Effects of chironomid density and dissolved oxygen on mercury efflux from profundal lake sediment

Abstract

Benthic macrofauna can dramatically affect the flux of dissolved compounds into and out of lake sediment. In this study, replicate experimental chambers containing profundal sediment from a relatively pristine lake were incubated under low (∼1000/m 2) and high (∼3800/m 2) chironomid densities and low (∼2.5 mg/L) and medium (∼5.0 mg/L) dissolved oxygen in chamber water. Dissolved methylmercury efflux rates were highest in high chironomid density/low oxygen chambers (0.35 ± 0.06 ng/m 2 /d, mean ± standard error, n = 4) and lowest in low density/medium oxygen chambers (0.06 ± 0.14 ng/m 2 /d). In contrast, dissolved total mercury efflux assessed at low dissolved oxygen (∼2.5 mg/L) was higher at low chironomid density (4.6 ± 0.7 ng/m 2 /d) relative to high chironomid density (2.5 ± 0.8 ng/m 2 /d, n = 4). Results indicate that oxygen addition, a common lake management practice, may enhance methylmercury efflux from profundal sediment as macrofauna recolonize previously anaerobic sediments. However, benthosmediated methylmercury efflux rates are lower than hypolimnetic methylmercury accumulation rates under anaerobic conditions; therefore, relative to anaerobic conditions, oxygenation should lower net methylmercury accumulation rates in relatively pristine lakes.

Spatio-Temporal Characterization Analysis and Water Quality Assessment of the South-to-North Water Diversion Project of China

“…The second and third PCs explained 22.26% and 11.75% of the total variance respectively, and were mainly contributed by Hg, NH 3 – N, SO 4 2− , and pH and F- respectively, which corresponded to the relatively high loadings on Axes 2 and 3, respectively (Figure 6). The Hg predominantly came from agrochemicals and industrial waste [10,11,69], while NH 3 – N and SO 4 2− are primarily derived from some soluble inorganic nitrogen and inorganic salts affected by some agricultural practices and mining engineering [6,12]. Therefore, the second PC was assumed to come from mixed exogenous sources of human activities.…”