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 CONSERVATION AND RESTORATION found in a review of 14 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 14 to 115. 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 or because they are not relevant in a European context. Besides, this review does not include peatlands and carbon rich soils, whose conservation, restoration and management are assessed in separate sets of fiches.
    • This review includes interventions in wetlands related to:
      • Conservation refers to the preservation (i.e., no transformation to other land uses) of natural non-disturbed wetlands compared to either degraded or restored wetlands. The degraded wetlands found in this review are mainly affected by alterations in their water regime due to drainage and/or conversion to cropland or pasture, or by their conversion into aquaculture ponds or other constructed wetlands. The restored wetlands found in this review have been subject to different interventions including water flow re-establishment, revegetation or addition of a sediment layer.
      • Restoration methods found in this review are classified into three main classes: management of invasive plant species, management of water regime and a general class with several restoration methods pooled together. Restoration by managing invasive plant species includes the use of chemical (herbicides) and mechanical (tilling, disking, mowing, crushing, cutting and uprooting) control methods, as well as burning, grazing and replacement of invasive plants with natives. Restoration by managing water regime includes the recovery of the duration, frequency and/or depth of inundation, waterlogging or environmental flow release. The creation of new wetlands is also considered here.
    • When different restoration methods are analysed together in the reviewed synthesis papers, we report them as several restoration methods analysed together. This pool includes active revegetation, enhancement of in-wetland and structural heterogeneity, habitat creation, passive restoration, restoration of hydrological dynamics, restoration of water quality, addition of soil amendments or wildlife management (i. e. reintroduction of native species and/or elimination of exotic ones).
  • 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.
    • The estimation of wetland conservation impacts is based on the spatial comparison between preserved natural wetlands (intervention) and nearby degraded or restored wetlands (comparator).
    • The estimation of wetland restoration impacts is based on the spatial and temporal comparisons between restored wetlands (intervention) and degraded wetlands (comparator). Spatial comparisons are those conducted simultaneously between restored wetlands and nearby degraded wetlands. Temporal comparisons are those conducted in the same wetland before and after restoration.
    • This review focuses on wetland under agricultural land use. However, lands use is not always clearly reported in the synthesis papers. Papers were retained unless clearly specified that studied wetlands were under urban lands use. The underlying reasoning is that many wetlands are in fact disturbed for agricultural purposes. Besides, in the case of restoration, some interventions such as those focused on the eradication or control of invasive species, could be valid experiences for the restoration of other wetlands, irrespectively to the land use.
    • This review does not include other management practices conducted in wetlands (i.e, grazing or fertilisation) which are assessed in separate sets of fiches (i.e. wetland management).

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

We reviewed the impacts of the conservation of natural wetlands as compared to degraded wetlands or to restored wetlands, and the impacts of restoration (or creation) of wetlands compared to degraded wetlands.

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 14 selected synthesis papers, 11 included studies conducted in Europe, and 13 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

Conservation of natural wetlands

Degraded/altered wetland due to water regime alteration

1

0

0

0

Conservation of natural wetlands

Restored (several restoration methods analysed together) or created wetland

3

2

3

0

Restoration (several restoration methods analysed together)

Degraded/altered wetland

1

0

1

0

Restoration by management of invasive plant species

No management of invasive species

1

2

2

0

Restoration by management of water regime

Degraded/altered wetland due to water regime alteration

0

0

1

0

Restoration by management of water regime

Drained wetland

0

0

0

1 (0)

Increase Carbon sequestration

Soil organic carbon

Conservation of natural wetlands

Restored by adding a sediment layer or created wetland

1

0

0

0

Decrease GHG emissions

CH4 emissions

Conservation of natural wetlands

Aquaculture pond

1

0

0

0

Conservation of natural wetlands

Created wetland

0

0

1

0

Conservation of natural wetlands

Degraded/altered wetland due to conversion to pasture

0

0

1

0

Conservation of natural wetlands

Degraded/altered wetland due to cultivation

0

1

1

0

Conservation of natural wetlands

Drained wetland

0

1

0

0

Decrease GHG emissions

CO2 and CH4 emissions

Restoration by management of invasive plant species

No management of invasive species

1

0

0

0

Decrease GHG emissions

CO2 emissions

Conservation of natural wetlands

Created wetland

1

0

0

0

Conservation of natural wetlands

Degraded/altered wetland due to conversion to pasture

1

0

0

0

Conservation of natural wetlands

Degraded/altered wetland due to cultivation

0

0

1

0

Conservation of natural wetlands

Drained wetland

1

0

0

0

Decrease GHG emissions

N2O emissions

Conservation of natural wetlands

Aquaculture pond

0

0

1

0

Conservation of natural wetlands

Created wetland

0

0

1

0

Conservation of natural wetlands

Degraded/altered wetland due to conversion to pasture

0

1

0

0

Conservation of natural wetlands

Degraded/altered wetland due to cultivation

1

0

1

0

Conservation of natural wetlands

Drained wetland

0

0

1

0

Decrease Pests and diseases

Pests and diseases

Conservation of natural wetlands

Restored (several restoration methods analysed together) or created wetland

0

1

0

0

Restoration by management of invasive plant species

No management of invasive species

2

1

2

0

Decrease Soil erosion

Soil erosion

Restoration by management of water regime

Degraded/altered wetland due to highly regulated flow regime

1

0

0

0

Increase Soil nutrients

Soil nutrients

Conservation of natural wetlands

Restored by adding a sediment layer or created wetland

1

0

0

0

Restoration by management of invasive plant species

No management of invasive species

0

0

1

0

Increase Soil water retention

Soil moisture

Restoration by management of invasive plant species

No management of invasive species

0

1

0

0

Increase Water quality

Water quality

Restoration (several restoration methods analysed together) or creation of wetlands

No previous wetland or degraded/altered wetland

2

0

0

0

Restoration by management of water regime

Degraded/altered wetland due to highly regulated flow regime

1

0

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

Biodiversity

Araneae (spiders) family (Ref14), Change in water flow (Ref8), Climate (Ref9), Colleoptera (beetles) family (Ref14), Duration of treatment (Ref8, Ref14), Environmental flow regime (Ref8), Intensity of hydrological alteration (Ref10), Invertebrate taxonomic group (Ref14), Taxonomic group (Ref8, Ref11), Time since tretament (Ref1, Ref5, Ref4), Water salinity (Ref14) and Wetland type (Ref8)

Carbon sequestration

Time since tretament (Ref4)

Soil nutrients

Time since tretament (Ref4)

Water quality

Hydraulic loading (Ref7), Hydraulic loading rate (Ref7), Inflow concentration (Ref7), Temperature (Ref7) and Wetland area (Ref7)

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 compare natural wetlands with nearby degraded or restored wetlands (for wetland conservation);, 5) The paper did not compare restored wetlands with nearby or previously (i.e., comparing impacts before and after restoration) degraded wetlands;, 6) The paper was focused on a wetland type not represented in Europe (i.e., mangroves);, 7) The paper analysed the same dataset that another synthesis paper already included in this review to explore the same impact;, 8) The paper was either a non-systematic review, a non-quantitative systematic review, or a meta-regression without mean effect sizes; and 9) The paper was not written in English. 

The search returned 470 synthesis papers from WOS and SCOPUS on Wetland conservation and restoration 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 125 after reading the full text according to the above-mentioned criteria. Finally, 14 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

Ning, ZH; Chen, C; Xie, T; Zhu, ZC; Wang, Q; Cui, BS; Bai, JH

2021

Can the native faunal communities be restored from removal of invasive plants in coastal ecosystems? A global meta-analysis

GLOBAL CHANGE BIOLOGY, 27, 4644-4656.

10.1111/gcb.15765

Ref2

Wails, CN; Baker, K; Blackburn, R; Del Valle, A; Heise, J; Herakovich, H; Holthuijzen, WA; Nissenbaum, MP; Rankin, L; Savage, K; Vanek, JP; Jones, HP

2021

Assessing changes to ecosystem structure and function following invasion by Spartina alterniflora and Phragmites australis: a meta-analysis

BIOLOGICAL INVASIONS, 23, 2695-2709.

10.1007/s10530-021-02540-5

Ref3

Carstensen, MV; Hashemi, F; Hoffmann, CC; Zak, D; Audet, J; Kronvang, B

2020

Efficiency of mitigation measures targeting nutrient losses from agricultural drainage systems: A review

AMBIO, 49, 1820-1837.

10.1007/s13280-020-01345-5

Ref4

Ebbets, AL; Lane, DR; Dixon, P; Hollweg, TA; Huisenga, MT; Gurevitch, J

2020

Using meta-analysis to develop evidence-based recovery trajectories of vegetation and soils in restored wetlands in the northern Gulf of Mexico

ESTUARIES AND COASTS, 43(7), 1692-1710.

10.1007/s12237-019-00536-y

Ref5

Hollweg, TA; Christman, MC; Lipton, J; Wallace, BP; Huisenga, MT; Lane, DR; Benson, KG

2020

Meta-analysis of nekton rRecovery following marsh restoration in the northern Gulf of Mexico

ESTUARIES AND COASTS, 43(7), 1746-1763.

10.1007/s12237-019-00630-1

Ref6

Tan, LS; Ge, ZM; Zhou, XH; Li, SH; Li, XZ; Tang, JW

2020

Conversion of coastal wetlands, riparian wetlands, and peatlands increases greenhouse gas emissions: A global meta-analysis

GLOBAL CHANGE BIOLOGY, 26(3), 1638-1653.

10.1111/gcb.14933

Ref7

Land, M; Graneli, W; Grimvall, A; Hoffmann, CC; Mitsch, WJ; Tonderski, KS; Verhoeven, JTA

2016

How effective are created or restored freshwater wetlands for nitrogen and phosphorus removal? A systematic review

ENVIRONMENTAL EVIDENCE, 5, 9.

10.1186/s13750-016-0060-0

Ref8

Yang, W; Sun, T; Yang, ZF

2016

Does the implementation of environmental flows improve wetland ecosystem services and biodiversity? A literature review

RESTORATION ECOLOGY, 24, 731-742.

10.1111/rec.12435

Ref9

Moreno-Mateos, D; Meli, P; Vara-Rodríguez, MI; Aronson, J

2015

Ecosystem response to interventions: lessons from restored and created wetland ecosystems

JOURNAL OF APPLIED ECOLOGY, 52, 1528-1537.

10.1111/1365-2664.12518

Ref10

Kuiper, JJ; Janse, JH; Teurlincx, S; Verhoeven, JTA; Alkemade, R

2014

The impact of river regulation on the biodiversity intactness of floodplain wetlands

WETLANDS ECOLOGY AND MANAGEMENT, 22(6), 647-658.

10.1007/s11273-014-9360-8

Ref11

Meli, P; Benayas, JMR; Balvanera, P; Ramos, MM

2014

Restoration enhances wetland biodiversity and ecosystem service supply, but results are context-dependent: A meta-analysis

PLOS ONE, 9(4), e93507.

10.1371/journal.pone.0093507

Ref12

Webb, JA; Wallis, EM; Stewardson, MJ

2012

A systematic review of published evidence linking wetland plants to water regime components

AQUATIC BOTANY, 103, 1-4.

10.1016/j.aquabot.2012.06.003

Ref13

Roberts, PD; Pullin, AS

2008

The effectiveness of management interventions for the control of Spartina species: A systematic review and meta-analysis

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, 18, 592-618.

10.1002/aqc.889

Ref14

Valkama, E; Lyytinen, S; Koricheva, J

2008

The impact of reed management on wildlife: A meta-analytical review of European studies

BIOLOGICAL CONSERVATION, 141, 364-374.

10.1016/j.biocon.2007.11.006

 

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

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