Primary Production in the Columbia River Estuary. I. Spatial and Temporal Variability of Properties

Abstract

Light, major nutrients, water temperature, turbidity and its organic and inorganic fractions, chlorophyll, phaeophytin, DCMU [3-(3,4dichlorophenyl)- l, 1 dimethyl ureal-enhanced fluorescence (DCMU ratio), particulate 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 lowsalinity intrusions. Mean values for properties in the main axis generally were not significantly different from those in the shallows, suggesting that the main axis and shallows experience similar , rapid flushing times. Total primary production for the estuary was almost 30,000 metric tons C yr-1", but areal production was only 100 g C m-2 yr-1" , which puts the Columbia system at the low end of North American estuaries. The low areal production was likely a result of light limitation, chlorophyll reduction at the low-salinity boundary, and a short residence time of water and viable cells in the estuary.