Estuarine Biogeochemical Dynamics of Nutrients and Organic Carbon in the Columbia River: Observing Transformations Using a Biogeochemical Sensor Network

Abstract:

The Columbia River estuary is an ecosystem dominated by both a large river discharge and strong tidal forcing that creates fast currents, intense and variable physical stratification, low water residence times, and large gradients in salinity, temperature and water quality across the river to ocean boundary. Assessing ecosystem function and biogeochemical cycling in this environment is hampered by the inherent variability in both temporal and spatial timescales. In recent years the NSF Science and Technology Center for Coastal Margin Observation and Prediction has established a comprehensive in situ observation network that spans the estuarine gradient and captures variability associated with tides, diel cycles, episodic events, and seasonal changes in the river and ocean end-members. Here we describe the major patterns of variability in nitrate, orthophosphate, fluorescent dissolved organic carbon and related variables that demonstrate the dominant physical forcing and the biogeochemical hotspots within the ecosystem. These hotspots include intertidal lateral bays, the tidal freshwater river, and the estuarine turbidity maxima. Improved understanding of the role of these estuarine hotspots has informed ecosystem stewardship activities related to juvenile salmon survival, hypoxia, and food web structure.