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

• Published in: Lake and reservoir management 2016-04, Vol.32 (2), p.158-167
• Main Authors: Beutel, Marc W., Cox, Suzanne E., Gebremariam, Seyoum
• Format: Article
• Language: English
• Subjects: chironomid; dissolved oxygen; Freshwater; lake oxygenation; methylmercury
• ISSN: 2151-5530; 1040-2381; 2151-5530
• DOI: 10.1080/10402381.2016.1143065

Beutel MW, Cox SE, Gebremariam S. 2016. Effects of chironomid density and dissolved oxygen on mercury efflux from profundal lake sediment. Lake Reserv Manage. 32:158–167. 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, benthos-mediated 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.