Dynamique hydrolog ique, s édimentaire et g éochimique des zones d inondation en Amazonie: résultats et perspectives

Transcription

1 Dynamique hydrolog ique, s édimentaire et g éochimique des zones d inondation en Amazonie: résultats et perspectives 1

2 Floodplain surface area estimation for the whole Amazon basin: between 3, and 6, km² (±67,) (Martinez et al.,27) 6 km 2

3 Floodplain and River interactions Landsat Image, High waters (8/July/21) Role of floodplains: attenuation of floods zone of sediment deposition modification of water chemistry (sorption & redox processes) 3

4 Study area: The Curuaí floodplain Location: W / 2.18 S System size: 126 x 2 km Iquitos U % # U % # U % # Manaus Santarem - N W Km S River level fluct. River slope : 7m : 1.4 cm.km-1 Watershed Area E Altitude (m) OCEAN -2 : 366 km² 4

5 Riverbank Aquatic-Terrestrial Transition zone Local Watershed 5

6 Methodology 6

7 Várzea lake hydrological modeling :Available data Bathymétrie No Data Surface-water level relationship 3 N Kilometers W S 2 (km²) SRTM + MOSAIC JERS DEM => relationship between the inundated surface area and water level 2 Flooded area: 575/243km Aquatic Terrestrial Transition Zone: /1855 km2 E (m) S=(216 ± 9.2)(Z-Z )+(551±46)7 12.5

8 Várzea lake modeling: available data for water discharge $ AI3 AI2$ $ $ AI $$$ $ AI7 $ $ $ AI8 $$ ATS AC Width (m) 3 19 déc Width Depth Max. depth(m) Discharge m.s Water level (m) Water level (m)

9 Várzea lake modeling: available data for rainfall -1 mm.day Annual rainfall (mm) Humid year 3 Curuai 25 Orixima 2 Juruti 15 Obidos around the varzea lake Rainfall recorded at 4 rain gauge stations Time Dry year Water year 9 76-year average of rainfall

10 Várzea lake modeling: available data for evaporation 5 Riou, 75 (Empirical transfert de masse formula) 4.5 Mass transfer (Dalton law) mm.j mars févr janv déc Good agreement between the 2 formulas Seasonal variations of evaporation are weak. Evaporation accounts for 5 to 73 % of rainfall. nov oct sept août juil juin mai avr mars

11 Várzea lake modeling: Analyses procedure Channel Local runoff Bank overflow Rainfall/evaporation AI2 Bank seepage Heva Model Rainfall t+ 1 L V Evaporation = V + QR QE + QWN + QWS ± QG ± t L Runoff from the aquatic-terrestrial transition 19 déc. 27zone QwN = Max( ( P E )( S BVN S L ),) Upland local discharge i Qci t Groundwater flow from bank-seepage dh dx K=-2m.s-1 QG = KL * dz Amazon- varzea channels discharge 11

12 Várzea lake modeling: Analyses procedure At each step of time Δt (daily time step) the hydrological mass balance is expressed as: t+ 1 L V = V + QR QE + QWN AI3 + QWS ± QG ± AI2 t L i Qci t B = Qci + QR + QwN + QwS ± QG QE i Evaporation Amazon- varzea channels discharge Rainfall Runoff from the aquatic-terrestrial transition zone Groundwater flow from bank-seepage dh dx K=-2m.s-1 QG = KL * dz QwN = Max( ( P E )( S BVN S L ),) Upland local discharge 12

13 Model calibration and validation Computed and measured water levels at Curuai station 12 measured computed.3.1 cm 8 Water level (m) Differences between observed and computed values calibratio n validation Sep-3 Mar-3 Sep-2 Mar-2 Sep-1 Mar-1 Sep- Mar- Sep-99 Mar-99 Sep-98 Mar-98 Sep-3 Mar-3 Sep-2 Mar-2 Sep-1 Mar-1 Sep- Mar- Sep-99 Mar-99 Sep-98 Mar-98 Sep-97 Sep-97 validation Time mean absolute differences and standard deviations:

14 wn G Month Month P wn VL 4 3) QG 6 I 5 QE 8 in 4 QwS 3) Cumulative fluxes (km QwN 7.5 in Volume (km I-O V/Σ Volume (km 2 Σ 3 3) QP b a Fraction of each source term Cumulative volume and fraction of the water flux components Month year (regular year) 11-6 Groundwater related flux 14

15 P wn 6 2 wn G Net contribution from the floodplain to the river: 6.7 km3 9 8 Month Month = 95% = 4% = 1% VL in I 2-2 Σ 3) Sink terms: Amazone River Evaporation 2.5 Seepage.5 b = 78% V=/Σ9% in = 5% = 5% =3% 1 3) 3) Cumulative fluxes (km Volume (km I-O 1-2 Volume (km a Source terms: Amazone River Q DirectP rainfall 7.5 Local QwS water basin QwN Runoff on ATTZ QE Seepage QG Fraction of each source term Cumulative volume fluxes of the water Monthflux year (regular year)

16 Cumulative volume related to source and sink terms for the 6 water years study 3 year Inflow Average SD % Source terms (km ) Rainfall Runoff wn Runoff ws Seepage Sink terms (km3) Outflow Evaporation Seepage Water mass balance (km3) Ra Rw m SD % m SD % m SD % m SD % m SD % m SD % m SD % m SD % m SD % m SD %

17 Inter-annual variation: temporal mixture in the lake Day Groundwater G& bank seepage Day in Day /Σ Mixture Vfrom year-1.3 Day I ws Local Basin discharge.4 Days wn Runoff ATTZ P Rainfall I Inflow Amazon 1. Day

18 Inter-annual variation: temporal mixture in the lake G 6 Day in 1. Day Day V/Σ Day I ws Days Input from the groundwater system represents between 7 and.3 times (1 and 5%) the maximum volume of stored water in the floodplain system. 3 Local Basin The discharge Curuai floodplain contributes to 9.3 km Mixture from year for 6.3 Groundwater & bank seepage to the Amazon flow Mean water residence time is about 3 ± months wn ATTZ Runoff P Rainfall.4 1. I Inflow Amazon 1. Day Bonnet et al., in press 18

19 Suspended solids mass balance 4 12 Flux liquide net (Mm3) Flux solide net (^3 t) Flux entrant 3 Cote Amazone 2 8 Flux sortant Nov-3 Sep-3 Jul-3 May-3 Mar-3 Jan-3 Nov-2 Oct-2 Aug-2 Jun-2 Apr-2 Feb-2 Dec-1 Oct-1 Aug-1 Jun-1 Apr-1 Feb-1-6 Dec- (cm) Une forte remise en suspension en période de basse eaux Un stockage de sédiment entre 14 et 5% des flux entrant Un taux d accrétion de 1 à 2 mm par an -4 Bourgoin et al.,

20 Bilan de certains éléments chimiques K T/an Ca T/an Sr T/an Mn T/an Fe T/an Ba T/an Cu T/an U T/an Q 3 m /s Flux moyen entrant dans la varzéa Flux moyen sortant de la varzéa Bilan de transfert Temps de résidence dans la varzéa pour le cycle (jours) Barroux, 26 A l échelle annuelle, seuls le Mn et le Fe semblent non conservatifs 2

21 Variations saisonnières de Ca2+ 2 Recharge par la nappe ou dégradation de la 15 végétation RCa 5 Uptake par la végétation Sale -5 Em Ec R= cl Comparaison du comportement du chlore (conservatif) avec celui du Ca2+ 21

22 Primary production in floodplains and impact on CO2 emission Lago de Curuai Lago de Janauaca about 16 km² Solimoes floodplain Clear and black waters Objectives : To quantify primary production and it s controlling factors in floodplains To track primary production fate and evaluate it s impact on CO2 emissions Method: Study of two contrasted sites to help extrapolation : Method based on in situ survey, water color and modelling program EC2CO 27 22

23 Thanks for your attention! 23