Going with the flow: Does recreational activity in the San Marcos River lead to nutrient changes?




Verrett, Christopher

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The San Marcos River is a physico-chemically consistent spring-fed river with exceptionally high water clarity and serves as the home for numerous endemic and threatened species, such as Texas wild rice (Zizania texana) and the San Marcos salamander (Eurycea nana). Excess nitrogenous compounds like ammonia can be toxic, while increased nitrates and phosphates can cause increased algal growth and loss of water quality. In addition, increased suspended sediment (and associated turbidity) can lead to decreased light penetration, reducing light for photosynthetic requirements and the ability for animals to see prey. In this study, I collected data at Pyramid Park, which is adjacent to a common tube-embarking spot over an 8-week period. For an hour each day of data collection, people on the shoreline and in the water were counted at 15-minute intervals. A continuous count was also kept of all tubers, kayakers, and similar vessels that passed by during the hour. During this hour interval, I also collected a surface water sample. Lastly, I deployed two water quality sondes in the upper river: immediately downstream from the activity observation point, and the other in a major spring opening in Spring Lake to serve as a measure of the groundwater water quality. Sondes continuously logged temperature, conductivity, and turbidity at 15-minute intervals. I then assessed if there was a correlation between the number of people on the river and changes in water quality (nitrates, phosphates, and ammonium) and turbidity. Results from this study have implications for the relationship between the environmental effects of recreational activities and conservation efforts, city planning, and habitat restoration efforts.



San Marcos, San Marcos River, water, aquatic biology, water chemistry, turbidity, recreation, nutrients, Chemistry, Honors College


Verrett, C. (2022). Going with the flow: Does recreational activity in the San Marcos River lead to nutrient changes? (Unpublished thesis). Texas State University, San Marcos, Texas.


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