than
1% of the total standing crop of the Headsprings Run and
Blue Hole area. Myriophyllum comprised 7% of the total
damage, but like Ludwigia, accounts for about 1% of the
total standing crop.
Although Sagittaria accounted for 40% of the total
damage, it also accounted for 35% of the total standing crop.
Figure 10 shows the relationship of plant damage to the
amount of daily recreational use in the three reaches of the
Ichetucknee River. The largest amounts of drift were netted
from the Rice Marsh reach. Similar amounts of vegetation,
about 2000 dry grams, or 45 Ibs. fresh weight, were netted
on May 21 and June 14, when 1500 and 500 people, respectively,
were counted. On July 9 and August 5, when 2200 and 2700
users were counted, the amounts of damage more than doubled;
about 4500 dry grams, or 100 ibs. fresh weight, was collected
on each of these days.
The amount of drift netted from the Floodplain Reach
was much less than the amounts netted from the Rice Marsh.
On June 14, 810 users were counted and about 1000 grams
netted. On May 21 and July 9, at use levels of 2024 and
2056, 2744 and 2322 grams of plants were netted. The plant
drift collected on August 5, when over 3000 users were
PLANT DAMAGE- SUMMER
A Heodsoringqs Reqch (---)
o Riice Marsh (---)
* Floodplain Reach (-)
Amounts of daily plant damage and daily use in
three reaches, Summer, 1978. Relationship of
damage (y) to users (x) for each reach is de-
scribed by a linear equation: Headsprings
Reach, y = 307.5 + 0.53x (r = 0.57); Rice
Marsh, y = 1000.1 + 1.32x (r = 0.35); Floodplain
Reach, y = 1250.0 + 0.43x (r' = 0.55).
counted in this reach, weighed 2637 grams, an amount similar
to that netted during the 2000-user days in May and July.
The amounts of vegetation netted from the Headsprings
Reach generally weighed less than the drift collected from
the other two reaches. Figure 10 shows that in the 500 to
1500 user range, plant damage consistently increased with
use. However, the amount of drift netted on the two 3000-
user survey days varied greatly. On Sunday, July 9, ,2851
users were counted, and about 2400 grams collected. On
Saturday,August 5, the amount of use (2864) was similar,
yet the amount of drift collected, 1083 grams, was less than
half the amount netted on July 9.
Figure 11 shows that, for all three reaches, the amount
of plant damage generally increased over increasing levels
of hourly recreational activity. However, the variability
of the results makes it difficult to predict the amount of
damage for a specified level of use. Despite this variabil-
ity, it is evident that over similar amounts of hourly use,
plant damage in the Rice Marsh was greater than the damage
in the Floodplain Reach or Headsprings Reach.
Figure 12 is similar to Figure 10, but describes
damage in each reach as a fraction of the total standing
crop of that reach. This figure clearly shows that recre-
ational use generally removes a much larger fraction of the
standing crop of the Headsprings Reach than it does in the
middle and lower reaches. One notable exception occurred
PLANT DAMAGE- SUMMER
* Headsprinqs Reach
O Floodplain Reach
0 Rice Marsh Reach
0 3 0
500 750 1000 125
Amounts of hourly plant damage and use in
three reaches, Summer, 1978.
* Heodsprinnqs Reach
0 Rice Marsh
A Floodplain Reach
Number of users and fractional loss of
standing crop, for three reaches, Summer,
Fractional loss =
total damage/day (oven dry wt., grams)
standing crop (oven dry st., grams)
The letter "a" indicates data points for
June 14 which is mentioned in the text.
on June 14, the only weekday sampled, when the damage was
low, and about the same, for all three reaches.
Species damage. Figure 13 shows the percentage damage
and percentage standing crop of each of the major species
in the three reaches of the Ichetucknee River.
In the Headsprings Reach, the amount of damage to a
species was generally proportional to the size of its,
standing crop (see Sagittaria, Zizania, Myriophyllum,
Ludwigia, and Nasturtium). A few species, however, sus-
tained disproportionate amounts of damage. The percent
Cicuta damage (22%) was twice as large as its percent
standing crop (11%). In contrast, the percent Chara damage
(8.1%) was less than half its percent standing crop (25%).
As previously stated, the data for Chara reflect the diffi-
culty of netting this species.
For most Rice Marsh species, the amounts netted were
generally proportional to their standing crops. Chara was,
again, an exception (1% damage, 20% standing crop).
Vallisneria was another, but the amount netted (25% total
damage) was disproportionately large relative to its
standing crop (5% standing crop).
In the Floodplain Reach, percent total damage was
similar to percent total standing crop for most species
except Myriophyllum and Sagittaria. Whereas Mlyriophyllum
appears ro be selectively damaged (37% damage, 16% standing
crop), Sagittaria appears to sustain relatively little
impact in this reach (16% damage, 30% standing crop).
E7z Percent of standing crop
D7 Percent of total netted in
Sagittaria Myriophyllum Valisnerio Nasturtium Ceratophyllum
Zizania Chara Ludwigia Cicuta
Percent total damage and percent of zotal standing
crop (total weight of plants in each reach) for
plant species in three reaches, Summer, 1978.
W 20 /
Figure 14 shows the average amount of spring force
required to tear or uproot the stems of several aquatic
species common to the Ichetucknee River. The large species,
Zizania and Sagittaria, offered considerable resistance: 1C
and 6 pounds(4.5 and 2.7 kg) of pull, respectively, were
required to dislodge these plants. In contrast, the stems
of Chara, Ludwigia, and Nasturtium tore under a light pull
equivalent to about 0.3 pounds (0.1 kg) of spring force.
Myriophyllum stems were moderately resistant, tearing at
0.5 pound (0.2 kg) of pull.
Figure 14 also shows a large variability among the in-
dividual plants tested for each species. Resistance measure-
ments on several different-sized plants showed that smaller
and/or shallow-rooted Zizania and Sagittaria plants pulled
free from the substrate much more readily than plants which
were buried under a layer of sediment. In fact, stems
buried at depths greater than 10 centimeters could not be
dislodged. Under increased pull the leaf clusters of deeply
buried plans tore free at the soil surface, leaving the
perennial stems intact below.
Changes in Plant Cover
Figure 15 shows the changes in plant cover in three
sections of the Headsprings Run over two successive seasons
(.winter and summer) of recreational use. It is evident that
a substantial amount of vegetative regrowth occurred between
NIovember-December, 1977, and April, 1978, and that over the
Zlzanla aquatlca (5)
SagIttarla kurzlania (6)
0 2 4 6 8 10 12 14 16 I
0 2 4 6 8 I0 12 14 16 18
(spring force, Ibs.)
Resistance to tearing and uprooting. The resistance of
several species was measured as the amount of spring stretch
required to tear, or uproot a plant. Bars show mean response
and lines ( ---| ) show standard deviations for species
subjected to several trials, the number of which are shown
in parentheses. A pound of resistance is equal to 0.45 kilo-
grams of spring force.
MAP J--7T: H
E Open are
Seasonal changes in plant cover in three
sections of the Headsprings Run. Section
H, 5 meters in length, is located itnedi-
ately downstream of the First Dock.
Sections Q and R, each 10 meers in length,
are ccntiguous and are located opposite
and just below the Third DoCx.
MAP SECTION Q
Figure 15. Continued.
MAP SECTION R
Figure 15. Continued.
following summer these same sections sustained a heavy loss
of plant cover.
Map sections Q and R show the winter recovery and
summer loss of Chara and Zizania cover in the Third Dock area.
Planimetric measurements showed that Chara cover in section
R increased about 12 m2 over the winter, but decreased about
Sm over the following summer. Zizania cover, almost non-
existent in section Q in December, 1977, increased greatly
in this area over the winter. However, this new growth was
trampled back during summer 1978 ro about the same level as
was originally mapped the previous November.
Hydrocotyle and Ceratophyllum, two minor species com-
ponents of the Headsprings Run, showed a large amount of
growth in section H between November, 1977, and April, 1978.
The increased coverage of these two species, as well as that
of Zizania, resulted in a narrowing of the open channel
floor from about 4 meters in November to about 2 meters in
April. Nearly all of the Ceratophyllum winter growth, as
well as a considerable amount of Zizania, was trampled out
the following summer, resulting in an enlargement of a
channel width to about 3 meters by September, 1978.
Two trends are apparent in Table 3 and Figures l-l,
which show the results of the Sagittaria growth experiment
Table 3. Regrowth of aquatic plants following cutting or uprooting. In cut plots, all stem
and leaf material was clipped back to substrate level. In uprooted plots, all rooted
plants were pulled from the substrate. The biomass values represent the mean sample
weight (g/m2) and standard deviation of: 1. the above ground material that was
recovered by vegetative regrowth in cut plots; 2. both the above and below ground
(rhizomes, roots) material that was recovered by colonization in uprooted plots.
Both harvest and indirect methods (Appendix A) of biomass measurement were used to
determine these values. The growth rate (g/m-/day) was determined by dividing
biomass change between successive sampling dates by the length (days) of the
Biomass Growth Rate
Number (Oven Dry Wt.) (Oven Dry Wt.)
Species of Plots Treatment Time g/m1 g/m2/Day
Sagittaria kurziana 3 Uprooted 2-20-78 0.0
3-21-78 10.8 + 0.5 0.03
4-30-78 16.9 + 9.] 0.40
6-31-68 193.7 7 72.8 4.02
3 Uprooted 6-18-78 0.0
7-28-78 34.0 + 8.9 0.85
8-28-78 154.5 T 29.4 3.88
3 Cut 2-20-78 0.0
3-22-78 13.9 + 5.8 0.46
4-30-78 50.9 T 6.9 1.24
6-13-78 278.9 + 34.5 3.52
3 Cut 6-18-78 0.0
7-28-78 119.2 + 14.8 2.98
3 Cut 7-28-78 0.0
8-28-78 99.2 + 11.3 3.20
Table 3. Continued.
Time g/m g/m2/ Day
(Oven Dr Wt.)
(Oven Dry Wt.)
Myriophyllum hertophyll um
480.0 + 208.2
124.8 + 83.7
50.0 + 36.8
Table 3. Continued.
(Oven Dry Wt.)
(Oven Dry Wt.)
aCut from a bed in the Headsprings Exclosure.
bA second uprooted plot, which failed to produce any new plants, is omitted from this table.
0 Leaf toMding crop
* Cut plots
V Time of cutting
Figure 16. Standing crop and recovery of Sagittaria leaves
following cutting. Bars show standard deviations
of means based on three replicate plozs (0.125 m2).
March I April I
January o Feor
V rime of uprooting
February March I April
May I June I July August
May i June I
Figure 17. Standing crop and seasonal recovery of Sagittaria
clumns following uprooting. Bars (-- show
standard deviations of means based on three
replicate plots (0Q.25 m2).
i II II
0 Starnding crop
* Uorooted ploit
Number of Sagittaria clumps counTced in
quadrats following uprooting, and
standing crop (no. of clumps) in
undisturbed quadrats sampled in February
and June, 1978.
conducted at the Devil's Eye Exclosure: 1. The rate of
regrowth following disturbance is much greater in summer
than winter. 2. Plots in which only above-ground parts
(leaf blades) were cut regrew more rapidly than plots in
which all plant material (leaves, stems, and roots) was
removed from the substrate.
Winter growth. Inspection of Table 3 shows the
differences in winter growth rates between cut plots and
uprooted plots. On March 21, about one month after the
initial disturbance (Feb. 20), the uprooted plots contained,
on the average, about 1 gram of biomass/m'. Over the same
period, the cut plots had produced about 13 grams of new
leaves. On June 13, nearly four months after the plots were
first disturbed, leaf material harvested from cut plots
weighed about 300 grams/m', while whole clumps, harvested
from uprooted plots, weighed about 200 grams/m2.
These results indicate that, following an initial lag
period (Feb.-March), clump production proceeded relatively
rapidly, reducing the magnitude of biomass differences
between the uprooted and cut plots.
Summer growth. The growth of Sagittaria clumps in
uprooted plots is much more rapid in summer than winter.
On July 28, 40 days after three sample plots were initially
uprooted (June 13), the mean weight of the new growth was
about 35 grams/m- (_ig. I7). In contrast, plots uprooted
in February had produced less than half this amount after
70 days of regrowth. Again, as in winter, there was a more
rapid accumulation of biomass in cut plots than uprooted
plots. Over the 40-day period mentioned above (June 13 -
July 28), the cut plots (Fig. 16) produced about 110 grams/
m of new leaf biomass, about three times the amount cf
clump biomass (35 grams/m ) produced in the uprooted plots
(Fig. 17) during the same period.
Standing crop. Results from sampling in undisturbed
plots show that the standing crop of Sagittaria is signifi-
cantly greater in summer than winter. The oven dry weight
of plants (including leaves, stems, and roots) sampled on
February 20 was 563.8 grams/m2. Plants sampled on June 18
weighed 1000.6 grams, nearly a 100% increase over the winter
weight (Fig. 17). The biomass of summer leaf blade samDles
was also significantly greater than the biomass of winter
leaf blade samples (Fig. 16). The mean weight of leaf
blades sampled on February 20 was 439 grams/m ; the summer
biomass was 692 grams/m2.
Interestingly, the number of clumps in sample plots
did not change seasonally (Fig. 18). On February 20,
sampling showed an average of 101 clumps/m On June 18
the mean number of clumps was 106/m 2, a nonsignificant
Myriophyllum, Chara, Zizania
The pattern of Myriophyllum recovery was markedly
different from that of Sagittaria. Myriophyllum plots cut
in February regrew at about the same rate as plots cut in
June (Fig. 19). Also, the relative recovery of Myriophyllum,
expressed as the ratio of biomass recovered to standing
crop, was greater than that of Sagittaria. Over a period
extending from February 22 to March 23, Myriophyllum plots
(0.125 m 2) in which all the above-ground material was
clipped to the substrate level, recovered about 98 grams/m2
of stem and leaf material, almost 60% of the original amount
cut (about 170 grams/m ). In contrast, Sagittaria plots,
clipped back to substrate level on February 20, had recovered
only 13 grams/mn or 3% of their original biomass (about 440
grams/m2 ) at the time of harvest on March 21.
Chara, like Myriophyllum, recovered relatively rapidly
following cutting (Table 3). Between February 20 and March
25, Chara plots in the Floodplain Reach produced, on the
average, 371 dry grams/m of new growth, almost 40% of the
original amount cut (961 dry grams/m ). Plots cut from a
bed in the Headsprings Reach in summer did not exhibit as
rapid a recovery as did the February plots at a downstream
site. After a 27-day period (the recovery period for the
February plots was 29 days), the Headsprings Reach plots
contained, on the average, about 125 dry grams, which was
only 20% of their original biomass (641 grams/m ).
0 Standing crop
o Standing crap
Standing crops and regrowth of Myriophyllum
following cutting. On February 22, March
30, and May 5, two plots (0.125 m2) were
clipped from a bed in the Floodplain Reach
and harvested after a 4-6 week recovery
period. One plot (0.125 m2) was cut on
June 12 from a bed in the Headsprings Run
and harvested on July 25. Bars show
standard deviations of sample means.
February $ March
Table 3 shows the recovery of several other species
following cutting. The pattern of recovery of Zizania
aquatica exemplified the ambiguity of results obtained from
some of the test plots. In June, several Zizania plants in
a quadrat in the Headsprings Exclosure were cut back to
substrate level. A month later, none of the plants origi-
nally cut could be found, and a thick felt-like layer of
algae covered the sample area. The only macrophyte observed
in the quadrat was one Zizania clump, not one of those origi-
nally cut, which appeared to have emerged from the substrate
during the recovery period. In contrast, several Zizania
plants, cut back in the channel of the Floodplain Reach,
recovered about 16 centimeters of leaf growth over a 5-day
period in February.
Results from Vallisneria plots indicate that the
recovery of this species may be dependent on the initial
vigor of the bed. Plots which showed a relatively large
standing crop prior to disturbance (cutting or uprooting),
exhibited much more regrowth (Table 3) than did pocts having
a low standing crop.
Figure 20 shows the change in channel profile and
shifts in the positions of the dominant plant beds in a
section (Site A) of the Headsprings Exclosure monitored over
[o- Zizania- emergent
0 1 2
SBI. Gn. Algae
Figure 2C. Change in plant cover, Site A, Headsprings
Exclosure, 6-12-78 to 8-24-78.
the summer of 1978. Between June 12 and August 24, 1978,
channel closure averaged about 70 centimeters over the
length of this 5-meter section. As the figure and time-
series photographs show (Plate 1), the vegetative expansion
of several species, including Chara, Myriophyllum, Ludwigia,
and Zizania, resulted in a narrowing of the channel.
Figure 21 shows the change in channel profile of a
second exclosure section (Site B), located just upstream of
the 5-meter map section. The average amount of closure,
measured at one-meter intervals over this 10-meter section,
was about 40 centimeters over a two-month period in summer.
A notable feature, evident in both the IC and 5 meter sec-
tions, is an increase in profile irregularity as natural
forces become more important than human disturbance in
shaping the growth patterns of submerged plant beds.
Second Dock Exclosure
The change in plant cover in eight 1 m. quadrazs,
protected from recreational disturbance by the fenced exclo-
sure opposite the Second Dock, is shown in Figure 22.
Between July 24 and October 26, plant cover increased in
four of the quadrats, but showed little change in the others.
Quadrats 1, 3, and 6, which contained largely bare sand
prior to exclosure, remained in essentially the same condi-
tion over the measurement period. Small patches of blue-
green algae shifted in position, but did not increase the
olant cover in quadrats 1, 2, and 3. In fact, the only
Headsprings Exclosure, July and November, 1978.
This section of the channel, lying immediately
above the downstream fence was photographed from
approximately the same position one month after
the exclosure was erected (A) and four months later
in November (B). Several changes are apparent:
the growth of individual plant patches, the closing
of the open channel, and the diversity and beauty
of a protected reach.
~ % ~ t tI~k
- 8- 3-78
I . |
Figure 21. Change in channel profile, Site B,
Headsprings Exclosure, 8-3-73 to 10-12-78.
SECOND DOCK [XCLUSURE
L J heterophyllum 6 17 is
SAlgae (blue- IMETER
1 Algae (brown color)
Z_ Chara and algae
Figure 22. Change in plant cover, Second Dock
Exclosure, 7-25-78 to 10-26-78.
evidence of new plant growth in 1, 3, and 6, was a Zizania
seedling, which appeared in quadrat 1 at the time of the
third mapping on October 26. Quadrat 2, tucked in a quiet
shallow, appeared to be dominated by algal growth which
showed a slight decrease in coverage during the study.
The vegetative cover in quadrats 4, 5, 7, and 8 in-
creased considerably between July and October. On June 25,
the date of the first mapping, Chara covered about 1.1 m of
the bottom in this four-quadrat section; 43 days later, on
September 6, Chara cover measured 1.6 m representing an
average rate of increase of 115 cm2/day.
On October 26, Chara beds covered 2.0 m of the 4.0 m'
section, having grown at an average rate of 80 cm /day
since September 6.
Myriophyllum cover did not change much over a three-
month period. On July 25, Myriophyllum cover in quadrats
4, 5, 7, and 8 was 0.25 m ; on October 26, this species
covered 0.26 nm a negligible increase.
Figure 23 shows that the number of Zizania plants in a
fixed quadrat did not change between August 3 and September
26, 1978. However, the size of the individual plants did
increase. On August 3, the mean length of Zizania plants
was 66 centimeters. On September 25, mean plant length was
The change in plant cover observed in this 1 m quadrat
was almost entirely due to the vegetative expansion of Chara.
2nd DOCK EXCLOSURE
* Zizania clumps
Figure 23. Growth of Zizania and Chara, Second Dock
Blue Hole Cages
Results from the Jug Cage in Blue Hole are summarized
in Figure 24. On June 6, shortly after the Jug Cage was
installed, the amount of Sagittaria leaf biomass in a sample
taken inside the cage (240 grams/m2) was about the same as
the amount of leaf biomass in a sample taken from the
Sagittaria bed surrounding the cage (220 grams/m ). On
September 11, after two months of protection, a sample of
leaf blades clipped from within the cage weighed over 300
grams/m whereas the biomass of a sample taken from the un-
protected area outside the cage was less than 200 grams/inm .
The biomass differences of the inside-outside cage
samples can be attributed to differences in the size of
individual leaves, not in the number of leaves. As Figure
24 shows, the number of leaf blades in the sample clipped
from the floor of the cage on September 11 was actually less
than the number of leaves in the sample taken from outside
the cage. The length of leaves inside the cage, however,
was much greater than leaf lengths in the surrounding bed.
Figure 24A, describing the frequency distribution of
leaf lengths, shows that the lengths of cage leaves were dis-
tributed relatively evenly over size classes ranging from
0-9 to 80-89 centimeters. In contrast, the leaf lengths of
the outside sample showed a skewed distribution with a modal
size class of 10-19 centimeters and class range of 0-9 to
o Inside cage
40-49 50-59 60-69 70-79 80-89 90-99 '100-109
LENGTH CLASS (cm)
Characteristics of Sagittaria leaves sampled
both inside and outside of Jug Cage. A. Size
distribution of inside-outside leaf samples.
B. Numbers of leaves of inside-outside
samples. C. Weight of leaves of inside-
The biomass, number, and size of Sagittaria leaves
cut inside and outside the Run Cage are shown in Figure 25.
The number of leaves in the two samples were about equal,
but they differed greatly in size and biomass. After three
months of protection, cage leaves weighed about 450 grams/m ,
and were distributed over a wide range of length classes
with maximum lengths between 100 and 109 centimeters. The
Sagittaria leaves in the surrounding bed appeared to be
stunted. They averaged about 25 centimeters in length, and
measured only 60 centimeters at the maximum. The biomass
of the outside sample was about 300 grams/m considerably
less than the inside sample.
Over the summer (May 29 to September 12), Sagittaria
plants colonized 0.55 m2 of the open sand area in the Run
Cage (Fig. 25). The 347 new clumps produced during this
period accounted for a net biomass accumulation of 202.7
grams. As is evident in the figure, the increase in
Sagittaria cover was greater on the downstream side of the
cage than on the side facing the flow.
Another feature which distinguished the inside cage
sample from the outside sample was the color and texture of
leaf blades. Leaves cut from the cage were bright green
and smooth. Leaves from the surrounding bed were brownish
and gritty. Results from ashing showed that the organic
weight of cage leaves was about 83% of their dry weight;
* Inside coge
S Outside cage
I 80-89 I 90-99 I 100-109
0-9 I 10-19 1 20-29 30-39 1 40-49 I 5-9 6-69 I 70-79
LENGTH CLASS (cm)
o Ash weigtil
D Sagittaria Colonization
....... -$. ,.
EDGE OF BED
Sagittaria colonization and characteristics of leaves
sampled both inside and outside of the Run Cage.
A. Distribution of leaf lengths of inside-outside
samples. B. Weight of leaves of inside-outside
samples. C. Numbers of leaves of inside-outside
samples. D. Colonization of open cage bottom by
m. 1IthrhrIiri n] H 0n1
the organic weight of leaves sampled outside the cage was
only about 63% of dry weight. Microscopic inspection of
the residue remaining after ignition showed, for the cage
sample, a clean white ash. The residue from the outside
sample was grayish in appearance, and consisted of relatively
large sand grains in addition to ash and other mineral
There was a considerable buildup of sediment in both
cages following installation. In the Jug Cage, sediment
depth increased 5.8 centimeters between May 29 and July 6,
1978. In the Run Cage, sediment depth increased 1.4 centi-
meters between May 29 and June 30.
Response to Repeated Cutting
Figure 26 shows the regrowth patterns of Sagittaria
plots subjected to varying intensities of cutting over a
four-month period extending from February 20 to June 13,
1978. Plots that were cut six times previous to the test
recovery period (June 13 to July 21) regrew just as
rapidly as plots that were cut three times or only once.
The figure also shows that the average growth rate (slope)
of plants cut every two to three weeks increased after each
Following the first cut on February 20, Sagittaria leaf
blades grew back at an average rate of 0.48 grams/m/day
blades grew back at an average rate of 0.48 grams/m /day
A*.-- Cut ofat 4 months
0- - Cut every 4-6 weeks
*- Cut every 2-3 weeks
/-/ / "*/7
Figure 26. gittaria leaf recovery in plots subjected to
reheated cutting. Three plots (0.125 m2) were
used for each of three treatments: 1. plots
cu, every 2-3 weeks, 2. plots cut every 4-5
weeks, and 3. plots cut after four months.
over the ensuing 15-day period. The same plots recovered
at an average rate of 3.7 grams/m /day after the last cutting
on June 13. This rate is comparable (no significant differ-
ence) to the rates of 3.6 and 3.8 grams/m /day measured for
plots cut three times and only once, respectively, prior to
the test recovery period. The growth rate of three new
plots, cut on June 18 and harvested July 28, was 3.0 grams/
Mollusks. Table 4 summarizes the results of the inver-
tebrate sampling in areas subject to varying degrees of
disturbance. The table shows that one of the samples from
the Headsprings Exclosure (No. 1), which at the time of the
survey had been undisturbed for over two months, contained
more species (4) and greater numbers (about 17,000/m2) and
biomass (about 720 grams/m including shell weight) of
mollusks than any other sample. Each of the other five sam-
ples contained fewer species, and less than half this number
or biomass. Of these, the sample taken from the moderately
disturbed Chara bed below the Third Dock (No. 5) contained
the greatest snail biomass. The number of snails in the
other Third Dock sample site (No. 6), a badly torn Chara
bed, was similar to the number found in a sample (No. 4)
taken from a less disturbed bed in the Second Dock Exclosure.
Table 4. Plant biomass and number and weight of mollusks and arthropods sampled in three areas
subject to varying degrees of recreational disturbance. Two samples were taken from
Ohara beds at each site in August 1978. The Headsprings Exclosure had been fenced two
months, and Second Dock Exclosure about three weeks prior to sampling. The Third Dock
area was unprotected and subject to trampling prior to the sampling day. The diameter
of the pipe was 1.5 em; the area sampled was 0.0177 in2.
Sample (Oven Dry
No. Wt., gais)
We i ght
214 10.26 2
86 4.57 0
48 2.45 0
97 5.00 0
Table 4. Continued.
Chara Palaemonetes Cambarus Crustaceans Insect Larvae Arthropods
Sample (Oven Dry Weight Weight Weight Weight Weight
Location No. Wt., gins) No. (g) No. (g) No. (g) No. (g) No. (g)
Exclosure 3 10.5 14 0.67 1 0.01 0 1e 0.36 16 1.04
4 8.3 14 0.70 0 0 1f 0.02 15 0.72
Area 5 10.6 7 0.29 5 0.47 0 1i 13 0.76
6 1.6 2 0.01 0 0 2 0.07 4 0.08
aFresh weight after draining preserved snails (10% Formaldehyde) for one-half hour.
bsample ; was taken from a moderately disturbed bed near the riverbank.
Sample 6 was taken from a badly torn bed at the edge of the main channel.
dOne was an Odonate, the other Rhagovelia sp.
gA Trichopteran, which was not removed from its larval case or weighed.
The weight and numbers of mollusks does not appear to
be related to the amount of vegetation at a site. Maximum
numbers and weight were found in a sample (Headsprings
Exclosure, No. 1) which ranked fourth in weight of plant
material. In contrast, the second sample in the Headsprings
Exclosure (No. 2) contained the most plant material, but
ranked fourth in both number and biomass of mollusks.
Arthropods. Table 4 shows that both the number and
biomass of arthropods in the sample taken from the heavily
disturbed Chara bed (Third Dock, No. 6) were considerably
lower than the number and biomass of samples taken in other
areas. This sample contained two insect larvae and two
small shrimp, which collectively weighed 0.08 grams (sampling
area 0.0177 m ) or 4.5 grams freshweight/m A second sample
taken from a less trampled portion of the same bed (Third
Dock, No. 5), contained a Trichopteran (Caddis fly) larvae.
5 small crayfish, and 7 shrimp, which collectively weighed
0.76 grams, or 43 grams freshweight/m The biomass of
arthropods sampled in the two fenced areas, the Headsprings
Exclosure and Second Dock Exclosure, was about the same as
that found in Third Dock, No. 5, with the exception of sam-
ple No. 3, Second Dock Exclosure, which weighed 1.04 grams.
Results of the fish survey are summarized in Table 5.
which shows the types and numbers of fish and other aquatic
Table 5. Types and numbers of fish in disturbed (First
Exclosure) sections of the Headsprings Reach.
an imunderwater observer recorded all fish seen
swim along a submerged rope)I each area.
Dock area) and undisturbed (Headsprings
On each survey day (8-10-78 and 10-13-78),
on two alternate runs (a slow upstream
Number of Fish
Run 1 Rim 2 Run 1 Run 2
Number of Fish
Run 1 Run 2
Run 1 Run 2
Stumpknocker Lepomis punctatus
Redbreast Lepomis auritus
Other Sunfish Lepomids spp.
Total Sunfish Lepomis spp.
Bass Micropterus spp.
Redfin Pickerel Esox americanus
Darter Percina sp.
Mosquitofish Gambusia affinis
Chub Hybopsis harper
Sucker Moxostoma sp.
Chubsucker Erimyzon sucetta
Golden Shiner Notemigonus crysoleucas
Table 5. Continued.
HEADSPRINGS EXCLOSURE FIRST DOCK
Number of Fish Number of Fish
8-10-78 10-13-78 8-10-78 10-13-78
Run 1 Run 2 Run 1 Run 2 Run 1 Run 2 Run 1 Run 2
Loggerhead Musk Sternothaerus minor 0 2 1 1 0 0 0 0
Yellow-bellied-- Pseudemys script 0 0 0 1 0 0 0 0
Other Pseudemys sp. 0 1 0 0 0 0 0 0
Crayfish Cambarus sp. 0 0 0 0 0 1 1 0
+ indicates that a species was seen, but the numbers of fish not recorded.
organisms in protected and unprotected areas of the Head-
springs Run. The majority of fish observed were represented
by two families, the sunfish family, the Centrachidae, and
the minnow family, the Cyprinidae. The table shows that
whereas only one Cyprinid species, the common chub, Hybopsis
harper, was seen in the disturbed area below the First Dock,
several members of this family, including chubs; chubsuckers,
Erimyson sucetta; suckers, "oxostoma sp.; and golden
shiner, Notemigonus crysoleucas were seen inside the fenced
exclosure. The figure also shows that two species of turtle,
the loggerhead musk, Sternothaerus minor, and yellow-bellied,
Pseudemys scripta, were observed in the exclosure. No
turtles were seen on four 20-meter runs in the area below
The numbers of Centrachids also differed greatly in the
two study areas. Large congregations of bass (Micropterus
spp.lj and bream (Lepomis spp.) were commonly observed in the
Headsprings Exclosure under the shelter of aquatic Dlants or
overhanging shrubbery. in the First Dock area, where much
of the vegetation had been trampled out, the few bass and
bream counted were generally observed feeding or resting
alone or in pairs. Despite heavy disturbance, crayfish were
seen near the First Dock during the survey. Although no
crayfish were seen in the exclosure during the four survey
runs, they were frequently observed in this area during work
on other aspects of the study.
In the Headsprings Reach, the loss of plant cover
resulting from recreational use is more visibly apparent
than is the loss of cover in either the Rice Marsh or Flood-
plain Reach. The data show, in fact, that the percentage
loss of standing crop in the Headsprings Reach is much
greater than the percentage loss in the middle and lower
reaches. For this reason, details of the impact of recre-
ation on the plant communities of the Headsprings Reach are
discussed first, followed by the impact of recreation on
the plant communities of the Rice Marsh and Floodplain
Reach; the impact of recreation on the animals of the river;
and the carrying capacity for recreational use.
Impact of Recreation on
the Plant Communities of the Headsprings Reach
The three sections of the Headsprings Run which were
mapped in April, 1978, and remapped in September, 1978, show
that there is a large loss of plant cover in this reach in
summer. A more detailed analysis of the data from the Dlant
damage survey reveals aspects of tuber impact which were not
shown in the figures included in the Results section.
Figures 10 and 11 in the Results section suggest that tuber
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