Modeling water quality and biota in the Colorado River below Austin, Texas

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1991

Authors

Barber, Michael E. (Michael Ernest), 1959-

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Abstract

A model, capable of performing both steady state and dynamic analyses, has been developed and used to predict changes in potential population densities of submerged rooted aquatic vegetation (SRAV) and epiphytic algae as well as the concentration changes of other water quality parameters associated with eutrophication problems. The model has been applied to the Colorado River between Austin and Bastrop, Texas to evaluate the impacts on the downstream river ecosystem due to potential changes in waste water treatment levels and increased waste water discharges caused by population growth. Nine steady state and twelve dynamic simulations were performed. Although phosphorus removal from Austin's waste water treatment plants reduced downstream phosphorus concentrations significantly, the SRAV growth potentials were not reduced proportionately. Similarly, the incremental difference in SRAV densities as a result of phosphorus and nitrogen removal suggested that removal of both nutrients is also unnecessary. The evidence does suggest a correlation between the level of waste water treatment and the growth potential of epiphytic algae. The largest reductions in growth potentials were due to phosphorus and nitrogen removal. However, less than half of the reductions were attributable solely to phosphorus removal. The results of the analyses indicate that the constant rhetoric claiming phosphorus removal is need to reduce SRAV growth in the lower Colorado River is incorrect. Furthermore, reductions of epiphytic algae potentials due to the removal of phosphorus alone were relatively small for several scenarios. Consistently significant reductions in growth potentials were only obtained by phosphorus and nitrogen removal. These results indicate that further scientific investigation is needed to determine the true "detrimental" effects of SRAV and epiphytic algae on the Colorado River before a cost/benefit analysis can be completed. Accordingly, the present conclusion would be not to expend the money and resources upgrading Austin's waste water treatment facilities solely on the basis of SRAV and epiphytic algae control

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