Assessing the chemical and biological recovery of Killarney Provincial Park lakes from historical acidification

Abstract

Since the mid 1900s, acidification has impacted water quality and threatened the ecological integrity of thousands of lakes and streams across Eastern North America and Europe. After the implementation of industrial emission reductions programs in the late 1960s, chemical recovery of historically acid-damaged lakes was observed, but a lag in biological recovery has been partially attributed to changes in multiple environmental variables, such as warming climate, shoreline development, and the introduction and spread of invasive species. To assess the continued recovery of historically acidified lakes, forty-four lakes were sampled for zooplankton and water chemistry in and around Killarney Provincial Park during peak emissions in 1972-73, through the decades after emission reduction programs were implemented in 1990, 2000, 2005, 2011, and 2016. We assessed changes in both univariate and multivariate zooplankton community metrics through time, and evaluated recovery using a reference lake approach that included 8 circumneutral lakes within Killarney Provincial Park and 55 non- acidified lakes in Algonquin Provincial Park. In addition, we assessed the relative importance of local biotic and abiotic variables in shaping recovering zooplankton communities in Killarney and Algonquin Provincial Parks. We found strong evidence for continued chemical and biological recovery in acidified lakes in Killarney Provincial Park. Species richness and diversity increased in acid-recovered lakes to values statistically indistinguishable from those of our reference lakes, and multivariate-based community composition shifted towards a community structure more similar to reference lakes. Several variables were identified as important drivers of zooplankton community structure, including pH and ion concentrations, nutrient concentrations, fish community, water clarity, maximum lake depth, and surface area, with environmental variables accounting for less variation in communities through time. Overall, these results indicated that recovery is still progressing in historically acidified lakes, and unlike similar Canadian Shield communities that did not experience severe acidification, pH and its legacy effects are still acting as primary drivers of zooplankton community structure in Killarney Provincial Park lakes.