Influences of Flow and Basin Morphometry on Nutrient Dynamics in a Series of Texas Reservoirs
Date
1996-05
Authors
Brown, Patrick F.
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Abstract
Nutrient dynamics in a series of reservoirs (Canyon Lake, Lake Dunlap, and Lake McQueeney) on the Guadalupe River, Texas, were highly dependent on flow regime, water column stability, basin morphometry, and water residence time during the record "wet year", 1992. Beginning in December 1991, record high flows in the Guadalupe River entered Canyon Lake and led to increased discharge downstream. Flows were extremely high through the winter and until mid-June 1992.
During the period of high discharge below Canyon Lake, longitudinal physical and chemical parameters in the lower two reservoirs, Lake Dunlap and Lake McQueeney, were relatively uniform due to their similar morphometry and very short residence times. As the discharge from the Guadalupe River decreased, two point sources, the spring-fed Comal River and a wastewater treatment facility, influenced physical and chemical parameters in Lake Dunlap and Lake McQueeney. The Comal River affected temperature, specific conductance, alkalinity, and nutrients, while the wastewater treatment facility had a large influence on nutrients. Due to the reduction in residence time, the hypolimnetic water leaving Canyon Lake reservoir was much warmer than during a typical flow year. Specific conductance was lower and longitudinally uniform during high flow, however during lower flows later in the year, a significant increase in specific conductance occurred below the confluence of the Guadalupe and Comal rivers. Soluble reactive phosphorus (SRP), N03+N02-N, and NH4-N were greatly influenced by the prolonged high Canyon Lake discharge. Hypolimnetic SRP concentrations leaving Canyon Lake were higher than epilimnetic concentrations. N03+N02-N concentrations leaving Canyon Lake were relatively high during the high flow period, however concentrations decreased as flows were reduced through the summer. Below Canyon Lake, N~-N concentrations were inversely related to N03+N02-N. N~-N increased markedly late in the summer and peaked in October, 1992.
Beginning in July, lower discharge from Canyon Lake allowed for the relatively constant spring flows of the Comal River to equal the Guadalupe River discharge into Lake Dunlap. This allowed for the Comal River to increase SRP and N03+N02-N concentrations in both Lake Dunlap and Lake McQueeney. N~-N concentrations remained minimal in Dunlap and McQueeney during high flow; however, under lower flow conditions, thy wastewater treatment facility increased N~-N concentrations in both reservoirs.
As a result of high discharge from Guadalupe and Comal rivers during 1992, phytoplankton biomass was extremely low throughout Lake Dunlap and Lake McQueeney. During periods of normal discharge from Canyon Lake, the Comal River and New Braunfels wastewater treatment facility had a greater chemical influence on Lake Dunlap and Lake McQueeney than did Canyon Lake.
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Keywords
reservoir ecology, Guadalupe River Watershed, Canyon Lake, Make McQueeney, Lake Dunlap
Citation
Brown, P.F. (1996). Influences of flow and basin morphometry on nutrient dynamics in a series of Texas reservoirs (Unpublished thesis). Southwest Texas State University, San Marcos, Texas.