Distribution patterns of redox potential in intertidal zone of Blanakan coast and their implication on the coastal ecosystem

The intertidal zone of Blanakan Coast has an area of approximately 15 ha. The Blanakan Coast itself is important fishing ground. Correspondingly, a study to assess the water quality in the coastal ecosystem is important. One of important water quality parameters is reduction and oxidation (redox/Eh) potential since it can indicate the anoxia condition. Nevertheless, the detailed spatial variation of Eh is poorly understood, especially in intertidal zone where anoxia may be a significant environmental constraint for marine organism. The Eh data were recorded from 7 sampling points in intertidal zone. Based on the result, the mean value of Eh is ranging from -20.0 to -50.67 mV. The poorest intertidal zone was found in the sampling point closed to the river mouth with mean value of Eh is -50.67 mV. Another poor intertidal zone was found in the eastern part of intertidal zone closed to the coast with mean value is -46.16 mV. The better condition of intertidal zone was found in the northern and western part of intertidal zone with mean value is -25.16 mV. The study also found that value of Eh is significantly correlated with the value of dissolved oxygen (DO). The DO is high when the value of Eh is high and the DO is low when the value of Eh is low. For example, the -50.67 mV redox potential significantly reduced the DO in the intertidal zone as low as 1.56 mg/l. Thereby, this Eh can cause anoxia condition in ecosystem of intertidal zone especially near river mouth and east side.