The western Lake Erie basin has experienced significant eutrophication over the past half century as a result of anthropogenic nutrient inputs. The nutrient inputs, specifically phosphorus and nitrogen, play a key role in freshwater eutrophication. Increases in the concentration of these two nutrients in a freshwater system can lead to algal blooms and subsequent hypoxia. Both nutrients are primarily derived from nonpoint sources (i.e.agricultural runoff, wastewater, and groundwater); however the relative contribution of each source must be understood to better plan management and mitigation strategies. To help isolate the contribution of residential septic wastewater to nitrogen and phosphorus loadings, caffeine was analyzed. Caffeine is a stable and readily quantifiable emerging contaminant, and has been identified as a specific marker for humans' wastewater input.  In this study, six tile drainage sites along Riley Creek in Putnam County, Ohio, were sampled and analyzed for total phosphorus, nitrite, ammonia, and nitrate concentrations. Riley Creek is a heavily impaired tributary in the Maumee River basin. The relationship of each nutrient to caffeine, and consequently septic wastewater, was quantified to ascertain whether septic system effluent is a significant contributor to either nutrient loading.  Our results suggest that there is a weak correlation between caffeine and total phosphorus on short time scales, but not between caffeine and nitrogen in any form. Although this correlation between caffeine and phosphorus may be due to direct inputs from wastewater, it is also possible that it is due to shallow groundwater carrying phosphorus deposited from septic drainage. Over longer time scales, caffeine and phosphorus are strongly and negatively correlated, suggesting that efforts to reduce nutrient loading from septic systems may be of limited utility.

Nutrient inputs from rural septic systems to a eutrophic watershed

247th National Meeting (2014)

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