Reply on RC2

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.