Upper Los Pinos Water Quality Report

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water from the high-altitude lakes. Trend ~uialvsis of the data using the Mum-ILendall test (Helsel and Hirsh, 1992; Sahni and others, 2002) indicated that the improving trends are significant. The causes for the improving trends are unlino~~n; however, placement of the time lines for the Clean Air Act and amendments seems to have a relationship to the improving trends. In particular, changes in pH over time seem to be related to the time lines for the Clean Air Act and amendments (fig. 7). The effects of atmospheric deposition from coal-fired power plants is sometimes described by changes in sulfate and nitrate (Turk and others, 1993); however, there were no observed trends for these parameters. The Bureau of Reclamation (BOR) conducted a ~~-ater-quality study in the Vallecito Reservoir area during 1992-9~ (Bureau of Reclamation, 1995). Samples were collected from 72 surface- and ground- water sites. Figure 8 shows all water-quality sites in the Vallecito Reservoir area, ilicluding the BOR sites. Water-quality parameters included in the BOR study included total arsenic concentrations and fecal colifonn counts (counts of fecal coliform bacterial colonies after incubation at 3~°C for 24 hours). Total arsenic concentrations were reported in water from 9 sites (fig. 9). Total arsenic concentrations in surface- water samples ranged from 2 to 3 ug/L; total arsenic concentrations in ground-water samples ranged from ~ to 44 ug/L (fig. 9). Positive fecal colifonn counts were reported in water from 126 sites (fig. 10); twelve of the positive counts were in water from wells. Fecal colifonn counts ranged from < 3 to 4,600 col/100 mL (colonies per 100 milliliters). The purpose of this report is not to report specific locations of arsenic concentrations and fecal coliform counts. The purpose is to notify the citizens in the watershed that arsenic concentrations and fecal coliform counts eiist in ~~-aters of the upper Los Pinos River watershed. Water-quality data have been collected from Los Pinos River upstream from the reservoir by the USGS, U.S. Forest Service, Colorado River Watch, and the Volunteer Lake Monitoring Program. Data have been collected from Los Pinos River downstream from the reservoir by the USGS, the Southern Ute Tribe. and the Volunteer Lake Monitoring Program. A consistent monitoi7ng program has not taken place for Los Pinos River upstream and downstream from the reservoir: hence, the anah~tical parameters and detection limits vain by collection date a«d agency. The Missionan_- Ridge Wildfire of 2002 may have impacted water- qualit<- parameters in Los Pinos River do~~mstream from the reservoir; however. there are not sufficient data to describe and- such impacts. The available water-quality data for Los Piiios River are shoe°n iii figure 11. The time line of the Missiona~-~- Ridge wild- fire is indicated. The USGS has collected research watcr-qualit<- data in streams and tributaries of the upper Los Pinos River watershed. The data collected are related to the occurrence of dissolved org~uiic carbon and its rela- tionship to geologic setting. These data ~~-ere not available to the public at the time of the writilig oftlus report. Vallecito Reservoir Lakes and reservoirs may be classified according to their biological productivity. Oligotrophic lakes are relatively unproductive and receive only small amounts of plant nutrients. Eutrophic lakes, due to an overabundance of nutrients, can produce algal gro«th and aquatic plants that impart taste and odor problems in water supplies, reduce transparency; and result in odorous scums. Aquatic plants choke shallow water near the edge of a lake, thus reducing the accessibility for recreation. Normally-, lakes that show depletion of dissolved oxygen in the bottom of the lake (hypoliinnion) during thermal sti7-atification are classified as eutrophic, while those that maintain high oz-ygen levels throughout the rear are oligotrophic. Mesotrophic is often used to classifi a moderately productive lake that is suitable for recreation but less desirable as awatcr-supply source. The major plant nutrients contributing tp eutrophication are orthophosphate, inorganic nitrogen (nitrate and a>mnonia), and carbon dioiide. Trace nutrients include iron and silica, and organic compounds (such as vitamins). Although not universallT accepted. phosphorus may be the key limiting factor for development of eutrophication (Clark, Viessman, and Hammer, 1977). The major physical factors that influence eutrophication include temperature, light- residence times of the lake water, and thermal stratification. Lakes thermally stratifi- during «inter and suimner and circulate (overturn) each spring and autumn. Figure 12 shows a schematic of thermal stratification in a lake. Water quality is directly affectcd by thermal stratification. The epilimnion (fig. 12) supports abundant algal growth, while the h~polimnion in 20 Water-Quality Data Synthesis for the Upper Los Pinos River Watershed, In cooperation with the Colorado Watershed Protection Fund and Southwestern Colorado, and Suggestions for a Watershed Plan, 2005 the San Juan Resource Conservation and Development Council