Add lime or similar chemicals: freshwater marshes

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

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.


  • 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.


  • 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.


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

  1. 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
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

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Marsh and Swamp Conservation

This Action forms part of the Action Synopsis:

Marsh and Swamp Conservation
Marsh and Swamp Conservation

Marsh and Swamp Conservation - Published 2021

Marsh and Swamp Synopsis

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