RESULTS OF BACTERIA SAMPLING IN THE WILSON RIVER Joseph M. Bischoff and Timothy J. Sullivan April 1999 Report Number 97-16-02 E&S Environmental Chemistry, Inc. P.O. Box 609 Corvallis, OR 97339 ABSTRACT Water quality monitoring was conducted at eight sites on the Wilson River during the period late September, 1997 through early March, 1998, from river mile 8.6 to river mile 0.2 near where the river enters Tillamook Bay. Samples were collected approximately weekly by the Tillamook County Creamery Association (TCCA) during the course of the study, plus at more frequent intervals during two storm events in October, 1997 and March, 1998. Samples were analyzed by TCCA for fecal coliform bacteria (FCB) and E. coli. E&S Environmental Chemistry, Inc. provided the data analysis and presentation for this report. FCB concentrations and loads in the Wilson River were higher by a factor of two during the October, 1997 storm than during any of the other five storms monitored by TCCA or E&S. Similar results were found for the Tillamook and Trask Rivers by Sullivan et al. (1998b). Lowest loads in the Wilson River were found during the monitored spring storms in 1997 (by E&S) and 1998 (this study). By far the highest FCB loads were contributed by the land areas that drain into Site 7 (in the mixing zone just below the TCCA outfall) during the October 1997 and March 1998 storms. This site was the only site in the Wilson River basin that has contributing areas occupied by urban land use. Relatively high FCB loads were also found at a variety of other sites. A consistent relationship was not observed between FCB loads and land use among the other sites sampled in the Wilson River watershed. There was little or no relationship observed between measurements of FCB versus E. coli. At FCB concentrations greater than about 200 cfu/100 ml, results of E. coli measurements showed no indication of increasing above 200 colonies/100 ml with increasing FCB, even to FCB measured values > 1,000 cfu/100 ml. The reason for the lack of correspondence between these two bacterial measurements is not known. 2 A. INTRODUCTION Tillamook Bay and its watershed have been the site of intensive water quality monitoring since November, 1996. E&S Environmental Chemistry, Inc. (E&S), under contract to the Tillamook Bay National Estuary Project (TBNEP), Tillamook County, Oregon, has conducted routine water quality monitoring in all of the five rivers that flow into Tillamook Bay. In addition, intensive storm sampling has been conducted by E&S at a variety of sites during six rain storm events between November, 1996 and March, 1998. Additional sampling was also conducted on behalf of TBNEP by other agencies and cooperating institutions during two of those storms. The Tillamook County Creamery Association (TCCA) sampled the Wilson River during the two storms and also performed routine monitoring of the Wilson River, beginning in September, 1997. Results of the work conducted by E&S has mainly been reported in two technical reports to TBNEP (Sullivan et al. 1998a,b). It is well known that several important water quality parameters typically exhibit significant episodic variability. Chief among these in the Tillamook Basin is fecal coliform bacteria (FCB). This study focused on episodic variability in the concentrations of FCB in the Wilson River during storm events that occurred during the rainy season. An additional objective of the storm sampling was to estimate the storm-based loading of FCB to the bay from the Wilson River watershed. Prior to and during the course of the monitoring effort, it became increasingly clear that FCB contamination was a widespread problem throughout the basin, with highest concentration in the Tillamook River, and highest loads in the Trask and Wilson Rivers (c.f., Jackson and Glendening 1982, Sullivan et al. 1998a). The source of this FCB was expected to be variable, with the primary contributors presumed to include dairy operations, septic systems, sewer treatment plants, and urban land use (c.f., Jackson and Glendening 1982). The storm monitoring effort was expanded in the fall of 1997 to include intensive sampling during two storms at about 30 sites on the Tillamook and Trask Rivers by E&S, and at eight sites on the Wilson River by the TCCA. One early fall and one late winter storm were selected for this component of the study. The principal objective of the intensive storm monitoring was to quantify the major contributing areas of bacterial loads along each of these river systems to allow evaluation of land use/bacterial load interactions. An additional objective was to evaluate differences in storm-driven pulses of bacteria at various locations in the watersheds of these three rivers. Most of the bacterial monitoring conducted to date in the Tillamook Basin has involved measurement of FCB. However, the Oregon Department of Environmental Quality (ODEQ) has recently changed its bacterial water quality standard from FCB to Escherichia coli. There is interest, therefore, in determining the extent of agreement between these two measures of bacterial contamination for Tillamook waters. The purpose of this report is to present the results of the intensive storm sampling and long term monitoring in the Wilson River conducted by the TCCA in a similar manner as were the long 3 term monitoring and intensive storm sampling results reported by Sullivan et al. (1998a,b). Results are presented for FCB concentrations and loads during the course of the study and comparisons are made of results for FCB versus E. coli measurements. B. METHODS 1. Site Allocation and Sampling Samples were collected approximately weekly from October 1997 through March 1998 at eight sites on the Wilson River for fecal coliform and E. coli bacteria (Figure 1). Samples were collected and analyzed by the TCCA. All samples were analyzed for E. coli and most were also analyzed for FCB. Storms were selected by the expected duration and intensity of rainfall. The storms were selected in an effort to represent storms of different intensity and differing hydrological response. The early fall storm was preceded by a long dry period when there was little flushing of the watersheds. The winter storm was preceded by wetter antecedent conditions and more continual flushing of the watersheds due to frequent large rainfall events. Figure 1. Sample site locations for long term monitoring and intensive storm sampling. 4 The Wilson River hydrograph throughout the period of study is depicted in Figure 2. It shows the pattern typical of the Tillamook Basin: low river flows (generally <500 cfs) during summer and frequent storms from October through March. The largest storms generally occur in the period November through January and often achieve peak discharge >10,000 cfs on the Wilson River. Flood stage on the Wilson River is designated as 14,100 cfs. The storms that were monitored by E&S and also those monitored by TCCA during this study are indicated in Figure 2. Two storms (October 1997 and March 1998) were sampled intensively at eight sites on the Wilson River from river mile 8.6 to the mouth. Site selection was determined jointly by TCCA and TBNEP staff. Priorities for site location and sampling included probable point sources of bacteria and nutrients and areas of intensive agriculture. River water samples were analyzed for FCB using the membrane filtration method described in Standard Methods for the Examination of Water and Wastewater (Greenberg et al. 1992). River water samples were also analyzed for E. coli bacteria using the Colilert method. This method reports the most probable value in colonies per 100 ml with a 95% confidence interval. 2. Estimation of River Discharge The USGS maintains gauging stations on the Trask and Wilson Rivers. These data have been gathered and included in the hydrologic data set. Because the Wilson River is large and there are no inflowing tributaries of any size below the forest/agriculture interface, discharge at the gauging station was used unaltered at all of the TCCA sites. The difference between the true discharge at the highest site compared to the lowest site is undoubtedly very small (< 2%). No attempt was made to adjust discharge values to account for the small differences in the sizes of the contributing areas to each site. 3. Watershed Analyses Site locations are listed in Table 1. Subbasins that drain into each sampling site were delineated and digitized into a GIS coverage. FCB loads (cfu/sec) were calculated by multiplying the FCB concentration (cfu/100 ml) by the instantaneous flow (ml/sec). Data were collected over about a four to six day period during each of the storms. Details of transect analyses and calculations can be found in a previous report on storm sampling in the Tillamook Bay watershed (Sullivan et al 1998b). This analysis resulted in the identification of the river segments and their associated subbasins that most frequently contributed the largest loads of FCB to the river during these two storms. Watershed factors thought to influence loading of fecal coliform bacteria to surface waters were quantified using coverages produced by Alsea Geospatial (Corvallis, OR) for the TBNEP. Details on the production of these coverages were reported by Sullivan et al (1998b). Coverages were 5 6 Figure 2. Wilson River hydrograph throughout the period of study. Numbers are added to the six storms sampled in the storm monitoring efforts of TCCA and E&S. Table 1. Wilson River site locations. Site Number Site Name River Mile WR1 Mills Bridge 8.6 WR2 DS RV Camp 7.4 WR3 Boat Ramp 6.2 WR4 Josi Farm 4.7 WR5 Sollie Smith Bridge 3.9 WR6 Highway 101 1.8 WR7 TCCA Outfall 1.3 WR8 Geinger Farms 0.2 projected in UTM zone 10 for this analysis.