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Chesapeake Bay Eutrophication

Scientific Understanding, Ecosystem Restoration, and Challenges for Agriculture

^a University of Maryland Center for Environmental Science, P.O. Box 775, Cambridge, MD 21613
^b College of Agriculture and Natural Resources, University of Maryland, Queenstown, MD 21658
^c Maryland Department of Natural Resources, 580 Taylor Avenue, Annapolis, MD 21401

View larger version (50K): [in a new window]   Fig. 1. The Chesapeake Bay and its major tributary subestuaries, showing the extent of hypoxic bottom waters (dissolved oxygen <2 mg L-1) during the summers of 1994–1996 (Chesapeake Bay Program, 1997) and place names mentioned in this paper

View larger version (21K): [in a new window]   Fig. 2. Annual averages of the total freshwater streamflow entering the Chesapeake Bay from 1951 through 1999; high inflow during 1972 resulting from Tropical Storm Agnes; record annual flow year of 1996 resulting from both winter and summer floods; and 1985, the base year for nutrient reduction goals (U.S. Geological Survey data)

View larger version (52K): [in a new window]   Fig. 3. Bottom sediments play an important role in recycling nutrients and as nutrient sinks, depending on the availability of dissolved oxygen. Positive feedbacks worsen eutrophication as coastal ecosystems degrade because more nutrients are recycled to the water column under anoxic conditions. The feedbacks work in the opposite direction as ecosystems are restored, by reducing nutrient loadings as more phosphorus is buried and more nitrogen is lost to the atmosphere

View larger version (29K): [in a new window]   Fig. 4. Watershed model estimates of controllable loads of nitrogen and phosphorus into the Chesapeake Bay for 1985 (the base year), 1996 (based on source reductions put in place), and 2000 (the targeted year for the 40% reduction goal). For 1996 and 2000 these are estimates adjusted to the average freshwater flow year and not estimates of nutrients that actually have been or will be delivered (Chesapeake Bay Program, 1997)

View larger version (52K): [in a new window]   Fig. 5. (A) Volume of summer hypoxic water in the mainstem of the Chesapeake Bay. (B) Area of Chesapeake Bay bottom habitat covered by beds of submersed aquatic vegetation based on annual aerial surveys compared with the interim restoration goal

View larger version (18K): [in a new window]   Fig. 6. Ground water nitrate levels under an experimental cornfield in Maryland's Coastal Plain managed for realistic crop yields with split nitrogen applications, no-till, and grassed waterways, showing the long-term effect of winter cover crop plantings (Staver and Brinsfield, 1998)