nants further degrade lakes that become surrounded by agricultural land. 

 Even systems receiving annual overflow are being degraded by agricultural 

 pollutants stemming from land-use activities. Though the literature is re- 

 plete with qualitative information expounding the value of wetland systems, 

 there is a paucity of quantitative information describing the effects of re- 

 duced overflow and contaminant effects on these ecosystems. Such informa- 

 tion is needed to verify and document the effects of flood control activi- 

 ties (damming, channelization, diking, levee construction, etc.) and agri- 

 cultural chemical impacts resulting from land use changes. 



Other environmental contaminant problems of potentially serious conse- 

 quence include the following: 



a) Impact of contaminants in irrigation return waters on the 

 anadromous fishes of the San Joaquin and Sacramento Rivers 

 in the Central Valley of California; 



b) Widespread toxaphene contamination of freshwater fisheries 

 from increased use and atmospheric transport of the chemical; 



c) Extensive use of herbicides in agriculture and silviculture; 



d) Accumulation and chronic toxic effects of relatively unstudied 

 industrial contaminants; 



e) Continuing contamination of the environment by PCBs, dibenzo- 

 furans, and dioxins. 



The proper evaluation of contaminant impacts of living resources in- 

 volves a multidisciplined approach with input from scientisits, resource 

 managers, industry, and academia. Matching the locations of more serious 

 contaminant problems with areas of high resource value can serve as a guide- 

 line for directing limited research resources to properly assess contaminant 

 threats or hazards to the environment. Researchers and resource managers 

 can then work together to recommend approaches to identify and avoid or mit- 

 igate serious contaminant impacts on the environment. 



17 



