How do we study the Columbia River estuary and its ETM?

When we conduct our research on the estuary or upriver, it typically involves two research vessels (Figure) working in tandem. One is usually in motion, uses instruments such as a Acoustic Doppler Current Profiler (ADCP), Conductivity-Temperature-Depth (CTD) sensors, and an Optical Backscatter Sensor (OBS) to sample the water column within and around the ETM as it moves. The other, which is usually anchored, uses many of the same instruments, in addition to instruments for assessing phytoplankton, particle aggregates, and pumps water from any point in the water column. During most of our cruises, we have utilized the UNOLS research vessels Clifford A. Barnes (based out of the University of Washington) in the roving mode and the Robert G. Sproul (based out of Scripps Institute of Oceanography) or Wecoma (from Oregon State University) in the anchored mode. Because ETM move with the tides and vary in location with the river flow and the estuary's bathymetry, we sample at a number of stations within the range of ETM, as well as above and below it. Many of our sampling locations within the ETM zone are near Astoria, OR, or about 23 km (14 miles) from the river mouth. Another station is 85 km (53 miles) above the mouth of the estuary (Beaver Terminal), well beyond the intrusion of seawater, where we assess the composition and amount of particulate matter that the river is delivering to the estuary. We have also conducted sampling even further upriver (above the lowest two dams) to sample variability in inputs from different tributaries and sub-basins of the watershed.

Shipboard activities and sampling equipment:

The instrumentation frame holds the electronic equipment (CTD, backscatter sensor, doppler current velocimeter, etc.) and the sampling pump. We use it to collect data on physical and biological parameters of the water column, and to collect water samples that are pumped from depth via a large diameter plastic hose (visible in figure).

Owen Tubes are deployed to collect suspended particles using an articulating crane. The tube is lowered in a horizontal orientation to the desired depth and triggered to shut using messengers sent down the wire. The tube is brought back on deck where it is set in a vertical position and samples are drawn from the bottom at specific time intervals corresponding to settling rates of particles of known sizes.

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