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DISTRIBUTION AND COMPOSITION OF DISSOLVED AND PARTICULATE ORGANIC CARBON IN NORTHERN SAN FRANCISCO BAY DURING LOW FRESHWATER FLOW CONDITIONS
Citation:
Murrell, M C. AND J. T. Hollibaugh. DISTRIBUTION AND COMPOSITION OF DISSOLVED AND PARTICULATE ORGANIC CARBON IN NORTHERN SAN FRANCISCO BAY DURING LOW FRESHWATER FLOW CONDITIONS. ESTUARINE, COASTAL AND SHELF SCIENCE 51(1):75-90, (2000).
Description:
The distribution of dissolved and particulate organic matter was studied in northern San Francisco Bay on seven dates during declining flow conditions from April to October 1996. Measurements were made at 3 to 11 stations (usually 8) along the salinity gradient from the Sacramento River to Central Bay. Dissolved constituents included monosaccharides (MONO), total carbohydrates (TCHO), dissolved primary amines (DPA), dissolved organic carbon (DOC), and the fluorescence of humic substances (HS). Particulate constituents included bulk suspended particulate matter (SPM), chlorophyll a (CHL), particulate organic carbon (POC), and particulate organic nitrogen (PON). April was distinct from subsequent months due to a very high DOC and MONO concentrations and somewhat elevated TCHO, DPA, and HS concentrations. In later months, DOC, MONO, TCHO and HS were distributed along the estuary suggesting a freshwater source; DPA had a bimodal distribution suggesting both freshwater and seawater sources. There was consistent evidence of an alternate source of organic matter in the oligohaline zone (2-8) located near Suisun Bay that was high in DOC and HS, but low in DPA. We speculated that this alternate source may have originated from one or more of the following: 1) the San Joaquin River, 2) exchange with the shoals and intertidal reaches of Suisun Bay, and 3) flux of DOC from suspended and deposited sediments. Downstream of this source, MONO, TCHO, DOC, and especially HS showed conservative mixing characteristics. The particulate organic constituents POC and PON, strongly correlated with SPM, but not with CHL, suggesting that sediments were relatively important, and phytoplankton were relatively unimportant, contributors to POM pools. We normalized DOC, MONO, TCHO, and DPA to the refractor HS fraction, reasoning that HS was a conservative tracer of terrestrially derived organic matter. The distribution of these normalized variables suggested that the composition of dissolved organic matter varied little spatially or temporally throughout much of the upper estuary, but underwent a sharp transition in the Central Bay. This transition was expressed by low HS concentrations and relatively high MONO, TCHO, DPA, and DOC concentrations, suggesting a seawater source of these constituents. A conceptual model was constructed to help illustrate the important processes that control fluxes of organic matter in northern San Francisco Bay, and to help guide future research.