A spatio-temporal assessment of seawater quality in Miri-Sibuti Coral Reef: Evaluating for metal pollution, sources and dynamics

Coral environments are sensitive to seawater quality, and their sustenance depends on understanding the dynamics of geochemical variables, especially in trace levels. Miri-Sibuti Coral Reef National Park (MSCRNP) is a unique marine reserve in the state of Sarawak, NW Borneo, Malaysia, which attracts tourists worldwide. In this study, seawater samples were collected from MSCRNP in three different diving sites (Eve’s Garden (EG), Anemone Garden (AG) and North Siwa (NS)) at different depths for three seasons (pre-southwest monsoon (PRSWM), post-southwest monsoon (POSWM) and northeast monsoon (NEM). Insitu parameters (temperature, pH, salinity and turbidity) were measured in the field. The concentration of trace metals was determined in the water column (sea surface layer, middle layer and bottom water) using standard procedure. Statistics and pollution indices were used to identify the possible sources of metals and the pollution status of the seawater. From the analytical results, the vertical distribution of trace metal concentrations with respect to the locations and seasons was identified. pH ranging from 7.8 to 8.4 with a depth-wise increasing trend in NS during NEM. Similarly, a decreasing trend of turbidity was observed in AG and EG in all the seasons with respect to depth. A higher concentration of trace metals was observed during NEM, particularly at EG and NS. Fe, Ni and Pb are the dominant metals in all the seasons. Fe concentration varies from 789 to 1478 µg/L, averaging 1112 µg/L irrespective of seasons and locations. The suspended solids/sediments discharged by the river runoff were the main contributor to the distribution of metals. The release of metals from the suspended particles through desorption at the surface layers and the exchange of metals between water-sediment interface at the bottom water were observed. In addition, coastal development and other anthropogenic activities in this region were also contributed to the metal pollution. •Spatial and temporal variations of trace metal concentrations were identified in MSCRNP.•Depth-wise increasing trace metal (Co, Cu, Mn, Pb, Zn, Fe) concentrations were observed.•Desorption of metals from suspended particles dominates in sea surface layer.•Exchange of metals between sediment and water interface at the bottom water.•Sediment discharge, coastal development and anthropogenic activities contribute to the metal distribution.