Responses of Fish Populations in Lake 223 to 8 years of Experimental Acidification. Can, J. Fish. For geologically young basins in resistant rock, such as Lake Helen in Lassen National Park, acid rain has an immediate effect. Because limited minerals leach from the rock basin, the system lacks buffering. Acid rain might slightly increase the weathering and input of minerals, but its chief impact would be direct lowering of lake pH. Oligotrophic Lakes in general are not well buffered and may be expected to change quickly in response to acid precipitation.
Events can be particularly important.
During the period of snow melt or a single rain with particularly bad atmospheric conditions, pH can be depressed more than usual. This causes stress to organisms and if it happens to coincide with a sensitive population stage, e.g. larval development, it may eliminate species. Accelerated weathering of the basin will liberate metallic ions which may be more toxic than the hydrogen ions. Initially, sensitive species disappear while others become more numerous. In the absence of fish, insects such as Corixids, Notonectids, and Odonates may become abundant, taking over the aquatic predator role.