Nitrous Oxide Emission From The Typical Wetlands In Poyang Lake

As China’s largest freshwater lake, Poyang Lake, because of its distinctivenatural and geographical conditions, as well as its complex relationship with theYangtze River, formed a lake wetland ecosystem. Researching into the releasingcharacteristics of nitrous oxide of typical wetland in Poyang Lake and its influentialfactors has important theoretical and practical significance on revealing the cyclingrules of wetland nitrogen and accurately assessing the release of nitrous oxide in lakesand wetlands. In order to reveal diurnal and seasonal variation of the release of nitrousoxide of typical wetland in Poyang Lake, clarify impact factors of its releasingprocess, and quantitatively evaluate whether typical wetland in Poyang Lake is the“source” or “destination” of nitrous oxide, the distributing districts of wetland plants,emergent plants and submerged plants were selected in typical wetland area of theNature Reserve of Southern Rocky Mountain, and the diurnal and seasonal variationsof nitrous oxide were observed and measured in the samples of typical Carexcinerascens community (TC: the treatment of soil and plant system, TJ: the clippingtreatment) and typical Triarrhena lutarioriparia community (DJ: the clippingtreatment) and the bare soil treatment (LT) by closed static chamber-gaschromatography during the priod from April2009to June2011. From late July2009to early September, when the area tested was in a sustained state of flooding, thediurnal variation of nitrous oxide flux in typical Carex cinerascens and submergedplants community was observed. At the same time, the inside temperature, soiltemperature, moisture, water temperature, water depth and other environmentalfactors were recorded. The results showed:(1) During the non-flooding period, the nitrous oxide emission of TC, TJ and LTtreatment wetland all show similar seasonal variation patterns, but there aresignificant differences in different treatments(F=17.19, P<0.01); during the floodingperiod, the TC and TJ treatment wetland has the inclination of absorbing nitrous oxidewhile two treatments of nitrous oxide show obvious release when the water leveldrops and the bottomland emerges; during wet season, the release of nitrous oxide inTC treatment possesses a certain daily variation mode which is roughly characterizedby “bimodal type”.(2) The seasonal variation mode of nitrous oxide release in the DJ treatmentwetland is in accordance with that of TJ treatment. The changing scope of the releasing rate of nitrous oxide is between-0.001to0.412mg N2O·m-2·h-1. Thereleasing rate of nitrous oxide of two kinds of phytocenosis (the Triarrhenalutarioriparia and Carex cinerascens communities) has remarkable difference(F=11.46, P<0.01).(3) The release of nitrous oxide in typical submerged plant community hasevident diurnal variation, which possesses the “bimodal” feature. The changing scopeof nitrous oxide releasing rate throughout the day is between-0.003to0.002mgN2O·m-2·h-1; the rate has a conspicuous positive correlation with the underground5cmtemperature and the air temperature.(4) Both temperature and moisture have certain influence on the release ofnitrous oxide in Poyang Lake typical wetland. However, because the temperatureduring all-year-around and the change of soil moisture in the studied area are mainlyin the appropriate range of nitrification and denitrification, the effect of the variationsin temperature and soil moisture are overshadowed by other influential factors. Theprominence of wetland flooding restrains the release of nitrous oxide in Poyang Laketypical wetland while the process of alternation of wetting and drying in wetlandintensely facilitates the release; the plants in Poyang Lake wetland make morecompetition with microorganisms for nitrogen nutrients. Surface mowing significantlyreduces the releasing rate, and the releasing rate of nitrous oxide in typical Carexcinerascens marshland shows a clear negative correlation with the total biomass ofCarex cinerascens (r=-5.0, P<0.05).(5) All the TC, TJ and DJ treatment wetland function as the “sources” of therelease of nitrous oxide throughout the year, but the weak “destinations” during thewet period; the warming potential of the release of nitrous oxide in Poyang Laketypical Carex cinerascens marshland has respectively reached26.8%of its carbondioxide and23.6%of its methane, and that in Triarrhena lutarioriparia wetland(58.8%) has outnumbered half of the CO2warming potential in Carex cinerascensmarshland.