| Agricultural non-point source pollution is an important factor leading to the eutrophication of water bodies worldwide.It has become a global consensus to carry out the prevention and control of agricultural non-point source pollution by taking river basins as small units.Small water area<0.01 km2 in the world not only on the number of landlocked body of water,and play an important role in the global cycle,is the worlds hot spots of biogeochemical processes.Ponds and small reservoirs are not only important water conservancy nodes for water storage and irrigation in agricultural production in China,but also important constructed wetlands to intercept and absorb nitrogen and phosphorus pollutants in watershed.Study watershed scales ponds and small reservoirs content of nitrogen and phosphorus and greenhouse gases(CH4,CO2,N2O)emission flux of space-time change rule,not only helps to understand the basin nitrogen phosphorus non-point source pollution mechanism,and the basin scale ecological environmental benefits brought by the non-point source pollution control,especially carbon neutral evaluation data play an important supporting role.In this study,Jinjing Small Watershed(105 km2),a typical agricultural source basin in the subtropical hilly region,was selected as the study area.Long-term field observation points of typical pond types were set to study the spatial and temporal variation of nitrogen and phosphorus content and greenhouse gas emissions in pond water of small watershed,and the following research results were obtained:1.Long-term positioning observation was carried out on 36 typical pond reservoirs in the study area(June,2017?May,2018,monthly sampling observation)to analyze the temporal and spatial variation of TN and TP and its influencing factors.The results show that:(1)The concentration of TN and TP in pond water exceeds the standard seriously,and the proportion of V-SuperV water all exceeds 50%.(2)The types of surrounding land use and fish farming affect the TN and TP contents of pond water.Compared with non-fish farming ponds,the TN and TP of pond water increased by 60%and 34%,respectively.(3)The nitrogen and phosphorus content of the pond water was also affected by the positions of the upper and lower reaches of the pond.In general,the TN(1.86 mg·L-1)of the upstream pond water was lower than that of the downstream pond(2.56 mg·L-1),and the TP content of the upstream pond water was close to that of the downstream pond.2.Based on the above observation results,four ponds with different typical landscape types and different management modes(natural reservoir,tea garden pond,grass pond and intensive fish pond)were further selected as the research objects.By using the indirect Thin Boundary Layer Equation(TBLE)and the direct static floating chambers,the temporal and spatial variations of methane(CH4),carbon dioxide(CO2)and nitrous oxide(N2O)diffusion fluxes at the gas-water interface of the ponds were studied.The results showed that:(1)The average emission fluxes of CH4,CO2 and N2O were 42.84?65200 ?g·m-2·h-1,-47020?79530?g·m2·h-1 and 5.33?290?g·m-2·h-1,respectively,showing a seasonal pattern of high emission in summer and low emission in winter.The seasonal variation may be related to temperature,rainfall and algal blooms in the study area.(2)The eutrophication of pond water reduces the CO2 emission flux and increases the CH4 and N2O emission flux.(3)Compared with the thin boundary layer formula method,the floating flux box technology can more accurately and continuously monitor the greenhouse gas emission flux at the water-gas interface of the reservoir.In general,the agricultural land use and fish farming in the subtropical hilly region intensified the eutrophication of the pond water,which indirectly increased the CH4 and N2O emission fluxes.Strengthening farmland drainage and fish pond tail water treatment will not only reduce eutrophication,but also reduce greenhouse gas emission. |
PDF Full Text Request