Estimating Watershed Mercury Contribution to Lake Fort Smith State Park, Arkansas, USA

2018

Mercury contamination associated with human activities poses global human health and environmental risks. A fish-consumption advisory has been in effect at Lake Fort Smith in central west Arkansas for more than a decade due to observed methylmercury concentrations in fish tissue. Lake Fort Smith is an important municipal drinking water supply and recreational resource. Water samples from the majority contributing tributary stream, Frog Bayou creek, were collected periodically, under differing hydrologic conditions in order to quantify the allochthonous mercury load delivered to the lake. Temperature, specific conductance, and turbidity data were collected and used to estimate dissolved organic carbon, methylmercury and mercury concentration in Frog Bayou creek. Dissolved organic carbon (DOC) concentration has been previously shown to have a strong correlation with total mercury (THg) and methylmercury (MeHg) presence and mobility in surface waters. Whereas a weak correlation was observed between DOC and THg concentrations (r2= 0.47), the relation between turbidity and THg was strong (r2 = 0.95), enabling use of turbidity as a proxy for the estimation of influx of THg in Frog Bayou creek. Analysis of water samples collected from streamflow indicated very little methylmercury contribution from the watershed, suggesting methylation of mercury is occurring predominantly within the body of Lake Fort Smith itself. Turbidity proved an inexpensive, real-time proxy for quantitative determination of mercury and methylmercury load in streamflow. This methodology provided better understanding of variations in mercury concentrations under differing hydrologic regimes and provided a tool for long-term watershed mercury load approximation to Lake Fort Smith.

University of Arkansas, Fayetteville

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