Urban Lakes: Ecosystem Services and Management

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Lakes provide a variety of ecosystem services and benefits that greatly contribute to urban sustainability. Despite the growing interest in integrating freshwater systems into management and policy decisions, urban lakes are often overlooked in land-use planning. Nutrient and pollutant runoff from the surrounding urbanized watershed result in water quality deterioration that negatively impact the lake ecological functions and related ecosystem services. The vulnerability and degradation of these urban ecosystems should be a matter of concern, especially considering that, in rapidly growing metropolitan areas, the demand for aesthetic and recreational services provided by urban lakes is increasing. The overall goal of this dissertation was to better characterize urban lakes and to provide a basis to improve the management of these systems. As a first step I defined as "urban" those lakes that were completely within areas with at least 50,000 people, and in a sub-watershed with a population density of at least 1,000 people per square mile and more than 10% of impervious cover. Based on this definition, by analyzing datasets from a variety of sources, I identified and characterized 1,950 "urban" lakes and reservoirs across the continental United States. These systems presented more eutrophic and disturbed conditions than non-urban lakes. Urban lakes are also impaired by contaminants (i.e., mercury and toxic compounds) that could harm recreational users. With the exception of a few systems, most urban lakes are not actively managed, which results in degradation of these valuable resources. In the second chapter I examined a case-study of an urban lake that has been intensively managed and monitored for the past 20 years. Intensive in-lake management efforts successfully improved the water quality and maintained the aesthetic and recreational benefits provided by the lake. However, high nutrient loading from the surrounded watershed partially reduced the effectiveness of management efforts. An accurate phosphorus budget for the lake is necessary to effectively implement nutrient reduction strategies. This study also showed some of the challenges faced by lake managers like the coordination of multiple stakeholders and jurisdictions with conflicting goals, guarantee of consistent high-quality data in long-term monitoring programs, and ensuring that the water quality meets user's expectations. In the third chapter, I used a new approach to analyze the impact that future urbanization could have on the water quality and ecosystem services provided by a major urban lake. I combined two modeling tools (InVEST software and a mass balance model) to estimate the