GSA Distinguished Lecturer to speak on Impacts of
Land Use Change on Water Resources

by Dr. Bridget R. Scanlon

 

Date: Thursday, January 25, 2007
Time: 4:00 - 5:00 PM
Location: Geology Building 2.324 (Boyd Auditorium)

Lecture Abstract

Most widespread changes in land use and land cover have occurred because of agricultural expansion. In the last 300 years, cultivated cropland has increased almost 70 fold in the U.S. and about 5 fold globally. Total irrigated agriculture has doubled globally in the past 4 decades, and agricultural lands are projected to increase ~20% globally in the next 50 years. Irrigated agriculture accounts for about 70% of global water withdrawals and 90% of global water consumption. What impacts have these land use/land cover changes had on water resources?

This talk will show that measurements of energy status, chemical composition of pore water above the water table (the vadose zone), groundwater levels, and groundwater quality provide an archive of system response to past land use/land cover changes. The presentation will focus on the Texas Southern High Plains, which is one of the largest agricultural areas in the U.S. This region consists of 44% natural rangeland, 44% nonirrigated (rain-fed) agriculture, 11% irrigated agriculture, and 1% other. Although irrigated land use represents only 11% of the area, it accounts for 94% of total water consumption. Cultivation of rangelands has changed the system from discharging through evapotranspiration to recharging. Evidence of discharge (no recharge, upward water movement) under natural rangeland ecosystems includes upward hydraulic-head gradients, high chloride concentrations, and no change in groundwater levels over time. These natural rangelands have been discharging since Pleistocene times (~10,000 to 15,000 yr). Recharge under rain-fed agricultural lands is shown by downward hydraulic-head gradients, high matric potentials, low chloride concentrations, and rising groundwater levels. Groundwater-level rises have ranged from 2 to 23 m and averaged 7 m over a 3,400-km2 area of predominantly rain-fed agriculture during the last few decades, indicating recharge rates from 5 to 50 mm/yr (median 21 mm/yr, 5% of precipitation). Change from discharge to recharge conditions reflects long fallow periods (~7 months/yr) associated with cultivation. Recharge under irrigated agricultural lands is shown by downward hydraulic-head gradients and high matric potentials. Low irrigation rates (0.3 to 0.6 m/yr) in this region result in accumulation of chloride and nitrate in shallow soils that may ultimately cause soil salinization. Large groundwater-level declines (as much as 75 m) under irrigated areas indicate that irrigated agriculture is not sustainable. Thick unsaturated zones under natural rangelands contain a reservoir of salts that are mobilized by recharge caused by cultivation, resulting in degradation of groundwater quality (for example, increased salinity, nitrate, and perchlorate). Results from land use/land cover changes in this region will be compared with those from other regions globally. Although past land-use changes had unintended impacts on the water cycle, a comprehensive understanding of these impacts could be used to alter land use/land cover for better management of water resources. Further increases in water resources may be achieved through expansion of rain-fed agriculture with potentially minimal negative environmental impacts.

Biography

Bridget Scanlon of the Bureau of Economic Geology, University of Texas at Austin (UT), has been selected as the 2007 Birdsall-Dreiss Distinguished Lecturer, sponsored by the GSA Hydrogeology Division. The Bureau of Economic Geology is one of three units within the newly formed Jackson School of Geosciences. Host institutions may select one of two lectures that Dr. Scanlon will present for audiences interested in broad aspects of water resources. The topics are ecological controls on water cycle response to climate variability and impacts of land use and land cover change on water resources.

Dr. Scanlon received a B.S. in Geology at Trinity College, Dublin (Ireland) and completed her M.S. at the University of Alabama, performing karst fieldwork in Ireland. Her Ph.D. at the University of Kentucky (Lexington) involved flow and transport studies in karst. She joined the Bureau of Economic Geology in 1987 and currently holds the position of Senior Research Scientist. At the Bureau she leads a research group whose primary objective is to assess sustainability of water resources, including both quantity and quality, within the context of climate variability and land use/land cover change. Studies integrate physical, chemical, and isotopic analyses and numerical modeling. Much of the research focuses on impacts of climate variability (ENSO) and conversion of natural ecosystems to agriculture on groundwater recharge in semiarid regions. Impacts of natural and anthropogenic sources of contamination, including nitrate and arsenic, on water quality are also addressed in many of the group’s research studies.

Dr. Scanlon has taught Vadose Zone Hydrology in the Departments of Geological Sciences and Environmental and Water Resources Engineering at UT. She has participated in focus groups on global groundwater recharge issues for the International Atomic Energy Agency, as well as serving on National Academy of Science (NAS) committees related to low-level and high-level radioactive waste disposal. Dr. Scanlon currently serves on an NAS committee on Integrated Observations on Hydrologic and Related Sciences.

For more information contact:

Contact: Mark Cloos
Email: cloos@mail.utexas.edu
Phone: 471-4170