Variability in the organic carbon stocks, sources, and accumulation rates of Indonesian mangrove ecosystems

Helmut W Fischer,Daniela Ransby,Mariska Astrid Kusumaningtyas,Manuel Pérez-Mayo,Andreas A Hutahaean,Tim C Jennerjahn

doi:10.1016/j.ecss.2018.12.007

Abstract

Mangrove ecosystems are an important natural carbon sink that accumulate and store large amounts of organic carbon (Corg), in particular in the sediment. However, the magnitude of carbon stocks and the rate of carbon accumulation (CAR) vary geographically due to a large variation of local factors. In order to better understand the blue carbon sink of mangrove ecosystems, we measured organic carbon stocks, sources and accumulation rates in three Indonesian mangrove ecosystems with different environmental settings and conditions; (i) a degraded estuarine mangrove forest in the Segara Anakan Lagoon (SAL), Central Java, (ii) an undegraded estuarine mangrove forest in Berau region, East Kalimantan, and (iii) a pristine marine mangrove forest on Kongsi Island, Thousand Islands, Jakarta. In general, Corg stocks were higher in estuarine than in marine mangroves, although a large variation was observed among the estuarine mangroves. The mean total Corg stock in Berau (615 ± 181 Mg C ha−1) is twice as high as that in SAL (298 ± 181 Mg C ha−1). However, the Segara Anakan Lagoon displayed large within-system variation with a much higher Corg stock in the eastern (483 ± 124 Mg C ha−1) than in the central lagoon (167 ± 36 Mg C ha−1). The predominant accumulation of autochthonous mangrove organic matter likely contributed to the higher Corg stocks in Berau and the eastern SAL. Interestingly, the CAR distribution pattern in SAL is opposite to that of its Corg stocks. The central SAL that receives high sediment inputs from the hinterland has a much higher CAR than the eastern SAL (658 ± 311 g C m−2 yr−1 and 194 ± 46 g C m−2 yr−1, respectively), while Berau has one of the highest CAR (1722 ± 183 g C m−2 yr−1) ever measured. It appears that these large differences are driven by the environmental setting and conditions, mainly sediment dynamics and hydrodynamics, landform, and vegetation conditions. It is inferred that quantifying carbon accumulation in sediments is a useful tool in estimating the present-day carbon storage of mangrove ecosystems. This is a precondition for taking measures under REDD+ (Reducing Emissions from Deforestation and Forest Degradation and the role of conservation, sustainable management of forests and enhancement of forest carbon stocks in developing countries) schemes.

Highlights

Situated in the transition zone between land and ocean, mangrove ecosystems are one of the most biogeochemically active areas in the biosphere due to permanent exchange of nutrients and organic matter with adjacent ecosystems
In order to better understand the spatial pattern of mangrove carbon storage and composition, we measured organic carbon stocks and accumulation rates, and we identified the sources of organic matter in three Indonesian mangrove ecosystems
It was lower in the estuarine mangroves in Berau (1.20 ± 0.36 g cm−3) and in the Segara Anakan Lagoon (0.62 ± 0.11 g cm−3 in the east, 0.74 ± 0.11 g cm−3 in the central area)

Summary

Introduction

Situated in the transition zone between land and ocean, mangrove ecosystems are one of the most biogeochemically active areas in the biosphere due to permanent exchange of nutrients and organic matter with adjacent ecosystems. The mean global carbon stock of mangrove ecosystems is estimated at 956 Mg C ha−1, which is much higher than those of rainforests, peat swamps, salt marshes, and seagrass meadows (Alongi, 2014). Their advantage over terrestrial forests is their much higher carbon accumulation in sediments/soils which is mainly due to high autochthonous and allochthonous inputs and low decomposition rates of organic matter because of the mostly anoxic conditions in the sediment (Donato et al, 2011; Kristensen, 2000). The rate of organic carbon accumulation in mangrove ecosystems is estimated to be around 20–24 Tg C yr−1 (Twilley et al, 1992; Jennerjahn and Ittekkot, 2002; Duarte et al, 2004)

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Discussion

Conclusion