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Janet K McHendrie

EMERITUS
Email: jmchendrie@usgs.gov
Office Phone: 650-329-4364
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Benthic invertebrate communities are monitored because the composition of those communities can affect and be affected by the water quality of an aquatic system. Benthic communities use and sometimes regulate the cycling of essential elements (for example, carbon). Benthic invertebrate taxa may also indicate acute and chronic stressors in an environment because they accumulate contaminants and can respond – sometimes dramatically - to oligotrophic and eutrophic conditions. Benthic communities affect water quality by grazing pelagic food resources and increasing the rate of nutrient regeneration through feeding and bioturbating sediments. South San Francisco Bay is a system dependent on phytoplankton as the base...
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Declining phytoplankton biomass and the resulting stress on the food web has been suggested as one contributor to the decline of Delta Smelt and other fish species in the San Francisco Bay (SFB) and the Sacramento San Joaquin River Delta. Filter feeding by two species of bivalves, Corbicula fluminea and Potamocorbula amurensis, has been shown to control phytoplankton growth rate in the SFB and Delta and both are thought to be partially responsible for the reduction in food for pelagic species. Phytoplankton growth rate is dependent on spatially and temporally varying nutrient concentrations, light availability, transport time, and pelagic and benthic grazing losses. Bivalve grazing has the potential to limit primary...
Mechanisms of Biological and Ecological Response in Disturbed Aquatic Ecosystems
My primary objective is to understand the function of the benthic community at various spatial scales with the goal of understanding and modeling the benthic community processes at the ecosystem level. Specifically, my goals are to (1) explore ecological and physical processes that are affected by the benthic community and that effect benthic community composition and function; (2) look at these processes at a variety of time scales (days to seasons and inter-annual time scales) so that hydrologic, climate, and exotic species effects on benthic communities and their ecosystems can be understood; (3) develop habitat and energetics models of dominant members of the benthic community that can be dynamically linked...
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San Francisco Bay and Estuary is largely urbanized and developed, and the southern bay is the most urbanized with many sources of nutrients, many concerns that the system might become eutrophic, and many questions about how South Bay has maintained its relatively good health. The hypotheses for why South Bay is not eutrophic, where other bays have not been so fortunate, include high bivalve grazing that limits net phytoplankton growth and high turbidity which also limits the phytoplankton growth rate. Understanding the bivalve grazing rates in the south bay includes the necessity of understanding temporal and spatial distributions of bivalves. Despite the critical need to understand all controls on eutrophication,...
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Phytoplankton is an important and limiting food source in the Sacramento-San Joaquin Delta and San Francisco Bay; the decline of phytoplankton biomass is one possible factor in the pelagic organism decline and specifically in the decline of the protected delta smelt. The bivalves Corbicula fluminea and Potamocorbula amurensis (hereafter Corbicula and Potamocorbula, respectively) have been shown to control phytoplankton biomass in several locations throughout the system, and their distribution and population dynamics are therefore of great interest. As one element of the California Department of Water Resources (DWR) and the U.S. Bureau of Reclamation’s (BOR) Environmental Monitoring Program (EMP), the Generalized...
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