WINDOW ON CLEAR LAKE: Fixing Clear Lake is a 4-part series.
Part 1: Three ecosystems must work together by Jim Steele
On this 4th of July and the 250th anniversary of our country’s founding, I sat on the shores of Clear Lake waiting for the fireworks display presented by the Clear Lake Oaks Business Association. It’s really a great event, but one must ignore the cyanobacteria-painted green water and the smell of dead fish littering the lake edge. The shoreline was strewn with carcasses of decaying Threadfin Shad and Carp. What’s interesting about this annual phenomenon is that it’s not unusual or unexpected in such a nutrient-rich warm-water lake full of introduced species from different climes. It has happened in similar lakes all over the world. But Clear Lake has all the attributes that make it a lake very sensitive to nutrient overabundance. After decades of science-based studies to determine the causes, these are now well known. So, what is the problem and can it be fixed?
The answer is yes to fixing, but first the problem. Ecosystems are described as naturally distinct biological and physical systems. As is the case for most freshwater lakes, the Clear Lake ecosystem requires the supporting function of a wetland ecosystem that settles out nutrient-laden sediments before they enter the lake. Complementing this function is a stable upland terrestrial ecosystem that contributes minimal amounts of sediment through several streams into the hundreds of acres of wetlands historically edging the lake. Recent history has not treated this three-ecosystem supporting formula very well.
Clear Lake is our largest natural freshwater lake in California, and lakebed drilling-core studies indicate the lake’s basin received aboriginal settlers thousands of years ago without much change until the last one hundred years. Recognizable changes in the mud cores were correlated to the advent of heavy equipment in the early 1900s from road building, altered streambanks, mineral mining, and they also marked the loss of wetlands to agriculture and housing. Other data-rich lake and watershed studies indicated that tons of sediment would flow off terrestrial uplands during major storms that were restrained by levees, bypassing the settling influence of remaining wetlands. These results stem from past uninformed decisions by policymakers who needed better information. That better information is available now.
Permissive land stewardship allows thousands of off-road vehicle users each year to access the hills and other areas of the lake basin. This sediment-disturbing activity is defended as needed for outdoor equipment use activists. The sediments move downstream past wetlands because of levee protection for housing and agriculture. Once the past decision to remove wetlands as a settling basin was discovered as a mistake, a long process to restore a portion of the wetlands began. But recovering a wetland proved more cumbersome than first imagined, and the project has stalled for over 20 years. During this 20-year delay, additional tons of sediment have entered the lake, forming a large island near Rodman Slough. The delay was not known to add to the problem at the time.
Studies reveal that the lakebed sediments contain nutrient components such as phosphorus that are released annually from the warm-water, low-oxygen environment of the lake bottom. Aiding the release is a sweep of Konocti winds across the lake, which often reach velocities supporting a bottom-stirring Langmuir Circulation. This corkscrewing suspension of bottom silts makes phosphorus available to primitive single-cell cyanobacteria, thereby fueling a scum bloom. The newest revelation is that this lakebed phosphorus component accumulates over the years, and this built-up amount recycles annually from the lakebed, thus creating more and more a cyanobacteria-dominated lake during warm weather.
All three ecosystems, the lake, wetland, and upland terrestrial, have become compromised by past uninformed policy decisions. Now with better information, what can be done? First, additional delays are not an option. The trick is to begin restoring the function of all ecosystems at the same time. Since each system has its own peculiarities, the methods must differ. Reducing the total lake nutrient is the common goal. Next is Part 2, fixing the lake.
