Post on 21-Dec-2015
Toby Ahrens
26 Oct 2004
Linking Spatial Variability of Soil N Retention Mechanisms to
Landscape-level Fates in Yaqui Valley, Mexico
Goals
Quantify degrees of N contamination under different management regimes
Investigate the value of spatial data sets varying in resolution
Integrate 10+ yrs of biogeochemistry research in the Valley
What do I need to do to get there?
Link process and transport models
Improve process models Include abiotic retention mechanisms
Develop spatial data sets Eg. soil type, texture, mineralogy,
management, leaching potential
Coastal eutrophication
Declassified Keyhole satellite image
March 8, 1978
(Thanks Mike!)
Nitrate-contaminated groundwater
<10 ppm10-40 ppm116 ppm
Hungate, unpublished data, 1997-98
Two Q’s guiding my efforts:
1. What soil characteristics control N availability, retention and loss in OM-deficient ag soils?
2. Can the spatial variability of these characteristics be linked to aqueous N fates throughout the Valley?
Model schematic…
soil properties
NLOSS
soil mineralogy
crop yield (+N use)
Solute transport
un/saturated boundary conditions
management unit
crop type
Output maps:• Leaching vulnerability• Aquifer contamination• Coastal N sources
groundwater depth
Lee Addams’s modelIrrigation Drains Irrigation Losses Main Canal Infiltration
250m-1km
“AQUIFER HORIZON”
“CONNECTOR HORIZON”
“SHALLOW HORIZON”
WellScreens
Irrigation Drains Irrigation Losses Main Canal Infiltration
250m-1km
“AQUIFER HORIZON”
“CONNECTOR HORIZON”
“SHALLOW HORIZON”
WellScreens
Major modeling efforts:
Soil submodel including sorption isotherms and mineral fixation
Solute transport component to saturated hydrology model
Saturated/unsaturated boundary layer conditions
Spatial data referencing
Applied N:250 kg/ha
Plant uptake:31%
Leached:2-5%
(14-26%)
Gaseous losses:
NO+N2O: 2-5%NH3: __%N2: __%
?
?
?
?
Drainage canals:NO3
- + NH4+: 2-5%
NO+N2O: <0.1%
References:
Riley et al. 2001Harrison 2003Matson et al. 1998Ortiz-Monasterio, pers. comm.
Applied N:250 kg/ha
Plant uptake:31%
Leached:2-5%
(14-26%)
Gaseous losses:
NO+N2O: 2-5%NH3: __%N2: __%
?
?
?
?
Drainage canals:NO3
- + NH4+: 2-5%
NO+N2O: <0.1%
Field experiments:
• abiotic fixation
• link leaching potential to actual fates
Future directions and broader implications…
Does better spatial resolution increase our ability to predict SW/GW vulnerability? And the degree of how mechanistic submodels
are?
Identify thresholds for N retention Or pesticides…
Investigate management scenarios Different irrigation or fertilization regimes
Resolution of input data:Field based…
Legend
ARCILLA
5.820000 - 27.820000
27.820001 - 38.940000
38.940001 - 49.300000
49.300001 - 59.460000
59.460001 - 87.300000
Legend
ARCILLA
5.820000 - 27.820000
27.820001 - 38.940000
38.940001 - 49.300000
49.300001 - 59.460000
59.460001 - 87.300000
Policy implications
The Danish and Dutch experiences: N control policies aimed at reducing N
leaching (SW + GW) and NH3 and N2O emissions
Importance of model validation