Spatial and Temporal Distributions of Dissolved Organic Carbon in the Setiu River, Malaysia

In general, higher concentrations of dissolved organic carbon (DOC) were measured at the downstream area of Setiu River basin, which associated with urban location. The high molecular weight (HMW, <100 kDa) DOC fraction generally was dominant consisting of 55–85 % of total DOC, within the DOC pool. Overall, HMW DOC dominance was associated with agricultural, aquaculture and urban areas, and was therefore likely to be a result of anthropogenic inputs. Re-suspension of bottom sediment in the river may have also played an important role in controlling the HMW DOC distribution in present study. The low molecular weight (LMW, <30 kDa) DOC, which constituted 34–70 % of total DOC, was generally showed the significant correlation with chlorophyll-a (chl-a), suggesting phytoplankton related processes may influence the LMW DOC in water column. DOC concentrations were climatological related with high values during the monsoon season and decreased significantly during non-monsoon season.