An Overview of 1993-1995 Research Activities
This summer McMurdo LTER scientists began field activities focused on the changes in lake chemistry and biology during the transition between total winter darkness and the return of light in the spring.
Robert Wharton, Jr.
In the LTER continuum of ecosystems, the dry valleys represent “end-member” environments which contain microbially dominated ecosystems
he McMurdo Dry Valleys LTER site is far colder and drier than any of the 17 other 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. In the LTER continuum of ecosystems, the dry valleys represent “end-member” environments which contain microbially dominated ecosystems. An important aspect of the McMurdo LTER (MCM) research is its potential contribution to general ecological understanding through studies of processes that may be better resolved in these relatively simplified ecosystems. The two key hypotheses addressed are:
- The structure and function of the Taylor Valley ecosystems are differentially constrained by physical and biological factors
- The structure and function of Taylor Valley ecosystems are modified by material transport
The McMurdo LTER is addressing these hypotheses and the five LTER core research areas through a program of systematic environmental data collection, long-term experiments, and model development. Research activities encompass several disciplines, including physical, chemical, biological, modeling and information science. During the first six years of the project, MCM is focusing its efforts on Taylor Valley.
The 1993-95 Field Seasons
The McMurdo LTER project has successfully completed two field seasons (October through February) during 1993-94 and 1994-95. During the 1993-94 field season, 18 scientists deployed to McMurdo Station and Taylor Valley to conduct research associated with the LTER project. These scientists initiated core measurement programs to obtain baseline ecologically-relevant data from the atmosphere, glaciers, streams, soils and lakes. During the 1994-95 field season, 26 LTER scientists visited the dry valleys to continue the core measurements and research program.
One of the first objectives of the MCM was to establish a meteorological network that would gather representative weather data year-round from the dry valleys. The McMurdo LTER Automatic Weather Network (LAWN) currently consists of nine stations with two new stations planned for deployment during the 1995-96 field season. Stations are now operational at Explorer’s Cove, on the shores of lakes Fryxell, Hoare, Bonney, Brownworth and Vanda, and on the Commonwealth, Howard and Taylor glaciers. The new stations to be deployed are on the shore of Lake Vida and the surface of the Canada Glacier.
Since the McMurdo Dry Valleys lacks significant precipitation, glacier meltwater is the primary source of water to the streams and lakes. In addition to recharging the lakes, this water carries dissolved gases and solutes. A major objective of the LTER glaciological program is to determine the mass balance and meltwater runoff of the glaciers in Taylor Valley that contribute water to the lakes. During the 1993-94 field season, the project established a network of surface-based measurements on the Commonwealth, Canada, and Howard glaciers to determine mass balance and meltwater flow. The following season, LTER scientists measured the major contributions to the surface energy budget of the Canada Glacier in Taylor Valley. Their measurements and modeling of glacier energy fluxes in Taylor Valley are comparable to other regions of the Antarctic. They conclude that the role of sublimation in the mass balance of dry valley glaciers is significant.
Soils in the dry valleys are influenced by a variety of factors including climate, glacial movement, parent material and site characteristics. In Taylor Valley, the oldest soils are found at higher elevations while those at lower elevations were probably deposited during relatively recent glacial activity. During the 1993-94 field season, LTER scientists established an elevational transect on the south shore of Lake Hoare to examine spatial variation in soil properties and nematode abundance. Using observations and samples collected during 1994-95, it appears that the distribution of nematodes in the dry valleys may be governed by pH and concentration of soluble salts.
Numerous ephemeral streams link the glaciers and lakes within the dry valleys for six to ten weeks during the austral summer. These glacial meltwater streams recharge the dry valley lakes, are important sources of nutrients, and support the growth of moss and microbial mat communities. The McMurdo LTER now has in place an extensive network of gauging stations where stream flow is measured continuously throughout the austral summer. During the first two field seasons, LTER scientists focused efforts on determining the influence of stream channel characteristics on stream flow and annual water budgets for lakes in Taylor Valley.
Their results show that there is interannual variation in relative flow, even among streams where stream length and location in the basin are similar. They also found that longer streams have generally higher concentrations of major ions due to greater interaction with the hyporheic zone. In parallel studies, LTER scientists have examined the role of stream gradient, sediment transport, and substrate stability on the distribution of mosses and microbial mats in streams. Results show that the range in abundance of algae and mosses appears to be controlled by gradient and flow conditions.
Lakes Program
The McMurdo LTER lakes program is focused on understanding the environmental conditions and ecological processes of former and present lakes in the dry valleys. The perennially ice-covered lakes support both phytoplankton and benthic microbial communities. The chemistry of each lake profoundly effects the biota within the lake. The LTER project is collecting major element and nutrient chemistry for lakes Fryxell, Hoare and Bonney in Taylor Valley at least three times per field season. One early result of this effort shows that the depth profiles of K’, Mg2’, Na’ and S042 normalized to the conservative ion C1 are extremely different among the lakes. Project scientists suggest that these differences cannot be explained by differences in current solute sources or in-lake biogeochemical processes. It appears that the climatological and hydrological histories of each lake need to be closely studied before definitive statements can be made about the overall geochemical evolution of the Taylor Valley lakes.
The LTER lakes project is also investigating phytoplankton nutrient deficiencies. Early results show that the nutrient concentrations are quite different among lakes Fryxell, Hoare, and Bonney (both lobes), as well as vertically within lakes, and suggest that phytoplankton biomass within a lake and levels of productivity between lakes are strongly related to the upward flux of dissolved inorganic nitrogen from deep water pools.
In a study of the benthic cyanobacterial mats in Lake Hoare during the 1994-95 field season, LTER scientists determined photosynthesis versus photon flux curves, the absorption spectra of the mats, and biomass mats from a range of depths.
Preliminary results show that the benthic mats are light limited and that there is a decrease in mat biomass with depth in the lake. LTER scientists have developed a mathematical model that simulates the productivity patterns of benthic microbial mats as a function of light intensity.
The McMurdo LTER is an explicitly synthetic effort—a comprehensive, multidisciplinary ecosystem study. Much of the data collected is being incorporated into a geographic information system (GIS) for data management and spatial analysis. LTER scientists have developed a GIS for Taylor Valley which now includes a number of thematic coverages. These include: base map, control points, topography, soils, geomorphology, lakes (with and without bathymetry, drill holes), glaciers (including stake locations), Taylor Valley drainage basin, streams (reach, transects, catchment area), and a coverage of station sites (met, melt holes, stream gauges, stream and soil transects, geodetic control points).
The 1995-1996 Field Season
The McMurdo LTER project is currently conducting its third field season, with 27 scientists scheduled for deployment to the site to continue its program of systematic environmental data collection and long-term experiments. One important new focus for the 1995-96 field season is data collection during the austral winter and spring. In late August 1995, LTER scientists began field activities focused on the changes in lake chemistry and biology during the transition between total winter darkness and the return of light in the spring.
Growing rapidly in size as well as visibility, the project has expanded to include wider student and scientist participation, now involving several undergraduate and graduate students and three postdoctoral positions. This September, MCM welcomed Dr. Valery Galchenko, Russian Academy of Sciences Institute of Microbiology, Moscow, who will be studying biogeochemistry of benthic communities in the lakes. Data Manager Jordan Hastings, currently teaching Computer Science classes at the University of Nevada-Reno, has implemented the Taylor Valley GIS and takes classtime opportunities to introduce the project to student volunteers for han4s-on experience. The McMurdo maintains an ftp server which provides public access to datasets collected, and is developing an online Internet presence—the site bibliography was recently added to the LTER All-Site Bibliography at LTERnet.edu.
For more information: Robert A. Wharton, Jr., 702/673-7469, rWharton@LTERnet.edu
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