INTERANNUAL VARIABILITY IN DISSOLVED INORGANIC NUTRIENTS 
IN NORTHERN SAN FRANCISCO BAY ESTUARY 
David H. Peterson, Richard E. Smith, Stephen W. Hagar, 
Dana D. Harmon, Raynol E. Herndon, and Laurence E. Schemel 
U.S. Geological Survey 
Abstract 
Nearly two decades of seasonal dissolved inorganic nutrient- 
salinity distributions in northern San Francisco Bay estuary 
(1940-1980) illustrate interannual variations in effects of 
river flow (a nutrient source) and phytoplankton productivity (a 
nutrient sink). During winter, nutrient sources dominate the 
nutrient-salinity distribution patterns (nutrients are at or 
exceed conservative mixing concentrations). During summer, 
however, the sources and sinks are in close competition. In 
summer of wet years, the effects of increased river flow often 
dominate the nutrient distributions (nutrients are at or exceed 
conservative mixing concentrations), whereas in summers of dry 
years, phytoplankton productivity dominates (the very dry years 
1976-1977 were an exception for reasons not yet clearly known). 
Such source/sink effects also vary with chemical species. 
During summer, the control of phytoplankton on nutrient distri¬ 
butions is apparently strongest for ammonium, less so for 
nitrate and silica, and is the least for phosphate. Further¬ 
more, the strength of the silica sink (diatom productivity) is 
at a maximum at intermediate river flows. This relation, which 
is in agreement with other studies based on phytoplankton 
abundance and enumeration, is significant to the extent that 
diatoms are an important food source for herbivores. 
The balance or lack of balance between nutrient sources and 
sinks varies from one estuary to another just as it can from one 
year to another within the same estuary. At one extreme, in 
some estuaries river flow dominates the estuarine dissolved 
inorganic nutrient distributions throughout most of the year. 
At the other extreme, phytoplankton productivity dominates. In 
northern San Francisco Bay, for example, the phytoplankton 
nutrient sink is not as strong as in less turbid estuaries. In 
this estuary, however, river effects, which produce or are as¬ 
sociated with near-conservative nutrient distributions, are 
strong even at flows less than mean annual flow. Thus northern 
San Francisco Bay appears to be an estuary between the two ex¬ 
tremes and is shifted closer to one extreme or the other, depend¬ 
ing on interannual variations in river flow. 
Abstract from: 
Cloern, J.E. and F.H. Nichols (eds.), 1985: Temporal Dynamics 
of an Estuary: San Francisco Bay . D.W. Junk Publishers, 
Dordrecht, the Netherlands. 
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