THE EFFECTS OF GLOBAL CHANGE ON WATERSHED ECOSYSTEM BIOGEOCHEMISTRY

In the 1950's, an ecosystem model was developed where major parameters could be measured directly in the field. By linking hydrology with other ecosystem processes, the "small watershed" model permitted quantification of biogeochemical cycles and other ecosystem processes sensitive to change. In the 1980's, a network of such research sites was established mainly in national parks. The network now includes Nolan Divide, Great Smoky Mountains National Park, Tennessee; Pine Canyon, Big Bend National Park, Texas; West Twin Creek, Olympic National Park, Washington; Loch Vale, Rocky Mountain National Park, Colorado; Fraser Experimental Forest, Colorado; Wallace Lake, Isle Royale National Park, Michigan; and the Asik watershed, Noatak National Preserve, Alaska. The sites are representative of a large fraction of land under Federal protection. The long-term research goal is to obtain some understanding of ecosystem structure and function. The focus of present research is on the effects of global change, especially atmospheric inputs and climate, on ecosystem processes as the carbon (C) and nitrogen (N) cycles. To quantify response, the ecosystem is studied as an integrated unit which requires understanding both above-ground and below-ground processes, and the linkage to hydrology. Terrestrial ecosystems may have >90% of total C and N in organic form below-ground. Half of total productivity can occur below-ground, and >95% of total ecosystem biodiversity may be in the forest floor and below-ground. The complex below-ground processes regulate the quality and quantity of nutrients and energy available to the ecosystem. This paper provides an overview of site characteristics and network research while the accompanying papers detail study results.