San Marcos Texas Wild Rice Enhancement and Restoration Project


Texas wild rice, Zizania texana, is a state and federally listed endangered species that only exists in the upper portion of the San Marcos River and is the focus of this project. The ultimate goal of this project is to better understand Texas wild rice and its habitat in order to focus conservation efforts on the primary stresses that have led to the plant's decline.

Study Area

San Marcos River, Texas

Project Period

2013 – 2016


The beautiful spring fed San Marcos River hosts a slew of endemic species, like the Texas wild rice plant, that are sensitive to alterations of their unique habitat. Due to the pristine water and nature of the river, development and recreation has led to a ripple effect of impacts extending toward the niches of this rare organism. Texas wild rice thrives in very clear, fast moving water with a constant temperature and low pollutant levels. This project focuses on spatial and temporal patterns in suspended solids, sedimentation rates, turbidity or light attenuation and periphyton growth in relation to the potential impacts on plant fitness and the survival of Texas wild rice. As a result, there are three sampling periods of high, medium and low recreation. Game cameras are being utilized to observe recreation during these times. The data obtained will be used to discover if a correlation exists between recreation and Texas wild rice's decline. The encroachment of invasive aquatic plant species has also been a problem and is being evaluated through physical habitat assessments and vegetation transects along the river.

Because water quality is of utmost importance to the survival of Texas wild rice, we are continually monitoring the water with six sondes located throughout the river from locations with abundant stands of wild rice to locations with no wild rice. Because the wild rice thrives in clear water, we are examining light attenuation with a photosynthetic active radiation (PAR) meter at each site. The further the site is from the headwaters the more turbid the water becomes, resulting in less light penetrating through the water column. This will establish a range of light intensities that Texas wild rice requires.

Sedimentation rates are being examined with a sediment sampler. Each sampler has eight PVC pipes with specific dimensions that capture sediment as it falls out of suspension.

Periphyton is a mixture of algae and microbes that attach to submerged strata like aquatic plants and rocks. When periphyton covers the leaves of Texas wild rice it can block photosynthesis, which causing chlorosisyellowing of the leaf. This weakens the plant and excessive amounts can threaten its survival. Due to observations of periphyton growth on the wild rice, we are studying this phenomenon. We have deployed two types of periphtyon samplers. One type floats on the water's surface and the other is submerged. Along with each sampler, we are measuring the velocity of the water and the depth of the submerged samplers. After it has collected on the sampler, the periphyton is removed from the tiles and analyzed for chlorophyll-a and biomass.

The research from this project will ultimately contribute to the conservation process of preserving biodiversity and our understanding of sustainability.

Publications and Presentations

Byrne, R., Guillen, G. 2015. Influence of Recreation on Water Quality in The San Marcos River. Texas Academy of Science, San Antonio, TX. Poster.

EIH in Action

Sewell Park on the San Marcos River is a popular recreation area on the TSU campus featuring the endangered Texas Wild Rice and other aquatic vegetation
Texas Wild rice (Zizania texana) at Sewell Park on the San Marcos River, Texas
Texas Wild Rice (Zizania texana), San Marcos River
EIH research assistant Natasha Zarnstorff records data for the San Marcos Texas Wild Rice Enhancement and Restoration Project
EIH research assistant Rachel Byrne deploys periphyton samplers used to measure periphyton Chlorophyll-a and biomass in the San Marcos River
EIH research assistant Rachel Byrne collects periphyton from the deployed samplers in the San Marcos River, Texas
Underwater view of Texas Wild Rice (Zizania texana), San Marcos River
Sedimentation sampler deployed in the San Marcos River, Texas
EIH research assistant Rachel Byrne collects samples from the sedimentation collectors

Project Sponsors

  • Environmental Institute of Houston

    Phone: 281-283-3950

    North Office Annex
    2700 Bay Area Blvd, Box 540
    Houston, TX 77058-1002

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