Long-Term Changes in Water Quality and Productivity in the Patuxent River Estuary: 1985 to 2003 |
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| Authors: | Jeremy M Testa W Michael Kemp Walter R Boynton III" target="_blank">James D Hagy III |
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| Institution: | (1) Horn Point Laboratory, University of Maryland Center for Environmental Science, P.O. Box 775, Cambridge, MD 21613, USA;(2) Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, P.O. Box 38, Solomons, MD 20688, USA;(3) US Environmental Protection Agency, National Health and Environmental Effects Research Laboratory, Gulf Ecology Division, 1 Sabine Island Drive, Gulf Breeze, FL 32561, USA |
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| Abstract: | We conducted a quantitative assessment of estuarine ecosystem responses to reduced phosphorus and nitrogen loading from sewage
treatment facilities and to variability in freshwater flow and nonpoint nutrient inputs to the Patuxent River estuary. We
analyzed a 19-year dataset of water quality conditions, nutrient loading, and climatic forcing for three estuarine regions
and also computed monthly rates of net production of dissolved O2 and physical transport of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) using a salt- and water-balance model.
Point-source loading of DIN and DIP to the estuary declined by 40–60% following upgrades to sewage treatment plants and correlated
with parallel decreases in DIN and DIP concentrations throughout the Patuxent. Reduced point-source nutrient loading and concentration
resulted in declines in phytoplankton chlorophyll-a (chl-a) and light-saturated carbon fixation, as well as in bottom-layer O2 consumption for upper regions of the estuary. Despite significant reductions in seaward N transport from the middle to lower
estuary, chl-a, turbidity, and surface-layer net O2 production increased in the lower estuary, especially during summer. This degradation of water quality in the lower estuary
appears to be linked to a trend of increasing net inputs of DIN into the estuary from Chesapeake Bay and to above-average
river flow during the mid-1990s. In addition, increased abundance of Mnemiopsis leidyi significantly reduced copepod abundance during summer from 1990 to 2002, which favored increases in chl-a and allowed a shift in total N partitioning from DIN to particulate organic nitrogen. These analyses illustrate (1) the value
of long-term monitoring data, (2) the need for regional scale nutrient management that includes integrated estuarine systems,
and (3) the potential water quality impacts of altered coastal food webs. |
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