The role of wetlands as environmental buffers: comparison of phosphorus retention capacity between hydrosedimentary environments

Since the middle of the twentieth century, human societies has quadrupled the environmental flow of phosphorus –P, dramatically impairing freshwater and coastal marine ecosystems (1). Wetlands act as environmental buffers retaining nutrients and pollutants delivered from upstream parts of river systems. This buffer effect also avoids the conveyance of these pollutants to the marine environment preventing eutrophication of coastal marine ecosystems.

The aim of this research is to assessing P concentrations within the S’Albufera (1,708 ha), the main wetland of Mallorca (Spain) and protected by the Ramsar list of wetlands of international importance. Since the middle of the ninetieth century, it is an artificial system, in which waters are forced to take the shortest route to the sea (2). The study of accretion rates by using ¹³⁷Cs measurements will be combined with the nutrient retention capacity analysing phosphorus concentrations in fine-grained sediments. Accordingly, 5 integrated sediment cores, composed by two replicas, sectioned at 5-cm intervals were collected in February 2016 in three representative hydrosedimentary environments of S’Albufera: two at the centre of the main artificial channel, one at the bank of this main channel and two within the lagoon areas. Total, inorganic and organic P were quantified in 532 samples in order to assess the nutrient dynamics into these representative hydrosedimentary environments and depths.

The ¹³⁷Cs measurements depicted how the sediment cores collected in the middle of the artificial channel as well into its banks were mainly characterized by erosional processes due to the lack of ¹³⁷Cs at any depth. On the other side, cores sampled at lagoon areas illustrated depositional processes with mean accretion rates since 1963 between ca. 0.139 g m^-2 yr^-1 to 0.169 g m^-2 yr^-1.

Total P concentrations were significantly higher in lagoon areas (0.082 mg P g^-1 sediment) than in the sediment from banks of the main artificial channel (0.037 mg P g^-1 sediment) or into the middle of this channel (0.03 mg P g^-1 sediment). The same pattern was observed for organic and inorganic P with concentrations within lagoon areas of 0.039 mg P g^-1 sediment and 0.043 mg P g^-1 sediment, respectively. Concentrations for the banks of the main artificial channel were 0.018 mg P g^-1 sediment for inorganic P and 0.019 mg P g^-1 sediment for organic P. At the middle of the artificial channel, concentrations were even lower, with 0.014 mg P g^-1 sediment for inorganic P and 0.016 mg P g^-1 sediment for organic P.

These results elucidate that the natural maintenance of wetlands is crucial to ensure their optimal functioning as environmental buffers.

 

References

(1) Lane and Autrey, 2017. MFR. DOI: 10.1071/MF16372

(2) Lopez et al., 1996. ECSS. DOI: 10.1006/ecss.1996.0014

This work was supported by the research project CGL2017-88200-R “Functional hydrological and sediment connectivity at Mediterranean catchments: global change scenarios –MEDhyCON2” funded by the Spanish Ministry of Science, Innovation and Universities, the Spanish Agency of Research (AEI) and the European Regional Development Funds (ERDF).