title: Changes in soil characteristics and C dynamics after mangrove clearing (Vietnam).
abstract: Of the blue carbon sinks, mangroves have one of the highest organic matter (OM) storage capacities in their soil due to low mineralization processes resulting from waterlogging. However, mangroves are disappearing worldwide because of demographic increases. In addition to the loss of CO2fixation, mangrove clearing can strongly affect soil characteristics and C storage. The objectives of the present study were to quantify the evolution of soil quality, carbon stocks and carbon fluxes after mangrove clearing. Sediment cores to assess physico-chemical properties were collected and in situ CO2fluxes were measured at the soil-air interface in a mangrove of Northern Vietnam. We compared a Kandelia candel mangrove forest with a nearby zone that had been cleared two years before the study. Significant decrease of clay content and an increase in bulk density for the upper 35cm in the cleared zone were observed. Soil organic carbon (OC) content in the upper 35cm decreased by >65% two years after clearing. The quantity and the quality of the carbon changed, with lower carbon to nitrogen ratios, indicating a more decomposed OM, a higher content of dissolved organic carbon, and a higher content of inorganic carbon (three times higher). This highlights the efficiency of mineralization processes following clearing. Due to the rapid decrease in the soil carbon content, CO2fluxes at sediment interface were >50% lower in the cleared zone. Taking into account carbonate precipitation after OC mineralization, the mangrove soil lost ~10MgOCha-1yr-1mostly as CO2to the atmosphere and possibly as dissolved forms towards adjacent ecosystems. The impacts on the carbon cycle of mangrove clearing as shown by the switch from a C sink to a C source highlight the importance of maintaining these ecosystems, particularly in a context of climate change.
authors.affiliation: Department of Spatial planning and Environment Engineering, CITERES UMR7324 CNRS, University of François Rabelais, Tours, France. Electronic address: seraphine.grellier@univ-tours.fr.
authors.forename: Séraphine
authors.initials: S
authors.lastname: Grellier
authors.affiliation: Institut de Recherche pour le Développement (IRD), iEES-Paris, UMR 242, IRD Bangkok, Thailand.
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Janeau
authors.affiliation: Institute of Marine Environment and Resources (IMER, VAST), 246 Da Nang Street, Hai Phong City, Viet Nam.
authors.forename: Nhon
authors.initials: N
authors.lastname: Dang Hoai
authors.affiliation: Department of Natural Resources Management, Thuy Loi University, 175, Tay Son, Dong Da, Ha Noi, Viet Nam; Mangrove Ecosystem Research Division (MERD), Centre for Natural Resources and Environmental Studies (CRES), Vietnam National University (VNU), 19 Le Thanh Tong, Ha Noi, Viet Nam.
authors.forename: Cuc
authors.initials: C
authors.lastname: Nguyen Thi Kim
authors.affiliation: Institute of Natural Products Chemistry (INPC), Vietnam Academy of Science and Technology, 1H, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Viet Nam.
authors.forename: Quynh
authors.initials: Q
authors.lastname: Le Thi Phuong
authors.affiliation: Department of Water, Environment, Oceanography, University of Science and Technology of Hanoi (USTH), 18 Hoang Quoc Viet, Cau Giay, Hanoi, Viet Nam.
authors.forename: Thao
authors.initials: T
authors.lastname: Pham Thi Thu
authors.affiliation: Faculty of Chemistry, University of Science - VNUHCM, 225 Nguyen Van Cu, Ho Chi Minh City, Viet Nam.
authors.forename: Nhu-Trang
authors.initials: NT
authors.lastname: Tran-Thi
authors.affiliation: Faculty of Chemistry, University of Science - VNUHCM, 225 Nguyen Van Cu, Ho Chi Minh City, Viet Nam; Institut de Recherche pour le Développement (IRD), UMR 7590, UR 206, BP A5, 98848 Nouméa, New Caledonia, France.
authors.forename: Cyril
authors.initials: C
authors.lastname: Marchand
keywords: Afforested mangrove; Carbon stocks; Sediment properties; Soil CO(2) fluxes; South East Asia; Xuan Thuy National Park