Indirect N 2 O emission of a rice paddydominated. XIA Yongqiu ( 夏永秋 )

Transcription

1 Indirect N 2 O emission of a rice paddydominated watershed XIA Yongqiu ( 夏永秋 ) yqxia@issas.ac.cn

2 Increasing N 2 O emission

3 Direct V.S. Indirect N 2 O emission Direct emission Indirect emission IPCC 28

4 Direct V.S. Indirect N 2 O emission N input rate 129 kg N hr -1 Water area 4% indirect N 2 O emission account for 46% of the total N 2 O emission Outram, et al. 212 EST

5 A significant indirect N 2 O emission from agriculture Water area.21% N input rate kg N hr -1 Vilain, et al. 212 Biogeosciences

6 Production mechanism Beaulieu et al. 211 PNAS

7 Question? England England 8 7 England France France France Taihu 7% Taihu Taihu region 6 region 5 46% region 4%.21% Water area N application rate %? the ratio of indirect N2O What is the ratio of indirect N 2 O emission? Is it a significant contributor to the agricultural greenhouse gas budget?

8 Study region Jurong watershed Water area 8.3% N input rate (paddy rice +wheat) kg N hr -1

9 Experiment design 5 ponds sites, 3 river sites, and 1 reservoir site dissolved N 2 O were collected in 29-mL serum vials previously evacuated according the method of Terry et al. ( 1981) two years continues sampling every 15-2 days DO inorganic N temperature ph, and Eh of surface water were also measured

10 N 2 O emission rate calculation Gas exchange across the water air interface is calculated by the stagnant two - film (Liss and Slater, 1974, Nature) F N2O =V tot (C w -C a /K H ) V tot : the transfer velocity (m s -1 ) for N 2 O across the waterair interface C w: the N 2 O concentration in the surface water of rivers, ponds, and reservoir (mol m -3 ) C a: the N 2 O concentration in ambient air (mol m -3 ), K H: the dimensionless Henry s Law constant (mol m a -3 mol m w -3 )

11 Climate parameters Ranfall (mm) Temperature Dainly average wind speed Monthly rainfall Wind speed (m s -1 ) Temperature (degree)

12 Indirect N 2 O emission rate ug N ug N 2 O-N m -2 2 O-N L -1 h N 2 O Dissolved N 2 O mean 平均 ug N ug m -2 N hl -1-1 Rivers Rivers Ponds Ponds Reservior Reservior

13 Compared to the references c ug N 2 O-N m -2 h a b b -2-4 Rivers Ponds Reservoir Literature

14 Total indirect N 2 O emission Water body Mean N 2 O emission rates Water area Indirect N 2 O flux µg N m -2 h -1 ha ton N year -1 River 12.9(± 21.8) Pond 4.5(± 16.3) Reservoir 7.9(± 1.) In Total

15 Compared to direct N 2 O emission crop Total area (ha) N applications rate (kg N ha -1 ) Emission factor Yang, et al. 21 SSPN Direct N 2 O emission (ton N year 1 ) Rice Cotton Maize Soybean Oil rape Wheat Tea Total Indirect N 2 O total N 2 O.24 X1% 1.8%

16 Compared to N removed by denitrifiation membrane inlet mass spectrometry method Li, et al. 213 JSS Water body Indirect N 2 O N removal N 2 O:N 2 ton N year -1 (ton N year 1 ) % River Pond Reservoir In Total

17 Compared to the references 6 5 d N 2 O yield (%) a b c Rivers Ponds Reservoir Literature

18 What are reasons resulting in low N 2 O emission? ug N2O-N m -2 h y = 22.18x R 2 =.64 P< NO 3 -N (mg N L -1 ) ug N2O-N m -2 h y = 4.6x R 2 =.39 P< NH 4 -N (mg N L -1 ) ug N2O-N m -2 h y =.18x R 2 =.15 P<.1 y = -.43x R 2 =.14 P= N O=18.4[NO N]+.9Eh Eh (mv) ug N2O-N m -2 h DO (% ) ug N2O-N m -2 h y = -2.39x R 2 =.86 P=.14 ug N2O-N m -2 h y =.27x R 2 =.17 P=.4

19 Great runoff is intercepted Construction and road 14.6 Run-off in million m 3 Uplands 5. Total river discharge Total river discharge 13.5

20 Great runoff is intercepted

21 Great runoff is intercepted Dissolved N, mg N L NO3--N NH4+-N T-N Upland 3cm Upland 6cm Upland 9cm Paddy surface Upland runoff Pond River Reservoir Rain N concentrations through transport

22 Great runoff is intercepted NO 3 - -N Rivers Ponds Reservior 8 6 NH 4 + -N Rivers Ponds Reservior mg N L mg N L As a result, N concentration of outflow is very low

23 High reducing condition Low water velocity

24 High reducing condition 14 5 DO (%) a a a a a a b b b Eh (mv) -5 a a a a a a a a b 2-1 Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8 Site 9-15 Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8 Site 9 Ponds site:site1-site 5 ; river sites: site 6-site 8 ; reservoir site: site 9

25 High reducing condition Bouman, 1998 Nature Decreasing N 2 O/N 2 ratio

26 High reducing condition NO 3- NO 2 - N 2 O N 2 18 ug N2O-N m -2 h y =.18x R 2 =.15 P< Redox potential (mv) -18.

27 Conclusions 1 Though water area is high and N input rate is as high as 6 kg N ha -1 per year in our paddy rice dominated watershed, indirect N 2 O emission is disproportionately low. 2 This could have resulted from the limited inputs of N into waterways 3 Strong reductive conditions as a result of low water velocity might also play a great role.

28 Sampling method? Sampling time? Sampling site? Question?

29 Floating chamber method 国家专利号 :

30 Hourly variated emission rate

31 The best sampling time

32 Study region and sample sites CR IAR TAR CR RES Jurong Nanjing

33 Spatial variation of riverine N 2 O emission 2 Flow distance downward from the reservior (km) N 2 O emission rate (ug N m -2 hr -1 ) Jurong city Average: 27 ug N m -2 hr -1 z2 z3 z4 z6 z9 z11 z12

34 Still continuing

35 References Xia Y, Li Y, Li X, Guo M, Yan X. Is indirect N2O emission a significant contributor to the agricultural greenhouse gas budget? A case study of a rice-paddy-dominated agricultural watershed in eastern China, Atmospheric Environment,213,77: Yan X., Cai Z., Yang R., Ti C., Xia Y. Nitrogen budget and riverine nitrogen output in a rice paddy dominated agricultural watershed in eastern China. Biogeochemistry. 211, 16: Xia, Y., Li, Y., Li, X., et al. Diurnal pattern in nitrous oxide emissions from a sewage-enriched river. Chemosphere, 213, 92: Xia, Y., She D., Yan X. Impact of sampling time on chamberbased measurements of riverine nitrous oxide emissions using spatial stability analysis, Geoderma, 214,214:

36 Thanks a lot!