Let's make Clear Lake, clear again? In fact, this is the stated goal by State representatives sponsoring lake research and watershed improvements. It's probably important to determine if that's even possible.
But first, let's ask the right question. The main issue leading to the investment of State dollars into Clear Lake research for decades has always been what causes smelly cyanobacteria blooms. This drives away tourists, supports some out of county bad press and turns your water skiing legs green. So, is determining the cause of these blooms the quest and not to make Clear Lake clear?
Research on this issue began back in the 1960's with a study by the California Department of Water Resources engineers. The results at that time indicated excessive winter sediment coming into the lake could fill it to meadow level in 5,000 years. Whoa, is that what causes the cyanobacteria? Why hasn't this been stopped and what's normal?
Actually, research indicates the lake hasn't filled in with incoming sediment even after 500,000 years. So far, the lake bed depth has remained pretty much the same over all that time because for special tectonic reasons, the bottom slowly gets deeper as the sediment comes in. Whew, dodged that bullet.
But, it does look like a significant uptick of sediment input after heavy equipment was introduced in 1930's to build roads, remove stream gravel, dig mines and scrape the land dozens of ways. That pretty much nails the problem or does it? This begs two questions: 1) does excessive historical sediment affect the cyanobacteria problem and 2) all we need to do is just slow down todays input to natural levels, right? Answers; yes and yes but.
Yes- on question 1 because the cyanobacteria competitive advantage in the lake is supported by very low dissolved oxygen and high summer water temperatures of our shallow lake. This is exacerbated when a high backdrop of phosphorus is delivered by watershed sediments (other things matter as well).
Yes but- on question 2, because phosphorus in the lake will recycle from bottom sediments each summer to again fuel cyanobacteria. Unfortunately more sediment comes in each storm increasing the lakes' recycling phosphorus burden. The problem can keep getting larger.
But, nutrients also fuel a very healthy ecosystem with single celled phytoplankton at the base of the food chain. This supports a very large biomass of vegetation and fish. That means during certain times of the year, water clarity will naturally be challenged from phytoplankton blooms. So don't expect a clear lake even without cyanobacteria blooms.
Over eons, levels of nutrients coming in to the lake and those being recycled are lost or locked up through natural processes. The recent higher levels have overwhelmed this process. The real question should be "what lake management plans should we employ to restore the appropriate phosphorus levels in the lake?" Hmmm, maybe that should be catchier.
The money spent on lake research so far is to treat the water with increased oxygen and to measure currents, water temperatures, oxygen levels using sophisticated equipment and even kill excess single-celled organisms with sonic waves. The bottom was mapped and the incoming sediment and water flows tracked. The phosphorus levels of the water column were measured through the seasons and some data collected on phosphorus recycling from the sediment. All good geek stuff and student projects.
— Jim Steele is a Clearlake Oaks resident and former District 3 Supervisor
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