Acid deposition recovery

Doka SE, McNicol DK, Mallory ML, Wong I, Mirms CK, Yan ND. 2003. Assessing potential for recovery of biotic richness and indicator species due to changes in acidic deposition and lake pH in five areas of southeastern Canada. Environ Monit Assess 88 53-101. 

Dahlgren R. A., McAvoy D. C., and Driscoll C. T. (1990) Acidification and recovery of a spodisol Bs horizon from acidic deposition. Environ. Sci. Technol. 24, 531-537. 

Mixtures of acetaldehyde and acetic acid may be obtained121 by passing acetylene (2 to 3 volumes) and air (10 volumes) mixed with a large excess of steam over the zinc, copper, nickel, or cadmium salts of vanadic, molybdic, or chromic acids deposited upon a suitable base, such as pumice, at temperatures ranging from 300° to 400° C. For example, yields of 75 to 80 per cent acetaldehyde along with 5 per cent acetic acid have been obtained by using basic zinc vanadate at 380° C. The aldehyde is separated by fractional condensation in a column and the condensed fraction which is poor in aldehyde is utilized to furnish steam for the catalytic treatment of more acetylene. The fractions rich in acetaldehyde serve for the direct recovery of the aldehyde or may be oxidized immediately to acetic acid by passage over a suitable catalyst. In this way, the process may also be applied directly to the preparation of acetic acid from acetylene. 

As a result of a major reduction in the emission of acidifying S and N compounds since the 1970s in Europe (see Section 7.4.5), acid deposition on boreal lakes and their catchments has also strongly declined. Recently, Stendera and Johnson (2008), assessing the recovery of boreal lake ecosystems from acidification, used different indicators (water chemistry, biota), different trophic levels (primary producers and consumers) and different habitats within the lakes (pelagic, benthic) to compare the response of both acidified and reference lakes to the reduction in acid deposition. 

Delay in recovery from acid deposition and threats to stream organisms from increased frequency and magnitude of high-discharge, low-pH events in upland regions of Northern Europe. 

Acid deposition is an on-going, long-term environmental problem with a greater environmental impact than previously projected. Since many ecosystems are now more sensitive to the input of additional acids, their recovery from the adverse affects of acid rain will most likely be delayed. In Acid in the Environment, vjq provide the perspectives of various authors with respect to the lessons learned and future prospects associated with the issue of acid deposition. We use an interdisciplinary approach that combines a discussion of important ecological issues associated with acid deposition with an analysis of domestic and international policies to control the emission of pollutants that cause acid rain. In this context. Acid in the Environ-... 

Acidic deposition results in the accumulation of sulfur and nitrogen in forest soils. As sulfate is released from the soil in response to decreases in emissions and atmospheric deposition of sulfur, it is transported to adjacent streams and lakes (Likens et al. 2000). The recovery of surface waters in response to emission controls has therefore been delayed and will not be complete until the sulfate left by a long legacy of acidic deposition is released from the soil. 

Recovery from acidic deposition involves decreases in emissions resulting from regulatory controls, which in turn lead to reductions in acidic deposi-... 

An analysis of the scientific literature suggests that five thresholds can serve as indicators of chemical recovery (see Table 3.3). If chemical conditions in an ecosystem are above these thresholds, it is unlikely that the ecosystem has been substantially impaired by acidic deposition. Conversely, if chemical conditions are below these thresholds, there is a high likelihood that the ecosystem is vulnerable to acidic deposition. 

Table 3.3. Indicators of chemical recovery from acidic deposition...

Terrestrial recovery is even more difficult to project than aquatic recovery. Given the life span of trees and the delay in the response of soil to decreases in acidic deposition, it is reasonable to suggest that decades will be required for affected trees on sensitive sites to recover once chemical conditions in the soil are restored. Overall, the timing and extent of chemi cal and biological recovery depend on how soon and how significantly emissions that cause acidic deposition are reduced. Moreover, human influences (e.g., land disturbance, introduction of exotic or invasive species), in addition to acidic deposition, can delay biological recovery after chemical recovery has occurred. 

To date, emissions targets set in the United States and Europe have been met or exceeded. There are widespread decreases in surface water concentrations of sulfate and some waters are showing increases in ANC. Nevertheless, data suggest that these targets may not be sufficient to achieve the full recovery of sensitive ecosystems. In order to evaluate the extent to which historic and future emissions reductions will facilitate ecosystem recovery from acidic deposition, it is necessary to use acidification models to project the future relationship between emissions, deposition, and chemical recovery of acid-sensitive forest watersheds (see Box 3.5). 

Long-Term Changes in Boreal Lake and Stream Chemistry Recovery From Acid Deposition and the Role of Climate... 

There are several consistent themes that run through this volume that indicate what we still need to do. One of the highest priorities is to find a more effective way to reduce major sources of acid deposition other than sulfur dioxide. This means reducing emissions of nitrous oxides and ammonia that are derived from dispersed sources (vehicles and farming activities, respectively) and so are more difficult to control. Another theme is that we need to understand and monitor the ecological effects of acid deposition in a wide range of ecosystems, and determine if there are ways to speed their recovery from decades of acid deposition. 

The ores of most importance are fluorspar, CaF2 fluorapatite, Ca (P0 2Fj cryoHte [15096-52-3], Na AlF. Fluorspar is the primary commercial source of fluoiine. Twenty-six percent of the world s high quaHty deposits of fluorspar are ia North America. Most of that is ia Mexico. United States production ia 1987—1991 was 314,500 metric tons, most of which occurred ia the Illinois-Kentucky area. Imported fluorspar ia 1990—1991 represented about 82% of U.S. consumption 31% of U.S. fluorspar imports were from Mexico and 29% from China compared to 66% from Mexico ia the 1973—1978 period. The majority of the fluorine ia the earth s cmst is ia phosphate rock ia the form of fluorapatite which has an average fluorine concentration of 3.5%. Recovery of these fluorine values as by-product fluorosiHcic acid from phosphate production has grown steadily, partially because of environmental requirements (see Phosphoric acid and THE phosphates). 

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