Quantifying the water balance of Mfabeni Mire (Isimangaliso Wetland Park, South Africa) to understand its importance, functioning and vulnerability

Grundling, P. L., et al., 2015. Mires and Peat

Original research (primary data)
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Peatlands occurring in regions with high rates of total evaporation (ET), matching or exceeding precipitation (P) during seasonal dry periods or longer-term dry spells, are dependent on sustained groundwater flows to ensure peat accumulation. The objective of this study was to quantify the water balance of Mfabeni Mire in South Africa over one year, and thereby define its contribution to downstream and adjacent ecosystems and identify risks and consequences likely to arise from future shifts in the water balance. P (1,031 mm) and ET (1,053 mm) dominated the water balance measured from May 2008 to April 2009. These were followed by groundwater inflows (14 mm), stream outflow (9 mm) and storage change (-3 mm, a net loss in water stored in the mire) with the smallest flux being groundwater outflow (0.3 mm). There were differences in the seasonal patterns of ET from the two dominant plant communities (swamp forest and sedge/reed fen), which probably resulted from their significantly different canopy structures. Limiting factors for ET were low vapour pressure deficit and cloud cover. Although the water balance of Mfabeni Mire was dominated by and equally split between ET and P, it still contributed a small efflux to downstream ecosystems by stream flow. Its value in a landscape where seasonality and long-term dry periods are major ecological drivers lies in its damping effect on climatic variability. This creates a more stable environment for adjacent aquatic ecosystems by contributing to a steady groundwater condition. Mires occurring in areas that experience dry periods, where water stress frequently threatens biodiversity, should be recognised as assets in natural resource management; and their potential to support adjacent ecosystems should be protected through planning and conservation practices. Management of the area should include careful consideration of any proposed changes in land use or encouragement of one plant community at the expense of another, as such changes will alter the equilibrium of the water balance. Mfabeni Mire is particularly vulnerable through the impact of adjacent commercial forestry, which has impacted river and estuary management over the last 80 years and depleted groundwater levels in the surrounding aquifers.

Case studies

Basic information

  • Case ID: INT-075-1
  • Intervention type: Protection
  • Intervention description:

    The site is a protected area; a peatland site located inside Simangaliso wetland park

  • Landscape/sea scape ecosystem management: Yes
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Reduced water availability  Positive measures – water balance measures/hydrometric techniques groundwater inflows and outflows (mm/yr), inking Mfabeni Mire with adjacent landscape units were measured on the ‘main transect’ which crossed swamp forest and fen on the widest part of the mire (Figure 1). also measured stream outflow (mm/month)
  • Approach implemented in the field: Yes
  • Specific location:

    Simangaliso Wetland Park, South Africa

  • Country: South Africa
  • Habitat/Biome type: Peatland |
  • Issue specific term: Not applicable


  • Notes on intervention effectivness: The ability of the peat system to buffer the impacts of drought/climatic variability, especially in the face of climate change depends on land-use and climate changes. Thus buffering the peatland system from any negative impacts on the water balance stemming from land-use or climate drivers is required to sustain it’s ability to provide water to downstream areas. on changes in evapotranspiration rates due to climate change as well as. “Any shift in these controls [on the system hydrology] (e.g. due to climate change) could disturb the water balance of the mire, and the resulting higher or lower water table in the western dune mound cause expansion or contraction, respectively, of the swamp forest”. ‘the mire contributed streamflow to downstream ecosystems – authors says it therefore dampens impact of climate variability in areas where long-term dry periods are an issue; creates a more stable environment by contributing to steady groundwater condition” “groundwater outflows from Mfabeni Mire contribute significantly to adjacent ecosystems such as Lake Bangazi and the smaller eastern wetlands.”
  • Is the assessment original?: Yes
  • Broadtype of intervention considered: Not applicable
  • Compare effectivness?: No
  • Compared to the non-NBS approach: Not applicable
  • Report greenhouse gas mitigation?: No
  • Impacts on GHG: Not applicable
  • Assess outcomes of the intervention on natural ecosystems: No
  • Impacts for the ecosystem: Not reported
  • Ecosystem measures:
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures:
  • Considers economic costs: No
  • Economic appraisal conducted: No
  • Economic appraisal described:
  • Economic costs of alternative considered: No
  • Compared to an alternative: Not reported

Evaluation methodology

  • Type of data: Quantitative
  • Is it experimental: No
  • Experimental evalution done: Not applicable
  • Non-experimental evalution done: Empirical case study
  • Study is systematic: