User:Hohl0020/Freshwater acidification

Freshwater vs. Ocean Acidification
The ocean and the atmosphere are constantly exchanging massive amounts of CO2. Over the last 800,000 years, the concentration of CO2 in the atmosphere has remained around 172-300 parts per million by volume (ppmv). With increasing anthropogenic CO2 emissions recently, this number has increased to 387 ppmv in 2009. From 2000-2008, 26% of anthropogenic CO2 was absorbed by the ocean. CO2 is the primary factor affecting ocean pH, though other factors also play a role. When dissolved in water, CO2 acts as a weak acid that primarily affects carbonate chemistry. Dissolved CO2 increases the concentration of bicarbonate ions (HCO3−), dissolved inorganic carbon (CT) and lowers the pH. Similar to oceans, freshwater bodies also absorb atmospheric CO2, lowering the pH. In addition to CO2, freshwater reservoir's pH values are altered by acid rain, nutrient runoff, and anthropogenic pollutants. Freshwater takes up CO2 in the same mechanism as seawater; however, freshwater alkalinity is much lower than seawater, due to the absence of a salt-buffer. Without this salt-buffer, pH changes in freshwater tend to be more evident than in ocean water. In freshwater systems, newly released H+ ions are not buffered by as many bicarbonate (HCO3−) ions as ocean water. Therefore, freshwater biota tends to have a higher evolutionary pH tolerance than seawater biota.

Harmful Effects on Aquatic Ecosystems
Acidification of freshwater ecosystems may have significant negative effects on these ecosystems. Changes in pH as a result of freshwater acidification imposes physiological challenges on individual organisms, may decrease native biodiversity, and can alter ecosystem structure and function entirely. Macro-invertebrates and large vertebrates alike are particularly sensitive to acidification; these species exhibit higher mortality and lower reproductive rates under acidified conditions. These species are forced expend more energy on buffering of their body conditions to retain a livable pH, and therefore must limit energy expenditure on processes such as hunting, sheltering, and reproducing. Embryonic development, and therefore species success, is also compromised in acidified freshwaters. Conversely, algae becomes far more successful in acidified environments, and may quickly dominate these habitats, outcompeting other species.

In most acidic freshwater reservoirs, there will be an increase in the development of mosses and algae. In particular, it is common to see an increase in the abundance of the moss Sphagnum. Sphagnum has a high capacity to exchange H+ for basic cations within freshwater. The thick layer of Sphagnum restricts the exchange between surface water and sediment, further contributing to reduction in nutrient cycling in the ecosystem.