Belowground carbon sequestration in a mature planted mangroves (Northern Viet Nam) Ha Thi Hien a , Cyril Marchand b,c , Joanne Aimé b,c , Dang Hoai Nhon d , Phan Nguyen Hong e , Nguyen Xuan Tung f , Nguyen Thi Kim Cuc a,e,⇑ a Thuyloi University, 175 Tay Son Str., Dong Da Dist., Ha Noi, Viet Nam b IMPMC, Institut de Recherche pour le Développement (IRD), UPMC, CNRS, MNHN, Noumea, New Caledonia, France c Analytical Chemistry Department, University of Sciences of Ho Chi Minh City, 225 Nguyen Van Cu, Ho Chi Minh, Viet Nam d Marine Geo-environment Department, Institute of Marine Environment and Resource, 246 Danang Street, Hai Phong, Viet Nam e Mangrove Ecosystem Research Division (MERD), Centre for Natural Resources and Environmental Studies (CRES), Vietnam National University (VNU), 144 Xuan Thuy, Cau Giay, Ha Noi, Viet Nam f Mangrove Ecosystem Research Centre (MERC), Hanoi National University of Education (HNUE), 136 Xuan Thuy, Cau Giay Dist., Ha Noi, Viet Nam article info Article history: Received 25 March 2017 Received in revised form 21 June 2017 Accepted 28 June 2017 Available online xxxx Keywords: Planted mangroves Soil Carbon stocks Carbon burial rates Viet Nam abstract Mangroves play a key role in carbon sequestration along tropical and subtropical coastlines, mainly as a result of their high primary productivity and the anoxic character of their soils, in which organic matter decay processes are slow. Unfortunately, these forests are disappearing worldwide, notably due to aqua- culture and the need for space on the shoreline. The mangrove area in Viet Nam decreased substantially until late 90’s, which was a concern for the Vietnamese government. Then, replantation programs were developed in order to protect the shoreline against the erosion; like in northern Viet Nam, where monospecific stands were planted from the mid 90’s. Within this context, our objectives were to deter- mine carbon stocks and carbon burial rates in the soil of a 18 years old Kandelia obovata (Sheue, Lui & Yong) mangrove forest. Three plots were set up in the planted mangroves and three in adjacent bare land (without any mangrove) at the mouth of Red River. Three geo-slicers up to 100 cm depth were taken in each plot; and in each core, ten soil samples were collected with a 10 cm depth interval. Later on, dead and live roots were sorted. Carbon contents in soils and in roots were determined using the Walkley- Black method and loss on ignition (LOI) method, respectively. Then, the total belowground carbon sequestration was estimated. There was a depth related distribution of organic carbon in soil with the highest concentrations measured between 20 and 60 cm depth. Accumulated carbon up to depth of 100 cm in soil and roots of the planted K. obovata were 146.78 ± 3.87 Mg OC ha 1 and 12.67 ± 0.14 Mg OC ha 1 , respectively. The value was 87.59 ± 1.08 Mg OC ha 1 for the adjacent bare land. Consequently, the mean carbon burial rate for this system was approximately 6.94 Mg OC ha 1 yr 1 , which is higher than most of the mangroves and may be related to a low export of the net primary pro- ductivity or most likely to a high sedimentation rate. These results were compared with previously pub- lished results on carbon stocks in younger planted forests of the same species in the same region, a positive and linear relationship was determined between the age of the planted stand and the below- ground carbon stocks. Ó 2017 Elsevier B.V. All rights reserved. 1. Introduction Mangroves are saline or brackish wetland environments, mainly anoxic due to waterlogging (Kristensen et al., 2008; Kauffman et al., 2011). This unique condition, combined with their high productivity (218 ± 72 Tg C y 1 ; Bouillon et al., 2008), induces a high ability of this ecosystem in fixing and storing CO 2 , one of the greenhouse gases that contribute to global warming. Carbon is assimilated and stored, both in aboveground and belowground bio- mass (stems, branches, leaves and roots) but also in their soils, with up to 90% of carbon stocks stored as soil organic matter (Donato et al., 2011; Stringer et al., 2015). Breithaupt et al. (2012) suggested that up to 15% of mangrove productivity can be buried, the remaining being decomposed or exported towards adjacent ecosystems through tidal flushing or tidal pumping (Maher et al., 2013; Leopold et al., 2015, 2016). Although http://dx.doi.org/10.1016/j.foreco.2017.06.057 0378-1127/Ó 2017 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: 175 Tay Son Str., Dong Da Dist., Ha Noi City, Viet Nam. E-mail addresses: nguyencucvn@gmail.com, nguyencuc@tlu.edu.vn (T.K.C. Nguyen). Forest Ecology and Management xxx (2017) xxx–xxx Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco Please cite this article in press as: Ha, T.H., et al. Belowground carbon sequestration in a mature planted mangroves (Northern Viet Nam). Forest Ecol. Man- age. (2017), http://dx.doi.org/10.1016/j.foreco.2017.06.057