The Continued Decline of Sulfur Emissions Into the 1990 s is Likely a Result of

Riders on the storm

Magnus Lindmark , Sevil Acar , in Handbook of Green Economics, 2019

Historical development of emissions

Fig. 8.1 shows the development of the emissions in physical units over the full investigated period.

Figure 8.1. SO₂, NO_x, and carbon emissions in the United States, 1870–2010.

Source: Authors' Own Illustration.

Sulfur emissions increased more rapidly than carbon and NO _x up until the early 1920s. After 1920, sulfur emissions stabilized and remained at this level until the late 1970s. From the late 1970s onward, there is evidence for a historically rapid decline of the sulfur emissions, and at the end of the period, they were down at approximately the same level as in the early 1890s.

Carbon emissions also experienced a rapid increase up to approximately 1920. While sulfur emissions stabilized, carbon emissions continued to increase even though the rate of increase was slower than previously. A second period of the rapid increase of carbon emissions occurred during the period 1960–1973. This period was followed by slightly falling emissions until the early 1980s, after which emissions increased at a comparatively low rate.

NO_x emissions followed a slightly higher growth rate than carbon emissions until the early 1970s, after which the NO_x emissions have fallen, however, at a slower rate than the sulfur emissions.

These emissions therefore represent three different development paths. The different development path of sulfur as compared with carbon reflects that sulfur emissions to a high degree were process-related emissions from the copper industry, meaning that they arose in the production process itself and not only as a consequence of fuel combustion (Schmitz, 2000). The rapid development of sulfur emissions during the early part of the period was, for instance, related to the rapidly increasing demand for copper during the second industrial revolution (Uekötter, 2009). Electrical equipment, in Gordon's phrasing a key innovation of the past, such as wires, generators, and motors were all depending on copper. As the sulfur content of copper ores (copper sulfide) is comparatively high, the smelting process itself caused the release of sulfur with the flue gases. Copper smelters were therefore equipped with high chimneys for diluting the gases and spreading the sulfur downfall over a larger area. Still, the downfall of sulfur in the form of the so-called acid rain caused extensive damage on agricultural land and the death of cattle, which in turn led to lawsuits. Prime examples were the legal processes in Ducktown, Tennessee, which led to the US Supreme Court's first verdict in an air pollution case in 1907 (LeCain, 2009; Maysilles, 2011). An important political outcome was Theodore Roosevelt to establish the Anaconda Smelter Smoke Commission (1911–20), with the directive to suggest measures that the company should undertake to address the smoke issue. Another outcome was the development of electrical scrubbers, which were used to abate the sulfur emissions. The introduction of such technology, along with the legal framework envisaged by the court cases and the Anaconda Smelter Smoke Commission, probably explains the stabilization of sulfur emissions over the period 1920–70.

Carbon emissions were, on the other hand, more or less directly a function of coal and oil combustion, with the exception of process emissions from cement production. These were, however, comparatively small as compared with the combustion of fossil fuels.

NO_x, finally, was mainly caused by chemical processes when air gets in contact with high-temperature metal surfaces in internal combustion engines, including jet engines. Internal combustion engines were, again, a basic innovation of the past which, according to Gordon, drove TFP growth and, thus, economic growth in the period from the 1920s to the 1970s. NO_x emissions were mainly abated through the introduction of catalytic converters in automobile exhaust pipes from approximately the mid-1970s.

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Biogeochemistry

P. Brimblecombe , in Treatise on Geochemistry (Second Edition), 2014

10.14.11.1 Combustion Emissions

Sulfur emissions from the combustion of high sulfur coals have been a problem from the thirteenth century when the fossil fuel began to be used in London after the depletion of nearby wood supplies. The intensity of coal use increased, reaching its peak within the early twentieth century in Europe and North America. Although the use of coal has declined in these areas, the late twentieth century saw a profound increase in coal use in developing countries, most notably in Asia (see Figure 20 ). Here, emissions have continued to grow with the enormous pressures for industrial development, although changing patterns of fuel use here may lead to decreased emissions in the twenty-first century.

Figure 20. Predicted sulfur emissions from anthropogenic sources.

http://sres.ciesin.org.

The combustion of fuels leads to release of SO₂ in a simple but effective oxidation:

$\mathrm{S}+{\mathrm{O}}_{2\left(\mathrm{g}\right)}\to {\mathrm{SO}}_{2\left(\mathrm{g}\right)}$

Many refining and extractive processes release large amounts of air pollution containing SO₂. For example, sulfide ores have been roasted in the past with uncontrolled emissions:

${\mathrm{Ni}}_2{\mathrm{S}}_3+{4\mathrm{O}}_2\to 2\mathrm{NiO}+{3\mathrm{SO}}_2$

This sulfur dioxide often destroyed large tracts of vegetation downwind from smelters, such as those at Sudbury in Canada. However, changes in the processes and the construction of a very tall chimney stack have lessened the problems.

The decline in sulfur emissions in Europe and North America has come as part of a shift away from coal as a fuel in all but extremely large industrial plants. Sulfur in coal is about half as pyrites, which is relatively easy to remove, but the rest is organically bound, which makes it difficult to remove at an economic rate. Improved controls on stack emissions increasingly rely on the treatment of exhaust gases. In the past, this was sometimes by scrubbing the exhaust gas with water to dissolve the SO₂, but the late twentieth century saw a range of well-developed methods. The use of lime (calcium hydroxide) or limestone (calcium carbonate) slurries to absorb sulfur dioxide is widely adopted. The main product, calcium sulfate, is notionally not seen as an environmental problem by-product, although it can be contaminated with trace metals. The process is also hampered by the large amounts of lime that can be required. Regenerative desulfurization processes, such as the Wellman-Lord procedure, absorb SO₂ into sodium sulfite solutions converting them to sodium bisulfite. The SO₂ is later degassed and can be used as a feedstock for the production of sulfuric acid, for example.

Sulfur is also found in petroleum in organic forms. It can occur at high concentration in some residual oils. This sulfur can be removed by catalytic hydrodesulfurization, but it leads to fuels that tend to become waxy at low temperature. In vehicles, catalytic converters have been used to remove nitrogen oxides, carbon monoxide, and hydrocarbons from exhaust streams. However, under fuel-rich driving cycles (i.e., lots of accelerating and decelerating), hydrogen gas is produced in the exhaust. Three-way catalysts containing cerium dioxide store sulfur from the exhaust stream, under driving conditions, as cerium sulfate. This can at other times be reduced by hydrogen gas to form hydrogen sulfide, which creates a noticeable odor, when traffic is heavy (Watts and Roberts, 1999).

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Volcanic Influences on the Carbon, Sulfur, and Halogen Biogeochemical Cycles

Pierre Delmelle , ... Clive Oppenheimer , in The Encyclopedia of Volcanoes (Second Edition), 2015

3.1 Volcanic Sulfur Emission Output

3.1.1 Present-Day Volcanic Activity

Inventories of volcanic sulfur emissions to the atmosphere reveal that a significant proportion of the total volcanic sulfur load at any one time may be attributed to a mere handful of quiescently degassing volcanoes. In recent decades, these have included Ambrym, Vanuatu; Anatahan, Mariana Islands; Bagana, Papua New Guinea; Mt Etna, Italy; Kilauea, Hawaii, United States; Miyakejima, Japan; Nyiragongo, Democratic Republic of Congo; and Popocatepetl, Mexico.

According to Oppenheimer et al. (2011), the total global sulfur flux from all volcanic sources amounts to ∼10.4 Tg a⁻¹ (∼20.8 Tg SO₂ a⁻¹), based on observations made over a 25 year period up to 1997. Averaged on centennial timescales, an estimated 1 Tg of sulfur (2 Tg SO₂) reaches the stratosphere annually. However, such estimates have significant margins of error because of the challenges of arriving at meaningful time-averages for the sporadic but large magnitude releases of SO₂ to the stratosphere from explosive eruptions, and of extrapolating field data for a comparatively small number of observed tropospheric volcanic plumes to the global volcano population. This is reflected in an uncertainty of around a factor of two in the global figure. Nevertheless, the majority of volcanic sulfur output worldwide comes from continuous volcanic degassing.

Another significant source of uncertainty in the global volcanic sulfur source is that estimates are based almost exclusively on observations of SO₂ emissions, which may neglect a potentially substantial contribution from H₂S degassing. The relative proportions of SO₂ and H₂S in volcanic emissions reflect temperature, pressure, and redox conditions in the source magma, although interaction between magmatic gases and a hydrothermal system, or sedimentary country rocks, can modify the composition of emissions reaching the surface. A more recent estimate of the total volcanic sulfur flux to the atmosphere attests to these uncertainties, reaching a figure of ∼9–46 Tg a⁻¹ of sulfur (Oppenheimer et al., 2011). This estimate is comparable to the present-day sulfur output of ∼76 Tg a⁻¹ from anthropogenic activities (Figure 50.4).

Figure 50.4. Diagram depicting volcanic (large igneous provinces, supereruptions, and subaerial activity) and anthropogenic sulfur (S) sources with the area of each circle scaled according to the source emission strength.

Values are taken from Beerling et al. (2007), Oppenheimer et al. (2011), Self and Blake (2008), Self et al. (2006) and Thordarson and Self (1996).

3.1.2 Supereruptions and LIP Eruptions

There are considerable uncertainties in the sulfur emission estimates from ancient supereruptions but values on the order of ∼200 and 1400 Tg of sulfur have been suggested for Yellowstone in the United States (∼2 Ma ago) and Toba, respectively, exceeding by far annual global sulfur emissions (∼9-46 Tg) from present-day volcanoes. The magnitude of sulfur release also appears to depend on the redox state of the magma; a small volume of oxidized magma can give off more sulfur than a larger volume of reduced magma.

Sulfur gas releases from ancient LIP eruptions, which emplaced huge volumes of mafic lavas are also poorly constrained, but detailed petrological studies of the Columbia River, United States (∼15 Ma ago) and Deccan Traps flood basalts reveal that ∼1.8 Tg (∼3.6 Tg SO₂) and ∼3.5 Tg (∼7 Tg SO₂), respectively, of sulfur per cubic kilometer of lava may have been injected into the atmosphere. This translates into enormous total sulfur outputs compared to the background atmospheric sulfur concentration of <1 Tg (Self et al., 2006). An estimated 500 Tg of sulfur (1 Pg SO₂) released per year during LIP eruptions corresponds to an emission rate 10–50 times greater than the present-day annual volcanic sulfur flux. As noted previously for CO₂, the type of crust through which magma intrudes also influences the sulfur output during LIP eruptions, such that contact metamorphism of sulfur-rich evaporites and dolomites may produce sediment-derived SO₂ release several times that of magmatic SO₂.

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Clean Coal Technologies for Advanced Power Generation

Bruce G. Miller , in Clean Coal Engineering Technology, 2011

Sulfur Emissions

An IGCC can readily reduce sulfur emissions to about 4 ppm SO ₂ (wet basis, referred to 1 percent O₂) in the turbine exhaust. This is equivalent to about 30 ppm total sulfur (H₂S + COS) in the dry, undiluted gas leaving the acid gas removal, a value achievable with an MDEA or Selexol system. If a selective catalytic reactor (SCR) is required for Denox, then this would typically need to be reduced to about half this value, which would also be possible with a rather more elaborate version of Selexol. A further two orders of magnitude reduction would be possible using Rectisol instead of the currently used chemical or synthetic fuel applications. This is, however, considered to be unnecessarily expensive.

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BIOGEOCHEMICAL CYCLES | Sulfur Cycle

P. Brimblecombe , in Encyclopedia of Atmospheric Sciences (Second Edition), 2015

Anthropogenic Sulfur Sources

The most pernicious source of human sulfur emissions has been from the combustion of high-sulfur coals. This began in thirteenth-century London with the depletion of nearby wood supplies and increased through the centuries that followed until it reached its peak within the early twentieth century in Europe and North America. In Asia, particularly, emissions have continued to grow with the enormous pressure of industrial development. In the North Atlantic sector there has been a general decline in sulfur emissions with a shift away from coal as a fuel, in all but extremely large industrial plants, as a response to the problems of urban air pollution and acid deposition. It is estimated that in south and eastern Asia more than 10 ⁷ km² of land will be subjected to sulfur deposition greater than 1 g(S) m⁻² year⁻¹ by AD 2020.

Sulfur in coal exists half as pyrites, which is relatively easy to remove, but the rest is organically bound. This makes it hard to remove except by methods such as coal gasification or in stacks after emission. Sulfur can be removed by catalytic hydrodesulfurization from residual oil, but it leads to fuels that tend to become waxy at low temperature.

The combustion of fuels leads to the release of SO₂ in a simple but effective oxidation:

S + O_2(g) → SO_2(g)

Many refining and extractive processes release large amounts of air pollution containing SO₂. For example, sulfide ores have been roasted in the past with uncontrolled emissions:

Ni₂S₃ + 4O₂ → 2NiO + 3SO₂

The SO₂ released often destroyed large tracts of vegetation downwind from smelters.

Various techniques are used to remove sulfur from stack gases. The use of lime (calcium hydroxide) or limestone (calcium carbonate) slurries to absorb SO₂ is widely adopted. The main product, calcium sulfate, is not seen as an environmentally hazardous by-product, although it can be contaminated with trace metals. However, the amounts of lime required can be extremely large. There are often problems where these are mined from attractive sites of great ecological and recreational value. Regenerative desulfurization processes such as the Wellman–Lord procedure absorb SO₂ into sodium sulfite solutions converting them to sodium bisulfite. The SO₂ is later degassed and can be used as a feedstock for the chemical industry (i.e., the production of sulfuric acid).

Catalytic converters in vehicles have been used to remove nitrogen oxides, carbon monoxide, and hydrocarbons from exhaust streams. However, under fuel-rich driving cycles (i.e., lots of accelerating and decelerating), hydrogen gas is produced in the exhaust. Three-way catalysts contain cerium dioxide, which stores sulfur from gasoline under driving conditions as cerium sulfate. Reduction of the cerium sulfate by hydrogen gas allows the formation of H₂S. This can create a noticeable odor, where traffic is heavy.

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Acid Rain and Deposition

George R. Hendrey , in Encyclopedia of Biodiversity, 2001

II.A. SO_x

SO₂ is the principal form of anthropogenic sulfur emission and it is released primarily by combustion of fossil fuels. SO ₂ dissolves in water droplets where it can be oxidized to H₂SO₄. This has a low vapor pressure and tends to form aerosol particles. These aerosols can form salts with Ca²⁺, Mg²⁺, or NH₄ ⁺ and can become nuclei for the condensation of water and formation of clouds.

The residence time of sulfur in the atmosphere is controlled by the processes that deposit it to the ground. About half of the sulfur burden of the atmosphere is removed by dry deposition, although the ratio of dry to wet deposition varies widely.

The total amount of sulfur emitted into Earth's atmosphere in 1985 (the reference year) was 90   Tg (calculated as elemental sulfur, equivalent to 180   Tg of SO₂) from all sources (Fig. 1). By 1990, global anthropogenic emission of sulfur was 85   Tg (170   Tg as SO₂). Emissions of SO₂ in the United States peaked in 1977 at 32   Tg. By 1985, U.S. emissions of SO₂ had declined to 25   Tg (Table I). The largest source of SO₂ is electric power plants, accounting for 69% of U.S. SO₂ emissions. More than 90% of these power plant emissions are from combustion of coal.

Figure 1. Annual sulfur oxide emissions as sulfur on a 1° × 1° latitude/longitude grid (1000   kg/year) (Canadian Global Emissions Interpretation Centre, a joint initiative of Canadian ORTECH Environmental, Inc., and Environment Canada). See also color Plate 1, this volume.

Table I. U.S. Sources of SO₂ and NO _x Emissions to the Atmosphere in 1985 in Tg per Year ^a

Source	SO2	NO a
Electric utilities	14.6	6.15
Nonutility combustion	2.4	2.98
Nonferrous smelters	0.6
Residential/commercial	0.6	0.64
Other industrial processes	2.1	0.63
Transportation	0.8	7.61
Miscellaneous		0.20
Total	21.1	18.21

a

From NAPAP (1990).

Natural sources of sulfur emissions globally contribute as much as 7% of total sulfur emissions. Dimethyl sulfide released from the oceans is oxidized in the atmosphere to sulfate and may account for 60% of these natural emissions. Volcanism (20%), decomposition processes in soils and plants (15%), and coastal wetlands (3%) are other sources. In eastern North America and northern Europe and Britain, natural sources of sulfur emissions are of little importance as sources of SO _x and NO _x , accounting for less than 1% of regional sulfur emissions according to Environmental Protection Agency (EPA) studies.

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Waste Materials in Construction

E.Peris Mora , ... M.V. Borrachero , in Studies in Environmental Science, 1997

3 – Antecedents and History

Enormous investments are required to reduce the sulfur emissions produced from coal power plants. In the United Kingdom, only one company has done the necessary investments to obtain a satisfactory reduction in the emissions of sulphur dioxide; this was accomplished when the factory was a public enterprise. In Spain only a public company ENDESA has decided for cleaner combustion after a hard public opinion struggle against the consequences of air pollution. All this suggests that funds are more easily obtained when political factors are presents.

In the United States, the protection of the environment has been promoted exclusively through the pressure of the social movements in the sixties. The market and the cost of energy has not stopped in the United States the enaction of laws for reducing the pollutant emissions. Title IV of the "Amendment to the Clean Air Act" of 1990 has imposed new limitations to the emission of SO₂ and NO_x from fuel power plants, which must be adapted to new fuels or procedures (Locker, 93; South & Bailey, 95; Barsotti & Kalyonku, 95).

In Japan, desulphuration gypsum has been employed as an alternative material to the traditional chemical plaster since the 70's ( Nagata, 1995 ). The Japanese anti-pollution laws and measures against the emission of sulphur oxides date of 1968; the first desulphuration plants are running since 1972. Other desulphuration facilities were installed between 1972-1977 in 18 central thermal and in 18 metallurgical industries, in addition to in other 13 industries.

In Canada ( Luckevich, 1993 ) desulfogypsum are an alternative to mineral plaster began to be applied in the 80's. The cited author thinks that "… in North America .. there is much to learn from the European and Asian experience insofar as the by-products utilization".

In Europe, during the last years, there has been an important increase in the non-polluting legislation, within in the European Union and in the OECD ( Franz Wirsching, Rolf Hüller & Rainer OlejnikJ, 1994 ). The Residues Directive (91/156/EEC, of 18 March 1991) contains a catalogue with by-products that are defined as: "substances or objects described in the Annex I and that are referred to waste materials". In the OECD Directive (Control of Transborder Residue Movements intended for Recovery: C(92)39) desulphogypsum is considered as a material included in the "green list" (non-dangerous). German legislation, which included initially plasters Fuel Gas Desulphuration (FGD) as residues, now considers it as a "product".

In the Netherlands, lignite power plants equipped with decontamination systems have introduced in the market important quantities of gypsum plaster (400.000 tons, Moonen, 1991 ). As consequence of mineral resources shortage, the Dutch administration favors the research and development of technologies that provide construction materials as recovery products (Winden, Zwan, Zeilmaker 1991).

The experience with desulphogypsum plasters is not extended to all the countries of the European Union. Experimental work with ashes and plasters in Italy, ( Gera, Mancini, Mecchia, Sarrocco & Scheneider 1991 ) appeals to the use of imported desulphogypsum plasters because there are not power plants in this country with systems of desulphuration.

In Sweden (Timm, 1991) 52 million tons of wastes are produced annually. 20 million are recovered, either as energetic material or as by-products. Within those, 500.000 tons are combustion wastes, including plasters. Environmental protection laws do not consider including the products of decontamination of gaseous emissions as dangerous materials, but the "Swedish Environmental Protection Agency" has developed environmental protection procedures, setting very strict limits, mainly to reduce the emissions that had caused the destruction of thousands of small lakes.

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Acid Deposition and Energy Use

Jan Willem Erisman , in Encyclopedia of Energy, 2004

4 Emissions from Energy Use

van Ardenne et al . provide a compilation of global sulfur emissions, mainly based on work by different authors. According to their estimates, anthropogenic contributions are on the order of 75% of the total sulfur emissions, 82% of which is related to energy production and use ( Fig. 3). Anthropogenic emissions exceeded natural emissions as early as 1950. Important natural sources are volcanoes and DMS emissions from the oceans. Fossil fuel use in industry, fuel production in refineries, and electricity generation are the main activities responsible for anthropogenic emissions. According to EMEP (Cooperative Program for Monitoring and Evaluation of Air Pollutants in Europe) studies, the maximum sulfur emissions in western Europe occurred from 1975 to 1980, at a level of 40   million tons of SO₂. The emissions have decreased since then and are currently at a level of approximately 30   million tons of SO₂.

Figure 3. Share of fuel emissions of the total global sulfur and nitrogen emissions of 148.5 Tg SO₂ and 102.2 Tg NO₂. Data from van Ardenne et al. (2001).

On a global scale, NO _x emissions are estimated to be equally divided between anthropogenic and biogenic sources. However, anthropogenic contributions are already much higher than the natural emissions in the Northern Hemisphere. Most natural emissions, through biomass burning, occur in agricultural areas of South America and Africa. In western Europe and the United States, traffic is the main source for NO _x , contributing 50% or more of the total NO _x emissions.

Globally, in 1995 the emissions from fossil fuels contributed 82, 59, and 0.1% to the total emissions of SO₂, NO _x , and NH₃, respectively. The contributions of fuel and other anthropogenic sources to the emissions of the three gases are shown in Fig. 4.

Figure 4. Contribution of different sources to the total anthropogenic emission of SO₂ (top of the figure), NO _x (middle), and NH₃ (bottom).

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Marine Transportation and Energy Use☆

Riley E.J. Schnurr , Tony R. Walker , in Reference Module in Earth Systems and Environmental Sciences, 2019

Conservation Concerns

Like the 2018 IMO policy on cutting greenhouse gas emissions, other directives in the marine transportation sector aim to greatly limit the sulfur emission allowances from international shipping that contribute to acid rain and climate change. For instance, the IMO also moved to reduce the maximum allowed sulfur content in marine fuels from the current 3.5% to 0.5%, starting at the beginning of 2020. Sulfur as a specific GHG is acutely harmful to human health and directly contributes to acidification of agricultural lands, forests, and oceans. In response to this, the IMO has been introducing progressively stringent regulations on sulfur emissions from shipping activities under its MARPOL Convention. However, these drastic changes from the IMO are considered risky given the dramatic changes that need to come from the shipping industry to accommodate ( George and Ghaddar, 2018). These accommodations can either manifest in the form of retrofitting, which would include installation of "scrubbers" that allow ships to continue burning higher sulfur content fuels but that "scrubs" the emissions before being released, or in the form of investments of new shipping technology and innovations that are designed for cleaner power systems.

In addition to GHG and conventional pollutants, marine transportation induces many other environmental concerns, such as underwater noise pollution, wildlife collisions, and can contribute to contamination via ballast or bilge water, oil or material spills, or other waste contaminations (see Taylor and Walker, 2017; Walker et al., 2019). Any increase in trade via marine transportation will also increase these environmental impacts, especially if mitigation or intervention measures are not implemented. Simultaneously, however, we recognize the overall societal reliance on international trade, and therefore, concerns about the ability to balance development and growth with environmental sustainability come into play.

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Lake Restoration

M. Hupfer , S. Hilt , in Encyclopedia of Ecology, 2008

External Measures

External measures include the (1) reduction of emissions, (2) neutralization measures in the catchment, and (3) the treatment of inflows.

The most important way to abate atmogenic acidification is the 'reduction of emissions' of sulfur and nitrogen into the atmosphere. International agreements aim at reducing sulfur emissions by reducing combustion of fossils fuels and using modern technology to minimize emissions. For example, many European countries have agreed on a reduction target for sulfur emissions of 70–80% by the year 2010 relative to 1980. The geogenic acidification due to mining activities can be influenced by reducing the exposure of sulfur-containing minerals (pyrite, marcasite) to atmospheric oxygen. Groundwater for filling the mining lake should be gained from regions where the soil is not, or is only minimally, oxidized. In regions without mining activity, the desiccation of wetlands and changing groundwater levels should be prevented.

'Neutralization in the catchment', achieved, for example, by liming with calcium carbonate, magnesium, or alkali carbonate (e.g., sodium carbonate), is one way to counteract the acidification. An alternative way is to stimulate alkalinity-producing processes such as microbial sulfate reduction and microbial denitrification in the soils of the catchment, provided that sufficient supply of organic substance and N fertilizers can be guaranteed. This can be realized by adding these substances to the recultivated mining waste heaps (e.g., as liquid manure) or by establishing reactive systems with increased decomposition of organic matter (e.g., fish ponds with feeding, constructed wetlands). For mining lakes, a number of measures aim at minimizing the groundwater influx. These include the installation of underground bulkheads, the draining of acidic water from the mining waste heaps, or afforestation, whereby water-bound transport of acid is lowered by evaporation. Another possibility is to fill the mining lake with well-buffered river water to avoid the influx of groundwater. In mining lake areas, the input of acids can also be decreased by the addition of basic materials to the heaps. This measure also introduces P which induces positive feedbacks for alkalinization by increased primary production (see the section titled 'Biological neutralization').

The acid waters can also be neutralized by 'treatment of inflows' in anaerobic systems such as ditches filled with straw bales, constructed wetlands, and anoxic limestone drains.

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