Action

Divert/replace polluted water source(s)

How is the evidence assessed?
  • Effectiveness
    70%
  • Certainty
    50%
  • Harms
    10%

Source countries

Key messages

  • Three studies evaluated the effects, on peatland vegetation, of diverting or replacing polluted water source(s). Two studies were in bogs and one was in a fen.
  • Characteristic plants (1 study): One study in a fen in the Netherlands found that after a nutrient-enriched water source was replaced (along with other interventions to reduce pollution), cover of mosses characteristic of low nutrient levels increased.
  • Vegetation cover (2 studies): Two studies (one before-and-after) in bogs in the UK and Japan reported that after polluting water sources were diverted (sometimes along with other interventions), Sphagnum moss cover increased. Both studies reported mixed effects on herb cover, depending on species.

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 before-and-after study in 1972–1987 in a historically mined raised bog in England, UK (Meade 1992) reported that after diversion of polluted inflow (along with rewetting), cover of Sphagnum moss, white sedge Carex curta and cottongrasses Eriophorum spp. increased, but cover of purple moor grass Molinia caerulea decreased. No statistical tests were carried out. Sphagnum was found in 7% of quadrats before intervention but 27% after, white sedge in 0.0% before but 0.8% after, and cottongrasses in 1.1% before and 1.5–1.7% after. In contrast, purple moor grass Molinia caerulea occurred in 100% of quadrats before intervention but only 74% after. Eighteen other herb, shrub and tree species showed variable responses (see original paper). In 1974, polluted inflow from adjacent farms was diverted away from a bog, whilst the water outflow was blocked to raise the water table. The study does not distinguish between the effects of these interventions. Vegetation cover was recorded before (1972–1973) and after (1987) intervention, as presence/absence of species in 8,945 contiguous 4 m2 quadrats covering the whole site.

    Study and other actions tested
  2. A study in 1980–2006 in a floating bog in Japan (Tsujino et al. 2010) found that after removing polluting water sources (sewage and tap water), cover of Sphagnum moss increased. Cover of vascular plant species showed mixed responses. Between 1980 and 2006, the area of moss hummocks (containing blunt-leaved bog moss Sphagnum palustre) increased from 5,900 m2 to 8,500 m2. The area of moss mats (dominated by feathery bog moss Sphagnum cuspidatum) increased from 420 m2 to 1,010 m2. Of nine abundant vascular plant species, cover of three decreased (including sedge Carex thunbergii and bogbean Menyanthes trifoliata), cover of three increased (including swamp millet Isachne globosa) and cover of three did not change (including common reed Phragmites australis). Historically, the lake under the bog was polluted by sewage from a hospital, discharge/leakage of tap water from a purification plant and runoff from a road. Interventions to reduce pollution were (a) construction of a sewage system in the 1960s and (b) pumping of tap water leakage from 2003. Deliberate tap water discharge also stopped in the 1960s. Road runoff continued. Vegetation cover was extracted from maps made in 1980 and 2006.

    Study and other actions tested
  3. A study in 1984–2013 in a floating rich fen in the Netherlands (Kooijman et al. 2016) found that after replacing a nutrient-rich water source with lower-nutrient water (along with other interventions to reduce pollution), moss cover changed to species characteristic of lower nutrient levels and vascular plant biomass decreased. Over 25 years following intervention, four of seven moss species characteristic of low nutrient levels increased in cover (from 1–62% to 11–83%). Meanwhile, six of seven moss species characteristic of high nutrient levels decreased in cover (from 7–78% to 1–32%). Over 28 years, vascular plant biomass decreased from 1,123 g/m2 to 287 g/m2. Since the 1970s, the fen water source was changed from a nutrient-rich river to a nutrient-poor lake, the input water was rerouted on a longer path to allow more time for nutrient reduction, and water purification facilities were built. The study does not distinguish between the effects of these interventions. In addition, there was a general reduction in nutrient input from urban areas. In 1988 and 2013, cover of every moss species was recorded in a 25 x 200 m area. In 1984 and 2012, above-ground vascular plant biomass was collected, dried and weighed.

    Study and other actions tested
Please cite as:

Taylor N.G., Grillas P. & Sutherland W.J. (2019) Peatland Conservation. Pages 375-438 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Peatland Conservation

This Action forms part of the Action Synopsis:

Peatland Conservation
Peatland Conservation

Peatland Conservation - Published 2018

Peatland Conservation

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, terrestrial mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read latest volume: Volume 17

Go to the CE Journal

Subscribe to our newsletter

Please add your details if you are interested in receiving updates from the Conservation Evidence team about new papers, synopses and opportunities.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust