Posted 11:30 AM PST, December 11, 2006
Over the past several months RNA has been studying and networking to find information about the growing dead zones off the Oregon and Washington coasts. There may be a direct connection to understanding the adverse impacts to Vancouver Lake. This research was conducted in partnership with Columbia Riverkeeper.
There may be a direct correlation between the causes of the dead zones off the coasts and the problems suffered by the lake. High nutrient levels in the Columbia River can cause tremendous increases in offshore phytoplankton production and when this phytoplankton dies within oxygen deprived zones offshore, they rot and consume oxygen. Also, high levels of phytoplankton in the Columbia River die when they hit salt water, then rot and consume oxygen. Both of these things may be happening in dead zones at the mouth of the Columbia River, where dead zones exist on either side off the Oregon and Washington coasts. The maps below indicate there is a strong correlation between the location o the Columbia River plume and the location of the dead zones. It is known that at times Columbia River nutrients are driving phytoplankton production near Newport, Oregon, which is where a major dead zone is located. Studies indicate that peak dead zone conditions correlate closely with primary production of phytoplankton in the Columbia River Estuary, which suggests that the increased plankton levels in July in the estuary could be flushed out to the ocean where they die and create dead zones without oxygen. Satellite photos from 2002 show a correlation between a dead zone and an especially strong southern flow of the Columbia River plume. Analysis of more recent photos would be strong evidence of an association of the two events, and we will continue to research this. Also, there may be information that correlates high Columbia River flows, such as what happened in 2006, and simultaneous larger than average dead zones.
The peak of phytoplankton production (freshwater diatoms in the Columbia River Estuary) are those species that are common to eutrophic lakes. As we know, Vancouver Lake is in advanced eutriphication. The peak of phytoplankton production in the Columbia River Estuary occurs during July, the same point when dead zones have been identified off the coast near the mouth of the Columbia River. This happens simultaneously with the appearance of blue-green algal blooms in Vancouver Lake and increased nutrient levels in the lake. The dead zones decrease in September, and there is a simultaneous decrease of phytoplankton in the Columbia River Estuary and the decline of the algal bloom in the Vancouver Lake. Whereas the flushing channel and Lake River contribute Columbia River water to Vancouver Lake, it could have a tremendous influence on the seasonal adverse impacts sustained by the Lake. The increase of nutrients in the lake water, or the increase of phytoplankton at specific times, coupled with summer heat, causes the explosive growth of the toxic algae in the Lake. The Clark County Health Department issues seasonal health advisories and has even closed the lake when this toxic algae appears. This would mean that in order to prevent the algal bloom, the increase of phytoplankton would have to be controlled within the lake environment.
This information has been shared with the Vancouver Lake Watershed Partnership, the Science Department of Washington State University, the US Army Corps of Engineers, Clark County Health Department, and the Washington State Department of Ecology.