Dissertation Archive, WMU Graduate College

Dissertation Defense

Candidate: Ahmed A. Murad

Degree of: Doctor of Philosophy

Department: Geosciences

Title: CHEMICAL AND ISOTOPIC INVESTIGATION OF GROUNDWATER IN EASTERN UNITED ARAB EMIRATES (UAE)

Date: Friday, March 12, 2004, 3:00 pm - 5:00 pm
1122 Rood

Committee:Dr. R.V. Krishnamurthy, Chair
Dr. Carla Koretsky
Dr. Alan Kehew
Dr. Eliot Atekwana

Abstract: UAE is located at the southeast of the Arabian Peninsula. Two main aquifers occupy the study area: the Eastern Gravel Plain aquifer that occurs near the coastal area, and the inland Ophiolite aquifer. Increasing salinity of groundwater and depletion of aquifers are a major concern in the UAE. Previous studies suggest that groundwater, particularly in the Eastern Gravel Plain aquifer, is affected by seawater intrusion and evaporation. Isotopes, namely oxygen, hydrogen, carbon and chlorine, and chemical analyses were used to investigate this problem in detail. Samples of groundwater from the Eastern Gravel Plain aquifer (Cl >1000 mg/l) have R36Cl values in the range of 13.3 to 17.4 x 10-15 while those from the Ophiolite aquifer (Cl <517 mg/dl) have R36Cl values in the range of 20 to 118 x 10-15. These values indicate the presence of bomb-produced 36Cl and are consistent with recent (post 1950) recharge of most of the samples.

dD - d18O relationship plots on a typical evaporation line, which suggests potential primary and secondary evaporation of the recharging waters prior to infiltration. Decreased deuterium excess may be attributed to the secondary evaporation such as return flow and evapotranspiration in unsaturated zone. The slope of 4 and the y-intercept of 4.4 also suggest that the evapotranspiration of return flow is significant in the study area. This argument is also supported by a positive correlation between potassium and nitrate in Eastern Gravel Plain aquifer which suggests that the salinity of this aquifer could be from irrigation water. The R36Cl values of the coastally bound Eastern Gravel Plain aquifer are lower than the Ophiolite aquifer. Seawater intrusion is absent or minimal based on oxygen-hydrogen isotopes, R36Cl and Cl/Br ratio. Measurements of bromide concentrations support the contention that originally bound Cl is being released into this environment. Agricultural practices, which are extensive in this region, are a possible source.

Samples of groundwater from Eastern Gravel Plain aquifer have d13C and DIC values in the range of -10 to -170/00 and 12 to 100 mg C/l respectively. While samples from Ophiolite aquifer have d13C and DIC values in the range -11 to -16.40/00 and 16 to 114 mg C/l respectively. The calculated d13C of CO2 source ranges from -17.5 to -23.30/00 and -13 to -23.20/00 with an average of -10.4 to -18.10/00 for Eastern Gravel Plain and Ophiolite aquifers respectively. This suggests that the control on DIC is via soil cover vegetated by C-3 and C-4 plants.

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