Effects Of Simulated Nitrogen Deposition On CO₂ And CH₄ Emissions From Freshwater And Brackish Marshes In The Min River Estuary

In recent years,global warming has become the focus of attention all over the world,and the increase of greenhouse gas content is the main cause of this problem.Along with the rapid development of industrial and agricultural production,the nitrogen substances discharged into the atmosphere are increasing.The nitrogenous substances in the air return to the ground through nitrogen deposition.This poses a serious threat to the existing ecosystem and carbon cycle.Tidal marshes is not only an important source/sink of greenhouse gases,but also a transitional zone between land and ocean,which undertakes dual effects of atmospheric and surface nitrogen sources.Based on this,this study takes freshwater and brackish from Cyperus malaccensis marshes in the Min River estuary as the research object,through the field simulation of different gradient of nitrogen deposition ofCK(0g·m-2·a-1),N1(24g·NH4NO3·m-2·a-1),N2(48g·NH4NO3·m-2·a-1),N3(96g·NH4NO3·m-2·a-1),the CO2 and CH4 emissions measured and analyzed,and recording the related environmental factors,hoping to provide reference for carbon emissions reduction work in the areas.The main results are as follows:(1)The soil temperature,soil EC and soil pH under different treatment were not significantly different in the freshwater and brackish marshes(P>0.05);however,except for soil EC of brackish marshes was significantly higher than that of freshwater marshes(P<0.05),the difference between soil temperature and soil pH were not significant(P>0.05).(2)Compared to the control,nitrogen deposition increased significantly of pore water NH4+-N and NO3--N concentration in the freshwater and brackish marshes(P<0.05),CK,N2,N3 treatments of pore water NH4+-N and NO3--N concentration in the brackish marshes was significantly higher than the freshwater marshes(P<0.5).(3)The different treatments of pore water SO42-concentration were not significantly different in the freshwater and brackish marshes(P>0.05),but the pore water SO42-concentration in the brackish marshes was significantly higher than the freshwater marshes(P<0.01);The different treatments of of pore water Cl-concentration were not significantly different in the freshwater and brackish marshes(P>0.05),however,the pore water Cl-concentration in the brackish marshes was significantly higher than the freshwater marshes(P<0.05).(4)Compared to the control,effects of the nitrogen deposition significantly increased CO2 emissions in the freshwater marshes(P<0.05),but the N1,N2,N3 treatments of CO2 emissions is not significantly different(P>0.05);the difference of CO2 emissions under different treatments did not reach significant level in the brackish marshes(P>0.05);CO2 emissions of CK and N2 treatment in the brackish marshes was significantly higher than that in the freshwater marshes,CO2 emissions from N1 and N3 treatment in the brackish marshes differences between freshwater marshes did not reach the significant level(P>0.05).(5)N2 and N3 treatment of CH4 emissions was significantly higher than CK treatment in the freshwater marshes(P<0.05),the difference of CK,N1 and N1,N2,N3 treatment of CH4 emissions were not significantly different(P>0.05);the difference of CH4 emissions under different treatments between also did not reach significant level in the brackish marshes(P>0.05);the CH4 emissions in the brackish marshes under different treatment were significantly lower than the freshwater marshes(P<0.01).(6)Compared to the control,the freshwater marshes of N1,N2 and N3 treatments TGWP at 20a and 100a scales were increased by 48.95%,63.85%,87.71%and 45.03%,51.44%,76.95%,respectively,indicating nitrogen deposition enhancing the greenhouse effect freshwater marshes greenhouse gas channel;the brackish marshes of N1 and N2 treatments TGWP at 20a and 100a scales were decreased by 3.48%,5.77%and 2.56%,3.93%,and N3 treatments TGWP decreased 0.45%in the 20a scale,in the 100a scale was increased by 0.60%,indicating the greenhouse effect of low concentration of nitrogen deposition suppression of the Shanyutan wetland greenhouse gases,high concentrations of nitrogen deposition in greenhouse effect may promote the brackish marshes greenhouse gases.(7)Stepwise regression analysis showed that environmental factors influence the emissions of CO2 and CH4 in the freshwater and brackish marshes,are different in different treatments,but generally speaking,air temperature,soil temperature,soil EC,soil pH,pore water NH4+-N and SO42-concentration are the main environmental factors affecting the freshwater and brackish marshes CO2 and CH4 emissions.