The lake landscape-context framework: linking aquatic connections, terrestrial features and human effects at multiple spatial scales

The principles of landscape ecology provide a powerful means to develop a more robust conceptual understanding of human and hydrogeomorphic controls of lake heterogeneity across space and time (MAGNUSON & KRATZ 2000; WIENS 2002; KRATZ et al. 2005). Using a landscape perspective, lakes can be conceptualized as patches (a fundamental unit of a landscape) that are hierarchically organized in a complex terrestrial and aquatic matrix of natural and human-influenced features that interact at multiple spatial scales. WIENS (2002) identified four properties of landscape structure that apply effectively to lakes when treated as patches: (1) patch quality describes the physical features of the patch (e.g., lake morphometry, sediment characteristics), (2) boundaries mark sharp transitions at patch edges (e.g., lake shorelines), (3) patch context describes nearby features (e.g., soils and geology), and (4) connectivity defines the degree to which materials and organisms move across the landscape through aquatic connections ( e.g. streams, groundwater and wetlands). Because the context for lake patches is hierarchical, a multiscale view that considers both spatial extent (i.e. the size of the study area that contains interacting features, such as lakes, geology, climate, etc.) and spatial grain (i.e. the resolution that features are characterized, such as ecoregion or lake district) is required to link aquatic, terrestrial, and human components into a practical framework. Such a framework empowers us to more explicitly integrate the myriad of landscape components that we know influence lake ecosystems at different spatial scales and to identify the factors contributing to the spatial structure of variation among lakes. Existing landscape frameworks have proven to be effective for understanding spatial heterogeneity across lakes (TONN 1990, KRATZ et al. 1997). For example, a combination of biogeographic barriers, abiotic constraints (determined largely by a lake’s morphometry and surface water connections) and biotic interactions can help to understand the presence/absence of aquatic species from fish to plants and invertebrates (TONN 1990; HERSHEY et al. 1999, LEWIS & MAGNUSON 2000, HRABIK et al. 2005, RAHEL 2007). In addition, a lake’s position in the regional groundwater and surface flow system (i.e. landscape position) is strongly related to lake water chemistry, clarity, biological measures, and human use of lakes (KRATZ et al. 1997, SORANNO et al. 1999, RIERA et al. 2000, QUINLAN et al. 2003, LEAVITT et al. 2006, PATOINE et al. 2006). Finally, the hydrogeomorphic setting generates large variation among lakes in their response to disturbance (WEBSTER et al. 2000, CHERUVELIL 2004). Despite these examples and calls for a more explicit landscape perspective for lakes (MAGNUSON & KRATZ 2000, WIENS 2002, KRATZ et al. 2005), we lack a formalization of these ideas into an integrated conceptual framework that is broadly applicable to a range of lakes and regions. Many existing lake frameworks have been developed for a particular hydrologic setting or omitted humans as important drivers of variation. Interestingly, stream ecologists have a rich history of considering stream ecosystems from landscape perspectives that integrate hydrogeomorphology with ecology (HYNES 1975, VANNOTE et al. 1980, FRISSELL et al. 1986, WILEY et al. 1997, POFF 1997). If the valley rules the stream, what rules the lake? Our goal in this paper is to present the lake-landscape context (LLC) framework. We propose this as a heuristic framework that allows us to understand multiple and interacting natural and human drivers of lake heterogeneity, as well as the relevant spatial scale of interactions among lakes and landscapes. We provide an example of how this framework can be applied at broad spatial scales to partition variance between local and regional spatial scales and end with a discussion of how such a framework will contribute to lake research, conservation, and management.