Stud Yon Nitrogen And Phosphorus Dynamics In Sediment-Water Interface In Different Aquaculture Models Ponds

Aquaculture pond is a relatively closed and fragile ecosystem, and sediment is an important part of the pond ecosystem. In order to ensure sustainable expansion of fresh-water fish farming it is essential to quantitatively understand how fish farming affects the sedimentary flux of the sedimentary particles between the Ctenopharyngodon idellus ponds and Pelteobaggrus fulvidraco ponds. The sedimentary flux variation and correlations with the culture activities were discussed. The objective of this study was to quantify the sedimentary flux and analyze nutrient characteristic of sedimentary particles from April to October of2012in two aquaculture models ponds. The sedimentary particles were collected respectively by self-made sediment trap in different aquaculture models ponds. And the sedimentary flux of total nitrogen (TN), total carbon (TC), total phosphorus (TP), total organic carbon (TOC) and total organic nitrogen (TON) were also measured in the settling particulate matter, aimed to estimate the release flux of sediment nitrogen and phosphorus. The concentration variation range of N02--N, NO3-N, NH4+-N, PO43--P, TN and TP across the sediment-water interface in the two aquaculture models were also estimated. At last carbon and nitrogen stable isotopes were as tracers to source artificial organic matter in which Ctenopharyngodon 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:(1) The vertical sedimentary weight of settling particles fluxes in the Ctenopharyngodon idellus cultured ponds were significantly higher than in the Pelteobaggrus fulvidraco cultured ponds. Meanwhile, the sedimentary weight of the sedimentary particles showed increasing trend in two aquaculture models ponds. Temperal variations of sedimentary fluxes of TN, TC, TOC and TON were not obvious in two aquaculture models ponds. The sedimentary fluxes of TN, TC, TOC and TON of the sedimentary particles were significantly higher in the Pelteobaggrus fulvidraco-cultured ponds than in the Ctenopharyngodon idellus-cultured ponds during culturing period. The temporal variation of the ratios of carbon to nitrogen of sedimentary particles was similar with the ratios of carbon to nitrogen in surface sediments in two aquaculture models ponds, which suggested it was similar material source between sedimentary particles and sediment.(2) 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 particles of Pelteobaggrus fulvidraco ponds were significantly higher than that of Ctenopharyngodon idellus ponds.The average content of δ15N and δ13C of organic matter in the deposited particulate matter were6.2%o and-25.3%o in Pelteobaggrus fulvidraco-cultured ponds,5.9%o and-25.4%o in Ctenopharyngodon idellus-cultured ponds, respectively. The contribution rate of residual feeds to the organic matter in the deposited particulate matter ranged from15.6%to35.4%in Pelteobaggrus fulvidraco-cultured ponds and from30.1%to70.1%in Ctenopharyngodon idellus-cultured ponds. Meanwhile, the contribution of residual feeds to organic matter in two polycultured models significantly decreased during this cultural period (Pelteobaggrus fulvidraco-cultured ponds, r=-0.537,p<0.05; Ctenopharyngodon idellus-cultured ponds, r=-0.800, p<0.01).(3) All the benthic fluxes of nitrogen and phosphorus nutrients were from water to sediments in the beginning of the culture period, while it changed to be from sediments to water in the middle and later of the culture period, which suggested that sediment was the major input and output of nitrogen and phosphorus nutrients.Results also showed that the difference of concentration variation range of NO2-N, NO3--N, TN and TP were not significant in overlying water in two aquaculture model ponds (p>0.05), and NH4+-N concentration Pelteobaggrus fulvidraco ponds were lower than that of Ctenopharyngodon idellus ponds (p<0.05). The difference of temporal variation of NO2--N、NO3-N and PO43--P fluxes in sediment-water interface in two aquaculture model ponds were not significant (p>0.05), however the variation of NH4+-N、 TN and TP fluxes were of great difference (p<0.05).