Multifunctional experimental assessment in a newly established Mediterranean restored marsh : marsh elevation, carbon accumulation and pollutant concentration reduction

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Juan Calvo-Cubero (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: The Delta of the Ebro River (Catalonia, Spain) is among the most important marsh areas in the Western Mediterranean Sea, highly valuable both economically and ecologically. Fluvial sediment reduction by dams in a relative sea-level rise (RSLR) scenario (eustatic sea-level rise + subsidence) has increased the delta plain flooding risk. Traditional and current agricultural practices have transformed large areas of marshes and lagoons into rice fields, now occupying up to 60% of the deltaic plain. Agricultural runoff carries substantial loads of pesticide and fertilizer to natural habitats. To reduce ecological impacts, several marsh restoration efforts have been initiated to improve water quality and increase wildlife habitat. However, previous experimental studies in the Ebro Delta and other Mediterranean marshes have not focused on overall ecological benefits and costs of restored marshes providing simultaneously vertical accretion to deal with flooding risk, carbon (C) sequestration and pollutant removal services. A need for more knowledge is required to optimize factors controlling these ecosystem services seeking to work as natural defence against flooding risk, sequestering C, as well as natural filters of agricultural runoff. The objective of this study was to assess the multifunctional use and factors controlling of vertical accretion, C accumulation and pollutant concentration reduction in Mediterranean oligohaline restored marshes. We conducted a 3-year experimental field study in a newly established restored marsh using two different freshwater input types, riverine irrigation water (IW) and rice field drainage water (DW) and three water levels (10, 20 and 30 cm depth). The results indicate overall benefits of the restored marsh providing marsh elevation, C accumulation and pollutant removal services. This study indicates that Mediterranean oligohaline restored marshes might buffer flooding risk dealing with sediment deficit and RSLR in the Ebro Delta due to high mean rates of vertical accretion (11.5±0.8 and 15.5±0.6 mm yr?¹) and elevation change (9.1±1.4 and 8.8±2.8 mm yr?¹) in both water type treatments (IW and DW respectively), at least during the initial phase of marsh establishment. Rice field drainage waters provided higher sediment concentrations to the restored marsh, which in turn promoted C accumulation. Two years after the establishment of the restored marsh, C accumulation rates in both water type treatments (99.44 and 126.10 g m?² yr?¹) showed similar values to global estimates for freshwater marshes, but only half of salt marshes. The restored marsh was also an efficient N-P and metal filters even when receiving higher nutrient concentrations from rice field drainage waters: nutrient concentration reduction varied for total N (50.66 ± 3.85 %), N-NO3? (96.10 ± 0.35 %), N-NH4? (80.76 ± 1.8 %), total P (49.96 ± 3.95 %) and P-PO4³? (17.99 ± 3.92 %). Significantly higher Mn, Pb and Zn from drainage waters caused higher concentration reductions (47.4 ± 9.2 %, 44.1 ± 4.4 % and 23.7 ± 4.6 % respectively) in the DW treatment than the IW treatment. Higher Cu water concentrations from irrigation water increased significantly Cu concentration reduction (85.4 ± 0.5 %). Net export of As and Hg in both water treatments may be caused by releasing from previously stored metals in the pre-restored rice field soils. Plant growth affected ecosystem services in different ways. Root growth favoured marsh elevation, C accumulation and metal concentration reduction, especially as the weed P. distichum colonized rapidly and densely the restored marsh. However, higher nutrient concentrations from rice field drainage waters may also inhibit root growth. Root growth may also decrease nitrate concentration reduction ability via denitrification inhibition, but increased metal soil content via aerobic adsorption due to the plant ability to oxygenate their rhizosphere. This research supports that the use of rice field drainage waters as a primary source of nutrient and sediment as beneficial for marsh restoration projects focused on marsh elevation, C accumulation and pollutant removal. Higher nutrient and sediments concentrations enhanced these ecosystem services at least during initial stages of the restored marsh. The experimental marsh units receiving higher metal concentrations from rice field drainage water than river irrigation waters reduced metal water concentrations via soil content and accumulation. Organic soils and oxygen conditions enhanced by plant growth may favor soil metal content and higher sediment concentrations from rice field drainage waters also enhanced soil metal accumulation.

Additional Information

Publication

Dissertation

Language: English

Date: 2023

Subjects

Ecology;Geology;Biology, Ecology

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