Acidic Deposition: Sources and Effects

Abstract

Acidic deposition delivers acids and acidifying compounds to the Earth's surface, which are then transported through soil, vegetation, and surface waters and, in turn, set off a cascade of adverse ecological effects. Acidic deposition has altered forest soil by accelerating the leaching of available base cations, enhancing the accumulation of sulfur and nitrogen, and increasing the concentration of dissolved inorganic aluminum in soil waters. Soils that are compromised by acidic deposition are less able to neutralize additional amounts of acidic deposition, and provide poorer growing conditions for plants. Acidic deposition has impaired the surface water quality by lowering pH, decreasing acid‐neutralizing capacity ( ANC ), and increasing concentrations of dissolved inorganic aluminum. These changes have reduced the species diversity and abundance of aquatic life. Regulatory controls initiated in Europe and North America over the last three decades have decreased emissions of sulfur dioxide and to a lesser extent nitrogen oxides. Emission reductions have resulted in widespread decreases in concentrations of sulfate in surface waters, with some waters showing an increase in ANC. Given the loss of acid‐neutralizing base cations and the accumulation of sulfur and nitrogen in soil, many ecosystems have become more sensitive to additional acidic deposition and recovery will likely be delayed. Long‐term research shows that deeper emissions cuts will lead to greater and faster recovery from acidic deposition in impacted regions.

Chemical weathering of a marine terrace chronosequence, Santa Cruz, California. Part II: Solute profiles, gradients and the comparisons of contemporary and long-term weathering rates

“…An additional possibility, to be addressed in more detail in a subsequent Santa Cruz paper, is that the exchange reservoir is currently in the process of slowing re-equilibrating from different past environmental conditions, analogous to that projected for long-term soil base cation recover from acid precipitation (Driscoll et al, 2005). In the case of Santa Cruz, exchange disequilibrium may be driven by changes in the intensity and depth of mineral nutrient cycling caused by a past transition from a forest to a present day grassland ecosystem, as implied by Holocene pollen records near Santa Cruz (Adam et al, 1981).…”

Biogenic and pedogenic controls on Si distributions and cycling in grasslands of the Santa Cruz soil chronosequence, California

“…Soluble Si, found in streams, groundwater and soil pore waters, partly reflect the net product of the weathering of thermodynamically unstable, Si-enriched primary silicate minerals and the concurrent formation of Si-depleted secondary pedogenic phases such as clays (Garrels, 1967). The mechanism and reaction rates associated with weathering, a focus of intensive research over the last several decades (see reviews in Brantley et al, 2007), have direct applications to buffering acid precipitation, long-term atmospheric CO 2 drawdown and climate change (Walker et al, 1981;White and Blum, 1995;Berner and Berner, 1997;Driscoll et al, 2005). Terrestrial biogenic silica is produced when soluble Si is extracted from soils by biopumping of plants and transformed into opaline silica principally as phytoliths (Epstein, 1999;Sparks et al, 2011).…”

Identifying streamflow sources during spring snowmelt using water chemistry and isotopic composition in semi-arid mountain streams

“…For example, increased discharge commonly correlates to decreased total dissolved solids (Durum, 1953;Hem, 1948). But processes related to microorganisms and plants that affect concentrations of nutrients in humid region streams (Drever, 1994;Soulsby et al, 2002) and preferential leaching of strong acids from atmospheric acid deposition in snowpack (Driscoll et al, 2005;Hall et al, 2002;Siegel, 1979) should not be as prevalent at Red Canyon as in eastern watersheds because Red Canyon Creek does not have strong atmospheric acid deposition or humic soil development. Thus, studying the response of dissolved solids to changing hydrologic conditions of Red Canyon Creek affords the opportunity to address how isotopic and solute concentrations change without these confounding variables.…”