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EVALUATION OF THE EFFECT OF SEPTIC SYSTEMS OF NITROGEN AND PHOSPHORUS LOADING IN CHATUGE RESERVOIR

Abstract

Nutrient loading through phosphorus and nitrogen results in the eutrophication of aquatic systems and can result in decreased water quality, specifically from hypoxia. Chatuge Reservoir has received poor water quality ratings due to increasing eutrophication; however, recent management actions, including improving wastewater treatment and repairing failing septic systems, have been implemented to reduce nutrient loading. This study investigated nitrogen (N) and phosphorus (P) levels at nine sites in Chatuge Reservoir to assess the relationship to problem septic systems. Based upon data from 2005 – 2007, sites were chosen among priority rankings given to sub-watersheds from an analysis of septic systems within a subwatershed. Thus, three sites were monitored for each priority (High, Moderate, and Low). N and P were measured weekly from mid-September to mid-November using portable photometers. Using a Kruskal-Wallis test, mean levels of N (P = 0.130) and P (P = 0.484) were not significantly different among priority rankings with measurements having large variations at a site over the sampling period. A score was developed for each watershed based upon the number of problem septic systems, and watershed score was significantly related to N (P = 0.024) but not P (P = 0.979). Failure to detect any differences between priority watersheds could indicate the effectiveness of management actions, such as septic repair, in the watershed. However, further investigation is needed to assess the relative impact of septic systems to nutrient loading in comparison to other activities in the watershed such as riparian zone removal, agriculture, and municipal waste water.

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