Scientists grapple with decline in clarity and species around Tahoe's near shore
Gary Scott has spent many a summer on the docks at Incline Village, overseeing his rental boat company, Action Water Sports. But, this year, keeping the boats clean has been more of a challenge.
"With our rental boats, in particular, we're seeing more algae growth than what we're used to."
Tahoe may not be in the same shape as some lakes in California, where the water levels are at record lows, but it's still feeling the impacts of a light winter and very little snowmelt. Scott says the water level here is down about 5 feet.
"Normally, we don't have to have our guys underneath with scrub brushes. And, all this year, we're cleaning them way more often and earlier in the summer. We've got warmer water."
That makes it nice for swimmers, but this kind of anecdote doesn't bode well for Tahoe's near shore ecosystem because it also provides a warm, hospitable climate for non-native species.
"Look off into the near shore, and look at that hue of green you see now. There's a slight hue of green this year."
Sudeep Chandra is a limnologist at the University of Nevada, Reno (UNR). His team navigates the shallows on a small boat they use to study water quality and invasive species. About 100 feet off shore, the water resumes its characteristic cobalt blue.
Annie Caires, also a researcher at UNR, drops a water sampler, known as a Van Dorne, off the side.
"I've got a sample of water here...from this we can collect anything like temperature, dissolved oxygen, water chemistry."
For years, research focused on clarity in the middle of the lake, and recently scientists have seen improvement there; clarity has stabilized. But Chandra says, despite that, the near shore seems to be getting worse. Some of that is from runoff: pollution and fine particles flow into the lake, clouding the water. Invasive species also disrupt the natural nutrient cycles when they excrete nitrogen and phosphorus. But Chandra and his team also believe that what's happening at the bottom of the lake could be hurting the near shore.
"What we found is that there's an 80 to 99 percent decline of species at the bottom of the lake in Tahoe that were here in the 1960s and are disappearing at a rapid rate. These are species only found in Tahoe--10 different species."
Those include special species of stone flies, shrimp and worms, to name a few. Chandra says one driver of this massive decline could be those non-native species cropping up in the near shore.
"Introduced species like crayfish move from the shallow water in the summertime and, like cattle in the landscape, they graze down to four hundred feet at the bottom, eating the native plants and eating the invertebrates."
Another driver could be the loss in clarity. Murky water prevents the sunlight from reaching plant life and animals at the bottom.
Last year, researchers from UNR, the Desert Research Institute, U.C. Davis and various agencies put together a comprehensive plan for studying the near shore, but so far funding has not been easy to come by. A program for monitoring invasive warm water fish is just now starting up, and several projects for controlling other invasive species are on hold, altogether.
Alan Heyvaert, who's with DRI, led the effort to develop that plan for the near shore. So far, they've implemented a few pilot programs, but, he says, they need a lot more data.
"The near shore links the watershed to the midlake and that's the place where we can identify where the problems are showing up, and where we're making progress or where things are getting worse, but the only way to do that is to go out and measure it on a periodic basis."
One successful pilot study, led by UNR researcher Jeff Baguley, has discovered a community of microscopic organisms in Tahoe, known as meiofauna.
"These animals live in the sediment. They live in the sand and in the muddy environments in the lake, so they're bottom dwelling organisms. They're actually so small that they move in between space between grains of sand. So they can be found from the beach environment, where the water meets the shore, all the way down, probably, to the deepest parts of the lake."
Baguley says these animals are at the very base of the food web, consuming bacteria, algae and decaying organic matter. The two they've identified aren't found anywhere else in the world.
Back on the boat, Chandra shows off a low-cost filter that his lab has been helping a company, known as Wake Works, develop. It's to clean the water that collects inside the bottom of boats, which often harbors invasive species.
"And water would come in on one side from the boat bilge; filter through here; all the particles would get taken out; and then the water would go through to the lake."
According to their tests, the device is more than 90 percent effective. It could potentially simplify or eliminate the costly boat inspection programs around Tahoe. This kind of technology, developed by private companies in partnership with public institutions, he says, is one way to deal with the lack of funding. Still, they have a long way to go until they begin to understand what's really needed to reverse the decline in clarity and native species.
"Often, we get questions, 'Well, how many crayfish need to be harvested out of the lake to have an impact on the algal clarity?' "
Chandra says the simple answer is: they just don't know yet.