Duality of Seasonal Effect and River Bend in Relation to Water Quality in the Chao Phraya River

The present study conducted a field survey of water quality along the Chao Phraya River during the past three years. The main objective was to better understand the spatial–temporal variations in water quality in relation to season and channel morphology. It assessed the water quality in terms of chemical parameters, bacteria, and phytoplankton. The results revealed a duality of seasonal effect for nutrients. The rainy season degraded the water quality by increasing the nutrient concentration in the waterway in the beginning, but cleaned it up by dilution in the end. However, this duality did not apply to Escherichia coli (E. coli), for which the highest level occurred during the second half of the rainy season and a sag curve variation pattern was displayed along the mainstream. Another duality found by this study is that there was no statistically significant difference in water quality in terms of chemical parameters between a river bend and the straight channel shortcutting the bend, but significant differences in the level of E. coli and the phytoplankton community structure were observed between the two. Of particular note, the present study revealed a coexistence of a saproxenous species (algae found in clean water) with a harmful species in the bend river reach.