Optimization of sampling frequency for coastal seawater quality monitoring

The selection of an appropriate sampling frequency is very important in monitoring coastal seawater quality. The present study sought to optimize the sampling frequency for coastal seawater quality monitoring. We combined mathematical models with natural and human activities by the analytic hierarchy process method. The study was designed to consider historical monitoring data, regulated seawater quality standard, tide, land use, and ship activities in optimizing coastal seawater sampling frequency in Ha Long Bay, Vietnam. The study results indicated that monitoring activities should focus in points having high human activities as well as high concentration of TSS, ammonium, and oil. Points S1-S8 should have high sampling frequency (16-30 samples/year), whereas points S23-S28 can have low sampling frequency (3-5 samples/year). In a year, monitoring activities should be focused in June, July, and August with the number of samples of 42, 54, and 44 pear year (weighting values 0.120, 0.161, and 0.112), respectively. It should consider the mathematical aspects associated with natural and human factors when calculating sampling frequency for coastal seawater quality monitoring. Proposed optimization method can be applied for other coastal regions.