Air pollution and freshwater ecosystems : sampling, analysis, and quality assurance

Air pollution adversely affects lakes and streams (collectively called surface waters) and their watersheds throughout the developed world. Some of the most widely studied air pollutants that affect freshwaters include acid precursors such as sulfur (S) and nitrogen (N); nutrients (mainly N); and toxics such as mercury (Hg), pesticides, and combustion by-products. These pollutants can have an impact on water quality and harm sensitive species of aquatic biota. They also alter the chemistry of watershed soils, with potential impacts on plant roots and other terrestrial life-forms. Scientists study freshwater to improve understanding of processes that govern the biogeochemistry of the entire landscape, not just the aquatic portions of it. The chemistry of drainage water integrates a host of terrestrial and aquatic processes, including acidification, nutrient cycling, and bioaccumulation of toxic substances. These processes interact with water as it moves from the atmosphere as precipitation through the soil and into the groundwater and eventually to streams, lakes, rivers, and estuaries.