Modelling the influence of seiche-events on phosphorous-loading dynamics in three Lake Ontario coastal wetlands

Abstract

Coastal Wetlands (CWs) provide critical ecosystem services that maintain biogeochemical processes and habitats in the coastal zone of the Great Lakes. When nutrient-laden surface waters flow into CWs from their watersheds, internal physical, chemical, and biological processes can alter the final nutrient loadings to the lake. However, CWs can periodically be inundated with lake water from seiche events, and little is known about the impacts of seiches on nutrient processing and loadings from CWs. To evaluate the influence of lake seiches on CW phosphorous-loading dynamics, we built a multi group structural equation model (SEM) using climatic and wave data, and interannual (2009–2018) estimated sediment and phosphorous loadings from three CWs on the north-shore of central Lake Ontario (Rouge Marsh, Duffin’s Marsh, and Carruthers Marsh). Wind speeds, lake levels, and an increased peak period of wave spectra were significant explanatory variables of seiche events (p-value < 0.001). We identified that seiche events caused significant sediment resuspension (p-value < 0.001) in CWs, which contributed to a significant increase of phosphorous loading to the coastal zone of Lake Ontario (p-value < 0.001). Our results indicate that lake-seiche events can influence CW phosphorous-loadings to Lake Ontario, and should be considered when modelling water quality in the nearshore zone.