Characterizing Water Quality in the
Muddy Creek Watershed

Measurements of Water Quality as a Benchmark

Water quality was chosen as one of the two benchmarks used to gauge the changes in relative environmental quality across the seven scenarios. The goal of assessing water quality in Muddy Creek was to estimate the water quality and quantity in the watershed, and to quantify the processes of the transport of nutrients and sediment in runoff associated with different land uses generally characterized as Non-Point Source pollution (NPS).

NPS pollution constitutes a significant portion of pollution loads to surface waters in landscapes across North America. The spatially diffuse nature makes measurement of the pollution loads difficult, but by correlating land use practice patterns with hydrologic characterizations of watershed features pollution contributions can be assessed. Major land uses associated with NPS pollution are forestry, agriculture, and urbanization (Eilers and Bernert 1995) . The U.S. Environmental Protection Agency estimates that for two-thirds of the impaired waters of the United States agriculture is the principle contributor of pollution loads.

Field Results

With the objective of understanding water quality conditions in the Muddy Creek Watershed and to develop a data set for the analysis of the future scenarios, E&S Environmental Chemistry (E&S) performed both base flow water quality monitoring (to provide a general assessment of overall water quality throughout the watershed as a baseline data set), and monitoring of pollution loads during storm events. Peak pollution loads occur in "pulses" during storm events. Ten sample sites were chosen for base flow monitoring: four along the mainstem of Muddy Creek, and six at the confluence of major tributaries to Muddy Creek. Measurements of physical and chemical parameters were performed at these 10 sties. Macroinvertebrate populations were sampled as another measure of environmental quality. The macroinvertebrate sampling was performed by Aquatic Biology Associates, Inc. Only physical and chemical parameters were used in the modeling efforts. Of the ten sites monitored for base-flow conditions, three were chosen for storm event monitoring: Beaver Creek, Oliver Creek, and the main stem of Muddy Creek at its effluence.

Early in 1996, E&S staff monitoredwater flow and pollution loads in the Beaver and Oliver Creek sub basins during two separate storm events (the first on January 15 to February 3, with 216 mm measured rainfall, and the second on March second to 8, with 44 mm measured rainfall). Monitored parameters included measures of stream discharge and concentrations of Total Suspended Solids ([TSS]), Total Phosphorus ([TP]), and nitrate ([NO3-]). The measured concentrations along with the gauged flow can then be used to calculate the total load (load = pollution concentration * stream discharge).

Measured concentrations of TSS and TP in Oliver and Beaver Creeks were moderate, while vales for TSS measured in the mainstem of Muddy Creek remained relatively low throughout the storm events. This suggests that the extensive riparian vegetation buffer along the main stem is effective in trapping sediments delivered from upstream tributaries. By contrast, for a given concentration of TSS, the TP measured in the mainstem was greater than in the measured tributaries. Concentrations of NO3- and other forms of nitrogen were low at all measured sites, suggesting that livestock operations or fertilizer applications are not widespread problems affecting surface water quality in the Muddy Creek Watershed.

Macroinvertibrate Sampling

Measurement of benthic invertebrates (bottom dwelling insects) is a direct measure of biotic integrity of stream systems, and can be used as an overall gauge of biodiversity. Macroinvertebrate sampling also provides a measure of overall environmental quality: the insects monitored are relatively immobile, have a relatively long residency time in the system, are sensitive to changes in environmental quality, and are the primary food source for many stream fish species. Unable to avoid pulses of pollution as well as base flow conditions, macroinvertebrates can indicate stresses on aquatic systems not easily measured by other sampling methods.

The sampled populations yield information on biotic and habitat integrity by assessing what species are present and in what abundance, and, perhaps more indicatively, what species are not present. The results of these assessments are categorized into three categories of "metrics" (or grades). Primary metrics give an overall picture of the community composition. Positive indicators are taxa, taxa assemblages, or feeding assemblages whose abundance is a positive indicator. Negative indicators are the presence of pollution tolerant taxa or feeding associations, whose increased abundance is a sign of a stressed system. The results of macroinvertebrate sampling are combined with assessments of the streams physical characteristics (parameters such as overstory vegetation, stream substrate, gradient, stream profile, etc.) to produce an overall metric of the integrity of macroinvertebrate community.

The metric rating system is expressed in terms of an overall score from 1-100%, with 80-100% rating high water quality, 60-79% rating moderate water quality, 40-59% rating low water quality, and a rating less than 40% considered severe water quality. Under this rating system, the bioassesment scores ranged from a low of 25% (on the m ainstem of Muddy Creek at Airport Rd.) to a high of 45% (at Gleason Creek). While these score are low, it is difficult to compare these ratings across all sites due to the naturally highly variable character of the habitats: all of the Muddy Creek sites are low gradient, slow-water environments with a silty or muddy substrate. Given this caveat, however, even tributary sites with rocky substrates were dominated by tolerant taxa associations indicating stress associated with poor water quality.

Summary

Of the ten stream sample sites, several sites showed moderately poor water quality in both the field data and the model simulations. Most of these sites also showed moderate to low dissolved oxygen, and pH values that were lower than expected (suggesting reducing environments). In particular Reese Creek had very poor water quality based on low dissolved oxygen, lower pH, and elevated concentrations of dissolved salts. Conductivity at Reese Creek was approximately twice as great as the other monitoring sites while the tributaries drain similar lithology. Reese Creek was the only site with measurable ammonium (NH4+), and had concentrations of total nitrogen an order of magnitude greater than the other sites. Total phosphorus concentrations also were greatly elevated in comparison with other sites. Reese Creek has among the highest modeled unit area erosion which may account for some of these results.

Nitrate concentrations during base flow and during the storm events differed little from forested sites in western Oregon and were quite low in comparison to agricultural sites elsewhere in the Willamette River Basin. Land use practices at this point have apparently caused little increase in NO3- loading judging from this modest sampling effort. Concentrations of NO3- at base flow were virtually undetectable and values during storm events remained below 0.5 mg/L (as N). By comparison, the drinking water standard is 10 mg/L, a criterion exceeded by streams in the Pudding River watershed (Eilers and Bernert 1995)

A comparison of these values with those from different watersheds within the Willamette Basin shows the loads for Muddy Creek to be within typical ranges. Table 11 presents values representing the total annual load, in kg/ha/year, for the present day land use categorization in Muddy Creek, as well as for a number of other watersheds and general watershed types.

Table 11 presents values representing the total annual load, in kg/ha/year, for the present day landuse categorization in Muddy Creek, as well as for a number of other watersheds and general watershed types.

Overall the water quality of Muddy Creek is currently fair to good, but in individual sub basins it is expected to experience major degradation under the development scenarios. Under these scenarios involving more intensive land use, total stream discharge increases as vegetation is replaced by impervious surfaces. TSS and TP are the primary nutrient variables expected to increase in these scenarios, while nitrate concentrations are expected to remain low.