Add lime or similar chemicals: freshwater swamps

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 swamps or their catchments. The study was in the USA.


  • Relative abundance (1 study): One replicated, controlled, before-and-after study of shrubby wetland vegetation in the USA found that liming had no significant effect on the relative abundance of plant taxa. For 49 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 shrubby wetland 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 31 of 31 herbaceous plant taxa, 16 of 16 woody plant taxa, and one of two 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 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
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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