ESTIMASI POTENSI KARBON SEDIMEN MANGROVE PADA HUTAN ALAM DAN HUTAN REHABILITASI DI TAMAN HUTAN RAYA NGURAH RAI BALI

Sediments play an important role in coastal ecosystems. Apart from being a growing medium, sediment is also a place for accumulation and storage of various components including carbon. Ngurah Rai Forest Park is the largest mangrove in Bali with a large potential for sediment carbon stocks. To determine the carbon storage of mangrove sediments in natural forest and rehabilitation forest and the relationship between diameter size and vegetation type to sediment carbon in two forest types, a study was conducted using purposive sampling method based on canopy density level with three repetitions with a plot size of 10 mx. 10 meters. Sampling was divided into three depths, namely 0-30 cm, 31-60 cm and 61-100 cm. The total carbon content of mangrove sediments in natural forest is 363,491.17 Mg C or equivalent to 363,491.17 tons C and rehabilitation forest is 160,401.33 Mg C or equivalent to 160,401.33 tons C. The total sediment carbon content in Ngurah Rai Forest Park is 523,892.50 Mg C or equivalent to 523,892.50 tons C. Tree diameter had no significant effect on sediment carbon content, while vegetation type significantly affected sediment carbon content. Sonneratia alba had a significant negative effect on natural forests, while Rhizophora stylosa had a significant positive effect on rehabilitation forests. The results of the study suggest that it is necessary to maintain the preservation of mangroves and carry out rehabilitation in damaged areas. To increase the carbon content of sediments in mangrove forests, consider selecting the type of vegetation Rhizophora stylosa for the implementation of rehabilitation activities, because the type of Rhizophora stylosa makes a positive contribution to increasing the carbon content of sediments, with a note that the rehabilitation location is suitable for Rhizoporaceae species. Keywords: Mangrove; Nature Forest; Rehabilitation; Sediment.

Improved the in-Situ Remediation Effect of Sediment Microbial Fuel Cells by Optimizing the Anode Structure

Six 60-L benthic microbial electrochemical systems (BMES) were built for the bioremediation of river sediment. Carbon mesh anodes with honeycomb-structure supports were compared with horizontal anodes, and the system was tested using different cover depths and anode densities. The pollutant removal, electricity generation, and electrochemistry of the six BMES with different anodes was examined using the Ashi River (Harbin, China) as a case study. Total organic carbon (TOC) and total nitrogen (TN) removal from sediments in BMES with three-dimensional anodes were 20%~30% and 20%~33% higher for the other reactors. Moreover, the honeycomb-structure of the anode also resulted in higher power density and improved humus removal.

Kleptoplast distribution, photosynthetic efficiency and sequestration mechanisms in intertidal benthic foraminifera

Foraminifera are ubiquitously distributed in marine habitats, playing a major role in marine sediment carbon sequestration and the nitrogen cycle. They exhibit a wide diversity of feeding and behavioural strategies (heterotrophy, autotrophy and mixotrophy), including species with the ability of sequestering intact functional chloroplasts from their microalgal food source (kleptoplastidy), resulting in a mixotrophic lifestyle. The mechanisms by which kleptoplasts are integrated and kept functional inside foraminiferal cytosol are poorly known. In our study, we investigated relationships between feeding strategies, kleptoplast spatial distribution and photosynthetic functionality in two shallow-water benthic foraminifera (Haynesina germanica and Elphidium williamsoni), both species feeding on benthic diatoms. We used a combination of observations of foraminiferal feeding behaviour, test morphology, cytological TEM-based observations and HPLC pigment analysis, with non-destructive, single-cell level imaging of kleptoplast spatial distribution and PSII quantum efficiency. The two species showed different feeding strategies, with H. germanica removing diatom content at the foraminifer’s apertural region and E. williamsoni on the dorsal site. All E. williamsoni parameters showed that this species has higher autotrophic capacity albeit both feeding on benthic diatoms. This might represent two different stages in the evolutionary process of establishing a permanent symbiotic relationship, or may reflect different trophic strategies.

Blue carbon stocks and exchanges along the California coast

Salt marshes and seagrass meadows can sequester and store high quantities of organic carbon (OC) in their sediments relative to other marine and terrestrial habitats. Assessing carbon stocks, carbon sources, and the transfer of carbon between habitats within coastal seascapes are each integral in identifying the role of blue carbon habitats in coastal carbon cycling. Here, we quantified carbon stocks, sources, and exchanges in seagrass meadows, salt marshes, and unvegetated sediments in six bays along the California coast. In the top 20 cm of sediment, the salt marshes contained approximately twice as much OC as seagrass meadows did, 4.92 ± 0.36 kg OC m−2 compared to 2.20 ± 0.24 kg OC m−2, respectively. Both salt marsh and seagrass sediment carbon stocks were higher than previous estimates from this region but lower than global and US-wide averages, respectively. Seagrass-derived carbon was deposited annually into adjacent marshes during fall seagrass senescence. However, isotope mixing models estimate that negligible amounts of this seagrass material were ultimately buried in underlying sediment. Rather, the vast majority of OC in sediment across sites was likely derived from planktonic/benthic diatoms and/or C3 salt marsh plants.

The potential for mobile demersal fishing to reduce carbon storage and sequestration in seabed sediments

Subtidal marine sediments are one of the planet's primary carbon stores and strongly influence the oceanic sink for atmospheric CO2. By far the most pervasive human activity occurring on the seabed is bottom trawling and dredging for fish and shellfish. A global first-order estimate suggested mobile demersal fishing activities may cause 160-400 Mt of organic carbon (OC) to be remineralised annually from seabed sediment carbon stores. There are, however, many uncertainties in this calculation. Here, we discuss the potential drivers of change in seabed OC stores due to mobile demersal fishing activities and conduct a systematic review, synthesising studies where this interaction has been directly investigated. Mobile demersal fishing would be expected to reduce OC in seabed stores, albeit with site-specific variability. Reductions would occur due to lower production of flora and fauna, the loss of fine flocculent material, increased sediment resuspension, mixing and transport, and increased oxygen exposure. This would be offset to some extent by reduced faunal bioturbation and respiration, increased off-shelf transport and increases in primary production from the resuspension of nutrients. Studies which directly investigated the impact of demersal fishing on OC stocks had mixed results. A finding of no significant effect was reported in 51% of 59 experimental contrasts; 41% reported lower OC due to fishing activities, with 8% reporting higher OC. In relation to remineralisation rates within the seabed, 14 experimental contrasts reported that demersal fishing activities decreased remineralisation, with four reporting higher remineralisation rates. The direction of effects was related to sediment type, impact duration, study design and local hydrography. More evidence is urgently needed to accurately quantify the impact of anthropogenic physical disturbance on seabed carbon in different environmental settings, and incorporate full evidence-based carbon considerations into global seabed management.

A structure–function based approach to floc hierarchy and evidence for the non-fractal nature of natural sediment flocs

Natural sediment flocs are fragile, highly irregular, loosely bound aggregates comprising minerogenic and organic material. They contribute a major component of suspended sediment load and are critical for the fate and flux of sediment, carbon and pollutants in aquatic environments. Understanding their behaviour is essential to the sustainable management of waterways, fisheries and marine industries. For several decades, modelling approaches have utilised fractal mathematics and observations of two dimensional (2D) floc size distributions to infer levels of aggregation and predict their behaviour. Whilst this is a computationally simple solution, it is highly unlikely to reflect the complexity of natural sediment flocs and current models predicting fine sediment hydrodynamics are not efficient. Here, we show how new observations of fragile floc structures in three dimensions (3D) demonstrate unequivocally that natural flocs are non-fractal. We propose that floc hierarchy is based on observations of 3D structure and function rather than 2D size distribution. In contrast to fractal theory, our data indicate that flocs possess characteristics of emergent systems including non-linearity and scale-dependent feedbacks. These concepts and new data to quantify floc structures offer the opportunity to explore new emergence-based floc frameworks which better represent natural floc behaviour and could advance our predictive capacity.