Limnology of Blue Mesa, Morrow Point, and Crystal Reservoirs, Curecanti National Recreation Area, during 1999, and a 25-Year Retrospective of Nutrient Conditions in Blue Mesa Reservoir, Coloradoby Nancy J. Bauch, U.S. Geological Survey, and Matt Malick, National Park ServiceAvailable from the U.S. Geological Survey, Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, USGS Water-Resources Investigations Report 02-4199, 101 p., 32 figs. This document also is available in pdf format:
WRIR 02-4199 (7,350 KB) AbstractThe U.S. Geological Survey and the National Park Service conducted a water-quality investigation in Curecanti National Recreation Area in Colorado from April through December 1999. Current (as of 1999) limnological characteristics, including nutrients, phytoplankton, chlorophyll-a, trophic status, and the water quality of stream inflows and reservoir outflows, of Blue Mesa, Morrow Point, and Crystal Reservoirs were assessed, and a 25-year retrospective of nutrient conditions in Blue Mesa Reservoir was conducted. The three reservoirs are in a series on the Gunnison River, with an upstream to downstream order of Blue Mesa, Morrow Point, and Crystal Reservoirs. Physical properties and water-quality samples were collected four times during 1999 from reservoir, inflow, and outflow sites in and around the recreation area. Samples were analyzed for nutrients, phytoplankton and chlorophyll-a (reservoir sites only), and suspended sediment (stream inflows only). Nutrient concentrations in the reservoirs were low; median total nitrogen and phosphorus concentrations were less than 0.4 and 0.06 milligram per liter, respectively. During water-column stratification, samples collected at depth had higher nutrient concentrations than photic-zone samples. Phytoplankton community and density were affected by water temperature, nutrients, and water residence time. Diatoms were the dominant phytoplankton throughout the year in Morrow Point and Crystal Reservoirs and during spring and early winter in Blue Mesa Reservoir. Blue-green algae were dominant in Blue Mesa Reservoir during summer and fall. Phytoplankton density was highest in Blue Mesa Reservoir and lowest in Crystal Reservoir. Longer residence times and warmer temperatures in Blue Mesa Reservoir were favorable for phytoplankton growth and development. Shorter residence times and cooler temperatures in the downstream reservoirs probably limited phytoplankton growth and development. Median chlorophyll-a concentrations were higher in Blue Mesa Reservoir than Morrow Point or Crystal Reservoirs. Blue Mesa Reservoir was mesotrophic in upstream areas and oligotrophic downstream. Both Morrow Point and Crystal Reservoirs were oligotrophic. Trophic-state index values were determined for total phosphorus, chlorophyll-a, and Secchi depth for each reservoir by the Carlson method; all values ranged between 29 and 55. Only the upstream areas in Blue Mesa Reservoir had total phosphorus and chlorophyll-a indices above 50, reflecting mesotrophic conditions. Nutrient inflows to Blue Mesa Reservoir, which were derived primarily from the Gunnison River, varied on a seasonal basis, whereas nutrient inflows to Morrow Point and Crystal Reservoirs, which were derived primarily from deep water releases from the respective upstream reservoir, were steady throughout the sampling period. Total phosphorus concentrations were elevated in many stream inflows. A comparison of current (as of 1999) and historical nutrient, chlorophyll-a, and trophic conditions in Blue Mesa Reservoir and its tributaries indicated that the trophic status in Blue Mesa Reservoir has not changed over the last 25 years, and more recent nutrient enrichment has not occurred. Table of ContentsForeword Abstract Introduction Purpose and Scope Acknowledgments Description of Study Area Precipitation and Reservoir Operations Previous Investigations Data Collection and Analysis Procedures Sample Collection Analysis Methods Laboratory Analysis for Nutrients and Suspended Sediment Nutrient Ratios and Loads Water-Quality Standards Phytoplankton and Chlorophyll-a Analysis Reservoir Classification Schemes Trend and Correlation Analysis Quality-Control Methods and Analysis Limnology of Blue Mesa Reservoir Physical Properties Nutrients Phytoplankton Chlorophyll-a Characteristics of Reservoir Inflows Physical Properties and Suspended Sediment Nutrients Characteristics of Reservoir Outflow Limnology of Crystal Reservoir Physical Properties Nutrients Phytoplankton Chlorophyll-a Characteristics of Reservoir Inflows Physical Properties and Suspended Sediment Nutrients Characteristics of Reservoir Outflow Comparison of Reservoirs, Inflows, and Outflows Physical Properties in Reservoirs Nutrients in Reservoirs Phytoplankton in Reservoirs Chlorophyll-a in Reservoirs Characteristics of Reservoir Inflows and Outflows Implications for Management Retrospective of Nutrient Conditions in Blue Mesa Reservoir Physical Properties Nutrients Phytoplankton Chlorophyll-a Nutrient Enrichment Summary References Supplemental Data |
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