Faculty

‘Thicketization’ likely inhibiting water flow into aquifer

Restoring Texas’ Post Oak Savanna ecoregion to reflect its historic native prairies could be a key to sustaining the Carrizo-Wilcox Aquifer.

Scientists from Texas A&M AgriLife Research and the College of Agriculture and Life Sciences are undertaking a project that will shed light on how changes in land use and the encroachment of woody plant thickets are dramatically reducing groundwater recharge. The three-year project is funded by a $750,000 U.S. Department of Agriculture National Institute of Food and Agriculture grant.

Bradford Wilcox, Ph.D., AgriLife Research professor of ecohydrology in the Department of Ecology and Conservation Biology, Bryan-College Station, said the project has broad implications related to water availability and land stewardship in Texas.

Over the past 150 years, native post oak savanna landscapes have been transformed due to numerous factors, including cultivation and subsequent abandonment, altered fire regimes, urbanization and land fragmentation. These changes in land use allowed undesirable plants, such as yaupon and junipers, to invade the understory, creating dense thickets of vegetation—a process described as thicketization.

Preliminary data indicates thicketization could be reducing recharge rates along the Carrizo-Wilcox Aquifer by 100-fold annually, Wilcox said.

“We are relatively confident parts of the recharge area is being dominated by thickets, causing dramatic reductions in recharge from rainfall,” he said. “This project will provide a comprehensive analysis of this phenomena across the Post Oak Savanna ecoregion and provide useful information that can guide long-term land stewardship and restoration efforts to help maintain one of the state’s most precious resources.”

Post Oak Savanna and Carrizo-Wilcox Aquifer study

Wilcox, collaborators Briana Wyatt, Ph.D., soil scientist in the Department of Soil and Crop Sciences; Jason West, Ph.D., plant physiologist, and Sorin Popescu, Ph.D., professor of remote sensing, both in the Department of Ecology and Conservation Biology; and a team of graduate students, including ecohydrology Ph.D. candidate Shishir Basant, will conduct the study. The project is based on Basant’s doctoral dissertation work.

The overarching goal of the project is to identify and quantify the impacts thicketization has had on the Carrizo-Wilcox Aquifer’s ability to capture water from rainfall across its recharge zone.

The Carrizo-Wilcox Aquifer has long been utilized by private well owners, municipalities, agricultural producers and industry. It is the third most important groundwater resource in Texas after the Edwards and the Ogallala aquifers.

Recoverable water storage in the Carrizo-Wilcox Aquifer is estimated to be between 1.3 billion to 3.9 billion acre-feet. An acre-foot is the amount of water needed to cover 1 acre of land with water 1 foot deep, almost 326,000 gallons. By comparison, Toledo Bend, the largest surface-water reservoir in Texas, was designed for a total storage capacity of 4.6 million acre-feet.

The aquifer’s water table has dropped more than 150 feet over the past several decades.

As land-use changes and fragmentation accelerates, Wilcox worries thicketization will worsen unless landowners and policymakers are made aware of its negative impacts.

“I think a lot of landowners have allowed their properties to slip back into what they believe to be the natural state,” he said. “But historically, the Post Oak Savanna ecoregion included vast open grasslands. So, identifying the underlying negatives of these habitat changes in ways that people can relate to, whether it is wildlife or water availability, helps educate and activate change.”

Wilcox said providing data could help guide policies and initiatives by the Texas Legislature and state agencies like the Texas Water Development Board to improve water recharge in the aquifer.

Testing a theory

Wilcox and his team believe the Post Oak Savanna holds particular promise for increasing groundwater recharge because about one-third of the ecoregion overlies the Carrizo-Wilcox recharge zone—a deep sandy formation that allows water to filter into the aquifer.

Recharge rates in the aquifer vary along the aquifer depending on the amount of annual rainfall – with about 0.5 inches every year in South Texas to about 5 inches every year in the piney woods part of the aquifer, Wilcox said. Areas in Northeast Texas have  greater potential for recharge than at the southwestern end of the aquifer.

Wilcox said the team’s theory is that thicketization is preventing water infiltration and percolation into the deeper sediments and the aquifer. Soil core samples collected within the Post Oak Savannah Groundwater Conservation District showed distinct differences in how water moved through open soils compared to the thickets.

Wilcox said impacts of thicketization will vary across the geological and regional gradiant, but he expects to find compelling evidence that invasive woody plants are connected to water table reductions in the aquifer.   

“If our suspicions are correct, the conversion to thicketization could present real implications for the sustainability of the aquifer,” he said. 

Analyzing, quantifying thicketization, water flux

The team will employ a variety of field measurements by taking core samples and using sensing equipment at various locations in the ecoregion. They will analyze and measure the natural give-and-take of water across these landscapes, specifically the aquifer’s recharge capabilities.

Wilcox said a primary location will be the Texas Parks and Wildlife Department-managed Gus Engling Wildlife Management Area north of Palestine. A second heavily monitored location will be in oak forests within the U.S. Forest Service-managed Caddo-L.B.J. Grasslands near Decatur.

Both areas have extensive savanna grasslands that are likely similar to what much of the Post Oak Savanna was prior to settlement. Open savannas at both locations are maintained by frequent fire regimes.

The team will take soil core samples 10 feet deep up to 30 feet deep to analyze atmospheric chloride deposits that reveal how water moves through the soil, Basant said. Atmospheric chloride is deposited with rainfall remains in the soil and moves deeper with water movement along the soil profile. The extent of chloride deposition and accumulation in the soils and deeper sediments indicate how fast or slow the water moves in the soil column.

“Water movement under the thicketized areas is slowed down because of higher transpiration demand by the trees in these areas,” Basant said. “There is a clear and measurable difference between those deposits and open areas where water moves more rapidly through the soil.”

Aside from answering questions related to thicketization’s impact on recharge and how much restoration efforts might enhance water collection, the team will also focus on other valuable data related to the Carrizo-Wilcox Aquifer. These will include what type of rain events drive aquifer recharge, how deeply trees are accessing soil water, evapotranspiration rates by vegetation, and the rate of thicketization over the past four decades. 

Researchers will also be able to scale up results for the entire region using both field and remote-sensing analysis, Basant said. The data can also be applied to modeling for other oak savannas.

“We believe this project will shed light on a solvable problem related to a historically important water resource for the state,” Wilcox said. “What we are doing could impact water and land conservation efforts within the Post Oak Savanna ecoregion and beyond.”

Kirk O. Winemiller, Ph.D., University Distinguished Professor and Interim Department Head in the Department of Ecology and Conservation Biology, Leslie C. Kelso Winemiller, Ph.D., Instructional Associate Professor in the Department of Ecology and Conservation Biology and Carmen Montaña, Ph.D., assistant professor at Stephen F. Austin State University and former Texas A&M University doctoral student coauthored and published “Peacock Bass: Diversity, Ecology and Conservation.”

The book describes the diversity and natural history of the various peacock bass species, including their geographic distributions, evolutionary relationships, ecology, and economic importance.

According to Kirk Winemiller, Ph.D., peacock bass are the most popular sportfish pursued by anglers in tropical freshwaters, and they support important subsistence and commercial fisheries in rivers and lakes in their native South America. However, peacock bass are more than just sportfish. Like other species of the Cichlidae, a large and diverse family of tropical freshwater fishes, peacock bass (species of the genus Cichla) have fascinating reproductive biology that includes aggressive defense of eggs and fry by both parents. 

“Research has revealed that peacock bass in rivers and lakes can exert strong control over prey-fish stocks and thereby have the potential to function as keystone predators affecting aquatic community dynamics,” Kirk Winemiller, PhD, said. “When people introduce peacock bass into waters outside their natural range, they can have a negative impact on fish diversity and ecological processes.”

Peacock bass are also of high value in fish markets, which oftentimes results in overfishing. Ecotourism for peacock bass fishing has emerged as a significant economic component in South America.

This book summarizes all that is currently known about the peacock bass and is essential reading for biologists, fisheries managers, anglers, naturalists, and aquarists interested in these remarkable fish and the diverse tropical rivers they inhabit.

The book can be purchased at most online bookstores, including Amazon, for $106.

Kirk O. Winemiller, PhD, University Distinguished Professor and Interim Department Dead in the Department of Ecology and Conservation Biology, Leslie C. Kelso Winemiller, PhD, Instructional Associate Professor in the Department of Ecology and Conservation Biology and Carmen Montaña, PhD, assistant professor at Stephen F. Austin State University and former Texas A&M University doctoral student coauthored and published “Peacock Bass: Diversity, Ecology and Conservation.”

The book describes the diversity and natural history of the various peacock bass species, including their geographic distributions, evolutionary relationships, ecology, and economic importance.

According to Kirk Winemiller, PhD, peacock bass are the most popular sportfish pursued by anglers in tropical freshwaters, and they support important subsistence and commercial fisheries in rivers and lakes in their native South America. However, peacock bass are more than just sportfish. Like other species of the Cichlidae, a large and diverse family of tropical freshwater fishes, peacock bass (species of the genus Cichla) have fascinating reproductive biology that includes aggressive defense of eggs and fry by both parents. 

“Research has revealed that peacock bass in rivers and lakes can exert strong control over prey-fish stocks and thereby have the potential to function as keystone predators affecting aquatic community dynamics,” Kirk Winemiller, PhD, said. “When people introduce peacock bass into waters outside their natural range, they can have a negative impact on fish diversity and ecological processes.”

Peacock bass are also of high value in fish markets, which oftentimes results in overfishing. Ecotourism for peacock bass fishing has emerged as a significant economic component in South America.

This book summarizes all that is currently known about the peacock bass and is essential reading for biologists, fisheries managers, anglers, naturalists, and aquarists interested in these remarkable fish and the diverse tropical rivers they inhabit.

The book can be purchased at most online bookstores, including Amazon, for $106.

Research model featured on Developmental Dynamics cover

A recently published paper by Kevin Conway, Ph.D., Associate Professor and Curator of Ichthyology, highlights the Danionella vertebrate model as an important resource for brain and nervous system research.

Species of Danionella, small freshwater fish, are among the smallest vertebrates in the world. The miniature size of Danionella is in part due to extreme cases of progenesis, a term used to describe development being cut short by early onset maturity.

Over time, progenesis has affected the skeleton of Danionella, resulting in the absence of 60 skeletal elements, including some of the roofing bones of the skull. The lack of a skull roof in Danionella combined with presence of a fully formed hearing and sound producing apparatus makes these organisms a useful model in neurophysiological studies.

Developmental Dynamics, a peer-reviewed scientific journal of developmental biology and one of three official journals of the American Association of Anatomists, featured Conway’s emerging vertebrate model of Danionella on the April 2021 cover.

Texas A&M Professors recognized for research contributions

Thomas Boutton, Ph.D., and Bradford Wilcox, Ph.D., were both recognized as 2021 Ecology Society of America (ESA) Fellows.

ESA Fellows are honored for their outstanding contributions to research in fields that advance or apply ecological knowledge in academics, government, non-profit organizations, and society.

Thomas Boutton, Ph.D., Regents Professor and Sid Kyle Endowed Chair in Biogeochemistry, was elected for outstanding scholarly contributions that have advanced understanding of the structure and function of grassland and savanna ecosystems, and for revealing how land cover and land-use changes in those systems have modified key biogeochemical processes in the carbon, nitrogen and phosphorus cycles at multiple scales.

Bradford Wilcox, Ph.D., Sid Kyle Endowed Professor in Arid and Semi-Arid Land Ecohydrology, was elected for his research elucidating causes and consequences of vegetation change on the ecohydrology of savannas and woodlands, including field studies conducted in North, Central and South America that have provided a deeper understanding of hydrological and other ecosystem changes during woody plant encroachment in semiarid regions.

To learn more about the ESA and its Fellows program, read the 2021 press release announcement.