Master of Science (MS)


Renewable Natural Resources

Document Type



Headwater streams are an integral part of any watershed system because they strongly influence the physical, chemical, and biological components of downstream reaches. Little information exists about macroinvertebrate community structure, spatiotemporal variation, or their relationships with environmental factors in low-gradient headwater streams of the subtropical coastal plain region in the Southern US. These headwater streams are typically slow moving, capable of accumulating large amounts of organic material, and often become intermittent during the dry season. Research is needed to understand the effects of these unique characteristics on stream health and ecology. This study aimed to determine aquatic macroinvertebrate community structure, identify spatial and seasonal patterns, and investigate relationships between the macroinvertebrate community and environmental variables in seasonally hypoxic, first- and second-order streams with varying flow permanence in a lowland subtropical watershed located in central Louisiana, USA. Eleven monitoring locations throughout the watershed were sampled twice over one year for macroinvertebrates and physicochemical parameters including velocity, wetted area, nutrients, and dissolved oxygen (DO). Aquatic benthic macroinvertebrates were sampled within a 160-m stream reach with a modified core sampler that was specially designed for the low-gradient system comprised. Seasonal and spatial differences between water quality characteristics, individual taxa, and biological metrics were determined. Correlation analysis detected seasonal differences in environmental variables that were related to abundances of individual taxa. Spring indicated by a positive correlation with total suspended solids and negatively with temperature and nitrate was positively associated with crustaceans and negatively associated with chironomids. Most notably, the burrowing mayfly, Hexagenia, was positively correlated to DO levels. Many of the metrics, including percent of Ephemeroptera, Plecoptera, Trichoptera (EPT) taxa, differed between sites with varying DO levels and flow permanence. Surprisingly, analysis of variance did not detect seasonal differences among the metrics. This study is one of the first comprehensive assessment on macroinvertebrate communities with detailed hydrologic and water quality measurements in the headwaters of a low-gradient, subtropical watershed. The study supports the importance of recognizing stream permanence in water quality assessments. In addition, the determination of useful metrics for low-gradient, headwater streams are suggested for future research.



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Committee Chair

Yi Jun Xu