A shoreline divided: Twelve-year water quality and land cover trends in Lake Ontario coastal wetlands

Water quality in Great Lakes coastal wetlands has been studied for decades, but few studies look at water quality changes in multiple sites over many years and relate that to land cover. In this study, water quality at 22 sites in two regions along the north shore of Lake Ontario (Bay of Quinte in the east and Durham Region in the west) was compared over a period of 12 years (2003-2014) and related to land cover data from two time periods (1999-2002 and 2009-2011) at four spatial scales; 500 m, 1000 m, 2000 m wetland buffers, and the quaternary watershed. Water Quality Index (WQI) scores significantly increased over time in both regions, and turbidity and pH both significantly decreased over time in both regions. Land cover data showed regional differences between east and west, with the western sites having higher percentage of urban land at all scales. There were significant relationships between land cover (% Natural and % Urban) and WQI score at several scales, but the relationships were strongest at the watershed scale. We found that sites in the western region showed a greater amount of change in land cover between the two time periods, compared to the eastern sites. The results of this study provide some key insights on the impact of urbanization on Great Lakes coastal wetlands, and on how they can be managed in the future.