The role of groundwater discharge fluxes on Si:P ratios in a major tributary to Lake Erie

Session: Poster session

Taylor Maavara, University of Waterloo, [email protected]
Stephanie Slowinski, University of Waterloo, [email protected]
Fereidoun Rezanezhad, University of Waterloo, [email protected]
Kimberly Van Meter, University of Waterloo, [email protected]
Philippe Van Cappellen, University of Waterloo, [email protected]

Abstract

Groundwater discharge can be a major source of nutrients to river systems, but the dependence of surface water silicon (Si) and phosphorus (P) concentrations on groundwater sources has rarely been determined. In this study, we quantify the seasonal dynamics of Si and P cycles in the Grand River (GR) watershed, the largest Canadian watershed draining into Lake Erie, to test our hypothesis that regions of Si-rich groundwater discharge increase surface water Si:P ratios. Historically, both the GR and Lake Erie have been considered stoichiometrically P-limited. We sampled groundwater and surface water for dissolved and reactive particulate Si as well as total dissolved P for 12 months within and downstream of a 50-km reach of high groundwater discharge. Our results indicate that groundwater Si:P ratios are lower than the corresponding surface water and that groundwater is a significant source of bioavailable P to surface water. Despite these observations, the watershed remains P-limited for the majority of the year, with localized periods of Si-limitation. We further find that groundwater Si:P ratios are a relatively minor driver of surface water Si:P, but that the magnitude of Si and P loads from groundwater represent a large proportion of the overall fluxes to Lake Erie.

1. Keyword
nutrients

2. Keyword
phosphorus

4. Additional Keyword
groundwater

5. Additional Keyword
silicon

6. Additional Keyword
nutrient ratios