diffuse pollution: groundwater pathways
DESCRIPTION
Thoughts on modelling diffuse nitrate pollution, and assessing cost effectiveness of measures.TRANSCRIPT
Diffuse Pollution:
Groundwater Pathways
Steve Buss
Summary
• Groundwater in catchment management• Groundwater in a rural catchment
– Predicting future concentrations– Mitigation & cost effectiveness
• Groundwater in an urban catchment
Why groundwater (water supply)?
Surface water
Ground-water
Public water supply, England OK
Other - closureOther - blending & treatmentPesticides - closurePesticides - treatmentPesticides - blendingNitrate - closureNitrate - treatmentNitrate - blending
Groundwater supply issues (by volume)
1975
-80
1980
-85
1985
-90
1990
-95
1995
-200
0
2000
-05
2005
-10
Why groundwater (regulation)?
Results of Water Framework Directive assessment of groundwater bodies at risk of failing to achieve good status in 2015 as a result of nitrate contamination across England and Wales
0% 20% 40% 60% 80% 100%
RiversLakes
EstuariesCoastal waters
Percentage of surface water bodies at risk of not achieving WFD
objectives: diffuse pollution
Groundwater catchments
!<!<
!<
Water!<
Nitrogen N(t) Time & Attenuation Prediction
Colour scale = 10-80 mg/lColour scale =1 – 0.05 %
%age of source yield contributed by the model cell Colour scale = 1 – 0.05 %
Groundwater catchments
!<!<!<
!<
Water!<
Nitrogen N(t) Time & Attenuation Prediction
Colour scale = 10-80 mg/lColour scale =1 – 0.05 %
mg/l of NO3 in water leaving the soil zoneColour scale = 10 – 80 mg/l
Groundwater catchments
!<!<!<
Dilution Delay
!<
Water!<
Nitrogen N(t) Time & Attenuation Prediction
Colour scale = 10-80 mg/lColour scale =1 – 0.05 %
Groundwater catchments
!<!<!<
Dilution Delay
!<
Water!<
Nitrogen N(t) Time & Attenuation Prediction
Colour scale = 10-80 mg/lColour scale =1 – 0.05 %
Opportunities for mitigation
Yellow = fertiliser applications to arable land
Nottinghamshire sources:% contribution to groundwater N loading
White = areas relevant forchange in arable land use
Cost effectivenessCOUNTERFACTUAL 64 mg/l
TARGET 50 mg/lReduction required 21.9 %Su
mmary
statistics
Peak
concentration vs.
target
Engineering vs.
catchm
ent
managem
ent
costs £0
£20,000,000
Min ML Max
0255075
Min ML Max
MEASURES:
Light touch scenario1. Cover crops before spring cereals 2. Reduce dietary intake of N and P3. Early harvesting and establishment of crops in autumn4. Use a fertiliser recommendation system 5. Integrate fertiliser and manure nutrient supply6. Avoid spreading manufactured fertiliser at high risk times
COUNTERFACTUAL 64 mg/lTARGET 50 mg/l
Reduction required 21.9 %Summary
statistics
Peak
concentration vs.
target
Engineering vs.
catchm
ent
managem
ent
costs £0
£20,000,000
Min ML Max
0255075
Min ML Max
Land use change scenario…plus…7. Convert 50% of arable land to low input extensive grazing
Timing
!<
Unsaturated zone thickness (5 to 65 m)
!<
Groundwater flow path length(0 to 9500 m)
!<
Travel time(3 to 60 years)
Timing
10 years
Groundwater catchments (2)
!< Colour scale = 10 – 0.05 %!<!<
Colour scale = 10 – 80 mg/l
Sewage treatment works, with population served
#
#
#
#
#
#
#
#
#
#
#!<
8777
2215
3763
32870
10990
24677
25352
20117
103043
Source apportionment
Treatedsewageeffluent
UrbanSurfacewater(other)
Groundwater (agriculture)
Urban groundwater
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Urban groundwater
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Conclusions• Groundwater is (mostly):
– Underground and slow-moving– Unconstrained by catchment boundaries– Vital for drinking water supply, for aquatic
ecosystems, for dilution of sewage effluent in the summer, for industry, for amenity…
• Challenging to predict and monitor effectiveness of measures but these can be constrained with simple tools