Mineral versus organic contribution to vertical accretion and elevation change in restored marshes (Ebro Delta, Spain)

Calvo-Cubero, J., et al., 2013. Ecological Engineering

Original research (primary data)
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The Ebro Delta (Catalonia, Spain) is one of the most valuable coastal zones within the Mediterranean Sea, supporting a highly productive rice agricultural system, as well as a myriad of coastal marsh habitats. However, chronic reductions of fluvial sediments coupled with accelerated relative sea-level rise have created an environment where approximately half of the Ebro Delta is now vulnerable to flooding impacts. To assess relative sea-level rise (RSLR) mitigation options through marsh restoration within abandoned deltaic rice fields, we established the experimentally restored marshes spanning three years. We used two freshwater input type treatments (riverine irrigation and rice field drainage water) and three water level treatments (10, 20 and 30 cm deep). Our hypotheses were that: (1) vertical accretion and elevation change in oligohaline restored marshes would be primarily controlled by organic contributions under sediment-deficit conditions, and (2) both vertical accretion and elevation change would demonstrate higher rates compared with predicted RSLR in the Ebro Delta (5-8 mm yr(-1)). Vertical accretion had higher mean values in both water type treatments (11.5 and 15.5 mm yr(-1)) than elevation change (9.1 and 8.8 mm yr(-1)). Vertical accretion (but not elevation change) was significantly higher in drainage water treatment receiving greater sediment mineral input, which caused higher surface soil mineral content. Conversely, experimentally restored marshes closer to rice fields in both water type treatments had greater elevation change (11.3 and 17.8 mm yr(-1)) than vertical accretion (8.3 and 15.1 mm yr(-1)) due to higher belowground biomass because of high weed colonization by Paspalum distichum L. These results showed that vertical accretion and elevation change were generally controlled by mineral contribution, although fast growing, ruderal plant species such as P. distichum can play a significant role in marsh elevation via root growth. The results supported the hypothesis that restored marshes using either water type promote marsh elevation gains higher than predicted RSLR at least during the initial marsh development (3 years). This study indicates that the use of agricultural runoff as a primary source of sediment, nutrient, and freshwater is beneficial for marsh restoration projects focused primarily on mitigating RSLR. This research also highlights how nuisance species such as P. distichum can play a key role in mitigating RSLR impacts when inexpensive and effective measures are needed to promote marsh elevation as the primary restoration goal.

Case studies

Basic information

  • Case ID: INT-101-1
  • Intervention type: Restoration
  • Intervention description:

    restoration of rice fields to marshes by adding freshwater from 2 different sources (riverine and rice field drainage)

  • Landscape/sea scape ecosystem management: No
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Coastal inundation  Positive vertical accretion (mmyr−1): surface accretion processes due to mineral sedimentation, leaf litter deposition and root growth elevation change (mmyr−1):change of marsh elevation due to vertical accretion, subsurface soil expansion by root growth and shallow subsidence by compaction and decomposition
  • Approach implemented in the field: Yes
  • Specific location:

    marshes in the Ebro Delta (Catalonia, Spain)

  • Country: Spain
  • Habitat/Biome type: Saltmarsh |
  • Issue specific term: Not applicable


  • Notes on intervention effectivness: no control, observation overtime of sediment acretion/elevation change and effectiveness is determined by comparing to a benchmark (i.e. expected sea level rise). Thus this shows that marsh restoration can be effective to address sea level rise. Looks at two variations of restoration technique by using different water source types, riverine irrigated vs rice field drainage water, and compares them to see which is most effective but these are not coded here as separate interventions (rice field water was better than riverine) measures valid for ecosystem assessment as well because habitat described as being important for conservation as well (eg important for migratory birds)
  • 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: Yes
  • Impacts for the ecosystem: Positive
  • Ecosystem measures: same measures as for climate impact: vertical accretion rate elevation change
  • 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: