Add lime or similar chemicals: freshwater swamps
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
Background information and definitions
Wetlands can become acidified through processes such as:
- deposition of sulfur dioxide and nitrogen oxides from the air. These originate from a range of man-made sources, e.g. transport exhausts and gas flaring on oil wells (Uyigue & Agho 2007).
- exposure of acid sulfate soils to oxygen, for example through drought, drainage or dredging. These soils are present in coastal wetlands such as mangroves (Dent 1986) and salinized inland areas (Baldwin 2011).
- inflows of acidic waste water from mining operations, for example in the Odiel Marshes, southwest Spain (Davila et al. 2019). This is formed when metal sulfide minerals, exposed during mining, react with oxygen.
Acidity can be reduced with calcium and/or magnesium-rich substances, such as lime CaO or Ca(OH)2, limestone CaCO3, magnesium oxide MgO, fly ash (residue from burning coal) or biochar (a type of charcoal). Adding these chemicals can also affect nutrient availability, because nutrients such as phosphorous become locked away in acidic soils or sediments (Weil & Brady 2016).
Neutralizing chemicals might be added directly to a focal site, added to an adjacent water body, or applied elsewhere in the watershed (which may reduce negative impacts on water quality associated with direct addition; Dorland et al. 2005).
Related actions: Clean waste water before it enters the environment, including diversion of acidified water into designated treatment wetlands; Add lime or similar chemicals to complement planting.
Baldwin D. (2011) National Guidance for the Management of Acid Sulfate Soils in Inland Aquatic Ecosystems, Environment Protection and Heritage Council and the Natural Resource Management Ministerial Council, Australia.
Davila J.M., Sarmiento A.M., Santisteban M., Luís A.T., Fortes J.C., Diaz-Curiel J., Valbuena C. & Grande J.A. (2019) The UNESCO national biosphere reserve (Marismas del Odiel, SW Spain): an area of 18,875 ha affected by mining waste. Environmental Science and Pollution Research, 26, 33594–33606.
Dent D.L. (1986) Acid Sulphate Soils: A Baseline for Research and Development. ILRI Publication 39.
Dorland E., van den Berg L.J.L., Brouwer E., Roelofs J.G.M. & Bobbink R. (2005) Catchment liming to restore degraded, acidified heathlands and moorland pools. Restoration Ecology, 13, 302–311.
Uyigue E. & Agho M. (2007) Coping with Climate Change and Environmental Degradation in the Niger Delta of Southern Nigeria. Community Research and Development Centre Nigeria (CREDC).
Weil R.R. & Brady N.C. (2016) The Nature and Properties of Soils, Fifteenth Edition. Pearson, USA.
Supporting evidence from individual studies
A replicated, controlled, before-and-after study in 1989–1991 of shrubby wetland vegetation around a lake in New York State, USA (Mackun et al. 1994) found that catchment liming had no significant effect on the absolute and relative abundance of most plant taxa. This was true for cover of 48 of 49 plant taxa, frequency of all 49 taxa, and relative abundance of all 49 taxa. Exceptionally, cover of Sphagnum spp. mosses was low and stable in limed areas (before: 1.0%; two years after: 0.9%) compared to a decline, albeit from a much greater value, in unlimed areas (before: 4%; two years later: 2.6%). Methods: In October 1989, pelleted limestone was added by helicopter to two of five subcatchments around Woods Lake (1100 Mg of limestone across 100 ha). The other three subcatchments were not limed. Plant taxa and their cover were surveyed in shrubby wetland vegetation around the lake, in summer before liming (1989) and for two years after (1990, 1991). “No significant effect” in this study means that differences or similarities between limed and unlimed subcatchments before intervention persisted after intervention. Surveys were completed in 52 permanent 1-m2 quadrats (18 in limed marshes; 34 in unlimed marshes). Substrate pH was 4.0–4.2 before liming, then 5.0–6.5 in limed areas and still 4.0–4.2 in unlimed areas.Study and other actions tested