PAIRING MODERN AND PALEOLIMNOLOGICAL APPROACHES TO EVALUATE THE NUTRIENT STATUS OF LAKES IN UPPER MIDWEST NATIONAL PARKS

Understanding what constitutes a reference (background) nutrient condition for lakes is important for National Park Service managers responsible for preserving and protecting aquatic resources. For this study we characterize water quality conditions in 29 lakes across four national parks, and compare their nutrient status to U.S. Environmental Protection Agency (USEPA) nutrient reference criteria and alternative criteria recently proposed by others. Where appropriate we also compare the nutrient status of these 29 lakes to state or tribal nutrient reference criteria or standards. For lakes that exceed reference criteria we investigate physical and chemical patterns, and for a subset of lakes compare modern nutrient conditions to paleolimnological (i.e., diatom-inferred [DI]) nutrient reconstructions. Many lakes exceeded USEPA nutrient reference criteria, but met alternative less restrictive criteria. Modern nutrient conditions were also largely consistent with DI historic (pre-1900) nutrient conditions. Lakes exceeding alternative nutrient criteria and with elevated nutrient levels relative to DI historic conditions were mostly small, shallow, and dystrophic; continued attention to their nutrient dynamics and biological response is warranted. Coupling modern and paleolimnological data offer an innovative and scientifically defensible approach to understand long-term nutrient trends and provide greater context for comparison with reference conditions.