| Grass carp (Ctenopharyngodon idellus) is considered as an economically important aquaculture species in China with largest production. And reasonable cultivation mode is the key to obtain higher economic benefits in grass carp ponds. At present, the studies has not been reported about carbon cycle in the grass carp ponds, three poly-culture systems, i.e. (1) GSB group:grass carp Ctenopharyngodon idellus, silver carp Hypophthalmictuthys molitrix and bighead carp Aristichthys nobilis, or GSBE group:grass carp Ctenopharyngodon idellus, silver carp Hypophthalmictuthys molitrix and bighead carp Aristichthys nobilis, topmouth culter Erythroculter ilishaeformis (2) GSBL group:grass carp, silver carp, bighead carp and Litopenaeus vannamei, (3) GSBC group:grass carp, silver carp, bighead carp and carp Cyprinus carpio. To investigate the seasonal variance of carbonic exchange in different grass carp ponds and explore the relationship between carbonic fluxes and environment factors of overlying water, Overlying water and sediment samples were collected from grass carp experimental ponds with different culture models. The characteristics of temporal-spatial distributions and correlations of carbons in overlying water, interstitial water of surface layer and sediment have been analyzed, and to provide a certain basis for the further research of carbon cycle in polyculture ponds. The main results of the research are as follows:1、Carbon fluxes across sediment-water interface in different grass carp poly-culture modelsTo investigate the seasonal variance of carbonic exchange in different grass carp ponds and explore the relationship between carbonic fluxes and environment factors of overlying water, three poly-culture systems, i.e. (1) GSB group:grass carp, silver carp and bighead carp, (2) GSBL group:grass carp, silver carp, bighead carp and, (3) GSBC group:grass carp, silver carp, bighead carp and carp, were studied by simulation in the laboratory from April to September,2013. The change of benthic fluxes of carbons across the sediment-water interface with time were studied, as well as the diurnal variation of carbons in the overlying water in August. The results showed that dissolved inorganic carbons (DIC) fluxes ranged from-0.65 mg/(m2.d)to 16.90mg/(m2.d), while dissolved organic carbons (DOC) fluxes and particulate organic carbon (POC) fluxes ranged from 0.16 mg/(m2.d)to 3.49 mg/(m2.d),-2.29 mg/(m2.d) to 3.32 mg/(m2.d), respectively. Different carbon fluxes were all maximum in August for GSB and GSBC group, but in July for GSBL group. During our experiments, the ex-fluxes of DIC and DOC were observed in every month. POC was up taken by the sediments from April to June, but released from the sediments in other months. In the mid to late cultivation time, a significant difference of the benthic fluxes of DIC, DOC and POC between treatments were significantly higher in GSB group compared to other groups (P<0.05). The diurnal variation of carbons had obvious characters in August, with the content of DIC and DOC being maximum at 4:00 am. The content of POC in the GSBL got the maximum value at 4:00 am and the minimum value at 12:00 am, which was opposite to that of GSBC group. The results demonstrated a significantly negative relationship of carbon fluxes with DO and pH in overlying water (P<0.01), but a significantly positive relationship with overlying water temperature (P<0.01).2 Study on carbons in overlying water and sediment interstitial water in different grass carp poly-culture models、Overlying water and sediment samples were collected from grass carp experimental ponds with different culture models from April to September,2013. The characteristics of temporal-spatial distributions and correlations of carbons in overlying water, interstitial water of surface layer and sediment have been analyzed. Three poly-culture systems, i.e. (1) GSB group:grass carp, silver carp and bighead carp, (2) GSBL group:grass carp, silver carp, bighead carp and white shrimp, (3) GSBC group:grass carp, silver carp, bighead carp and carp. The results showed that the concentrations of dissolved organic carbons (DOC) and dissolved inorganic carbons (DIC) in the interstitial water of surface layer were significantly higher than those in the overlying water (P<0.05). DOC and DIC were all highest in August for GSB and GSBC groups, but in July for GSBL group. The trend of those in the overlying water was similar to those in the interstitial water of surface layer during farming time. In different culture models, the distribution of DIC in the interstitial water of surface layer and overlying water were GSBC>GSB>GSBL, but the distribution were GSBC>GSBL>GSB for DOC, the content of DIC and DOC were significantly different among treatments in August (P<0.05). As to total organic carbon (TOC) and total inorganic carbon (TIC) in the sediment of surface layer, the distribution were GSB>GSBL>GSBC. The content of TOC were significantly different among treatments in August and September (P<0.05). And the content of TIC in the GSB were significantly higher than others in June and July (P<0.05).TOC in sediment of surface layer were all highest in September for three models, but TIC were lowest in July for GSBL group and in August for GSB and GSBC groups. There was no significantly difference in 2～4cm and 4～7cm for GSB and GSBL group, except for GSBC group in 2～4cm. The correlation analysis results demonstrated that DOC in overlying water was extremely significant positive correlate with DIC in overlying water (P<0.01) and DOC in the interstitial water of surface layer (P<0.01), but there was extremely significant negative correlation between DOC in overlying water and TIC in the sediments (P<0.01). In addition, the results demonstrated an extremely significant positive relationship of DIC in overlying water with that in the interstitial water of surface layer (P<0.01), but an extremely significant negative relationship with TIC in the sediment of surface layer (P<0.01).3、 Fluxes of CO2 and CH4 across sediment-water interface in different grass carp poly-culture modelsTo investigate the seasonal variance of carbon dioxide(CO2) flux and methane(CH4) flux exchange in different grass carp ponds and explore the relationship between fluxes and environment factors of overlying water, three poly-culture systems, i.e. (1) GSBE group:grass carp, silver carp and bighead carp, topmouth culter (2) GSBL group:grass carp, silver carp, bighead carp and, (3) GSBC group:grass carp, silver carp, bighead carp and carp, were studied by simulation in the laboratory from May to September,2014. The change of benthic fluxes of CO2 and CH4 across the sediment-water interface with time were studied, as well as the diurnal variation of CO2 and CH4 in the overlying water in August. The results showed that CO2 fluxes ranged from 10.86 mmol/(m2·d)to 67.71 mmol/(m2·d), while CH4 fluxes ranged from 0.25 mmol/(m2·d) to 5.29 mmol/(m2·d). Fluxes of CO2 and CH4 were all maximum in August for all group. During our experiments, the ex-fluxes of CO2 and CH4 were observed in every month. In the mid to late cultivation time, a significant difference of the benthic fluxes of CO2 and CH4 between treatments were significantly higher in GSBE group compared to other groups (P<0.05). The diurnal variation of CO2 and CH4 had obvious characters in all groups in August, with the content of CO2 being maximum at 4:00 am, the minimum at 16:00 pm. The content of CH4 got the minimum value at 4:00 am and the maximum value at 8:00 am. The correlation analysis results demonstrated that fluxes of CO2 was extremely significant positive correlate with CH4 (P<0.01). And fluxes of CO2 and CH4 were extremely significant negative correlate with DO, pH of overlying water and Eh of sediment (P<0.01), but extremely significant positive correlate with water temperature (P<0.01).In addition, fluxes of CO2 and CH4 were positive correlate with organic matter, TN and TC of surface sediment(P>0.01). |
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