Study on water quality of rice - shrimp farming in Ca Mau province

Abstract

Ca Mau has the largest area of brackish shrimp culture in the Mekong Delta with different systems such as integrated mangrove shrimp, improved - extensive, rotational rice - shrimp, intensive and super-intensive ones. Among these, rotational rice - shrimp is known as more developed in Thoi Binh district. This system has been considered a suitable model with natural conditions and ecology - friendly. Towards sustainable development and adaptation to climate change and saline water intrusion, it is crucial to deeply understand the variations of the water quality in the rice - shrimp farming systems. Therefore, the aim of this study is to assess the water quality in rice - shrimp farms to provide the scientific data for water quality in rotational rice - shrimp system in the future. Water samples were collected at 3 rice - shrimp farms with 4 sampling periods including beginning and end of shrimp crop (February/July), beginning and end of rice crop (October/December) in Bien Bach Dong commune, Thoi Binh district, Ca Mau province. The results showed that salinity rapidly declined during shrimp culture period. Total alkalinity concentrations were relatively high and stable. Dissolved oxygen levels were in an acceptable range. However, the results of TSS, BOD, TAN, NO₂^-, NO₃^-, PO₄^3-, TN, TP and chlorophyll-a indicated that the rice - shrimp farms were in mesotrophic conditions. It is therefore suggested that in order to increase the productivity of rice - shrimp farming, the technical solutions for improving nutrient levels in rearing water should be considered during shrimp crop.