NUTRIENT CONCENTRATIONS AND CONSEQUENTIAL ECOSYSTEM CHANGES RECORDED IN SMALL ALPINE LAKES IN THE WESTERN CORDILLERA OF NORTH AMERICA

The Cordillera of North America is characterized by numerous small, remote alpine lakes that contain records of environmental change that typically span the Holocene. Because these lakes are located far from most direct human activity they provide an ideal setting to evaluate the specific causes and effects of atmospheric pollution (mainly nutrients – nitrogen (N) and phosphorus (P)) on terrestrial and aquatic ecosystems. Here we review our research findings, which combine a variety of paleolimnological techniques with a modern mechanistic approach, from the Uinta Mountains, Utah and Jasper National Park, Alberta to highlight their contribution to our understanding of human activities on remote ecosystems. Paleolimnological research provides a long-term perspective of environmental change that is not typically available from modern studies; however, a modern mechanistic approach greatly enhances our interpretation of paleolimnological records. Our research shows that 1) despite local human disturbances, such as grazing and fish stocking, almost all recorded changes in nutrient delivery to alpine lakes is atmospheric in origin; 2) because alpine lakes are so oligotropic, even small changes in nutrient inputs can shift nutrient limitation from N to P; 3) because nutrient limitation varies spatially and temporally, changes in either N or P deposition can cause dramatic changes in alpine lake ecosystems, including changes in lake production, species community composition and diversity; 4) lake response to increased nutrient inputs is dependent on the lake’s history and its catchment characteristics, and 5) climate change, particularly warming temperatures and increased precipitation, will exacerbate the changes observed to date. Our research highlights the usefulness of alpine lake records to providing information about the causes and effects of atmospheric nutrient fertilization that should improve ecosystem management .