Zilberbrand M, Rosenthal E, Shachnai E
Research Division, Hydrological Service of Israel, P.O. Box 6381, 91063 Jerusalem, Israel.
J Contam Hydrol. 2001 Aug;50(3-4):175-208. doi: 10.1016/s0169-7722(01)00118-8.
The coastal city of Tel Aviv was founded at the beginning of the 20th century. The number of its inhabitants and its water consumption increased rapidly. This study analyses a 15-year record (1934-1948) of pre-industrial development of groundwater chemistry in the urban area. Archive data on concentrations of major ions, dissolved gases (CO2 and O2), organic matter, and pH were available for each half-year during the period of 1934-1948. The major factors causing changes in the chemistry of groundwater flowing in three sandy sub-aquifers have been seawater encroachment due to overpumping, and infiltration of effluents from pit-latrine collectors. Influence of these factors decreases with depth. Landward-penetrating seawater passed through clayey coastal sediments, interbedded among sands and calcareous sandstones, and spread into the Kurkar Group aquifer. This has led to exchange of sodium (dominant in seawater) with calcium adsorbed on clay particles, enriching groundwater with calcium. Intensity of cation exchange decreases inland and with depth. Infiltration of pit-latrine effluents has introduced large amounts of ammonium into the unsaturated zone. Its rapid oxidation in unsaturated sediments has caused massive nitrate production, accompanied by pore-water acidification. This process induces dissolution of vadose carbonate, resulting in enrichment of groundwater recharge in calcium. Anthropogenically induced dissolution of calcite in the unsaturated zone has been the major factor for the increase of Ca2+ concentration in groundwater, accounting for about 80% of this increase. In the interface zone, an additional 20% of calcium has been supplied by cation exchange. Owing to pH increase caused by denitrification in the aquifer, Ca(2+)-rich waters supersaturated with calcite could be formed, especially in the capillary fringe of the uppermost sub-aquifer, which could induce calcite precipitation and ultimately lead to the cementation of sandy aquifers. Urban development has caused drastic changes in the gas content in the unsaturated zone and in groundwater. Carbon dioxide was intensively generated by nitrification-denitrification processes, by hydration of urea, to a lesser degree by oxidation of organic matter, and probably by anoxic biodegradation of organics. Between 1934 and 1948, concentrations of CO2 in unsaturated sediment air rose from 3.2% to 7.6%. In the unsaturated zone, oxygen consumption for oxidation of ammonium and organic matter lowered O2 concentrations in sediment air to unusually low values of 3.9-12.9%. Nitrification in the urban unsaturated zone could thus serve as a pump, sucking in atmospheric oxygen at a rate of about 0.3-0.5 g m-2 day-1. The extreme concentrations of CO2 and O2 in unsaturated sediments have been preserved due to production and consumption of gas under conditions of diminishing areas open to the atmosphere, uncovered by buildings and by roads.
沿海城市特拉维夫始建于20世纪初。其居民数量和用水量迅速增加。本研究分析了该城市地区15年（1934 - 1948年）工业化前地下水化学演变记录。可获取1934 - 1948年期间每半年主要离子、溶解气体（二氧化碳和氧气）、有机物浓度及pH值的存档数据。导致三个砂质亚含水层中地下水化学变化的主要因素是过度抽水引起的海水入侵以及化粪池污水的渗入。这些因素的影响随深度而减小。向陆地渗透的海水穿过夹在沙子和钙质砂岩之间的黏性海岸沉积物，扩散到库尔卡组含水层。这导致海水中占主导的钠与吸附在黏土颗粒上的钙发生交换，使地下水中钙含量增加。阳离子交换强度在内陆和随深度降低。化粪池污水的渗入将大量铵引入非饱和带。其在非饱和沉积物中的快速氧化导致大量硝酸盐生成，同时伴有孔隙水酸化。这个过程促使渗流带碳酸盐溶解，导致地下水补给中钙含量增加。人为引起的非饱和带中方解石溶解是地下水中钙离子浓度增加的主要因素，约占增加量的80%。在界面带，另外20%的钙由阳离子交换提供。由于含水层中反硝化作用导致pH值升高，可能形成富含钙离子且方解石过饱和的水体，特别是在最上层亚含水层的毛细边缘，这可能引发方解石沉淀并最终导致砂质含水层胶结。城市发展导致非饱和带和地下水中气体含量发生剧烈变化。二氧化碳由硝化 - 反硝化过程大量产生，由尿素水合作用少量产生，在较小程度上由有机物氧化产生，可能还由有机物的缺氧生物降解产生。1934年至1948年期间，非饱和沉积物空气中二氧化碳浓度从3.2%升至7.6%。在非饱和带，铵和有机物氧化消耗氧气使沉积物空气中氧气浓度降至异常低的3.9 - 12.9%。城市非饱和带中的硝化作用因此可充当一个泵，以约0.3 - 0.5克每平方米每天的速率吸入大气中的氧气。由于在建筑物和道路覆盖导致向大气开放区域减少的条件下气体的产生和消耗，非饱和沉积物中二氧化碳和氧气的极端浓度得以保留。
