CHEMICAL AGENTS AND OTHER POLLUTANTS

Chemical Agents and other pollutants in Pennsylvania's Chesapeake Watershed

Chesapeake Watershed

Introduction

Inputs of nitrogen and phosphorus to the Chesapeake Bay are of major concern (Chesapeake Bay Program, 1995). These are the source of excessive plankton production (Boynton; Malone; Malone; Correll and Jordan) which has been implicated in the major decrease of submerged aquatic vegetation (Kemp et al., 1983) and the expansion of the anoxic zone (Taft and Officer). Because of these impacts, the 1983 Chesapeake Bay Agreement between Maryland, Pennsylvania, Virginia, District of Columbia, and the US Environmental Protection Agency was modified in 1987 to set a 40% reduction goal for both N and P entering the bay by the year 2000. It was then amended in 1992 to maintain the 40% reduction goal beyond 2000, and to address nutrient reduction at its upstream sources in the tributaries The Chesapeake Basin includes major (Pennsylvania Maryland and Virginia) and minor (New York, Delaware and West Virginia) portions of six states and the District of Columbia (Fig. 1).

[Fig. 1: Location of the Chesapeake Bay basin and the WE-38 watershed]

One of the main issues facing watershed planners is how land use and management at the small scale ties to the quality of watershed outflow. In humid hill-land watersheds, relatively small and well-defined areas typically contribute much of the nonpoint source water, sediment, P and N exported in watershed outflow. From a prediction, management and control perspective, it is important that we recognize and develop the concepts, modeling tools and sampling protocols to delineate and assess the impacts of these critical source areas. These are the highest priority areas for control, treatment and remediation within the watershed.

Within the Chesapeake Basin, the critical source area concept applies to many watersheds where much of the agricultural P or N exported originates from relatively small areas. Typically these critical source areas result from combinations of high hydrologic activity due to climate, topography and geology with high nutrient loss potential due to intensive agricultural activity. In many humid, temperate climate landscapes, variable source area (VSA) hydrology (Ward, 1984) controls where surface runoff occurs. The control is usually caused by little or no infiltration of rainfall because of high water tables or soil moisture. These critical surface runoff areas are most apparent, definable and predictable in hilly and rolling landscapes, although active in flatter areas as well. Similar to surface runoff, ground water recharge varies areally, but much less and it occurs over most of the landscape. About 50% of agricultural lands within the basin are located in the Appalachian Province (hill-lands), 25% in the Piedmont Plateau (gently rolling to hill-lands), and 25% in the Atlantic Coastal Plain (relatively flat) (NCRI, 1982).

Nutrient inputs to Chesapeake Bay

The nutrient input totals to the Chesapeake Bay from sources discussed below are estimated to be about 151×106 kg N and 14×106 kg P. Nutrient entry to the Chesapeake Bay waters is either direct, such as by oceanic (e.g. tidal), atmospheric precipitation, water traffic and shoreline erosion inputs, or indirect by ...