Transport of organic carbon via rivers to estuary is a significant geochemical proc- ess in the global carbon cycle. This paper presents bulk total organic carbon （TOC） from the Dongjiang catchment to the adjacent H...Transport of organic carbon via rivers to estuary is a significant geochemical proc- ess in the global carbon cycle. This paper presents bulk total organic carbon （TOC） from the Dongjiang catchment to the adjacent Humen outlet, and discusses the applicability of 613C and ratio of carbon to nitrogen （C/N） as indicators for sources of organic matter in the surface sediments. Survey results showed that organic carbon concentration in summer were higher than in the winter. An elevated trend of TOC occurred along the river to the Humen outlet in both surveys, and the highest mean values of dissolved and particular organic carbon （DOC-279 μmol L-1 and POC-163μmol L-1） were observed in the urban deltaic region in summer flood flow. Winter samples had a wide range of b＇13C and C/N （5-3C -24.6%o to -30.0%o, C/N 4-13）, and summer ones varied slightly （8-3C -24.2%o to -27.6%0, C/N 6-18）. As results suggest that POC in the three zones of upstream-delta-outlet dominantly came from riverbank soil, phytoplankton and agricultural C3 plants in winter, whereas main sources were from the riverbank and mangrove soil in summer. Moreover, anthropogenic sewage inputs had 11% and 7% contribution to POC in the deltaic and outlet. Transport accompanied with seasonal freshwater variation, phytoplankton production and degradation, and removal be- havior caused variation of organic carbon concentration. The results also discovered that TOC export bulk in Dongjiang was approximately one quarter of Humen flux in the dry flow, and anthropogenic activity significantly impacted the river export contribution.展开更多
Air samples in China were collected and determined for the concentration of N_2O. The production rates of N_2O from agricultural soils were measured with the chamber method.The results in- dicate that the background c...Air samples in China were collected and determined for the concentration of N_2O. The production rates of N_2O from agricultural soils were measured with the chamber method.The results in- dicate that the background concentration of N_2O averages(308±5)×10^(-9)in 1989,which is close to that ob- tained at the other background stations abroad.However,at both urban and rural areas,atmospheric N_2O concentrations are higher.N_2O emission fluxes from several farmlands are different and dependent on the fac- tors of agricultural practice and climate.But their magnitudes are at the same order.Preliminary calculation shows that the released N_2O-N from agricultural sources(cultivated soil and N-fertilizers)amounts to 122 Gg/a in China in 1990.展开更多
Denitrification-induced nitrogen(N) losses from croplands may be greatly increased by intensive fertilization.However,the accurate quantification of these losses is still challenging due to insufficient available in s...Denitrification-induced nitrogen(N) losses from croplands may be greatly increased by intensive fertilization.However,the accurate quantification of these losses is still challenging due to insufficient available in situ measurements of soil dinitrogen(N) emissions.We carried out two one-week experiments in a maize-wheat cropping system with calcareous soil using theN gas-flux(NGF) method to measure in situ Nfluxes following urea application.Applications ofN-labeled urea(99 atom%,130-150 kg N ha) were followed by irrigation on the 1 st,3 rd,and 5 th days after fertilization(DAF 1,3,and 5,respectively).The detection limits of the soil Nfluxes were 163-1 565,81-485,and 54-281 μg N mhfor the two-,four-,and six-hour static chamber enclosures,respectively.The Nfluxes measured in 120 cases varied between 159 and 2 943(811 on average) μg N mh.which were higher than the detection limits,with the exception of only two cases.The Nfluxes at DAF 3 were significantly higher(by nearly 80%(P<0.01)) than those at DAF 1 and 5 in the maize experiment,while there were no significant differences among the irrigation times in the wheat experiment.The Nfluxes and the ratios of nitrous oxide(NO) to the NO plus Nfluxes following urea application to maize were approximately 65% and 11 times larger,respectively(P<0.01),than those following urea application to wheat.Such differences could be mainly attributed to the higher soil water contents,temperatures,and availability of soil N substrates in the maize experiment than in the wheat experiment.This study suggests that theNGF method is sensitive enough to measure in situ Nfluxes from intensively fertilized croplands with calcareous soils.展开更多
Nitrogen (N) is the most important determinant nutrient for plant growth and crop yield. Plants lacking N show stunted growth and yellowish leaves. Plant growth and crop yield usually increase when N is added. However...Nitrogen (N) is the most important determinant nutrient for plant growth and crop yield. Plants lacking N show stunted growth and yellowish leaves. Plant growth and crop yield usually increase when N is added. However, too much N leads to weak stems in grain crops (lodging) which result into low yield. The aim of the study was to delineate changes of N concentration, its direction of movement and its pattern of disposition in the soil as influenced by amount of applied water and nitrogen so as to reduce N losses and maximise its absorption by maize roots.The study was conducted during irrigation seasons of 2011 and 2012 at Nkango Irrigation Scheme, Malawi. The trials consisted of factorial arrangement in a Randomised Complete Block Design (RCBD). The factors were water and N and both were at four levels. The Triscan Sensor was used to measure total N concentration at different vertical and lateral points. The study inferred that changes of N concentration, its direction of movement and its pattern of disposition in the soil are influenced by water flux and absorption rate of plants roots due to gradient created by absorption. The study noted that when N is in low supply, its movement towards maize roots is greatly influenced by diffusion. The study concluded that to maximise N absorption by maize roots, the point of N application should be at5 cmaway from the planting station to minimise N losses through drifting away from the maize rooting zone.展开更多
Because of the increasing amount of oily wastewater produced each day,it is important to develop superhydrophilic/underwater superoleophobic oil/water separation membranes with ultrahigh flux and high separation effic...Because of the increasing amount of oily wastewater produced each day,it is important to develop superhydrophilic/underwater superoleophobic oil/water separation membranes with ultrahigh flux and high separation efficiency.In this paper,a superhydrophilic/underwater superoleophobic N-isopropylacrylamide-coated stainless steel mesh was prepared through a simple and convenient graft polymerization approach.The obtained mesh was able to separate oil/water mixtures only by gravity.In addition,the mesh showed high-efficiency separation ability(99.2%)and ultrahigh flux(235239 L·m^(−2)·h^(−1)).Importantly,due to the complex cross-linked bilayer structure,the prepared mesh exhibited good recycling performance and chemical stability in highly saline,alkaline and acidic environments.展开更多
基金National Natural Science Foundation of China, No.41101152 No.40901090+5 种基金 No.41172315 The Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry The talents in- troduced into Universities Foundation of Guangdong Province of China The China Scholarship Council （CSC） funding in 2013 The Universities Disciplinary and Special Construction Funds of Guangdong Prov- ince Foundation, No.C 10092 The Scientific Research Foundation of Graduate School of South China Nor- mal University
文摘Transport of organic carbon via rivers to estuary is a significant geochemical proc- ess in the global carbon cycle. This paper presents bulk total organic carbon （TOC） from the Dongjiang catchment to the adjacent Humen outlet, and discusses the applicability of 613C and ratio of carbon to nitrogen （C/N） as indicators for sources of organic matter in the surface sediments. Survey results showed that organic carbon concentration in summer were higher than in the winter. An elevated trend of TOC occurred along the river to the Humen outlet in both surveys, and the highest mean values of dissolved and particular organic carbon （DOC-279 μmol L-1 and POC-163μmol L-1） were observed in the urban deltaic region in summer flood flow. Winter samples had a wide range of b＇13C and C/N （5-3C -24.6%o to -30.0%o, C/N 4-13）, and summer ones varied slightly （8-3C -24.2%o to -27.6%0, C/N 6-18）. As results suggest that POC in the three zones of upstream-delta-outlet dominantly came from riverbank soil, phytoplankton and agricultural C3 plants in winter, whereas main sources were from the riverbank and mangrove soil in summer. Moreover, anthropogenic sewage inputs had 11% and 7% contribution to POC in the deltaic and outlet. Transport accompanied with seasonal freshwater variation, phytoplankton production and degradation, and removal be- havior caused variation of organic carbon concentration. The results also discovered that TOC export bulk in Dongjiang was approximately one quarter of Humen flux in the dry flow, and anthropogenic activity significantly impacted the river export contribution.
文摘Air samples in China were collected and determined for the concentration of N_2O. The production rates of N_2O from agricultural soils were measured with the chamber method.The results in- dicate that the background concentration of N_2O averages(308±5)×10^(-9)in 1989,which is close to that ob- tained at the other background stations abroad.However,at both urban and rural areas,atmospheric N_2O concentrations are higher.N_2O emission fluxes from several farmlands are different and dependent on the fac- tors of agricultural practice and climate.But their magnitudes are at the same order.Preliminary calculation shows that the released N_2O-N from agricultural sources(cultivated soil and N-fertilizers)amounts to 122 Gg/a in China in 1990.
基金jointly supported by the National Natural Science Foundation of China(41877333,41830751 and 41761144054)the Basic Research Program of Frontier Sciences of Chinese Academy of Sciences(ZDBSLY-DQCOO7)the National Key Research and Development Program of China(2017YFD0200100)。
文摘Denitrification-induced nitrogen(N) losses from croplands may be greatly increased by intensive fertilization.However,the accurate quantification of these losses is still challenging due to insufficient available in situ measurements of soil dinitrogen(N) emissions.We carried out two one-week experiments in a maize-wheat cropping system with calcareous soil using theN gas-flux(NGF) method to measure in situ Nfluxes following urea application.Applications ofN-labeled urea(99 atom%,130-150 kg N ha) were followed by irrigation on the 1 st,3 rd,and 5 th days after fertilization(DAF 1,3,and 5,respectively).The detection limits of the soil Nfluxes were 163-1 565,81-485,and 54-281 μg N mhfor the two-,four-,and six-hour static chamber enclosures,respectively.The Nfluxes measured in 120 cases varied between 159 and 2 943(811 on average) μg N mh.which were higher than the detection limits,with the exception of only two cases.The Nfluxes at DAF 3 were significantly higher(by nearly 80%(P<0.01)) than those at DAF 1 and 5 in the maize experiment,while there were no significant differences among the irrigation times in the wheat experiment.The Nfluxes and the ratios of nitrous oxide(NO) to the NO plus Nfluxes following urea application to maize were approximately 65% and 11 times larger,respectively(P<0.01),than those following urea application to wheat.Such differences could be mainly attributed to the higher soil water contents,temperatures,and availability of soil N substrates in the maize experiment than in the wheat experiment.This study suggests that theNGF method is sensitive enough to measure in situ Nfluxes from intensively fertilized croplands with calcareous soils.
文摘Nitrogen (N) is the most important determinant nutrient for plant growth and crop yield. Plants lacking N show stunted growth and yellowish leaves. Plant growth and crop yield usually increase when N is added. However, too much N leads to weak stems in grain crops (lodging) which result into low yield. The aim of the study was to delineate changes of N concentration, its direction of movement and its pattern of disposition in the soil as influenced by amount of applied water and nitrogen so as to reduce N losses and maximise its absorption by maize roots.The study was conducted during irrigation seasons of 2011 and 2012 at Nkango Irrigation Scheme, Malawi. The trials consisted of factorial arrangement in a Randomised Complete Block Design (RCBD). The factors were water and N and both were at four levels. The Triscan Sensor was used to measure total N concentration at different vertical and lateral points. The study inferred that changes of N concentration, its direction of movement and its pattern of disposition in the soil are influenced by water flux and absorption rate of plants roots due to gradient created by absorption. The study noted that when N is in low supply, its movement towards maize roots is greatly influenced by diffusion. The study concluded that to maximise N absorption by maize roots, the point of N application should be at5 cmaway from the planting station to minimise N losses through drifting away from the maize rooting zone.
基金supported by the National Natural Science Foundation of China(Grant No.51473070).
文摘Because of the increasing amount of oily wastewater produced each day,it is important to develop superhydrophilic/underwater superoleophobic oil/water separation membranes with ultrahigh flux and high separation efficiency.In this paper,a superhydrophilic/underwater superoleophobic N-isopropylacrylamide-coated stainless steel mesh was prepared through a simple and convenient graft polymerization approach.The obtained mesh was able to separate oil/water mixtures only by gravity.In addition,the mesh showed high-efficiency separation ability(99.2%)and ultrahigh flux(235239 L·m^(−2)·h^(−1)).Importantly,due to the complex cross-linked bilayer structure,the prepared mesh exhibited good recycling performance and chemical stability in highly saline,alkaline and acidic environments.
