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

Abstract

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 μg/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.