Thoughts on modelling diffuse nitrate pollution, and assessing cost effectiveness of measures.

1. Diffuse Pollution:
Groundwater Pathways
Steve Buss

2. Summary
• Groundwater in catchment management
• Groundwater in a rural catchment
– Predicting future concentrations
– Mitigation & cost effectiveness
• Groundwater in an urban catchment

3. Why groundwater (water supply)?
Public water Groundwater supply issues (by volume)
supply, England OK
Other - closure
Other - blending & treatment
Pesticides - closure
Surface Ground- Pesticides - treatment
water water Pesticides - blending
Nitrate - closure
Nitrate - treatment
Nitrate - blending
1995-2000
1975-80
1980-85
1985-90
1990-95
2000-05
2005-10

4. Why groundwater (regulation)?
Rivers
Lakes
Estuaries
Coastal waters
0% 20% 40% 60% 80% 100%
Percentage of surface water bodies
at risk of not achieving WFD
objectives: diffuse pollution
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

5. Groundwater catchments
!
<
%age of source yield contributed by the model cell
Colour scale = 1 – 0.05 %
Time &
Water Nitrogen N(t) Prediction
!
< !
<
Attenuation
Colour scale =1 – 0.05 % Colour scale = 10-80 mg/l

6. Groundwater catchments
!
<
mg/l of NO3 in water leaving the soil zone
Colour scale = 10 – 80 mg/l
Time &
Water Nitrogen N(t) Prediction
!
< !
<
Attenuation
Colour scale =1 – 0.05 % Colour scale = 10-80 mg/l

7. Groundwater catchments
Delay
Dilution
!
<
Time &
Water Nitrogen N(t) Prediction
!
< !
<
Attenuation
Colour scale =1 – 0.05 % Colour scale = 10-80 mg/l

8. Groundwater catchments
Delay
Dilution
!
<
Time &
Water Nitrogen N(t) Prediction
!
< !
<
Attenuation
Colour scale =1 – 0.05 % Colour scale = 10-80 mg/l

9. Opportunities for mitigation
Nottinghamshire sources:
% contribution to groundwater N loading
Yellow =
fertiliser applications
to arable land
White = areas relevant for
change in arable land use

10. Cost effectiveness
COUNTERFACTUAL 64 mg/l COUNTERFACTUAL 64 mg/l
concentration vs. Summary
concentration vs. Summary
statistics
statistics
TARGET 50 mg/l TARGET 50 mg/l
Reduction required 21.9 % Reduction required 21.9 %
75 75
50 50
25 25
target
target
0 0
Peak
Peak
Min ML Max Min ML Max
£20,000,000 £20,000,000
Engineering vs.
Engineering vs.
management
management
catchment
catchment
£0 £0
costs
costs
Min ML Max Min ML Max
MEASURES:
Light touch scenario Land use change scenario
1. Cover crops before spring cereals …plus…
2. Reduce dietary intake of N and P 7. Convert 50% of arable land to low input
3. Early harvesting and establishment of crops in autumn extensive grazing
4. Use a fertiliser recommendation system
5. Integrate fertiliser and manure nutrient supply
6. Avoid spreading manufactured fertiliser at high risk times

11. Timing
Unsaturated
zone thickness
(5 to 65 m)
!
<
Groundwater
flow path length
(0 to 9500 m)
!
<
Travel time
(3 to 60 years)
!
<

12. Timing
10 years

13. Groundwater catchments (2)
2215
# #
10990
# 20117
Source apportionment
#
!
< Colour scale = 10 – Treated
0.05 %
Surface Urban sewage
Colour scale = 10 – 80 mg/l
water effluent
(other) Sewage treatment works,
with population served
103043
#
8777
# 3763
#
Groundwater
(agriculture)
32870
# 24677
#
#
25352
#

14. Urban groundwater
Ú
Û
Ú
Û
Ú
Û
Ú
Û

15. Urban groundwater
Ú
Û
Ú
Û
Ú
Û
Ú
Û

16. 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