Assessment of the Red Rock River subbasin and wetlands of the Centennial Valley
By: prepared for Bureau of Land Management, Montana/Dakotas State Offices ; by Linda K. Vance ... [et al.].
Contributors: Newlon, Karen Rachel; Clarke, Jessica L.; Stagliano, David M.; Montana Natural Heritage Program; United States. Bureau of Land Management. Montana State Office
Publisher: Montana Natural Heritage Program
Published: 2009
Place of publication: Helena, Mont
Language: eng
Description: This report summarizes results from a multi-scale ecological assessment of fourteen watersheds in the Red Rock River subbasin in southwestern Montana, and an in-depth assessment of wetlands on BLM-managed lands in the Red Rock Creek and Lima Reservoir watersheds of the Centennial Valley. The goal of the project was to provide landscape-level assessments of watershed health and integrity, as well as site-specific evaluations of wetland and aquatic condition, using a probabilistic survey approach. This was accomplished using both broad-scale GIS analysis and field sampling.  The value of watershed-level assessments lies in identifying areas where impacts are currently occurring or may occur, rather than merely documenting effects that have already occurred. By combining both site-level and watershed-level assessments, it is possible to select areas where management can make a substantial difference in future wetland and aquatic health.  Our broad-scale GIS assessment examined underlying biological diversity, measured current conditions, and evaluated potential threats. Several key findings emerged from the GIS data analysis:  -- The assessment area lies in a sparsely-populated part of Montana, where most of the land is in public ownership. Across the Red Rock River subbasin area, the BLM Dillon Field Office owns or manages approximately 411,977 acres (206,497 hectares). The BLM State Office owns an additional 21,328 acres (8,631 hectares) in the Centennial Mountains Wilderness Study Area. Altogether, the BLM has responsibility for 433,305 acres (175,352 hectares) in the Red Rock River subbasin, almost 29% of the area. The Forest Service is the next largest public land owner, managing 391,924 acres (158,606 hectares). In the two watersheds containing the Centennial Valley (Lima Reservoir and Red Rock Lakes), the BLM owns or manages approximately 106,213 acres (42,983 hectares). The U.S. Fish and Wildlife Service manages almost 100,000 acres (40,469 hectares) in these two watersheds, and both the Nature Conservancy and Montana Land Reliance have substantial easements on private lands in the Centennial.  -- Across the subbasin as a whole, 45% of the land cover is grassland, 31% is shrubland, 17% is forest, and 4% is agriculture. Wetlands make up less than 2% of the land cover. In the Centennial Valley, 35% of the land cover is grassland, 37% is shrubland, 16% is forest, 8% is wetland and 2.5% is open water. Throughout the subbasin, both public and private grasslands and shrublands are used primarily for cattle grazing.  -- In terms of hydrology, topography, and vegetation communities, the Red Rock Lakes 5th code hydrologic unit has the most complexity of the watersheds we evaluated, while the Muddy Creek 5th code hydrologic unit has the least.  -- Watershed condition, as measured by a broad landscape integrity index and a separate stream corridor integrity index, was relatively high.  The Red Rock Lake 5th code hydrologic unit had the highest score on our Composite Watershed Integrity Index, while Lower Horse Prairie Creek had the lowest score. These indices are based on the amount and density of landscape level disturbances (roads, stream diversions, mines, etc.), and do not necessarily reflect site-specific impacts. However, landscape disturbance is often correlated with site specific disturbance. For example, in the Lower Horse Prairie Creek watershed, floodplains have been altered by agriculture and associated water extraction.  -- The primary human-caused threat to wetland and watershed integrity in the subbasin as a whole is riparian grazing. The highest potential threat is in the Lima Reservoir watershed, where most streams and waterbodies are on land used primarily for grazing. However, this potential threat can be offset by proper grazing management practices.  Our fine-scale assessments focused on wetlands and streams in the Red Rock Lakes and Lima Reservoir watersheds in the Centennial Valley. We conducted Proper Functioning Condition (PFC) assessments at 103 lentic and lotic sites, and found:  -- 74 in Proper Functioning Condition;  -- 19 Functional at Risk with a downward trend;  -- 3 Functional at Risk with an undetermined trend;  -- 7 Nonfunctional.  All lotic sites sampled (8) were in Proper Functioning Condition.  Of 83 sampling sites on or immediately adjacent to BLM-managed lands, we found:  -- 56 in Proper Functioning Condition with a stable trend;  -- 17 Functional at Risk with a downward trend;  -- 3 Functional at Risk with an undetermined trend;  -- 7 Nonfunctional.  We also carried out aquatic assessments at 37 sites using macroinvertebrate-based metrics. Because the streams in the Centennial Valley exhibited characteristics of both foothill-valley streams and mountain streams, we used two multimetric indices to interpret our findings. With the Montana DEQ's Foothill-Valley index, 15 of the 16 lotic sites sampled were ranked non-impaired (good to excellent biological integrity) and 1 was slightly impaired.  Using the DEQ Mountain index, 6 of 15 were nonimpaired, 5 slightly impaired and 4 moderately to severely impaired. In both cases, the macroinvertebrate index scores showed little correlation with riparian and instream habitat assessments.  The best opportunities for wetland protection in the Centennial Valley involve grazing management.  Upland condition in the Centennial Valley indicates that good grazing practices are the norm. We suggest two specific strategies for wetlands: identification of clusters of high-quality or restorable fens and/or carrs where exclusion could be an option, and identification of areas with high concentrations of seasonally flooded wetlands, where seasonality of grazing could be adjusted to prevent damage to wet soils.
Notes: "June 2009."-cover date.

Includes bibliographical references (p. 41-43).

The Montana State Office of the Bureau of Land Management provided funding assistance for the overall watershed assessment.  Agreement Number L08AC14562