Distribution And Flux Of Carbon, Nitrogen And Phosphorus In The Soil Of WLFZ Of TGR

Water-level-fluctuating zone(WLFZ) was formed by the periodic flooded water ofThree Gorges Reservoir(TGR). WLFZ is in the state of alternating flooded andnon-flooded every year, and its ecosystem is cross-impacted by the water and land twointerfaces. Therefore, the study of soil carbon, nitrogen and phosphorus in WLFZprovided the basic data for pollution load control and management. In this work, thedistribution characteristics of organic matter(OM), total nitrogen(TN) and totalphosphorus(TP) in the soils of WLFZ of the TGR were analyzed. According the changeof soil OM, TN and TP contents during the flooded and non-flooded period, aconstructed flux estimation method had been use to estimate the flux of carbon, nitrogenand phosphorus in WLFZ. The influencing factor of the flux of carbon, nitrogen andphosphorus in WLFZ was studied. The conclusions of the study are as follows:①In study areas, soil OM contents which obeyed the normal distribution rangedfrom1.10to26.10mg/g. Soil TN contents which approximately obeyed the normaldistribution ranged from0.54to3.29mg/g. Soil TP contents which obeyed the normaldistribution ranged from0.28to1.32mg/g. Compared with non-flooded soil samples,the differences of OM and TP contents among difference WLFZ of study areas could bereduced by cyclic drying and wetting of WLFZ periodically. The differences of OM andTN contents among different soil types were insignificantly, while TP content in yellowsoil was significantly higher than that in purple soil and alluvial aquic soil.②In study areas, Soil grain sizes in sampling sites were mainly composed of siltand sand, which accounted for90.93%. Soil pH values in sampling sites ranged from5.60to8.09, and the vast majority of soil samples belonged to the neutral and alkaline.Soil redox potentials in sampling sites ranged from-64.40to81.20mV, and the soil ofreduction accounted for83.10%. Soil water contents in sampling sites ranged from3.1%to74.2%. Soil electrical conductivities in sampling sites ranged from0.03to0.76ms/cm.③Soil OM and TN in WLFZ showed a highly significant and positive correlation,and the result indicating that soil OM and TN have roughly the same input and outputpathways. The ratio of C/N of the soils of WLFZ is relatively low, which ranged from0.94to12.24. The result indicated that soil organic nitrogen of WLFZ was easymineralized, and the possibility of releasing to water bodies was increased. In addition, soil OM was significantly and positively correlated with soil C/N ratio. The resultindicated that soil C/N ratio is determined mainly by soil OM content.④During the non-flooding period, soil OM contents of WLFZ decreased slightly.During the flooding period, soil OM was not conducive to decomposition, and it ledOM was accumulated. Soil OM contents of WLFZ increased after alternating floodedand non-flooded. During the non-flooding period, soil OM contents of WLFZ increased.During the flooding period, soil nitrogen may be released to overlying water ordenitrified. Soil TN contents of WLFZ changed slightly after alternating flooded andnon-flooded. During the non-flooding period, soil TP contents of WLFZ changedslightly. During the flooding period, soil phosphorus may be released to overlying water.Soil TP contents of WLFZ decreased slightly after alternating flooded and non-flooded.⑤According to the characteristics of WLFZ and soil carbon, nitrogen andphosphorus contents, an estimation method of the flux of carbon, nitrogen andphosphorus in WLFZ was constructed. The results of the flux of carbon, nitrogen andphosphorus in WLFZ during the non-flooded period were-42208t,43845t and-2025t,respectively. The results of the flux of carbon, nitrogen and phosphorus in WLFZ duringthe flooded period were-62117t,48764t and7932t, respectively. After a cycle, theincrease of soil OM content was19909t, and the decrease of soil TN, TP content were4919t and9958t, respectively.⑥Laboratory simulation experiment indicated that the exchange fluxes ofinorganic nitrogen, phosphate and total organic carbon in the soil-water interfaceincreased with temperature. The exchange fluxes of ammonia and total organic carbonwere maximum under neutral condition, and the fluxes of nitrate increased with pHvalue. The exchange fluxes of phosphate expressed as U-shaped curve while the pHvalue increased. The exchange fluxes of inorganic nitrogen, phosphate and total organiccarbon decreased while the overlying water concentration increased. Soil OM contentswould significantly impacted the exchange fluxes of nitrate and phosphate in thesoil-water interface, and the exchange fluxes increased with the soil OM contents.This work was sponsored by the subject of “Research on the characteristics of thepollution load and the impact on water environment for the WLFZ” of Major NationalWater Special Project (2009ZX07104-003-02).