Properties and Accumulation Rate of Sediments in Nile Tilapia (Oreochromis niloticus) Ponds and Ponds with Cages Containing Red Hybrid Tilapia (Oreochromis niloticus x mossambicus)

Sediment samples were collected from six earthen ponds: three ponds for Nile tilapia culture and the other three ponds containing cages with red hybrid tilapia. All study ponds were located in the same farm in Nakhon Pathom Province, Thailand. The bulk density of Nile tilapia and red tilapia ponds did not differ (P>0.05), with average bulk densities of 0.77±0.12 g•cm -3 and 0.86±0.10 g•cm -3 , respectively. The percentage of silt and sand did not differ (P>0.05) between the two culture systems, however, the percentage of clay in ponds with red tilapia cages was significantly (P<0.05) higher. Dry sediment pH of both tilapia culture systems were considered acidic, especially from ponds with red tilapia cages at an average of pH 4.47. The Nile tilapia ponds had 0.53±0.03% of total nitrogen while the  average percentage of total nitrogen in the ponds with reed tilapia cages was 0.35±0.09. The percentage of organic carbon in the ponds with red tilapia cages was 3.36±0.39, which was significantly (P<0.05) higher than that in Nile tilapia ponds at 2.84±0.44. Therefore, the ponds with red tilapia cages had a significantly higher (P<0.05) C:N ratio than the Nile tilapia ponds. The percentage of total phosphorus ranged between 0.11- 0.12 in both systems. The sediment depth ofthe three ponds with red tilapia cages averaged 15.82±1.63 em, whereas that in Nile tilapia ponds averaged 2.29±0.44 em. All analysis results of total sediment depth, sediment accumulation rate, and carbon burial rate differed (P<0.05) between the two culture systems. There were strong positive correlations (P<O.Ol) among C:N ratio, total sediment depth, and sediment accumulation rate. The sediment layers in all ponds were not suitable with regard to low pH level especially in ponds with red tilapia cages. Highly organic matter accumulation occurred underneath the cages in ponds over time. Following these findings, pond management practices related to pond bottox soil are strongly recommended to enhance and improve the capacity of the earthen ponds.