Lake and Stream Sensitivity Explained How aquatic environments respond to acid deposition depends on their sensitivity to acids and the quantity of acids received. Most environments are naturally buffered against acid input by neutralizing materials such as limestone. The soils, bedrock, and vegetation of watersheds largely determine the capacity of aquatic resources to accommodate acid deposition, but other factors play an important role. Acid neutralizing capacity can have its full effect only when the incoming precipitation has sufficient contact time with the neutralizing material. Areas with steep slopes, shallow soils or frozen ground tend to minimize contact time, resulting in incomplete neutralization of water entering lakes and streams.
Additional neutralization is provided by the biota.
For example, algae generate buffering materials during photosynthesis, and microbes living in bottom sediments reduce sulfur compounds to inert forms. Then, small additions of acid cause large changes in pH. Finally, pH drops precipitously and permanently to levels that few aquatic organisms can tolerate. With lower pH, levels of toxic metals leached from the watershed increase, aquatic growth is reduced, and sensitive species ranging from fish to algae disappear. If this occurs in a drinking water supply, metals will dissolve from distribution pipes resulting in high levels of iron, copper, lead and other metals. This report details the organizational effort that permitted maintenance of this ten year effort, the quality control efforts needed to insure that resulting data met scientific standards for quality, and the findings of ten years of extensive monitoring.