Ruchi Bhattacharya, Simon G.M. Lin, Nandita B. Basu (2022). Windows into the Past: Lake sediment phosphorus trajectories act as integrated archives of watershed disturbance legacies over centennial scales . Proceedings of the GWF Annual Open Science Meeting, May 16-18, 2022.

Historic land alterations and agricultural intensification have resulted in legacy phosphorus (P) accumulations within lakes and reservoirs. Internal loading from such legacy stores can be a major driver of future water quality degradation. Yet, little is known about the magnitude and spatial patterns of legacy P accumulation in lentic systems, and how watershed disturbance trajectories drive these patterns. Lake sediments are known integrators of long-term global change and here, we use a meta-analysis of 113 paleolimnological studies across 128 lakes in 20 countries to quantify the linkages between the 100-year trajectories of P concentrations in lake sediments, watershed inputs, and lake morphology. We find five distinct clusters for lake sediment P trajectories, with lakes in the developing and developed world showing distinctly different patterns. Lakes in the developed world (Europe and North America) with early agricultural intensification had the highest sediment P concentrations (1,176-1,628 mg/kg), with a peak between the 1970-1980s and a decline since then, while lakes in the developing world, specifically China, documented monotonically increasing sediment P concentrations (857-1,603 mg/kg). Sediment P trajectories reflected watershed disturbance patterns and were driven by a combination of anthropogenic drivers (fertilizer input and population density) and lake morphology (watershed to lake area ratio). Specifically, we found the largest legacy accumulation rates to occur in shallow lakes experiencing long-term land-use disturbances. These links between land-use change and P accumulation in lentic systems can provide insights about inland water quality response and help to develop robust predictive models useful for resource managers and decision-makers.

AOSM2022 Lake Futures project First Author: Ruchi Bhattacharya Additional Authors: Simon G.M. Lin2, Nandita B. Basu1,2,3 1Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada 2Department of Civil and Environmental Engineering, University of Waterloo, Waterloo, Ontario, Canada, 3. Water Institute, University of Waterloo, Waterloo, ON, N2L 3G1, Canada