NEW PHOSPHORUS BUDGET FOR LAKE ERIE IMPLIES MAJOR INPUT FROM COASTAL EROSION

In large lakes, phosphorus (P) input from coastal erosion, including the fraction that can be incorporated in the aquatic food web (AFW), is often overlooked compared to P inputs brought by river discharge and atmospheric deposition. Here, we compare two independent approaches to estimate the P input to Lake Erie (Canada, USA) associated with coastal erosion processes. The first approach relies on direct coastline retreat measurements while the second approach is based on whole-lake P mass balance modeling. The latter builds on a recently revised lake budget of total P (TP) averaged over the period 2003-2016. We expand this budget by explicitly accounting for TP that is incorporated in phytoplankton, zooplankton, fish, and zoobenthos. The difference between known external inputs and output via lake outflow and sediment burial reveals that (1) an additional amount of 3,400 metric tonnes per year (MTA) of TP must enter the lake, and (2) P uptake in the AFW is significantly unbalanced, hence, further highlighting the existence of an additional source of bioavailable P.  We propose that the additional P input is caused by coastal erosion. Mapping of coastline retreat rates combined with preliminary P concentration data for soil samples from eroding bluffs in Lake Erie shows that the magnitude of the P input related to coastal erosion is of the same order of magnitude as that derived from the TP budget calculations. An emerging concern for Lake Erie, and similar large freshwater lakes, is the possible acceleration of P enrichment by coastal erosion driven by climate change.

Presentation Preference: Oral

Primary Presenter: Serghei Bocaniov, University of Waterloo (sbocaniov@uwaterloo.ca)

Authors:

Serghei Bocaniov, Ecohydrology Group, Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada  (sbocaniov@uwaterloo.ca)

Chris Houser, Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada  (chouser@uwaterloo.ca)

Alexander Karatayev, Great Lakes Centre, SUNY Buffalo State University, Buffalo, NY, USA  (karataay@buffalostate.edu)

Lyubov Burlakova, Great Lakes Centre, SUNY Buffalo State University, Buffalo, NY, USA  (burlakle@buffalostate.edu)

Philippe Van Cappellen, Ecohydrology Group, Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada  (pvc@uwaterloo.ca)