ScholarWorks at University of Montana

Water for new uses -- including development, population growth, and fishery restoration-- is in short supply in the Clark Fork Basin. Basin Closure and over-allocation (when surface water flows are less than existing water rights on a source) require that new and changed water uses develop plans to re-allocate water to eliminate depletions of surface water. Mitigation and aquifer recharge are the two primary mechanisms used to offset surface water depletions and provide a mechanism for new water uses to be permitted. But mitigation and aquifer recharge are far from simple to accomplish.

This project evaluates mitigation opportunities for three examples of new water use in the Basin: New municipal water use in the Bitterroot Basin Closure; new subdivision water use in the Middle Clark Fork where the river is over-allocated due to hydropower water rights; and an instream flow change for fishery habitat restoration in the Upper Clark Fork Basin Closure. The challenges & options for moving forward in each of these situations will be discussed.

Smelting activities in Anaconda resulted in a persistent aerial plume of contaminants that settled on the landscape, with devastating impacts on upland vegetation. Extensive logging activities to fuel the first smelters, in combination with aerial emissions, have left some upland areas near the continental divide south of Anaconda void of vegetation (including weeds) for nearly 100 years. Gully erosion of impressive scale has transformed the uplands from zones of sediment retention and stability to a network of sediment delivery superhighways. For the last 5 years, the Mt. Haggin Technical Working Group has been studying these impacts and testing remedy and restoration techniques to capture sediment and restore native vegetation to the mostly roadless areas of the Mt. Haggin Wildlife Management Area.

Variations in geologic parent material, slope and aspect, as well as secondary factors such as surface roughness have been assessed to prioritize areas for treatment in the years to come. Intensive soil studies, assessments of the potential to enhance the landscape’s wetland and riparian areas and multiple soil amendment and planting trials have been conducted and hundreds of sediment catchment BMP structures have been installed. Progress in upland sediment retention and vegetation enhancement will be illustrated as well as the challenges of restoring a Montana moonscape.

Benthic macroinvertebrates have been used as indicators of biological integrity in the Clark Fork River basin for over 25 years. In more recent years the efforts of multiple monitoring programs have been harmonized to create synoptic analyses of biological integrity. The collaborative efforts of state and federal agencies have reduced duplication, enhanced data comparability and increased spatial completeness of invertebrate community data. The goals of this analysis are to summarize current benthic invertebrate monitoring programs efforts in the Upper Clark Fork basin, present the findings of trends analyses at several sentinel locations in the basin, and document the longitudinal gradient of biological integrity in the Upper Clark Fork River.

The Montana Department of Environmental Quality (DEQ) has developed total maximum daily loads (TMDLs) for metals in Silver Bow Creek and the Clark Fork River. TMDLs are watershed-scale pollutant budgets and are important planning tools because they provide a basin-wide context for individual pollutant sources. This context can provide a different perspective on individual point source discharges than a traditional point-of-discharge analysis and may result in different effluent limits.

The effects of decades of remediation in Butte and Silver Bow Creek are evident in trends of Clark Fork River water quality. Remediation of the Clark Fork River mainstem has begun in recent years, and the trend is expected to continue. Using the cleanup levels established in the Superfund Records of Decision, DEQ predicts the trajectory of these water quality trends. Presently, water quality targets (standards) are generally met below the Blackfoot River. DEQ predicts that assimilative (dilution) capacity will be provided from below the Blackfoot River confluence to as far upstream as the Little Blackfoot River for most metals of concern. Remediation work in major tributaries (e.g. Flint, Little Blackfoot) and/or exceeding Superfund cleanup targets can provide additional assimilative capacity within Silver Bow Creek and segments of the Clark Fork River.

Nutrients are essential to support stream ecosystems, however, if present in excess may lead to algal blooms, excessive aquatic weeds, and alternation of natural aquatic ecosystems. Silver Bow Creek (SBC), the headwater stream of the Clark Fork River, is listed as impaired for nutrients (total nitrogen (TN) and total phosphorus (TP)), by the Montana Department of Environmental Quality. Browns Gulch is a major tributary to SBC, and drains agricultural and forested lands. To meet target nutrient TMDL concentrations in SBC, the tributary load inputs of TN and TP must be reduced by 93% in Browns Gulch. To identify the sources of nutrients, surface water samples were collected and analyzed for TN and TP at three flow stages from locations distributed along the stream. Browns Gulch water quality data suggests that runoff from agricultural lands (during spring and summer) is the main source of TN and TP loads. For all the flow stages, TN and TP loads increase from up to down-stream. Irrigated and grazed areas correspond with a sharp increase in the stream nutrient load. Specific conductivity and alkalinity concentrations were highly correlated with TP concentrations at each flow stage. The Lowland Creek Volcanics are the predominant geologic formation in the Browns Gulch watershed and may be contributing consistent low levels of TP via groundwater. To reduce agricultural nutrient inputs, riparian buffer zones and off-stream winter pastures are recommended. It is believed that effective implementation of the proposed BMPs will significantly reduce tributary nutrient load inputs to SBC.

Remediation and restoration of the Upper Clark Fork River (UCFR) is occurring under nutrient-rich conditions associated with non-point source and sewage treatment inputs. Restoration is designed to enhance river-floodplain interaction with potential influences on river nutrient loads. Assessment of the long-term record for nitrogen (N) and phosphorus (P) illustrate that the upper river consistently exceeds water quality standards for total N (300 μg N/L) and total P (20 μg/L P). However, data from the past three decades also show substantial reduction in nitrate-N loads during summer and autumn despite inputs from tributaries and sewage treatment facilities. During these time periods, benthic algal standing crops can be substantial (150 – 275 mg/m² as chlorophyll) and measures of primary production support the potential for algal uptake to remove inorganic N and generate high atomic N:P ratios. Nutrient-diffusing assays suggest N-limitation of algal growth despite an overabundance of total N in the river water. Along with a plentiful supply of P, these conditions are optimal for the growth and proliferation of N-fixing microbes (i.e., bluegreen algae). Genetic assessment of epilithic biofilms along a 10-km reach near Drummond shows that bluegreens are indeed an abundant and diverse part of the microbial community. Preliminary assessment of the potential for N-fixation to add to nutrient enrichment and promote nuisance algal blooms points to the need to investigate elemental interactions and manage multiple water quality issues simultaneously as restoration continues concomitant with development of waste water and sewage treatment capacity on the UCFR.