Spatial and temporal dynamics of suspended sediment concentrations in coastal waters of the South China Sea, off Sarawak, Borneo: ocean colour remote sensing observations and analysis

[摘要] High-quality ocean colour observations are increasingly accessible to support various monitoring and research activities for water qualitymeasurements. In this paper, we present a newly developed regional total suspended solids (TSSs) empirical model using MODIS Aqua's Rrs(530) andRrs(666) reflectance bands to investigate the spatial and temporal variation in TSS dynamics along the southwest coast of Sarawak, Borneo, with theapplication 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. Thetemporally 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 of15–20  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 variationprovides further evidence that monsoonal patterns drive the TSS release in these tropical water systems, with distinct and widespread TSS plumevariations observed between the northeast and southwest monsoon periods. A map of relative TSS distribution anomalies revealed strong spatial TSSvariations in the Samunsam–Sematan coastal areas, while 2010 recorded a major increase (approximately 100 %) and widespread TSS distributionwith respect to the long-term mean. Furthermore, study of the contribution of river discharge to the TSS distribution showed a weak correlationacross time at both the Lupar and Rajang river mouth points. The variability in the TSS distribution across coastal river points was studied byinvestigating the variation in the TSS pixels at three transect points, stretching from the river mouth into territorial and open-water zones, for eightmain rivers. The results showed a progressively decreasing pattern of nearly 50 % in relation to the distance from shore, with exceptions in thenortheast regions of the study area. Essentially, our findings demonstrate that the TSS levels on the southwest coast of Sarawak are within localwater quality standards, promoting various marine and socio-economic activities. This study presents the first observation of TSS distributions inSarawak coastal systems with the application of remote sensing technologies and aims at enhancing coastal sediment management strategies for the sustainableuse of coastal waters and their resources.

[学科分类] 大气科学