The southeastern drought of 1985-86 is an event expected to have long-term impacts on two LTER sites: Coweeta Hydrologic Laboratory in the Southern Appalachian Mountains of western North Carolina and North Inlet in the coastal marshlands of South Carolina. To assess those impacts, a coordinated research program is now underway at these sites to determine and compare ecosystem responses that follow drought. At Coweeta, objectives of the drought response research include five activities:
- Long-term analyses of the drought as related to long-term climatic data
- Effects on water budget (soil moisture, evapotranspiration, and short-term stream flow responses) as compared with more normal years
- Effect of drought upon precipitation and stream chemistry with emphasis on nutrient cycling
- Effects on forest dynamics with emphasis on reduced vigor or decline symptoms
- Use available simulation models to investigate potential long-term effects of several drought and non-drought scenarios
Total flow for mountain headwater streams is only partly due to stormflow. Most of the total annual flow is derived from slow drainage of soil moisture from the large soil mass upslope from the stream. Thus, the 1984-86 pattern of low precipitation during soil moisture recharge periods is reflected by falling streamflow levels. At the beginning of the growing season in May 1986, cumulative streamflow over 18 months was 59 percent of the 52-year mean. Minimum monthly flow records were set for 6 consecutive months, April through September 1986.
This issue focuses on stream studies at the Coweeta LTER site; terrestrial research will be covered in a future issue. Continuous climatic and streamflow studies at Coweeta were initiated in the mid 1930s and continuous baseline precipitation and stream chemistry studies have been conducted since the early 1970s for seven streams draining control watersheds and nine streams draining disturbed catchments. The disturbed catchments include hardwood-to-pine conversions, grass-to-forest succession, clearcut and natural re-growth, selection cutting, and understory cuts. These records have provided a valuable extensive data base for evaluating the integrated biogeochemical function in southern Appalachian forest ecosystems, as well as for evaluating system-level responses to natural epsiodic events, atmospheric deposition, and forest management practices.
Several studies are examining nutrient dynamics in Coweeta streams. Steve Golladay’s recently completed Ph.D. research (Jack Webster’s and Fred Benfield’s laboratory - VPI & SU) examined nutrient retention in disturbed and undisturbed streams, and Donna D’Angelo (VPI & SU) is investigating the influence of disturbance on dissolved nutrient uptake in streams. Nancy Munn’s research (Judy Meyer’s Laboratory - UGA) is focusing on nutrient uptake and extent of mixing between surface and interstitial waters. Exchange of surface and interstitial waters is rapid, which suggests that ions in transport in water may have great opportunity to interact with sediments. Other research in Meyer’s laboratory is focusing on bacterial biomass and organic matter content of sediments, as well as melofauna in streams at Coweeta. Uptake of DOC and long-term trends in DOC concentration streams following watershed disturbance are being studied by Judy Meyer. Webster and Benfield have developed a computer model of transport of particulates in streams and are examining effects of long-term hydrologic patterns on particle transport.
Traditionally, studies of macroinvertebrates in Coweeta streams, which were initiated in the 1950s, have examined the influence of disturbance from related forestry practices. The most recent studies have focused more directly upon the role of invertebrates in mediating ecosystem processes such as organic matter processing and nutrient spiraling. Benfield and Webster are examining effects of forest disturbance on food quality available to stream detritivores and Ben Stout (VPI & SU) is measuring detritivorous insect production in disturbed and reference streams. The influence of drought and manipulation of invertebrate populations on ecosystem processes (leaf litter processing, export of dissolved, fine and coarse organic matter, and nutrients) of three headwater streams is being examined in Bruce Wallace’s laboratory (UGA). The severe drought of 1986 influenced the amount and form of organic matter exported to downstream reaches; however, the influence of macroinvertebrate reduction (via pesticide treatment) on export of fine particulate organic matter has been much greater than the drought effects. Recently, a study has been completed on the influence of local geomorphology on spatial patterns of macroinvertebrate production and functional structure in a high elevation stream. This study was designed to serve as a point of reference in order to assess any future changes in the biota should acidification occur (Alexander Huryn and B. Wallace, UGA). Huryn, a research associate in Wallace’s lab, is currently studying growth patterns and developmental phenology of larval chironomid communities in watersheds of different elevation, aspect, and disturbance history in order to assess these influences on overall patterns of production across the Coweeta Basin.
Studies in Gary Grossman’s laboratory (UGA) are concerned primarily with fish studies. At Coweeta, these include the following:
- Long-term monitoring of fish assemblage structure and environmental variables to ascertain the relationship between these two ecosystem properties
- Evaluation of the effects of an experimentally induced resource depression on food and microhabitat use in two benthic fishes
- A field removal experiment to test for the presence of competition between mottled sculpin and longnose dace
- Construction of an energetic model of microhabitat selection for two water-column species (rainbow trout and rosyside dace)
- Quantification of dietary selectivity in this assemblage
The Coweeta synthesis volume “Forest Hydrology and Ecology at Coweeta” has been published by Springer-Verlag. The book, edited by W. T. Swank and D. A. Crossley, Jr., is Volume 66 in the Ecological Studies series. The content is divided into eight sections including baseline data on hydrology, geology, climate, and water chemistry; forest dynamics and nutrient cycling; canopy arthropods and herbivory; forest floor processes; stream biota and nutrient dynamics; management of forested watersheds; and long-term research perspectives. Forty-nine co-authors contributed to the 30 chapters.
Substantial improvements in research facilities at Coweeta are nearing completion. A new building for data processing, office space, library, and other support services will be occupied in April. The building previously used for these functions is being renovated for dormitory, living, and work space to accommodate up to 30 investigators. The renovation is partly supported by a NSF Grant from the Biological Research Resources Program.
For additional information on the book volume and facilities, contact Wayne T. Swank, Coweeta Hydrologic Laboratory, 999 Coweeta Lab Road, Otto, North Carolina 28763, (704) 524-2128.