Effects of Nutrient Loading and Mercury Chemical Speciation on the Formation and Degradation of Methylmercury in Estuarine Sediment

• Published in: Environmental science & technology Vol. 50; no. 13; pp. 6983 - 6990
• Main Authors: Liem-Nguyen, Van, Jonsson, Sofi, Skyllberg, Ulf, Nilsson, Mats B, Andersson, Agneta, Lundberg, Erik, Björn, Erik
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 05.07.2016
• Subjects: Agricultural Science; Biodegradation; Biogeochemistry; Ecosystem; Forest Science; Geologic Sediments - microbiology; Jordbruksvetenskap; Mercury; Methylmercury Compounds - metabolism; Nutrients; Organic chemicals; Sediments; Skogsvetenskap; Water Pollutants, Chemical
• ISSN: 0013-936X; 1520-5851; 1520-5851
• DOI: 10.1021/acs.est.6b01567

Net formation of methylmercury (MeHg) in sediments is known to be affected by the availability of inorganic divalent mercury (HgII) and by the activities of HgII methylating and MeHg demethylating bacteria. Enhanced autochthonous organic matter deposition to the benthic zone, following increased loading of nutrients to the pelagic zone, has been suggested to increase the activity of HgII methylating bacteria and thus the rate of net methylation. However, the impact of increased nutrient loading on the biogeochemistry of mercury (Hg) is challenging to predict as different geochemical pools of Hg may respond differently to enhanced bacterial activities. Here, we investigate the combined effects of nutrient (N and P) supply to the pelagic zone and the chemical speciation of HgII and of MeHg on MeHg formation and degradation in a brackish sediment-water mesocosm model ecosystem. By use of Hg isotope tracers added in situ to the mesocosms or ex situ in incubation experiments, we show that the MeHg formation rate increased with nutrient loading only for HgII tracers with a high availability for methylation. Tracers with low availability did not respond significantly to nutrient loading. Thus, both microbial activity (stimulated indirectly through plankton biomass production by nutrient loading) and HgII chemical speciation were found to control the MeHg formation rate in marine sediments.