Primary production in the columbia river estuary I. Spatial and temporal variability of properties. Pacific Sci

ABSTRACT: Light, major nutrients, water temperature, turbidity and its or-ganic and inorganic fractions, chlorophyll, phaeophytin, DCMU [3-(3,4-dichlorophenyl)-l, I dimethyl ureal-enhanced fluorescence (DCMU ratio), par-ticulate organic carbon (POC), particulate organic nitrogen (PON), and primary production were measured from April 1980 through April 1981 in a 65-km stretch of the Columbia River estuary. Daily solar input, light attenuation in the water, and chlorophyll concentration accounted for 75 % of the variability of daily primary production in the main estuarine axis and 85 % in the shallows. The rapid appearance of a turbidity load created by the Mt. Saint Helens volcanic eruption in May 1980and the subsequent clearing of the water as the load moved out of the estuary became a natural experiment to show that light availability was indeed the limiting factor to phytoplankton production in the estuary. Spatial variability in chlorophyll concentration was caused mainly by large summer reductions at the location where freshwater cells were lysed on contact with low-salinity intrusions. Mean values for properties in the main axis generally were no