GIS Speaks for the Bay

Modeling the impact of human activity on the upper Chesapeake.

by / June 30, 1998 0
According to Johns Hopkins University paleoecologist Grace Brush, there are no closed ecosystems. What happens to one is likely to affect others. The Chesapeake Bay and its 64,000-square-mile watershed demonstrate this. Human activity in the watershed over the past 300 years, particularly in the last century, is the primary cause of the long, downhill slide of the Chesapeake ecological system, including the vanishing wetlands, clogged rivers and streams, agricultural and industrial runoff, polluted water, destroyed bottom habitats, diversity decline, and the local extinction of whole communities of fish, oysters, clams, crabs and other benthic organisms.

Environmental Records

Studies by Brush and others show that habitat destruction in the bay is caused primarily by the continuous flow of pollution, nutrients and soil-eroded sediment from extensive deforestation, development and agriculture in the upland watershed. From bottom core samples taken in the bay and its tributaries, Brush reconstructed a history of estuarine changes over time. Core samples contain environmental records, not only of the chemical composition of sediment layers but, like tree rings, the rates at which layers have accumulated, including during storm peaks. As long as the watershed was primarily forested, the ecology of the bay remained relatively diverse and healthy. However, from the late-1800s on, increases in sediment, nutrients and pollutants draining into the Chesapeake via its freshwater streams and tributaries followed the expanding human population within the watershed.

Sediment, in turn, diminished light needed by aquatic grasses and plants on the bottom -- the habitat of small fish, shellfish and many other benthic organisms that compose the ecosystem of the bay. As vegetation died out, the decaying biomass depleted the oxygen in the water. The process was accelerated by high levels of nutrients that encouraged surface growth of blue-green algae, blocking light still further. By the 1970s, the bottom of the upper Chesapeake, once a substrate of sand and rock, thriving with plant and animal diversity, had become a floor of lifeless mud. Environmental decline was further accelerated by over-harvesting of fish and shellfish, particularly oysters and clams essential for filtering nutrients, stabilizing pH and regulating oxygen concentrations in the water.

Decline Threatens Economic Health

Despite present conditions in the largest estuary in North America, 5 1/2 times the area of San Francisco Bay, the Chesapeake continues to be vitally important to the economies of Maryland and Virginia. Recreation anglers in Maryland spend more than $467 million annually pursuing various fin fish. In 1996, seafood contributed over $125 million to the state's economy. Boating in Maryland represents a $1 billion industry.

However, without significant reductions in pollution and sedimentation, the system cannot support oysters in numbers needed to effectively filter water in the bay. Without oysters, even existing communities of fish may not be sustainable, especially with the rapid development taking place in this part of the Atlantic Coast. In Maryland, for example, where the current rate of urban sprawl is described by Gov. Parris Glendening as a "living organism out of control," loss of farm and forest land has reached alarming proportions.

In the past six months, approximately 5,000 people have left Baltimore City; 3,000 septic permits have been issued [for new urban homes]; and nearly 10,000 acres of forests and farmlands have been lost. If these trends continue, Maryland could use as much land for development in the next 25 years as it has used in the entire history of the state.

Recovery Efforts

There is an upside to all this: Environmental awareness has made the Chesapeake the most intensely studied and monitored estuary in the world, and millions of dollars are being spent in cleanup programs.

Numerous government agencies, private groups and individual scientists are involved in efforts to restore and protect the bay's natural resources and habitats, develop pollution-reduction strategies and promote environmental awareness through a broad range of educational programs. Since 1996, Maryland has reopened 173 miles of fish-spawning habitats, pledged 600 miles of new forest buffers and earmarked up to $17.5 million for oyster habitat rehabilitation. To advance environmental research and education, the state developed Maryland Environmental Resources and Land Information Networks (MERLIN), a dedicated geographic information system (GIS) for producing maps and models of the Chesapeake system and coastline. Environmentalist groups are also contributing to the recovery. In some areas, local efforts have produced a reduction in pollution, a restoration of aquatic grasses, cleared streams and brought about the return of striped bass. Through efforts to stem inner-city abandonment and runaway urbanization, Maryland's Neighborhood Conservation and Smart Growth initiatives may also help to reduce deterioration of Chesapeake habitats.

Environmental scientist Greg Pasternack said fishermen are suddenly understanding what the scientists have been saying about the effects of waste being dumped into the bay from the chicken and hog farms: "The fish and oysters are dying from it. Now, instead of fishermen fighting the scientists, they are working with us to stop the dumping."

Modeling Sedimentation

For the past three years, Pasternack, a former student of Grace Brush, has focused his doctoral studies on sediment accumulation that takes place where freshwater streams drain into small tributaries of the upper Chesapeake Bay. Pasternack explained that this is where sediment settles out and forms deltas, vast piles of mud that build in the direction of the bay. "In the process, the piles overrun the habitats of all the fish and benthic organisms in the tributaries -- the last aquatic vegetation beds driving the bay's ecosystem. The sediment piles are growing so fast you can see how they change the landscape. As deltas build, the mud fills in the tributaries, transforming them into wetlands. Areas once under 10 feet of water a few centuries ago are now forests."

Sponsored by the National Oceanic and Atmospheric Administration (NOAA) and the Maryland Department of Natural Resources (MDNR), Pasternack's research includes computer modeling to simulate wetland evolution and field monitoring of the wetlands at Otter Point Creek (OPC) -- an area near the northern end of the Chesapeake in a NOAA National Estuarine Research Reserve.

Variables being monitored include: precipitation, winds, watershed runoff, wetland water levels, sedimentation rates, beaver activity and plant associations. Aquatic plants, Pasternack explained, can affect sediment dispersion. "Different plants have different trapping capabilities; depending on their size and density, plants can trap sediments by slowing their movement, causing them to settle out."

Field surveys with a global positioning system are used to map plant species, study sites, habitat boundaries and sediment-trap locations. The data is put into Environmental Systems Research Institute's ArcView and ArcInfo systems. Variables are analyzed using standard statistical methods and spatial algorithms applied to an ArcView GIS database of the OPC tidal freshwater system. The basemap is a color-infrared, digital ortho quarter quad (DOQQ) with a resolution of four feet. Pasternack is developing two models of the sedimentation process using different time periods: one to simulate seasonal and interannual activity, the other to project long-term trends in sediment accumulation and habitat distributions under changing land-use conditions.

By modeling the sedimentation process, Pasternack believes that it will be possible to predict the impact of human activities in the watershed -- on the transformation of habitats -- from tributary to wetlands to forest. "The information will allow managers to evaluate the longevity and effectiveness of proposed restoration projects. The models could also be used by planners to regulate land-use changes upstream, to prevent desirable and existing habitats from becoming unstable."

Adviser and Teacher

Pasternack also works closely with MDNR and other county and state agencies on management and education issues. In one instance, for example, county engineers wanted to stabilize a delta channel that was migrating toward a sewer line. By showing that the channel was part of an unstable network, subject to periods of erosion or sedimentation, Pasternack was able to show that the effort would be a waste of money. "I helped them understand that some parts of the system are moving around quickly -- in this instance, 15 feet a year -- and that it would be a mistake to spend a lot of money to go in with concrete and try to stabilize it, because the next big storm will carve a new channel and simply leave this one dry."

Pasternack conducts workshops for state and county land-use planners and volunteers, and he gives presentations for secondary-school students and teachers. Since the computer models are not yet complete, he uses high-resolution DOQQs and GIS-generated maps for presentations. "We use the maps to convey the point that a lot of sediment is coming into the tributaries as a result of human activities in the watershed. We need to look at these tributaries, because that's where the vital habitats are; they are what H.L. Mencken once called the 'protein factory of the bay.' That's where it all happens. Eventually, we will be able to do the presentations with GIS modeling."

Katherine Buppert, education coordinator for the Chesapeake Bay National Estuarine Research Reserve (CBNERR) in Maryland, said the workshops provide ongoing information about estuarine ecosystems and are helpful to the state and county, particularly in understanding the processes of sedimentation in the estuary. "The county and the MDNR is in the process of completing a watershed survey [of the CBNERR]. The next step will be to look at the problem areas determined by the survey and begin formulating restoration plans. The work that Greg [Pasternack] and his predecessor, Grace Brush, have done forms a basis for understanding all of those processes."

Expanding Role For GIS

Even partial recovery of the Chesapeake ecosystem calls for significant reductions in the major factors directly affecting aquatic life in the bay -- sedimentation, toxic wastes and over-harvesting. Education and understanding of the interrelationship between the watershed and the bay into which it drains must be part of that effort. In efforts like this, GIS will be an essential tool in plotting strategies to reduce the impact of human population on the environment, and in bringing home the message.

Bill McGarigle is a writer based in Santa Cruz, Calif.

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