Regionalization of long-term ecological research (LTER) on north temperate lakes
The North Temperate Lakes LTER project has. as its main goal the understanding of how processes occurring at multiple spatial and temporal s ales interact to affect lake ecosystems. Within this central goal we have five areas of special attention: 1) to detect long-term trends in lake ecosystem properties; 2) to understand interactions of physical, chemical, and biological processes in lakes and with their surrounding landscapes; 3) to determine the temporal responses of lake ecosystems to disturbance and stress; 4) to evaluate the interaction between spatial heterogeneity and temporal variability of lake ecosys, terns, and 5) to expand our understanding of lake-ecosystem properties to the broader, regional context. The research program began in 1980 (MAGNUSON et al. 1984, KRATZ et al. 1986) as one of the U.S. National Science Foundation’s (NSF) Long-term Ecological Research Sites (CALLAHAN 1984, FRANKLIN et al. 1990, MAGNUSON \& BowsER 1990). The eighteen LTER sites operating in 1995 are a diverse set in Antarctica, Alaska, and across the 48 contiguous states of the United States. They include other primarily aquatic sites such as the Dry Valley Lakes in Antarctica, the Antarctic Ocean of Palmer Station, lakes and streams at Toolik Lake on the north slope of Alaska, as well as a variety of primarily terrestrial sites such as temperate rain forests in northwestern U.S., taiga forests in Alaska, deserts and grasslands in western U.S., deciduous forests in eastern and southeastern U.S., coastal wetlands and barrier islands on the east coast, and agricultural sites in the midwest. Many of the terrestrial LTER sites have studies on stream ecology (MEYER et al. 1994). All have a charge to understand ecological processes and changes that occur on local to more regional scales (SwANSON \& SPARKS 1990) over decades to centuries (MAGNUSON 1990). The North Temperate Lakes Site in Wisconsin was augmented in 1994 with a broader set of disciplines and study lakes to place more effort into regionalizing our concepts and findings. The augmentation allowed us to extend our study to include lakes in the · Madison Lake Region of southern Wisconsin (Fig. 1,right). Previously, from 1980 until 1994, the North Temperate Lakes site had focused on seven primary study lakes in the Trout Lake Region of northern Wisconsin (circled lakes in Fig. 1, left). To gain an understanding of lakes at the landscape level we have structured the selection of study lakes, measurements and data bases, and analyses to respond to information on landscape level legacies. These legacies are primarily the template of lakes, streams, wetlands, and landforms left by the Wisconsin glaciation some 10,000 years ago, the biotic assemblages that formed on the land and in the fresh waters, and the human influences on these fresh waters from a variety of land and water uses. Most lakes in Wisconsin were formed by the glaciers; they are either ice block kettle lakes formed by the melting of glacial blocks in the outwash and till or impoundments of valley’s dammed by terminal and recessional moraines. The fauna and flora dispersed from the south through the Mississippi Valley and from the east through the Laurentian Great Lakes, but in addition many species were transported into the area by humans. Primary land uses are agriculture, urbanization, forestry, and recreation. Primary water uses of small, inland lakes include various extractions for drinking water, agriculture, and industry; as the recipients of various point and nonpoint wastes from the watersheds; and recreational uses such as boating, swimming, and fishing.