A Statewide Assessment of BLM-Managed Streams and Rivers in Colorado

Throughout Colorado, the Bureau of Land Management (BLM) oversees approximately 33,800 square kilometers of land containing more than 3,600 km of perennial streams and rivers. This technical note presents the results of a statewide assessment of chemical, physical, and biological conditions of BLM-managed streams and rivers in Colorado. From 2013 to 2017, 209 reaches (2,313 stream kilometers) were sampled during summer baseflow conditions using the BLM’s Assessment, Inventory, Monitoring methods. Benchmarks were established for 12 indicators that relate to BLM Colorado land health standards. Results are reported in terms of the extent of streams having minimal, moderate, or major departure from benchmarks with a ±90% confidence interval. For water quality indicators, such as pH, water temperature, and nutrients (i.e., total nitrogen and phosphorus), with standards set by the Colorado Department of Public Health and Environment, less than 16% of stream kilometers exceeded these standards. Similarly, more than 85% of BLM managed stream kilometers met the state’s macroinvertebrate biological condition criteria. Although not in exceedance of state standards, nutrient and specific conductance levels were elevated above reach potential for 34–51% of streams, which is a potential concern for downstream cumulative effects. Indicators characterizing riparian and instream habitat, such as bank stability and cover, fine sediment, nonnative woody riparian vegetation, and floodplain connectivity, generally identified more exceedances of BLM land health standards than those related to water quality. Floodplain connectivity was compromised for 48% of stream and river kilometers, and 47% had nonnative woody riparian vegetation species. The BLM can use this quantitative, unbiased baseline assessment to track the cumulative effectiveness of management actions over time.