MISSISSIPPI DELTA SHALLOW ALLUVIAL AQUIFER

CLIMATOLOGICAL AND CULTURAL INFLUENCES ON ANNUAL GROUNDWATER DECLINE IDENTIFYING THE CAUSES AND SOLUTIONS

Charles L. Wax, Geosciences; Jonathan Pote, Ag and BioEngineering; Joe Massey, Plant and Soil Sciences, Mississippi State University

The shallow alluvial aquifer is the main source of groundwater in the Mississippi Delta region. It is used for irrigation of crops such as cotton, soybeans, and corn, as well as filling aquaculture ponds in the catfish industry and rice flooding. Water levels vary due to seasonal declines and annual fluctuations caused by climatological and crop water use variations from year-to-year. Some of the declines can be very dramatic and are most prominent during April-October each year when normal crop water demands are accentuated by concurrent abnormally dry climatic conditions. In the past few years, recharge of the aquifer during the remainder of the year has been insufficient to restore water levels. The aquifer is now being mined at the approximate rate of 300,000 acre-feet per year. Not to under-estimate the critical nature of this water problem, the most recent water level decline in the aquifer during October 2005-2006 was estimated at 500,000 acre. While this may be the worse case scenario, it warrants research as to the importance of understanding how climatological variability and cultural uses of the water cause the groundwater level in the aquifer to vary.

Scientists at Mississippi State University received funding through the Mississippi Water Resources Research Institute from a U.S. Geological Survey grant to construct a model for addressing climate changes, cultural uses, and the decline in the alluvial aquifer. The most conservative irrigation method for each crop was used to determine the effects water conservation efforts could have on the aquifer for a 46 year period. For example, 100% of cotton irrigation was assigned to center-pivot irrigation. The result of this type of irrigation is an increase of approximately 3,000,000 acre-feet of water in the aquifer over the entire period, with a consistent increase in water volume throughout time as recharge overcame withdrawal year after year. This particular scenario and its resulting output would be a good example to use when conveying to farmers, producers, other water consumers, and planners the need for conservation practices. If the most consumptive irrigation method was used for each crop, the aquifer would lose approximately 30,000,000 acre-feet of water over the 46-year period by experiencing a consistent annual loss of water volume as more water was withdrawn than recharge could replace.

Scientists also quantified current water use from the delta aquifer by crop, acreage, and irrigation method. A relationship between growing season rainfall and irrigation water use was developed to link interannual variations in water use to variations in rainfall. A complete prototype water use model was completed using acreages, irrigation methods, and management strategies in place during 2006 in Sunflower County to predict annual water demand for cotton, rice, soybeans, corn, and catfish.

The growing season climate data for the last 45-years were used to run the water demand model for a 45-year (2008-2053) period into the future to assess aquifer drawdown and recharge characteristics annually and cumulatively over the long-term period. Changes in acreages of the major crops, specific irrigation methods, and water management strategies were used to create various scenarios, then conduct multiple model runs to assess the effects of the instituted changes on aquifer drawdown and recharge characteristics over the long-term period.

The model has been made interactive, allowing single or multiple changes in land use, irrigation methods, or climate to be reflected in the characteristic responses of the aquifer. The next step in the research is to extend the model from only Sunflower County to the entire Delta region. Proportions of irrigation methods and irrigated acres for each crop type as compiled for Sunflower will be assumed as representative for the entire Delta. Spatial variation in recharge rates will be taken into account as much as possible.

The Mississippi Water Resources Research Institute has been busy this summer planning for the 2009 Mississippi Water Conference to be held August 5-7. For the first time, we are combining the program with Mississippi Water Resources Association, which brings water transportation and intermodal issues to the conference. The three day conference promises to be exciting with a line up of national speakers, 11 technical tracks and numerous extracurricular activities. Held at Harrah's Mid-South Convention Center in Tunica, this will be a water conference you will not want to miss. I hope to see you there.

I am also pleased to announce that Jim Shepard has accepted the position of associate director for the Mississippi Water Resources Research Institute. An alumnus of Mississippi State University; Shepard brings a wealth of water-related experience to the position, serving as forest wetlands program manager for the North-Carolina-based National Council for Air and Stream Improvement. Shepard holds a bachelor's degree in forestry and a doctorate in forest soils from Mississippi State in 1979 and 1985, respectively. He also completed a master's in tree physiology from Purdue University.

USGS Projects

Multi-scale Evaluation and Analysis of Precipitation Patterns Over the Mississippi Delta

Jamie Dyer, Geosciences, Mississippi State University

The Mississippi River floodplain in northwestern Mississippi, often referred to as the Mississippi Delta, is extremely important for regional economic stability and growth due to the widespread agriculture in the area. The region is unique in that there are currently three sources of precipitation measurements available: (1) radar-derived precipitation estimates from National Weather Service NEXRAD network, surface observations from weather service recording stations, and surface observations from US Department of Agriculture Soil Climate Analysis Network recording stations. In terms of water resource management and climatological precipitation research, quantitatively defining the biases associated with available precipitation data sources is critical in choosing which source to use for a given application. Additionally, due to the importance of precipitation in agriculture along with recent drought in the Mississippi Delta region, precipitation patterns should be reevaluated in terms of duration frequency, and extent. The inclusion of long-term data from surface gages along with shorter-term but higher resolution radar-derived rainfall estimates allow for a detailed analysis of past and current precipitation trends. This will lead to a better understanding of rainfall trends and patterns and potentially better prediction of future rainfall.

Water Quality and Floristic Habitat Assessments in the Coldwater River Basin: Comparing Traditional Measures of Water and Habitat Quality to Index of Biotic Integrity Findings

Todd Tietjen, Wildlife and Fisheries; and Gary Ervin, Biological Sciences, Mississippi State University

This project focuses on the wetland habitat and water quality assessments of the Coldwater and Sunflower River Basins of Western Mississippi and the Lower Mississippi Alluvial Valley. Addressed in the research will be Mississippi water research priorities by providing alternative measures of overall water quality and wetland health. Supplemental supporting efforts will be included in order to characterize the fish community included in the project research. The combination of chemical, physical, community, and habitat data from the studies will provide decision makers with a comprehensive approach to criteria establishment.

Natural enhanced transport of agricultural Pb and As through riparian wetlands

Gregg Davidson, Geology and Geological Engineering, University of Mississippi

Riparian wetlands are widely regarded as efficient scavengers of a broad range of contaminants. Confidence in the ability of riparian zones to buffer anthropogenic inputs has derived primarily from studies of active inflow and outflow of chemical-laden water and sediment entering and exiting riparian systems. While studies document short-term scavenging of specific chemicals, they tell little about the permanence of sequestration.A wetland core from Hampton Lake, an oxbow lake in the Delta, was successfully acquired, sectioned and dried. Portions were submitted for 210Pb analysis to determine sedimentation rates. Completion of all analyses for cores from open water and wetland cores is anticipated soon.

Watershed Assessment and Education

Maifan Silitonga, Mississippi River Research Center, Alcorn State University

The Coles Creek Watershed, located in the southwestern quadrant of the state of Mississippi, is listed under the US EPA impaired water section 303(d). Degradation of the ponds/lakes and streams/creeks in this watershed is caused mostly by biological impairment, followed by nutrients, organic enrichment or Low Dissolved Oxygen, sediment/siltation, pesticides, and pathogens. These impairments cause the degradation of water quality thus causing euthrophication or algal bloom that can lead to fish kills and can also adversely affect human health. Community participation is much needed to improve, maintain, and restore the quality of water in this area. Thus, educational materials are necessary to engage the community in protecting the quality of water in this area.

Monitoring and Modeling Water Pollution in Mississippi Lakes

Cristiane Q. Surbeck, Civil Engineering, University of Mississippi

Many important recreational waters, such as lakes and coastal beaches, suffer from fecal pollution. Studies have shown that swimmers become ill or avoid these recreational waters as a result of pollution. This research will take steps towards understanding and preventing fecal pollution in a largely ignored type of recreational waterbody: lakes. The approach to this type of research includes monitoring surface waters and then developing mathematical and statistical models to understand and predict pollution. Research on the water and sediments of the Sardis Lake System (including Lower Lake and a tributary), in Mississippi, will be conducted to understand and mathematically model fate and transport of fecal pollution with the goal of understanding pollution sources to Mississippi lakes.

Should you ever need to find information about any presentation made at the Mississippi Water Resources Conference, it can be found on the Institute’s webpage: www.wrri.msstate.edu. The publications database can be searched by the author’s last name, topic, or year. The database has an archive of articles dating back to the first water conference in 1966.

USGS Investigations on Ground-Water Trends Released in Journal of Environmental Quality

Scientists in the USGS have recently released publications featured in the Journal of Environmental Quality on national and regional trends in ground-water quality in the United States. The release of these investigations, primarily focusing on nitrate, pesticides, and pesticide degradates, marks the first of many trends-studies to follow by the USGS National Water-Quality Assessment Program, which has collected consistent and comparable data for a large number of chemical constituents at wells across the Nation since its inception in 1991.

The program allows for the integration of water chemical data with spatial features—such as land use, geo-chemical conditions, aquifer type, and soils—that may affect quality and the transport and fate of selected chemicals within ground-water systems. Wells included in these investigations represent diverse aquifers, environmental settings, and land uses across the U.S. so that findings can be compared within and among the sampled aquifers and throughout broad regions. In addition, the NAWQA design highlights the role of physical factors controlling water quality, including when the water entered (or "recharged") the ground-water system and the timing and nature of ground-water flow.

Findings highlight national trends over the last 10-15 years, including increasing concentrations of nitrate in ground water in selected aquifers underlying agricultural areas associated with oxygenated conditions and well-drained soils. National analyses also show decreasing trends, overall, in selected agricultural pesticides, such as atrazine. Detailed studies in specific regions of the Nation, however, demonstrate that trends vary geographically and by aquifer, and depend on many factors, including chemical use, aquifer type, age of the ground-water recharge, and geo-chemical conditions.

Reference Material

Whether it's drought, global climate change, ecological impacts, or weather disasters across America, researchers continue to seek answers to hopefully solve issues.

August 5-7, 2009
The 2009 Mississippi Water Resources Conference

September 13-17, 2009
2009 Ground Water Protection Council Annual Forum

November 17-18, 2009
MWRRI Advisory Board meeting at Mississippi State University

Mississippi Water Resources Research Institute (MWRRI)

The institute exists as both a federal and a state research unit. Established in 1964, the MWRRI is one of 54 institutes (one in each state, The District of Columbia, Guam, Puerto Rico, and the Virgin Islands) that form a national network to solve water problems of state, regional, or national significance. In 1983, the Mississippi legislature formally designated the MWRRI as a state research institute. Federal funds designated for the institute are used to consult with state water officials to develop coordinated research, technology transfer and training programs that apply academic expertise to water and related land-use problems. These various activities are funded through an annual grant from the United States Geological Survey (USGS). Mississippi state appropriations provide additional funds for cost share. The institute also assists state agencies in the development of a state water management plan, maintaining a technology transfer program, and serves as a liaison between Mississippi and federal funding agencies.

Discrimination based upon race, ethnicity, religion, gender, national origin, age, disability, or veteran's status is a violation of federal and state law and MSU policy and will not be tolerated. Discrimination based upon sexual orientation or group affiliation is a violation of MSU policy and will not be tolerated.