The Llano River, a spring-fed perennial river, is a key component of the Texas Hill Country in which, aquifer withdrawals, invasive species encroachment, and loss of riparian habitat have had substantial effects on the watershed. One way that the cumulative effects of these threats can be assessed is using benthic macroinvertebrates as indicator species. Benthic macroinvertebrates span a range of trophic levels and tolerances, so changes in the community can help characterize localized alterations in stream conditions. Although the South Llano River is overall considered a healthy ecosystem, there are “hotspots” of potential problems in expansion of degraded riparian zones. While there has been previous analysis of the macroinvertebrate community, the links of aquatic-terrestrial ecotones have not been addressed yet. Therefore, this study analyzes the effects that degrading riparian zones have on drift of macroinvertebrates. We placed drift nets at two different riffles near the shore line in a degraded riparian zone and mid-river at each site. Drift samples were collected in a 2-hour interval for 24 hours; then, they were preserved in 70% ethanol and stored. The specimens were counted and generally identified to genus using taxonomic keys focusing on indicator species to assess the river condition.
Results/Conclusions
Drift patterns at both sites exhibited a single peak at night (3:00am) decreasing to lower levels before noon. This trend differs from classic bigeminus pattern in which the largest peak occurs at sunset and a smaller peak occurs prior to sunrise. From the total number of macroinvertebrates, the order Ephemeroptera contributed 58.5% of the total followed by Diptera 15%, and Trichoptera 10.9%. Within those orders, Tricorythodes sp. (17.6%), Chironomidae (10.9%), and Procloeon sp. (7.7%) were the three most dominant taxa. Insects from these taxa are good indicator species because they are particularly sensitive to changes in environment, so the high numbers imply a good water quality. Since, both sites shared similar species diversity as well as exhibit similar drift pattern, there doesn’t seem to be a significant effect of degraded riparian vegetation on behavioral drift. Perhaps effects of degraded riparian areas in this study were not extensive enough longitudinally to show a local effect on drift and those effects would be manifested downstream. Nonetheless, this study proved that macroinvertebrate drift is an effective technique on assessing water quality using indicator species. Also, it will help in properly allocating conservation efforts and improve the management of the vast riparian resources.