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1 Changing carbon of the Mekong River Siyue Li 1,2*, Richard T. Bush 1 1. Southern Cross GeoScience, Southern Cross University, New South Wales, 248, Australia 2. Key Laboratory of Reservoir Aquatic Environment, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 4714, China Supplementary materials Figs. S1-S9 Tables. S1-S5 References. 1

2 Fig. S1. Lower Mekong River showing main-channel stations (Chiang Saen represents the Upper Mekong catchment, while Pakse, the most downstream station with available water discharge, thus represents the whole basin) (This map is created using Photoshop CC 214). 2

3 TSS =.1825Q , R² = F TSS = 3.33E-5Q 2.182, R² = Ca = Q -.128, R² = F Ca =.233Q , R² =.96 1 Mg = Q -.219, R² = F Mg =.44Q , R² = Concentration (mg/l) Na = Q -.366, R² =.59 K = Q -.4, R² =.29 HCO 3 = Q -.148, R² =.6 SO 4 = Q -.37, R² =.23 Flux (kg/s) F Na =.48Q , R² =.83 F K =.17Q +.735, R² =.93 F HCO =.858Q , R² =.98 3 F SO =.121Q , R² = Cl = 237.4Q -.452, R² =.42 6 F Cl =.36Q , R² = (a) Si= Q -.11, R² = Q (m 3 /s) 4 2 F Si =.43Q , R² = (b) Q (m 3 /s) Fig. S2. Scatter plot s between instantaneous water discharge and concentrations (a) and fluxes (b) in the station Chiang Saen of Mekong River. 3

4 TSS =.1Q , R² = F TSS = 1E-7Q , R² =.84 3 Ca = Q -.143, R² = F Ca =.18Q , R² = Mg = -.783ln(Q) R² = F Mg =.32Q , R² = Concentration (mg/l) Na = Q -.39, R² =.36 K = -.79ln(Q) , R² =.1 Flux (kg/s) F Na =.39Q , R² =.76 F K =.15Q , R² = HCO 3 = Q -.137, R² = F HCO 3 =.664Q , R² = SO 4 = 152.4Q -.267, R² = F SO4 =.152Q.7329, R² = Cl = Q -.464, R² = F Cl =.37Q , R² = Si= Q -.16, R² =.1 F Si =.5Q , R² =.88 (a) Q (m 3 /s) (b) Q (m 3 /s) Fig. S3. Scatter plot s between instantaneous water discharge and concentrations (a) and fluxes (b) in the station Pakse of Mekong River. 4

5 Modelled TSS (kg/s) y =.866x R² =.79, p<.1 Modelled Ca (kg/s) y =.966x R² =.96, p<.1 Modelled Mg (kg/s) y =.834x R² =.82, p<.1 Modelled Na (kg/s) Modelled Cl (kg/s) Observed TSS (kg/s) y =.8331x R² =.83, p< Observed Na (kg/s) y =.4795x R² =.48, p< Observed Cl (kg/s) Modelled K (kg/s) Modelled SO 4 (kg/s) Observed Ca (kg/s) y =.9189x R² =.93, p< Observed K (kg/s) y =.712x R² =.7, p<.1 Modelled HCO 3 (kg/s) Observed SO 4 (kg/s) Modelled Si (kg/s) Observed Mg (kg/s) y =.9831x R² =.98, p< Observed HCO 3 (kg/s) y =.9367x R² =.95, p< Observed Si (kg/s) Fig. S4. Validation of modelling approach (comparison of instantaneous observed fluxes and modelled values, data are from station Chiang Saen). 5

6 .4 Mean: 27.6% (2.1%-37.7%).3 Discharge rate Mean: 42.5% (17.1%-18.8%).8 TSS rate Mean: 36.4% (28%-47.4%).4 TDS rate Year Fig. S5. The contributions of water discharge, TSS and TDS from upper catchment to the Mekong River (reflected by the ratio of the fluxes from Chiang Saen to Pakse). 6

7 45 4 y = 2.381x , R 2 = y = 7.815x.683, R 2 =.293 Q Pakse 35 3 TDS Pakse (a) TSS Pakse (b) Q Chiang Saen TSS Chiang Saen TDS Chiang Saen y = x.52, R 2 = y = x.385, R 2 = Pakse TDS (c) Chiang Saen 1 y = x.283, R 2 = (d) TSS Fig. S6. The relationships between water discharge (a), TSS (b) and TDS (c) loads, as well as between TDS and TSS (d) at the both stations (Chiang Saen and Pakse) (unit in km 3 /y for water discharge, Mt/y for TSS and TDS loads). 7

8 Fig. S7. Ternary plot showing relative abundance of cations (a and b) and anions (c and d) (unit in mg/l). 8

9 1 Silicate 1 Na/Ca.1.1 Dolomite Calcite (a) Chiang Saen 1 Mg/Ca Silicate 1 Na/Ca.1.1 Dolomite Calcite (b) Pakse Mg/Ca Fig. S8. Scatter plots between Na/Ca and Mg/Ca (molar ratio) in the stations (a-chiang Saen, b-pakse) of the LMR (End-members of rocks are from Gailardet et al., 1999 and Li et al., 214). 9

14 12 y =.572x + 5.7534 R² =.42, p<.1 Flow (km3/y) 1 8 6 (a) (c) 4 1 12 14 16 18 Precipitation (mm/year) 25 2 15 P/R 1 5 (b) (d) 196 197 198 199 2 21 Year Fig. S9.

10 14 12 y =.572x R² =.42, p<.1 Flow (km3/y) (a) (c) Precipitation (mm/year) P/R 1 5 (b) (d) Year Fig. S9. Temperature (a) and rainfall (b) in five stations (Lincang, Simao, Lancang, Jinghong and Mengla) of upper Mekong River over Mean temperature variations as year: T =.284Year , R²=.72, p<.1. (c) Relationships between river discharge at Chiang Saen and annual mean precipitation in the upper basin, (d) Changes in the ratio of precipitation (P) to runoff (R) (P/R; unit in mm for precipitation, while km 3 /year for runoff) in the upper basin (red line means smoothing analysis that averages the values at neighboring points). 1

11 Table S1. Main channel stations of the LMR included in this study Stations Country Location Distance from the River mouth Drainage area Pre-regulated period Regulated period Total latitude longitude km 1 3 km Chiang Thailand Saen a Water discharge (km 3 /y) TSS (Mt/y) TDS (Mt/y) Pakse b Lao PDR Water discharge (km 3 /y) TSS (Mt/y) TDS (Mt/y) a data are from the time period of , b data are from the time period of

12 Table S2. Comparison of annual mean concentrations in the LMR (unit in mg/l). TSS Ca Mg Na K HCO 3 Cl SO 4 Si TDS Chiang Saen Observed mean Mean Max Min S.D Observed Q-weight mean Mean Max Min S.D Q-weight mean (predicted) Mean Max Min S.D Pakse Observed Mean Mean Max Min S.D Observed Q-weight mean Mean Max Min S.D Q-weight mean (predicted) Mean Max Min S.D Observed mean is measured variables, Observed Q-weight mean is measured variables with water discharge weight, while Q-weight mean (predicted) is concentration derived from models. 12

13 Table S3. Statistics of dissolved and particulate material fluxes in the LMR. Discharge Flux (Mt/y) Chiang Saen km 3 /y TSS 1 Ca 1 Ca 2 Mg 1 Mg 2 Na 1 Na 2 K 2 HCO 31 HCO 32 Cl 1 Cl 2 SO 41 SO 42 Si 1 Si 2 TDS 2 Mean Max Min S.D Pakse Mean Max Min S.D represents model1 2 represents model 2 13

14 Table S4. Comparison of global watershed physical characteristics, concentrations, fluxes and yields of DIC and major solutes. (a) Lithology (data are from Amiotte Suchet et al., 23) Area Discharge Runoff Sands and sandstone Shales Carbonate Shield Acid Volcanic Basalts 1 3 km 2 km 3 /y mm % % % % % % 1(a) Amazon (upper) (b) Amazon (lower) Amur Brahmaputra Chao Phraya Colorado Columbia Danube Don Fraser Ganges (a) Ganges-Brahmaputra (b) Ganges-Brahmaputra Godavari Yenisei Indigirka Indus Irrawaddy Kolyma Lena Limpopo Mackenzie Magdalena (a) Mekong (Chiang Saen)

15 22(b) Mekong (Pakse) (c) Mekong Mississippi Murray Darling Niger Nile Ob Orange Orinoco Parana Red Salween Sao Francisco Senegal Severnaia Dvina Xijiang St. Lawrence Tigris-Euphrates Yana Yangtze Yellow Yukon Zaire Zambesi World total

16 (b) Land cover composition (data are mainly from Ludwig et al., 1996 and FTSS Elev. Slope SoilH APPT AT Veg C SoilC NPP PopD FDOC FPOC POC% DOC POC Land cover (%) t/km2/yr m radian cm mm C kg/m2 kg/m3 kg/m2 h/km2 t/km2/yr t/km2/yr % tss Forest Grass, Savanna And Shrub Vegetation Wetland Cropland Irrigated Cropland Urban 1(a) 1(b) (a) 11(b) mg/l mg/l

17 22(a) 22(b) 22(c)

18 (c) Concentrations (data without reference are from Gaillardet et al., 1999) ph TDS TSS Na K Ca Mg Cl SO 4 HCO 3 SiO 2 T z + mg/l mg/l μmol/l μmol/l μmol/l μmol/l μmol/l μmol/l μmol/l μmol/l Source 1(a) Stallard and Edmond, (b) Stallard and Edmond, Galy and France-Lanord, Galy and France-Lanord, (a) Sarin et al., (b) Galy and France-Lanord, SCOPE 42 - Biogeochemistry of Major World Rivers Karim and Veizer, SCOPE 42 - Biogeochemistry of Major World Rivers Huh et al., 1998a

19 (a) This study 22(b) This study 22(c) Nemeth et al., Moon et al., Zhang et al., Varol et al., SCOPE 42 - Biogeochemistry of Major World Rivers Chen et al., Chen et al., Meybeck, WSM Meybeck, 24 WDWA Meybeck, 24 19

20 WSM-World spatial median; WDWA-World discharge-weighted average. (d) Fluxes TDS TSS Na K Ca Mg Cl SO 4 HCO 3 SiO 2 Source Mt/y Mt/y 1 9 mol/y 1(a) Stallard and Edmond, (b) Stallard and Edmond, Galy and France-Lanord, Galy and France-Lanord, (a) Sarin et al., (b) Galy and France-Lanord, SCOPE 42 - Biogeochemistry of Major World Rivers Karim and Veizer, SCOPE 42 - Biogeochemistry of Major World Rivers Huh et al.,

21 (a) This study 22(b) This study 22(c) Nemeth et al., Moon et al., Zhang et al., Varol et al., SCOPE 42 - Biogeochemistry of Major World Rivers Chen et al., Chen et al., Meybeck, Sum World total Glay and France-Lanord,

22 Fluxes are calculated by multiplying concentrations by annual discharge. 22

23 (e) Specific flux TDS TSS Na K Ca Mg Cl SO 4 HCO 3 SiO 2 t/km 2 /y t/km 2 /y 1 3 mol/km 2 /y 1(a) Amazon (upper) 1(b) Amazon (lower) Amur Brahmaputra Chao Phraya 68 5 Colorado Columbia Danube Don Fraser Ganges (a) Ganges-Brahmaputra (b) Ganges-Brahmaputra Godavari Yenisei Indigirka Indus Irrawaddy Kolyma Lena Limpopo Mackenzie Magdalena

24 22(a) Mekong (Chiang Saen) (b) Mekong (Pakse) (c) Mekong Mississippi Murray Darling Niger Nile Ob Orange Orinoco Parana Red Salween Sao Francisco Senegal Severnaia Dvina Xijiang St. Lawrence Tigris-Euphrates Yana Yangtze Yellow Yukon Zaire Zambesi World mean Specific flux (areal yield) is annual flux normalized to drainage area 24

25 Table S5. Statistically historical trends as year for concentrations and fluxes of TSS and major ions in the Mekong River. (a) Chiang Saen Y R 2 Adjusted R 2 p Chiang Saen Observed mean (Y 1985) TSS * Y <.1 Ca * Y Mg * Y Na * Y K * Y HCO * Y Cl * Y SO * Y Si * Y Discharge-weighted mean (Y 1985) TSS * Y Ca * Y Mg * Y Na * Y K * Y HCO * Y Cl * Y SO * Y Si * Y Historical discharge-weighted mean (Y 196) TSS * Y Ca * Y Mg * Y Na * Y K * Y HCO * Y Cl * Y SO * Y Si * Y Annual flux (Model 2; Y 196) TSS * Y Ca * Y Mg * Y Na * Y K * Y HCO * Y Cl * Y SO * Y Si * Y

26 (b) Pakse Pakse Observed mean (Y 1985) Y R 2 Adjusted R 2 TSS * Y <.1 Ca * Y Mg * Y Na * Y K * Y HCO * Y.6.71 Cl * Y SO * Y Si * Y Observed mean in the recent decade (21-211) Ca *Y Na *Y HCO *Y Cl *Y Discharge-weighted observed mean (Y 1985) TSS * Y Ca * Y Mg * Y Na * Y K * Y HCO * Y Cl * Y SO * Y Si * Y Historical discharge-weighted mean (Y 1923) (modelled) Annual flux (Model 2; Y 1923) TSS * Y Ca * Y Mg * Y Na * Y K * Y HCO * Y Cl * Y SO * Y Si * Y TSS * Y Ca * Y Mg * Y Na * Y K * Y HCO * Y Cl * Y SO * Y Si * Y p 26

27 References Amiotte Suchet P, Probst JL, Ludwig W. Worldwide distribution of continental rock lithology: Implications for the atmospheric/soil CO2 uptake by continental weathering and alkalinity river transport to the oceans. Glob Biogeochem Cycles 23;17: (read on 2 April 214) Huh Y, Tsoi MY, Zaitsev A, Edmond JM. The fluvial geochemistry of the rivers of Eastern Siberia: I. Tributaries of the Lena River draining the sedimentary platform of the Siberian Craton. Geochim Cosmochim Acta 1998a;62: Gaillardet J, DuprèB, Louvat P, Allègre CJ. Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers. Chem Geol 1999;159:3 3. Galy A, France-Lanord C. Weathering processes in the Ganges Brahmaputra basin and the riverine alkalinity budget. Chem Geol 1999;159:31 6. Karim A, Veizer J.Weathering processes in the Indus River Basin: implications from riverine carbon, sulfur, oxygen, and strontium isotopes. Chem Geol 2;17(1 4): Ludwig W, Probst JL, Kempe S. Predicting the oceanic input of organic carbon by continental erosion. Global Biogeochem. Cycl. 1996; 1: Meybeck M. Les fleuves et le cycle ge'ochimique des elements. Paris: Univ. Pierre et Marie Curie; 1984 [The'se de Doctorat d'etat]. Meybeck M. Global occurrence of major elements in rivers. In: Drever JI, editor. Treatise on geochemistry, vol. 5. New York: Elsevier; 24. p Moon S, Huh Y, Qin J, Pho NV. Chemical weathering in the Hong (Red) River basin: rates of silicate weathering and their controlling factors. Geochim Cosmochim Acta 27;71: Nemeth A, Paolini J, Herrera R. Carbon transport in the Orinoco River: the preliminary results. In: Degens ET, editor. Transport of carbon and minerals in major world rivers. Hamburg, Germany: Univ. of Hamburg; p Sarin MM, Krishnaswamy S, Dilli K, Somayajulu BLK, Moore WS. Major ion chemistry of Ganga Brahmaputra river system: weathering processes and fluxes of the Bay of Bengal. Geochim Cosmochim Acta 1989;53: Stallard RF, Edmond JM. Geochemistry of the Amazon 2. The influence of geology and weathering environment on the dissolved load. J Geophys Res 1983;88(C14): SCOPE 42 - Biogeochemistry of Major World Rivers ( read on 2 April 214) 27

28 Varol M, Gokot B, Bekleyen B, Sen B. Geochemistry of the Tigris River basin, Turkey: spatial and seasonal variations of major ion compositions and their controlling factors. Quat Int 213;34: Zhang SR, Lu XX, Higgitt DL, Chen CTA, Sun HG, Han JT. Water chemistry of the Zhujiang (Pearl River): natural processes and anthropogenic influences. J Geophys Res 27;112:F

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