Seasonal and longitudinal investigation on the impacts of recreational activities on the aquatic macroinvertebrate community within the San Marcos River
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In the San Marcos River, recreational activities are most pronounced between April and October. Given the continued urbanization and increasing population in San Marcos there is need for a quantitative study on the possible effect of elevated recreational activities on the aquatic macroinvertebrates within the river. Furthermore, currently, there has been no study which quantified patterns in macroinvertebrate drift and benthic community structure simultaneously in the San Marcos River. Information on drift patterns and benthic macroinvertebrate habitat relationships is necessary to understand mechanisms for species persistence within the San Marcos River. In this study, I examined the seasonal and longitudinal patterns of benthic macroinvertebrate community composition at three different sites within the San Marcos River. I also examined the seasonal and longitudinal response of the drifting aquatic macroinvertebrates to changes in their habitat as a result of recreational activities in the San Marcos River. Tubing and swimming accounted for most of the recreation activity (>90%). Across all seasons, the upstream most study site had the highest drift densities compared to two downstream study sites. Canonical Correspondence Analysis (CCA) results explained 15.3% of the variability in the San Marcos River benthic macroinvertebrate community among vegetated habitats and 23.9% among open substrate habitats. Study results indicated that drift is related to benthic abundance. Macroinvertebrate drift densities followed the typical circadian pattern observed in other river systems and results indicated no increase in macroinvertebrate drift density during the peak recreation period. Conclusively, study results indicated that macroinvertebrates at the two upstream sites were not impacted by recreation and turbidity. However, the lower most study site, based on the CCA results indicate that substrate and turbidity are factors influencing the macroinvertebrate community.