The Role of soil as a carbon sink in coastal marsh and agricultural systems at La Pletera (Girona province, Spain)

Phang, Chantha
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The concentration of atmospheric CO2 is now one third higher than it was during the eighteenth century, and significantly increased during the last several hundred thousand years. CO2 concentration is causing substantial warming and other changes in global climate by altering the heat and water balances of Earth’s surface and atmosphere. Today, scientists, engineers, and researchers on the carbon cycle are working not only to be sure that the experiment is adequately documented, but also to provide information and tools that can be properly managed. The challenge of controlling atmosphere CO2 level is a topic of expanding public concern, national policies, and international agreement. The importance of soil dynamics on the organic carbon cycle has been outlined to remark that the soil system may capture and reserve almost 16% of the global CO2 emissions. It is therefore important to have a wide knowledge of which are the soil compartments having a high potential for carbon sequestration. The present work is associated to the life project “De-urbanizing and recovering the ecological functioning of the coastal systems of La Pletera” and reports the first preliminary results in order to verify the carbon sequestration potential of different areas either altered by anthropic activities or having a proper and natural ecological development. The main question arisen is the convenience to maintain saltmarsh coastal systems and demonstrate that these areas are strong contributors of soil organic carbon storage, instead of disregard in favour of new land use. It is known that the saltmarsh ecosystems may retain until 37% of organic carbon due its peculiar dynamics of wet-dry cycles. Similarly, organic agriculture and pastureland may also be consistent in preserving organic carbon in soil if adequately managed. Six soil environments were selected in the whole area of study such as: Ruderal (RU); soil under Elymus elymoides (ELY); soil under Arthrocnemum fruticosum (SAAR); soil under Salicornia patula (SAER); soil under corn cultivation (AGR); soil under pasture (PAS) and soil samples collected at three depths (0-5 cm, 5-20 cm, and 20-40 cm) in order to differentiate the development of soil properties along profiles. Soil characterization included mineralogical and physical analyses such as texture and structural stability of aggregates, determined in order to compare the resistance of the various soils to degradation, together with soil chemical characteristics such as pH, electrical conductivity (EC), Soil organic carbon (SOC), Soil extractable carbon (FA&HA), Total nitrogen (TN), Extraction of easily extractable glomalin (EE-GRSP), Extraction of total glomalin (GRSP), Dissolve organic carbon (DOC), and soil respiration. Results clearly showed that SAAR soil was the most adequate to preserve organic carbon as it showed the highest clay content, structural stability, glomalin and soil organic carbon, whilst the carbon loss by respiration was the lowest among the other soils. Similarly, the mineralization coefficient of SAAR soil was 1360%, 1220%, 580%, 360%, 280% lower than AGR, SAER, PAS, RU and ELY respectively. This trend provided a twofold information, on the one end the agricultural soil should be managed differently as it showed a large carbon loss with respect to the carbon content; on the other hand the carbon lost by the SAER soil which should has been apparently a suitable carbon sink was absolutely inadequate to preserve organic carbon. The overall results of this work should be used for eventual soil restoration practices at the Pletera ​
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