Abbotsford-Sumas Aquifer

Transcription

1 Abbotsford-Sumas Aquifer Long-Term Groundwater Monitoring and Nitrogen Isotope Study Abbotsford-Sumas Aquifer Groundwater Nitrate Science Forum II May 1, 12 Abbotsford, BC Gwyn Graham Environment Canada

2 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

3 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.

4 Groundwater Monitoring Network Environment Canada BC MoE/FLNRO CWN Research Municipal Supply Wells

5 Abbotsford-Sumas Aquifer Long-Term Nitrate Trend ASA Nitrate Indicator Graph Monthly Average, Maximum & Minimum (1995-Present) 0 90 Min Nitrate Avg Nitrate Max Nitrate 80 [NO3] (mg-n/l) GCDWQ

6 Uneven Spatial Distribution of Nitrate Data sources include EC and BCMoE monitoring wells and selected private wells (McArthur and Allen, 05) Nitrate Distribution in the Abbotsford-Sumas Aquifer, 02-04

7 Trend Analysis on Different Time Periods NO 3 -N Linear Trends: Varying Time Series 5 Year Series 3 Year Series Average 25 Linear (Average) NO 3 -N (mg/l) Flat Trend (18 yr period of record) 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?

8 Precipitation: Driver for Nitrate leaching Average Nitrate vs Precipitation (Abbotsford-Sumas Aquifer) NO3-N (mg/l) 25 5 Sep-91 May Aug-96 Apr-98 Dec-99 Jul-01 Mar-03 Nov-04 Jul-06 Feb-08 Oct Precipitation (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 = mg/l NO 3 -N)

9 Frequency Analysis (Nitrate) Deseasonalized Fourier Amplitude Spectrum Strong signal at 4-6 yr period (Possible ENSO effect) Peak at 1 yr period (seasonal effect) Frequency (wavenumber)

10 SAGES Groundwater Isotope Study Objectives Identify temporal patterns of δ N 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. 08 to Aug. 11 (3 years) Bi-monthly frequency (with some exceptions)

11 δ N vs. NO 3 : Current Groundwater Data GCDWQ δ N-NO 3 ( ) Poultry Manure General relationship between nitrate concentrations and δ N NO3. Higher Nitrate generally corresponds w/ more enriched values. 4 2 Ammonia Fertilizer NO 3 -N (mg/l)

12 Nitrate δ 18 O vs. δ N : All Data 25 Nitrate Fertilizer ASA - Nitrate Isotopes (All results except for FT1-24) All wells show temporal variability in N NO3. Potential mixing/dilution effect between fertilizer and poultry sources Different Grouping δ 18 O-NO 3 ( ) 5 0 Ammonium Fertilizer Poultry Manure Manure Group identified based on N NO3 ranges Q-14 ABB02 ABB03 ABB05 FT5-12 FT5-25 PA-25 PA-35 PB- PB-35 PC-25 PC-35 US-02 US-04 US-05 Group 3-5 Group 1 Group δ N-NO 3 ( )

13 δ N NO3 Spatial Grouping 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) G1 2 3 G 4

14 Example of δ N Trend for Individual Well Piezometer PA-25 Group 1 δ N-NO3 & δ 18 O-NO3 ( ) dn NO3 Depth of screen below water table = 2.9 m NO3-N (mg/l) <5 year age <5 m below water table Aug-08 Oct-08 Dec-08 Feb-09 Apr-09 Jun-09 Aug-09 Oct-09 Dec-09 Feb- Apr- Jun- Aug- Oct- Dec- Feb-11 Apr-11 Jun-11 Aug-11 Oct-11 Dec-11 Feb-12 Apr-12 Jun-12 Aug-12 Located d/g of Airport Relatively depleted δn Lack of clear seasonal pattern Enrichment trend in summer 11, follows spike in nitrate

15 Example of clear δ N NO3 Seasonal Trend Piezometer Group 3 dn NO3 Group 4 Depth of screen below water table = 16.7 m >5 year age δ N-NO3 & δ 18 O-NO3 ( ) NO3-N (mg/l) >5 m below water table δn inversely related to NO3 Clear seasonal pattern -5 Enrichment trend in fall - Aug-08 Oct-08 Dec-08 Feb-09 Apr-09 Jun-09 Aug-09 Oct-09 Dec-09 Feb- Apr- Jun- Aug- Oct- Dec- Feb-11 Apr-11 Jun-11 Aug-11 Oct-11 Dec-11 Feb-12 Apr-12 Jun-12 Aug-12 0 Depletion trend in winter

16 Conclusions of Isotope Study (so far) General trend of enriched δn with higher Nitrate concentration (points to organic sources) Apparent Grouping of temporal δn ranges Some spatial grouping of δn ranges Generally difficult to discern clear seasonal δn 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)

17 Closing Suggestions Apply much less manure (and less chemical fertilizer) Irrigate with shallow groundwater Drink deep groundwater