Willamette River plankton & water-quality update: August 2024
See what Phytoplankton we saw in our Willamette River water samples on August 14, 2024.
A boat-based USGS survey conducted on August 14 included collection of plankton net tow samples from the Ross Island Lagoon and the Willamette River downstream from the Holgate Channel (at the OMSI dock). All three types of cyanobacteria were present in the sample from the Ross Island Lagoon (Figure 1) during the mid-August survey, although Microcystis was dominant. Dolichospermum was relatively more abundant downstream at the OMSI dock, but Microcystis was still present. Several other phytoplankton, including other cyanobacteria, diatoms, and green algae were also found in the samples (see Table 1, data release).
The USGS survey included high-frequency data collected from the lagoon downstream to the Steel Bridge, resulting in extensive tabular data on several parameters including algal and cyanobacterial pigments and photosynthesis indicators (pH and dissolved oxygen), and color maps showing the spatial variation in values that will be published in an upcoming data release.
A crew from Oregon State University captured this image of cyanobacteria starting to accumulate near the mouth of the Ross Island Lagoon on August 15 (Figure 2).
Although there have been some signs of cyanobacteria exiting the lagoon and passing by the water-quality monitor, the magnitudes of the periodic increases in phycocyanin fluorescence units, and estimated concentrations, reveal a somewhat higher baseline in 2024 compared with 2023. After similar June conditions, occasional spikes in values began in mid-July 2024, but large exoduses of cyanobacteria such as occurred in mid-August 2023 have not occurred in 2024 (Figure 3).
The continuous water-quality monitor downstream at the Morrison Bridge (Figure 4) also shows phycocyanin fluorescence units in 2024 slightly elevated compared with data collected during the previous decade, but the 2024 data do not include the common large peaks.
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