Effect of Direct Droppings from Bridge Nesting Birds on Bacterial Concentration of Underneath Surface Water

Concentrations of indicator bacteria, such as E. Coli, fecal coliform, and Enterococci were measured from upstream, underneath, and downstream of a bridge over the Guadalupe River near Kerrville, TX, to evaluate the effect of direct droppings of birds residing under the bridge structures on the bacterial loading in the underneath water. The bacterial loadings in all sampling locations increased as soon as the migratory birds started nesting on the bridge. The concentrations of bacteria in water beneath the bridge were significantly higher than those in upstream water. The concentrations of bacteria in downstream water were slightly higher than those in upstream water and significantly lower than those in water underneath the bridge due to dilution and decay. The probability analysis of the concentration of bacteria in water underneath the bridge showed that the concentrations of E. Coli, fecal coliform, and Enterococci are likely to remain within the Texas Commission on Environmental Quality specified contact recreation limit for 71, 68, and 35 percent of the time, respectively, during the nesting season.