The effects of storm events on the behavior of hydropsychid net-spinning caddisflies

Physical disturbance in the form of storm events has been implicated as a major determinant of community structure in streams. But there has been limited study of this effect on individual taxa within the communities. Such work is needed because of untested assumptions regarding the behavior of bioindicator species in these systems. Development of intricate indices of insect tolerances to organic pollution have become commonplace in environmental monitoring. However, research on the effects of natural disturbance on biological water quality assessment is lacking. Hydropsychid caddisflies are relatively intolerant to organic pollution and the United States Environmental Protection Agency has outlined the use of these organisms and others as an indication of clean water. If a species is recorded as absent from samples when it is present but hidden, this false negative would bias the water quality assessment. I tested hypotheses regarding the behavior of hydropsychid caddisflies facing increased discharge, and the effect of stream size on the magnitude of this phenomenon.Three sites along the West Fork of the White River, Indiana USA were studied during nine storms between 2001 and 2004. Stratified sampling from the upper 15 cm of substrate prior to and just after a storm, and again following reestablishment of normal flow, revealed alterations of hydropsychid distributions. During storms all but one species sought refuge in the hyporheic zone at depths dependent upon storm intensity. The possibility that poor water quality resulting from increased discharge caused the hydropsychid behavior was refuted by chemical analysis. Family level biotic index (FBI) data demonstrated that increased discharge results in a reduction of stream FBI values. These results indicate that high intensity storm events influence biological monitoring and should be factored into sampling protocol.Department of BiologyThesis (D. Ed.