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For example, consider timber harvest and its relation to the aesthetic values of a viewscape. At one time a forest land manager could make decisions on timber harvest based largely upon silvicultural and engineering considerations, generally ignoring visual concerns because the area of harvest would not be part of a sensitive landscape. Harvest units that looked like brown sheets on a clothesline against a green background were not readily seen and, thus, not a real problem. However, such hidden terrain has become scarce and harvest decisions must now involve greater consideration of visual resource values and impacts to them. Not all interactions consequent to a land management decision are as easily defined as timber harvest and its influence upon scenic views. Particularly complex, and thus difficult to assess, are the resource interactions which relate to water development and use. Decisions on the development and use of water resources have always demanded great consideration of effects, both onsite and offsite. Such considerations have included complicated engineering and economic issues which have always been challenging. However, the number of issues which now must be considered are far greater and they are generally more complex, requiring greater sophistication in analysis. For example, consider a decision to dedicate a unit of land and existing aquatic and riparian ecosystems for use as a reservoir. This decision begins a process which will almost immediately affect the natural environment, initiating a series of changes which will continue for many years. The changes which occur onsi te are obvious - a lake replaces a flowing stream with an associated change in recreational opportunity ,and aesthetics, local economies change or arise at 'new locations, changes in fluvial processes begin at the dam outlet and at the reservoir's influent points, and the fish species mix shifts to favor those that can best survive in the lake (Johnson and Carothers, 1987). Less obvious are the changes which occur offsite. Organic matter which had been flowing through the system may be trapped by the reservoir as coarse fragments and passed in finely divided or dissolved form. Insects, and other benthic organisms, which utilized coarse organic matter below the reservoir may become stressed and replaced by others adapted to the finer forms of organic matter. Fish or other higher organisms may also be stressed or replaced when their food sources change. An example of these biotic effects was described for Soldier Creek _ dam in Utah. Wi th the closure of the dam there occurred the elimination of "... those species [of macroinvertebrates] specialized to exist on clean rock surfaces" (Williams and Winget, 1979, p. 373). With regard to fish, Minckley and Mefee (1987, p. 104) point out that, "If floods are curtailed by damming, nonnative fishes typically increase in numbers to approach 100% of the fauna." Similarly, the balance between sediment and kinetic energy found in the fluvial system before construction of the dam, begins to disequilibrate as sediment is trapped by the reservoir. As observed by Williams and Wolman (1984 p. 60), "... Hundreds of kilometers of river distance downstream from a dam may be required before a river regains, by boundary erosion and tributary sediment contributions, the same annual suspended load or sediment concentration that it transported at any given site prior to dam construction." The hydrograph which produced the existing river form changes with reservoir operations and further alters the physical form of the river below the dam as, for example, has occurred on the Green R1 ver in Colorado and Utah (Andrews, 1986). Va ter temperature and quality may also change due to reservoir operations making uninhabitable to fish and other aquatic organisms previously sui table stream reaches (Minck1ey and Mefee, 1987). 448 -~ ^ r,;