Water quality of the Bangpakong River during 2016 – 2018

Abstract

Seasonal variations of water qualities including temperature, salinity, dissolved oxygen (DO), pH, suspended sediment (SS), ammonia, nitrite, nitrate, orthophosphate, silicate and chlorophyll-a (Chl-a) in the Bangpakong River were investigated during 2016 and 2018. Dry season and wet season were specified for the periods from December to May and from June to November, respectively. The results showed that the variations of all water qualities were related to the river discharge.  Water temperature was high during summer and rainy seasons, and was low during winter, with not much variations among sampling stations. High salinity was observed from the mouth toward the headwater of the river in dry season, while fresh water occupied the entire river in wet season. The pH data indicated that the water was weak basic and weak acidic in dry and wet seasons, respectively. Hypoxic water developed in wet season which was resulted from the leaching of organic material into the river. The SS, nitrite, nitrate and orthophosphate were high near the river mouth in dry season, whereas ammonia was high throughout the river in wet season. Silicate was high in the area where fresh water and seawater were mixed. High Chl-a in some area during dry season in 2017 was supposedly related to the levels of dissolved inorganic nitrogen (ammonia + nitrite + nitrate) and orthophosphate, of which that the highest values were observed in the entire rivers during that time. Most water qualities, except dissolved oxygen and ammonia, met the water quality standard of Pollution Control Department. The dissolved oxygen of lower than 4 mg/L was found in the entire river in wet season. Meanwhile, ammonia which was higher than 35.7 µM was observed in the river mouth and the headwater of the river during the same season. Keywords:  water quality, the Bangpakong River, seasonal variation