Carbon, Nitrogen And Phosphorus Release From The Vegetation And Flux Of Nitrogen, Phosphorus Of WLFZ In The Three Gorges Reservoir

Water-level-fluctuating zone（WLFZ） was formed by the periodic flooded water ofThree Gorges Reservoir（TGR）. Regard as the cohesion zone between the water and landarea, the impact of WLFZ on reservoir water environment is more complex. During theexposed period, the WLFZ can intercept and filter pollutants, cut down the amount ofcarbon, nitrogen and phosphorus to into the water body. At the same time, carbon,nitrogen and phosphorus in the soil can also enter the water body by the ways of runoff,soil erosion, etc. During the flooded period, the organic residues from the decline andfall of vegetation on the WFLZ enter into water body inevitably, then release carbon,nitrogen, phosphorus after decomposition. At the same time, there are complex materialexchange and migration process between the soil of WLFZ and the overlying water.The alternation of wetting and drying of WLFZ makes WLFZ become the source orsink of carbon, nitrogen and phosphorus. Therefore, the study of regularity andinfluence factors of carbon, nitrogen and phosphorus release from soaked plants and theflux of nitrogen and phosphorus of WLFZ in the TGR has great practical significance.This paper has studied the characteristics and influence factors of carbon, nitrogen andphosphorus release from soaked plants. According to the established estimation modeland quantitative study of nitrogen and phosphorus migration transformation way, theflux of nitrogen and phosphorus of WLFZ are calculated. The conclutions of the studyare as follows:①The results of indoor simulation experiment show that: The decomposition ofsoaked plants make the water produce peculiar smell, and cause the water color more,the decrease of pH, the increase of Eh, the decrease of DO. The maximal unitcumulative release amount and the release rate exist significant difference betweenCynodon dactylon, Hemarthria altissima, Echinochloa crusgalli, Setaria viridis,Digitaria sanguinalis. The maximal unit cumulative release amounts of total organiccarbon（TOC） are21.03⁴3.65mg·g^-1, account for5.3%¹0.7%of plant initial matrixcarbon content, the release rates are1.48².91mg·g^-1·d^-1. The maximal unit cumulativerelease amounts of total nitrogen（TN） are0.50³.23mg·g^-1, account for4.5%²5.4%ofplant initial matrix nitrogen content, the release rates are0.01⁰.22mg·g^-1·d^-1. Themaximal unit cumulative release amounts of total phosphorus（TP） are0.54².69mg·g^-1,account for43.9⁸5.9%of plant initial matrix nitrogen content, the release rates are 0.01⁰.18mg·g^-1·d^-1. The forn of nitrogen released from soaked plants is dominated byorganic nitrogen（ON）, the forn of phosphorus released from soaked plants is dominatedby dissolved inorganic phosphorus（DIP）. The release amount of TOC, TN and TP reachthe max at15²0d, indicates that deterioration of water quality may appear at localwater in the initial impoundment period.②The results of influence factor experiment show that: Microorganism in thewater is a major environmental factor, but the most of carbon, nitrogen and phosphorusin plant body is released into the water from plant tissue dissolution. The higher thetemperature, the easier release of carbon, nitrogen and phosphorus, the bigger releaserate and maximal unit cumulative release amount. The bigger the pH, the easier releaseof carbon and nitrogen. The effect of pH on the release of phosphorus from differentplant are different, acidic or alkaline environment help to the release of phosphorus. Thecarbon, nitrogen and phosphorus in the overlying water can be used for microorganismsto increase the activity of microorganisms and promote the release of carbon, nitrogenand phosphorus, and they also can change the concentration difference between aqueousphase with solid phase to affect the release of carbon, nitrogen and phosphorus.③Based on the theory of mass balance and combined with the reservoir waterlevel variation characteristics and the migration way of nitrogen and phosphorus, theestimation model of the flux of nitrogen and phosphorus in WLFZ was constructed. Theresults of the variations of nitrogen and phosphorus in soil, nitrogen and phosphorus invegetation, ammonia volatilization, denitrification show that: The results of the flux ofnitrogen and phosphorus in WLFZ during the exposed period are862.38and-33.00kg·km^-2·d^-1, respectively, indicating that the WLFZ is the sink of nitrogen and thesource of phosphorus during the exposed period. The results of the flux of nitrogen andphosphorus in WLFZ during the flooded period are-671.66and^-110.35kg·km^-2·d^-1,respectively, indicating that the WLFZ is the source of nitrogen and phosphorus duringthe flooded period. After a cycle, the decrease of TN, TP content were4079.48t and9813.02t, most of them run off through the soil media. The results of the flux ofnitrogen and phosphorus in WLFZ are-32.03and-77.05kg·km^-2·d^-1, respectively. Thecontents of nitrogen and phosphorus in the soil of WLFZ are the potential pollutionsource, that cannot be ignored, for reservoir eutrophication.