CRS-50 



widely varying assimilative capacities and some re-release of wastes also 

 occurs. Plants can also take up heavy metals, toxic chemicals, and other 

 waste materials. 29 / Some small wetland areas are being used for waste 

 treatment; scientists are closely following these experiments. 



The ability of wetlands to treat wastes varies with the wetland' s con- 

 dition. Stressed wetlands usually have diminished capacities, and further 

 introduction of waste increasingly stresses the overall system. Waste assim- 

 ilation reduces other functional values, especially for living resources. 

 Waste assimilation capacity of wetlands also varies with "time (diurnal, sea- 

 sonal, historical) and water flow distance," according to a recent review 

 of the scientific literature. 30 / 



Harvest and Heritage 



Harvest functions are difficult to define because wetland boundaries are 

 not respected by many of the harvestable resources, such as fish and fur 

 bearers, and because timber resources lie on both sides of wetland boundaries. 

 Harvesting includes recreational activities, especially hunting and fishing, 

 as well as commercial activities. The potential yield of a wetland can be 

 estimated as a composite of all harvestable resources present in optimum pro- 

 portions. Actual catch figures are lower than the potential yield. Many 

 studies have been published on individual resources, such as ducks, crab or 

 mink, but there are no data on the composite harvest for all plants and animals 

 of commercial and recreational value in a wetland site or wetland type. 31 / 



29/ Clark and Clark, Scientists' Report, p. 90-94. 



30 / Kadlec, Robert H. and John A. Kadlec. Wetlands and Water Quality. 

 In Greeson, Clark and Clark, eds. Wetlands Functions and Values, p. 451-452. 



31/ Ibid., p. 102. 



