BEHAVIOUR OF WATER QUALITY PARAMETERS DURING EBB TIDE IN DUNGUN RIVER ESTUARY, TERENGGANU

Abstract: A study has been carried out to determine the behaviour of selected water quality (WQ) parameters in Dungun river estuary. Samplings were carried out twice during October 2001 under similar tidal conditions (ebb tide) whereby samples were collected as a function of salinity i.e. along the salinity gradients from 0 ppt (freshwater end-member) to 31 ppt (coastal water end-member). WQ parameters monitored were the general physical parameters (viz. temperature, pH, dissolved oxygen, suspended solids and redox potential), dissolved metals (copper, cadmium and lead), dissolved nutrients (nitrogen- and phosphate-based nutrients) and chlorophyll-a. The physical water quality parameters were measured in situ using a multi-parameter data logger whilst nutrients and chlorophyll-a analyses were carried out based on the colorimetric method. Dissolved metals were analysed using GF-AAS technique following the pre-concentration step using APDC-MIBK method. Results in general indicated that most of the parameters measured appear to behave non-conservatively with salinity. In the case of nutrients, with the exception of nitrate which exhibited removal behaviour, all other nitrogen- and phosphorus-based nutrients, exhibited addition behaviour in the estuary. Cadmium and lead were also found to behave in a non-conservative manner in the estuary i.e. positive deviation was observed for cadmium whilst lead exhibited a negative deviation from the theoretical dilution line. These observations suggest that the estuary act as a source for cadmium but a sink for lead. Copper on the hand exhibited a linear relationship with salinity indicating a conservative distribution along the estuary. Results obtained in the present study clearly show the different behaviour of a given water quality parameter in the estuary and also illustrate the important role played by Dungun River estuary in modifying the nutrient and metal concentrations during the transportation from the river to the coastal waters.