Changing trend of chemical oxygen demand (CODMn) in different breeding pond and its influence factors

To understand the variations of chemical oxygen demand (COD) in culturing ponds, water samples were collected from four different breeding species(Oxyeleotris marmoratus, Mylopharyngodon piceus, Micropterus salmoides, Channa argus) ponds of Shunde District, Foshan City in 2012. The results indicated that CODMn content of the four breeding ponds ranged from 3.71 to 50.76 mg/L, and there existed significant seasonal differences in CODMn content for M. salmoides and C.argus ponds, but no seasonal difference in O. marmoratus and M. piceus ponds. The sequence from low to high for breeding pond CODMn content was O.marmoratus >M. salmoides> M. piceus >C. argus. CODMn pollution index (Pi) ranged from 0.67 to 8.46, and the over standard rate reached 92.9%. Atlas analysis showed that from May to August, CODMn in ponds of O. marmoratu and M. salmoides had relatively similar characteristics. However, ponds of M.piceus and C.argus featured a larger difference from other ponds. From September to December, CODMn in ponds of O.marmoratus, M.piceus and M.salmoides had relatively similar characteristics, while pond of C.argus differed from other ponds. The relationship between Permanganate index (CODMn) and 14 water quality factors showed that potassium permanganate (CODMn) was negatively correlated with transparency, pH and silicate, and was positively correlated with salinity, conductivity, chlorophyll, phosphate, nitrate, ammonia nitrogen, but not related with dissolved oxygen and non ion ammonia.