Acidic deposition ecosystems

Nodvin, S.C., Van Miegroet, H., Lindberg, S.E., Nicholas, N.S. and Johnson, D.W. (1995). Acidic deposition, ecosystem processes, and nitrogen saturation in a high elevation Southern Appalachian watershed. Water, Air, and Soil Pollution, 85, 1647-1652. 

Receptors. The receptor can be a person, animal, plant, material, or ecosystem. The criteria and hazardous air pollutants were so designated because, at sufficient concentrations, they can cause adverse health effects to human receptors. Some of the criteria pollutants also cause damage to plant receptors. An Air QuaUty Criteria Document (12) exists for each criteria pollutant and these documents summarize the most current Hterature concerning the effects of criteria pollutants on human health, animals, vegetation, and materials. The receptors which have generated much concern regarding acid deposition are certain aquatic and forest ecosystems, and there is also some concern that acid deposition adversely affects some materials. 

A variety of models have been developed to study acid deposition. Sulfuric acid is formed relatively slowly in the atmosphere, so its concentrations are beUeved to be more uniform than o2one, especially in and around cities. Also, the impacts are viewed as more regional in nature. This allows an even coarser hori2ontal resolution, on the order of 80 to 100 km, to be used in acid deposition models. Atmospheric models of acid deposition have been used to determine where reductions in sulfur dioxide emissions would be most effective. Many of the ecosystems that are most sensitive to damage from acid deposition are located in the northeastern United States and southeastern Canada. Early acid deposition models helped to estabUsh that sulfuric acid and its precursors are transported over long distances, eg, from the Ohio River Valley to New England (86—88). Models have also been used to show that sulfuric acid deposition is nearly linear in response to changing levels of emissions of sulfur dioxide (89). 

The harmful effects of air pollutants on human beings have been the major reason for efforts to understand and control their sources. During the past two decades, research on acidic deposition on water-based ecosystems has helped to reemphasize the importance of air pollutants in other receptors, such as soil-based ecosystems (1). When discussing the impact of air pollutants on ecosystems, the matter of scale becomes important. We will discuss three examples of elements which interact with air, water, and soil media on different geographic scales. These are the carbon cycle on a global scale, the sulfur cycle on a regional scale, and the fluoride cycle on a local scale. 

One of the major effects of acidic deposition is felt by aquatic ecosystems in mountainous terrain, where considerable precipitation occurs due to orographic lifting. The maximum effect is felt where there is little buffering of the acid by soil or rock structures and where steep lakeshore slopes allow little time for precipitation to remain on the ground surface before entering the lake. Maximum fish kills occur in the early spring due to the "acid shock" of the first meltwater, which releases the pollution accumulated in the winter snowpack. This first melt may be 5-10 times more acidic than rainfall. 

Consider a lake with a smaU watershed in a forest ecosystem. The forest and vegetation can be considered as an acid concentrator. SO2, NO2, and acid aerosol are deposited on vegetation surfaces during dry periods and rainfalls they are washed to the soil floor by low-pH rainwater. Much of the acidity is neutralized by dissolving and mobilizing minerals in the soil. Aluminum, calcium, magnesium, sodium, and potassium are leached from the soil into surface waters. The ability of soils to tolerate acidic deposition is very dependent on the alkalinity of the soil. The soil structure in the... 

The most evident damage from acid depositions is to freshwater lake and stream ecosystems. Acid depositions can lower the pH of the water, with potentially serious consequences for fish, other animal, and plant life. Lakes in areas with soils containing only small amounts of calcium or magnesium carbonates that could help neutralize acidified rain are especially at risk. Few fish species can survive the sudden shifts in pH (and the effects of soluble... 

Ecological Effects studies to determine the nature or extent of air pollution and acid deposition to ecosystems. 

Acid deposition and the associated particulate nitrates and sulfates are implicated in the deterioration of certain sensitive ecosystems, decreased visibility, negative human health effects, and increased degradation of certain stone building materials and cultural resources, especially those made of limestone and marble. Fine particulate nitrate and sulfate particles... 

In many cases estimating the impact of acid deposition on various ecosystems can be a difficult process because acid deposition is only one of many impacts that can effect a response. However, wet and di y acid deposition has been documented as a major factor in the following ecosystem responses. 

The documentation of regional level terrestrial consequences of acid deposition is complicated. For example, forested ecosystems m eastern North America can he influenced by other factors such as high atmospheric ozone concentrations, drought, insect outbreaks and disease, sometimes from non-native sources. However there is a general consensus on some impacts of acidic depositon on both soils and forests m sensitive regions. 

The sensitivity of a region to acidic deposition is related primarily to its capacity to reduce or chemically neutralize acidity. If there is an ability to quickly and effectively return conditions to nearly normal, the effects of the deposition will be minimized and the ecosystem is not considered to be sensitive. However, if there is little or no capacity to reduce the acidity, the ecosystem is highly sensitive and severe damage can occur if the acidic deposition is significant. 

Driscoll CT, Lawrence GB, Bulger AJ, Butler TJ, Cronan CS, Eagar C, Lambert KF, Likens GE, Stoddard JL, Weathers KC. 2001. Acidic deposition in the northeastern U.S. sources and inputs, ecosystems effects, and management strategies. BioScience 51 180-198. 

The critical load concept is intended to achieve the maximum economic benefit from the reduction of pollutant emissions since it takes into account the estimates of differing sensitivity of various ecosystems to acid deposition. Thus, this concept is considered to be an alternative to the more expensive BAT (Best Available Technologies) concept (Posch et al., 1996). Critical load calculations and mapping allow the creation of ecological-economic optimization models with a corresponding assessment of minimum financial investments for achieving maximum environmental protection. 

PROFILE is a biogeochemical model developed specially to calculate the influence of acid depositions on soil as a part of an ecosystem. The sets of chemical and biogeochemical reactions implemented in this model are (1) soil solution equilibrium, (2) mineral weathering, (3) nitrification and (4) nutrient uptake. Other biogeochemical processes affect soil chemistry via boundary conditions. However, there are many important physical soil processes and site conditions such as convective transport of solutes through the soil profile, the almost total absence of radial water flux (down through the soil profile) in mountain soils, the absence of radial runoff from the profile in soils with permafrost, etc., which are not implemented in the model and have to be taken into account in other ways. 

ERA in general is a process, as is EIA (Environmental Impact Assessment), and not the occasional report or document that is published at various steps. The framework for the orderly process, which has been developed for various environmentally sound projects can be applied also for acidification oriented projects and especially for an evaluation of ecosystem sensitivity to acid deposition and critical load calculations. Central management of the process is an essential feature. 

The environmental pathway evaluation considers various routes by which ecosystems could be exposed to acid deposition (Figure 2). 

The Eastern Canadian Acid Rain Program was highly successful at reducing SO2 emissions and sulfate wet deposition in eastern Canada (see Figure 10). Sulfur emissions actually declined more than the desired 50% by 1994, and have continued to decline modestly in the present. These SO2 emissions in the United States have also reduced dramatically, particularly since the implementation of the Canada-United States Air Quality Accord in 1991. This has been especially important to the aquatic and terrestrial ecosystems in eastern Canada, since US emissions are responsible for a large proportion of the acid deposition received in eastern Canada due to transboundary transport. 

Table 4. Percentage of various endpoints contribution to total environmental risk assessment of ecosystem sensitivity to acid deposition in Northern Asia (Bashkin, 1998).

CNcrit, included in the calculation of critical nitrogen leaching, Ni(crit), values, the input of this endpoint parameter into the uncertainty of CL(N) is expressed in a lesser degree. Furthermore, the runoff processes are practically not significant for ecosystems of Luvic Phaeozems, Chernozems and Kashtanozems due to low P PE ratio. During the calculations of CL(N) for ecosystems of North East Asia, the values of critical immobilization and denitrification from N depositions as the endpoints both in relative and absolute meanings played a subordinate role that obviously reflects their minor contribution into uncertainty and sensitivity analysis of the computed output values of ecosystem sensitivity to acidic deposition. 

The critical loads of acid deposition have been mapped for the Chinese ecosystems, as shown in Figure 17. 

Bashkin, V. N., Park, Soon-Ung (Eds.). (1998). Acid Deposition and Ecosystem Sensitivity in East Asia, Nova Science Publishers, Ltd., New York, 427 pp. 

Bashkin, V. N., Kozlov, M. Ya. (1999). Biogeochemical approaches to the assessment of East Asian ecosystem sensitivity to acid deposition. Biogeochemistry, 47, 147-165. 

Bashkin, V. N., Tankanag, A. V. (2001). Assessment of East European ecosystems to acid deposition loading, Problems of Regional Ecology, 4, 15-29. 

Chen, Z. S., Liu, J. C., Cheng, C. Y. (1998). Acid deposition effects on the dynamic of heavy metals in soils and their biological accumulation in the crops and vegetables in Taiwan. In Bashkin, V. N., Park, S-U. (Eds.). Acid Deposition and Ecosystem Sensitivity in East Asia, NovaScience Publishers, USA, pp. 189-228. 

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