Title: Cumulative impacts in landscapes dominated by humanity,
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Title: Cumulative impacts in landscapes dominated by humanity,
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^ W^^--C -CFW-86-09
Mark T. Brown
Center For Wetlands
University of Florida
Concepts of cumulative impacts are explored, and
defined. Organizational principles of landscapes are given
and applied to the Florida landscape. Problems associated
with development in low and high relief watersheds are
explored, and cumulative impacts on watersheds, wetlands,
and water explained. The major cumulative effects of
increasing utilization of the landscape for humanities
purposes are the drying out of the ]aid, and loss of
headwaters functions that result in changing species
composition of ecosystems and loss of valuable ground and
surface waters. A program of monitoring and managing
cumulative impacts is proposed.
Proceedings of a Conference on Managing Cumulative Effects on Florida
Wetlands: New College, Sarasota, FL 1-18
** >~~~~~~~~~~~~~~~~

Mark T. Brown
Center For Wetlands
University of Florida
As lands are developed and utilized for humanities purposes, there
is a shift in the balance of uplands and wetlands and a change in the
ratio of developed lands to natural lands. Those who are concerned with
these changes often refer to the cumulative impacts of development with
great concern. The concern ultimately centers around the loss of
landscape functions. Usually, however, the evidence for cumulative
impacts is a symptom of a loss of function, and the-cause is often given
as some-physical manifestation of development.
Those things that are easily measured (the area of development, or
number of boat docks for example) are equated with the symptom (number of
dead fish, or decrease in the population of some animal species) and cause
and effect are established in the-public consciousness. More boat docks
mean more dead fish; therefore manage the construction of boat docks and
the fish population is managed. The symptom is treated insteadof the
"disease". ;
Other symptoms are often not even recognized for they-are slow in
showing themselves or take place in areas-of the landscape that are little
noticed. By the time they are noticed it-is too late for any corrective
action, since the disease has progressed to such an extent that treatment
has no effect.
Management of landscapes starts with understanding the system that

is to be managed, then initiates a program to monitor changes within the
system, and finally develops a strategy to control the activities that
impact the system. Today, landscape management pays little attention to
the whole system, but rather manages the parts. The business of landscape
management is divided amongst a multitude of agencies having overlapping
jurisdiction, and yet many parts of the landscape are left unmanaged. A
whole system approach to landscape management is needed, and the issue of
cumulative impacts, is the one issue that shows this need the most.
Concepts of Cumulative Impact
There are two concepts of cumulative impact for which there are two
distinct management alternatives. One concept deals with the cumulative
impacts of a bit by bit development of the landscape that slowly
"consumes" natural areas, turning them into developed lands. This concept
might be called the cumulative loss syndrome, for it is concerned with the
loss of landscape functions as a result of the loss of natural areas a bit
at a time. While the first acre lost to development may not have an
effect on landscape functions the cumulative impact of developing acre
after acre may cause serious erosion of function.
A second concept is the cumulative .effects syndrome. The various
impacts of development (pollution, lowered water tables, increased runoff,
dredging, filling etc.), may act synergistically to cause serious erosion
of landscape function, but the loss is not necessarily correlated with the
area of natural lands that is developed. Losses are more related to
intensity and-spatial distribution of development activity. Activities of
high intensity effect wider areas of the surrounding landscape than those
of low intensity, and the effects of a wipe distribution of activities may
have greater spatial effect than those concentrated in a single area.
The end results of both syndromes are much the same; a net loss of
landscape functions. However the mechanisms of each are very different
and the symptoms of each are not equally monitored. Cumulative loss of
natural areas is easily tabulated by simply measuring areas acre by acre
as they are developed, and projections based on past rates of conversion

can be 'forecasted. Cumulative effects, on the other hand, are not easily
measured since they require monitoring the "health" of the landscape. The
synergistic effects of various development activities occurring at
different locations and at different times are not understood, and are not
easily monitored. In many cases there is no organization that keeps up
with the changing environment other than a few "old timers" who remember
things being different in the old days.
A landscape is the physical manifestation of inflowing energies that
interact in cause and effect relationships. Each landscape has its own
energy signature that organizes and maintains its elements in some
characteristic pattern. The Florida landscape has a pattern, as a whole,
resulting from its location, terrain and driving energies. Within the
whole are elements, like uplands, wetlands, forests, prairies, lakes, and
rivers. How the elements are organized spatially and temporally, results
from the larger driving energies, and gives the landscape its overall
character. Florida's abundant rainfall is the main driving energy,
organizing watersheds, wetlands, and water.
In many of Florida's coastal counties, the maximum relief is less
than 20 meters from the highest inland elevations to the coasts. With
such low reliefs, the-landscape organization is much different than those
that are characteristic of inland counties and other areas of the
continental United States. Where reliefs are higher, watersheds have
highly organized drainage patterns, and Waters flow relatively quickly
from highlands to lowlands through drainageways, streams and rivers to the
sea. In low relief watersheds, waters are slow in developing head and in
running off the land. In such flat terrains, well developed dendritic
patterns are not common, but instead, patterns of isolated swamps and
marshes in the headwaters that connect to sloughs and meandering streams

are dominant.
The stream energies resulting from low relief landscapes develop
fluvial patterns that carry less sediments and that do less stream channel
work, instead putting energies into the work of maintaining a diverse
array of floodplain swamp and marsh vegetation. Broad floodplains of
wetland vegetation adapted to the yearly rise and fall of flood waters,
slow discharges, filter organic matter and sediments, and stabilize soils
along the banks of the coastal streams and rivers. In Florida's panhandle
where relief is greater, streams develop fluvial patterns that carry
large amounts of sediments and continually alter channelways, developing
wide floodplains near their mouths.
The most common Florida watersheds are low in relief, typically with
an abundance of wetlands in their headwaters as shown in Figure 1.
Channelways have fewer wetlands and therefore less water storage capacity
than their headwaters. Higher relief watersheds (Figure 2) are the
opposite; having less wetlands storage in headwaters, and a greater
percentage of their wetlands associated with the channelway floodplains of
lower reaches.
Wetlands of the Florida landscape can be grouped into three broad
categories according to their hydrologic regime: isolated wetlands like
cypress domes, flatwoods marshes, bayheads, and bogs; Seepage wetlands
like hydric hammocks and bay seeps; and flowing water wetlands like
floodplain swamps and cypress sloughs (see Figure 3).
Isolated wetlands are dominated by precipitation and ground water,
sometimes recharging groundwaters and other times being recharged from
high ground water tables. Many times they alternate between these modes
from the dry to the wet season. Their primary function is water storage
and filtration, holding wet season waters long after ground waters have
receded and then recharging ground waters:slowly and maintaining higher
water tables and base flows for downstream sloughs and rivers.
Seepage wetlands are located where cjround waters intersect the soil

surface; Dominated by vegetation that is not typically inundated, they
occur at the bases of sand hills or where the flatwoods topography dips
exposing surficial ground waters. In many instances, seeps may go nearly
dry during the dry season while in other cases with a large enough
catchment area they may flow year around. They are important because they
act as filters and maintain base flow of downstream sloughs and streams.
Flowing water wetlands line the streams and rivers of low relief
watersheds and the lower reaches of high relief watershed rivers. Sloughs
act as the very slow water connections between upland isolated wetlands
and channelways. Many times sloughs resemble long linear isolated wetlands
when viewed on aerial photographs. The flowing water wetlands help to
maintain water quality, slow water flows to minimize flood peaks, trap
sediments and exchange organic matter.
Florida receives nearly 1400 mm of rainfall per year divided between
a sumner wet season and a winter dry season. Much of this water is
evapotranspired back into the atmosphere;-a small amount (0%-5%) recharges
deep aquifers, and the remaining (about 25%) runs off the landscape
driving wetlands and estuaries. The water that is not lost through
evaporation becomes part of an intricate system of ground and surface
waters that intermingle and at times are difficult to tell apart.
Surface waters filter through soils, and where there are cracks and
holes in confining layers, recharge deep aquifers that are utilized for
potable water supplies. Where ever there .are direct connections between
surface waters and deep aquifers, there is great potential for
contamination of drinking water supplies. Fortunately, there -are few such
connections .
Surface waters, prior to mixing with ground waters and decaying
organic matter are neutral, picking up organic and nutrients as well as
possible toxins from agricultural and urban lands as they flow across the
landscape. Surficial ground waters (those at at or near the surface in
contact with the root zone of most vegetation) are usually acidic,

carrying organic acids from decaying vegetation. Filtering through soils
and wetlands helps to maintain high quality surface waters as they flow
through the landscape, seep from higher ground, and accumulate in rivers
and streams.
The separation of surface and deep ground waters is important. When
they intermingle, contamination of potable water supplies results.
Wetlands act as one of the first and maybe most important filters to
insure that deep waters are clean and toxin free. Elimination of any
wetland whether isolated, seepage, or flowing water decreases the
filtering capacity of the landscape and increases the potential of
contamination of water supplies.
Developing Florida's landscape has always been somewhat difficult.
Early settlers had to contend with disease, insects, and much to much
water. From the very beginning, the main goal was to "tame" the
wilderness by draining the swamps and turning them into good productive
land. Later strategies were to "control" flooding and protect life and
property. Modern strategies are to "manage" growth and its impacts on
environmental, social, and fiscal systems of Florida.
Today Florida's landscape, while still driven by the energies of
nature is more dominated by the energies released by humanity and policies
fostered over the last century that treat it as something to tame, control
and manage.
The Development Process -
The process by which native landscapes are altered and used for the
purposes of humanity occur in waves of consumptive use followed sooner or
later by regenerative phases. In the first wave, easily extractable
storage of resources are removed or extracted (timber in the early part
of this century, phosphate ore at the present time). A second wave of

exploitation follows utilizing soil fertility that has accumulated over
centuries. If land is not limiting, that is, if there is new exploitable
land yet to be utilized, development moves on, allowing previously used
and "discarded" lands to enter a regenerative phase where natural
succession and the soil building processes of forests re-establish the
original fertility. When regenerated, these lands await another wave of
consumptive use.
Urban uses of lands short circuit this cycle of consumption and
regeneration. Lands are sequestered into relatively permanent uses and
the regenerative phase is eliminated. This third wave of utilization has
the greatest impacts, since lands developed for urban uses are generally
stripped of their natural characteristics and maintained in some state
that is far from the original landscape. Drainage is altered, natural
diversity is greatly reduced or eliminated and replaced with a diversity
of non native vegetation, and new flows of nutrient rich runoff and solid
wastes are added to nutrient cycles.
The cumulative losses of wetlands and uplands, savannas and forests,
and rivers and lakes are easily tabulated as the waves of consumption
proceed across the landscape. However, little understood and even less
actively measured are the cumulative effects.
The consequences of development are.intuitively obvious throughout
Florida. Native habitat is diminishing as lands are converted for
agricultural, silvacultural, and urban uses. Wildlife, responding to the
losses of habitat are diminishing as well' Water quality in lakes, rivers
and estuaries deteriorates yearly as increased flows of nutrient laden
runoff flow from an ever increasing area of developed land. Yearly dry
season droughts are now common place in many regions of Florida as water
balances are altered through increased consumptive use, increased runoff
and decreased storage. These consequences might )e termed primary

impacts.' The secondary impacts or cumulative effects are more subtle,
often not recognized, and even more often not interrupted as negative
consequences of development.
Drying Out The Landscape
The most far reaching effects of developing the Florida landscape
are the long term changes to hydrologic patterns that result from
manipulation of ground and surface waters under the guise of "flood
control" or "storm water management". No other impact is so pervasive,
and alters landscape processes to such an extent as the engineered
solutions to developing "wet" lands in a landscape whose main driving
energy is rainfall. As shown in Figure 4, on lands where wet season rains
once to saturated the soil column, collected in depressions, and slowly
ran off through sloughs and meandering streams, developments now sit that
are engineered to respond in exactly an opposite manner. Ground water
levels are lowered to accommodate storm water retention and detention
basins and the management system is designed to discharge storm waters as
quickly as the law allows; all in the name of flood protection.
The practice of systematically drying out the landscape creates
multiplicative impacts that effect a much wider area than the individual
development project. Water tables lowered in one area lower water tables
in surrounding lands and runoff waters effect all downstream water bodies
including estuaries. These practices are at odds with most well
intentioned management and regulatory programs. Programs designed to
protect water quality, for the most part, do not address nonpoint sources
of pollution. Programs to protect wetlands, for the most part, do not
address the losses of wetland function-as a result of lack of water and
natural hydroperfods due to lowered-ground water levels. Management
programs for natural areas that find themselves at the downstream ends of
watersheds are at the mercy of all upstream development interests. Loss
of upstream storage results in down stream flooding in wet years and
drought in dry years.

Cutting Up the Landscape
Recognizing the importance of Florida's streams, rivers, and lakes
to the economy and well being of the state, there are numerous regulatory
programs at both the local and state level designed to protect "waters of
the state". Wetlands that are connected to surface waters are considered
waters of the state and fall under the protection of these programs.
Isolated wetlands and possibly seepage wetlands fall outside state waters
and remain unprotected unless local programs are initiated. Most programs
are designed to protect water quality and as a result only indirectly
regulate water quantity. Some Water Management Districts have "surface
water management rules" giving wider powers to regulate development that
affects surface waters.
By their nature, programs designed to protect surface waters only
when they become surface waters clearly do not protect them. In the very
flat topography of Florida, where the headwaters of most rivers are a
patchwork of isolated wetlands and sloughs, and surface and ground waters
intermingle, development in headwaters has greater overall potential to
effect water quality and quantity than development of an equal amount of
land in downstream locations. In other words, regulating development in
floodplain wetlands in the lower reaches of streams and rivers under the
pretext of protecting waters of the state has far less potential of
realizing its goal than regulating development in the headwaters. There
are no programs designed to regulate the alteration of headwater areas to
insure that storage, baseflow, and attenuation of peak flow are
maintained. "Save our rivers" must begin with saving our headwaters.
This has been demonstrated again and-again through out Florida.
Agricultural development of the headwaters of the St. Johns River
continues to plague all attempts to improve its conditions.
Channelization and subsequent agricultural:development of the Kissimmee
River, the headwaters of the Kissimmee/Everglades system, and continued
development in its headwaters near Orlando have forever altered the River
of Grass (not withstanding the "water conservation areas"). The Peace
River no longer has a headwaters, having !'--en mined for phosnhate in tho

last several decades. The Alafia River is soon to follow. No regulatory
program no matter how good, can reverse the trends of deterioration of
water quality and loss of quantity in the Peace and Alafia rivers without
addressing past and present activities in their headwaters.
Changing Ecological Systems
The landscape is a patchwork of micro climatic, hydrological, and
chemical conditions that define physical environments to which various
plant species are adapted. Some areas are extremely well drained, with a
hot dry micro climate and plant species adapted to life in "desert like"
conditions even though there is abundant rainfall. Other areas are
periodically inundated with nutrient rich acidic waters, and still others
are inundated with almost pure rain water. Some areas have standing water
year round, others, for only short periods of time. The vegetation that
grows in each of these environments is adapted to the set of physical
conditions (or energy signature) that is characteristic. Alteration of
these physical conditions causes shifts in the species composition of the
plant community. The degree of alteration and the tolerances of the
original plant species to change determine the extent of the change in the
community composition. In some cases the responses to alterations in
environmental parameters are subtle, in others quite complex. Some well
documented changes in community structure are known and others can be
inferred from trends noted as a result of natural succession.
The drying of the landscape causes shorter hydroperiods and
shallower depths of inundation in isolated wetlands. These conditions
favor plant species adapted to dryer conditions, build greater
accumulations of organic matter, and favor, more frequent fires. In areas
that do not burn, cypress seem to be replaced with several species of bays
as the dryer conditions may favor bays and their seeds move more readily
around the landscape. Where fire is frequent the dryer conditions result
in "peat fires" within the wetland killing most trees and reversing
succession re-establishing a deeper wetland back in contact with ground
waters. Table 1 compares several characteristics of a "natural" wetland

and three altered wetlands in North Central Florida
In south Florida, where exotic vegetation is prevalent, dryer
landscapes favor some of the exotics over native species. With lowered
water tables, the hydroperiod and pulsing of wet and dry may be more
characteristic of the conditions to which the exotics are adapted. It has
been suggested that evapotranspiration of exotics is greater than native
wetland species and therefore may exacerbate the problem by increasing
water loss and subsequent drying.
In non wetland areas, lower water tables increase the likelihood of
drought conditions during portions of the year. Since the root zone of
most vegetation is within the first meter of the soil column, water levels
much below this zone produces drought stress and favors more drought
tolerant species. To combat drought, as a result of lowered water tables
in developed areas, irrigation of lawns and shrubbery is required.
Lowered base flows and a general decline in quantity of waters
flowing in the lower reaches of some rivers as they meet the gulf and
Atlantic has increased salinity of these near coastal waters eliminating
fresh water floodplain vegetation in favor of salt tolerant species. In
other rivers runoff from urban lands has radically changed timing and
increased fresh water inputs altering species composition of tidal
Increased flooding and longer hydroperiods in wetlands as a result
of drainage of higher lands and impoundments will cause shifts in
community structure as well. Many wetland species are not adapted to
prolonged periods of deep inundation but require periods of low water or -
even dry conditions. Prolonged deep inundation will kill most wetland
tree species and will favor herbacious communities.
In order that cumulative impacts might be minimized and controlled,
cumulative losses should not be confused with cumulative effects. Each
} 1

requires very different management approaches. The cumulative loss of
wetlands as the direct result of development is fairly simple to control.
It requires local or state legislation to regulate and control development
of the habitat in question. The control of cumulative effects of
insensitive and misinformed development practices is much harder. They
are not easily observed in the short run, they are not limited spatially,
and they take many forms. The following is intended as a set of guiding
principles for developing programs in controlling cumulative effects of
development in landscapes dominated by humanity:
1. Recognize that cumulative effects are a whole systems
problem and approach control in an integrated manner by not
dividing up the landscape into governmental departments of
overlapping jurisdiction.
2. Institute landscape monitoring networks and data banks
that can track change and isolate potential problems before
they become critical. There is a strong need for
"institutional memory" that can track change instead of
relying on a few "old timers" recollections of the good old
3. Where ever possible institute control at the local level
since it is closer to the problems and potential solutions,
has a better understanding of all the actors involved and
can be more responsive to the needs of the local population.
4. Develop local planning and decision making mechanisms
that begin and end with complete watersheds. Decisions
concerning development types, intensities, and timing should
be made always with the entire watershed in mind. In large
watersheds, this may require cooperation between separate
local government bodies.
5. Pursue intensive funding of applied research in fields
that typically deal with all aspects of planning, design,
and construction, and other fields of human ecology and
landscape ecology. Fresh, creative ideas are needed that
can guide environmentally sensitive -development.
6. Develop a network of local landscape extension personnel
familiar with development techniques, environmental
constraints, and research initiatives to consult with anyone
manipulating the landscape to provide information that will

minimize impacts and enhance environmental quality.
7. Educate the public in the values of wetlands, the
organization of watersheds, and the impacts of insensitive
development practices to insure informed decision making and
public involvement.
8. Reverse current trends of dryer landscapes by using
valuable treated wastewaters on the landscape instead of
injecting in deep aquifers, or shunting to the oceans.
9. Rethink current design standards for retention and
detention basins and storm water conveyance systems that
make sterile grassed systems requiring continual
maintenance, in favor of self maintaining wetland
Monitoring and managing cumulative impacts of development of the
landscape is as much an art as it is science. The art is in the design and
creation of of landscapes dominated by humanity that are sound hydrologic
and ecologic systems. The science is in developing the principles by which
landscapes are organized and by which humanity need live. The challenge to
solve many of the environmental problems associated with Florida's rapidly
expanding population will require both the art and the science. The
response to the challenge can either be creative solutions and examples of
"how to do things right" or tighter controls and a multitude of new
regulations designed to limit creativity. The former is far more

N -I e S--
Q I 2 Weil&"
Figure 1. Map of Low Relief Watershed in North Central Florida, showing
the preponderance of wetlands (stippled areas) in headwaters,
Prepared by M, Sullivan, Center for Wetlands.

/ V (, \ 3 'WETLANDS
Figure 2. Map of High Relief Watershed in the Panhandle of Florida.
Wetland areas in headwaters are absent, but line the flood-
plain of the channelway. Prepared bylM. Sullivan, Center for

T ~ f"' -" ->
itt SEEPAGE- ..
a /U^"1'^of^ s&^6|t /' ^ 3-
> ST /
wJ ;ip- l* w $Icu'!
Figure 3. General wetland types found in the Florida Landscape and
their location within watersheds,

-m- Cypreaass Dome V Floodplaln_ Stream _
J-<- 8wamp TChannel-
Ground Surface w +
| rWei Season Dry Season Water Storage
Dry Season Filtering Action
Groundwater of Organic Layers
Recharge Wetland Recharge
Maintain dry
season base flow.
}S.L-" 8 81------ Storm W^atrI
Retention Basin -| Soils drought. channeW
zWet Season rrequire irrigation
4. Ground Surface Dry Season Year roun
developmet Storm waters heldoun
b Short time only I
2 meters
or more
Figure 4. Generalized Crossections of the Landscape before and after the
development showing fluctuations of groundwater table from wet
to dry seasons.- To accommodate development water tables-are low-
ered by the construction of drainage canals.

Table 1. Comparison of Various parameters between 3 disturbed 1. and an
undisturbed wetland in North Central Florida
Parameter Undisturbed Drained & Logged Drained & Burned Impounded
Cypress Dome Cypress Strand Cypress Strand Wetland
Apparent High &
Low Water Level 2.
(Cm.) 0 to +60 -40 to +10 0 to +10 +40
Basel Area
(M2/ha) 3.
Cypress 40.9 9.0 22.1 6.9
Black Gum 0.4 0.8 -- 4.9
Bays -- 27.1 1.5 10.1
All Other 3.8 3.9 3.9 19.6
Total 45.1 40.8 27.5 41.5
1. The comparisons between basel area illustrate differences in species
composition in these wetlands that may have resulted from disturbance. Data
for species composition prior to disturbance does not exist, and therefore
determination of change within communities is not possible. Between
community comparisons should be made with some caution since there is little
evidence of original species composition within each site.
2. Apparent high & low levels are the maximum and minimum depth of water
observed during 1985; Measured from ground surfaces.
3. Basel area is a measure of the area of the stem of a tree at a right angle to
its longitodinal axis and of breast height.

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