Geochemistry, isotopic composition (δ18O, δ2H, 87Sr/86Sr, 143Nd/144Nd) in the groundwater of French Guiana as indicators of their origin, interrelations

The current use of untreated river water for drinking purposes by the population of French Guiana has important impacts on public health. Consequently, groundwater is of major importance as a possible alternative drinking water supply to reduce these impacts. Since French Guiana belongs to the Guyana Shield, sustainable water management can be expected to depend increasingly on water from fissured aquifers in hard rocks. Groundwater samples were collected from shallow drill holes in the densely populated coastal area, and deeper wells in the basement (around Cayenne and along the Maroni and Oyapock rivers). This study reports on major and trace elements for which Na+ and Ca2+ excess with regard to Cl reflect the role of water-rock interaction, as well as Sr and Nd isotopes that reflect the role of the different lithologies. δ18O and δD in waters give constraints on the water cycle (recharge and evaporation processes).