CH4and N2O are important greenhouse gases, which play significant roles inglobal warming and atmospheric chemistry. There is a relatively high concentration ofC and N in rivers and estuaries, where more CH4and N2O is produced and released tothe atmosphere due to human activities. Hence studies on the dissolved CH4and N2Oin the rivers and estuaries are becoming more important, and it may help to quantifythe emission from different rivers and estuaries in order to understand their influenceon the future climate changes.In this dissertation, distributions, seasonal variations, fluxes and relatedinfluencing factors of dissolved CH4and N2O in the Yangtze River, Yellow river andtheir estuaries were studied. To explore the production mechanism of N2O and CH4,slurry incubation experiments aiming at estimating the potential CH4production andoxidation rate, the potential nitrification and denitrification rate, were carried out atKenli station. The main results are as follows:(1)The seasonal variation of dissolved CH4and N2O was studied during surveys atStation Kenli of the Yellow River from March2010to December2011. The resultsindicated that the average dissolved CH4and N2O concentrations were (20.14±14.68)nmol/L and (21.89±14.12) nmol/L, respectively. Dissolved CH4at station Kenli ofthe Yellow River showed seasonal variations with the highest values in winter and thelowest in spring. There is little change of dissolved CH4in other seasons. Unlike CH4,dissolved N2O showed a relatively high concentration in winter and summer whilelow concentration occurred in spring and autumn. CH4concentrations in the YellowRiver correlated positively with the monthly flow rates, while N2O showed a negativecorrelation with water temperature. The input of CH4and N2O from the Yellow Riverto the Bohai Sea in2010-2011was estimated to be4.4×105mol/yr and5.1×105mol/yr,respectively. The incubation experiments at Station Kenli showed that the potentialproduction and oxidation rate ranges for CH4in the water of the Yellow River waterwere (0.40.9) nmol CH4·L-1·d-1nmol CH4·L-1·d-1and (0.33.5) nmol CH4·L-1·d-1, andthe sedimentary potential CH4production and oxidation rate ranges are (1.37.4)nmol CH4·Kg-1·d-1and (05.0) nmol CH4·Kg-1·d-1. The seasonal variations of potential production and oxidation rate showed a higher value in summer and autumn and alower value in winter. The highest sedimentary potential production rate occurred insummer and the lowest in winter, while for sedimentary oxidation production rate, themaximum appeared in autumn and no obviously oxidation was detected in winter. Asfor N2O, the ranges of potential total production rate, potential nitrification anddenitrification rate in the Yellow River water were (-0.801.05) nmol N·L-1·h-1、0.420.46nmol N·L-1·h-1and29.4661.09nmol N·L-1·h-1, while in the sediment therate ranges were (-0.641.12) nmol N·Kg-1·h-1,(0.210.52) nmol N·Kg-1·h-1and(4.17314.4) nmol N·Kg-1·h-1, respectively. The potential total production rates in theYellow River correlated positively with incubation temperature, and these potentialrates in water and sediment have seasonal variation with a higher value in summerand lower one in autumn, and in winter the water and sediment are sinks of N2O.(2) The seasonal variation of dissolved CH4and N2O was studied from January2010to December2011in Yangtze River. The average concentrations of CH4and N2Owere (143.08±49.73) nmol/L and (18.05+8.20) nmol/L. CH4and N2O had seasonalvariations with the highest values occurring in autumn and the lowest in spring. Thedissolved CH4and N2O inputs to the East China Sea and Yellow Sea via the YangtzeRiver were estimated to be3.5Gg·a-1and0.4Gg·a-1respectively, which plays animportant role for the distribution of CH4and N2O and the biogeochemical cycles of Cand N in the Yangtze River estuary. A cruise was conducted on the Yangtze estuary inJuly2011. Horizontal and vertical distribution of CH4and N2O showed that theaverage dissolved CH4in the surface and bottom waters were (64.29±29.82) nmol/Land (87.94±43.80) nmol/L, respectively, and N2O were (30.16±12.68) nmol/L and(33.37±15.91) nmol/L. CH4and N2O concentrations in bottom waters are higher thanthose in surface, which illustrated the sediment act as sources of CH4and N2O. Thehorizontal distributions of CH4and N2O in Yangtze estuary decreased gradually fromthe inner to the outer estuary. Dissolved CH4and N2O concentrations initiallydecreased with increasing salinities at0–10psu. The CH4and N2O in surface water ofYangtze River estuary are supersaturated, which indicates that the Yangtze Riverestuary was net sources of atmospheric CH4and N2O in the summer of2011. |