Methane in the Changjiang (Yangtze River) Estuary and its Adjacent Marine Area: Riverine Input, Sediment Release and Atmospheric Fluxes

Transcription

1 Methane in the Changjiang (Yangtze River) Estuary and its Adjacent Marine Area: Riverine Input, Sediment Release and Atmospheric Fluxes Guiling Zhang 1, Jing Zhang 2, Sumei Liu 1, Jingling Ren 1 1 Department of Marine Chemistry, Ocean University of China 2 State Key Laboratory of Estuarine and Coastal Research, East China Normal University 1

2 Introduction CH 4 is an important atmospheric trace gas, which plays significant roles in the global warming and atmospheric chemistry (IPCC, 2001). CH 4 is a gaseous constituent of C cycle in marine environment Global oceans are net natural source of atmospheric CH 4 Oceanic emissions of CH 4 is Tg Yr -1,which is about 2-4% of atmospheric CH 4 (Bange et al., 1994) Estuaries have been estimated to contribute to 7.4% of the total oceanic CH 4 emissions (Bange et al., 1994). The oceanic source for CH 4 may be further enhanced by the increase in emission rates induced by eutrophication and other human-induced changes in highly perturbed coastal regions 2

3 Study Area Latitude (N) DA2 DA3 DA4 DA1 DB5 DB6 DB7 DB8 DC9DC10 DC11 DC12 DC10A DD13 DD14 DD15 DD16 DE17 DE18 DE19 DE20 DF21 DF22 DF23 DF24 DG25 DG26 DG DG (a) Longitude (E) Latitude (N) (b) Longitude (E) Latitude (N) Changjiang XLJ Longitude(E) (c) (a) April ( ) and November (ο) of 2002 (b) August of 2005 (circled area indicating the turbidity maximum) (c) June, Aug., Oct. of 2006 ( ) and Xuliujing (XLJ, solid triangle) 3

4 CH 4 in the Changjiang estuary and its adjacent marine water Table 1. Observed CH 4 concentrations in the surface and bottom waters of the Changjiang Estuary and its adjacent area (Numbers in the parentheses are the saturations of methane in %) Date Apr. 25-May 3, 2002 Nov. 4-11, 2002 Surface CH 4 (nm) Bottom CH 4 (nm) Range Average Range Average ± ±6.26 ( ) (6±205) ± ±2.55 ( ) (244±1) Aug.21-, ± ±15.6 June 2-11, 2006 n ( ) (810±667) ± ±9.67 (149-15) (423±368) Oct.3-13, ± ±8.89 ( ) (454±478) 4

5 Study Area Date Sur. CH 4 (nm) CH 4 in various estuaries in the literatures Sur. R (%) S Flux (μmol m -2 d -1 ) References Tomales Bay Sansone et al., 1998 Columbia R. estuary Aug Parker River estuary 1996/ Oregon estuaries De Angelis and Lilley, Alsea estuary (181.3) c 1987 Yaquina estuary Salmon estuary Hudson River estuaty 350 De Angelis and Scranton, 1993 Tyne Estuary Jan (164) ,000 (5843) Upstill-Goddard et al., 2000 Elbe R. estuary May Rehder et al., 1998 Rhone R. plume June Marty et al., 2001 European estuaries (1) c Middleburg et al., 2002 Elbe Apr (580) Rhine Oct.96-Nov (8400) 0-.8 Scheldt Jun. 96-Oct (10) Gironde Oct. 96-Feb (580) Sansone et al., 1999 Danube Estuaries July-Aug, 95 (1±42) (50) (260) a ; (470) b Amouroux et al., 2002 Pulicat Lake Dec (242) (54) a ; (0) b Shalini et al., 2006 Changjiang estuary (10.1) (451) This study a. K w was estimated by the LM86 equation; b. K w was estimated by the W92 equation; c. Averaged value for all of the studied estuaries; Numbers in the parentheses are the average value 5

6 Horizontal distributions of CH 4 in the Changjiang Estuary Surface CH4 (May 2002) Surface CH4 (Nov. 2002) Surface CH4 (Aug. 2005) Surface Surface CH4 (June 2006) Surface CH4 (Oct. 2006) 6

7 Bottom CH4 (May 2002) Bottom CH4 (Nov. 2002) Bottom CH4 (Aug. 2005) Bottom Bottom CH4 (June 2006) Bottom CH4 (Oct. 2006) 7

8 CH 4 and Turbidity 35 Bottom/May 2002 Bottom/Aug CH4 (nm) y = x R 2 = TSM (mg/l) CH4 (nm) y = x R 2 = TSM(mg/L) 8

9 CH 4 vs. salinity in surface waters of the Changjiang Estuary CH 4 (nm) Apr Nov Aug June 2006 Oct Salinity 9

10 CH 4 in the Changjiang (April/May 2003) 0 Main Stream Southern Trib. Northern Trib. 0 CH 4 (nm) 200 CH 4 (nm) HJ JL TJ MJ YJ GJ XJ NL WJ CS JS YB JJ WZ JZ HH HS AQWH YZ NT Stations Distance from the river mouth (km) CH 4 : nm 106±76.7 nm 10

11 Compilation of dissolved methane in various rivers (Numbers in the parentheses are the average value) Rivers Description CH 4 (nm) CH 4 (%) References Oregon rivers McKenzie Willamette Alsea Yaguina Siletz , , ,0 9,500-59,800 17,500-38,500 De Angelis and Lilley, 1987 Mississippi ,600-15,200 Swinnerton & Lamontagne, 1974 Hudson In summer In spring ,400-42,400 2,700-8,100 De Angelis and Scranton, 1993 Walker creek ,000-40,000 Sansone et al., 1998 Amazon Open water 460-3,700 16,100-1,500 Devol et al., 1990 Main stem (180±) (6,0±1,050) Bartlett et al., 1990 Orinoco Main stem, Sep.-March (170) Smith et al., 2000 Ouse Dec (119±47) (3,861±667) Upstill-Goddard, 2000 Tyne Dec ,1 Upstill-Goddard, 2000 Scheldt Jun Oct (2±138) Middelburg et al., 2002 Elbe ,750-3,500 Wernecke et al., 1994 April Middelburg et al., 2002 Douro Sep Middelburg et al., 2002 Rhine Oct Apri Gironde Oct Feb Thames April Yangtze River Oct Sep Apr/May 2003, main stem (71.6±36.3) 106±76.7 This study 11

12 Riverine input of CH 4 via Changjiang (Oct. 04-Sep. 05) Methane Flow rate Flow rate (m 3 /s) CH4 (nm) y = 2.02x R 2 = Flow rate ( 10 3 m 3 /s) 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Month Latitude (N) Changjiang XLJ Longitude(E) (c) CH 4 in Xuliujing (XLJ) ranged between 16.2 to nm with an average of 71.6±36.3 nm CH 4 input via Changjiang is estimated to be mol/yr 12

13 Sediment release of CH 4 from Changjiang Estuary Station Date Description CH 4 emission rate μmol.m -2.d -1 DB6 Apr Silt, depth 23m 2.42 DC10 Apr Clay, depth 10m 1.91 Sediment release of CH 4 from the Changjiang Estuary was estimated to be mol yr -1, which is equal to about 40% of the riverine input of CH 4 CH 4 production in the sediments may be much higher in summer than in spring Li et al., 1999 More measurements on the CH 4 emission rates at different seasons in the Changjiang Estuary will be conducted to assess the source strength of sediment release accurately 13

14 Air-sea fluxes of CH 4 from the Changjiang Estuary Estuary (LM86) Estuary (W92) Marine (LM86) Marine (W92) 100 Estuary: LM86: 35.7±23.9 W92: 69.8±46.8 CH 4 flux (umol m -2 d -1 ) Marine area: LM86: 9.1±4.6 W92: 17.8± May-02 Jun-06 Aug. 05 Oct. 06 Nov. 02 May-02 Jun-06 Aug. 05 Oct. 06 Nov. 02 Estuary Marinearea Sea to air CH 4 fluxes from the Changjiang Estuary is obviously higher than those from the adjacent marine area. Annual CH 4 emission from the studied region was yr -1 by LM86 and W92 equation. and mol 14

15 Conclusions Riverine input and sediment release are important sources of CH 4 in the Changjiang estuary and its adjacent area The Changjiang estuary and its adjacent area acts as a significant source of atmospheric CH Latitude (N) Changjiang Riverine input XLJ Sea to air flux Longitude(E) Sediment release Unit: 10 6 mol/yr 15

16 Thank you! 16

17 Computation of sea-to-air fluxes Saturation:R (%) = C obs /C eq Sea-to-air flux:f=k (C obs -C eq ) Where C obs is the observed concentration of dissolved gases; C eq is the airequilibrated seawater gases concentration; k is gas transfer velocity References Liss and Merlivat ( 1986, LM86) relationships to estimating k U 10 (m/s) k=0.17u 10 (Sc/600) -2/3 k=(2.85 U )(Sc/600) -1/2 k=(5.9 U ) (Sc/600) -1/2 0< U < U < U 10 Wanninkhof (1992, W92) Raymond and Cole (2001, RC01) k=0. U 102 (Sc/660) -1/2 k=0.39 U 102 (Sc/660) -1/2 k=1.91exp(0.35u 10 ) In situ wind speed Long term wind speed Sc= T T T 3 CH 4 (Wanninkhof, W92) 17

18 Source: Abril et al.,