Modelling of surface water and groundwater exchange and denitrification process in the floodplain shallow aquifer at the catchment scale

Transcription

1 Modelling of surface water and groundwater exchange and denitrification process in the floodplain shallow aquifer at the catchment scale Xiaoling Sun, Youen Grusson, Grégory Espitalier-Noël, Léonard Bernard-Jannin, Jeffrey G. Arnold, Sabine Sauvage, Raghavan Srinivasan, José Miguel Sánchez Pérez

2 Introduction Riparian wetlands River water Floodplain Biodiversity conservation Flood water retention Water quality control e.g. NO 3 removal from agricultural area Groundwater Denitrification Groundwater riparian wetlands surface water nutriment elements organic matters

3 Hydrological Models 1 km² 10 km² 1000 km² km² km² km² Physically based model Conceptual model Complex Require detail input data MODFLOW Long computation time Mcdonald and Harbaugh 1988 MOHID Braunschweig et al., 2004 HBV Seibert et al GR4J Simple Basic input data Empirical model Input ex: precipitation SW-GW exchange is not included Makhlouf 1994 Output ex: discharge GR1A Perrin et al

4 Objectives o Quantify SW-GW exchange in the floodplain o Quantify nitrate removal in a simplified way NO 3 + Carbon Denitrification o Apply at large catchment scale

5 SWAT-LU (Landscape Unit) model Watershed subbasin HRU River high Divide (LU 3 ) Landscape Unit Slope position Low Hillslope (LU 2 ) Floodplain (LU 1 ) Volk et al. 2007

6 SWAT-LUD (Landscape Unit Darcy) model Subbasin-LU F S S S LU 3 Darcy s equation (1856): WL L LU 2 LU 1 L I I G G L G I GWL Q = K A H L Impermeable layer Subbasin-LU LU 3 LU 2 LU 1 Channel LU 1 LU 2 LU 3 Based on flooded water volume Sun et al. Hydrological 6 processes. Accepted

7 Nitrogen and organic carbon in SWAT-LUD model Soil Organic Carbon Dissolved Organic Carbon Particulate Organic Carbon Organic pool input Organic C, N, P Plant uptake Leaching Flood leaching Denitrification DOC POC Shallow aquifer Shallow aquifer River LU 3 LU 3 LU 2 LU 1 LU 1 LU 2 Deep aquifer Impermeable layer 7

8 SWAT-LUD model-denitrification Nitrate consume rate: DOC consume rate: R NO3 = 0.8(ρ 1 φ φ. k POC POC. 106 M C +k DOC DOC ). R DOC = k DOC DOC NO3 k NO3 + NO3 Organic carbon. anaerobiose term POC consume rate: R POC = k POC POC bacteria CO 2 N 2 O POC particulate organic carbon DOC dissolved organic carbon NO 3 - N 2 Parameters Units Description φ - Sediment porosity ρ kg.dm -3 Dry sediment density k POC d -1 Mineralisation rate constant of POC k DOC d -1 Mineralisation rate constant of DOC k NO3 μm Half-saturation for nitrate limitation 8

9 Study sites Area: around km 2 Discharge: 600 m3 s-1 Alluvial soil: 6% Agriculture: 31% Area: around km 2 Daily discharge: 200 m3 s-1 Alluvial soil: 4% Agriculture: 72% 9

10 Results floodplain section SL3 SL2 SL1 Input: discharge of Portet Nitrate input: 5mg L -1 10

11 SL3 Results Floodplain Groundwater nitrate concentration SL2 SL1 Nitrate input: 5 mg L -1 LU 1 LU 2 LU 3 11

12 107m3 Results Floodplain Annually river-aquifer exchanged water quantity flooded river to aquifer aquifer to river recharged net Annually dentirification rate (kg N/ha/y) DOC denitrification POC denitrification

13 Results Denitrification observed Observed and simulated nitrate flux Simulated Observed R² = 0.56 RMSE = PBIAS = Ton d Simulated T River water Groundwater level 821 T 434 T Denitrification 6057 T 13

14 Results Garonne Catchment Observed(m3s-1) Observed(m3s-1) Annually SW-GW exchanged water volume in the Garonne catchment Flood R to G G to R Net 10 8 m Year m 3 s SW-GW exchanged water accounted for around 5% of the river discharge Simulated river water discharge of SWAT and SWAT-LUD model observations at the Tonneins Gauging station SWAT SWAT-LUD Observed 0 J-00 J-01 J-02 J-03 J-04 J-05 J-06 J-07 J-08 J-09 J R² = NS = Simulated (SWAT-LUD) (m3s-1) 5000 R² = NS = Simulated (SWAT) (m3s-1) 14

15 Conclusions Conclusion and perspectives SWAT-LUD could represent the SW-GW exchange and shallow aquifer denitrification appropriately at the floodplain scale The main water flow direction is from aquifer to river: 66% of the total exchanged water volume Consumed nitrate correspond to 50% of nitrate originated from the surrounding area Perspectives Simulation of dynamic variation of organic carbons Connection of upland and floodplain subbasin-lu Sensitivity analyses of the added parameters Application of the SWAT-LUD model at large catchments

16 Xiaoling SUN

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18 Definition of Landscape Unit Landscape Unit Flood return area LU1: one-year return flood area LU2: two to five years flood return area The area has the probability to be flooded in certain period (N years) LU3: ten or more years flood return area 18