Riparian and Terrestrial Issues in The
Chesapeake
: A Landscape Management Perspective
Paper prepared for the conference • •
'Human Activities and Ecosystem Function: Reconciling Economics and
Ecology"
Organized by the Renewable Natural Resource Foundation
.At Solomons, Maryland
October 13 to -16,1994
Curtis G. Bohlen1
and
Rupert Friday 2
1. Chesapeake Biological Laboratory, Center for Environmental and Estuarine Studies,
University of Maryland System, Box 38, Solomons, Maryland 20688
2. Chesapeake Bay Foundation, Maryland Office, 164 Conduit Street, Annapolis,
Maryland 21401. Present Address: Maryland Office of Planning, 301 West Preston
Street, Baltimore," Maryland 21201
This work was supported in part under Cooperative Agreement CR-818227-CI from the U.S.
Environmental Protection Agency with the University of Maryland Center'for Environmental
and Estuarine Studies.
EPA-230-R-94-021
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Introduction
The Chesapeake Bay watershed covers approximately 64,00.0 square
miles, including portions of six states and the District of Columbia. This vast
hydrologic network has been profoundly altered by a gradual transformation
of the landscape that started with changes in forests caused by native
American populations and accelerated soon after European, settlement of the
watershed three hundred years ago. j
The transformation of the watershed was accomplished without
forethought or planning, by the cumulative effects of millions of decisions
made by tens thousands of landowners. Settlers: cleared fields for homesteads,
foresters harvested timber, builders constructed houses and towns, businesses
built mills, warehouses and factories, farmers-planted tobacco and small
grains. Individuals, acting in response to what 1;hey thought best, within the
institutional frameworks of their day, have transformed the land, and
transformed the Bay. When European settlers arrived, the Chesapeake .
watershed was more than 95% forest. Today the watershed is approximately
58 percent forest/33 percent agricultural lands, 8J percent developed land—
including low, medium and high density residential; commercial; and
industrial lands—and 1% water (Neumiller'et. al. 1994). Only about one half
of the region's original wetlands remain (Tiner e;t al. 1987). The decisions that
led to these landscape changes were, and to a large extent continue to be,
driven by human needs and wants on local spatial and short temporal scales,
yet over time they have had profound effects at the scale of the Bay
watershed. j
Paleoecological information suggests that soon after the arrival of
European settlers in the watershed, the ecology of the bay began to change
(Brush, this volume). Sedimentary records suggest that sedimentation rates
climbed as forests were cleared for agriculture. Anoxic conditions in the bay
became more frequent, and signs of nutrient enrichment appeared in Bay
sediments and ecosystems (Cooper and Brush 1?>91). A profound hydrologic
alteration of the bay also occurred. Increases in isurface runoff and decreases
in evapotranspiration throughout the watershed, triggered by the removal of
forests, caused an increase in freshwater flows to the Bay, reducing salinity in
the upper Bay. The State of Maryland now mines oyster shell from once-
productive oyster bars in the upper Chesapeake] where salinity in the water is
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now too low to support oysters, and places the shell in the lower Bay, where
oysters can still survive. •
The transformation of landscapes within the Chesapeake watershed
not only continue, but have accelerated. The population of the watershed,
slightly over 13 million people today, is expected to increase.by about twenty
percent in the next quarter century. But development patterns have changed
.dramatically in the last fifty years, and consumption of land will climb faster
than population. New development consumes nearly twice as much land
. per capita as existing development has (2020 Panel 1988). Thus while forest
loss in the Chesapeake watershed has slowed, and even reversed in some
regions, urbanization and suburbanization have increased. .
The potential implications of these trends for the Chesapeake and its.
tributaries are troubling. Without implementation of more sophisticated
approaches to understanding and managing watershed-scale consequences of
local land use decisions, continued loss of forest and wetlands, increased ." •'
human .populations, and more abundant roads, rooftops, parking areas and '
other "impervious, surf aces" will increase flow of pollutants, especially
nutrients, to the Chesapeake, and degrade both terrestrial and aquatic habitats.
A variety of local environmental services, from provision of habitat for
migratory birds and protection of human populations from flooding, are
likely to be disrupted. And regional environmental services such as support
of biodiversity, production of anadromous fishes and support of commercial
fisheries will be increasingly strained. These reductions in environmental
services represent real social costs of landscape change in the Chesapeake
watershed, costs that in many cases could be reduced by consideration of
landscape dynamics to guide policy and steer investments in environmental
restoration and enhancement.
Landscapes. Scale. And Land Management
Landscapes are hierarchically structured (O'Neill et al. 1986, Forfnan
and Godrpn 1986). Larger landscapes (e. g. the Chesapeake Watershed) are
composed of smaller landscapes (counties, sub-watersheds), which, in turn,
are composed of smaller units. The hierarchical nature of landscapes implies
a dependence of dynamics (patterns of change over time) at one spatio-
temporal scale on those occurring at other scales.' Local changes and changes
at the/landscape scale are necessarily linked, if only because landscapes are
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built up of local-scale features. Those linkages, however, take particular
forms because differences in the characteristic frequencies or response times at
successive levels in hierarchical systems partially insulates each level from
adjacent (higher or lower) levels (O'Neill et al.t 1986, Rollings 1992).
Phenomena occurring on landscape scales provide a slowly-changing
background for events at smaller, local scales (O'Neill et al. 1986). Thus the
Chesapeake Bay watershed provides a gradually [changing context for
phenomena occurring on individual land parcels.' A decision to-build a
seafood processing facility or a commercial fishing pier, for example, is
predicated on an abundance of fish, crabs, and oysters. As the bay's
production of these resources has declined, commercial coastal lands have
become available for marinas, ^vacation homes, and other uses .not as
dependent on abundant seafood. The landscape dynamics are slow enough,
however/ so that local events—whether land use decisions or changes in the
abundance of muskrats—are predominately controlled by the current
condition of the Bay, and only secondarily by ho;w the condition of the Bay is
changing. ;
Similarly, rapid changes at local scales are often attenuated by the slow
response times of landscapes. For example, the annual decisions farmers
make selecting among commodities to produce pn their farms induce short-
term fluctuations in land cover and land use. These fluctuations, however, •
have only limited effects on the Chesapeake watershed as a whole. The
watershed is too large and changes too slowly to! respond to such short term,
local fluctuations. ,
I
The cumulative impacts of local land use decisions on watershed or
landscape processes can be profound (Bedford arid Preston 1988). .The
relationship between the health of a landscape arid the health of component
ecosystems, lands, and habitats, however, is a cqmplex one. Both the scale of
changes in land condition and the location of lar^ds so affected are important
for determining overall landscape response. A limited degree of agricultural
or suburban development is possible within larger landscape units without
serious impairment of landscape processes (Klein 1979,'Schueler and Galli
1991). However, there are limits to this flexibility. When dynamically
important lands within a landscape (e.g., wetlands, riparian areas,
floodplains) are disturbed, or when ecological processes are altered or
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disrupted on a sufficient proportion of less sensitive, lands, landscape-level
processes and thus landscape-level environmental services may be impaired.
Current efforts to institute "ecosystem management" are, in part,
efforts to recognize landscape-scale ecological and social processes that have
traditionally been outside the range of consideration of land managers
(Grumbine 1994, Lackey 1994)..
Scale and the Management of Landscapes
Land managers operating at different spatial scales perceive different
incentives for management action, and are capable of effectively managing
different resources (Bohlen and King 1995). Land owners' primary -
management focus tends to be on-site resources. Local governments perceive
the effects of development decisions on the local landscape, including effects
on tax revenues, human health, costs of county services, aesthetics, and local
environmental effects. Federal managers are charged with protecting
resources at national scales/and attend to' interstate resources such as ,
migratory birds and major rivers, that local and state governments are
. unable, or unwilling to manage effectively. • -
The scale' of environmental management necessary for supporting or
enhancing environmental benefits depends on the particular benefit under
consideration. Landowners, for example, are capable of effective
management for timber, because most management actions to increase
timber production can be carried out without reference to practices on
adjacent lands. Since landowners also receive many of the benefits of
managing their lands for timber (see figure >1), investments in timber
management are, freely undertaken (provided harvest is not too far in the
future). In contrast, managing a wetland or a stream reach to support stocks
of anadromous fishes is impossible for most landowners. Even .a high quality
stream reach or wetland in a watershed that provides poor habitat for
anadromous fishes will support few fish. In addition, many of the benefits of
efforts to support anadromous fishes will accrue rriany tens of kilometers
from the stream .reaches in which the fish reproduce. Therefore land
managers (like many landowners and local governments) who focus on local .
environmental benefits would have difficulty protecting anadromous fishes,
but equally important, they may perceive weak incentives to dp so/since they
or their constituencies would receive only a small share of the benefits.
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Larger scale (regional, or national) managers, on the other hand, serve larger
constituencies that include those who benefit from improved commercial
and recreational fishing downstream. Thus regional or national authorities
are more likely to invest in protecting them.
Scales At Which Wetland Values
Are Received and Managed
1000 Km
100 Km
o>
*. 0) C
O E .2
0) *-
(fl D) O
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hard for individual land owners to manage, even if they want to, because
local benefits are supported by ecological processes occurring outside the local
area. In the presence of institutions such as elected governments, markets,
and voluntary associations that are capable of aggregating preferences of
, scattered individuals, cooperative, minimally coercive management may be
possible (e. g. , bag limits on waterfowl).. Management may be minimally
coercive in the sense that many local decision makers will receive benefits
from management actions, and-coercion is needed primarily to discourage
"free riders".
Resources below the diagonal line, on the other hand, present
fundamental conflicts of interest between landowners and others in society.
The resources generally must be managed at small scales (often at cost to
' landowners), but they produce benefits that accrue primarily, to others. Thus
landowner-dominated decisions generate externalities, and there may be calls
for regulation in order to" protect others' interests. Resulting regulations are
coercive in the sense that they impose real costs on local decision makers,
thus engendering non-compliance and political opposition. This conflict
between local and regional benefits underlies much of the current political •
controversy over regulation and property rights.
Landscapes in the Chesapeake Region
.,.. In this paper we focus on two contrasting landscapes in the Chesapeake
Watershed. The two landscapes are (1) rapidly suburbanizing Anne Arundel
County, Maryland, and (2) the largely agricultural Nanticoke river watershed
of Maryland and Delaware. Neither landscape can be considered "natural".
Both are products of a long history of human management. The Nanticoke
watershed is highly agricultural; Anne Arundel county is a county in the
midst of a suburban transition.
Case 1: Anne Arundel County
Anne Arundel County, Maryland is a suburbanizing county located ..
east of Washington D. C. and south of Baltimore. North of Annapolis, the
county is highly suburbanized, while "south county" retains much of its rural
character. Most of the county is now within an hour's drive of either '
Washington D. C. or Baltimore, making the entire county attractive for
suburban development. The county is underlain by deep, poorly consolidated
coastal deposits. Soils tend to be sandy and easily eroded. The Patuxent river,
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which forms the western boundary of the county!, is the only large non-tidal -
river in the county. Most streams are small, and; drain to tidewater within a
few miles of their headwaters, either to the tidal Patuxent, or to one of several
tidal rivers to the east. Stream valleys are often steep-sided, with narrow, but
well developed riparian areas. Extensive forests remain in the central and
western part of the county, with a few large forests in the north, and abundant
small woodlands to the south.
Anne Arundel County Land Use
1973
1990
Other
Developed
Land
Low Density
Residential
Other
Resource
Lands
Wetland
Forest
Agriculture
Figure 2: Land use in Anne Arundel County, Maryland, 1973 and 1990.
Agricultural and forest lands have declined, low density residential lands and
other developed lands have increased. (Based oh data From The Maryland
Office Of Planning). \
' T •
Land use changes in the county over the last twenty years have been
profound (Figure 2). Between 1973 and 1990, total developed land in the
county increased from 28% to 35% 'of county land area. Low density
residential development (which increased by almost 50% over the period)
accounted for almost half of that increase. Overjthe same period, forest lands
and agricultural lands declined by 10%. Almost half of the loss of forest and
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agricultural lands occurred in the last five years of the period, from 1985 to
1990 (all statistics on land use from Maryland Office of Planning 1991),
These statistics are a symptom of a general acceleration of land
consumption both in Anne Arundel county, in Maryland as a whole, and in
the Chesapeake Bay watershed (Maryland Office of Planning 199" 3, 2020 Panel
1988). The population of the state, while growing overall, has been
abandoning developed areas and moving into newly suburbanizing areas.
From 1970 to 1990, Maryland's urban and inner suburban areas have-shown
declines in population. The (mostly urban) areas of the state that declined in
population over that twenty year period witnessed a 21% loss in total
population, despite state-wide population growth. In contrast, newly
suburban areas of the state have shown strong population increases. Existing
suburban areas arid most rural areas have had slight population increases
(Maryland Office of Planning 1993). Per capita land consumption has .
increased substantially in the last few decades. As of 1950, an average of 0.18
acres of land had been developed per person in the Chesapeake Bay
Watershed. By 1980, land intensity of development had increased to the
extent that 0.65 acres of land were being developed per new Maryland resident
(2020 Panel 1988). /
Consequences of Suburbanization
Clearing of forest and the transformation of agricultural land into
lawn, roads, and buildings triggers profound hydrological, physical and
chemical changes at the landscape scale.
Abundant impervious surfaces in urban and suburban landscapes
(roads, parking.lots and roofs) prevent water-from infiltrating into the soil.
Infiltration on what pervious areas remain is reduced in comparison to that
which occurs in forested or even most agricultural landscapes. Little water
falling on suburban landscapes finds its way into the ground water, where
water flow rates are slow, and opportunities for biological and physical
removal of pollutants, great (figure 3, Schueler 1987);'
Under pre-development conditions, a substantial portion of .
precipitation enters the grpundwaiter, which slowly, drains to streams over
weeks or months. Flow paths to surface drainage networks' are long. Natural
ephemeral and low order s.treams dissipate a substantial proportion of the
energy of falling water in turbulent flow and friction, slowing water -.
movement. Thus water levels in streams remain higher between
- 8
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precipitation events, maintaining sufficient base-flows to protect aquatic
organisms, and the pulse of water that reaches tljie stream after a storm event
I "
(arrow in the figure) arrives slowly, spread put in time, resulting in a
relatively low peak discharge. |
Developed landscapes, on the other hand are "flashy". Structurally
complex natural drainage networks are replaced with simpler storm drain
systems, in which turbulent flow and friction are reduced. Water moves via
engineered surface water conveyances, instead of via a combination
ground water, surface sheet flow, and natural channels. Flood pulses are
rapid and high, but between-storm flows are low; most of the stream flow
occurs in brief flashes immediately following rainfall events.
Effects of Development
on Stream Hydrology
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urban streams in Anne Arundel county is sometimes severe enough io turn
streams into biologically depauperate gullies. In one extreme,case (the west
branch of Weams Creek on the outskirts of Annapolis) the stream has cut a
gully over 3 meters deep in places (personal observation). Sediments from
downcutting ,are also transported downstream.where they go on to harm
other aquatic ecosystems, and trigger dredging and other activities to
ameliorate their effects on waterfront land owners.
Second, urban and suburban streams are often unable to support
normal riparian communities. Riparian areas and associated wetlands trap
sediments and remove nutrients thus protecting downstream water quality.
Riparian areas are also important to a variety of landscape-scale processes
. . including creation of high quality aquatic habitats, water storage and support
of biodiversity (Peterjohn and Correll 1984, Welsch 1991, Schlosser 1991, ^
Richardson 1994, Bohlen 1992, Lowrance et al. 1995). Downcutting of streams
can dry out adjacent riparian areas and wetlands, reducing water quality and
other values. Even where downcutting has not been severe, flashy
conditions and reduced infiltration shrink the residence time of waters in
riparian areas, lessening opportunities for biological processing of nutrients.
Third, urban and suburban streams provide poor habitat for most
aquatic organisms. Abundance, number of species, and total diversity of
stream fish 'and invertebrates generally declines with watershed
. imperviousness, which is highly correlated with the abundance of urban-and
suburban lands within the watershed (Klein 1979, Schueler and Ga'lli 1991).
With even moderate levels of suburban development and extensive use of
urban BMP's (Best Management Practices), few species of fish survive, and
those that do survive are generally of little recreational value. The biotic -•'
integrity of urban and suburban streams is generally low (Karr et al. 1985,
Hall et al. 1994)
In addition to its physical effects, suburbanization _also increases the
flow of various pollutants to receiving waters. Urban and suburban
landscapes release substantial quantities of nutrients, sediments,
' hydrocarbons, metals, and other pollutants into surface waters (EPA 1991,
Schueler 1987, Ailstock and Horner 1989, Olsenholler 1991). Flows of
nutrients have been especially problematic in the larger context of the
Chesapeake restoration effort. The Chesapeake Bay Program adopted in 1987
an ambitious goal of reducing nitrogen and phosphorous flows to the Bay by
10
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40% by the year 2000 (Chesapeake Bay Program 1994). Suburbanization
increases nutrient flows in a number of ways.
i
(1) Nitrogen and phosphorous are released from suburban landscapes
simply because of their large human populations. Large quantities of
nutrients are imported into the Chesapeake Watershed in food. Those
nutrients are seldom exported from the region, but are released into
ground and surface waters via septic tanks and sewage treatment
plants. i
i
(2) Maryland now has more acres in lawn than in corn production
(Horton and Eichbaum 1990), Grass for oi|riamental purposes is thus
one of the state's major "crops". Many lawns receive high levels of
fertilizer/and leaching of nutrients can be significant.
i . •
(3) Approximately a quarter of the total nitrogen entering the Chesapeake
Bay is derived from atmospheric sources (MDE 1992, Hinga 1991). Of
that, about one third is thought to be derived from automobiles
(Waheed 1994). In suburban landscapes, people are widely scattered
and residences are far from shopping and work. Although emissions
per vehicle mile traveled have fallen, increased travel (in part
encouraged by suburban development patterns) has more than made
up for the difference. |- .
"C
(4) Loss of forest also contributes to increased nutrient loadings since
forests are both the region's least polluting land use, and highly
conservative of nutrients. Suburbanization replaces a non-polluting
land use with a much more polluting onei.
i
I
Sediment releases from suburban landscapes and from development
sites also cause problems for aquatic ecosystems,! Sediments fill navigation
channels, reduce light penetration in the water ciolumn, bury benthic
communities, reduce feeding efficiency of suspension feeders, and cause
physical damage to gills and other delicate biological structures. In streams
and rivers, sediments may also alter water flow patterns, sediment transfer
processes, and stream bottom properties in ways harmful to fish and other
desirable aquatic life. The impacts of sediments, may be further exacerbated
because phosphorus and a variety of toxic chemicals often travel adsorbed to
sediment particles. ! ,
Case 2: The Nanticoke Watershed !
The Nanticoke watershed drains approximately 400,000 acres in
Caroline, Dorchester, Wicomico and Somerset counties in Maryland, as well
11
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as approximately 315,000 acres in Sussex and Kent counties, Delaware (Nature
Conservancy 1994). Agriculture accounts for approximately 42% of the
watershed by area. Forests/ many intensively managed, cover an additional
45% of the watershed. Less than 2% of the watershed area is in urban lands.
The landscape is one of low topographic relief, developed on a variety
of unconsolidated sediments, mostly-derived from sandy and silty coastal
plain deposits. With little elevation change, water potential gradients are
low, so both ground water and surface water flows are slow. In particular,
without artificial drainage, water drains slowly and ponds extensively.
Extensive wetland complexes were once found along drainage divides
throughout the region where topographic gradients are low, and drainage
patterns ill-defined. In the upper, Delaware portion of the watershed
substantial areas were drained for agriculture, many of them as WPA projects
during the depression. -
Nanticoke Watershed Land Use
Urban
Wetlands 2%
Agriculture
42%
Forest
45%
Figure 4: Land Use in the JSJanticoke Watershed. Forested wetlands have been
included in the "Forest" land use category. Total wetland area therefore is
somewhat higher than this diagram suggests.
12
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There has been little change in land use irt the watershed over the last
few decades. There has been only a slight increase in urban land over this
period, although development of suburban strips along major roads has
occurred around the watershed's larger towns and cities. Data from the
Yearbooks of Agriculture (U.S. Department of Commerce 1954, 1959,1964,
1969,1974,1982,1987, and 1992) for Dorchester County, Maryland and Sussex
County, Delaware show that between 1948 and the present, total cropland area
has remained more or less constant, or increased slightly. Simultaneously,
the total number of farms has declined/ and average farm size has risen
(Figure 5). • j
Changes in Agricultural Land Use,
Two Nanticoke Counties
1500 i
Number
of Farms
(Dashed Line)
and 0
4000
.Average
Size
In Acres
(Light Line)
Dorchester County, MD
150000
Sussex County, DE
300000
Total
Cropland
H
(Heavy Line)
O) ^" O5 ^d" OJ ^" t*^*
O) O> O) O3 O> O) O5
Year of Census
Figure 5: Changes in Land use in Two Nanticoke Counties, 1948-1992. Source:
Census of Agriculture.
Consequences of Agriculture
Much of modern agricultural practice is an effort to keep agricultural
fields in early successional states. Repeated disturbances (in the form of
plowing, disking, cultivating, applying herbicidips, and harvesting) prevent
the development of later successional ecosystems (e.g., forests) that would be
13
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undesirable for agricultural production. Early successional ecosystems
generally show an excess of primary productivity over respiration. In many
agricultural production systems, that excess is captured for human use in the
form of crops (Odum 1969). .Unfortunately, early successional ecosystems also
tend to be leaky. Early successional or disturbed ecosystems retain nutrients
and sediments less tightly than do less frequently disturbed communities
(Odum 1969, Bormann and Likens 1979). Thus agricultural efforts to
maintain early successional conditions in order to produce crops are ,
associated with releases of sediments and nutrients to adjacent ecosystems.
Careful agricultural management efforts can limit the losses;'but they are
extremely difficult to eliminate entirely.
On a landscape scale/agriculture increases nutrient flows to the Bay by
importing nutrients into the .Chesapeake watershed, especially in the form of
fertilizers and animal feeds. Nutrients are also exported from the region in
agricultural products, but because of nutrient losses within the agricultural
production system, a portion of the imported nutrients remains within'the
watershed, increasing total loadings to the bay.
The agricultural community has, for years, worked hard to reduce soil
erosion and the export of nutrients from agricultural lands. Various
management practices, from fertilization practices, to strip cropping, to low-
till or no-till farming systems can increase or decrease the loss of nutrients
and soil from agriculture. A variety of federal and state agencies have worked
with farmers to develop management techniques to reduce the loss of
sediment and nutrients from farm fields. Maryland now requires many
farms within the 1000 foot "critical area" adjoining the Chesapeake and its
tidal tributaries to have detailed nutrient management plans. These plans,
which vary in their complexity, represent a concerted effort on the part of
farmers to reduce the loss of nutrients from agriculture. The Soil" .
Conservation Service worked for decades with farmers to implement
agricultural Best Management Practices (BMPs) targeted on reducing soil loss.
The SCS's mission was gradually broadened by legislation and policy to
incorporate a wider, and wider range of resource protection issues, including
protection of water quality, the reduction of nutrient runoff, wildlife
conservation, and wetland protection. Near the end of 1994, the agency's ' -\
name was officially changed to "Natural Resources Conservation Service" in
order to reflect its broader mission.
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Despite these and related efforts, agriculture remains a major source of
nutrients to surface and ground water. Water quality in the tidal fresh
portion of the Nanticoke river reflects the impacts of agriculture. The
consequences are shown in water quality monitoring records collected
between 1985 and 1989 at the tributary water quality monitoring station on the
tidal freshwater portion of the Nanticoke river, near Sharpstown, MD (MDE
1994). Dissolved inorganic nitrogen (sum of nitrate, nitrite, and ammonium
concentrations) 'was routinely available in excess, and sometimes in
tremendous excess of levels limiting to phytoplankton growth. Ratios of the
concentrations of total nitrogen to total phosphorus were also very high,
indicating that phytoplankton growth was generally limited by available
phosphorous. Chlorophyll A concentrations (a measure.of phytoplankton
abundance) were high, and Secchi depths (a measure of water clarity) were
low. Conditions were poor enough to preclude growth of submerged aquatic
plants, which grow best when waters are clear.' Ecologically, the Nanticoke is
suffering negative effects from nutrient enrichment, especially enrichment by
nitrogen.
The USGS has found that agriculture on the Delmarva peninsula also
contributes nitrate to ground water. Detectable levels of nitrate were found
throughout 'the upper portions,of the Nanticoke watershed, but
concentrations of nitrate exceeded EPA drinking water standards (10 mg/1,
approximately 15 times the level at which phytoplankton growth would be
limited) only in a few hotspots (Hamilton et al. 1992). Over time (sometimes
measured in decades in the flat Nanticoke watershed) this nitrate-enriched
ground water will flow to streams and other surface water systems,
eventually increasing nitrate loadings to the Chesapeake.
Consequences of Drainage
The construction of drainage systems throughout the upper portion of
the Nanticoke represents a significant change in landscape dynamics, and has
had a series of ecological consequences. j
Construction of drainage ditches successfully sped the removal of water
from the landscape, thus allowing expansion of iagricultural production. The
same increase in the speed with which water drains off of the landscape,
however, changes the patterns of water flow entering downstream.
ecosystems. Construction of drainage systems removes surface water, and in
the sandy soils that predominate in much of the; Nanticoke watershed, can
15
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lower the water table aquifer as well. The net effect is to reduce the ability of
landscape to trap and store water.-. Rainfall from storm events, instead of
being stored within the upstream portions of the watershed is now passed
downstream, increasing peak discharge following storms, and increasing the
variability of the salinity and other chemical characteristics of estuarine
waters downstream. • , ,
Drainage has resulted in the loss of substantial areas of wetland and the
degradation of 'riparian areas. Wetlands and riparian areas can be remarkably
effective at removing, transforming, or neutralizing sediments, nutrients and
certain other common agricultural pollutants from surface and groundwater-
flows (e. g. Moshiri 1993, Peter John and Correll 1984, Welsch 1991, Lowrance
et-al. 1995). The potential water quality benefits of these areas have been
reduced because (1) the area of wetland and riparian forest within the
landscape has been reduced, (2) ground and surface waters draining
agricultural areas and carrying heavy loads of pollutants are now more likely
to bypass riparian areas, and (3) those waters that do pass through a riparian
area are likely to flow through the biologically active zones'of the soil more
quickly under the increased hydraulic gradient provided by drainage systems.
These changes reduce the extent of denitrification, physical trapping of
sediments, and biological uptake of. nutrients within the upper portions of -
the watershed.
It is possible, although not yet proven/that hydrologic changes in the
river have exacerbated the impacts of acid deposition on rockfish (Morone .
saxitalis). Rockfish larvae are unable to survive in the Nanticoke river,
apparently because of low pH and elevated levels of aluminum in the water
(Hall et al 1985). The shorter time that water from storm events resides on
the landscape reduces the extent to which storm waters are mixed with less
acidic groundwater. Moreover, decreased contact of storm waters with
wetland and riparian systems may limit biogenic buffering processes capable
of reducing the detrimental effects of the acid deposition. Thus hydrologic
modifications may have increased the severity of acidic "flashes" that follow
precipitation events, indirectly limiting rockfish recruitment, and reducing
populations of other acid-sensitive fish species (Hall et al. 1994)
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Landscape Management
Management Of Landscapes Via Natural Vs. Cultural Processes.
Landscapes maintain and change their physical structure through
endogenous (ecological and physical) processes,: through maintenance
processes carried out by humans, or through some combination of the two. •
In human-dominated ecosystems, maintenance processes may derive from
government expenditures, general economic activity, engineering, or other
human behaviors. In unmanaged landscapes, ecological maintenance
processes predominate. These non-anthropogenic maintenance processes are
known as "functions" in the wetlands science and policy literature
(Richardson 1994). We use the term "ecological processes" to emphasize that
these phenomena need not have any utilitarian benefit to be significant from
the perspective of landscape dynamics. j
The choices land managers face can be depicted schematically in a
Landscape Management Ternary Diagram (figure 4). Human activity may
sever or alter one or several of the environmental processes that maintain
the ecological and physical structure of an unmanaged landscape. The
resulting landscape change may be perceived either as beneficial (e. g., when
agriculture is established) or as detrimental (e. §;., when suburbanization
leads to degradation of stream ecosystems). When humans like the landscape
changes, cultural processes develop or are established that maintain the
landscape in its new, desirable form. Therefore^ the landscape moves from
the lower right region of the ternary diagram labeled "Maintained by
Ecosystem Processes" toward the top of the diagram, labeled "Maintained By
Cultural Processes" to reflect the increased importance of human activity in
maintaining the structure of the landscape. If humans do not like the
landscape changes, two outcomes are possible. First, cultural management
may not develop, and the landscape moves towiard the lower left part of the
diagram, labeled "Low Environmental Quality". Second, human societies
may undertake defensive expenditures to resist the landscape changes, again
increasing the degree to which the landscape is maintained by cultural
processes, and moving toward the upper portion of the ternary diagram.
The landscape management ternary diagram depicts, in a schematic
way, the relative intensity or importance of cultural and ecological processes
in structuring landscapes. A healthy urban landscape, for example, might rest
17
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somewhere near the "I" on the diagram, A wilderness area, somewhere near
the "2". An agricultural landscape dominated by conventional agricultural
practices might lie at "3", while a small, heavily managed nature reserve in a
suburban landscape might lie somewhere near the "4". More generally, the
• diagram represents a state space over which landscapes evolve as they are
. disturbed, managed, and abandoned by humans. The diagram provides a
framework for understanding a variety of land management decisions.
LandscapeTernary Diagram
Maintained by
Human .and Cultural Processes
Restoration
Low Environmental
Quality
Maintained by
Ecosystem Processes
Figure 6: The Landscape Management Ternary. Diagram.
>
It is important to point out that both high quality and low quality lands
may be maintained predominately by either cultural processes or ecosystem
processes. The relative importance of cultural and ecosystem maintenance is
not, in general, related to any subjective evaluation of environmental quality.
Relatively stable, culturally dominated landscapes—of both low and high
quality—have existed in Europe and Asia for a millennium or more.
Moreover, the conceptual separation we are using between cultural and
ecosystem processes is in no way an effort to separate humans from nature.
In fact, it is in large part motivated by an effort to develop analytic
18
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alternatives to a simplistic dichotomy between natural landscapes and other
(unnatural?) landscapes. If such a dichotomy ever had any validity, it
certainly has little in a world in which even the global radiation budget has
been altered by human activity (McKibben 1989),: Essentially all landscapes
today are maintained or altered by some combination of ecosystem and
cultural processes.
Indeed, land managers, in deciding how to achieve environmental and
social goals may rely primarily on cultural processes or on ecological processes
to maintain, restore, or enhance landscapes. The resulting landscapes would
be very different (city versus forest) and would therefore provide different
combinations of environmental and economic benefits, risks, and ;
opportunities. Direct maintenance costs for landscapes maintained by
ecological processes are, by definition, low. The direct costs of maintaining a
landscape by cultural processes will be higher. In general, reliance on cultural
processes will require ongoing effort (and expense) to prevent succession,
decay, erosion, sediment deposition, and other ecological or physical processes
from changing the landscape in undesirable wayb. In addition, landscapes
maintained primarily by cultural processes often change the rate of flow of
sediments, nutrients, water, -and other chemicals to adjacent ecosystems,
perturbing them in unplanned, and often undesirable ways. Thus human-
dominated landscapes often induce environmental externalities.
To understand why externalities arise, it is necessary to consider
landscapes as hierarchical systems. Landscapes have usually been managed
primarily at small scales; less attention has been ;paid to the effects of small-
scale land use changes on larger-scale landscape and watershed processes,
perhaps because the benefits to be derived are often public goods. The
intercalation of cultural processes into the landscape hierarchy therefore is
dominated by social, .economic, and behavioral processes occurring at certain
characteristic scales. At larger scales, we just do not pay much attention until
some sort of a problem develops. ,
Within a dynamic hierarchy, however, changes in dynamics at specific
scales are communicated up and down the hierarchy. Altering dynamic
processes at one scale will trigger unplanned effects at other scales. One
manifestation of this is that landscapes maintained predominately by cultural
processes often export environmental problems to other landscapes with
which they are linked (for example the agricultural landscape of the
19 '
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Nanticoke exports nutrients to the estuary). These problems represent
, conditions imposed on adjacent ecosystems inconsistent with their previous
ecologically-driven dynamic regimes. Establishment of culturally-maintained
, landscapes at one scale often has the effect of disrupting ecosystem
maintenance-processes at larger scales. At the smaller scale, culturally-
controlled landscapes may be of .high quality (toward the top and right of the
ternary diagram), yet at the next higher level in the landscape hierarchy, the
landscape will begin to change. At least in the short term., it is likely that at
some of these unplanned and often unanticipated landscape changes willbe
undesirable;
In the Chesapeake watershed, small-scale landscape transformation has
been going on for 'centuries, with different results in different areas. In
suburban or agricultural landscapes, as elsewhere, we have just begun to
institute cultural processes aimed at maintaining the larger (watershed scale)
landscape system. It should, therefore, not come as a surprise that the
Chesapeake watershed shows signs of dynamic instability and functional ,
change. In this case, many of the changes we see have been unpleasant, with
the result that a concerted effort has developed to manage the bay to maintain
more of its environmental benefits, either by shoring up disrupted ecosystem
processes, or by implementing riew cultural processes to .partially replace .
them. , . ,
Management Of Chesapeake Landscapes
Consider the management options faced by managers of the
Chesapeake Bay and its watershed hoping to restore environmental services
once provided by the Chesapeake. (I) The Bay may be managed in a manner
that relies on cultural processes to assist in the production of .desired
environmental outputs (for example, oyster aquaculture, rockfish hatcheries).
• We would call this approach environmental enhancement, since it would
not be restoring the Bay system to previous dynamic conditions, but instead .
working to replace them with a new dynamic regime. Such a strategy is likely
to become increasingly difficult and expensive as ecosystem services of the
Bay watershed continue to decline. (2) Alternatively, the Bay could be
managed to'reinstate fundamental ecological relationships that previously
produced desired environmental benefits. This approach could be called
environmental restoration because it focuses on restoring ecological processes
20
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that previously dominated the dynamics of the watershed. Environmental
restoration, in this sense, may place more stringent limits on the scale or
character of human activities within the Chesapeake watershed, inducing a
variety of social costs. Different approaches or combinations will be most
feasible in each landscape.
Environmental restoration is likely to play a significant role in
agricultural landscapes such as the Nanticoke, where land use is relatively
stable, and the physical structure of the watershed is less profoundly
disturbed. Impervious surfaces are not widespread in the Nanticoke
watershed. The basic topographic structure necessary to reestablish ecological
linkages between agricultural fields, drainage systems, and largely intact (but
dewatered) 'riparian area remain in place. Restoration of wetlands and
riparian areas would reestablish biological processing of nutrients and other
chemicals. Such an effort would require that water be retained on the
landscape for longer periods of time than is now the case. Increased retention
would increase the exposure of both ground and surface waters to biological
processing, and reestablish and maintain conditions in the soil conducive to
denitrification. While restoring the hydrology of the Nanticoke watershed to
something resembling its historical condition may be technically feasible,
such a change would be expensive and probably unacceptable to local
inhabitants. To be practical, restoration of landscape functions must be
carried out in such a way that farmers' and other residents' need, for drainage
can continue to be met, while simultaneously retaining more water on the .
landscape, at least at some locations and at some times of year.
Much of the Nanticoke watershed once consisted of seasonal wetland
systems, wet in the late winter and spring, but drier once evapotranspiration
of growing trees and other plants removed water from the poorly drained
soils. A major goal of many drainage systems thus was to remove water early
in the growing season in order to ensure that agricultural lands could be
planted. Ironically, some areas are now irrigated during the summer because
they lack sufficient water to maintain plant growth. The ditches that remove
water in the spring also reduce the availability of water the rest of the year.
Thus while full restoration of natural hydrology is impractical for the
Nanticoke, partial restoration of ecological functions may be possible. Using
simple water control structures that can be opened a certain times of year, and
closed at other times. Installation of such structures within selected ditches
21
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may allow removal of water from these lands in the spring (when the control
structures are open), while permitting increased retention of- waters in the
floodplains during the remainder of the growing season, when agricultural as
well as riparian and wetland areas could benefit. • . '
In contrast to the rural landscapes of the Nanticoke watershed, few
opportunities for large scale landscape restoration are likely within urban and
suburbanizing landscapes such as those in. Anne Arundel County. Tree
plantings and other typical urban and suburban restoration efforts build
public awareness of environmental issues, but often have only, marginal
impacts on landscape-level processes. Larger-scale efforts at restoration are ,.
.generally precluded because they would require the displacement of high-,, •
value land uses and removal of existing structures. .Instead, most
opportunities for managing landscape processes in suburban landscapes rely
on enhancement of environmental functions with engineered structures like
storm water management devices.
Over the last two decades, stormwater management has increasingly
been used to protect streams and surface waters from the consequences of
local land use change (e. g. Schueler 1987). Infiltration, detention and
retention basins have become a fixture of the Maryland landscape, found
wherever recent development has occurred. Stormwater management <
substitutes engineered structures designed to provide particular hydrologic
and water quality services for physical and ecological processes disrupted by
development. Installation of stormwater management structures represents
a prime example of a landscape being managed to achieve environmental
purposes in a way that increases reliance on cultural processes.
The potential value of stormwater management is great, but it comes
with substantial costs. The engineered structures being used for stormwater
management are costly, and require ongoing maintenance to protect their
environmental function. .Maintenance shortcomings are common (Roberts-
and Lindsey 1990). Even when properly maintained, most stormwater
management structures have a variety of unintended side effects (Schueler
and Galli 1991). Infiltration devices, for example, not only infiltrate water, but
also inject dissolved pollutants into the ground water, where biological
contact and treatment are low. ''Detention and retention basins increase
surface water temperatures. In general, high maintenance requirements and
22
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a variety of environmental side effects are to be expected whenever cultural
maintenance processes substitute for ecological ones.
Recent developments in stormwater management have tried to reduce
or eliminate many of these problems (Schueler and Galli 1991). One answer
has been to design stormwater management structures as shallow, vegetated
wetlands (Moshiri 1993, Schueler 1992). These basins not only provide the
water quality and quantity control required of stormwater management
devices by state laws, but also provide an artificial context for ecological
processes in a largely human-dominated landscape where such processes
would otherwise be rare. Using artificial wetlands in this way reflects a
growing understanding that environmental technologies can be most
effective when built to exploit, rather than resist ecological processes (Mitsch
and Jorgensen 1989). On a larger scale, these artificial wetlands represent an
effort to build a hybrid landscape that is neither natural nor artificial, but in
which important natural processes are sustained in the context of a landscape
that provided for human wants and needs. Such, hybrid management
systems, part nature, part culture, will, we suspect, become ever more
common, as our society learns to reconcile the self-sustaining character of
ecosystems and the focused functionality of manufactured artifacts, and
equally important, as we learn to recognize how; human activity affects
landscape-scale systems.
Conclusions
Residents of the Chesapeake Bay watershed have made, and continue
to make, many land management decisions basecl on local benefits and short-
term needs. Cumulatively, these decisions have provided food, housing, and
other direct benefits for many, but have simultaneously altered landscape
systems and initiated changes in landscape functions that reduced other
benefits provided by the Bay, its watershed and its tributaries.
We suggest that long term restoration and protection of the
Chesapeake Bay and its many values will require recognition of the
hierarchical properties of landscapes. In the long run, successful
management of the Chesapeake will require tools and approaches to
environmental management able to assess landscape functions at various
scales and able to recognize cumulative effects of apparently isolated
decisions. Efforts should be expanded to inform individuals how their
23
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actions impact, the landscape, as well as to communicate what can be done to
achieve individual land management goals; while avoiding or mitigating
negative impacts on landscape systems. Landscape-scale management should
.also provide feed-back to individuals and local governments so that their
actions can be better coordinated to reduce threats to landscape-functions. In
the long run/ economic, legal and other incentives and disincentives may
have to be tailored to reduce local activities that create negative externalities
at landscape scales, and encourage those that support landscape processes.
Some landscape-centered management,approaches already exist. For '
example, Local governments and soil and water conservation districts which
oversee land management within political boundaries have initiated various
programs to promote land management practices that help to maintain
landscape-level functions. Federal, state, and local regulations have also been
adopted that coerce land managers to reduce certain impacts on landscape-
scale systems and to provide mitigation for impacts that do occur. Such
regulations, however, are facing strong opposition because they generally
impose direct costs on individual land owners. •
Interestingly, recent changes in efforts to manage Chesapeake
watershed also reflect the need for management that better reflects the
hierarchical nature of landscape dynamics. The Chesapeake Bay Program, a*
regional cooperative'effort to study and manage landscape-scale was
established by the federal government and the main Chesapeake Bay states,
(Pennsylvania, Maryland, Virginia, as well as the District of Columbia) as a
way to better study and manage landscape-scale problems that have led to loss
of benefits from the Bay. Recently, leaders of the Chesapeake Bay Program
initiated the "Tributary Strategies" which decentralize the watershed
restoration effort, and focus attention on the peculiarities of the different sub-
watersheds of the Chesapeake. Coalitions of citizens, local governments, and
soil and water district officials have been created to evaluate specific problems
within the watersheds of the major Chesapeake Bay tributaries, and to
promote regional management at a landscape scale. A major component of
this initiative is education of residents so that they may make land-
management decisions informed by how they impact the larger landscape
system. ' ' -
In the Chesapeake Bay watershed, re-establishing landscape processes
able to support a healthy, more productive Bay will require recognition of and
24
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investment in landscape-scale processes. We will have to be far more
sophisticated landscape and watershed managers than we are today if we are
to support anticipated human populations of 15 million or more in the
watershed by the year 2020 without causing further declines in the physical,
chemical, and biological integrity of the Bay and its tributaries. In the future,
management efforts that focus explicitly on enhancing or restoring
watershed- or landscape-scale processes must became a central part of all
efforts to protect the environmental benefits of the Chesapeake. Otherwise,
' the combination of the landscape-scale externalities associated with land use
decisions and the limited ability of markets to efficiently allocate public goods
will lead to continued deterioration of the Chesapeake watershed,
unnecessarily impoverishing the region.
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