Texas Wild-Rice: Umbrella Species of the San Marcos River by Jackie M. Poole
While adequate water is a necessity, too much water may make the river too deep or the current too swift for even the most tolerant organisms. Although floods are needed to refresh the system, if floods are too frequent or of biblical proportions, recovery and restoration may not be possible. Texas wild-rice grows best in water between 6 inches and 4 feet deep with a moderate current. It dies when water levels remain below 6 inches for more than a few days. When Texas wild-rice grows in still, shallow water, it flowers and disperses seeds while in deeper, swifter water, it remains submerged and reproduces vegetatively by rooting at the stem nodes. Having two reproductive strategies is a good plan for living in a constantly changing environment such as a spring-fed river in a semi-arid urban habitat.
The upper San Marcos River, home to several endangered species, relies on springs of the Edwards Aquifer. In pre-European times, the springs were artesian, shooting water into the air over the free flowing river. Now there are several dams, including the Spring Lake dams that back up enough water to hide this former fountain. Creation of the lake and deeper water levels led to the extirpation of Texas wild-rice here. Two colonies have been reestablished in the shallower areas of the lake. Other dams on the upper San Marcos River have a similar effect, producing deep, sluggish pools where Texas wild-rice cannot grow.
Other changes to the river include habitat modifications such as dams and channelization (for example the concrete walled banks in Sewell Park); invasion by non-native plants and animals, both along the banks and in the river; intense recreation leading to unintentional harassment through trampling and uprooting vegetation; water pollution including abnormal sediment loads; and the most influential change, pumping of the Edwards Aquifer.
Water levels in the San Marcos River and the Edwards Aquifer naturally respond to climate, depending on the amount of precipitation that falls on the watershed. Various factors can modify how much of this precipitation actually gets into the river or aquifer. While high rainfall causes an immediate rise in the river, recharge of the aquifer takes weeks and can be affected by hard surfaces such as rock, pavement, rooftops, etc. that can cause run-off to be too swift to percolate into the aquifer. During drought the levels of the river and the aquifer fall. This is exacerbated by aquifer pumping for urban, industrial, rural, and agricultural needs.
Due to the high number of endangered species in the San Marcos River as well as recreational uses of the river and the necessity to have water continue to flow downstream to the bays and estuaries of the Gulf, there is a need to balance the water requirements of all these species and people. The U.S. Fish and Wildlife Service with the assistance of the Texas Legislature through Senate Bill 3 implemented the Edwards Aquifer Recovery Implementation Program, a group of stakeholders from all affected groups to work together to achieve a solution to the water allocation problem. After almost three years the program has determined the flow requirements for the endangered species, water management that would allow adequate flows for the endangered species survival and increase, and various mitigation measures that would protect the species during times of extreme drought. For Texas wild-rice this would require restoring wild-rice to as much suitable habitat as possible without removing native species, keeping floating mats of vegetation and debris off wild-rice at all times, and developing a recreation plan that would address river access points, safe sites for wild-rice, and ways to route recreational traffic around wild-rice, especially during times of low flow.
We all need to plan ahead for rainy days and have our umbrellas functional and in good repair. But we also need to have good functional umbrellas like Texas wild-rice that protect us and the San Marcos River during times of drought and keep the San Marcos free flowing.
Jackie M. Poole is a botanist with the Wildlife Diversity Program at Texas Parks and Wildlife Department working out of Austin.
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