Spatial and temporal dynamics of Laurentian Great Lakes coastal marshes

Abstract

<p>Despite their ecological and economical values, degradation of coastal marshes in the Laurentian Great Lakes is widespread. In order to restore degraded marshes and protect high-quality ones we need to understand the interactions between abiotic and biotic factors and how these change over space and time. The over-arching goal of this thesis is to gain greater understanding about the temporal and spatial dynamics that shape coastal marshes.</p> <p>Chapter 1 evaluates the response of the biotic and abiotic components to restoration efforts at Cootes Paradise, a degraded coastal marsh of Lake Ontario. We used three approaches: 1) we analysed changes in water quality parameters and the community composition of zooplankton, macrophytes and fish 2) we used ecological indices based on water quality, zooplankton, macrophyte and fish communities to track changes in quality and 3) we evaluated changes in the wetland quality in comparison with two other coastal wetlands of the Laurentian Great Lakes for which long-term data exist. Our results show that there has been variable improvement in wetland quality at Cootes Paradise, but compared to the two other wetlands, it is still the most degraded in all aspects studied. We detected an overall trend towards moderately better water quality conditions in Cootes Paradise over the past decade but this is not directly reflected in the zooplankton, macrophyte and fish communities. We believe that high nutrient levels and high turbidity are preventing the progression to a clear-water macrophyte dominated system.</p> <p>Chapter 2 examines the influence of environmental variation on the zooplankton assemblage at nearshore Long Point Bay, Lake Erie. We visited 102 sites along the nearshore and sampled for zooplankton and a suite of environmental variables. Afterwards, we evaluated the impacts of exposure using wind and fetch data to calculate a Relative Exposure Index (REI). Ordination techniques revealed a large variation in physical disturbance, water clarity, nutrient concentrations, water chemistry and aquatic vegetation that explained the distribution pattern of zooplankton at the 102 sites. Gradients of REI are strongly positively correlated with environmental variables, such as pH, dissolved oxygen, and temperature and highly negatively correlated with conductivity and dissolved organic carbon. The results of this study highlight the impacts of exposure on the zooplankton community and the effects of connectivity to larger water bodies.</p>