How Thicketization within the Post-Oak Savannah Ecoregion Affects Baseflow and Groundwater Throughout the Carrizo-Wilcoxs Aquifer

Abstract

Availability of surface and groundwater in the Post-Oak Savannah ecoregion of Texas is critical for local agriculture, municipal use, and energy production. However, woody-plant encroachment or 'thicketization' in this region is suspected to be a source of reduced groundwater recharge to the Canizo-Wilcox Aquifer and may also affect local baseflow volumes. To test this hypothesis, I examined the changes in woody landcover in Texas watersheds since the 1950s using U.S. Geological Survey (USGS) Historical Topographic Maps and the National Land Cover Dataset (NLCD) to compare any changes to local baseflow volumes (90% flow duration) and zero-flow exceedance percentages (percentage of time streamflow exceeds zero-flow) from USGS streamflow data across the Canizo-Wilcox Aquifer. I discovered substantial evidence suggesting a positive correlation (p = 0.0133) between thicketization and baseflow within the dataset, with a 2% increase in baseflow anomaly for every 1 % increase in wooded area density anomaly. I also found that increased baseflow reflects an increase in depth to groundwater table (p = 0.005). These results suggest that thicketization increases local baseflow volumes, resulting in a lower the groundwater table. Although I hypothesized thicketization reduced baseflow and reduced groundwater recharge, the data suggest that there is a strong relationship between wooded landcover and local baseflow affecting groundwater recharge. Further research has the potential to reveal the mechanism behind thicketization's effect on baseflow's contribution to groundwater recharge.