Effects on ionic composition of blood and tissues ofAnodonta grandis grandis (Bivalvia) of an addition of aluminum and acid to a lake

To test the hypothesis that summer low pH, episodic events cause stress and mortality in aquatic organisms including mussels, alum (aluminum sulfate) was added near the point of inflow to Lake 114 in the Experimental Lakes Area, northwestern Ontario from 3 to 5 July 1984. Lake 114 was at pH 5.9 before the alum addition. The alum produced measured extremes of pH 4.5 and Al] of 2,237 g/L near the point of addition. This study examined the effects of the alum addition on ionic concentrations of blood and tissue (gills, adductor muscle, foot and visceral mass) of the floater mussel,Anodonta grandis grandis. Mussels were collected from a second lake, 377, and introduced into Lake 114 at five locations five days before the alum addition. In response to transfer from the oligotrophic, unmanipulated Lake 377 to acidified Lake 114 (pH 5.9), blood of mussels showed a marked elevation of Ca⁺⁺], decline in Mg⁺⁺] and a temporary increase in Cl^–] but no change in Na⁺], K⁺] or SO₄ ⁼]. During the alum addition, in mussels near the point source of the alum addition, blood Na⁺] and Cl^–] declined and Ca⁺⁺] became still more elevated. Mussels suffered no mortality associated with the alum addition and almost no mortality during 26 days in Lake 114. Gill increased in Al], Ca], Mn], declined in Na] and showed no change in Cd] in mussels near the alum addition. Visceral mass and adductor muscle also had lower Na] in mussels near the point of alum addition. We attribute the increase in blood Ca⁺⁺] to the dissolution of the Ca stores in the shell and/or mantle of mussels. This would provide protection to the mussels during short-term declines in pH such as spring or summer episodic events. Never-theless, chronic exposure to small decreases in pH by mussels, already near the limits for obtaining sufficient Ca⁺⁺, might be intolerable. It follows that acidification to the pH of 5.9 of soft water lakes containing mussels would be expected to lead to the loss of A.g. grandis from these waters.