ORCID Profile
0000-0002-8672-8021
Current Organisations
University of Southampton
,
Universiti Malaysia Sarawak
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Copernicus GmbH
Date: 19-05-2022
DOI: 10.5194/BG-2021-347
Abstract: Abstract. High-quality ocean colour observations are increasingly accessible to support various monitoring and research activities for water quality measurements. In this paper, we present a newly developed regional total suspended solids (TSS) empirical model using MODIS-Aqua’s Rrs(530) and Rrs(666) reflectance bands to investigate the spatial and temporal variation of TSS dynamics along the southwest coast of Sarawak, Borneo. The performance of this TSS retrieval model was evaluated using error metrics (bias = 1.0, MAE = 1.47, and RMSE = 0.22 in mg/L) with a log10 transformation prior to calculation, as well as a k-fold cross validation technique. The temporally averaged map of TSS distribution, using daily MODIS-Aqua satellite datasets from 2003 until 2019, revealed large TSS plumes detected particularly in the Lupar and Rajang coastal areas on a yearly basis. The average TSS concentration range of 15 – 20 mg/L was estimated at these coastal areas. Moreover, the spatial map of TSS coefficient of variation (CV) indicated strong TSS variability (approximately 90 %) in the Samunsam-Sematan coastal areas, which could potentially impact nearby coral reef habitats in this region. Our findings on temporal TSS variation provide further evidence that monsoonal patterns drive the TSS release in these tropical water systems, with distinct and widespread TSS plume variations observed between the northeast and southwest monsoon periods. Map of relative TSS distribution anomalies revealed strong spatial TSS variations in the Samunsam-Sematan coastal areas, while 2010 recorded a major increase (approximately 100 %) and widespread TSS distribution with respect to the long-term mean. Furthermore, our findings on the contribution of river discharge to the TSS distribution showed a weak correlation across time at both the Lupar and Rajang river mouth points. The variability of TSS distribution across coastal river points was studied by investigating the variation of TSS pixels at three transect points, stretching from the river mouth into territorial and open water zones, for eight main rivers. Our findings showed a progressively decreasing pattern of nearly 50 % in relation to the distance from shore, with exceptions in the northeast regions of the study area. Essentially, our findings demonstrate that the TSS levels at the southwest coast of Sarawak are within local water quality standards, promoting various marine and socio-economic activities. This study presents the first observation of TSS distributions at Sarawak coastal systems with the application of remote sensing technologies, to enhance coastal sediment management strategies for the sustainable use of coastal waters and their resources.
Publisher: Copernicus GmbH
Date: 16-11-2018
Abstract: Abstract. South-East Asia is home to one of the world's largest stores of tropical peatland and accounts for roughly 10 % of the global land-to-sea dissolved organic carbon (DOC) flux. We present the first ever seasonally resolved measurements of DOC concentration and chromophoric dissolved organic matter (CDOM) spectra for six peatland-draining rivers and coastal waters in Sarawak, north-western Borneo. The rivers differed substantially in DOC concentration, ranging from 120–250 µmol L−1 (Rajang River) to 3100–4400 µmol L−1 (Maludam River). All rivers carried high CDOM concentrations, with a350 in the four blackwater rivers between 70 and 210 m−1 and 4 and 12 m−1 in the other two rivers. DOC and CDOM showed conservative mixing with seawater except in the largest river (the Rajang), where DOC concentrations in the estuary were elevated, most likely due to inputs from the extensive peatlands within the Rajang Delta. Seasonal variation was moderate and inconsistent between rivers. However, during the rainier north-east monsoon, all marine stations in the western part of our study area had higher DOC concentrations and lower CDOM spectral slopes, indicating a greater proportion of terrigenous DOM in coastal waters. Photodegradation experiments revealed that riverine DOC and CDOM in Sarawak are photolabile: up to 25 % of riverine DOC was lost within 5 days of exposure to natural sunlight, and the spectral slopes of photo-bleached CDOM resembled those of our marine s les. We conclude that coastal waters of Sarawak receive large inputs of terrigenous DOC that is only minimally altered during estuarine transport and that any biogeochemical processing must therefore occur mostly at sea. It is likely that photodegradation plays an important role in the degradation of terrigenous DOC in these waters.
Publisher: Copernicus GmbH
Date: 19-12-2022
Abstract: Abstract. High-quality ocean colour observations are increasingly accessible to support various monitoring and research activities for water quality measurements. In this paper, we present a newly developed regional total suspended solids (TSSs) empirical model using MODIS Aqua's Rrs(530) and Rrs(666) reflectance bands to investigate the spatial and temporal variation in TSS dynamics along the southwest coast of Sarawak, Borneo, with the application of the Open Data Cube (ODC) platform. The performance of this TSS retrieval model was evaluated using error metrics (bias = 1.0, MAE = 1.47, and RMSE = 0.22, in milligrams per litre) with a log10 transformation prior to calculation as well as using a k-fold cross-validation technique. The temporally averaged map of the TSS distribution, using daily MODIS Aqua satellite datasets from 2003 until 2019, revealed that large TSS plumes were detected – particularly in the Lupar and Rajang coastal areas – on a yearly basis. The average TSS concentration in these coastal waters was in the range of 15–20 mg L−1. Moreover, the spatial map of the TSS coefficient of variation (CV) indicated strong TSS variability (approximately 90 %) in the Samunsam–Sematan coastal areas, which could potentially impact nearby coral reef habitats in this region. Study of the temporal TSS variation provides further evidence that monsoonal patterns drive the TSS release in these tropical water systems, with distinct and widespread TSS plume variations observed between the northeast and southwest monsoon periods. A map of relative TSS distribution anomalies revealed strong spatial TSS variations in the Samunsam–Sematan coastal areas, while 2010 recorded a major increase (approximately 100 %) and widespread TSS distribution with respect to the long-term mean. Furthermore, study of the contribution of river discharge to the TSS distribution showed a weak correlation across time at both the Lupar and Rajang river mouth points. The variability in the TSS distribution across coastal river points was studied by investigating the variation in the TSS pixels at three transect points, stretching from the river mouth into territorial and open-water zones, for eight main rivers. The results showed a progressively decreasing pattern of nearly 50 % in relation to the distance from shore, with exceptions in the northeast regions of the study area. Essentially, our findings demonstrate that the TSS levels on the southwest coast of Sarawak are within local water quality standards, promoting various marine and socio-economic activities. This study presents the first observation of TSS distributions in Sarawak coastal systems with the application of remote sensing technologies and aims at enhancing coastal sediment management strategies for the sustainable use of coastal waters and their resources.
Publisher: Copernicus GmbH
Date: 11-09-2018
Publisher: Springer Science and Business Media LLC
Date: 17-04-2023
Publisher: American Geophysical Union (AGU)
Date: 28-04-2021
DOI: 10.1029/2020GL092130
Abstract: Terrigenous dissolved organic matter (tDOM) carried by rivers represents an important carbon flux to the coastal ocean, which is thought to be increasing globally. Because tDOM is rich in light‐absorbent chromophoric dissolved organic matter (CDOM), it may also reduce the amount of sunlight available in coastal ecosystems. Despite its biogeochemical and ecological significance, there are few long‐term records of tDOM, hindering our understanding of its drivers and dynamics. Corals incorporate terrestrial humic acids, an important constituent of CDOM, resulting in luminescent bands that have been previously linked to rainfall and run‐off. We show that luminescence green‐to‐blue (G/B) ratios in a coral core growing in waters affected by peatland run‐off correlate strongly with remote sensing‐derived CDOM absorption. The 24‐year monthly resolution reconstructed record shows that rainfall controls land‐to‐ocean tDOM flux from this protected peatland catchment, and suggests an additional impact by solar radiation, which degrades tDOM at sea.
Publisher: Copernicus GmbH
Date: 11-09-2018
DOI: 10.5194/BG-2018-389
Abstract: Abstract. South-East Asia is home to one of the world's largest stores of tropical peatland, and accounts for roughly 10 % of the global land-to-sea dissolved organic carbon (DOC) flux. We present the first-ever seasonally-resolved measurements of DOC concentration and chromophoric dissolved organic matter (CDOM) spectra for six peatland-draining rivers and coastal waters in Sarawak, north-western Borneo. The rivers differed substantially in DOC concentration, ranging from 120–250 µmol L−1 (Rajang river) to 3,100–4,400 µmol L−1 (Maludam river). All rivers carried high CDOM concentrations, with a350 in the four blackwater rivers between 70–210 m−1, and 4–12 m−1 in the other two rivers. DOC and CDOM showed conservative mixing with seawater except in the largest river (the Rajang), where DOC concentrations in the estuary were elevated, most likely due to inputs from the extensive peatlands within the Rajang delta. Seasonal variation was moderate and inconsistent between rivers. However, during the rainier north-east monsoon, all marine stations in the western part of our study area had higher DOC concentrations and lower CDOM spectral slopes, indicating a greater proportion of terrigenous DOM in coastal waters. Photo-degradation experiments revealed that riverine DOC and CDOM in Sarawak are photo-labile: up to 25 % of riverine DOC was lost within five days of exposure to natural sunlight, and the spectral slopes of photo-bleached CDOM resembled those of our marine s les. We conclude that coastal waters of Sarawak receive large inputs of terrigenous DOC that is only minimally altered during estuarine transport, and that any biogeochemical processing must therefore occur mostly at sea. It is likely that photo-degradation plays an important role in the degradation of terrigenous DOC in these waters.
Publisher: Copernicus GmbH
Date: 19-05-2022
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-6864
Abstract: & & The flux of terrigenous dissolved organic carbon (tDOC) from land to the coastal ocean is an important component of the global carbon cycle, and can impact coastal marine ecosystems. A potentially large fraction of this tDOC flux can be oxidised to CO& sub& & /sub& , resulting in coastal ocean acidification and ultimately degassing to the atmosphere. tDOC is also rich in chromophoric dissolved organic matter (CDOM) which is the fraction of dissolved organic matter that absorbs light. CDOM plays an important role in aquatic systems by absorbing sunlight and reducing its transmission through the water column. This is a partially beneficial effect since photodegradation reactions release nutrients and protect biota from harmful UV radiation. However, CDOM light absorption also reduces the light available for primary producers. Long running tDOC and CDOM measurements from North America and Europe show that tDOC fluxes have been increasing in the 20& sup& th& /sup& century in response to climate and land-use change. However, despite the biogeochemical and ecological significance of tDOC, there are few long-term records of tDOC, and none at all from tropical shelf sea environments. This severely limits our understanding of its drivers and processes.& & & & & Here, we show that luminescence green-to-blue (G/B) ratios in coral skeleton cores are an accurate proxy for tDOC concentration in seawater. Coral luminescence is generated by humic-like substances, which are highly fluorescing compounds that are incorporated by corals into their skeletons during growth, forming sub-annual growth layers that luminesce under UV light. These humic-like substances are an integral component of tDOC and are an important constituent of the CDOM pool. We used solution fluorescence excitation emission matrix (EEM) measurements of dissolved powders of coral skeletons collected from multiple locations on the Sunda Sea Shelf along with abiogenic aragonite growth experiments to show that coral luminescence G/B is quantitatively related to the fluorescence intensity of terrestrial humic substances. We then combined a satellite-retrieved time series of CDOM with an analysis of a coral core section from an area of Borneo affected by run-off from tropical peatlands. We show that coral G/B ratio is a quantitative proxy for CDOM concentration at monthly resolution over a period of 12 years at this site (R& sup& & /sup& = 0.57). Furthermore, we examine data from a multi-year biogeochemical time series in Singapore combined with recently collected coral cores from the monitoring site. These results show that coral luminescence G/B ratios are highly correlated with terrestrial CDOM absorption across the ultraviolet and visible wavelength spectrum, as well as with the tDOC concentration as estimated from stable isotopes of dissolved organic carbon. Taken together, our results show that coral G/B ratios can be a powerful proxy to reconstruct bio-optical and biogeochemical variability resulting from tDOC input. Corals can therefore allow us to potentially reconstruct tDOC flux variability across tropical seas over past centuries, and therefore to investigate seasonal to inter-annual drivers of tDOC dynamics.& &
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Aazani Mujahid.