2002 Natural Resources Management

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loading from the watershed, a large amount of phosphorus has been adsorbed by the sediment in the lake. If the nutrient load from the watershed is reduced — always a good idea — and its concentration in the water drops, phosphorus release from the bottom sediments of the lake can become an important nutrient source for the algae. This delays the response of the lake water concentration to the reduction of loading from the watershed. There are other ecological mechanisms associated with the biology of a disturbed lake that tend to perpetuate a turbid water state as well. This is not to say that reducing the flow of nutrients from a lake's watershed to the lake should not be done. Reduction of incoming nutrients and other pollutants to urban lakes is always a good idea. It does mean that careful consideration of the costs and likely benefits (some of which may take a long time to appear) is needed. In addition, a lake system itself is inherently variable over time due in part to differences in precipitation and temperature patterns as well as land management activities in the watershed. Thus, visible improvements may follow a "two steps forward, one step back" track. Finally, it means that no single action is likely to change an urban lake dramatically. There are numerous "tools in the toolbox" and many need to be used in order to generate an improvement in lake quality, especially in lakes that have been severely impacted for along period of time. Or,anization of Manaizement Options A matrix of management options was developed to guide future management activities for Langton and Bennett lakes. The options are based on the results of field surveys, watershed and in -lake water quality modeling, and — most importantly — on actual experience in restoration efforts on urban lakes elsewhere in the Metro area and the upper midwest. The management options are assigned to one of three phases. Those in Phase I can be pursued now with no little or no additional resources from the City, supplemented perhaps by volunteer assistance. Options assigned to Phase 2 are more costly and in some cases require a more detailed assessment beyond the scope of this study. Those assigned to Phase 3 require a significant commitment of financial resources and may not move forward unless supplemental outside funding is secured. Also, additional work to establish feasibility, refine costs, and develop designs will likely be necessary. In most cases, these management actions can also be expected to have the greatest potential for improving the quality of the target resource. City of Roseville 55 Parks Natural Resource Management