hydrogeochemistry

Hydrogeochemistry is the science that studies the chemical characteristics of groundwater and surface waters and the chemical processes that control the distribution and evolution of dissolved substances. It integrates geology, hydrology, chemistry, and geochemistry to understand water‑rock interactions, the transport of dissolved species, and the development of water quality in aquifers and watersheds.

Key processes in hydrogeochemistry include dissolution and weathering of minerals, precipitation and secondary mineral formation, ion exchange on clays and oxides, redox reactions and microbial activity that alter oxidation state and solute composition, gas exchange with the atmosphere, and complexation with inorganic and organic ligands. These processes shape the concentrations of major ions, trace elements, and dissolved gases in freshwater systems.

Data collection and interpretation rely on field measurements (temperature, pH, electrical conductivity, dissolved oxygen, redox potential) and laboratory analyses for major ions (calcium, magnesium, sodium, potassium, bicarbonate, carbonate, sulfate, chloride), silica, alkalinity, and trace elements. Isotopic and age-dating techniques (stable isotopes such as 18O and 2H; carbon isotopes; tritium and radiocarbon) help identify recharge sources, flow paths, and groundwater ages. Geochemical modeling and diagnostic tools—saturation indices, mineral stability, speciation calculations, and mixing analyses—are used to interpret observations and predict system behavior, often with software like PHREEQC and hydrogeochemical plots.

Applications of hydrogeochemistry include groundwater quality assessment, aquifer characterization, resource management, contaminant fate and transport studies, and investigations of geothermal and hydrothermal systems. Interpretations must consider spatial and temporal variability, sampling biases, non‑equilibrium conditions, and incomplete mineralogical knowledge.