University scientists can and must take an active role in ecosystem management, says John Reuter, the director of the Lake Tahoe Interagency Monitoring Program and a researcher at the University of California, Davis. In a presentation at the June 11-14 meeting of the American Society of Limnology and Oceanography at University of Nevada, Reno, Reuter will be reviewing how recent UC Davis research findings at Lake Tahoe and Pyramid Lake can be practically applied to lake and watershed management. The meeting is co-sponsored by the UC Davis Lake Tahoe Research Group. Lake Tahoe is world renowned for its clarity and pristine water quality, which have been declining for the nearly 30 years that UC Davis researchers have been monitoring the alpine lake's health and studying the impact of human activities and development. Under the direction of UC Davis professor Charles Goldman, the monitoring and research efforts are leading to practical solutions to environmental problems for the famous lake as well as others in the Sierra Nevada, according to Reuter's presentation at noon Tuesday, June 13. The interagency monitoring program, for example, was organized by UC Davis researchers to better coordinate data collection and analysis efforts among the 13 state and federal agencies that oversee aspects of the lake and surrounding watershed. In tracking down the source of the lake's diminishing clarity, the UC Davis Tahoe Research Group found that algal growth was historically dependent on nitrogen, much of which was blown in from outside sources, such as the agricultural fields of the Central Valley and the automobile emissions of the San Francisco Bay area. Deposition of atmospheric nitrogen from automobile exhaust from traffic within the basin is also important. The vulnerability of the Tahoe basin ecosystem to pollution from other regions in this state shows the connectedness between air pollution and water pollution, as well as the significant distances environmental contaminants can travel, Reuter says. Algae need both nitrogen and phosphorus; the nutrient in shortest supply becomes the key factor in controlling algal growth. With the nitrogen now accumulated in the lake, phosphorus has become the important nutrient nourishing the water-clouding algal growth, UC Davis researchers have found. Phosphorus comes from the basin's watershed, which suggests that erosion control is important for preserving the lake's famed clarity. In other studies, the UC Davis Tahoe Research Group is reconstructing the lake history through paleolimnological studies, further exploring the impact of human activity upon the watershed. Ultimately, the researchers hope to develop water quality modeling tools to help preserve Lake Tahoe. In a paper regarding the impact of human activity upon the lake, UC Davis graduate student Alan Heyvaert will discuss findings from underwater sediment core samples taken from the lakebed under the deepest part of Lake Tahoe. The last 30 years of urbanization of the Lake Tahoe basin has caused as high a sedimentation rate as the clear-cut logging of the late 1800s that removed timber from more than 60 percent of the basin, according to Heyvaert and his co-authors. That's the bad news. In better news, the study also revealed a period of recovery by the lake and basin in the early 1900s. UC Davis researchers will be using these results, along with continuing watershed studies, to see if current mitigation efforts in the basin will result in a similar recovery period. The paper will be presented at 9:50 am, Wednesday, June 14. The UC Davis Tahoe group has also been conducting studies to develop better management tools for nearby Pyramid Lake, Reuter says. Pyramid Lake is hydrologically connected to Tahoe by the umbilical cord of the Truckee River, which drains water from Lake Tahoe 120 miles east through the city of Reno and past agricultural fields in Nevada. Reuter notes that increasing water flow to Pyramid Lake and the lower Truckee River is critical for water quality. In response to a request by the Pyramid Lake Paiute Tribe, which has taken responsibility for developing water-quality standards for this slightly saline desert lake, UC Davis researchers have developed a water-quality model that links nutrient pollution to levels of dissolved oxygen. Dissolved oxygen, in turn, is an important concern to Pyramid Lake's trout fishery, as well as to an endangered species, the cui-ui. Unlike Tahoe, Pyramid Lake is also threatened by increasing salinity. At 4:20 p.m. Monday, June 12, postdoctoral researcher Martin Lebo will discuss a model for managing the influx of nitrogen, whose sources can be traced back primarily to a waste water treatment facility that discharges into the Truckee River, agricultural runoff from the lands surrounding Reno and resident nitrogen-fixing algae. Tours of both Lake Tahoe and Pyramid Lake are being offered as part of conference activities. Other research highlights to be presented by members of the UC Davis Limnology Research Group include answers to lingering questions about the importance of aquatic food webs, as well as results from a study of mercury in an aquatic ecosystem. A recent statistical tool used extensively in certain other scientific fields, meta-analysis provides a way of comparing results from many different studies. UC Davis postdoctoral researcher Michael Brett applied meta-analysis to help resolve a long-standing controversy about how freshwater food webs are structured. In particular, among data from 41 studies with apparently conflicting results, Brett found general support for the "trophic cascade hypothesis," which holds that changes in the aquatic food web can alter the structure of the entire community. Brett will present his findings at 9:50 a.m. Tuesday, June 13. Results are also in from a 10-year study of biological uptake of mercury by fish and aquatic invertebrates in a California Coast Range reservoir downstream from historic mercury mines. These reservoir fish have some of the highest mercury levels in the state, according to a paper that will be presented by Darell Slotton at 3:40 p.m. Tuesday, June 13. The evidence supports two mechanisms of mercury uptake -- from the water through the gills, as well as through the food web. Historically used in gold mining, mercury is also finding its way down rivers and into reservoirs in the Sierra Nevada. UC Davis researchers are expanding the program, hoping to determine the extent of mercury contamination throughout Northern California, to better understand mercury's biological dynamics and to develop effective mitigation options. The group is investigating the use of biological indicator organisms as better tools to monitor mercury in the ecosystem than analysis of water and sediment.