Higher and more variable methylmercury biomagnification factors for floodplain than the contiguous river (South River, Virginia USA)

Abstract

Extending previous trophic transfer studies of the mercury-contaminated South River watershed, predictive models were built for mercury biomagnification in floodplain food webs at two more locations (North Park and Grand Cavern). Four of five models built to date based on methylmercury and δ15N met the a priori requirement for useful prediction (prediction r2≈0.80). An additional factor included in models was organism thermoregulatory strategy (poikilothermy or homeothermy). The methylmercury food web biomagnification factors (FWMFs, fold increase per trophic level) for the North Park and Grand Cavern locations were 17.4 (95% CI of 9.5–31.6) and 6.2 (95% CI of 3.5–11.0) respectively. FWMF calculated in 2009 were 9.3 (95% CI of 5.4–16.2) for the Augusta Forestry Center and 25.1 (95% CI of 12.6–50.1) for Grottoes Town Park. The overall South River floodplain FWMF generated by meta-analysis of the four locations was 12.4 (95% CI of 6.8–22.3). These results supported previous findings that the South River floodplain food webs had higher biomagnification factors than the contiguous aquatic food web (4.6, 95% CI of 3.6–5.7). Floodplain FWMFs were also more variable than those of the river.