PART VII — WATER RESOURCES, FORESTRY, AND AGRICULTURE 



others must be devised. In a few 

 fragile landscapes only limited ac- 

 cess and use may be allowable. 



There can be no simple, universal 

 prescriptions for reconciling conflict- 

 ing uses with each other or with 

 water quality. The land classified as 

 forest comprises an enormous number 

 of combinations of vegetation types, 

 soil and bedrock characteristics, land- 

 forms and slopes, and climatic re- 

 gimes. The latter include variation 

 in total precipitation, its distribution 

 and intensity on the watersheds, and 

 features such as snowpack accumula- 

 tion. This great number of combina- 

 tions prevents easy generalization of 

 studies on one watershed to others 

 with different soil, slope, or precipi- 

 tation features. It also emphasizes 

 the need for much better charac- 

 terization data — climate, geology, 

 hydrology, and soils — for many 

 important watershed regions, for in- 

 vestigation of predictive models, and 

 for expansion of on-the-ground 

 "adaptive research" aimed at convert- 

 ing principles discovered thus far into 

 locally feasible guides for day-to- 

 day operation. 



Factors Affecting Water Quality 



To a considerable degree, water 

 quality has always figured in a larger 

 concern with the protective function 

 of forest cover upon stream flow — 

 that is, flood control, water yield, 

 and watershed maintenance or im- 

 provement. The same natural or 

 man-induced features that make for 

 low infiltration rates, rapid surface 

 runoff, and reduced storage in the 

 soil mantle also lead variously to 

 higher flood peaks but reduced flows 

 in low water periods, to surface ero- 

 sion and channel cutting, to sedimen- 

 tation of downstream channels and 

 empoundments, and to high turbidi- 

 ties and sometimes high contents of 

 material swept from the soil surface. 

 Thus, turbidity and sediment content 

 are valuable indices of impairment 

 or improvement of the protective 

 function of watershed, in addition 



to being direct measures of water 

 quality. 



Water "quality" is a nebulous fea- 

 ture until described in terms of spe- 

 cific attributes such as turbidity, or- 

 ganic content, temperature, nitrate, 

 phosphate, pesticide or other chemical 

 content, and bacteriological quality. 

 These are sometimes discussed as 

 considerations of equal probability, 

 hazard, and rank, but in fact, turn 

 out to be far from equivalent in any 

 respect. 



Temperature and Oxygen — Re- 

 moval of trees or brush greatly in- 

 creases direct radiation to small 

 streams and materially raises maxi- 

 mum temperatures in the warm sea- 

 sons — up to 7 to 8 centigrade 

 higher, according to some studies. 

 Such increases may be unfavorable 

 or lethal to desirable fish, especially 

 to salmon and trout species which 

 spawn in small headwater streams, 

 and they also contribute to higher 

 average temperatures of downstream 

 waters. The physical basis of this 

 effect is fairly straightforward, of 

 course, and the temperature in- 

 crease of small streams has been 

 predicted quite accurately through 

 use of an energy-balance technique. 



Experimental observations are lim- 

 ited and there can be no generaliza- 

 tion about the importance of this 

 effect to quite different climate and 

 ecological regions. Within the Pacific 

 Northwest, however, knowledge of 

 temperature increase and oxygen de- 

 crease following removal of cover 

 is sufficient to call for protection of 

 spawning waters. 



A highly effective management 

 remedy is to leave narrow strips of 

 live vegetation for shade; such strips 

 are also important safeguards against 

 stream or bank disturbance by log- 

 ging operations. Such remedies may 

 entail substantial sacrifice of timber 

 values, as well as higher costs for 

 harvesting and regeneration, and ap- 

 plication may well hinge on benefit/ 

 cost analyses. Further, one can fore- 



see occasional instances of con- 

 flict between retention of shade and 

 decreased water temperature on the 

 one hand, and efforts to increase 

 low water flow through reducing 

 vegetation in the riparian zone on 

 the other. 



Pesticides — A number of plant- 

 protection or plant-control chemicals 

 have been applied to forest vegeta- 

 tion, and the need for such agents 

 will certainly continue even though 

 particular classes of compounds, such 

 as chlorinated hydrocarbons, are 

 banned. Reduction of losses during 

 major insect outbreaks, control of 

 competing vegetation, and protection 

 of new plantations or regeneration 

 areas are three common situations 

 in which use of chemicals might be 

 essential to timber, recreation, or 

 watershed values. 



In principle, any such materials 

 might enter streams either by direct 

 application from aircraft or sprayers, 

 or after washing over or through 

 the soil, or through gross spills and 

 carelessness. The first of these is 

 sometimes thought to be the major 

 concern, although the latter is likely 

 to be the most difficult to predict 

 and control. 



For the most part, the compounds 

 applied to forests will be similar to 

 those used elsewhere in properties 

 such as persistence, toxicity, mode 

 of decomposition, and fixation or 

 accumulation by soil, and will be 

 subject to similar precautions. In 

 some instances, however, there may 

 be special problems of forest use aris- 

 ing from difficulties of precise appli- 

 cation on rough terrain, or to coarse 

 or rocky soils, or to the possibility 

 of rapid, short-distance transport into 

 streams — as, for example, after 

 treatment of riparian areas. Further- 

 more, the quality standards applied 

 to headwater streams may well be 

 more stringent than tolerated else- 

 where. 



But in all this it should not be 

 forgotten that by far the largest frac- 



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