|Title:||Community and ecosystem attributes of the Cedar River watershed above Landsburg Diversion before arrival of Pacific salmon|
|Author/Editor:||Peter M. Kiffney, C. J. Volk, C. Eberhart, Jason E. Hall|
|Institution:||Report of the National Marine Fisheries Service to the City of Seattle Department of Public Utilities. Seattle|
Our research has established baseline conditions in the upper Cedar River between Landsburg diversion and Cedar Falls, including the tributaries of Rock, Taylor and Williams Creeks, for the following attributes:
(1) physical habitat;
(2) resident fish populations (salmonids and cottids);
(3) water chemistry; and
(4) the carbon and nitrogen isotopic composition of terrestrial plants and aquatic organisms (Rock, Taylor, and Cedar River).
We conducted two additional studies that increase our understanding of the ecology of fishes in the upper watershed: aging of scales to validate age classes for salmonids used in our snorkel surveys. This study is ongoing, as scales and otoliths from fish collected during 2001 will be analyzed this summer. The second study examined stomach contents of salmonids and cottids collected during 2000 and 2001. These data augment the stable isotope study, as together they can be used to unravel food web relationships and trophic structure in the Cedar River and its tributaries, and how these relationships change with colonization of Pacific salmon.
Overall, our results show that streams in the Cedar River watershed are oligotrophic with low levels of dissolved materials, including nutrients (nitrogen (N) and phosphorus (P)) that limit productivity of primary and secondary consumers. We also observed large differences between mainstem and tributary sites in water chemistry. Tributary sites had N and P concentrations that were two times higher than mainstem sites. Salmonid abundance was negatively correlated with stream size; highest salmonid abundances occurred in Williams and Rock Creeks. No relationships were observed between woody debris and other physical variables and trout density. However, we found that dissolved nitrate was positively correlated with trout abundance. Estimates of fish density and biomass in 2000 and 2001 were similar, suggesting that our survey methods were robust despite the high turnover of snorkelers between years.