USGS1994
The pilot program described here is motivated by a fundamental principle of the Regional Monitoring Strategy, namely “...the development of data that will provide information on status and trends in the Estuary.” As pointed out in the Strategy, knowledge of status and trends serves two primary purposes: (1) to become aware of or anticipate deleterious conditions in the Estuary, and (2) to assess the effectiveness of management actions. This program addresses these two purposes by focusing on aquatic resources, one of the five key management issues identified by the Comprehensive Conservation and Management Plan and central to the Regional Monitoring Strategy. It also bears on at least two of the other management issues - pollutants and water use. A regional monitoring program must cover many types of resources, including pelagic and benthic channel habitat, shoal habitat, wetlands, river channels, sloughs, and small bays and harbors. This particular program centers on the pelagic channel habitat. However, because of the intimate connection between channel habitat and many or most of these other habitats, channel measurements reflect to some extent the status of and trends in other resource types as well. A primary aim of this program is to provide a high-resolution description of critical aspects of habitat quality, which can be used along with other information (1) to determine the suitability of habitat for aquatic resources; (2) to monitor responsiveness of the habitat to freshwater flow variability; and (3) to provide a context for understanding pollutant distributions. In a single transect, measurements are made throughout the water column at up to 37 stations to define physical (salinity, temperature, suspended particulate matter, and light penetration), chemical (dissolved oxygen) and biological (chlorophyll a ) characteristics that influence both chemical and biological reactions. A second aim of the program is to investigate planktonic indicators of ecosystem structure and function. Phytoplankton production is the major single source of energy for the San Francisco Bay food web. Our measurements of chlorophyll and light penetration can be used to provide an estimate of this production, and therefore the availability of food for organisms at higher trophic levels. Phytoplankton community composition at the species level, which can be a sensitive indicator of habitat change, is also a standard component of this program. Community composition data enable detection of species known to be responsible for harmful or nuisance algal blooms. In 1993, two other indicators were also evaluated, photosynthetic parameters and water column respiration . Photosynthetic parameters partially characterize the physiological state of the phytoplankton and may provide indirect evidence of nutrient deficiency or the effects of pollutants. Water column respiration serves as a simple integrated measure of organic matter metabolism by the plankton, including bacteria, phytoplankton, and microzooplankton. It therefore reflects the total supply of organic matter, whether from photosynthesis, tidal marsh efflux, point sources, or upstream in the Delta. These biological indicators therefore contain much information about the flow of energy into the food web.