Abbotsford-Sumas Aquifer
Long-Term Groundwater Monitoring and
Nitrogen Isotope Study Abbotsford-Sumas Aquifer
Groundwater Nitrate Science Forum II May 1, 2012
Abbotsford, BC
Gwyn Graham Environment Canada
Outline
• Background – Aquifer setting
• Environment Canada’s Groundwater Monitoring Network – Locations – Operations
• Long-Term Monitoring Results – Update – Trends – Climate factor considerations
• SAGES Groundwater Isotope Monitoring Program – Program – Results
The Abbotsford-Sumas Aquifer
• Largest unconfined aquifer unit in south-western British Columbia
• Transboundary aquifer (~50/50 Canada/USA)
• Highly permeable sand and gravel composition (Glacial outwash deposit)
• Important Source of Water Supply
• High intrinsic vulnerability to contamination from land use activities
• High Rainfall (Fall-Winter Rainy Season) – seasonal recharge.
• Long-term Environment Canada groundwater monitoring study in partnership with other agencies.
Groundwater Monitoring Network
Environment Canada
BC MoE/FLNRO
CWN Research
Municipal Supply Wells
Abbotsford-Sumas Aquifer Long-Term Nitrate Trend
ASA Nitrate Indicator GraphMonthly Average, Maximum & Minimum
(1995-Present)
0
10
20
30
40
50
60
70
80
90
100
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
[NO
3] (m
g-N
/L)
Min NitrateAvg Nitrate
Max Nitrate
GCDWQ
Uneven Spatial Distribution of Nitrate
(McArthur and Allen, 2005)
Nitrate Distribution in the Abbotsford-Sumas Aquifer, 2002-04
Data sources include EC and BCMoE monitoring wells and selected private wells
Trend Analysis on Different Time Periods
NO3-N Linear Trends: Varying Time Series
5
10
15
20
25
Jan-92
Jan-94
Jan-96
Jan-98
Jan-00
Jan-02
Jan-04
Jan-06
Jan-08
Jan-10
NO 3
-N (m
g/L)
Average
Linear (Average)
Flat Trend (18 yr period of record)
5 Year Series
5
10
15
20
25
Jan-04
Jan-06
Jan-08
Jan-10
3 Year Series
5
10
15
20
25
- Jan-06
Jan-08
Jan-10
Downward Trend? (5 yr period of record)
Upward Trend? (3 yr period of record)
What causes the variable (shorter-term) nitrate trends? - Climate variability? - variable nutrient management practices?
Precipitation: Driver for Nitrate leaching
Average Nitrate vs Precipitation (Abbotsford-Sumas Aquifer)
5
10
15
20
25
30
Sep-91 May-93 Jan-95 Aug-96 Apr-98 Dec-99 Jul-01 Mar-03 Nov-04 Jul-06 Feb-08 Oct-09
NO
3-N
(mg/
L)
0
50
100
150
200
250
300
350
400
450
500
Prec
ipita
tion
(mm
)
• Long-term aquifer monitoring (1992-present) shows apparent correlation between monthly nitrate and precipitation (average of all monitoring sites) as seen using polynomial fit curves.
• Longer period cycles appear to influence average nitrate concentrations in groundwater by ~30% of the Maximum Acceptable Concentration (MAC = 10 mg/L NO3-N)
Frequency Analysis (Nitrate)
Strong signal at 4-6 yr period (Possible ENSO effect)
Peak at 1 yr period (seasonal effect)
Deseasonalized Fourier Amplitude Spectrum
Frequency (wavenumber)
SAGES Groundwater Isotope Study
Objectives • Identify temporal patterns of δ15N in groundwater nitrate; • Evaluate trends in nitrate source isotope signatures
Approach • Approx. 18 gw monitoring sites identified in nitrate “hotspots”; • Focus on Groundwater ages <5 years;
– Monitoring wells screened close to water table (<5 m) • Monthly sampling of nitrate isotopic analysis concentrations.
• To date: Data from Aug. 2008 to Aug. 2011 (3 years) • Bi-monthly frequency (with some exceptions)
δ15N vs. NO3 : Current Groundwater Data
0
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100 120 140
NO3-N (mg/L)
δ15
N-N
O 3
(‰)
• General relationship between nitrate concentrations and δ15NNO3.
• Higher Nitrate generally corresponds w/ more enriched values.
Poultry Manure
Ammonia Fertilizer
GC
DW
Q
Nitrate δ18O vs. δ15N : All Data
ASA - Nitrate Isotopes(All results except for FT1-24)
-10
-5
0
5
10
15
20
25
-5 0 5 10 15 20
δ 15N-NO3 (‰)
δ18
O-N
O 3
(‰)
91-0391-0791-1091-1391-1594Q-14ABB02ABB03ABB05FT5-12FT5-25PA-25PA-35PB-20PB-35PC-25PC-35US-02US-04US-05
Ammonium Fertilizer
Poultry Manure
Group 1
Group 3
Group 2
Group 4
Nitrate Fertilizer
Manure
• All wells show temporal variability in 15NNO3.
• Potential mixing/dilution effect between fertilizer and poultry sources
• Different Grouping identified based on15NNO3 ranges
δ15NNO3 Spatial Grouping
G1 G2 G3 G4
Group 1 – fertilizer source (less enriched…) Group 2 – Poultry and “mixed” source Group 3 – Poultry and enriched (organic) source Group 4 – Poultry and enriched (organic) source (deeper well/>5 yrs old groundwater)
Piezometer PA-25 Group 1
-10
-5
0
5
10
15
20
Aug
-08
Oct
-08
Dec
-08
Feb-
09
Apr
-09
Jun-
09
Aug
-09
Oct
-09
Dec
-09
Feb-
10
Apr
-10
Jun-
10
Aug
-10
Oct
-10
Dec
-10
Feb-
11
Apr
-11
Jun-
11
Aug
-11
Oct
-11
Dec
-11
Feb-
12
Apr
-12
Jun-
12
Aug
-12
δ15
N-N
O3 &
δ18
O-N
O 3 (‰
)
0
15
30
45
60
75
90
NO 3
-N (m
g/L)
d15N
NO3
Depth of screen below water table = 2.9 m
Example of δ15N Trend for Individual Well
• <5 year age
• <5 m below water table
• Located d/g of Airport
• Relatively depleted δN15
• Lack of clear seasonal pattern
• Enrichment trend in summer 2011, follows spike in nitrate
Example of clear δ15NNO3 Seasonal Trend
Piezometer 91-13 Group 3
-10
-5
0
5
10
15
20
Aug
-08
Oct
-08
Dec
-08
Feb-
09
Apr
-09
Jun-
09
Aug
-09
Oct
-09
Dec
-09
Feb-
10
Apr
-10
Jun-
10
Aug
-10
Oct
-10
Dec
-10
Feb-
11
Apr
-11
Jun-
11
Aug
-11
Oct
-11
Dec
-11
Feb-
12
Apr
-12
Jun-
12
Aug
-12
δ15
N-N
O3 &
δ18
O-N
O 3 (‰
)
0
15
30
45
60
75
90
NO 3
-N (
mg/
L)
d15N
NO3
Depth of screen below water table = 16.7 m
Group 4
• >5 year age
• >5 m below water table
• δ15N inversely related to NO3
• Clear seasonal pattern
• Enrichment trend in fall
• Depletion trend in winter
Conclusions of Isotope Study (so far)
• General trend of enriched δN15 with higher Nitrate concentration (points to organic sources)
• Apparent Grouping of temporal δN15 ranges • Some spatial grouping of δN15 ranges • Generally difficult to discern clear seasonal δN15 patterns
across all wells (variable temporal trends) • A few wells display discernable seasonal trends • More work needed on trend analysis and potential linkages to
above-ground processes. • Potential value in continuing sampling/analysis (for some of
the wells)
Closing Suggestions
• Apply much less manure (and less chemical fertilizer) • Irrigate with shallow groundwater • Drink deep groundwater