MANAGING LANDSCAPES FOR HUMANITY AND NATURE:
THE ROLE OF WETLANDS IN REGIONAL NUTRIENT DYNAMICS
Mark T. Brown, Ph.D.
Summary: Wetland ecological systems should be viewed as part of an integrated
landscape mosaic that is driven and organized by water, and exhibits mechanisms for
cycling, conserving, and transporting of nutrients. Effective management of the entire
landscape can be facilitated by utilizing a wide range of new "values" possessed by
wetlands, which include processing wastewater and attenuating floods. "Artificial"
wetlands can be used to reverse trends in wetland loss and add new values to the
Increasingly, attempts to integrate the concept of landscape with the principles of
environmental management are receiving mention in the literature and at public
forums. Concerned primarily with the spatial manifestations of landscape processes, this
new "science of the landscape" is striving to generate theoretical principles to better
understand large-scale spatial and temporal phenomena (see, for instance Brown and
Odum, 1981 and Brown, 1981). Management strategies are beginning to reflect this new
awareness of and emphasis on landscape, as evidenced by incorporation of a broader
systems approach. Resource managers are increasingly being asked to seek the "bigger
picture" and more fully understand the implications of their management decisions on the
This paper suggests an alternative management approach that recognizes the
wholeness of the landscape, and then applies that approach to the management of
humanity, wetlands, and water.
Water, Nutrients, and the Landscape
Water is one of the main driving energies of the landscape, organizing it through
solution, erosion, percolation, and evapotranspiration. Wetlands, as well as nutrient
* Center for Wetlands, University of Florida
Proceedings of Wetlands of the Chesapeake: Protecting the Future of the Bay. :63-75
transport, are manifestations of such a landscape. The landscape, when viewed as a
system driven and organized by water, exhibits mechanisms for cycling, conserving, and
transporting nutrients chiefly from areas of low concentration to points of high
concentration. Thus, the ecosystem, at one scale, concentrates carbon, nitrogen, and
phosphorus into organic matter, and at the larger scale, nutrients one concentration in
wetlands and estuaries as a result of transport pathways that are generally downhill.
Since most wetlands are low points in the landscape are wetlands, nutrients and other
chemicals are concentrated within them.
Until recently, land functions and processes were little influenced by human
actions. Nutrient dynamics, for example, were largely a function of relatively closed
cycles within native ecosystems, with some input from the atmosphere and weathering of
parent materials. As humanity's influence on the landscape has increased, nutrient
cycles have been greatly modified.
The impact of humanity on regional nutrient budgets and cycling is widespread and
pervasive. Conversion of forests and meadows to agricultural and urban uses has altered
regional nutrient dynamics by changing soil chemistry and increasing soil erosion and the
harvesting of forest products. Yet, the role of humanity as consumer of raw materials in
concentrated forms and spatial concentration has had a far greater influence on the
larger environment. Materials are collected from far and wide, spatially concentrated,
and consumed. In the process, by-products are released to the environment. This
concentrated consumption and eventual release of by-products has influenced the
chemical character of the larger environment.
The great urban areas release, each day, tons of nutrients in very concentrated
forms which must be assimilated into the landscape. Until very recently, wastes like
sewage, were diluted to some acceptable level and then discharged to the environment.
Since the dilution agent was most often water, the discharge points were associated with
rivers, streams, lakes, and estuaries. As long as the water body was large and the
discharge relatively small, further dilution was achieved and the nutrients and other
chemicals were finally reduced to concentrations typical of the landscape and
assimilated by it.
As a result of the increase in the size and number of urban concentrations, the
amount of nutrients released to the environment far exceeds anything the landscape has
ever seen before. Thus, new environmental systems are emerging at points of release
and adjusting and self-designing to the new conditions.
The landscape, having evolved over millions of years, is an efficient chemical
machine cycling, converting, and changing species of chemicals and associations of
elements. The relatively recent rise of human influence in the landscape has not changed
the basic processes, only the speed at which they occur. While some new and unfamiliar
chemical species have been released to the environment, the major influence is the
spatial concentration of chemicals.
The Role of Wetlands in Regional Nutrient Dynamics
Wetlands have historically been at the receiving end of the landscape hierarchy.
Surface water run-off was cycled through wetlands and then either released to rivers,
lakes, and estuaries or allowed to slowly filter through accumulated organic matter into
ground waters. In either way, surface waters were filtered and nutrients retained on the
lands. The organic matter released from the wetlands became the basis for some aquatic
food chains and enriched aquatic plant production. As a result of humanity's efforts to
pave uplands, drain wetlands, and by-pass normal drainage systems in order to increase
run-off rates, the landscape hierarchy has been short circuited and downstream waters
enriched with unfiltered and ill-timed releases.
Other wetland values such as wildlife values, scenic qualities, and flood
modification stem from their place in the landscape hierarchy. As elements in the
landscape that receive nutrient laiden runoff, they are productive, and attract wildlife to
feed, breed, and nest. Wetlands are appreciated for their scenic qualities because, in
many areas, they are the only remaining vestige of a natural landscape. Their potential
for attenuating floods results from their position within the landscape as storage devices
and friction against the flow of water.
Wetlands and Wastewater
Since the early 1970's, researchers have been examining the potential for
discharging treated sewage effluent to wetland ecological systems (See Odum et. al 1970;
Odum and Ewel 1974, 1975, 1976, 1978, 1980; Boyt et. al 1977; Kadliec et al. 1979;
Zoltek et. al 1979). They have generally concluded that wetland systems are well-
adapted to this role and thus might be considered natural, low energy, tertiary treatment
facilities (see Basstain and Benforado, 1983; Engler and Patrick, 1977; Ewel and Odum,
1979; Fetter et. al., 1978; Fritz and Helle, 1978; Heimburg, 1977; Kadlec, 1979,
Lakshman, 1979; Mechenich, 1980: Nicholas, 1983; Stanlick, 1976; Stewart and Ornes,
1975; Sutherland, 1977; Tilton, 1976; Tilton and Kadlec, 1979; and Wighan and Simpson,
1976). While the success of wetland treatment systems varies, nitrogren and phosphorus
removal rates are generally better than 90 percent within wetlands that are not
overloaded (see Table 1).
As a result of this research, the Florida Department of Environmental Regulation
(DER) in the mid-1970's amended the Florida Administrative Code (FAC Chapter 17-
4.243) to provide for the "experimental use of wetlands for low-energy water and
wastewater recycling." Most recently, the Warren S. Henderson Wetlands Act, as passed
by the Florida Legislature in June 1984, specifically requires DER to develop new rules
to provide for the use of wetlands for storm and wastewater recycling.
Table 1. Effectiveness of nutrient removal by wetland systems
(from Kobriger et. aL, 1983)
Location Wetland type Nutrient removal Source
City of Freshwater Inorganic N 95% Hermann,
Clermont, FL Marsh Total P 97% 1980
East Lansing, Macrophyte Total N 95% King,
MI Marsh 1978
Gainesville, Cypress Total P 90-95% Odum,
FL Total N 90-95% Ewel
Inorgan N 90-95% 1980
Bellaire, Freshwater NH + N03N 91% Kadlec,
MI Marsh Total P 97% 1978
Hay River Northern NH4-N 96% Hartland
,NW Terr., Swampland Total P 97% -Rowe,
Canada P04-P 98% 1974
City of Hardwood Total N 90% Boyt
Wildwood, Swamp Total P 98% et aL
Hougton Lk., Freshwater NH4-N 77% Kadlec
MI Marsh Nox-N 99% et aL
Total dis.P 95% 1979
A Model of Wetlands and Wastewater
Fiqure 1 is a simplified model for determining a wetlands potential for treating
wastewaters. Since wetland treatment potential varies among wetland types, the type
and size of the wetland, as well as the quality and quantity of the wastewaters, are
necessary input variables. Additional input variables include mean monthly rainfall and
the quality and quantity of entering surface run-off.
Figure 2 presents the micro-computer simulation results of the Figure 1 model.
Those results show the various species of nitrogen and total phosphorus, on a daily basis
throughout one year, for a central Florida cypress wetland receiving two different
application rates of secondary effluent.
The model can be used by local governments and utility departments to determine
options available for wastewater disposal within the context of anticipated growth and
additional treatment capacity needs. Generally, wetlands are under considerable
pressure in those areas exhibiting the fastest growth. Some wetlands are simply in the
"way of development" and their elimination from the landscape is imminent. However,
the option of wetland wastewater disposal provides additional incentives for the
preservation of otherwise unprotected wetlands, as well as renewed hydroperiods and the
potential for reestablishment of conditions more conductive to wetlands.
"Artificial" Wetlands in the Landscape Mosaic
The creation of "artificial" wetlands may be an important method for reversing
trends of wetland loss and adding new vitality to the landscape mosaic. Experience in
Florida (Brown, 1975, 1980; Brown et. al. 1975) and ongoing research on the reclamation
of phosphate-mined lands (Brown et. al. 1984a, 1985b) have shown that the creation of
wetlands is possible and that hydroperiod is the most critical factor. The creation of
wetlands using wastewater flows has great potential.
Figure 3 is a drawing of an artificial wetland planned for the City of Orlando,
Florida. The wetland will be constructed on what is now improved pasture along the
floodplain of the St. Johns River. The project has received considerable attention since
much of the river's base flow has been diverted and the additional fresh water coming
from the wetland is considered beneficial by most management personnel. Additionally,
artificial wetlands are being planned for storm water renovation as part of major quality
improvements planned by the city of Orlando. Numerous other municipalities throughout
Florida are in various stages of planning for the use of artificial wetlands for both storm
and waste water recycling.
Managing The Landscape Mosaic
Changes'in land use patterns and alteration of watershed drainage networks have
had a major influence on the quality and quantity of surface water flows. Changes in the
timing, quality, and quantity of freshwater inflows to estuaries have recently gained
considered attention (see for instance Cross and Williams, 1981) and are probably the
foremost reasons for the decline in the quality of coastal systems.
The loss of wetlands, channelization of streams and rivers, diversion of runoff,
increased impervious surfaces, and discharges of sewage effluent to rivers and bays have
all contributed to changing antecedent conditions and speeding the decline of riverine
and estuarine systems. In order to reverse these trends, landscape managers must use
what ever means possible to re-establish wetlands and surface water base flows, slow
down run-off from developed watersheds, enhance the quality of run-off waters, and
recycle wastewaters for productive purposes. In all, great potential exists for the
effective utilization, creation, and management of wetland ecological systems as part of
an integrated landscape mosaic.
Effective management of systems located at the downstream ends of the landscape
hierarchy is not possible if managers do not plan for effective utilization, re-creation,
and protection of the entire hierarchy. Wetland managers should view themselves as
managers of the landscape mosaic of which wetlands are an integral part. And they must
realize that utilization, when done properly, adds a new "value" to systems considered by
some to be of little or no value. "
(01 HAM /^S /(""NofF ) ITRIFICATION ?y WME
VS \ SSRECHARGE
Figure 1. Energy systems diagram of the wetland and wastewater
model, showing the inflows of rain, overland flow, and sewage
effluent carrying concentrations of nitrogen and phosphorus.
The out flow pathway carries nutrient concentrations when water
is high enough during the height of the rainy season. There is
some ground water recharge that caries lower concentrations of
nutrients. plant nutrient uptake is during the growing season
with a return of organic nutrients during the autumn leaf fall.
NAXIMI VALUES / I
TOT.P = .55 ppm /
ORG.N 10.81 ppm // \ /
NH3 2.18pp/ //
NOX 2.22 pp -, / \
1 2 3 4 5 6 7 8 9 10 11 12
TOT.P ORG.N -OX
WATER = 408 mm // /
TOT.P = 6.82 ppm \- -
ORG.N = 4.1 ppm / \
NH3 = .54 ppm / _/' -
NOX = .36 ppm
1 2 3 4 5 6 7 8 9 10 11 12
Figure 2. Simulation results of the model in figure 1 when
programmed for a cypress wetland and typical secondary quality
effluent. The top graph shows the natural conditions without
discharge, and the bottom figure shows the variations in
nutrient concentrations as a result of a discharge rate of 2"
per week. There is outflow from the wetland during the height
of the rainy season from June to September. Note that the
verticle scales on each graph are different.
.AH II APLE,8WLS0
( U' 1I 526 51.9 ACRES 22&2 ACR :; .
SYSTEM SWALES TOTAL WETLAD AREA 986 ACES
B IRON BRIDGE ARTIFICIAL WETLANDS -
Figure 3. Conceptual drawing of an artificial wetland planned for the City
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