Simulated effects of reduced spring flow from the Edwards Aquifer on population size of the fountain darter (Etheostoma fonticola)

The Edwards Aquifer in south-central Texas, U.S.A. is recognized worldwide for its aquatic species of flora and fauna, many of which are endangered or threatened, and also is the sole water source supporting the industrial, agricultural, municipal, and recreational needs of nearly 2 million people. Because it is generally the first species affected by low spring flows, the endangered fountain darter (Etheostoma fonticola) has been a focal point for controversies involving the endangered species act, state of Texas groundwater law, and private property rights. We developed an ageand sex-structured population model for the fountain darter, calibrated the model within the constraints of published parameter estimates such that populations simulated under historical spring flows resembled those documented in the field from 1973 to 2007, and used the model to project population dynamics under scenarios of reduced spring flows that could occur as a result of a drought or increased urban water demands. Our simulations suggested that even extending the low spring flows associated with the record drought of 2011 for three consecutive years would have no noticeable effect on population dynamics, and that minimum annual population levels were relatively unaffected until flows were reduced below 2.8 m3/s, with minimum population levels falling sharply when flows were reduced beyond about 1.68 m3/s. We view our model as a base model representing the impacts of changes in spring flow on the fountain darter which could be developed further to represent the impacts not only of changes in spring flow but also changes in water quality resulting from increases in the runoff of contaminants associated with continued urban development. © 2012 Elsevier B.V. All rights reserved.