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The McMurdo Dry Valleys Long-Term Ecological Research (LTER) project is an interdisciplinary study of the aquatic and terrestrial ecosystems in a cold desert region of Antarctica. The McMurdo Dry Valleys, the largest ice-free area (approximately 4,800 square kilometers) on the antarctic continent, are located on the western coast of the Ross Sea (77°00'S 162°52'E). The McMurdo Dry Valleys LTER site (currently research is focused in Taylor Valley) is far colder and drier than any of the other 17 established LTER sites. The perennially ice-covered lakes, ephemeral streams, and extensive areas of soil within the valleys are subject to low temperatures, limited precipitation, and salt accumulation. The dry valleys represent "end-member" environments that contain microbial-dominated ecosystems. An important aspect of the McMurdo LTER research is its potential contribution to general ecological understanding through studies of processes that may be better resolved in these relatively simplified ecosystems (cf. more complex ecosystems). The McMurdo LTER advances two key hypotheses:
In addressing these hypotheses, the interdisciplinary group is conducting a program of systematic data collection, long-term experiments, and model development. Research activities, which are spread across different disciplines, include physical, chemical, and biological modeling and information science.
The McMurdo LTER project has successfully completed three field seasons beginning in 1993. During the 1993-1994 field season, 18 scientists deployed to McMurdo Station and Taylor Valley to conduct research associated with the LTER project. These scientists initiated a core measurements program to obtain baseline, ecologically relevant data from the atmosphere, glaciers, streams, soils, and lakes. During the 1994-1995 field season, 26 scientists visited the dry valleys to continue the core measurements and research program. The first two seasons took place during the austral summer period (October to February). The third field season, 1995-1996, began in August (winter) so that research could focus on the changes in lake chemistry and biology during the transition between total winter darkness and the return of light in the spring.
We now summarize some of the research highlights resulting from the efforts of 27 scientists during the 1995-1996 field season. These highlights are expanded upon in eight subsequent papers prepared by LTER scientists.
Because of the lack of precipitation, the major source of water in the dry valleys is the melting of glaciers during the austral summer. Lewis, Fountain, and Langevin explain how the terminus cliff melt from the Canada Glacier in Taylor Valley is the largest contributor to streamflow in Anderson Creek. They report that the melt on the terminus cliffs is surprisingly heavier than the flow from surface ablation from the glacier. Local energy balance of the Canada Glacier terminus was measured along with the resulting flow in Anderson Creek. Lewis et al. conclude that because of the large radiation flux along the terminus cliffs, ablation was possible with temperatures as low as -20°C. They concluded that peak streamflow from the Canada Glacier can be mostly attributed to terminus cliff melt as melt continues from the cliffs with cooler temperatures.
In a related study, Dana, Wharton, and Fountain report the effects of solar radiation on three different glaciers--Commonwealth, Howard, and Taylor. Incoming and outgoing solar radiation were measured using Eppley pyranometers located on the three glaciers. They show that Taylor Glacier had a greater net solar radiation compared to the Commonwealth and Howard glaciers due to its relatively lower albedo. The Taylor Glacier's lower albedo is attributed to lack of snow cover and a greater extent of "bare ice." The Commonwealth and Howard glaciers, both closer to the coast, receive more snowfall due to the prevailing winds and cloud coverage. The resulting snowfall on these glaciers produces higher albedos and lower net solar radiation.
In another paper focused on the influence of the Taylor Valley glaciers on the dry valley ecosystems, Fountain, Lewis, and Dana discuss "calving" and its contribution to mass loss on the Canada, Commonwealth, Howard, and Taylor Glaciers. Photographs and on-site observation of glacier cliffs indicate that on average, calving blocks are 50 centimeters thick and that they can occur in widths of 10-100 meters. In this study, the energy balance of the ice surfaces was determined to assess the mass loss resulting in potential meltwater. In comparing precipitation totals for winter and summer snowfall to the amount of ablation, Fountain et al. find totals for ablation to be generally the same for both seasons. Therefore, they conclude, calving is the result of stress and strain from ice movement, rather than from fatigue of daily heating and cooling from solar radiation.
During the austral summer, meltwater from the glaciers results in ephemeral streams, which contain variably productive microbial communities. In an effort to understand more fully the stream ecosystems in Taylor Valley, Moorhead and McKnight examine the correlation between discharge patterns for streams in McMurdo Dry Valleys and evaluate the relationship between daily discharge, mean daily temperature, and total incident shortwave radiation. Using data obtained from the LTER's network of stream gauges and meteorological stations, they conclude that a weak relationship exists between stream discharge and incoming shortwave radiation. Factors that appear to be important in affecting stream discharge include location and orientation of the glaciers that feed the streams, as well as stream geometry and slope.
The perennially ice-covered lakes in the McMurdo Dry Valleys contain relatively productive planktonic and benthic microbial communities. Kepner and Wharton studied the protozoan communities in lakes Fryxell and Hoare using polyurethane foam units (PFUs) as artificial substrates to collect protozoa. These scientists used a method similar to one used 18 years earlier to collect and classify protists taken from six sampling holes in the same two lakes. Forty-one taxa of protozoa were identified from lakes Fryxell and Hoare. On a site-by-site basis, 32 taxa were found in Fryxell (western end), 18 taxa were found in the center of Lake Hoare, and 15 taxa were found in the western end of Lake Hoare. In detailed comparisons of community composition, made at a variety of spatial scales, Kepner and Wharton found that fewer protist species inhabit deeper anaerobic waters compared to shallower aerobic waters.
The perennial ice covers also affect lake dynamics by minimizing temperature-driven turnover and wind-driven mixing. Lyons, Welch, Tyler, and Sharma question the past belief of permanent stratification and little or no advective movement within the dry valley lakes. A relative argument showed that downward mixing due to water density occurred in Lake Fryxell with the discovery of tritium at depth. For a better understanding of the source of solutes in the McMurdo Dry Valley lakes, they compared Miller and Aiken's data (1996) to Carlson's earlier data (1990), then observed their own samples taken from Lake Hoare at depths of 10 and 12 meters. The samples taken from Lake Hoare indicated relatively modern chlorofluorocarbon concentrations, suggesting that lake "mixing" occurred. They conclude that the biogeochemical dynamics of the valley lakes may have to be rethought if density-driven mixing is found to be a major process.
Understanding the biogeochemical cycles in the ice-covered lakes also requires accurate assessments of lake bathymetry. Doran, Wharton, and Schmok report on new bathymetric maps developed for lakes Bonney, Fryxell, and Hoare, created from a combination of
These maps should allow for more accurate determinations of lake productivity and nutrient chemistry.
The soils in the McMurdo Dry Valleys are indeed a harsh environment--low temperatures and moisture and high salt concentrations. Studying the genetic diversity of the Taylor Valley's soil nematodes, Courtright et al. find that the cold temperatures and low moisture of the dry valley limit the dispersal and establishment of soil nematodes. They provide results of genetic analyses, which allow them to suggest that two distinct species of Scottnema lindsayae, the dominant nematode, are evolving in the dry valleys.
Data from the above research are now being incorporated into an interactive database, which is specifically designed for the McMurdo LTER by McMurdo's data and information manager, Ken McGwire. Data management activities for the LTER site over the last 8 months have included the development of direct Internet access to online datasets through user-friendly World Wide Web interfaces. Initial examples include
The next generation of data management being developed for the LTER site will use a hybrid relational/object-oriented database management system (DBMS) to allow direct access to data. This approach will give the DBMS the flexibility to handle a wide variety of data types, such as temperatures, species lists, and stream chemistry measurements, within a consistent query-based interface. Existing data submissions to the LTER data management office are being tested against this hybrid DBMS model to ensure that a variety of data sources can be handled.
The McMurdo Dry Valleys LTER Web Site can be accessed through http://mcm.maxey.dri.edu/lter.
This research is supported by National Science Foundation grant OPP 92-11773.