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)

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90

100

1995

1996

1997

1998

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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

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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)

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50

100

150

200

250

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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

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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

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-5

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-08

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-08

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-10

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-10

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11

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-11

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11

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-11

Oct

-11

Dec

-11

Feb-

12

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-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

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20

Aug

-08

Oct

-08

Dec

-08

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-09

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-11

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-12

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-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