Drain/replace acidic water

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
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How is the evidence assessed?

Effectiveness

40%
Certainty

35%
Harms

10%

Calculating overall effectiveness category

Background information and definitions

Peatlands can hold onto acidic water, especially in thick carpets of moss. This is a natural process in the development of peatlands from fens to bogs (Rydin & Jeglum 2013). However, where the desired plant community is a fen, intervention may be needed to reduce acidity. Fen plants prefer weakly acidic, neutral or even alkaline peat (approximately pH 6–8, similar to saliva, tap water or sea water). Ditches can be dug to drain excess surface water (especially during periods of heavy rain). This may be replaced by less acidic water naturally, or with further intervention.

Caution: Peatland vegetation is very sensitive to water quantity and quality (Rydin & Jeglum 2013). If acidic water is drained, it will probably have to be replaced to prevent the peatland drying out. The chemistry of this water should be carefully monitored or controlled to avoid changing the chemical conditions of the peatland. This intervention is generally not applicable to bogs, which are naturally acidic.

Related actions: remove plants, including mosses that can store acidic water; divert/replace other sources of polluted water.

_{Rydin H. & Jeglum J.K. (2013) The Biology of Peatlands, Second Edition. Oxford University Press, Oxford.}

Study locations

Key messages

Two studies evaluated the effects on peatland vegetation of draining/replacing acidic surface water. Both studies were in fens.
Vegetation cover (2 studies): Two controlled studies in fens in the Netherlands reported that draining acidic water had mixed effects on cover of Sphagnum moss and herbs after 4–5 years, depending on the species and whether moss was also removed.
Overall plant richness/diversity (1 study): One controlled, before-and-after study in a fen in the Netherlands reported that draining and replacing acidic water increased plant species richness.

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 controlled study in 1989–1993 in a degraded floating fen in the Netherlands (Beltman et al. 1996) reported that draining acidic surface water increased herb cover, but only when moss was also removed. These results were not tested for statistical significance. Drainage alone had no effect on vegetation cover. After four years, a drained and undrained plot had similar vegetation cover (total moss: 93%; Sphagnum: 62%; herbs: 3%). However, drainage in combination with moss removal favoured herbs. A plot drained and cleared of moss developed 76% herb cover with 0% moss cover. In contrast, a plot cleared of moss but not drained regained high moss cover (total moss: 96%; Sphagnum: 53%; herbs: <1%). In 1989, a ditch was built to drain surface water from two 16 m² plots in an acidified, nutrient-enriched fen. Two other plots were not drained. In 1991, the moss carpet was also cleared from one drained and one undrained plot. In 1995, vegetation cover was recorded in six 1 m²quadrats/plot.
Study and other actions tested
Referenced paper
Beltman B., van den Broek T., Bloemen S. & Witsel C. (1996) Effects of restoration measures on nutrient availability in a formerly nutrient-poor floating fen after acidification and eutrophication. Biological Conservation, 78, 271-277.
A controlled, before-and-after study in 1991–1996 in a degraded floating fen in the Netherlands (Bootsma et al. 2002) reported that draining acidic surface water (and replacing it with less acidic water) increased plant species richness and Sphagnum moss cover, but had no effect on sedge or common reed abundance. These results were not tested for statistical significance. Before intervention, plots contained approximately 16 species. After five years, drained plots contained 22–43 plant species, compared to 14–16 species in undrained plots. Drained plots had 41–100% Sphagnum cover, compared to 21–40% in undrained plots. Drain and undrained plots had similar cover of sedge Carex nigra (0–20%) and abundance of common reed Phragmites australis (in 81–100% of quadrats). Effects of drainage on cottongrass Eriophorum angustifolium abundance were more complicated and depended on whether moss was also removed (see original paper). In January 1992, ditches were built to drain surface water from one plot in an acidified, nutrient-enriched fen. An inflow of less acidic water was also created. Water was not manipulated in a neighbouring plot. Within each plot, surface moss was cleared from three subplots but not three others. Between 1991 and 1996, vegetation was estimated in quadrats covering 6–8 m² of each subplot.
Study and other actions tested
Referenced paper
Bootsma M. C., van den Broek T., Barendregt A. & Beltman T. (2002) Rehabilitation of acidified floating fens by addition of buffered surface water. Restoration Ecology, 10, 112-121.

Please cite as:

Taylor, N.G., Grillas, P. & Sutherland, W.J. (2020) Peatland Conservation. Pages 367-430 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Peatland Conservation

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