Publication Summary

Prevalent surface water quality problems in Portage Creek are probably exacerbated by land use in the watershed and by ground water influences. Quantified land use and activity information for the Portage Creek watershed was useful in interpretation of patterns of pollution observed during this study. Land use types such as pasturing and cropland appeared to significantly influence water quality in Portage Creek. Total suspended solids and total inorganic nitrogen concentrations and loads were probably influenced by over-application of manure or commercial fertilizers during the wet season. Total phosphorus and fecal coliform concentrations were not found to be seasonally influenced.

Prevalent surface water quality problems in Portage Creek are probably exacerbated by land use in the watershed and by ground water influences. Quantified land use and activity information for the Portage Creek watershed was useful in interpretation of patterns of pollution observed during this study. Land use types such as pasturing and cropland appeared to significantly influence water quality in Portage Creek. Total suspended solids and total inorganic nitrogen concentrations and loads were probably influenced by over-application of manure or commercial fertilizers during the wet season. Total phosphorus and fecal coliform concentrations were not found to be seasonally influenced.

Fecal coliform, turbidity, and dissolved oxygen concentrations violated Washington State Class A water quality standards during both the wet and dry seasons. Fecal coliform concentrations consistently violated the standard at all Portage Creek stations during the dry season (April-November). Dissolved oxygen concentrations violated the standard at mid- and lower-reach stations during both the wet and dry seasons. Turbidity exceeded the standard at mid- and upper-reach stations during both seasons. Exceedance of water quality standards by these parameters was influenced by one or more of the following: manure spreading, cattle grazing, and instream decaying organics. Ground water influences on surface water quality may have been prevalent at mid- and lower-reach regions of Portage Creek. Quantities of arsenic, chromium, copper, and nickel were detected in sediments at the mid-reach of Portage Creek. Benthic macroinvertebrate samples were collected at sites corresponding with sediment analysis. The benthic epifauna at the mid-reach of Portage Creek was highly impacted, possibly by the unstable organic substrate.