CARBON AND NITROGEN STABLE ISOTOPES AS TRACERS TO SOURCE ARTIFICIAL ORGANIC MATTER OF SEDIMENTARY PARTICLE IN GRASS CARP AND YELLOW CATFISH POLYCULTURED PONDS

Carbon and nitrogen stable isotopes were as tracers to source artificial organic matter in which Ctenopha-ryngodon idellus or Pelteobaggrus fulvidraco were mainly cultured, and meanwhile the characteristic of carbon and nitrogen nutrient in the deposited particulate matter in different culture modes were also analyzed. Results showed that Total nitrogen (TN), Total carbon (TC), Total organic carbon (TOC) and Total organic nitrogen (TON) concentrations of the deposited particulate matter declined from April to October. Nitrogen and carbon concentration in sedimentary par-ticles of Pelteobaggrus fulvidraco ponds were significantly higher than that of Ctenopharyngodon idellus ponds. The average content of 15N and 13C of organic matter in the deposited particulate matter were 6.2 and -25.3 in Pel-teobaggrus fulvidraco-cultured ponds, 5.9 and -25.4 in Ctenopharyngodon idellus-cultured ponds, respectively. The contribution rate of residual feeds to the organic matter in the deposited particulate matter ranged from 15.6% to 35.4% in Pelteobaggrus fulvidraco-cultured ponds and from 30.1% to 70.1% in Ctenopharyngodon idellus-cultured ponds. Meanwhile, the contribution of residual feeds to organic matter in two polycultured models significantly de-creased during this cultural period (Pelteobaggrus fulvidraco-cultured ponds, r= -0.537, P0.05; Ctenopharyngodon idellus-cultured ponds, r= -0.800, P0.01).