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, Colorado
by Nancy J. Bauch, U.S. Geological Survey, and Matt Malick, National Park Service
Available 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.
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Abstract
The 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 Contents
Foreword
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
