The Effect of Timber Management on Stream Water Quality 



tershed types; from very small streams 

 to large creeks, from no to high timber 

 harvest activities in the watershed, and 

 from widely different geologies (Swan 

 drainage. North Fork drainage, Upper 

 Stillwater drainage. Upper Tally Lake 

 drainage). 



(2) Concentration of sediment in transport 

 was closely associated with the slope 

 of the watershed and the gradient of the 

 stream at the sample site. However, 

 comparison of annual maximum sus- 

 pended sediment concentration be- 

 tween paired-stream study sites re- 

 vealed that moderate and high activity 

 watersheds had a general pattern of 

 significantiy higher suspended sedi- 

 ment concentration (p < 0.05) than 

 their respective no to low activity wa- 

 tershed site. 



(3) Nutrient concentrations, particularly N 

 and P fractions of Total Phosphorus 

 (TP) and Total Persulfate Nitrogen 

 (TPN), were significantly higher 

 (p < 0.1) among stream sites within 

 high activity watersheds compared to 

 streams from no or low activity water- 

 sheds. 



(4) Attached algae growth was measured 

 at each sample site using artificial sub- 

 strates for colonization of algae. The 

 density of Chlorophyll a on substrates 

 incubated in streams with high timber 

 management activities in the water- 

 shed was significantly higher 

 (p < 0.05) than in streams from no or 

 low activity in the watershed. 



(5) No significant differences in inverte- 

 brate trophic relationships, taxa rich- 

 ness , or taxa equitability were observed 

 between streams of differing water- 

 shed timbermanagementactivity; how- 

 ever, there was a general trend toward 



increased species richness associated 

 with harvest activity. 



Conclusions 



Because the conclusions drawn from this 

 research are best expressed holistically as they 

 relate to the other empirical studies, most con- 

 clusions and recommendations of this study 

 appear in the "Summary of Conclusions" and 

 "Summary of Recommendations" sections at 

 the end of this document. However, the follow- 

 ing points should be made here in the context of 

 the cooperative studies: 



(1) Timber management activity has a 

 quantifiable effect on stream water 

 quality in several important areas: 



(a) increased maximum suspended 

 sediment concentration during 

 spring runoff, 



(b) increased mean annual concen- 

 tration of algal growth nutrients 

 (nitrogen and phosphorus), and 



(c) increased maximum algal den- 

 sity on the stream bottom. 



These factors not only profoundly af- 

 fect the ecology of the stream, but also 

 that of downstream lakes. 



(2) Future monitoring of timber manage- 

 ment effects on streams should con- 

 centrate on measurement of suspended 

 sediment, nutrient concentrations (TP, 

 SRP, TPN, N0„, NH3), and attached 

 algal growth (Chlorophyll a density). 



(3) Monitoring of macroinvertebrates will 

 be most useful when used to define the 

 most severe of impacts that result in 

 catastrophic degradation of the stream 

 biota. General baseline data of inverte- 

 brates is therefore needed among 

 streams at risk. 



Page 50 



Flathead Basin Cooperative Program Final Report 



