Tracing hydrologic soil carbon loss from a mountainous watershed during extreme rainfall events

Transcription

1 Tracing hydrologic soil carbon loss from a mountainous watershed during extreme rainfall events Ji-Hyung Park & the TERRECO hydro-biogeochemistry partnership: Hyun-Ju Lee, Jong-Jin Jeong, Kyeong-Won Jo & Bomchul Kim (KNU) Svenja Bartsch, Yan Fleckenstein, Chris Schope & Egbert Matzner (U. Bayreuth)

2 Guesstimating C Fluxes from Black Box Soil

3 Missing Soil C Fluxes Hydrologic soil C losses DOC, DIC, POC & PIC POC & PIC DOC &DIC Lal. 24. Science 34:

4 Missing Fluxes in C Balance 연구결과 정기수질모니터링 The gap between the atmospherebased and land-based estimates of terrestrial C sinks in Europe 7 Tg C (CarboEurope) Janssens et al. 23. Europe s terrestrial biosphere absorbs 7 to 12% of European anthropogenic CO 2 emissions. Science 3: Drainage export of dissolved organic C and inorganic C 114 ± 83 Tg C Siemens. 23. Science 32: 1681

5 Hydrologic C loss a Missing Flux? 연구결과 정기수질모니터링 CarboEurope NPP 52 kg C ha -1 yr -1 NBP 75 kg C ha -1 yr -1 River C 96 kg C ha -1 yr -1 Luyssaert et al. 21. GCB 16:

6 Hydro Carbon Tracking in Haean Basin ( Punch Bowl ) How much soil C is lost via hydrologic export from a mountainous, mixed land-use watershed in response to rainfall variability & extremes? Major sources & fates of DOC & POC released during rainfall events? Punch Bowl Watershed Dirty capitalist Mandae Stream DMZ (North Korea) Clean communist Inbuk River

7 Study Site Punch Bowl Watershed 연구결과 정기수질모니터링 Lysimeter Forest YSI: ph, EC, Turb, NO 3 - TDR Cabolyser: DOC & TOC Rain gauge Auto sampler Agri.. stream

8 Annual Mean DOC & POC Conc. (May 8 Apr 1) 연구결과 정기수질모니터링 2-yr biweekly monitoring results Higher conc. of DOC than POC along hydrologic pathways Relatively low stream C conc. (esp. POC) compared to those for throughfall & forest floor leachates Bulk ppt Throughfall DOC POC Oa leachate Forest stream Agricultural stream Concentration (mg C L -1 ) Lee et al. unpublished data

9 Rapidly 연구결과 Changing 정기수질모니터링 C Conc. during Storm Events Lower streamwater POC conc. under base- to low-flow conditions Stronger, non-linear responses of POC to intense storm events Event 1 (72 mm) Event 2 (17 mm) Conc. (mg C L -1 ) Ppt (mm hr -1 ) DOC POC Precipitation Event 3 (292 mm) Event 4 (137 mm) 6/17/8 21: 6/18/8 4: 6/18/8 11: 6/18/8 18: 6/19/8 1: 7/16/8 11: 7/16/8 13: 7/16/8 15: 7/16/8 17: 7/24/8 4: 7/24/8 11: 7/24/8 18: 7/25/8 1: 7/25/8 8: 7/25/8 15: 7/25/8 22: 7/26/8 4: 7/26/8 12: 7/26/8 2: 7/27/8 4: 7/27/8 12: Event 5 (15 mm) Event 6 (167 mm) Event 7 (69 mm) Event 8 (21 mm) Lee et al. unpublished data Conc. (mg C L -1 ) Ppt (mm hr -1 ) Forest stream DOC POC Precipitation /2/9 3: 6/2/9 1: 6/2/9 17: 7/9/9 2: 7/9/9 6: 7/9/9 1: 7/9/9 14: 7/9/9 18: 7/9/9 22: 7/17/9 21: 7/18/9 4: 7/18/9 11: 7/18/9 18: 7/19/9 1: 7/19/9 8: 8/11/9 12: 8/11/9 2: 8/12/9 4: 8/12/9 12: 8/12/9 2:

10 Differential 연구결과 Responses 정기수질모니터링 of DOC & POC during Storm Stronger, non-linear increases in both event mean and max. POC conc. with increasing mean rainfall intensity of each storm event 12 DOC POC R 2 =.98 (P <.1) R 2 =.61 (P =.24) 5 DOC R 2 =.73 (P =.12) POC R 2 =.94 (P <.1) Mean conc. (mg C L -1 ) Max conc. (mg C L -1 ) Mean rain intensity (mm hr -1 ) Mean rain intensity (mm hr -1 ) Lee et al. unpublished data

11 Real-Time Monitoring of DOC & POC Measurements of streamwater DOC & POC Carbolyser (starting July 29): measuring TOC & DOC conc. every 5 min, based on UV/Vis spectrophotometry Lab analysis: measuring DOC & POC conc. in samples taken every 2 hr using an autosampler Carbolyser TM

12 Short-Term Changes in DOC vs. POC during Storm Real-time measurement of DOC & POC conc. every 5 min Baseflow: very low POC conc. vs slightly higher DOC conc. Peakflow: higher increases in POC relative to DOC conc. 1 Event 8 (21 mm) 1. Concentration (mg C L -1 ) POC (Carbolyser) DOC (Carbolyser) DOC (Lab analysis) POC (Lab analysis) Discharge Precipitation Discharge (m 3 S -1 ) Precipitation (mm hr -1 )..1 8/11/9 8/12/9 8/13/9 8/14/9 Jeong et al. unpublished data 1

13 Non-Linear Responses of POC/DOC Export Six storm events (Jul 17 Sep 3, 29) 5 POC 3 4 Y = X - (6.85E-6)X 2 + (4.9886E-7)X 3 r 2 = 1. p <.1 DOC 25 C export (kg C ha -1 ) 3 2 Y = X + (5.5617E-5)X 2 + (2.3346E-8)X 3 r 2 = 1. p <.1 Discharge Y = X +.225X 2 + (4.6792E-6)X 3 r 2 = 1. p < Discharge (t ha -1 ) Rainfall (mm) Jeong et al. unpublished data

14 Hydrologic C Loss Importance of Extreme Events DOC/POC export (Jul 17, 29 Jul 16, 21) DOC: Baseflow export comprised 8% of the annual DOC export. POC: 1-d extreme event accounted for 29% of the annual POC export. Period Event # Ppt (mm) Duratioin (d) POC (kg C ha -1 ) DOC (kg C ha -1 ) Stormflow (%) (7.4) (46.7) (18.3) Event (%) (.3) (29.2) (8.1) Baseflow (%) (92.6) (53.3) (81.7) Total CarboEurope (%) (1) (1) (1) (1) NPP 52 kg C ha -1 yr -1 NBP 75 kg C ha -1 yr kg C ha -1 yr -1 Jeong et al. unpublished data River C 96 kg C ha -1 yr -1

15 Carbon in Suspended Sediments z Silt-size sediments in forest & agricultural stream SEM coupled with EDX: C comprising a sizable proportion of silt element composition C: 18 Wt % Forest stream C: 24 Wt % Agricultural stream Jo et al. unpublished data

16 Tracing Sediment Sources Sediment source tracing using Pb stable isotopes E S Silt (2-6 μm) July 29 Forest stream: forest floor & streambank Agricultural stream: vegetable field & forest soils (added to croplands by farmers) 28 Pb/ 26 Pb S E E E Sand (> 6 μm) S S Upslope forest Oi Upslope forest Oe/Oa Upslope forest soil Forest streambank Oe/Oa Forest streambank soil Downslope forest Oe/Oa Downslope forest soil Paddy Vegetable field Bulk precipitation Forest floor leachate Streambed sediment Agricultural stream SS Forest stream SS Pb/ 27 Pb Jo & Park. Environmental Science & Technology (revision in review)

17 Tracing POC Sources δ 15 N Carbon source fingerprinting using C & N isotopes Forest stream: forest floor & streambank Agricultural stream: vegetable field & forest soils (added to fields) July 29 Silts (2-6 μm) Start End End Start Forest A site upper Oi Forest A site upper Oe/Oa Forest A site upper Soil Forest A site mid Oi Forest A site mid Oe/Oa Forest A site mid Soil Forest A site low Oi Forest A site low Oe/Oa Forest A site low Soil Forest A site streambank2 Oi Forest A site streambank2 Oe/Oa Forest A site streambank2 Soil Forest C site exposed slope Oi Forest C site exposed slope Oe/Oa Forest C site exposed slope Soil Paddy field Cropland Silts in forest stream Silts in agricultural stream δ 13 C Lee et al. unpublished data

18 Summary & Implications DOC & POC export an important soil C loss Bi-weekly sampling: DOC conc. were usually higher than POC from precipitation through the forest to the basin outlet. Storm sampling & real-time monitoring: Flashy, nonlinear responses of POC (& DOC) to intense rainfall events can result in a missing C loss that is not captured by routine monitoring. Erosion of soil C in a changing climate Deforestation and agricultural expansion on steep terrain can amplify the vulnerability of soil carbon loss (via erosionassociated POC export) to rainfall variability & extremes.

19 To protect soil C leaks, protect your mountains. To protect your rivers, protect your mountains. - Emperor Yu, China.