The Effect of Timber Management on Stream Water Quality 



comparatively moderate levels of algal density; 

 while the highest Chlorophyll a concentrations 

 were measured within streams in high timber 

 management activity watersheds. An analysis 

 of variance (ANOVA) of maximum Chloro- 

 phyll a data, in which sites falUng into the three 

 different activity levels were collectively com- 

 pared, revealed that algal production was sig- 

 nificantly less (p < 0.05) among no to low 

 activity sites when compared to sites represent- 

 ing high timber management activity water- 

 sheds. Moderate activity sites were not statisti- 

 cally significantly different from either high or 

 low activity sites, although the general trend of 

 increased algal density above that observed for 

 low activity watersheds is readily apparent. 

 (See Figure C-2.) This trend was not significant 

 concerning algae mass accumulations because 

 of the high variance between similar activity 

 sites; however, mean values of ash-free-dry- 

 mass were generally much higher at high activ- 

 ity stream sites. 



Based on this study, which involved a range 

 of stream types and sizes with a mix of open and 

 closed canopy sites among streams with differ- 

 ing levels of upstream timber harvest, increased 

 timber harvest results in increased stream algae 

 production even in streams that are well cano- 

 pied. These results are consistent with the pat- 

 tern of increased nutrient concentrations among 

 streams flowing from high activity basins. Thus, 

 these data are mutually supportive from an 

 ecological perspective. 



acterized among Flathead Basin zoobenthic 

 species as having high biodiversity and broad 

 trophic function. Thus, some of the differences 

 between sites should be observable during this 

 period. 



We identified a total of 67 taxa from the 12 

 study sites. Most taxa were identified to the 

 species level of organization, particularly the 

 mayflies {Ephemeroptera), stoneflies (JPlecop- 

 tera) and caddisflies (Trichoptera). Our analy- 

 sis of taxa frequency revealed high variability 

 between sites that reflect the multitude of fac- 

 tors affecting zoobenthic species distributions 

 and abundance (for example, stream type, stream 

 size, habitat, substrate, source of food, stream 

 velocity, competition, predation). Measures of 

 taxa richness and Simpson's index of equitabil- 

 ity (Figure C-3) at each study site were highly 

 variable. No specific pattern of either reduced 

 richness or taxon dominance could be attrib- 

 uted to any of the measured physical or nutrient 

 variables, or specifically increased algal pro- 

 duction. This was documented by no significant 

 relationships being apparent employing non- 

 parametric tests of taxon abundance among 

 paired comparative streams. 



This does not mean that timber manage- 

 ment has no effect on stream zoobenthos or that 

 zoobenthic organisms are a poor indicator of 

 change in stream ecosystems, but rather that 

 within the constraints of this study, no statisti- 

 cally significant patterns associated with the 

 level of timber management activity could be 

 determined. 



Zoobenthos 



Summary 



We collected benthic samples during au- 

 tumn to determine quantitatively and qualita- 

 tively the possible effects of timber manage- 

 ment on benthic invertebrates. We were limited 

 to a single sampling period because of time and 

 financial constraints. However, autumn is char- 



( 1 ) An experimental design of stream sites 

 was chosen for study of the effects of 

 timber management activity on the 

 waterquality of FlatheadBasin streams. 

 Stream sites were chosen to represent a 

 broad cross-section of stream and wa- 



Flathead Basin Cooperative Program Final Report 



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