Stakeholders with an interest in water quality conditions on the segment of the upper Roaring Fork River near Aspen include Colorado Department of Health and Environment (CDPHE), Pitkin County, City of Aspen, Aspen Consolidated Sanitation District, and Roaring Fork Conservancy (RFC). In September of 2012, the Roaring Fork Conservancy, in partnership with City of Aspen and Pitkin County, initiated benthic macroinvertebrate sampling at seven locations near Aspen. This effort compliments past and ongoing water quality monitoring at multiple sites on the upper Roaring Fork by CDPHE Water Quality Control Division (WQCD), RFC, and Colorado Riverwatch volunteers.
In 2011, RFC conducted an extensive basin-wide macroinvertebrate sampling effort. This effort increased existing datasets for several long-term sites, and provided baseline conditions for many previously unsampled sites in the watershed. Subsequently, biomonitoring took place at seven sites on the Upper Roaring Fork River in 2012. Benthic macroinvertebrate communities were sampled and assessed using Colorado’s Multi-Metric Index (MMI) and several additional metrics. Scores displayed a clear trend of increasing stress and disturbance from the upstream sites to the most downstream site. MMI scores identified attainment of Colorado Water Quality Control Division standards for aquatic life use at the upper five sites, but the lowest two sites near the City of Aspen rated as impaired. Impaired scores echoed 2011 sampling results from the Roaring Fork River near Slaughterhouse Park and continue to support the State’s 2012 Provisional 303(d) listing of the segment below Hunter Creek.
The MMI assessment methodology does not identify specific causes of impairment; low scores indicate a general stress to macroinvertebrate communities from one or more sources. Suspected stresses to the Roaring Fork in Aspen include regularly occurring summer flow impairment from transbasin and local diversions, and the spectrum of effects associated with urbanization including alteration or destruction of riparian habitat, physical channel alteration, stormwater runoff, and others. In addition, the Roaring Fork River in Aspen may continue to be impacted by legacy effects of past land use practices or pollution. In general, the downstream negative trend in site MMI scores is spatially correlated with increasing flow depletion, urbanization and episodic stormwater inflows. Targeted investigation into these potential disturbances and associated pollutants may help elucidate the reasons for poor macroinvertebrate conditions observed near the City of Aspen.
Based on MMI scores, stream conditions in the James H. Smith and North Star Open Space parcels adequately supported aquatic life. Although previous assessments at these sites are in conflict regarding the geomorphic stability of the area, the presence of healthy aquatic communities indicated that aggressive management actions to improve macroinvertebrate populations may currently be unwarranted.
Importantly, results from this study do not constitute a legal declaration of aquatic life use attainment or impairment on the Roaring Fork River; only the CDPHE may make such designation. Sample results are shared with the Water Quality Control Division to aid their surface water assessment mandate. Under the agency’s listing methodology, a segment may be provisionally listed based on one failing sample. However the State may choose to review all other relevant data concerning a particular stream segment before final determination of impairment and 303(d) listing.