benefits (if the cause of the stress has been eliminated); others must be applied continuously (aeration) or repeatedly (liming of acidic lakes; herbicide treatment of macrophyte problems) to maintain the benefits of treatment.

Lake restoration and management techniques are listed in Table 4.7 according to the type of problems they seek to remedy, and the sections below briefly describe the most important of these techniques. More comprehensive reviews of the techniques are provided by Cooke et al. (1986) and Cooke and Kennedy(1989)

Problems caused by excess nutrients have received the most attention over the past two decades, and more techniques have been developed to address these problems than all other types of stresses combined. Excessive nutrient enrichment manifests itself in several distinct problems; algal blooms, macrophyte proliferation, oxygen depletion, and loss of sport fisheries are the most important.


Nutrient Source Reduction

High loading of nutrients to lakes produces algal blooms and other problems. In many cases, oxygen-demanding organic matter, silt, or toxic materials accompany the nutrient loadings. Reduction of nutrient loadings (and related inputs) can be accomplished (Table 4.8) by (1) diverting point sources of nutrients (e.g., municipal sewage effluents) or nutrient-laden streams out of the lakes watershed; (2) modifying products to contain lower amounts of nutrients (mainly phosphrous); (3) removing nutrients from wastewater in engineered treatment systems; (4) intercepting nutrients in pre-lake impoundments (storm water detention and retention ponds, natural or artificial wetlands); (5) decreasing nutrient runoff from agricultural lands by "best management practices"; and (6) instituting land use and management controls.

Diversion Wastewater effluent is rarely diverted out of watersheds because of the difficulty of finding an alternative disposal site, but a few well-known diversions have occured. The lower lakes of Madison, Wisconsin (Monona, Waubesa, and Kegonsa) have deteriorated drastically during the twentieth century because of sewage discharges (Sawyer, 1947; Lathrop, 1979). By 1958, most of the effluent have been diverted downstream from the lakes, and all effluent was

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