Acidification of lakes and streams

Since SO2 and NO2 are criteria pollutants, their emissions are regulated. In addition, for the purposes of abating acid deposition in the United States, the 1990 Clean Air Act Amendments require that nationwide SO2 and NO emissions be reduced by approximately 10 million and 2 million t/yr, respectively, by the year 2000. Reasons for these reductions are based on concerns which include acidification of lakes and streams, acidification of poorly buffered soils, and acid damage to materials. An additional major concern is that acid deposition is contributing to the die-back of forests at high elevations in the eastern United States and in Europe. 

Nr is responsible (together with sulfur) for the acidification and loss in biodiversity of lakes and streams in many regions of the world (Vitousek et al., 1997). 

The hydrology and chemistry of lakes and streams are highly individualistic. Lakes surrounded by poorly buffered soil and underlain by granitic bedrock appear to be more susceptible to acidification when exposed to acid rain (Havas et al. 1984). Other lake characteristics such as dominance of atmospheric input or surface/subsurface runoff as the major source of water, type and depth of soil, bedrock characteristics, lake size and depth, area of the drainage basin, and residence time of water in the lake are all features that influence the response of a lake to acid rain. 

There are many ways the acidification of lakes, rivers and streams harm fish. Mass fish mortalities occur (during the spring snow melt) when highly acidic pollutants— that have built up in the snow over the winter—begin to drain into common waterways. Such happenings have been well documented for salmon and trout in Norway. 

The need to determine accurately the phase-specific concentrations of these pollutants reflects several concerns Compared to gaseous materials, particle-phase materials may penetrate more deeply into the human respiratory tract particle-phase pollutants scatter light much more effectively than gaseous materials, and they thus have a greater contribution to visibility reduction gaseous nitric acid has a much higher deposition velocity than particulate nitrates and can be a substantial contributor to the acidification of lakes, streams, forests, and vegetation. 

Acid rain primarily affects sensitive bodies of water, that is, those that rest atop soil with a limited ability to neutralize acidic compounds (called buffering capacity ). Many lakes and streams examined in a National Surface Water Survey (NSWS) suffer from chronic acidity, a condition m which water lias a constant low (acidic) pH level. The survey investigated tlie effects of acidic deposition in over 1,000 lakes larger than 10 acres and in thousands of miles of streams believed to be sensitive to acidification. Of the lakes and streams surveyed in the NSWS, arid rain has been determined to cause acidity in 75 percent of the acidic lakes and about 50 percent of tlie acidic streams. Several regions in the U.S. were identified as containing many of the surface waters sensitive to acidification. They include, but are not limited to, the Adirondacks. the mid-Appalachian highlands, the upper Midwest, and the high elevation West. 

In some sensitive lakes and streams, acidification has completely eradicated fish species, such as the brook trout, leaving these bodies of water barren. In feet, hundreds of the lakes in the Adirondacks surveyed in the NSWS have aridity levels indicative of chemical conditions unsuitable for the survival of sensitive fish species. 

The acidification problem in both the United States and Canada grows in magnitude if episodic acidification (brief periods of low pH levels from snowmelt or heavy downpours) is taken into account. Lakes and streams throughout the United States, including high-elevation western lakes, are sensitive to episodic acidification. In the Mid-Appalachians, the Mid-Atlantic Coastal Plain, and the Adirondack Mountains, many additional lakes and streams become temporarily acidic during storms and snowmelt. Episodic acidification can cause large-scale fish kills. ... 

Numerous experiments have been conducted to understand the chemical linkages between atmospheric deposition of acidic compounds and acidification of soils, lakes, and streams. Experiments have included additions of acid, exclusion of acids, and the application of limestone (CaC03) or other acid neutralizing compounds to add ANC directly to surface water or sods. Many of the studies are discussed in Dise and Wright (1992), Rasmussen et al. (1993), and Jenkins et al. (1995). We highlight a few studies here. 

The many spatial and temporal lake and stream surveys conducted in many countries plus experiments have demonstrated the linkages between the emissions of acidic compounds to the atmosphere and terrestrial and aquatic acidification. Mandated and implemented reductions in air pollution in North America and Europe have occurred since the 1980s. The long-term experiment of ecosystem acidification from air pollution is seeing a reduction of the dose. 

The ability of forests to withstand acid rain depends on the capacity of the soil to neutralize the inputting acidity. This is largely determined by local geology, in much the same way that it affects the acidification of lakes. Acidification is mainly a problem in areas where the underlying rocks provide poor buffering capacity. Rocks such as granite offer little buffering protection. Chalk and limestone neutralize added acid, and so soils, lakes and streams in limestone areas are fairly insensitive to acidic precipitation. 

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