Environmental Engineering Reference
In-Depth Information
Although San Francisco Estuary is one of the most studied estuaries in the world
(Flegal et al. 2005), large uncertainties still remain regarding the processes and fac-
tors controlling mercury methylation and bioaccumulation within the system. One
initial step in addressing these uncertainties was the development of a conceptual
model of mercury in San Francisco Estuary (Tetra Tech 2006) by the Clean Estuary
Partnership, a consortium of stakeholders from industry and municipalities, environ-
mental organizations, resource management agencies, and academic institutions.
The conceptual model used existing data to develop an overview of mercury biogeo-
chemistry and also identified the key management questions (Table 5) that must be
answered to meet the needs of resource managers and other stakeholders.
Table 5 Management questions, data requirements, and technical approaches identified in con-
ceptual model of mercury
Management question
Key data requirements
Technical approach
What is the relative
Chemical and physical form
Direct measurements
bioavailability
of the mercury from
of MeHg
of mercury from
natural and anthropogenic
Mesocosm experiments to
different sources to
sources to prioritize
quantify bioavailability under
San Francisco Bay?
remediation strategies
controlled conditions
At what locations are
Characterization of existing
Direct measurements of net
current methylation
methylmercury
methylation rates
rates and
pool in sediments to
Simultaneous measurement
methylmercury
determine whether hotspots
of factors affecting
flux highest?
are present
methylation rate: DO, TOC,
SO 4 , H 2 S, chloride
Can existing wetlands be
Quantification of the
Mesocosm experiments to
managed or new
response in bioaccumulation
quantify bioavailability under
wetlands be designed to
to wetland characteristics
controlled conditions
minimize net methylation that can be fully
rates, or limit exposure or partially controlled,
to methylmercury e.g., nutrient salinity,
that is produced? depth, vegetation levels,
type, hydroperiod
Given various scenarios for Characterization of local and
Localized interventions
management actions,
bay-wide sediment mercury
to remove or cap
when will we likely see
concentrations in response
high-mercury sediments
improvements in
to localized interventions;
Measurement of responses
sediment and tissue
quantification
to localized interventions and
concentrations?
of the effects of
mass-loading reductions
sediment deposition
Dated, deep-sediment cores
and erosion on
to estimate effects of sediment
estimates of recovery
erosion on recovery
How should we best monitor Detection of statistically
Measurements of total and
to detect changes in
significant changes in
methylmercury
mercury concentrations
reliable indicators
concentrations in
in sediments
surficial sediments in shallow,
and tissue?
depositional areas
Characterization of mercury
concentrations in fish
indicator species
Source: Tetra Tech (2006).
 
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