Tahoe Research challenges tailor-made for DRI's interdisciplinary research approach

Tahoe turbidity probed with new technology. Dr. Ken Taylor prepares the instrumented probe that colllects real-time data on turbidity on the DRI research platform at Lake Tahoe. Behind him, Graduate Research Assistant Crystal Harrison readies additional instrumention, which includes a global positioning system and a database management system.

As more than a dozen DRI scientists work to find solutions for the decline of the Lake Tahoe Basin's environmental health, they're helping to bring an unprecedented level of attention to an area that has been scientifically neglected, despite its worldwide fame. From its dark, cold, 1,600-foot depth to its glacial peaks and scarps, Tahoe's ecology is an extremely complex system. It is dynamically interactive and highly susceptible to natural and human influences, both from within and beyond the ridges that define the basin.

This is just the sort of complexity that makes the Lake Tahoe Basin the ideal challenge to show off DRI's most potent scientific strength: the Institute's broad-based multidisciplinary approach to environmental research. So far, DRI's Tahoe research involves hydrologists, hydrogeologists, geologists, geographers, geomorphologists, forest ecologists, systems microbial ecologists, biologists, atmospheric chemists, watershed ecosystem specialists, and remote sensing specialists working in at least ten different ongoing project areas.

"It's the water" is more than a catch line for a once-popular beer; it's also the issue at the core of Lake Tahoe's future. From a distance, Tahoe's incredible blue color seems unaffected, but up close, the startling clarity that has long been its hallmark is noticeably declining. Two specific DRI projects are now analyzing water near the lake's shoreline for turbidity-a measure of how material in water scatters light-and for chlorophyll, the green pigment that gives most plants, including algae, their color and enables them to photosynthesize.

Seasonal change in near shore turbidity. The turbidity of the near shore water s indicated by the color: the red areas are turbid, blue areas are clear; and green areas are intermediate levels of turbidity. This data came from the initial tests of the prototype sampling instrument towed behind DRI's research platform. (Graphic by Dr. Ken Taylor)

Drs. Ken Taylor and Chris Fritsen are using new techniques that allow them to determine the lake water's turbidity while in motion along its surface, instead of collecting samples and carrying them back to the lab in Reno. "We'll be able to look at how much of Tahoe's increasing turbidity is a result of sediments and siltation entering the lake, and how much is from the growth of phytoplankton and other microscopic lifeforms due to availability of nutrients," says Taylor.

This winter they will launch a new DRI research boat equipped specifically for lake projects, which will allow them to sample along the shoreline year-round. Year-round sampling will create a profile of seasonal variations in sediment and chlorophyll levels.

In a related project, Dr. Joe McConnell is working with Taylor and Fritsen to analyze years of turbidity data from the water intake records that have been kept-as required by law-by the basin's water utilities. McConnell and Graduate Research Assistant and University of Nevada, Reno (UNR) grad student Christine Kirick, have also placed their own instruments at the water intake points to calibrate and supplement the existing data network.

"The products from this project will include the development of methods to measure spatial variability of near shore turbidity as well as the development of statistical and modeling techniques using the continuous intake data," says McConnell. "This will help us understand the processes that drive changes in turbidity, and hence clarity, in the near shore environment."

The new data will complement more than 40 years of clarity measurements in the center of the lake directed by Dr. Charles Goldman of the University of California, Davis' (UCD) Tahoe Research Group (TRG). Taylor says TRG's measurements are conducted by determining how deep into the lake a white disk can be seen. Goldman's annual reports of the steady reduction of the lake's clarity have provided an excellent indication of the overall health of the lake and served as a constant reminder of the continuing threat to the basin's most precious asset.

From another perspective. Tim Minor and Dr. Mary Cablk of DRI are using the revealing spectral capabilities of satellites to determine the amount of surface area that is impervious to snowmelt, adding to the runoff of silt and pollutant-laden water into the lake. This photo, an IKONOS ™ image acquired August 10, 2000 shows natural absorbent surfaces in black, and imperious areas —paved roads, parking lots, etc. —in red, in the vicinity of the intersection of U.S. 50 and Highway 89 in South Lake Tahoe, California. (Graphic by Tim Minor)

Another DRI project seeks new knowledge about the extent of the surface area in the Lake Tahoe Basin that contributes to rapid runoff and nutrient loading in the lake. Dr. Mary Cablk and Tim Minor are applying satellite remote sensing techniques to estimate impervious coverage surface areas that do not permit the snowmelt and rainfall to soak into the ground.

How much of the change in Tahoe's shoreline over the years is from human development is highly debatable because natural processes can also greatly influence erosion at the water's edge. Proof of this comes from damage caused to many lakeside properties in the last decade as lake levels first dropped, then rose rapidly, only to drop again, as drought turned to plentiful snow years, then back to drought. To gain insight into this process, Dr. Ken Adams and Minor have pored over more than 60 years of aerial photograph records to analyze changes to Tahoe's shorelines and estimate the pattern of erosion. The study concluded that between 1938 and 1998 some 190,000 square meters of shore zone land was lost to erosion while 51,000 square meters of new beach areas were formed. The difference amounted to 429,000 metric tons of sediment eroding into the lake from shore zone sources.

Adams will follow up by looking at the wind and wave processes in the lake's erosion activity, incorporating the factors of rising and falling lake levels and the frequency, timing, and direction of storms across the basin.

Lake Tahoe's changing shoreline. Dr. Ken Adams' study of 60 years of aerial photos produced this map of the erosion and accretion of different parts of the sore. Related studies are examining the role of storm-driven wave action and other factors that affect shore zone change. (Graphic by Ken Adams)

In the past 20 years, much effort has gone into reducing the erosion from watersheds contributing sediment and nutrients to Lake Tahoe. Dr. John Tracy, executive director of DRI's Center for Watersheds and Environmental Sustainability, is working to determine how these applications of land use regulations and restoration activities have affected the level of sediment entering the lake. His analyses show significant decreases in five important watersheds, with increases in two others. The Tahoe Regional Planning Agency (TRPA) and local governments are applying Tracy's findings in the new policy of "adaptive management" that will improve the effectiveness of future land use decisions. Tracy is also assessing fish habitats in certain stressed Tahoe watersheds for the TRPA.

Other DRI scientists are looking into the basic origins of Tahoe's water. Dr. Jim Thomas' investigation concerns the significance of groundwater entering the lake, whether from snowmelt that has soaked into the alluvial hillsides surrounding Tahoe, or from deeper, wider-based aquifers.

Dr. Gayle Dana, whose usual focus is the glaciers of Antarctica, is improving estimates of evaporation from Lake Tahoe, which will result in a better water budget. Along with Dr. Paul Verburg, she is also examining the impact of prescribed burning operations-designed to reduce fuel that would support catastrophic basin forest fires-on the algae-supporting nutrients entering the lake.

The restoration project for the critical Trout Creek watershed in South Lake Tahoe is one of the highest profile efforts by basin governments to restore a local ecosystem and once-thriving fish habitat. Dr. Roger Jacobson has been directly involved in the development of a scientific strategy to reestablish a sustainable fishery and resurrect the creek's natural capacity to filter its water before it enters the lake.

Compared with high profile issues of sediment loading and surface water runoff, the role of air pollution in Lake Tahoe's health has not been seriously considered until recently. Dr. Alan Gertler is working with air quality experts from UCD to better characterize this pollutant source. In addition to the human health aspects of air pollutants, Gertler and his associates want to determine the extent of nitrogen, phosphorous, and sediment that might be entering the lake and forest ecosystem from airborne deposition.

Another wrinkle in this line of research is that people and their various activities within the basin have pretty much been blamed as the source of all the lake's pollution. That assumption is changing with new data that show significant levels of air pollutants may be entering from outside the basin. Assisted by DRI Graduate Research Assistant and UNR grad student Leland Tarnay, Gertler has established a monitoring network in the basin to help distinguish between local and "imported" pollutants.

Tracy suspects this initial group of Tahoe research projects is just the beginning for DRI. "There's finally a real commitment for Tahoe studies among major research sponsors," he says. "Now, all those good research ideas that died for lack of any funding potential should start showing up as solid research proposals."
"We've got all the pieces in place here," he notes. "This is exactly the kind of work DRI was designed to do."

- John Doherty