maintenance procedures. They can be applied before, during, 

 or after pollution-producing activities. BMPs use the land 

 in the wisest possible way, whether it be for growing crops 

 or grazing cattle, building highways or cutting trees. BMPs 

 are the coordinated, judicious timing of activities and use 

 of vegetation and materials as components of a total land 

 management system. 



Categories and subcategories of nonpoint source 

 pollution are listed in Table 3-20. A brief discussion of 

 the major categories is followed by a summary of specific 

 nonpoint problems and programs in the Clark Fork Basin. 



Agriculture 



Agricultural activities can result in the addition of 

 sediments, nutrients, pesticides, pathogens, salts, and other 

 pollutants to natural waters. Among these activities are 

 irrigation, poor feedlot and pasture management (overgraz- 

 ing) , trampling and erosion of streambanks by livestock, poor 

 row-crop practices, improper pesticide application, altera- 

 tion of streambanks and channels, and improperly designed 

 irrigation return flows. Irrigation withdrawals can cause 

 dewatering, which may result in elevated temperatures that 

 adversely affect aquatic life. 



Silviculture 



Silvicultural practices are another important source of 

 nonpoint pollutants to streams. Because logging activities 

 typically occur in headwater areas, the waters that are 

 affected are usually of very high quality. Silviculture 

 activities that can cause nonpoint pollution include road 

 construction, harvesting operations, use of chemicals 

 (fertilizers, insecticides, and herbicides) , removal of 

 trees, and preparation of sites for revegetation. Sediment 

 is the major pollutant by volume. Debris from forest 

 operations can contribute organic matter to surface water 

 bodies, and removal of vegetation that shades water bodies 

 can lead to elevated water temperatures (EPA 1985b) . Clear- 

 cutting can significantly increase water yield, and a 

 substantial increase in runoff may result in channel degrada- 

 tion and increased turbidity and sediment loading. 



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