In this study, the water quality of three agricultural impoundments in Oklahoma is
simulated. A deterministic, one-dimensional water quality model (MINLAKE98)
simulating physical, chemical, and biological processes in a lake or impoundment was
used. The model operates on a time step of one day and makes year-round simulations of
temperature, dissolved oxygen, phosphorus, and chlorophyll a. The model is designed for
simulating the effect of different weather conditions including global warming for
individual lakes. Input requirements include daily weather data, lake morphometry,
initial Secchi depth, initial nutrient and chlorophyll concentrations and inflow quantity
and quality from the watershed. A process oriented model, the Soil and Water
Assessment Tool (SWAT), calibrated for the Little Washita River watershed by Hanaratty
and Stefan (1997) was used to obtain estimates of the runoff into the impoundments,
including flow rate, nutrient load, temperature, dissolved oxygen, and biochemical
The effect of climate warming on the individual impoundments was simulated.
Previous research on the effect of a 2XC02 climate assumed steady trophic state and lake
volumes. The new simulations use both a dynamic trophic state (determined by the
simulated time-variable phytoplankton popUlation) and variable lake volume (as a result
of inflows and outflows). Simulations of three conditions were made and compared: (l)
past climate conditions (lxC02); (2) 2xC02 weather impact on lake/impoundment waterquality
(with past watershed input); and (3) 2xC02 weather impact on both the watershed
input and the resulting lake/impoundment water-quality. The results indicate that
atmospheric conditions have a stronger impact on water temperature than watershed
inputs. Nutrient levels and phytoplankton populations in the impoundments are strongly
impacted by the watershed. However, the uncertainties in projecting the effects of land
use on water quality are larger than the projected potential changes due to climate
warming. Land use decisions are likely to have a larger impact on these small
agricultrual impoundments than projected climate warming.
Grazing Lands Research Laboratory, US Department of Agriculture; Mid-Continent Ecology Division, US Environmental Protection Agency
West, Deborah E.; Stefan, Heinz G..
Modeling of Watershed Input and Potential Climate Change Effects on Water Quality in Agricultural Reservoirs in the Little Washita River Watershed.
St. Anthony Falls Laboratory.
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