Mercury Content in Volcanic Soils of Isla Santa Cruz (Galápagos, Ecuador)

Mercury is closely associated with volcanic environments such as Islas Galápagos. Isla Santa Cruz, one of the oldest Galápagos islands, has undergone intense land-use transformations that have likely affected mercury cycling. A pre-transformation mercury baseline is approached here with a unique collection of 40 soil profiles (114 samples) collected in 1962 during the geopedological survey performed by researchers at Ghent University (Belgium). The influence of soil properties and bioclimatic conditions is assessed by combining mercury analysis, vibrational spectroscopy, elemental analyses (Fe), and chemical weathering data, using covariation analysis and structural equation modeling (SEM). In the 1960s, Isla Santa Cruz soils were enriched in mercury (36–679 ng g−1) with concentrations in line with those of other volcanic soils, but no differences between topsoils and subsoils were found. Mercury content correlated with soil components (organic matter, Fe) and degree of chemical weathering. The SEM model (R2 0.87, SRMR 0.09) indicated that primary minerals (negative) and altitude (positive) have the largest controls, suggesting that bioclimatic conditions and mineral weathering drive the mercury spatial distribution. Our results establish a reference state for Isla Santa Cruz, and additional research may help to understand the potential impacts of land-use changes on the mercury cycle in the island.