Opinion: Questioning Tahoe’s clarity improvement
By David McClure
Have you heard? Lake Tahoe clarity is getting better now.
Recent press releases claim a second year of improved lake clarity, “the best in 10 years,” no doubt misleading the casual observer to infer that Lake Tahoe’s water quality problems are behind us.
Have you seen the near shore, shallow water lately? More to the point, do you remember what it was like 25 years ago? Many of us do, which raises the questions of what was omitted from the press releases and why create the false impression?
In the Tahoe Environmental Research Center’s (TERC) annual State of the Lake Report for 2012, “A factor different to last year was the depth of mixing. This year the entire 1,645-foot depth of the lake mixed.” To data analysts this periodic mixing of clear, deep water dilutes contaminants and shows improved Secchi measurements often for a couple of years.
Why was this fact omitted from the improved clarity claim?
Drought and numerous other factors influence clarity. But even with the upwelling of deep water and improved winter clarity, TERC’s State of the Lake Report continues, “There is the continued decline in summer time clarity. In 2011, summer clarity was the second worst value on record.”
The fact that summer clarity continues to decline during years of deep water mixing has caused some consternation among TERC scientists.
In the comprehensive Lake Tahoe Watershed Assessment, “An important lesson contained in the Secchi depth data is that by using a short-term subset of even five to six years, it is easily possible to arrive at a totally incorrect interpretation of the data (Goldman 1993).” So why was a press release made which prematurely interprets incomplete information?
The Tahoe Environmental Research Center leads the way for data gathering and monitoring of numerous variables effecting Lake clarity. This scientific organization performs so noble a purpose that it deserves independent funding. Today, TERC’s funding is channeled through the Tahoe Regional Planning Agency, which is embroiled in political and legal controversy, and is hardly an unbiased funding source.
Lake clarity is directly affected by sediment flowing into the lake. To substantiate any claim of long-term clarity improvement there must be factual evidence that lake inflows from storm water pipes and specific projects are measurably reducing the fine sediments and nutrients that cause water quality degradation. That evidence is lacking.
The best management practices that are intended to infiltrate runoff (i.e. seep into the ground) from every parcel have only been installed on a small percentage of properties, and many of those are not maintained. The vaults which are intended to filter storm water from roadways (before it discharges directly into the lake) lack evidence that the filters actually remove the super fines that comprise 75 percent of the fine sediment contamination.
Models of what these measures are supposed to do is no substitute for actual field measurements. And sadly, the models and their modeled results often direct spending on ineffective but politically expedient activities to reduce contaminants.
Lake Tahoe water quality is in peril. Only to the extent that the science is divorced from politics can there be an accurate representation of reality. This is a call for independent funding of TERC’s monitoring activities, real-time provisional release of water quality data, and an end to misleading press releases aimed at influencing public opinion.
David McClure is president of the North Tahoe Citizen Action Alliance.
Neat article… So The lake fully mixed in 2011. What depth did it mix to in 2012? What changed in 2012 that could have caused such a huge spike clarity improvement? Is this showing that what is being done is working or perhaps is everyone focusing on the wrong probem? My hunch is that 2012 is going to make all scientists scratch their heads very hard and re evaluate many of the things they thought they already knew.
I understand there is so much particulate matter in the lake that it will become a meadow in a few years.
The god tahoe is getting angry and may pull the plug.
Talk about spin! What a hypocrite McClure. Maybe if jerks like you didn’t dredge up the SEZ on their property to make a profit plowing snow, sediment flowing into the Lake wouldn’t be such a problem. If you spent more time putting your own house in order and less time suing the people actually trying to protect the lake, we’d all be better off.
While dis-regarding the personal faults of Mr. McClure, this article is well done, and sheds some light on some very interesting facts about Lake clarity and ecology (i.e. deep water mixing). I also find it funny how the media didn’t mention (or briefly mentioned) that summer clarity rates are getting worse. In fact, they never look at the statistical benefits of using the yearly average in the reporting; the low winter rates skew the annual averages to look more favorable. Also, we still need to be looking at long-term trends in clarity not short-term ones.
Another interesting fact about the clarity measurements is that it only looks at the clarity rates in the deep open waters of Lake Tahoe. It doesn’t take into account the near-shore water quality, which is a problem. In fact, researchers are still trying to devise a means to accurately measure near-shore clarity.
The clarity is currently measured by dropping a white plate into the lake depths until it cannot be seen by the human eye. This is called subjective. The method is subjected to the quality of eyesight of the persons using the plate, or their secret needs. To eliminate this problem the clarity could be measured through use of an electric eye. At one end of the process, a light shines through the water. At the other end a receiver measures the amount of light that is received. Perhaps two or three hundred feet of distance between the light and receiver would be appropriate. Obviously, the difference in clarity would no longer be subjected to human opinion. The receiver would report the amount of light received, and you would have your clarity measurement. Obviously if we did this in polluted water, the receiver would report nearly no light received. This would be a much better way to measure water clarity.
Pizza: Do you really think that they only use the secchi disk?
Does anyone know how the secchi disk method compensates for visibiity impacted by time of day, cloud cover or surface water motion?
West Shore Gal, doesn’t the TRPA plan directly address nearshore clarity problems as a major focus?
Didn’t the UC Davis Lake Clarity Report in 2009 say that the clarity trend had flattened over a seven-year period, now a 12-year time frame?
Following up on Smells BS’s comment, I googled “dave mcclure violation trpa” and found the packet explaining how this person waited for TRPA inspectors to return his security bond and then proceeded to move into the SEZ, started driving snow removal equipment in and out of it and piling sand next to it. He also fought his violation for several years of process manipulation without every producing one piece of evidence that he did nothing wrong. I wonder how much he has cost public tax dollars and the environment. I question his judgment and his motivations.
People must be joking about this sez McClure issue. Who cares… Everyone is focusing on the wrong stuff in the wrong places anyway… His article is great..