Nutrient Sources in the Clark Fork River Basin

 

Gary L. Ingman and Mark A. Kerr
Department of Health and Environmental Sciences
Water Quality Bureau
Cogswell Building
Helena, Montana 59620

 

Abstract--Under Section 525 of the 1987 amendments to the federal Clean Water Act, Montana initiated an intensive monitoring program to identify and rank the major point and nonpoint sources of nutrients to the Clark Fork River. A 51 station monitoring network was established, including 19 stations on the Clark Fork River, 22 stations on tributary streams, and 10 municipal and industrial wastewater discharges to the river. In the first year of monitoring, samples were collected 15 times and analyzed for total and soluble forms of phosphorus and nitrogen. 

   Several small tributaries to the upper Clark Fork (Gold, Flint, Lost, Racetrack, and Dempsey creeks and the Mill-Willow Bypass) and all 10 wastewater discharges exhibited elevated nutrient concentrations. The Missoula, Butte, and Deer Lodge municipal wastewater discharges were responsible for the largest nutrient concentrations in the Clark Fork. Inflows from good quality tributaries such as Rock Creek and the Blackfoot, Little Blackfoot, Bitterroot, and Flathead rivers were important in diluting nutrient concentrations in the Clark Fork.

    Overall, soluble phosphorus loading to the Clark Fork originated about equally from tributary inflows and wastewater discharges. About two-thirds of the soluble nitrogen loading came from tributaries, with effluents contributing the remaining third. During the summer low flow period, an even greater share of the soluble nutrient loading came from effluents.

    Tributary sources of soluble nutrient loading were dominated by the Flathead, Bitterroot, and Blackfoot rivers. Gold and Flint creeks ranked fourth in importance as tributary sources of soluble phosphorus and nitrogen, respectively.

    The Missoula, Butte, and Deer Lodge municipal wastewater treatment plants and the Stone Container Corporation kraft mill discharged most of the soluble nutrient loading from effluents. However, the Warm Springs treatment ponds on Silver Bow Creek removed most of the Butte nutrient load prior to reaching the Clark Fork River.

Introduction

    In 1987, the Section 525 amendments to the federal Clean Water Act authorized a comprehensive water quality assessment of the Clark Fork/Pend Oreille Basin, which encompasses a three-state area. Funding was appropriated for a three-year study beginning in 1988. Montana, Idaho and Washington were each directed to conduct water quality evaluations in portions of the drainage basin within their states and a steering committee was established to coordinate the interstate project.

    Because of a growing concern over nutrient pollution in the basin and limitations in the available data, a plan was developed to identify, monitor and rank the major point and nonpoint sources of nutrients to the Clark Fork River in Montana. The upper and middle reaches of the Clark Fork are some of the most productive stream waters in Montana west of the Continental Divide from the standpoint of nutrient concentrations and the potential to grow algae (Bahls et al., 1979a. 1979b). Elevated concentrations of phosphorus and nitrogen stimulate the growth of nuisance levels of attached algae, which negatively affect the use of well over 100 miles of the river (MDHES. 1990). Dense algal mats reduce dissolved oxygen levels in the Clark Fork, impair aesthetics, and impede irrigation and recreation (MDHES. 1988a. Johnson and Schmidt. 1988; Ingman and Kerf .1989a).

    In the lower Clark Fork, concerns have focused on nutrient loading to Idaho’s Lake Pend Oreille, which has exhibited subtle signs of eutrophication in recent years (Watson. 1985; MDHES. 1985; Johnson and Schmidt. 1988; IDOHW .1989). The Clark Fork provides greater than 90 percent of the lake's inflow.

    The Section 525 study emphasizes the nutrient problem in the Clark Fork/Pend Oreille Basin because it is the primary interstate issue. Additionally, it was recognized that the 525 study would provide the resources to assess the nutrient problem on a basin-wide scale. Goals of the project include: I) investigating the sources and fates of nutrients in the basin, 2) quantifying the extent and severity of eutrophication problems, and 3) the recommending of appropriate control measures. The objectives of Montana's Clark Fork Basin nutrient source assessment are to:

·        Document nutrient concentrations and loads in the Clark Fork from its headwaters to Idaho.

·        Document nutrient contributions from tributaries and waste- water discharges.

·        Identify the most important sources of nutrients.

·        Identify controllable sources of nutrients.

METHODS

    Water quality data was collected approximately 15 times during the year (monthly from July 1988 through March 1989, excluding February, and twice monthly from April through June 1989) at 51 stations in the Clark Fork Basin. The monitoring network included 19 stations on the Clark Fork River, 22 stations on tributary streams, and 10 municipal and industrial wastewater discharges (Table 1 and Figure 1). Tributaries were selected on the basis of size, the suspected or known and presence of significant nutrient sources within the watershed, and the presence of active U S. Geological Survey stream flow gaging stations (MDHES, 1988b). Collectively, the tributaries accounted for about three-fourths of the stream flow in the Clark Fork at the Idaho border, based on annual mean discharges. Thus, the majority of potential nonpoint source contributions of nutrients from tributary watersheds were inventoried. The wastewater discharges represented the majority of those present in the basin. Four municipal discharges (Towns of Phillipsburg, Lolo Stevensville, Hamilton) were not sampled. However, all four discharge to either Flint Creek or the Bitterroot River -tributaries that were included in the monitoring network.

    Grab-samples for nutrient analysis were collected at each monitoring station during each visit. Subsamples for dissolved nutrients were filtered on site. Samples were stored on ice and delivered to the laboratory for analysis within 48 hours of collection. All sample collection, handling, preservation, and storage procedures followed EPA-approved methods (Table 2).           

  Discharge rates for effluents were measured at the time of sample collection with the primary flow measuring device located at each outfall (weir, flume, or totalizer). Mainstem and tributary streamflows were gaged with standard streamflow gaging equipment at the time of sampling, except for those locations where USGS gaging stations were present.

    Nutrient samples were analyzed by the Montana Department of Health Chemistry Laboratory Bureau. Variables analyzed included dissolved orthophosphate (or soluble reactive phosphorus), dissolved nitrate plus nitrite nitrogen, dissolved ammonia nitrogen, total phosphorus, and total Kjeldahl nitrogen. The Stone Container Corporation wastewater proved to be unfilterable and was analyzed for total forms of all the above nutrient variables. Analytical methods and detection limits are summarized in Table 2. Extensive field and laboratory quality assurance measures were employed to insure the integrity of the nutrient data. These included 1) acid-washing of all sample collection and filtration equipment, 2) the use of standardized sample collection procedures, 3) analysis of field-originated filter blanks and blind duplicate samples, and 4) analysis of lab originated duplicates, spikes, known standards, and EPA audit samples (Ingman and Kerr, 1989a; MDHES 1988c).

     Analytical results were used to tabulate concentration ranges and means for total and soluble phosphorus (P) and nitrogen (N). Soluble P was measured as soluble reactive phosphorus (SRP). Total N was computed by summing total Kjeldahl nitrogen and dissolved nitrate plus nitrite nitrogen concentrations. Soluble nitrogen (TSIN) was computed by summing dissolved nitrate plus nitrite nitrogen dissolved ammonia nitrogen concentrations. Mean daily nutrient loads were computed for the entire year (July through June) and for the summer period only (July through September).

RESULTS AND DISCUSSION 

Nutrient Concentrations

    Nutrient concentrations were used to evaluate water quality at each mainstem, tributary, and effluent station. They are an important factor controlling the distribution and abundance of attached algae in the Clark Fork River (Watson, 1990).

    Nutrient concentrations in the Clark Fork River were highly variable spatially temporally (Table 3 and Figure 2). In general, mean concentrations declined with increasing distance downstream from wastewater discharges. An initial decline in mean concentrations in the upper Clark Fork was attributable to increasing distance from the Butte municipal wastewater treatment plant (WWTP) discharge to Silver Bow Creek and increased dilution from incoming tributaries.

    Notable increases in P concentrations and the highest mean concentrations found anywhere in the river occurred immediately downstream of the Deer Lodge and Missoula municipal WWTP discharges, at stations 10 and 18, respectively. Highest mean N concentrations were found in the extreme headwaters, downstream of several tributaries to the upper Clark Fork (station 9), and below the Deer Lodge and Missoula WWTPs (stations 10 and 18, respectively). Smaller increases in mean p and N concentrations were observed at station 22, downstream from the Stone Container Corporation kraft mill discharge. Lowest mean P concentrations were measured in reaches of the Clark Fork immediately above Deer Lodge and Missoula (stations 9 and 16 respectively) and in the lower Clark Fork below the Flathead River confluence (stations 27-30). Lowest N concentrations were found above Missoula (stations 15-16) and below the Flathead River. Tributary inflows from Rock Creek (entering the river between stations 12and 13), and the Little Blackfoot (bracketed by stations 10and 11), Blackfoot (stations 13 to 15), Bitterroot (stations 18 to 20), and Flathead rivers (stations 25 to 27) caused notable decreases in mean Clark Fork nutrient concentrations.

    The EPA total P criterion of 50 ug/l, which is a general guideline recommended to control excessive developments of attached algae and to prevent accelerated eutrophical of lakes (U.S. EPA, 1986), was commonly exceeded in the Clark Fork from its headwaters downstream to Bonita (station 12) (Table 3 and Figure 2A). The Clark Fork downstream to Bonita harbored dense growths of attached filamentous algae (Cladophora) and is known to suffer from seasonal depressions in dissolved oxygen concentrations (Watson, 1989a). Mean total P concentrations also regularly exceeded the EPA criterion in the river immediately below Missoula. The river here supports dense growths of diatom algae and also experiences reduced dissolved oxygen levels during summer low flows (Kerr, 1988; Watson, 1989b).

    The EPA criterion for TSIN of 1000 ug/l (water quality criteria matrix in MDHES 1986), which has been recommended to prevent nuisance instream levels of algae, was never exceeded in the Clark Fork (Table 3 and Figure 2).

    Nutrient criteria for the control of Nuisance attached algae in the Clark Fork River have recently been proposed (Watson et al., this volume). Based on artificial stream experiments, the maximum standing crops of certain attached algae communities increases with nutrient additions up to about 30 ug/l SRP and 250 ug/l TSIN. Above these levels more nutrients do not appear to produce higher standing crops. Below these nutrient levels, attached algae levels may be controlled by nutrients. In 1988, from July to September (when algal standing crops generally reach their peaks), mean SRP concentrations exceeded the criterion at only four monitoring locations in the river (Figure 3A). Summer mean TSIN concentrations in the Clark Fork newver exceeded the criterion at any station although it was closely approached at Deer Lodge (Figure 3B). These data suggest that summer algae standing crops might be reduced in many reaches of the Clark Fork through nutrient control measures.

    Concentrations of P and N in Clark Fork tributaries provided evidence of additional nutrient sources. Nutrient concentrations in Silver Bow Creek below Butte (stations O1-03) were an order of magnitude larger than at all other monitoring stations in the Clark Fork Basin. The source of those nutrients was the Butte WWTP discharge and the problem was inadequate dilution. On average the Butte WWTP discharge nearly doubled the volume of flow in Silver Bow Creek. Silver Bow Creek does not support nuisance growths of algae because of the presence of toxic levels of heavy metals (Greene et al, 1986; Ingman and Ken, 1990). Nutrient concentrations in lower Silver Bow Creek were greatly reduced as a result of treatment provided by the Warm Springs Ponds before discharging to the Clark Fork headwaters. However, they remained noticeably higher than in other Clark Fork tributaries.

    Gold Creek and Flint Creek exhibited elevated soluble P concentrations relative to other Clark Fork tributaries. Gold Creek crosses the geologic Phosphoria and Cabbage Patch formations (Carey) 1989; Ingman and Bahls) 1979) and P sources are at least in part) natural. Flint Creek receives the Phillipsburg WWTP discharge and is a heavily irrigated agricultural subbasin (Johnson and Schmidt) 1988). Tributaries Lo the Clark Fork below Missoula had the lowest P concentrations.

    Most tributaries to upper Clark Fork, and especially the Mill- Willow creeks bypass, Lost Creek, Racetrack Creek, and Dempsey Creek contained elevated mean concentrations of soluble N. The Mill-Willow Bypass flows adjacent to an unsewered suburb of Anaconda (Opportunity) with a shallow groundwater table. The other streams drain heavily irrigated agricultural areas and their quality was seasonally variable as a result of agricultural dewatering and irrigation return flows. Cottonwood Creek, the Little Blackfoot River, Rock Creek, and tributaries to the lower Clark Fork contained the lowest N concentrations.

    All of the monitored wastewater discharges to the Clark Fork contained very high concentrations of P and N (Table 3). The Stone kraft mill discharge contained some of the lowest nutrient concentrations relative to the other point source discharges. Its quality reflected extensive efforts by management over the previous five years to reduce nutrient levels in the effluent (Stone Container Corporation, 1990; Ingman and Ken, 1989b). The Missoula WWTP discharge contained some of the highest nutrient concentrations P concentrations in this wastewater have subsequently been reduced by nearly half following the adoption in May 1989 of a county-wide phosphorus detergent ban (Aldegarie, 1990). Most sampling was done prior to this ban.  

Nutrient Loads

    Nutrient loads define the quality of nutrients discharged by the river, it tributaries, and effluents per unit of time. Nutrient loads were used to identify and rank the most important sources of nutrients in the Clark Fork Basin from the standpoint of controlling nuisance algae. They are also an important consideration in assessing the trophic status, or state of enrichment, of lakes. Because lakes such as Pend Oreille have long hydraulic retention times, the overall rate of nutrient loading has a strong influence on a lake's ability to grow & algae.

    On a year-round basis, nutrient loading to the Clark Fork River appeared to be dominated by a handful of tributaries and wastewater discharges (Table 4 and Figure 5). Of the Clark Fork tributaries monitored, the Flathead, Bitterroot, and Blackfoot rivers contributed the bulk of soluble nutrients. Nutrient concentration in these rivers were low, but because they are the largest tributaries to the Clark Fork, their cumulative loadings were sizeable. Gold Creek discharged a substantial SRP load compared to many of the other Clark Fork tributaries, despite its small size (annual mean discharge for this period was 32.5 cubic feet per second). The TSI loads contributed by Flint Creek and by Silver Bow Creek via the Pond Two discharge were also noteworthy.

    Nutrient loadings from effluents were clearly dominated by the Missoula and Butte WWTP discharges. The Deer Lodge WWTP and Stone kraft mill discharge contributed smaller loads of soluble nutrients. The remaining six monitored municipal discharges, even collectively, were responsible for only a small fraction of the measured nutrient loading from effluents.

    Summer soluble nutrient loading (mean for months July through September) was computed to determine which sources were likely to be most important in supporting the dense summer growths of attached algae in the Clark Fork River (Figure 6). This loading was clearly dominated by effluents. Overall, effluents where contributed 75 and 38 percent of the SRP and TSIN loading. In the upper Clark Fork, where attached algae densities reach peak proportions, wastewater discharges provided 56 and 57 percent of the SRP and TSIN loading, if loading from the Butte WWTP via the Pond Two discharge is considered. The single largest effluent source of nutrient loading to the upper Clark Fork was the Deer Lodge WWTP. Wastewater discharges provided 93 and 42 percent of the SRP and TSIN loading to the middle Clark Fork, with most coming from the Missoula WWTP. In the lower Clark Fork, where attached algae are not a common problem, most soluble nutrient loading came from the Flathead River, with effluents contributing one percent or less of the total.

CONCLUSIONS AND MANAGEMENT IMPLICATIONS

    Tables 5 and 6 give summary rankings to the Clark Fork tributaries and wastewater discharges on the basis of quality (nutrient concentrations) and quantity (loads) of nutrients discharged to the Clark Fork River. All of the wastewater discharges, Silver Bow Creek, and several other tributaries to the upper Clark Fork contained elevated concentrations of nutrients. While nutrient loading from some of the smaller, upper Clark Fork tributaries are relatively small, their nutrient-rich inflows probably supported localized developments of nuisance algae in their mixing zones. These tributaries included Gold, Flint, Lost, Dempsey, and Racetrack creeks and possibly the Mill-Willow Bypass.

    The Missoula, Deer Lodge and Butte WWTP discharges were the sources most responsible for elevated soluble nutrient concentrations in the Clark Fork River. They also provided the largest share of soluble nutrient loading to the reaches where, and during the times of year when, algae problems are most prevalent. As such, efforts to reduce instream nutrient concentrations to control nuisance algae should initially focus on these sources. The Missoula County phosphorus detergent ban is a large step in this direction.

    Inflows from tributaries with low nutrient concentrations were important in diluting soluble nutrient concentrations in the river. Thus, preserving adequate stream flows in tributaries should be an integral part of efforts to reduce instream concentrations.

    Overall, SRP loading from tributaries nearly equalled that contributed by effluents (Figure 8). About two-thirds of the TSIN loading came from the tributaries, with the remaining third originating from wastewater discharges. During the low flow summer period, point source discharges were responsible for most of the SRP and nearly half of the TSIN loading.

    Tributary sources of soluble nutrient loading were dominated by the Flathead, Bitterroot and Blackfoot rivers (Figure 9). Gold Creek appeared to be the fourth most important tributary source of soluble phosphorus loading. Flint Creek was a significant source of soluble nitrogen loading.

    The Missoula, Butte and Deer Lodge WWTPs and the Stone Container Corporation kraft mill discharged the majority of the soluble nutrient loading from effluents (Figure 10). Most of the nutrient load from Butte was removed in the Warm Springs treatment ponds on Silver Bow Creek prior to reaching the Clark Fork River. Nutrient loading from the Missoula WWTP has declined since this study was undertaken, as a result of the countywide phosphorus ban.

    It is reasonable to assume that a sizeable percentage of the nutrient loading to Lake Pend Oreille from the Clark Fork River originated from wastewater discharges, considering the relative importance of wastewater nutrient loading throughout the Clark Fork watershed. Our data indicate that, prior to the Missoula County phosphorus ban, the Missoula WWTP was the single largest effluent source of soluble nutrient loading to the Clark Fork. Consequently, we are convinced that the phosphorus detergent ban, put into effect in 1989, was the single most effective measure that could have been taken to reduce soluble nutrient loads from the Clark Fork to Lake Pend Oreille.    

ACKNOWLEDGMENTS

    Loren Bahls of the Montana Water Quality Bureau served as Montana's  representative on the three-slate Section 525 Clean Water Act Study steering committee, performed administrative duties associated with the Slate grant and provided valuable guidance to the monitoring program. Lee Shanklin of the U.S. EPA Montana Operations Office served as steering committee chairperson and coordinated the administration of EPA grant funds. Judy Halm and Diane Ertman of the MDHES Chemistry Laboratory Bureau performed all chemical analyses and consistently went out of their way to accommodate the variable sample collection schedules and short sample holding times. Brad Towle and Robert Bukantis assisted with field monitoring activities and prepared field filtration gear. Mel White of the U.S. Geological Survey courteously provided streamflow data, oftentimes on short notice. Stewart Guttenberger of the Idaho U.S. Geological survey and Guy Engebretson of the Montana Power Company provided stream flow data for the Clark Fork below Cabinet Gorge and Thompson Falls Dams, respectively. Pamela Brewster performed all computer data entry and typed the report. Dr. Vicki Watson, Dr. Jack Stanford and Dr .Howard Peavy provided valuable editorial suggestions.  

LITERATURE CITED 

Aldegarie. Joe. 1990. Memorandum summarizing phosphorus discharge rates for the Missoula wastewater treatment plant for the period January 1986 through August 1990. City of Missoula. Public Works Department. September 1990.

Bahls, L., M. Fillinger, R. Greene, A. Horpestad, G. Ingman and E. Weber .1979a. Biological water quality monitoring: Northwest Montana. 1977-1978. Montana Department of Health and Environmental Sciences. November 1979.

Bahls, L.L., G.L. Ingman and A.A. Horpestad. 1979b. Biological water quality monitoring: Southwest Montana, 1977-1978. Montana Department of Health and Environmental Sciences. February 1979.

Carey, Jennifer. 1989. Looking for Phosphorous (not Gold) in Gold Creek. Unpublished student paper. Environmental Studies Program. University of Montana. December 1989.

Greene, J .C., M. Long, C.L. Bartels and J .U. Nwosu. 1986. Results of Algal Assays Performed on Waters Collected from Silver Bow Creek, the Warm Springs Pond and the Upper Clark Fork River: May 10-16, 1985. U.S. Environmental Protection Agency. May 19R6.

Idaho Department of Health and Welfare. 1989. Compilation of Water Quality Study Efforts on Pend Oreille Lake. 1984-1988. Bonner and Kootenai Counties. Idaho. Division of Environment Quality. Water Quality Bureau. 1989.

Ingman, G .L. and L.L. Bahls. 1979. An Assessment of Mining Impacts on Quality of Surface Waters in the Flint Creek Range, Montana. Montana Department of Health and Environmental Sciences. September 1979.

Ingman, G.L., and M.A. Ken. 1989a. Clark Fork River Basin Nutrient Pollution Source Assessment -Interim Report to the Section 525 Clean Water Act Study Steering Committee. Montana Department of Health and Environmental Sciences. April 1989.

Ingman, G.L. and M.A. Kerr. 1989b. An Evaluation of the Instream Effects of Reduced Wastewater Nutrient Loading from the Stone Container Corporation Missoula Mill. Montana Department of Health and Environmental Sciences. September 1989.

Ingman, G.L. and M.A. Kerr. 1990. Water Quality in the Clark Fork River Basin, Montana, State Fiscal y ears 1988-1989. Final Project Report to the Resource Indemnity Trust Grant Program. Montana Department of Health and Environmental Sciences. January 1990.

Johnson .H .E. and C. L. Schmidt. 1988. Clark Fork Basin Project Status Report and Action Plan. Clark Fork Basin Project. Montana Governor's Office. December 1988.

Kerr, Mark A. 1987. Dissolved Oxygen in the Clark Fork River near the Missoula Wastewater Treatment Plant and Stone Container Corporation, July 8-9 and August 5-6, 1986. Montana Department of Health and Environmental Sciences. June 1987.

Montana Department of Health and Environmental Sciences. 1985 Draft Environmental Impact Statement for Champion International Frenchtown Mill Discharge Permit MT -0000035. December 1985.

Montana Department of Health and Environmental Sciences. 1986. Montana Water Quality -The 1986 Montana 305(b) Report. May 1986.

Montana Department of Health and Environmental Sciences. 1988a. Preliminary Environmental Review -Missoula wastewater treatment plant MPDES Permit No. MT-0022594 January 1988.

Montana Department of Health and Environmental Sciences. 1988b. Clark Fork River Basin Expanded Nutrient Monitoring Program Work Plan. February 1988.

Montana Department of Health and Environmental Sciences. 1988c. Lab Procedures Manual -Analysis and Reporting of Water Quality Samples. Revised March 1988.

Montana Department of Health and Environmental Sciences. 1990. Montana Water Quality -The 1990 Montana 305(b) Report. June 1990.

Stone Container Corporation. 1990. Stone's position on (the) nutrient (reduction) goal (contained in MPDES Permit No. MT -0000035). July 1990.

U.S. Environmental Protection Agency. 1983. Methods for the Chemical Analysis of Water and Wastes. EPA600/4-79-020. March 1983.

U.S. Environmental Protection Agency. 1986. Quality Criteria for Water. EPA 440/5-86-001. May 1986.

Watson, Vicki. 1985. A synthesis of water quality problems in the Clark Fork River Basin. In Proceedings of the Clark Fork River Symposium. Montana Academy of Sciences, Montana College of Mineral Science and Technology. April 1985.

Watson. Vicki. 1989a. Dissolved Oxygen in the Upper Clark Fork River. Summer 1987. In Proceedings of the Montana Academy of Sciences. Volume 49. April 1989.

Watson, Vicki. 1989b. Dissolved Oxygen in the Middle Creek Fork River, Summer 1987. In Proceedings of the Montana Academy of Sciences. Volume 49. April 1989.

Watson, Vicki. 1990. Control of Algal Standing Crop by p and N in the Clark Fork River. In Proceedings of the Clark Fork River Symposium. Montana Academy of Sciences. Apri11990.