Calcium Dynamics in a Subtropical Impoundment




Allemand, Thomas M.

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Canyon Reservoir is a hardwater, oligo-mesotrophic impoundment located on a fourth order stretch of the Guadalupe River in Comal County, TX Canyon Reservoir is distinct from other hardwater systems in that it can have lake-like features during low or no inflow periods, and reservoir properties during average or high inflow, setting up patterns befitting the reservoir zonation model By analyzing the chemical data from the headwaters to the tailrace below the dam the process of decalcification is apparent In the summer months of 2000 the lack of substantial inflow decreased the influence of the watershed and the impact biologically-induced decalcification had on the reservoir was particularly evident. The mechanism controlling calcium sedimentation in Canyon Reservoir appears to be dominated by flow in the riverine zone, predominately biologically controlled in the transitional zone, and biologically and physically controlled in the lacustrine zone by being isolated from the upper reaches of the reservoir. By constantly being supersaturated, with respect to calcite, Canyon Reservoir retards eutrophication via nutrient and trace metal loss and the hastened sedimentation of dissolved organic carbon and phytoplankton An increase in primary production in the transitional zone of the reservoir appears to catalyze calcite precipitation, thereby inhibiting further production downstream by accelerating the process of algal sedimentation upstream When phytoplankton sink out of the water column, as a result of nucleating calcite, organically-bound as well as inorganically-bound nutrients, such as phosphorous, are lost to the sediments This phenomenon is most likely to occur in the spring and summer months, when primary production is greatest.



calcite, sedimentation and deposition, eutrophication, reservoirs


Allemand, T. M. (2001). Calcium dynamics in a subtropical impoundment (Unpublished thesis). Southwest Texas State University, San Marcos, Texas.


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