Add lime or similar chemicals: freshwater marshes

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

25%
Certainty

20%
Harms

0%

Calculating overall effectiveness category

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.}

Study locations

Key messages

One study evaluated the effects, on vegetation, of adding neutralizing chemicals to freshwater marshes or their catchments. The study was in the USA.

VEGETATION COMMUNITY

Relative abundance (1 study): One replicated, controlled, before-and-after study of marsh vegetation in the USA found that liming had little effect on the relative abundance of plant taxa. For 48 of 49 taxa, differences or similarities in relative abundance between limed and unlimed areas before intervention persisted over two years after intervention.

VEGETATION ABUNDANCE

Individual species abundance (1 study): One replicated, controlled, before-and-after study of marsh vegetation in the USA found that for most plant taxa, differences or similarities in abundance between limed and unlimed areas before intervention persisted over two years following intervention. This was true for 33 of 38 herbaceous plant taxa, eight of eight woody plant taxa, and two of three moss taxa.

VEGETATION STRUCTURE

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated, controlled, before-and-after study in 1989–1991 of marsh 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 45 of 49 plant taxa, frequency of 48 of 49 taxa, and relative abundance of 48 of 49 taxa. Liming increased cover of one taxon, sawtooth sedge Cladium mariscus (before intervention: 1–2% cover; limed areas after two years: 6% cover; unlimed areas after two years: 1% cover). Liming reduced, or prevented increases in, cover of two taxa (sundew Drosera intermedia, bog muhly Muhlenbergia uniflora) and frequency of one (lesser St. John’s wort Hypericum canadense; see original paper for data). Cover of one taxon – inland sedge Carex interior – was low and stable in limed areas (before: 0.3%; two years after: 0.2%) but declined, albeit from much greater values, in unlimed areas (before: 1.4%; two years later: 0.3%). Methods: In October 1989, pelleted limestone was added by helicopter to two of five subcatchments around Woods Lake (1,100 Mg of limestone across 100 ha). The other three subcatchments were not limed. Plant taxa and their cover were surveyed in marshes 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 50 permanent 1-m² quadrats (21 in limed marshes; 29 in unlimed marshes). Substrate pH was 4.5 before liming, then 6.6 in limed areas and 5.0 in unlimed areas.
Study and other actions tested
Referenced paper
Mackun I.R., Leopold D.J. & Raynal D.J. (1994) Short-term responses of wetland vegetation after liming of an Adirondack watershed. Wetlands, 4, 535-543.

Please cite as:

Taylor N.G., Grillas P., Smith R.K. & Sutherland W.J. (2021) Marsh and Swamp Conservation: Global Evidence for the Effects of Interventions to Conserve Marsh and Swamp Vegetation. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Retain/restore/create vegetation around brackish/saline swamps Action Link	No evidence found (no assessment)	0	Synopsis Link
Add lime or similar chemicals: freshwater swamps Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Introduce plants to marshes or swamps to control pollution Action Link	No evidence found (no assessment)	0	Synopsis Link