Research at the North Temperate Lakes Long-Term Ecological Research site (NTL-LTER) extends beyond the traditional boundaries of ecosystem studies to encompass multiple temporal and spatial scales. We consider a suite of adjacent lakes that share a common climate but differ dramatically in their physical, chemical, and biological characteristics. We employ a long-term perspective that permits us to place analyses of seasonal and annual patterns into the broader context of year-to-year variability and to evaluate the implications of such variability for community and ecosystem processes. We use a nested series of spatial scales ranging from within individual lakes to the entire Northern Highlands Lake District. This permits us to consider how processes occurring in a lake are related to factors in adjacent systems and the surrounding landscape (Figure 1).

Within the synthetic goal of understanding the ecological complexity generated by multiple processes acting over many temporal and spatial scales, we aim to develop a series of broad- scale evaluations of factors controlling lake processes. These evaluations are interrelated but can also be considered independently. They can be classed generally into five major objectives: (1) to perceive long-term trends in physical, chemical, and biological properties of lake ecosystems; (2) to understand the dynamics of internal and external processes affecting lake ecosystems; (3) to analyze the temporal responses of lake ecosystems to disturbance and stress; (4) to evaluate the interactions between spatial heterogeneity and temporal variability of lake ecosystems; and (5) to expand our understanding of lake-ecosystem properties to a broader, regional context. The first four objectives have played a key role in our research to date; the last object is relatively new.

Of particular interest at the NTL-LTER is the issue of how to make useful predictions across scales. We wish to scale-up from our site to not only the Northern Highland Lake District but to other north temperate lake districts (Figure 2) to assess: (1) how well can we transfer our understanding of processes within the LTER lakes to a larger region, (3) regional diversity, and (4) effects of regional changes in conservation, forestry, land development, and recreation policies.