Student Pilot Projects

Two Awards Announced for Intersite Comparisons

Comparison Of Hydrologic Patterns And Processes Across Four Landscapes

Reed Perkins – H.J. Andrews Experimental Forest LTER

Patterns of streamflow hydrology are an important research theme at 11 LTER sites. To date, however, no cross-site comparative hydrologic analyses have been done. Because streamflow is regulated by climatic variation and terrestrial processes, such analyses would provide a natural link between existing cross-site studies on climate and stream ecology. Small (<200 ha) control watersheds, originally intended for comparison of paired basins within a site, provide a logical basis for analysis of hydrologic processes underlying streamflow patterns across the LTER Network.

This study will provide a preliminary and descriptive comparison of the hydrologic processes and runoff patterns occurring at each site. It is also intended to develop hypotheses about links between differences in the relative importance of hydrologic processes across sites and differences in runoff patterns. This fall, I will collect necessary streamflow, climate, and physiographic data at the Coweeta, Hubbard Brook, and Luquillo LTER sites and at Caspar Creek, a U.S. Forest Service research forest in northern California. Cooperators include Lloyd Swift and Wayne Swank at Coweeta, Wayne Martin and Jim Hornbeck at Hubbard Brook, Doug Schaefer at Luquillo, and Bob Ziemer at Caspar Creek.

Specific research objectives include:

  • Characterize basic components of each site’s annual and monthly water budgets
  • Describe dominant hydrologic processes and flowpaths operating
  • Catalog status and availability of hydrologic datasets
  • Describe hydrologic research objectives being pursued

Products of the work will include an article to be published in the spring/summer 1996 LTER Network News and a working document which will be used to stimulate further intersite communication among hydrology researchers.

Influences On Precipitation-Borne Sulfate Retention At Two Watersheds

Bryan Dail—Coweeta Hydrologic Laboratory LTER

Precipitation-borne sulfate is a major source of sulfur to ecosystems. As such, it is readily available to plant and microorganism populations. At the Coweeta LTER site, we have been investigating the fate of this form of sulfur input into headwater watershed soils and sediment, measuring two major sulfur immobilization processes:

  • Primarily non-biological adsorption of sulfate directly to soil and sediment
  • Biologically-mediated incorporation of sulfate into organic matter

Both processes have been linked to soil organic matter content, intrinsic sulfur content, and activity of the soil or sediment microbial community. that scours the stream basin during late summer monsoon rains. In addition, the flash floods deliver organic matter to the parafluvial soils and support blooms of microbial activity, a phenomenon measured in initial visits to the Sevilleta. In continuing work with cooperators Robert Parmenter and Doug Moore in the Rio Salado, with support from the Pilot Project grant and both sites, we will be using selective agents to “knock out” several microbial communities in microcosm experiments to determine their relative importance in immobilizing sulfate.

By enlarging our study to include watersheds of different physical as well as biological features, we hope to better explain these influences on retention of S in ecosystems. The Rio Salado drainage at the Sevilleta LTER offers many such contrasting features, including:

  • High native sulfate due to a gypsum formation
  • Apotential for higher primary productivity
  • A flash flood regimen