The Effect of Timber Management on Stream Water Quality 



distinct, quantifiable, and statistically signifi- 

 cant differences between streams associated 

 with differing levels of timber management 

 activity for several of the water quality parame- 

 ters. 



Sediment Transport and Nutrient 

 Concentrations 



We compared sediment transport, nutrient 

 concentrations, and various physical variables 

 between watershed sites and upstream/down- 

 stream study sites. We selected four sampling 

 dates to represent time periods of distinctly 

 different stream discharge dynamics — three 

 during the spring runoff period (that is, rising 

 limb of runoff, peak runoff, falling limb of 

 runoff) and stable stream discharge (that is, 

 autumn low flow). Total suspended sediment, 

 both organic and inorganic combined, was stud- 

 ied because of the broad effect of sediment on 

 all stream biota (for example, microbial growth, 

 attached algae growth, invertebrate communi- 

 ties, fish reproduction). Dissolved and particu- 

 late forms of nitrogen (NOj^; NH^; total persul- 

 fate nitrogen — TPN) and phosphorus (soluble 

 reactive phosphorus — SRP; total phospho- 

 rus — TP) were analyzed because of their 

 importance to algal production and their well- 

 documented effects on eutrophication of down- 

 stream lakes. 



We found that all study sites had low con- 

 centrations of suspended particulates during 

 base flow conditions and, not surprisingly, that 

 maximum suspended materials occurred dur- 

 ing June, the peak in spring runoff in 1990. 

 However, results also indicated that total sus- 

 pended sediment (TSS) was closely associated 

 with stream gradient; and, that among paired 

 streams, higher annual maximum concentra- 

 tions of total suspended sediment was found 

 among streams associated with moderate to 

 high levels of timber management compared to 



streams from no to low activity watersheds. 

 (See Table C-1.) 



We also compared annual mean nutrient 

 values paired as no to low activity watershed 

 sites with moderate to high activity watershed 

 sites. Results of these comparisons revealed 

 that statistically there was a very high signifi- 

 cant difference (p < 0.001; Low 

 Activity < High Activity) among all forms of 

 nutrient variables combined and a significant 

 difference (p < 0.1; Low Activity < High 

 Activity) among TPN and TP concentrations. 

 (See Table C-1.) 



Differences were particularly distinct for 

 maximum concentrations of total phosphorus 

 and total persulfate nitrogen. (See Figure C-1.) 

 In this cross- watershed comparison, total phos- 

 phorus (TP) and total persulfate nitrogen (TPN) 

 concentrations were progressively higher be- 

 tween respective no to low activity, moderate 

 activity and high activity paired watersheds. 



Stream Algae 



We monitored attached algal growth and 

 biomass in each of the study streams by placing 

 artificial substrates in riffle habitats. Artificial 

 substrates consisted of pre-leached, non-glazed 

 clay tiles held above the stream bed by a solid 

 frame to minimize invertebrate colonization 

 and grazing. We removed three substrate 

 samples from each stream after 2, 4, and 8 

 weeks of incubation and algal colonization. We 

 analyzed the collected algae fi-om each sub- 

 strate for Chlorophyll aconcentrations and ash- 

 free-dry-mass. Analyses of these data revealed 

 a general pattern of increased algal growth 

 associated with higher levels of watershed man- 

 agement activity. (See Figure C-2.) Stream 

 sites within no to low activity watersheds had 

 very low algal production. Sites located within 

 streams of moderate watershed activity had 



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Flathead Basin Cooperative Program Final Report 



