Abstract: When assessing the origin of salinity and the mechanisms of salinization in coastal aquifers, hydrogeologists may consider the combined use of certain geochemical tools to assess critical aspects of the hydrogeological setting of the system. These tools are based in the integrated use of chemical (major ions, trace elements and ionic ratios) and isotope parameters (oxygen, hydrogen, sulphur, carbon, strontium and boron). The problem of groundwater salinization in coastal aquifers, besides active seawater intrusion, may be affected by several human activities that accelerate the progressive deterioration of water quality, such as concentrated pumping, intensive agricultural practices including return flows or reuse of waste waters from urban or industrial origin. The characterisation of the perating processes and mechanisms of salinization is a requisite for a proper management of groundwater resources and for adopting remediation strategies. In this contribution the potential role of several isotopic tools in these studies is briefly described.

Abstract: It has been suggested in a number of historical notes that it was neither Willem Badon Ghijben nor Alexander Herzberg who formulated the famous principle now carrying their name, which relates the water-table elevation to the depth of the freshwater saltwater interface in coastal aquifers. In this paper, a systematic review of the literature pre-dating the publication of their work is presented. The aim is to establish to what extent these previous works captured the essence of the Ghijben-Herzberg principle, that is, the combination of a correct conceptual model of the hydrogeological conditions with a quantitative relationship. It was found that references to coastal fresh groundwater reserves can be traced back to Roman times, while the earliest detailed descriptions of a freshwater lens that could be found dates from the eighteenth century. The correct understanding of the hydrostatic equilibrium between fresh and salt groundwater is evident in works from the early nineteenth century. However, it was Badon Ghijben and Herzberg who combined this with the correct understanding of the groundwater conditions of a freshwater lens. It was further found that Herzberg had already recorded his findings in 1888 in a hand-written report, confirming speculation that such a report might exist.