Study On Distribution Characteristics And Flux Of Organic Matter, Nitrogen And Phosphorus In The Soil Of WLFZ Of Three Gorges Reservoir

With regard to cohesion zone between the water and land area, complicatedmaterial and energy exchange and transformation processes would occur in thewater-level-fluctuating zone （WLFZ） of Three Gorges Reservoir （TGR）. Duringperiodical impoundment and flooding in TGR area, organic matter, nitrogen andphosphorous in the submerged soil of WLFZ can have physical, chemical and biologicalexchanges through interstitial water and overlying water. Therefore, the study of organicmatter, nitrogen and phosphorous distribution characteristics in the soil of WLFZ andtheir impact on water environment has great significance in illustrating biogeochemicalcycles. The physical and chemical indicators and the contents of organic matter,nitrogen and phosphorus in the center （from Wushan County to Chongqing city） ofWLFZ in TGR area are studied in this paper. Organic matter, nitrogen and phosphorusflux model by the break-even method are also built, and exchang fluxes in inundatedsoils and non-inundated soils of WLFZ using the simplied model are calculated. At last,combined with the actual environmental conditions of TGR, organic matter, nitrogenand phosphorus diffusion fluxes under different environmental conditions are simulatedby the experiment. The results are as follows:①The pH in the soils of WLFZ is mainly neutrality and alkalescency. ORP is low,showing reduction. Water content is high. Conductivity in the soils is vaired from0.25to0.75ms/cm, which is different among different sampling sites. The silt fraciton is themajor fraction in the study area. The clay fraction is the minor fraction. The chemicalcomposition of the soils in WLFZ is mainly made up of SiO₂, accounting for41.13%-74.88%of the total.②The average value of SOM in the soil of WLFZ could be ordered as yellowsoil>Fluvo-aquic soil>purple soil. The average contents of SOM in different basins areas follows: Tributaries basin>Yangtze River basin （excepting Ganjing River）. Duringnon-inundated period in2010, the content of SOM has little change. While Duringnon-inundated period in2011, the content of SOM has increased. During inundatedperiod from September2010to April2011, the concentration of SOM has increased,too.③The average value of TN was in the descending order of yellow soil>purplesoil>Fluvo-aquic soil. The average contents of TN in Longxi River are highest among different basins and there was no significant difference in the others. Duringnon-inundated period in2010, the content of TN has little change. While Duringnon-inundated period in2011, the content of TN has decreased. During inundatedperiod from2010to2011, the concentration of TN has also decreased. The contents ofvarious of nitrogen indicate that TF-N, IEF-N, WAEF-N, IMOF-N and OSF-N havedecreased during non-inundated, while IEF-N and OSF-N have declined a little. Thecontents of NTF-N have increased during non-inundated period in2010, but decreasedin2011. During inundated period, TF-N, IEF-N, WAEF-N, IMOF-N and have increased;NTF-N has declined. Positive correlation exists among the contents of TN, OSF-N andSOM, between WAEF-N and OSF-N, between TP and IEF-N, water content and OSF-N.TP is negatively correlated to IMOF-N, and pH is negatively correlated to IEF-N too.④The order of the average value of TP is as follow: Yellow soil>Fluvo-aquicsoil>Purple soil. In this study, the average contents of TP in different basins are asfollows: Yangtze River basin> Tributaries basin （excepting Ganjing River）. Duringnon-inundated period in2010, the content of TP has a little change. While Duringnon-inundated period in2011, the content of TP has increased. During inundated periodbeween2010and2011, the value of TP has decreased. The value of several of nitrogenindicates that IP, Fe/Al-P, Ca-P and OP have little change during non-inundated, whileIP and OP in2011have increased. During inundated period, IP and Fe/Al-P haveincreased; Ca-P and OP have changed a little. Positive correlation exists among thecontents of Ca-P, TP and IP, between Fe/Al-P and OP, among TN, OP and SOM, SOMand Fe/Al-P, between OP and pH. The contents of P released from the soils havepositive correlations with Fe/Al-P and OP. OP is negatively correlated to ORP.⑤The phosphate sorption on soils mainly occurs within12h and then reaches todynamic equilibrium. Its sorption rates are obviously affected by the volume percentageof fine particles less than50μm. The sorption rates increase rapidly with the percentageof fine particles increasing. The maximum phosphate sorption capacity of the soils isranged from137.79to1975.59mg/kg and the phosphate sorption efficiency of the soilsfrom47.34to230.88L/kg.⑥During the non-inundated period, the results of the flux of TN, TP and SOM inWLFZ are-43845t,2025t and42208t, respectively. During the inundated period, theresults of the flux of TN, TP and SOM in WLFZ are48764t,7932t and-62117t,respectively. After a cycle, the decrease of TN, TP content are4919t and9958t, theincrease of SOM content is19909t, and, respectively. ⑦TOC of the soil in WLFZ varied from source to sink with the concentration ofTOC in the overlying water increased; The exchange fluxes content of TOC expressedas inverted “U” curve under different pH; and the exchange fluxes value of TOC rangedfrom sink to source with the temperature increased. Ammonia, nitrate and inorganicnitrogen varied from source to sink under the different concentration of ammonia,nitrate and inorganic nitrogen in the overlying water, respectively; the exchange fluxescontent of ammonia described as inverted “U” curve and nitrate, inorganic nitrogenvaried from sink to source under different pH; the exchange fluxes value of ammoniaincreased, the fluxes value of nitrate decreased and inorganic nitrogen ranged from sinkto source with the temperature increased. Phosphate varied from source to sink underthe different concentration of phosphate in the overlying water; the exchange fluxescontent of phosphate characterised as “U” curve under different pH; and phosphateranged from sink to source with the increase of temperature. Positive correlation existsamong the contents of SOM and the exchange fluxes of nitrate and phosphate underdifferent content of nitrogen and phosphorus.