9317 (2) - Laserfiche WebLink

Home Browse Search

Within the UCOL, there are changes in the algal and invertebrate communities in areas of urban develop- ment. Algal biovolume (amount of algae) and midges (insects considered more tolerant of degraded conditions) were greater at sites with urban development than sites with little urban development. However, with the excep- tion of algal status at the Gore Creek site, biological indices for UCOL urban sites are in the lowest 25 percent of urban sites from other NA WQA Study Units. The Gore Creek watershed is more urbanized than the East River watershed, and the changes in the algal community reflect increased nutrient concentrations at this site, making it more typical of other urban sites nationally. The invertebrate and fish communities are ranked among the least degraded nationally at both UCOL urban sites. Explanation of Biological Rankings The three selected biological indicators respond to changes in stream degradation. Degradation can result from a variety of factors that modify habitat or other environmental features such as land use, water chemistry. and flow. Algal status focuses on the changes in the percentage of certain algae in response to increasing siltation and often is positively correlated with higher nutrient concentrations in many regions of the Nation. Invertebrate status is the average of 11 invertebrate metrics that summarize changes in richness, tolerance, trophic conditions, and dominance associated with water-quality degra- dation. Fish status focuses on changes in the percent- age of tolerant fish species that make up the total number of fish. "Tolerant" fish are reported to thrive in degraded water quality. For all indicators, higher values indicate degraded water quality. Biological indicators Algal Invertebrate Fish status status status Site name D D D D D D Colorado River below Baker Gulch (reference site) East River (area of urban development) Gore Creek (area of urban development) EXPLANATION D Lowest 25 percent nationally, least degraded sites D Middle 50 percent nationally D D D Ground water was sampled from shallow monitoring wells in the Crested Butte, Gunnison, Silver- thorne, Vail, and Winter Park! Fraser areas (fig. 6). Domestic (household and private) and public supply drinking-water wells of var- ious depths were also sampled in urban areas throughout the South- ern Rocky Mountains. Some ground-water samples collected in urban areas con- tained elevated levels of nitrate. Nutrients in ground water can orig- inate from various natural sources (such as atmospheric deposition or dissolution of geologic materials); however, elevated concentrations in ground water are often related to human activities, such as effluent from septic systems or the applica- tion of fertilizers. Nitrate concen- trations greater than the USEPA Maximum Contaminant Level (MCL) drinking-water standard of 10 mg/L (U.S. Environmental Pro- tection Agency, 1996) were detected in one sample collected from a shallow monitoring well in an urban area but in none of the drinking-water wells. Nutrient con- centrations in undeveloped areas (determined from data from the 20 NA WQA Study Units that began in 1991) indicate a national background concentration for nitrate of 2.0 mg/L (U.S. Geologi- cal Survey, 1999). The undevel- oped areas are considered to be minimally affected by agriculture, urban development, or associated land uses. Twenty percent of the samples collected from monitoring wells (and none of the samples col- lected from drinking-water wells) contained nitrate concentrations greater than 2.0 mg/L. These find- ings indicate that portions of the 8 Water Quality in the Upper Colorado River Basin