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What Exactly Are Urban Lakes?
For the purposes of watershed management, urban lakes are defined by six operational criteria. First, they tend to be rather small, and generally have a surface area of 10 square miles or less (this excludes larger lakes). Second, they tend to be shallow, with an average depth of 20 feet or less. Third, they have a watershed area/drainage area ratio of at least 10:1, meaning that their watersheds exert a strong influence on the lake. Fourth, the lake watershed must contain at least 5% impervious cover as an overall index of development. Fifth, whether natural or man-made, the lake must be managed for recreation, water supply, flood control or some other direct human use. Finally, our definition excludes several types of lakes with unique hydrology or nutrient cycling. These include solution lakes that are strongly influenced by groundwater, the rare nitrogen- limited lakes, saline lakes and playa lakes. While these lake types can be found in urban areas, it is not clear whether they share the same water quality response to watershed development as other freshwater lakes
Curiously, the unique problems and conditions of urban lakes have received little attention in the limnological and watershed management literature. This is particularly surprising given that many of our management efforts are devoted to lakes and reservoirs that are distinctly urban in character. While the watershed management literature is replete with phosphorus budgets and watershed models, it is very unusual to find generalizations about the influence of watershed development on lake quality. Instead, urban land use is generally confined to a line item in a phosphorus budget, and it is exceptionally rare to find studies that have tracked changes in lake quality as a function of watershed development over time.
Similarly, limnologists tend to treat the influence of a watershed on its lake as a constant, and devote most of their attention to the internal dynamics within each individual lake. From their perspective, lakes, as a group, defy easy classification. For example, Hutchinson (1957) described some 76 types of lakes, simply based on their geomorphic origin. Other have classified lakes primarily on the basis of their trophic state. Indeed, lakes differ so much in their size, depth, drainage area/surface ratio, water balance, nutrient...