3. Mississippi River Flood Plain prior to landscape modifications for agriculture Land Characterization:  Bottomland hardwood wetlands  Annual flooding distributes nutrient-rich matter  Artesian conditions in underlying alluvial aquifer Logged, drained, channelized Levees built Land Characterization: > 80% Agriculture  Row crops  Rice  Aquaculture Primary concerns for sustainability:  Water Quality  Water Availability

4. Arkansas LouisianaMississippi  Agriculture / Irrigation  3 rd most intensively used aquifer in US in 2000  MS 2 nd largest user behind AR 50-150 ft Gravel/Sand Alluvial extent MS Alluvial aquifer Cone of Depression

5.  Irrigation is necessary in the Delta to reach optimum productivity › 28% of annual precipitation › 4 billion gallons per day  Flow in Delta streams is at or near baseflow during the growing season (May-August) › Unknown amount comprised of irrigation return flow The Bogue Phalia (a northwest MS River) at lowest flow in July 2009 Mississippi River Alluvial Aquifer

7. Water-level altitude, in feet above sea level ~1 ft per year decline

9.  Groundwater/Surface-Water Exchange Benefits: › Sustains baseflow in streams › Bank storage dampens overall flood impacts › Streambank stabilization – supplies moisture to riparian vegetation › Temperature regulation for aquatic biota › Supplies nutrients and inorganic ions to stream › Buffer the transport of contaminants through the streambed interface

10. Stream/Aquifer in ConnectionStream/Aquifer not in Connection Losing Stream Gaining Stream -Increased flow in stream -Decreased deposition of fine sediments -NO3 concentrations in stream reduced -Stream recharges alluvial aquifer -Decreased flow in stream -Increased deposition of fine sediments -NO3 concentrations in stream concentrated -What are the affects on recharge? GW dilutes NO3 in stream Anaerobic conditions in aquifer promote denitrification Disconnected Stream

13. Recharge 0.307 Mississippi River 0.011 Bluff Hills 0.052 Underlying Units -0.022 Discharge to wells -2.19 Stream Leakage 0.120 Water-Table Conditions in 2007 How have water-level declines changed the condition of the alluvial aquifer? Mississippi River -0.002 Bluff Hills 0.035 Underlying Units 0.095 Recharge 0.066 Stream Leakage -0.192 Confined Conditions in 1870 (Predevelopment)

15.  Employ existing regional flow model to assess future groundwater supply  Develop water use conservation scenarios that vary in amount and distribution  Assess the effects of amount and location of water use conservation

16. Water- Use Reduction (%) Cone of Depression Area (approx. extent)

20. Study Objective Assess the role of groundwater/surface-water exchange on the transport of nutrients in the northwestern MS Assess the feasibility of monitoring groundwater/surface-water exchange at existing streamgaging locations Near-stream piezometers installed July 2010 near existing stream gages Big Sunflower at Clarksdale Big Sunflower at Sunflower Big Sunflower at Anguilla Pressure Transducer: Head Conductance, and Temperature 41.5’ EastWest ~100’ *not to scale Deck for access during high flow Existing Gage House: Stage, Conductance, and Stream Temperature DCP to relay transducer data

21. Losing Conditions: Groundwater Level < Stream Stage Pressure Transducer: Head Conductance, and Temperature 41.5’ EastWest ~100’ *not to scale Deck for access during high flow Existing Gage House: Stage, Conductance, and Stream Temperature DCP to relay transducer data

22.  Loss of baseflow to streams › Groundwater is pumped into streams to sustain flow - cost $$ and could exacerbate current water situation › During the growing season, irrigation return flow can make up most of the water in streams › Overuse of surface-water for irrigation has resulted in recent fish kills

23.  Increased recharge from the surface › Increases the vulnerability of the aquifer to surface contamination › Recharge is still not sufficient to replace withdrawals

24.  Future concerns over water supply for irrigation › State initiated Conjunctive Water Use task force › Dissension over who actually is part of the problem – within the cone of depression versus outside of the cone of depression › Amount of irrigated acreage increasing each year along with new permits for groundwater and surface-water irrigation