Sensitivity of Sierra Nevada lakes to acid deposition (1983-1989)

In a sense, the Emerald Lake watershed study began with a meeting of university, National Park Service and USGS scientists and resource managers held at the Pear Lake cabin July 4th 1983. The winter of 1982-83 being the snowiest on record, meeting participants had to snow-shoe, ski and post-hole to the cabin. At this meeting, the outlines of the Emerald Lake integrated watershed study (IWS) were drawn up. This plan envisioned a multidisciplinary, multi-institutional study of the impacts of acid rain on vegetation, soils, streams, and limnetic components of the Emerald Lake watershed. The Emerald Lake IWS was part of a larger paired watershed study that examined ecosystem responses to acid deposition in the Kaweah River drainage. The paired watersheds included Log Meadow and Tharp's Creek (mixed conifer forest sites near the Giant Forest) and Chamise Creek and Elk Creek (chaparral sites near Potwisha).

During the next 6-years, funding from the National Park Service and the California Air Resources Board, supported baseline measurements of acid deposition rates (wet and dry deposition), soil surveys, vegetation surveys, stream surveys and acidification experiments, acidification experiments conducted in limnocorrals in Emerald Lake and the first paleolimnological investigations of air pollution effects ever made in the Sierra Nevada.

Remote sensing of snowmelt and regionalization of Emerald Lake results (1990-2001)

During this second phase of research, remote sensing and modeling of snowmelt processes was initiated to support application development for the NASA Earth Observing System (EOS). Much of this work was conducted at the Tokopah Valley scale and it was at this time that gauging of the upper Marble Fork river was initiated. The first large-scale, intensive snow surveys were conducted and used to validate remote sensing of snow-covered area, snow water equivalence, and snowmelt models based on energy balance.

Also, during this period, work was begun to place the results from the Emerald Lake Integrated Watershed Study in a regional context. With additional funding from the California Air Resources Board, atmospheric deposition measurements were expanded to alpine/subalpine sites stretching from Lake Tahoe to the extreme southern Sierra Nevada. Watershed studies were also begun at six additional lakes - this study was called the Lake Comparison Project. Two of these lakes, Pear and Topaz are located in the Tokopah Valley and are still studied. Three of the lakes are located along the eastern slope of the Sierra Nevada: Ruby Lake (Rock Creek Basin), Crystal Lake (Mammoth Mt) and Spuller Lake (Tioga Pass). Lost Lake is located near Lake Tahoe. 

In addition to the Lake Comparison Project, two projects aimed at smaller ponds and small watersheds were begun. The first of these projects was known as the "Mini-watershed Study" and was conducted on a ridge above the Pear Lake Cabin. This project investigated soil processes involved with watershed acidification.

The second project was modeled after the Emerald Lake watershed study, but it focused on small ponds in watersheds with sparse soils and vegetation near the present location of the M3 met station (i.e., the M-Site Watersheds) and at additional sites in and near the Ruby Lake basin along the eastern slope of the Sierra Nevada (the R-Site Watersheds). This project was designed to assess the sensitivity of the lakes and ponds to acid precipitation.

Drivers of long-term change in aquatic ecosystems of the Sierra Nevada (2002-present)

The current phase of research in the Tokopah Valley and Emerald Lake watershed began in 2002 with funding from the National Science Foundation. By this point, strong connections had been identified among climate, snowpack, biogeochemistry and aquatic ecology. Research was conducted to gain better understanding of the watershed nitrogen cycle during seasonal transitions (winter-to-spring and summer-to-autumn). Complementary work on nitrogen biogeochemistry was conducted at the Chamise watershed. Research activities during the early 2000s including detailed measurements of nitrogen pools and transformations in soils, soil gas flux measurements, isotope sourcing tracing of nitrogen sources and continued limnological and hydrochemical measurements.

By the mid-2000s our long-term data had shown significant changes in lake ecology since 1983. Phytoplankton had shifted from phosphorus limitation to nitrogen limitation and phytoplankton biomass had increased by 2-3 fold compared to conditions in the early 1980s. Periodic regional surveys of other lakes in the Sierra Nevada, suggested that a regional eutrophication problem was emerging in the Sierra Nevada. Funding from the National Science Foundation-LTREB program allowed for the testing of hypotheses regarding these observed changes in lake ecology. More information on these activities can be found in Current Research Activities and in recent publications listed on the Publications.