Aluminum Contamination of Groundwater: Spring Melt in Chalk River and Turkey Lakes Watersheds — Preliminary Results

Abstract

Two watersheds with seasonal pH depressions in the groundwater exhibit high aluminum concentrations associated with these acidification events. The watersheds receive similar atmospheric loadings of H+ and SO42− but are covered by different surficial deposits. The aluminum is measured in four fractions by varying the pH and time conditions during analysis. The resulting classes calculated from these fractions are Class a, containing fast-reacting monomeric aluminum, predominantly inorganic Al3+ and hydroxy compounds; Class b, containing fast-reacting complex aluminum species, mainly inorganic F− complexes and simple organic complexes; Class c, containing slow-reacting amorphous and some polymeric aluminum species; and a class containing a residue of unknown aluminum species adding to the total acid-extractable aluminum. There are significant differences in the distribution of the various aluminum species between the two watersheds, both with depth and in the predominant class identified. The generally higher values measured at one watershed are consistent with the lower carbonate content of the overburden. In both locations it appears that the controlling factor is the pH of the groundwater, with all but Class c species increasing with decreasing pH. The difference between the distributions of aluminum species in groundwater and surface water is under investigation to determine the influence of groundwater-bourne aluminum on the surface water into which it flows.

Ionic aluminium concentrations exceed thresholds for aquatic health in Nova Scotian rivers, even during conditions of high dissolved organic carbon and low flow

“…Al in freshwater can exist as inorganic monomers, inorganic polymers, in amorphous and microcrystalline inorganic forms, and in fast reactive or unreactive organic forms (Chew et al, 1988;Driscoll et al, 1980;LaZerte, 1984). While a variety of Al species in circumneutral waters are toxic to fish (Gensemer and Playle, 1999), including precipitated forms (Gensemer et al, 2018), the cationic species of Al (Al i ), such as Al 3+ , Al(OH) 1+ 2 , and Al(OH) 2+ , are considered to be the most labile and toxic to salmonids.…”