netic aeration permits the establishment of a cold-water fishery such as 

 trout or salmon, whereas destratif ication may preclude such a fishery by 

 eliminating the cold-water region. 



Examples of aeration projects for eutrophication control are at Cline's 

 Pond, Oregon, where destratif ication aeration was used; at Lake Waccabuc, 

 New York, where the "Limno" hypolimnetic aerator is being used; and at 

 Ottoville Quarry, Ohio, where hypolimnetic aeration is achieved by a pro- 

 cess called "side stream pumping". 



Nutrient inactivation --A promising approach for a wide range of situa- 

 tions is nutrient inactivation. This involves treatment of lake waters in 

 situ with a chemical to precipitate phosphorus. Inactivant materials that 

 have shown particular promise in laboratory and field studies are aluminum, 

 zirconium, and fly ash. Experiments with aluminum compounds are presently 

 being conducted on lakes in Wisconsin, New England, Ohio, and Washington. 

 Zirconium is being tested in a controlled pilot field study in Oregon, and 

 a similar experiment, utilizing fly ash, is under way in Indiana. It is 

 anticipated that such treatments will be particularly efficacious in lakes 

 with wery long retention times. 



Hypolimnetic withdrawal/selective discharge --Hypolimnetic withdrawal 

 has been used to improve dissolved oxygen conditions near the bottom of a 

 lake and to increase nutrient export. In bodies of water that stratify, 

 this technique permits the removal of anaerobic, nutrient-rich deep 

 waters. The technique is suitable for waters with outlet controls, such as 

 reservoirs, or in lakes with surface withdrawals by installation of a 

 siphon from a point of maximum depth. The surface discharge is, or can be, 

 completely blocked off. This technique has been used in Wisconsin, Ohio, 

 and other states. A potential problem with its use is the triggering of 

 increased macrophytic growth and low dissolved oxygen in the downstream 

 channels. 



Drawdown -- Sediment exposure and desiccation via lake drawdown has been 

 undertaken on impoundments for various purposes. In favorable sites this 

 procedure can reduce the rooted aquatic plants by desiccation. The effect 

 of drying on sediment chemistry and possible nutrient release is now being 

 studied, particularly in Florida and Louisiana. Presently 13 Louisiana 

 impoundments are being managed by water drawdown to aid in control of 

 aquatic vegetation and fish populations. 



Biological control --The control of particular problem species by mani- 

 pulation of biotic interactions has been a much desired goal in recent 

 years. Evaluation of biological controls has been limited, however; most 

 testing has been done in the laboratory or experimental ponds. Con- 

 siderable publicity has been given to programs which have sought to 

 decrease the density of weed species through the introduction of host- 

 specific predators, and a great amount of research has been expended in 

 predator control of macrophytes. One such program has been relatively 

 successful: the flea beetle has reduced populations of alligator weed 

 considerably in some areas of the Southeast. 



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