The Importance of Understanding Ecological Complexity to Predicting the Effects of Multiple Stressors on Coastal Ecosystems--Watershed Studies

Contact:
Dr. Don Weller
Smithsonian Environ. Res. Ctr.
P.O. Box 28
Edgewater, MD 21037-0028
weller@serc.si.edu

The watershed component of the NOAA-COP COASTES project seeks to understand the land discharges of nutrients and trace elements to the Patuxent estuary. The project is directed by David Correll, Thomas Jordan, and Donald Weller of the Smithsonian Environmental Research Center. The study is an integrated program of stream sampling, geographical analysis, and modeling. The objectives are to:

  1. quantify the major sources of nutrient (N, P, and Si) and toxic trace element (As, Cd, and Cu) discharges from the Patuxent watershed;
  2. determine the spatial and temporal variability of nutrient and trace element discharges from the watershed;
  3. relate spatial variability in watershed discharges to spatial heterogeneity in natural and human factors;
  4. investigate the effects of riparian buffers for reducing watershed discharges; and
  5. predict the changes in watershed discharges of nutrients and trace elements for a range of plausible land use and land management changes.

We measure non-point source discharges from the Patuxent watershed with a combination of continuous automated sampling of 26 streams and periodic grab sampling of over 130 stream reaches throughout the Patuxent watershed.

Automated sampling integrates the effects of both episodic stormflow and groundwater discharge. The automated sampling will concentrate on 3 clusters of streams: one in the Piedmont Province (Cattail Creek) and two in the Coastal Plain (Western Branch and the Rhode River). The nested watersheds have been selected to exclude point sources and to include various mixtures of forest, suburban, and agricultural land use in a variety of spatial configurations. Water samples will be pumped in proportion to flow and composited over weekly intervals.

Grab sampling is useful for estimating discharge of dissolved substances and for efficiently sampling large numbers of watersheds. We take monthly grab samples of all the major tributaries to the Patuxent and seasonal grab samples of about 100 small streams with watersheds that differ in land use. We also collect grab samples at different rates of stream flow to characterize the partitioning of dissolved and particulate materials as a function of stream flow.

At the Rhode River, we collect data on weather and precipitation chemistry. We also plan to measure deposition near our Piedmont cluster. Information on point sources will be obtained from other monitoring programs.

We are assembling a wide variety of geographic data for comparison to flow and water quality measurements. These include data on weather, topography, hydrography, land use, soils, geology, and land management.

We use a suite of models in our watershed research program:

  1. theoretical models of simple, hypothetical landscapes to deduce general principles of landscape structure and function;
  2. statistical models that relate nutrient discharges to geographic data on weather, geology, soils, land use, land use arrangement, and land management;
  3. GIS-based spatial models that trace the movement of water and water-borne nutrients through the different units of the landscape;
  4. simulation models to predict nutrient discharge from data on rainfall and temperature and from geographic data on geological, land use, and land management factors.

We strive for parsimonious, empirically based models that are appropriate for project objectives and our scale of observation.

Funding for the COASTES project has been awarded through the year 2000. The watershed work described here is integrated into the larger COASTES and is also strongly synergistic with SERC's ongoing NSF-funded studies of watershed discharges throughout the Chesapeake Bay drainage basin. Over the next years of effort, we hope to build collaborative relationships with other research and management groups working in the Patuxent watershed.