Mercury Strategy for the Bay-Delta Ecosystem - CALFED Bay-Delta ...

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influence food-web structure, affecting the biomagnification of methylmercury and exposure of
organisms atop aquatic food webs (Wiener et al. 2003).
Channel reconstruction: Potential changes in bioavailability of mercury. Inventories of mercury
are large in riverine sediments and overbank soils in parts of the Bay-Delta ecosystem. That
mercury, however, may not be readily available for methylation, either because it is not
physically located in zones of active methylation or because it has undergone diagenesis to forms
with low solubility or low bioavailability for methylation. Disturbance of such contaminated
sediments may increase the bioavailability of in-place mercury for methylation.
Steelhead and chinook salmon habitat restoration: Potential affects on mercury cycling. The
removal of dams or other physical modifications of rivers can affect the transport, distribution,
and transformations of sediment-associated mercury. The Upper Yuba River Studies Program,
funded by CALFED, is evaluating the long-term biological, environmental, and socio-economic
feasibility of introducing wild chinook salmon and steelhead trout to the Upper Yuba River
Watershed. The fate of mercury in gold-mining debris accumulated above the Englebright Dam
(a barrier to fish migration), the loading of mercury downstream, and the bioaccumulation of
methylmercury in fish are key issues being examined in that Program (see Attachment F, Water
Quality Presentation, at http://www.nasites.com/pam/yuba/documents.asp).
The risk of negative effects on the resource is inherent in resource management and cannot be
eliminated entirely. Ecological restoration in a mercury-contaminated ecosystem – particularly
the restoration of wetlands – could affect methylmercury production, increasing methylmercury
contamination of food webs and exposure of biota.
IV. DEVELOPMENT OF THE MERCURY STRATEGY
Development of a mercury strategy was prompted by the recognized need for an integrated,
systemic framework for addressing key management and scientific questions concerning the
sources, biogeochemical cycling, effects, and mitigation of mercury in the Bay-Delta ecosystem.
It was also recognized that critical evaluation of the effects of ecosystem restoration on mercury
cycling and methylmercury exposure would require an integrated approach in an ecosystem of
such large scale, dynamic character, and complexity.
Programmatic Guidance
The CALFED Science Program provided the following guidance regarding the mercury strategy.
First, the strategy should include recommendations concerning (1) integrated monitoring of
mercury in fish to assess risks to human health and wildlife, (2) holistic investigations that are
systemic or process oriented, and (3) locally focused investigations, including remediation at
mine sites. Second, the total cost of implementing the strategy should not exceed $7 million to
$10 million per year. Third, the strategy should have a duration of 4 years.
In developing the strategy, we have also provided a framework conducive to adaptive
management, an iterative learning and management approach used in CALFED programs to
critically evaluate management actions and to apply both expert advice and the results of
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