کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
6320669 | 1619719 | 2016 | 12 صفحه PDF | دانلود رایگان |
- First reported long-term decline in methylmercury in San Francisco Bay biota
- Methylmercury concentration decline in preserved bivalves since mine closure
- Stable isotopes indicate methylmercury trends not attributable to food web changes.
- δ15N and δ13C trends likely caused by both natural and anthropogenic drivers
There are ongoing efforts to manage mercury and nutrient pollution in San Francisco Bay (California, USA), but historical data on biological responses are limited. We used bivalves preserved in formalin or ethanol from museum collections to investigate long-term trends in methylmercury (MeHg) concentrations and carbon and nitrogen isotopic signatures. In the southern reach of the estuary, South Bay, MeHg in the Asian date mussel (Musculista senhousia) significantly declined over the study duration (1970 to 2012). Mean MeHg concentrations were highest (218 ng/g dry weight, dw) in 1975 and declined 3.8-fold (to 57 ng/g dw) by 2012. This decrease corresponded with closure of the New Almaden Mercury Mines and was consistent with previously observed declines in sediment core mercury concentrations. In contrast, across all sites, MeHg in the overbite clam (Potamocorbula amurensis) increased 1.3-fold from 64 ng/g dw before 2000 to 81 ng/g dw during the 2000s and was higher than in M. senhousia. Pearson correlation coefficients of the association between MeHg and δ13C or δ15N provided no evidence that food web alterations explained changing MeHg concentrations. However, isotopic composition shifted temporally. South Bay bivalve δ15N increased from 12â° in the 1970s to 18â° in 2012. This increase corresponded with increasing nitrogen loadings from wastewater treatment plants until the late 1980s and increasing phytoplankton biomass from the 1990s to 2012. Similarly, a 3â° decline in δ13C from 2002 to 2012 may represent greater utilization of planktonic food sources. In a complimentary 90 day laboratory study to validate use of these preserved specimens, preservation had only minor effects (< 0.5â°) on δ13C and δ15N. MeHg increased following preservation but then stabilized. These are the first documented long-term trends in biota MeHg and stable isotopes in this heavily impacted estuary and support the utility of preserved specimens to infer contaminant and biogeochemical trends.
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Journal: Science of The Total Environment - Volume 572, 1 December 2016, Pages 782-793