Higher-dimensional environmental modelling in soil Tom Schröder BASF SE

Transcription

1 Higher-dimensional environmental modelling in soil Tom Schröder BASF SE 15/10/2010 1

2 Processes in soil rainfall evaporation Soil surface runoff Vadose zone Flow of water (gravity dominating) Transport of solute in the water groundwater Water flow mainly dependent on soil properties and boundary conditions Solute transport mainly affected by solute properties (degradation, sorption) 15/10/2010 2

3 Processes in soil rainfall evaporation Soil surface runoff Vadose zone Flow of water (gravity dominating) Transport of solute in the water groundwater Idea: to model transport of a substance in soil after application to the soil, with the goal to estimate its concentration over space and time either in the liquid or solid phase 15/10/2010 3

4 Modelling status Current status: 1-D modelling applied to the most common used application type: spray application to a hectare of agricultural soil to determine e.g. the concentration in the liquid phase at a certain depth, representing the groundwater level (PECgw) 15/10/2010 4

5 Modelling status Current status: 1-D modelling applied to the most common used application type: spray application to a hectare of agricultural soil to determine e.g. the concentration in the liquid phase at a certain depth, representing the groundwater level (PECgw) Advantages: - geometry independent harmonisation of problems is easier - worst-case estimate no lateral flow accounted for Disadvantage: - 1-D can not be used for more realistic, geometry-based problems 15/10/2010 5

6 1-D modelling / geometry-based problems 1-D: Advantages: - geometry independent harmonisation of problems is easier - worst-case estimate no lateral flow accounted for Disadvantage: - 1-D can not be used for more realistic,geometry-based problems Geometry-based problems: require a higher dimensional modelling approach (2-D/3-D) harmonisation of geometry-based problems is not possible 15/10/2010 6

7 1-D, 2-D, 3-D modelling 1-D 2-D / 3-D geometry independent: geometry dependent: - vertical transport only - vertical and lateral transport - average estimates over lateral domain - location-based (x,y,z) estimates throughout the domain useful to derive worst-case estimates for large dimensions useful to derive more realistic estimates for small to medium dimensions y x top y x top y x z z z bottom bottom 15/10/2010 7

8 Application categories for modelling Geometry independent Spray applications to a hectare of agricultural land Seed treatment to a hectare of agricultural land use Geometry dependent Spray applications to geometry-based land use Seed treatment to a hectare of agricultural land use Scientific support 15/10/2010 8

9 Application categories Application category Spray application to a hectare of agricultural land Seed treatment (to a hectare of agricultural land) Spray application to geometry-based land use Geometry dependent No Yes Current modelling dimension X (0-D,) 1-D X X (0-D*,) 1-D* X - Desired modelling dimension Scientific backup (beyond actual modelling dimension, i.e. 1-D) X - * for geometry independent calculations 15/10/2010 9

10 Application categories Application category Spray application to a hectare of agricultural land Seed treatment (to a hectare of agricultural land) Spray application to geometry-based land use Geometry dependent No Yes Current modelling dimension Desired modelling dimension X (0-D,) 1-D (0-D,) 1-D X X (0-D*,) 1-D* (0-D,) 1-D, 2-D, 3-D X - 2-D, 3-D Scientific backup (beyond actual modelling dimension, i.e. 1-D) X - 2-D, 3-D * for geometry independent calculations 15/10/

11 Higher dimensional modelling Aim: To estimate concentrations in solid and liquid phase for geometrydependent applications over space and over time 15/10/

12 Higher dimensional modelling No standard model available for 2-D/3-D simulations of environmental fate 15/10/

13 Modeling tool: Hydrus 2D/3D Best available model to assess water flow and solute transport in variable saturated media in multiple dimensions: Hydrus 2D/3D (Simunek et al., 2006) Hydrus can be found at: Hydrus is available since 1998 and is validated in a large extent over the years 1 Used by many scientific communities and companies Easy to use Graphical User Interface (GUI) Capable of simulating all processes that are required for the assessment of environmental fate (water flow, solute transport, heat flow) 1 e.g. Boivin et al. Comparison of pesticide transport processes in three tile-drained field soils using HYDRUS-2D. Vadose Zone J. 5(3), , /10/

14 Hydrus 2D/3D Advantages: various processes can be investigated in depth: irrigation, precitipation, volatilization, drainage, macropore flow etc. continuous development of the model can be used for version control Disadvantages: model not yet compatible with current 1D registration models - plantgrowth not incorporated on the same level as existing 1D models - no water content correction for sorption/degradation parameters yet 15/10/

15 Worked out Examples: Categories (geometry-based) - Spray application - Seed treatment - Scientific backup 15/10/

16 Spray application to geometry-based land use (2-D) 15/10/

17 Spray application to geometry-based land use: boundary conditions Atmospheric boundary conditions (rainfall/evaporation) Constant pressure potential/ free drainage / deep drainage 15/10/

18 Initial conditions concentration [mg kg -1 ] z [cm] initial concentration in solid phase initial water potential/temperature (after a warm-up phase) x [cm] 15/10/

19 Results concentration [mg kg -1 ] z [cm] concentration in solid phase after long simulation period x [cm] 15/10/

20 Seed treatment [potato tuber] (to a hectare of agricultural land) Geometry Furrows Ridges soil surface Boundary conditions: - atmospheric / variable pressure head (top) - potential or gradient (bottom) Initial conditions (pre-phase): - pressure head (h = -z cm) - concentration (= 0 µg l -1 ) - temperature (20 C) groundwater FOCUS Hamburg scenario Initial conditions (actual simulation): - pressure head / temperature from pre-phase - geometry-based concentration 15/10/

21 Results Water content Temperature X (red = more water; blue = less water) Temperature - T[ C], Min=6.856, Max=8.861 (red = higher temp.; blue = less temp.) 15/10/

22 Another Seed treatment example: Lateral transport in soil from treated onion seeds Spatial extent of exceedence of the regulatory acceptable concentration (RAC) in soil and hence the opportunities for recolonisation from unaffected soil compartments Side View 100 cm 25 cm 4 cm F r o n t V i e w (c) Top View 15/10/

23 PPP transport in soil from treated seeds: boundary conditions 40 cm 100 cm 14 cm 4 cm 2 cm 5 cm 25 cm 25 cm 2 cm 5 cm 140 cm 140 cm No Flux Boundary Atmospheric Boundar Constant Head Bound (a) Side View (b) Front View 15/10/

24 Contours (dotted lines) showing the spatial extent of exceeding the RAC at different time steps for the side view (= within the rows) 15/10/

25 Contours (dotted lines) showing the spatial extent of exceeding the RAC at different time step for the front view (= between the rows) 15/10/

26 Scientific backup: Infiltration from surface water body into ground water How is an active substance, from a permanent water body, transported to groundwater? 3.2 m Interested in e.g.: 1 m 2D transport profile 1 m effect of various initial concentrations in the water carrier on the concentration over time (e.g. after mitigation measures) 4 m No Flux Atmospheric Variable Head Constant Head Sediment Layer 15/10/

27 Concentration plume at day = O(10) 0.8 m Water height in water body 1 m Concentration - c[ng/cm^3], Min=0.000, Max= /10/

28 Concentration plume at day = O(100) 0.8 m Water height in water body 1 m Concentration - c[ng/cm^3], Min=-0.003, Max= /10/

29 Concentration over time at 1 m depth Buffer C ini,1 0 Buffer C ini,2 5 Buffer C ini,3 10 Concentration [µg/l] /10/ Day

30 3D approach of a permanent water carrier 2D vs 3D Half - cylindrical spherical-like Lateral transport in missing direction will have a large effect on the concentration gradient and ist magnitude Step from 2D to 3D is relatively small: 1) 3D grid generator is available, Z 2) general parameters stay equal, Y X 15/10/

31 Summary Geometry-based applications / scientific problems can hardly be evaluated in one dimension and can often better be modelled in higher dimensions (2D/3D) A tool is available based on same physical and mathematical principles as 1D models already available Provides geometry-based (vertical and lateral) information for characterization of the hydrology/temperature and fate of substances over time Calculated concentrations in liquid and solid phase can be used for risk assessment (to derive e.g. PEC values) or, more generally, for trend analysis 15/10/

32 Discussion Regulatory perspective Acceptance of higher-dimensional models In depth knowledge of the physical processes is required, to understand the assumptions and input choices for each simulation as the scenarios are not standardized Hydrus is not freeware, but a completed simulation can be loaded into the program (demo version) and can be assessed in depth, including the results 15/10/

33 Discussion Scientific perspective Compatibility with current 1-D models 15/10/