Thicketized oak woodlands reduce groundwater recharge

Area of Science:

• Environmental Science
• Hydrology
• Ecology

Background:

• Post Oak Savannas (POS) in Texas are experiencing thicketization due to shrub encroachment and eastern redcedar expansion.
• This phenomenon is significant as much of the POS overlies the Carrizo-Wilcox (CW) aquifer, a vital water resource.
• Understanding land management impacts on groundwater recharge is crucial for water resource sustainability.

Purpose of the Study:

• To evaluate the influence of post oak (Quercus stellata) stand thicketization on deep drainage (DD) in the Post Oak Savannas.
• To quantify groundwater recharge rates under varying vegetation covers within the POS.
• To inform land management strategies aimed at enhancing groundwater recharge.

Main Methods:

• Chloride mass balance was applied to soil cores collected up to 260 cm depth.
• Soil pore water chloride concentrations were measured at multiple depths.
• Soil moisture was continuously monitored at depths of 140-260 cm using a neutron moisture meter across four distinct vegetation types.

Main Results:

• Negligible deep drainage (DD) was observed in thicketized oak woodlands.
• Open sites exhibited significant DD, ranging from 3-18 cm/year.
• Woodland mosaics showed minimal DD (0-1 cm/year), and soil moisture data indicated higher deep drainage fluxes under open areas.

Conclusions:

• Thicketization in Post Oak Savannas substantially reduces groundwater recharge.
• Reduced recharge under dense woodlands has significant implications for regional water budgets.
• Land management practices that maintain open areas can enhance groundwater recharge in these crucial ecosystems.