The Impact of Fish Cage Culture on Water Quality of Taasarn-Bangpla Canal, Nakhon Pathom Province,Thailand

Abstract

Concerns over the impact of cage culture on water quality alteration arose when the number of fish cages in the Taasarn-Bangpla Canal in Nakhon Pathom province, Thailand increased. This study aimed to assess the impact of cage culture on the water quality of the canal. Water quality in three stations around the dense cage culture areas were monitored monthly from October 2013 to August 2014. Dissolved oxygen, pH, temperature and transparency were monitored in situ. Water samples for analysis of phosphorus, ammonia and BOD₅ were analyzed at the Water Chemistry Laboratory by standard methods.  The study found that water quality is influenced by wastes released from different activities and apparently influenced by seasonal water flow regime. Water quality, particularly dissolved oxygen, from January to July are considerably good when the accumulated water flow was more than 40x10⁶ m³/month. Poor water quality occurs when the flow was less than 40x10⁶ m³/month. High flow period had significantly higher dissolved oxygen than during the low flow period, whereas alkalinity, hardness, ortho-phosphate phosphorus, and total ammonia were significantly low. Statistical indifference in water quality among the three stations was due to predominating temporal variation. However, water quality tended to be altered from upstream to downstream due to wastes generated from different activities in and along the river basin. The approximately 1,057 tonnes annual production of red tilapia currently has, no doubt, worsened the situation. Self-inflict of cage culture and other water users living downstream could suffer from poor water quality if the current situation is allowed to continue without environmental impact mitigation/prevention measures.