Data extracted in May 2022
Fiche created in December 2023

Note to the reader: This general fiche summarises all the environmental and climate impacts of WETLAND MANAGEMENT found in a review of 6 synthesis papers[1]. These papers were selected from an initial number of 471 obtained through a systematic literature search strategy, according to the inclusion criteria reported in section 4. The impacts reported here are those for which there is scientific evidence available in published synthesis papers, what does not preclude the farming practice to have other impacts on the environment and climate still not covered by primary studies or by synthesis papers.

The synthesis papers review a number of primary studies ranging from 65 to 178. Therefore, the assessment of impacts relies on a large number of results from the primary studies, obtained mainly in field conditions, or sometimes in lab experiments or from model simulations.

1.      DESCRIPTION OF THE FARMING PRACTICE

  • Description:
    • Wetlands are areas where water is the primary factor controlling the environment and the associated plant and animal life. The Ramsar Convention on Wetlands adopts a broad definition of wetlands. It includes lakes and rivers, underground aquifers, swamps and marshes, wet grasslands, peatlands, oases, estuaries, deltas and tidal flats, mangroves and other coastal areas, coral reefs, and all human-made sites such as fish ponds, rice paddies, reservoirs and salt pans.[2]
    • However, this review does not include all these wetland types either because they are not well represented in the scientific literature, because they are not relevant in a European context or because they are not under agricultural use. Besides, this review excludes peatlands and carbon rich soils, as their conservation, restoration and management are assessed in a separate set of fiches (i.e., wetland conservation and restoration).
    • This review focuses on wetlands under agricultural use and thus, and though not clearly stated on the papers reviewed, includes mostly drained wetlands.[3]
    • This review includes interventions towards an improved and more sustainable management of wetlands. Specific interventions have been proposed such as low tillage, ban of burning, paludiculture, etc.[4]
    • In this literature review we have found evidence for the following management interventions:
      • No fertilisation. Fertilisers are natural or synthetic substances containing chemical elements such as nitrogen (N), phosphorus (P) and potassium (K) that are applied to soils to improve growth and productiveness of plants.[5] Fertilisation, and in particular N inputs in wetlands, might promote greenhouse gas emissions by changing element cycling.[6] Here, no fertilised wetlands are compared to fertilised ones.
      • Grazing is a method of animal husbandry in which livestock are allowed to feed outdoors consuming cultivated or wild vegetation. The direction and magnitude of grazing impacts on ecosystem properties depends on grazing management, such as stocking density, grazing duration and grazer species.[7] Here, grazed wetlands are compared to wetlands with grazing exclusion or where only wild herbivores graze in natural conditions.
    • Key descriptors:
      • This review includes a wide variety of wetland types in terms of: level of human intervention: natural and human-made; water salinity: fresh, brackish (i.e., intermediate level of salinity) and saline; water regime: lotic (flowing) and lentic (stagnant); permanent and temporary; elevation: alpine and coastal.
      • These fiches focus on wetlands and the management practices conducted in these habitats. However, some of these farming practices are also explored more broadly without distinguishing the habitat type devoted to agricultural use in other sets of fiches (i.e, organic fertilisation and grazing fiches).
      • This review does not include wetland conservation or restoration, which are assessed in separate sets of fiches (i.e., Peatland conservation and restoration and Peatland management).

2.     EFFECTS OF THE FARMING PRACTICE ON CLIMATE AND ENVIRONMENTAL IMPACTS

We reviewed the impacts in wetlands of different management practices, namely, the no fertilisation and grazing (intervention) compared, respectively, to fertilised and no grazed wetlands as comparators.

The table below shows the number of synthesis papers with statistical tests reporting i) a significant difference between the Intervention and the Comparator, that is to say, a significant statistical effect, which can be positive or negative; or ii) a non-statistically significant difference between the Intervention and the Comparator. In addition, we include, if any, the number of synthesis papers reporting relevant results but without statistical test of the effects. Details on the quality assessment of the synthesis papers can be found in the methodology section of this WIKI.

Out of the 6 selected synthesis papers, 5 included studies conducted in Europe, and 6 have a quality score higher than 50%.

Table 1: Summary of effects. Number of synthesis papers reporting positive, negative or non-statistically significant effects on environmental and climate impacts. The number of synthesis papers reporting relevant results but without statistical test of the effects are also provided. When not all the synthesis papers reporting an effect are of high quality, the number of synthesis papers with a quality score of at least 50% is indicated in parentheses. Some synthesis papers may report effects for more than one impact, or more than one effect for the same impact.

 

 

 

 

Statistically tested

Non-statistically tested

Impact

Metric

Intervention

Comparator

 Significantly positive

Significantly negative

Non-significant

Increase Biodiversity

Biodiversity

Grazing

No grazing

2

2

2

0

Increase Carbon sequestration

Soil organic carbon

Grazing

No grazing

0

0

1

0

No fertilisation

Fertilisation

0

0

1

0

Decrease GHG emissions

CH4 emissions

No fertilisation

Fertilisation

3

1

0

0

Increase GHG emissions

CO2 emissions

No fertilisation

Fertilisation

0

0

1

0

Decrease GHG emissions

N2O emissions

No fertilisation

Fertilisation

2

0

0

0

Increase Plant nutrient uptake

Plant nutrient uptake

No fertilisation

Fertilisation

0

1

0

0

Increase Soil biological quality

Soil biological quality

No fertilisation

Fertilisation

1

1

1

0

Increase Soil nutrients

Soil nutrients

No fertilisation

Fertilisation

0

1

0

0

3.      FACTORS INFLUENCING THE EFFECTS ON CLIMATE AND ENVIRONMENTAL IMPACTS

The factors significantly influencing the size and/or direction of the effects on the impacts, according to the synthesis papers included in this review, are reported below. Details about the factors can be found in the summaries of the meta-analyses available in this WIKI.

Table 2: List of factors reported to significantly affect the size and/or direction of the effects on environmental and climate impacts, according to the synthesis papers reviewed. The reference number of the synthesis papers where those factors are explored is given in parentheses.

Impact

Factors

GHG emissions

Climate (Ref1), Duration of treatment (Ref1), Interaction between wetland type and N addition rate (Ref1), Nitrogen form (Ref1) and Wetland type (Ref1)

Soil biological quality

Climate (Ref2), Fertiliser type (Ref2) and N application rate (Ref2)

4.     SYSTEMATIC REVIEW SEARCH STRATEGY

Table 3: Systematic review search strategy - methodology and search parameters.

Parameter

Details

Keywords

WOS:
1) TS=("wetland*" OR "marsh*" OR "fen*" OR "peatland*" OR "carbon-rich soil*" OR "carbon rich soil*" OR "wet meadow*" OR "wet soil*" OR "peat layer*" OR "water table*" OR "water layer*" OR “peat swamp*” OR “peat*” OR “water-saturated soil*” OR “black water*” OR “floodplain*” OR “histosol*” OR “mire*” OR “organic soil*” OR “estuar*” OR “mudflat*” OR "bog*") AND TS= ("rewett*" OR "land use change*" OR "land-use change*" OR "conserve*" OR "preserv*" OR "restor*" OR "conver*" OR "drain*" OR "undrain*" OR "protect*" OR "water retention" OR "colonization W/4 Thyfa" OR "colonization W/4 Sphagnum" OR "colonisation W/4 Thyfa" OR "colonisation W/4 Sphagnum" OR "set aside" OR “dry-rewet*” OR “irrigat*” OR “reveget*”) AND TS=("meta-analy*" OR "systematic* review*" OR "evidence map*" OR "global synthes*" OR "evidence synthes*" OR "research synthes*")
2) TS=("wetland*" OR "marsh*" OR "fen*" OR "peatland*" OR "carbon-rich soil*" OR "carbon rich soil*" OR "wet meadow*" OR "wet soil*" OR "peat layer*" OR "water table*" OR "water layer*" OR “peat swamp*” OR “peat*” OR “water-saturated soil*” OR “black water*” OR “floodplain*” OR “histosol*” OR “mire*” OR “organic soil*” OR “estuar*” OR “mudflat*”) AND TS= ("plough*" OR "till*" OR "drain*" OR "water use" OR "machinery" OR "integrated pest management*" OR "IPM" OR "fertilis*" OR "fertiliz*" OR "paludicult*" OR "extensive W/4 management*" OR “burn*” OR “sustainable W/4 management*” OR “traditional W/4 management*” OR “prevention W/4 inva*” OR “eradication W/4 inva*” OR “control w/4 inva*” OR “graz*” OR “afforest*”) AND TS=("meta-analy*" OR "systematic* review*" OR "evidence map*" OR "global synthes*" OR "evidence synthes*" OR "research synthes*")

 and

SCOPUS:
1) (SUBJAREA(AGRI OR ENVI) AND TITLE-ABS-KEY("wetland*" OR "marsh*" OR "fen*" OR "peatland*" OR "carbon-rich soil*" OR "carbon rich soil*" OR "wet meadow*" OR "wet soil*" OR "peat layer*" OR "water table*" OR "water layer*" OR “peat swamp*” OR “peat*” OR “water-saturated soil*” OR “black water*” OR “floodplain*” OR “histosol*” OR “mire*” OR “organic soil*” OR “estuar*” OR “mudflat*” OR "bog*") AND TITLE-ABS-KEY("rewett*" OR "land use change*" OR "land-use change*" OR "conserve*" OR "preserv*" OR "restor*" OR "conver*" OR "drain*" OR "undrain*" OR "protect*" OR "water retention" OR "colonization W/4 Thyfa" OR "colonization W/4 Sphagnum" OR "colonisation W/4 Thyfa" OR "colonisation W/4 Sphagnum" OR "set aside" OR “dry-rewet*” OR “irrigat*” OR “reveget*”) AND TITLE-ABS-KEY("meta-analy*" OR "systematic* review*" OR "evidence map*" OR "global synthes*" OR "evidence synthes*" OR "research synthes*"))
2) (SUBJAREA(AGRI OR ENVI) AND TITLE-ABS-KEY("wetland*" OR "marsh*" OR "fen*" OR "peatland*" OR "carbon-rich soil*" OR "carbon rich soil*" OR "wet meadow*" OR "wet soil*" OR "peat layer*" OR "water table*" OR "water layer*" OR “peat swamp*” OR “peat*” OR “water-saturated soil*” OR “black water*” OR “floodplain*” OR “histosol*” OR “mire*” OR “organic soil*” OR “estuar*” OR “mudflat*”) AND TITLE-ABS-KEY("plough*" OR "till*" OR "drain*" OR "water use" OR "machinery" OR "integrated pest management*" OR "IPM" OR "fertilis*" OR "fertiliz*" OR "paludicult*" OR "extensive W/4 management*" OR “burn*” OR “sustainable W/4 management*” OR “traditional W/4 management*” OR “prevention W/4 inva*” OR “eradication W/4 inva*” OR “control w/4 inva*” OR “graz*” OR “afforest*”) AND TITLE-ABS-KEY("meta-analy*" OR "systematic* review*" OR "evidence map*" OR "global synthes*" OR "evidence synthes*" OR "research synthes*"))

Time reference

No time restriction.

Databases

Web of Science and Scopus: run on 01 May 2022

Exclusion criteria

The main criteria that led to the exclusion of a synthesis paper are: 
 1) The paper did not deal with wetlands or the effects on wetlands could not be disentangled from those on peatlands;, 2) The paper clearly specified that was on urban wetlands for waste water management or coastal wetlands for tidal and coast erosion regulation, otherwise, papers were included even if authors did not clearly stated that studied wetlands were under agricultural lands uses;, 3) The paper was about small wetlands (ponds), which are already explored as landscape features in a different set of fiches;, 4) The paper did not deal with wetland management practices by comparing wetlands with and without the implementation of such management practice;, 5) The paper was focused on a wetland type not represented in Europe (i.e., mangroves);, 6) The paper analysed the same dataset than another synthesis paper already included in this review used to explore the same impact;, 7) The paper was either a non-systematic review, a non-quantitative systematic review, or a meta-regression without mean effect sizes; and 8) The paper was not written in English. 

The search returned 470 synthesis papers from WOS and SCOPUS on Wetland management plus other 1 retrieved in the search of other farming practices, potentially relevant for the practice object of our fiche. 
From the 471 potentially relevant synthesis papers, 332 were excluded after reading the title and abstract, and 133 after reading the full text according to the above-mentioned criteria. Finally, 6 synthesis papers were selected.

5.     SYNTHESIS PAPERS INCLUDED IN THE REVIEW

Table 4: List of synthesis papers included in this review. More details can be found in the summaries of the meta-analyses.

Ref Num

Author(s)

Year

Title

Journal

DOI

Ref1

Wu, JJ; Cheng, XL; Xing, W; Liu, GH

2022

Soil-atmosphere exchange of CH4 in response to nitrogen addition in diverse upland and wetland ecosystems: A meta-analysis

SOIL BIOLOGY AND BIOCHEMISTRY, 164, 108467.

10.1016/j.soilbio.2021.108467

Ref2

Chen, M; Chang, L; Zhang, J; Guo, F; Vymazal, J; He, Q; Chen, Y

2020

Global nitrogen input on wetland ecosystem: The driving mechanism of soil labile carbon and nitrogen on greenhouse gas emissions

ENVIRONMENTAL SCIENCE AND ECOTECHNOLOGY, 4, 100063.

10.1016/j.ese.2020.100063

Ref3

Davidson, KE; Fowler, MS; Skov, MW; Doerr, SH; Beaumont, N; Griffin, JN

2017

Livestock grazing alters multiple ecosystem properties and services in salt marshes: A meta-analysis

JOURNAL OF APPLIED ECOLOGY, 54(5), 1395-1405.

10.1111/1365-2664.12892

Ref4

He, Q; Silliman, BR

2016

Consumer control as a common driver of coastal vegetation worldwide

ECOLOGICAL MONOGRAPHS, 86(3), 278-294.

10.1002/ecm.1221

Ref5

Li, Y; Niu, SL; Yu, GR

2016

Aggravated phosphorus limitation on biomass production under increasing nitrogen loading: a meta-analysis

GLOBAL CHANGE BIOLOGY, 22(2), 934-943.

10.1111/gcb.13125

Ref6

Liu, L; Greaver, TL

2009

A review of nitrogen enrichment effects on three biogenic GHGs: The CO2 sink may be largely offset by stimulated N2O and CH4 emission

ECOLOGY LETTERS, 12(10), 1103-1117.

10.1111/j.1461-0248.2009.01351.x

 

Disclaimer: These fiches present a large amount of scientific knowledge synthesised to assess farming practices impacts on the environment, climate and productivity. The European Commission maintains this WIKI to enhance public access to information about its initiatives. Our goal is to keep this information timely and accurate. If errors are brought to our attention, we will try to correct them. However, the Commission accepts no responsibility or liability whatsoever with regard to the information on these fiches and WIKI.


[1] Synthesis research papers include either meta-analysis or systematic reviews with quantitative results. Details can be found in the methodology section of the WIKI.

[2] Ramsar Convention on Wetlands: https://www.ramsar.org/sites/default/files/documents/library/current_convention_text_e.pdf

[3] Joosten, et al. 2012. Peatlands—Guidance for climate change mitigation, conservation, rehabilitation and sustainable use. Mitigation of climate change in Agriculture Series 5 (FAO).

[4] Joosten, et al. 2012. Peatlands—Guidance for climate change mitigation, conservation, rehabilitation and sustainable use. Mitigation of climate change in Agriculture Series 5 (FAO).

[5] https://ec.europa.eu/eurostat/statistics-explained/index.php?title=Glossary:Fertiliser

[6] Chen, M; Chang, L; Zhang, J et al. 2020. Global nitrogen input on wetland ecosystem: The driving mechanism of soil labile carbon and nitrogen on greenhouse gas emissions. Environmental Science and Ecotechnology, 4, 100063.

[7] Paz-Kagan, T; Ohana-Levi, N; Herrmann, I et al. 2016. Grazing intensity effects on soil quality: a spatial analysis of a Mediterranean grassland. Catena, 146, 100–110.

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