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THE ROLES OF ANTHROPOGENIC WATERSHED LOADING AND CLIMATE VARIABILITY ON NITROGEN FLUXES TO THE POTOMAC RIVER ESTUARY
Citation:
Berounski, V., H A. Walker, AND N A. Jaworski. THE ROLES OF ANTHROPOGENIC WATERSHED LOADING AND CLIMATE VARIABILITY ON NITROGEN FLUXES TO THE POTOMAC RIVER ESTUARY. Presented at New England Estuarine Research Society, Block Island, RI, November 2, 2000.
Description:
To better anticipate responses of estuaries and coastal ecosystems to human activity and climate variation, it is useful to examine the historical record of nitrogen fluxes from watersheds to receiving waters and the factors affecting them. This study undertook a statistical examination of long-term data sets (approximately 90 years) of monthly nutrient concentrations and stream flow values for the Potomac River in relation to climate variables (air temperature, precipitation, and Palmer drought severity index), and nutrient inputs from atmospheric emissions, fertilizer use, and wastewater sources to the watershed. There is a general increasing trend in the yearly nitrate flux over this period. Since the 1920's to the mid-1990's, there has been a three-fold increase in the slope of the nitrate flux vs. river flow relationship, although some years in the 1960's were anomalously low, and some years in the 1980's were much higher. Increased anthropogenic loading increases the nitrogen flux per unit flow. Climate also plays a role in that wet years I generally have a higher nitrogen flux per unit flow than do dry years, such as the severe drought of the 1960's. This reduction of nitrogen loading from the watershed during dry years maybe due to storage in groundwater, soils, or plant matter, or it may be lost as a result of denitrification. When comparing droughts of the 1930's with the 1960's, it appears that increased anthropogenic loading amplifies storage or loss.