Geochemical processes controlling the partitioning of metals between water and sediments / marsh soils in an estuary affected by acid mine drainage leachates

Abstract

All climate change predictions foresee a rise in sea level in the coming decades. Estuaries are environments particularly affected by this change due to their biodiversity. The Estuary of Huelva (SW Iberian Peninsula) is one of the most vulnerable ecosystems on the coastline on a global scale because it represents a transition zone between an acid fluvial environment severely polluted by acid mine drainage and alkaline seawater. Sediments and marsh soils are rich in iron and aluminium precipitates, which are highly reactive due to their nano-particle size. They also act as sinks for numerous pollutants, particularly arsenic. This research focuses its attention on the study of the set of geochemical and mineralogical processes that affect the mobility of metals and the stability of the particulate material under estuarine mixing, especially those processes that would be triggered by a foreseeable rise in sea level. Moreover, this study provides insight into the high contribution of the acid mine drainage discharges to the release of other elements (S, Zn, Cd, Ni and Co) to the coastal areas, as their initial concentrations behaved conservatively in mixing solutions with no participation in sorption processes. Some potentially toxic elements that remain mobile after reaching the estuary, finally end up to the Atlantic Ocean contributing significantly to the total pollutant loads and threatening the environmental conditions of coastal areas. Knowing the stability and mobility of pollutants in the estuarine areas that will be flooded in the next years according to most predictive models of climate change is essential for the design of adaptation strategies and minimization of impacts on the estuarine environment.   Acknowledgements This work was supported by the Spanish Ministry of Science and Innovation under the research project TRAMPA (PID2020-119196RB-C21).