Identifying lake water quality trends and effective monitoring strategies in a rapidly urbanizing region

Abstract

Water quality degradation in freshwater lakes is widely observed and largely attributed to human activities, particularly in urban regions. The city of Halifax, NS, is among the fastest growing urban centers in Canada, potentially threatening the health of surrounding waterbodies. This thesis analyzed water quality trends in a set of ~50 lakes that have been sampled on a decadal-basis over a 40-year period in the Halifax Regional Municipality (HRM). Trophic state was also tracked in a subset of lakes over the 2021 open-water season to evaluate common and novel strategies for monitoring lake health. Aluminum, chloride, manganese, and arsenic concentrations were found to exceed national guidelines for the protection of aquatic life in one or more of the study lakes in 2021. Urban development was identified as an important driver of increasing chloride, conductivity, sodium, calcium, and total phosphorus (TP) concentrations. Regional factors, including climate change and decreasing acid deposition, hydrology, and watershed characteristics are believed to be stronger drivers of other observed changes. Decadal spring synoptic surface sampling was determined to be useful at highlighting emerging water quality concerns but may be less effective at characterizing parameters that are more spatially and temporally variable, such as nutrients, particularly in lakes where internal P loading occurs. More rigorous sampling is required to accurately characterize nutrient dynamics, and parameters that appear to be influencing trophic state (e.g., color, and chloride and DOC concentrations) require further exploration. Research findings support the continued use of TP as a trophic state indicator and demonstrated that the TP-chlorophyll a relationship identified by the Organization for Economic Cooperation and Development (OECD) Cooperative Programme on Eutrophication in the 1970s remains applicable in HRM lakes despite changes in climate and varied lake and watershed characteristics. This thesis contains baseline data for lake water quality in HRM which will inform future lake management efforts and highlights water quality concerns that should be the target of monitoring efforts in the broader context of temperate urban lakes.