Acid deposition aquatic systems

Acid deposition and the alteration of the pH of aquatic systems has led to the acidification of lakes and ponds in various locations in the world. Low-pH conditions result in lakes which contain no fish species. 

Land, vegetation, and bodies of water are the surfaces on which acidic deposition accumulates. Bodies of fresh water represent the smallest proportion of the earth s surface area available for acidic deposition. Yet, the best-known effect is acidification of freshwater aquatic systems. 

Eutrophication. Thus far N has been discussed in terms of its prominence as an acidic anion (i.e., as N03 ). As in terrestrial ecosystems, inorganic forms of N also act as nutrients in aquatic systems, and a possible consequence of chronic N loss from watersheds is the fertilization of lakes and streams. Establishing a link between N deposition and the eutrophication of aquatic systems depends on a determination that the productivity of the system is limited by N availability and that N deposition is a major source of N to the system. In many cases the supply of N from deposition is minor when compared to other anthropogenic sources, such as pollution from either point or nonpoint sources. 

Acid rain control will produce significant benefits in terms of lowered surface water acidity. If acidic deposition levels were to remain constant over the next 50 years (tlie time frame used for projection models), the acidification rate of lakes in the Adirondacks that are larger than 10 acres would rise by 50 percent or more. Scientists predict, however, that the decrease in SO emissions required by the Acid Rain Program will significantly reduce acidification due to atmospheric sulfui Without the reductions in SO2 emissions, the proportions of aquatic systems in sensitive ecosystems that are acidic would remain high or dramatically worsen. 

Acids and alkalis. Most freshwater lakes, streams, and ponds have a natural pH in the range of 6 to 8. Acid deposition has many harmful ecological effects when the pH of most aquatic systems falls below 6 and especially below 5. 

The relative neutralization capacity of an aquatic system to acid deposition or acid drainage may be assessed using Table 6.11. 

Effects of acid deposition on life aquatic systems... 

Gilmour C. C. and Henry E. A. (1991) Mercury methylation in aquatic systems affected by acid deposition. Environ. Pollut. 71(2-4), 131-169. 

An important alternate pathway of hydrocarbons to aquatic systems, however, is deposition of airborne particulates including anthropogenic (e.g., soot particles) and natural biogenic (e.g., monoterpenes, difunctional carboxylic acids) aerosols (Simoneit, 1984, 1986 Strachan and Eisenreich, 1988 Baker and Eisenreich, 1990 Eisenreich and Strachan, 1992 Currie et al., 1999). Indeed, the importance of organic... 

The produced sulphuric acid facilitates the solution of Cu in waters and its migration in the form of sulphates or other compounds like organic and inorganic complexes, especially chelates. The migration of Cu in aquatic systems is hindered by the presence of CaC03, by adsorption on hydrous Fe-Mn-oxides, clay minerals and organic substances. In addition to this, the presence of H2S in extreme situations may reduce completely the aureole of waters enriched in Cu around the deposit. 

The loss of fish also puts pressure on other animals higher up the food chain osprey, otters, and other birds and mammals. It has been suggested that the toll of acid deposition on aquatic systems is not best measured by the number or particular kind of species being lost, but by the fact that whole ecosystems are being altered or destroyed, in some cases irrevocably. 

---