THE APPLICATION OF PALEOLIMNOLOGY TO INFORM FRESHWATER MANAGEMENT: THE CASE OF URBAN LAKES IN HALIFAX REGIONAL MUNICIPALITY, NOVA SCOTIA, CANADA

Abstract

Watershed-scale stress from urbanization can negatively impact ecosystem services communities rely on. Yet, a lack of historical context for individual-lake conditions impedes management planning that promotes evidence-based restoration/remediation targets and the efficient allocation of resources. Halifax Regional Municipality (HRM) Nova Scotia, Canada, has hundreds of lakes that are increasingly influenced by residential development, and most lakes in the urban/suburban core are developed to some degree. Here, I assessed surface sediment subfossil chironomid assemblages (Diptera: Chironomidae) from 40 HRM lakes and used a development index to determine if there is a relationship between assemblage structure and watershed development level. Chironomid assemblages were analyzed to understand the broader context of urban influence and to identify lake-specific environmental stressors that influence assemblage structure with water quality parameters for a subset of 29 lakes. Through the additional biostratigraphic analysis of three lakes we used paleolimnology to fill the gap in long-term monitoring data and to infer the influence of watershed development on urban lakes (Chocolate Lake and Settle Lake lie in residentially developed watersheds, and Spider Lake is in an undeveloped watershed). I found that chironomid assemblages followed a productivity gradient with development level, and that conductivity and ions were the primary drivers explaining variation in surface sediment assemblages. In the two lakes in developed watersheds, shifts in chironomid assemblages over time reflected documented patterns of human disturbance and indicate increased productivity. In contrast, the lake in an undeveloped watershed has remained oligotrophic throughout its history. Our results could facilitate informed decisions related to restoration/remediation targets and assist in the planning and management of freshwater resources.