Plankton and nutrient ecology of the Columbia River estuary

Graduation date: 1970Monthly samples of nutrients, phytoplankton and zooplankton\ud were taken in the Columbia River estuary over a period of 16 months\ud in order to determine distribution with season and salinity, and interrelationships\ud between plankton and nutrients.\ud Nitrate and phosphate levels in the river water entering the\ud estuary are high in the winter and show depletion during the summer.\ud Silicate levels are high in the river water at all seasons. Nitrate\ud and phosphate levels are high in the entering ocean water during summer\ud offshore upwelling. The nutrient levels in the estuary generally\ud show a linear relationship with salinity, resulting from the levels of\ud nutrients in the entering river and ocean water. Superimposed upon\ud this linear relationship is a tendency for the nutrients to be enriched\ud in the bottom waters of the central part of the estuary.\ud The estuary phytoplankton are primarily composed of freshwater\ud forms, and probably represent a downstream extension of the\ud river flora. Regression analysis of phytoplankton levels vs. light,\ud nutrients, and river flow indicates that light probably limits phytoplankton\ud abundance on most dates.\ud The zooplankton of the estuary are composed of three groups,\ud preferring fresh, oligohaline, and polyhaline waters respectively.\ud Regression analysis indicates a strong correlation between abundance\ud of the freshwater group and river temperature. The factors controlling\ud the abundance of the oligohaline and polyhaline groups are less\ud obvious. The oligohaline group, principally Eurytemora affinis,\ud reaches the greatest population density (100,000/m³ or more).\ud Regression analysis indicates a close correlation between\ud Eurytemora abundance and phosphate levels. This indicates a strong\ud potential for zooplankton regeneration of phosphate necessary for\ud phytoplankton growth