A diverse ecosystem response to volcanic aerosols

Unexpectedly high aluminium concentrations beside fluoride and essential elements are released from metal salts adsorbed to volcanic ash. Through simulation of the mixing of pristine volcanic ash leachate with fresh water and seawater using PHREEQC, we found an increased potential toxicity in fresh waters through the combination of high aluminium and fluoride concentrations. Owing to the mixing of acid ash leachate with fresh water, aluminofluoride complexes (AlF_x^{+ 3-x}) persist in aqueous systems with low turnover rates, and could be toxic to both plants and animals. In contrast, due to the well-buffered and relatively high pH in seawater, the speciation of the ash leachate/seawater mixture shows that complexes of fluoride and aluminium (i.e. AlF_x^{+ 3-x}) will not dominate in a well-mixed marine system; instead, Al(OH)_x^{+ 3-x} species will occur at greatest concentration. Consequently, compared with fresh water environments, the mixing of ash leachate with seawater indicates reduced toxic effects due to decreased formation of AlF_x^{+ 3-x} complexes and the low solubility of Al-hydroxides. In addition, the deposition of volcanic aerosols may enhance biological activity in the marine environment by providing micronutrients as some oceanic phytoplankton species tolerates extreme concentrations of fluoride (F).