How Low Does the Oxygen Go?
New report on Ventura River’s water quality released
Algae on Matilija Creek last weekend (3-3-12).
Once a month during the algae season, Channelkeeper’s Stream Team volunteers can be found during the wee hours of the morning, before the sun comes up, grabbing dissolved oxygen (DO) measurements at various locations along the Ventura River. They are gathering these samples to help us understand what chemical effects algae growth may have in the river.
Al Leydecker, Ph.D., Channelkeeper’s technical advisor for the last 11 years, has just released a report that analyzes four years’ worth of the sampling results.
“The Ventura River problem presently being considered is nutrient enrichment, excessive concentrations (and amounts – these are not quite the same thing) of nitrogen and phosphorus, i.e., eutrophication,” explains Al. “Algae are a symptom of the problem and not necessarily the problem itself. Other than esthetic considerations, algae become a problem in and of themselves only (1) if they are toxic to aquatic life (only a very small subset of all algal species are toxic and none of these have ever been found in the Ventura River) or (2) if their growth is excessive enough to cause serious dissolved oxygen deficiencies.”
Channelkeeper’s sampling program is intended to document the extent of these oxygen deficits. As Al summarized, “Simply put, how low do oxygen concentrations get when algae are present and/or excessive? The simple answer to the question seems to be, not all that low. In the report I try to explain why.”
In 60 percent of our years we have below average rainfall according to Al, and in these years we don’t see all that much algae. “What we do see instead,” said Al “is lots of aquatic plants and low flows with lots of sediment buildup. And this, when combined with some, but not a lot of, algae, give us our worse problems with low DO.” (As the report states, “Aquatic plants also photosynthesize, but since the vast majority of their green parts are located above the water surface they add oxygen to the atmosphere and not the water column.”)
Ben Pitterle heads up the Channelkeeper’s water quality sampling program in the Ventura River. Ben commented recently, “This watershed is very fortunate to have Al and the contribution he makes. Al has really studied this particular issue, and from a very technical perspective. And he draws his own conclusions. He is a very impartial, knowledgeable expert on this issue.”
Click here for the report.
