Raise water level to restore/create brackish/salt marshes from other land uses

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Source countries

Key messages

  • Two studies evaluated the effects, on vegetation, of raising the water level to restore/create brackish/salt marshes from other land uses or habitat types. Both studies were in the same area of Iraq, but used different study sites.

VEGETATION COMMUNITY

  • Community types (1 study): One before-and-after study of a slightly brackish marsh in Iraq reported that fewer plant community types were present three years after reflooding than before drainage.
  • Overall richness/diversity (2 studies): Two before-and-after studies of brackish marshes in Iraq reported that fewer plant species were present three years after reflooding than before drainage. One of these studies also reported that individual plant communities typically had lower diversity after reflooding than before drainage.

VEGETATION ABUNDANCE

  • Overall abundance (1 study): One before-and-after study of a slightly brackish marsh in Iraq reported that six of seven studied plant communities had lower spring and/or summer biomass three years after reflooding than before drainage.

VEGETATION STRUCTURE

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, before-and-after study in the early 1990s and 2006 of two brackish marshes in southern Iraq (Al-Abbawy & Al-Mayah 2010) reported that after reflooding, the marshes contained fewer plant species than they contained before drainage. Approximately three years after reflooding, 24–27 plant species were recorded in each marsh (10–12 emergent, 12 submerged, 2–3 floating). Before drainage, 38–44 plant species were recorded in each marsh (18–19 emergent, 12–16 submerged, 8–9 floating). Methods: Monthly surveys were carried out between January 2006 and December 2007 to record plant species in Central Marsh (two sites) and East Hammar Marsh (two sites). These brackish marshes were drained in the 1990s – becoming “almost totally desiccated” by 2000, but retaining small pockets of remnant marsh vegetation. The marshes were reflooded from 2003 (details not reported). Previously published data from the same marshes, collected in the early 1990s before drainage, were used for comparison.

    Study and other actions tested
  2. A before-and-after study in 1973–2006 of a brackish marsh in southern Iraq (Hamdan et al. 2010) reported that after reflooding, the marsh contained fewer plant species and communities than before it was drained, and that those communities typically had lower diversity and biomass. Statistical significance was not assessed. Within three years of reflooding, 38 plant species were recorded in the marsh (vs 48 before drainage). Twenty-six species were present both before and after reflooding. Three years after reflooding, 10 distinct plant communities were recorded in the marsh (vs 14 before drainage). For six of seven communities with comparable data, plant diversity was lower after reflooding than before drainage (data reported as a diversity index). Results for above-ground vegetation biomass were more mixed and depended on the season of comparison, but for six communities biomass was lower after reflooding than before drainage in at least one season (for which after: 50–3,247 g/m2; before: 60–4,923 g/m2). Methods: In 2003, local residents released water from canals and reservoirs to reflood marshes on the Mesopotamian Plain that had been almost completely drained in the 1990s. In spring and summer 2006, vegetation was surveyed in three sites within the slightly brackish (salinity 1–2 ppt) reflooded Central Marsh. Species, cover and biomass were recorded/collected in seven hundred 1-m2 quadrats. Biomass was later dried and weighed. Previously published data from the 1970s (from different sites within the marsh) were used for comparison.

    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.

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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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