This study focuses on the impact of surface reservoirs (fish ponds) on a multi aquifer coastal system, and the relation between the aquifer and the sea. The study was conducted in an Israeli Mediterranean coastal aquifer, which includes a sandy phreatic unit and two confined calcareous sandstone units. The geological description is based on 52 wells, from which 33 samples were collected for stable isotope analysis and 25 samples for organic and inorganic parameters. Hydraulic head and chemical measurements suggest that there is an hydraulic connection between the fish ponds above the aquifer and the phreatic unit, whereas the connection with the confined units is very limited. The phreatic unit is characterized by a low concentration of oxygen and high concentrations of ammonium and phosphate, while the confined units are characterized by higher oxygen and much lower ammonium and phosphate concentrations. Organic matter fluorescence was found to be a tool to distinguish the contribution of the pond waters, whereby a pond water signature (characterized by proteinaceous (tryptophan-like) and typical humic-matter fluorescence) was found in the phreatic aquifer. The phreatic unit is also isotopically enriched, similar to pond waters, with δ18O of −1‰ and δD of −4.6‰, indicating enhanced evaporation of the pond water before infiltration, whereas there is a depleted isotopic composition in the confined units (δ18O = −4.3‰, δD = −20.4‰), which are also OM-poor. The Phreeqc model was used for quantitative calculation of the effect of pond losses on the different units. The Dissolved Inorganic Nitrogen (DIN) in the upper unit increases downstream from the ponds toward the sea, probably due to organic matter degradation, suggesting contribution of DIN from shallow groundwater flow to the sea. 87Sr/86Sr and Mg/Ca in the brackish and saline groundwater of the lower confined units increase toward seawater value, suggesting that the salinization process in the region is connected to seawater intrusion and not to old brine from the underlying Cretaceous aquitard.
Bibliographical noteFunding Information:
We thank the people from the Geological Survey of Israel for their support: H. Hemo for his help in the field sampling, Iyad Swaed who helped with the drilling and sampling of the new wells, Dina Stiber, Avner Ayalon and Tami Zilberman for the chemical and stable isotope analyses, Nili Almog and Bat-Sheva Cohen from the Graphic Department and Marcelo Rosensaft for his help with the GIS program. We also thank to Keren Rodionov from IOLR for analyzing the nutrient and especially thank Michael Zilberbrand for his help with the PHREEQC program and for useful discussion. We thank Dr. Vincent Post and two anonymous reviewers for their constructive comments which improved the paper significantly. This project was funded by a Water Authority of Israel grant 4500445470 and by a USAID MERC grant M29-073.
© 2017 Elsevier B.V.
- Fish ponds
- Specific dissolve organic mater
- Surface reservoir