Primary production in the Columbia River estuary. I. Spatial and temporal variability of properties

ABSTRACT: Mean loss of phytoplankton carbon as a result ofmicrocrustacean grazing ranged from 0.03 to 8.94 mg C m- 3 da y", depending upon time of year and location in the estuary. On an annual basi s, median grazing rate was 1893 mt C yr-1, which represented 6.3 % of the annual primary production in the es-tuary. Daily transport of phytoplankton carbon decreased from the fluvial regions to the ocean, with the largest decrease occurring at the freshwater-brack-ish water interface. Annual import to the study area from upriver (excluding the May 1980 data, which were affected by the eruption of Mt. Saint Helens) was 61,440 mt C yr " , while annual export to the ocean was 40,560 mt C yr- 1 • Total phytoplankton carbon input to the estuary was 91,316 mt C yr- 1, a summation of import from upriver and in situ primary production (29,876 mt C yr", from a previous report). Export to the ocean plus median in situ grazing loss equalled 42,453 mt C yr", so that there was an unaccounted balance of48,863 mt C yr" ". Som e of this was night-time respiratory loss from the phytoplankton, estimated at 12,209 mt C yr- 1 • If the standing stock ofphytoplankton carbon in the estuar