Evaluation of mercury cycling and hypolimnetic oxygenation in mercury‐impacted seasonally stratified reservoirs in the Guadalupe River watershed, California. Issue 10 (8th October 2016)

• Record Type: Journal Article
• Authors: McCord, Stephen A.; Beutel, Marc W.; Dent, Stephen R.; Schladow, S. G.
• Is Part Of: Water resources research. Volume 52:Issue 10(2016:Oct.)
• Page Start: 7726
• Page End: 7743
• Publication Date: 2016-10-08
• Subjects: bioaccumulation -- hypolimnetic oxygenation -- water quality management -- mercury -- reservoirs; Hydrology -- Periodicals; 333.91
• DOI: 10.1002/2016WR019061
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Surface water reservoirs trap inorganic mercury delivered from their watersheds, create conditions that convert inorganic mercury to highly toxic methylmercury (MeHg), and host sportfish in which MeHg bioaccumulates. The Santa Clara Valley Water District (District) actively manages and monitors four mercury‐impaired reservoirs that help to serve communities in South San Francisco Bay, California. The Guadalupe River watershed, which contains three of those reservoirs, also includes the New Almaden mercury‐mining district, the largest historic mercury producer in North America. Monthly vertical profiles of field measurements and grab samples in years 2011–2013 portray annual cycling of density stratification, dissolved oxygen (DO), and MeHg. Monitoring results highlight the role that hypolimnetic hypoxia plays in MeHg distribution in the water column, as well as the consistent, tight coupling between MeHg in ecological compartments (water, zooplankton, and bass) across the four reservoirs. Following the 2011–2013 monitoring period, the District designed and installed hypolimnetic oxygenation systems (HOS) in the four reservoirs in an effort to repress MeHg buildup in bottom waters and attain regulatory targets for MeHg in water and fish tissue. Initial HOS operation in Calero Reservoir in 2014 enhanced bottom water DO and depressed hypolimnetic buildup of MeHg, but did not substantially decrease mercury levels in zooplankton or small fish. Key Points: Hypolimnetic hypoxia plays a critical role in methylmercury production and distribution in four seasonally stratified reservoirs Methylmercury is tightly coupled in water, zooplankton, and fish Pilot hypolimnetic oxygenation rapidly decreased methylmercury in bottom waters, but not in small fish