A pinboard by
Xiaoguang Ouyang

PhD candidate, Griffith University


Unravel the factors controlling carbon flux via ex-and in-situ methods in coastal ecosystems

Coastal ecosystems, such as mangroves and saltmarshes, are 'blue carbon' ecosystems that have been increasingly recognized for their high capacity in sequestering carbon dioxide from the air and accumulating carbon in sediments, and hence have high potential to mitigate climate change. In particular, their carbon accumulation capacity is an order of magnitude higher than terrestrial ecosystems. However, the area of these coastal ecosystems has been shrinking due to deforestation and transformation to aquaculture ponds and agricultural lands. Their area is far less than terrestrial ecosystems but they play an disproportionately important role in carbon sequestration and act as a natural avenue of climate mitigation. Above-ground biomass of coastal ecosystems sequesters carbon dioxide from the air and allocate carbon to below ground roots and rhizosphere. Root/rhizosphere carbon decomposes, and either releases from sediments or accumulates in sediments, irrespective of some carbon dissolving in pore-water. Tides input sediments and organic matter from marine environment. Vegetation in coastal ecosystems attenuates the flow of tides. Sediments accrete over time to build lands and carbon accumulates in the process. Many coastal ecosystems receive sediment inputs from rivers and riverine organic matter also contribute to sediment carbon accumulation in coastal ecosystems. Sediments in coastal ecosystem are only oxic in the upper few centimeters and are anoxic or anaerobic in the deep sediments below the thin oxic layer. The generally anoxic and/or anaerobic conditions in sediments of coastal ecosystems result in low carbon mineralisation and thus facilitate carbon accumulation. Nonetheless, the range of carbon accumulation and mineralisation may vary due to a series of factors, including but not constrained to species, elevation, latitude, tidal conditions, sediment physio-chemical properties and coastal geomorphology. My research aims to promote effective blue carbon management. To arrive at this goal, it is urgent to understanding the mechanisms of carbon mineralisation and accumulation. As such, I conduct research to reveal the factors regulating sediment carbon accumulation, root carbon decomposition and carbon dioxide emissions. Please refer to my researchgate webpage for my research. https://www.researchgate.net/profile/Xiaoguang_Ouyang


Structural equation modelling reveals factors regulating surface sediment organic carbon content and CO2 efflux in a subtropical mangrove

Abstract: Mangroves are blue carbon ecosystems that sequester significant carbon but release CO2, and to a lesser extent CH4, from the sediment through oxidation of organic carbon or from overlying water when flooded. Previous studies, e.g. Leopold et al. (2015), have investigated sediment organic carbon (SOC) content and CO2 flux separately, but could not provide a holistic perspective for both components of blue carbon. Based on field data from a mangrove in southeast Queensland, Australia, we used a structural equation model to elucidate (1) the biotic and abiotic drivers of surface SOC (10 cm) and sediment CO2 flux; (2) the effect of SOC on sediment CO2 flux; and (3) the covariation among the environmental drivers assessed. Sediment water content, the percentage of fine-grained sediment (< 63 μm), surface sediment chlorophyll and light condition collectively drive sediment CO2 flux, explaining 41% of their variation. Sediment water content, the percentage of fine sediment, season, landform setting, mangrove species, sediment salinity and chlorophyll collectively drive surface SOC, explaining 93% of its variance. Sediment water content and the percentage of fine sediment have a negative impact on sediment CO2 flux but a positive effect on surface SOC content, while sediment chlorophyll is a positive driver of both. Surface SOC was significantly higher in Avicennia marina (2994 ± 186 g m− 2, mean ± SD) than in Rhizophora stylosa (2383 ± 209 g m− 2). SOC was significantly higher in winter (2771 ± 192 g m− 2) than in summer (2599 ± 211 g m− 2). SOC significantly increased from creek-side (865 ± 89 g m− 2) through mid (3298 ± 137 g m− 2) to landward (3933 ± 138 g m− 2) locations. Sediment salinity was a positive driver of SOC. Sediment CO2 flux without the influence of biogenic structures (crab burrows, aerial roots) averaged 15.4 mmol m− 2 d− 1 in A. marina stands under dark conditions, lower than the global average dark flux (61 mmol m− 2 d− 1) for mangroves.

Pub.: 09 Nov '16, Pinned: 25 Aug '17

The role of root decomposition in global mangrove and saltmarsh carbon budgets

Abstract: Publication date: Available online 19 January 2017 Source:Earth-Science Reviews Author(s): Xiaoguang Ouyang, Shing Yip Lee, Rod M. Connolly This study aims to determine the drivers of root decomposition and its role in carbon (C) budgets in mangroves and saltmarsh. We review the patterns of root decomposition, and its contribution to C budgets, in mangroves and saltmarsh: the impact of climatic (temperature and precipitation), geographic (latitude), temporal (decay period) and biotic (ecosystem type) drivers using multiple regression models. Best-fit models explain 50% and 48% of the variance in mangrove and saltmarsh root decay rates, respectively. A combination of biotic, climatic, geographic and temporal drivers influence root decay rates. Rainfall and latitude have the strongest influence on root decomposition rates in saltmarsh. For mangroves, forest type is the most important; decomposition is faster in riverine mangroves than other types. Mangrove species Avicennia marina and saltmarsh species Spartina maritima and Phragmites australis have the highest root decomposition rates. Root decomposition rates of mangroves were slightly higher in the Indo-west Pacific region (average 0.16% day−1) than in the Atlantic-east Pacific region (0.13% day−1). Mangrove root decomposition rates also show a negative exponential relationship with porewater salinity. In mangroves, global root decomposition rates are 0.15% day−1 based on the median value of rates in individual studies (and 0.14% day−1 after adjusting for area of mangroves at different latitudes). In saltmarsh, global root decomposition rates average 0.12% day−1 (no adjustment for area with latitude necessary). Our global estimate of the amount of root decomposing is 10 Tg C yr−1 in mangroves (8 Tg C yr−1 adjusted for area by latitude) and 31 Tg C yr−1 in saltmarsh. Local root C burial rates reported herein are 51–54g C m−2 yr−1 for mangroves (58–61 Tg C yr−1 adjusted for area by latitude) and 191g C m−2 yr−1 for saltmarsh. These values account for 24.1–29.1% (mangroves) and 77.9% (saltmarsh) of the reported sediment C accumulation rates in these habitats. Globally, dead root C production is the significant source of stored sediment C in mangroves and saltmarsh.

Pub.: 21 Jan '17, Pinned: 25 Aug '17