Guangxi Xing

Nitrous Oxide and Methane Emissions as Affected by Water,Soil and Nitrogen

Specific management of water regimes, soil and N in China might play an important role in regulating N2O and CH4 emissions in rice fields. Nitrous oxide and methane emissions from alternate non-flooded/flooded paddies were monitored simultaneously during a 516-day incubation with lysimeter experiments. Two N sources (15N-(NH4)2SO4 and 15N-labeled milk vetch) were applied to two contrasting paddies: one derived from Xiashu loess (Loess) and one from Quaternary red clay (Clay). Both N2O and CH4 emissions were significantly higher in soil Clay than in soil Loess during the flooded period. For both soil, N2O emissions peaked at the transition periods shortly after the beginning of the flooded and non-flooded seasons. Soil type affected N2O emission patterns. In soil Clay, the emission peak during the transition period from non-flooded to flooded conditions was much higher than the peak during the transition period from flooded to non-flooded conditions. In soil Loess, the emission peak during the transition period from flooded to non-flooded conditions was obviously higher than the peak during the transition period from non-flooded to flooded conditions except for milk vetch treatment. Soil type also had a significant effect on CH4 emissions during the flooded season, over which the weighted average flux was 111 mg C m−2 h−1 and 2.2 mg C m−2 h−1 from Clay and Loess, respectively. Results indicated that it was the transition in the water regime that dominated N2O emissions while it was the soil type that dominated CH4 emissions during the flooded season. Anaerobic oxidation of methane possibly existed in soil Loess during the flooded season.

Assessment of Nitrogen Pollutant Sources in Surface Waters of Taihu Lake Region

Abstract The nitrogen (N) pollution status of the 12 most important rivers in Changshu, Taihu Lake region was investigated. Water samples were collected from depths of 0.5–1.0 m with the aid of the global positioning system (GPS). The seasonal variations in the concentrations of different N components in the rivers were measured. Using tension-free monolith lysimeters and 15 N-labeled fertilizer, field experiments were carried out in this region to determine variations of 15 N abundance of NO 3 − in the leachate during the rice and wheat growing seasons, respectively. Results showed that the main source of N pollution of surface waters in the Taihu Lake region was not the N fertilizer applied in the farmland but the urban domestic sewage and rural human and animal excreta directly discharged into the water bodies without treatment. Atmospheric dry and wet N deposition was another evident source of N pollutant of the surface waters. In conclusion, it would not be correct to attribute the N applied to farmlands as the source of N pollution of the surface waters in this region.

Pathways of N2O emission from rice paddy soil

Abstract The pathways of nitrous oxide (N 2 O) emission from a paddy soil were investigated in a pot experiment. The results indicate that the main pathway of N 2 O emission from rice–soil system depends on the soil water status. When the soil was flooded, the emission was predominantly (87.3% on average) through the rice plants, while in the absence of floodwater, N 2 O was emitted mainly through the soil surface, with only 17.5% on the average released through the plants. Cutting the rice stems below water surface immediately decreased the N 2 O flux to 55.8% of that before cutting, while the N 2 O flux from the pots with intact plants did not change. Two days after the cutting, the average N 2 O flux from the cut pots was 51.1% of that from the intact pots. During the absence of floodwater, cutting the rice stems did not significantly affect the N 2 O flux compared with that from the pots with intact plants.

Nitrous oxide emission from wetland rice soil as affected by the application of controlled-availability fertilizers and mid-season aeration

Abstract N2O emission from a wetland rice soil as affected by the application of three controlled-availability fertilizers (CAFs) and urea was investigated through a pot experiment. N2O fluxes from the N fertilized paddy soil averaged 44.8–69.3 μg N m–2 h–1 during the rice growing season, accounting for 0.28–0.51% of the applied N. The emission primarily occurred during the mid-season aeration (MSA) and the subsequent re-flooding period. Fluxes were highly correlated with the NO3– and N2O concentrations in the soil water. As there were relatively large amounts of NH4+-N present in the soil of the CAF treatments at the beginning of MSA, leading to large amounts of NO3–-N during the MSA and the subsequent re-flooding period, the tested CAFs were not effective in reducing N2O emission from this paddy soil. The potential of applied CAFs to reduce N2O emissions from paddy soil is discussed.

N pollution sources and denitrification in waterbodies in Taihu Lake region

Herein presented are the researches of the past few years related to characteristics of N pollution of waterbodies and N transport from croplands to the waterbodies in Suzhou and Wuxi regions, the center of the Taihu Lake valley. Based on the types of waterbodies, concentrations of inorganic N of different forms, concentrations of, PO 4 3− , δ15NH4 values in river and lake waterbodies, the pollution sources of N in the river, lake and well waters are distinguished, and comparisons are made of trend of variation and amplitude of concentration between years, seasons and N pollutants in waterbodies. The increase in N2O concentration in different waterbodies and high δ15NO- 3 value in different waterbodies are deemed as an evidence of the existence of denitrification in the river, lake and well waters. Moreover, the role of denitrification in the waterbodies plays in stabilizing chronically concentration of N as pollutant in the waterbodies and mitigating N load in the waterbodies.

Monitoring the concentration of N2O in the Fildes Peninsula, maritime Antarctica

AbstractsGases in the marine boundary layer in Fildes Peninsula, maritime Antarctica were sampled and analyzed for the first time. Sampling sites included areas covered by moss and lichen growth, penguin colonies and an area where scientific research stations are located. A total of 211 samples were analyzed for N2O concentrations, with an average of (321.33±3.07) nL/L. This is above the global average value of 314 nL/L. It is found that the N2O concentrations evidently increase during the summer months. Concentrations around the research stations are higher than at remote areas, indicating a potential source from human activities on the island. N2O concentrations at a large penguin colony on Barton Peninsula are the highest among the sampled areas. This may explain why N2O concentrations in Fildes Peninsula are higher than the global average. Our preliminary conclusions are that human activities and emissions from penguin dropping-amended soil and vegetation soil constitute the major sources of N2O in the maritime Antarctic atmosphere.

Natural 15N abundance in soils

According to the classical definition, the isotopic composition or relative abundance of an element is a fixed value, and the behaviour of the light and heavy isotopes in chemical reactions is strictly identical. These are two basic assumptions for conducting tracer experiments with stable isotopes. However, it is now known that the variation in natural abundance of the isotopes of elements is a biogeochemical phenomenon existing universally in nature (Hoering 1955; Hauck 1973). For instance, variations are found in the natural abundance of the stable isotopes of C, H, O, N and S in organisms. Moreover, the behaviour of the light and heavy isotopes involved in various reactions is not strictly identical. The variation in the natural isotopic abundance is caused by isotopic fractionation, also called the mass discriminatory effect, which is brought about by a series of biological, chemical and physical processes in nature and, especially, in living organisms. The so-called mass discriminatory effect refers to the preference of the light isotope of an element 14N, for example over the heavy one, 15N, to take part in a reaction. Consequently, in a reaction the newly-formed reaction product is relatively enriched in 14N, while the remaining reaction substrate becomes enriched in 15N. The deviation in natural 15N abundance of a substance from that of the standard (atmospheric N2) is referred to as δ15N which is calculated by the equation:

Measurements of nitrous oxide emissions from vegetable production in China

{\delta ^{15}}N = \frac{{R\left( {sample} \right) - R\left( {standard} \right)}}{{R\left( {standard} \right)}}1000\%