Littoral Zone Structure, Energy Mobilization and Benthic Food Webs in Oligotrophic Northern Temperate Lakes

Lakes are usually described by pelagic-based characteristics such as trophic status or stratification and mixing regimes. These categorization schemes neglect among-lake differences in the physical and biological structure of the littoral zone. The extensive use of stable isotopes has led to a better integration of pelagic dynamics and littoral processes in limnology. In order to further our understanding of littoral trophic dynamics I conducted a detailed investigation of benthic primary production, littoral sediment bacterial production, and zoobenthic consumer resource use in oligotrophic temperate lakes. I have found that among-lake variation in benthic primary and bacterial production reflects littoral zone structure. Specifically, the magnitude of benthic primary production relative to benthic bacterial production is influenced by the amount of organic carbon associated with littoral sediments. I determined resource use among zoobenthic functional feeding groups using stable isotopes. Macroinvertebrate production was strongly dependent on benthic algae, but variation in algal isotope signatures associated with lake depth and sediment depth complicates the interpretation of mixing models. I compared estimates of whole-lake benthic primary production with various levels of spatial variability of photosynthetic parameters incorporated into primary production models to determine how much effort is needed to accurately quantify whole-lake benthic primary production. Estimates of mean areal littoral primary production using mean light-saturated maximum primary production were comparable to estimates calculated with highly resolved, depth-specific estimates of maximum primary production. Thus, accurate estimates of whole-lake benthic primary production can be obtained with relatively simple models, but an accurate, depth-averaged estimate of maximum benthic primary production is crucial. This study demonstrates that littoral primary production is a major source of energy for aquatic consumers, and the contribution of littoral processes to whole-lake trophic dynamics is dependent on littoral zone characteristics. Further integration of littoral processes into whole-lake food webs is vital to a comprehensive understanding of lake ecology