Age and quality of groundwater in New Zealand - Chris Daughney

Age and quality of groundwater in New Zealand Chris Daughney Groundwater Research Leader

National Groundwater Monitoring Programme (NGMP): Introduction • Current size 112 sites, 15 regions • Quarterly collection of samples by regional council staff (GNS method) • Analysis of 25+ parameters at GNS Wairakei • Lots of data on quality of New Zealand groundwater! GNS Science

NGMP: National Status of Groundwater Quality 7E+006 • A simple summary of 6.8E+006 N groundwater quality: Northland 6.6E+006 – “Natural Fresh” (32%): Auckland Bay of Plenty little or no human impact, 6.4E+006 Waikato Gisborne low ion concentrations Taranaki 6.2E+006 Manawatu - Wanganui Hawkes Bay Tasman – “Natural Evolved” (26%): 6E+006 Wellington risk of high iron, West Coast Marlborough manganese, arsenic but 5.8E+006 no risk of high nitrate Canterbury Southland 5.6E+006 – “Impacted” (42%): 5.4E+006 Otago 0 100 200 Kilometers elevated nitrate, but no risk of high iron, 5.2E+006 2E+006.2E+006 2 2.4E+006 2.6E+006 2.8E+006E+006.2E+006 3 3 3.4E+00 manganese or arsenic GNS Science

NGMP: Groundwater Nitrate-Nitrogen Levels 11.3 mg/L 7.2 mg/L 5% Background 6% Significant Impact 14% Substantial Impact 3.5 mg/L 58% 17% Threat to Ecosystem Unsafe for Human Consumption 1.6 mg/L GNS Science

Nitrate concentrations are independent of surrounding land use 2 1 log10(no3) 0 -1 -2 -3 Unknown Urban Park/Reserve Industrial Horticultural Dairy Agriculture GNS Science

Why is it difficult to relate groundwater quality to surrounding land use? • It is land use in the aquifer’s recharge zone that has the potential to influence groundwater quality, and the recharge zone might be far away from the monitoring site. • There may be a long travel unconfined time from the recharge zone confined to the well, such that the Impacted groundwater we are Groundwaterwater Contaminated monitoring today might pre- date land use intensification. • Indicators of land use activity, e.g. nitrate, can be removed from groundwater by natural processes. GNS Science

NGMP: Relating groundwater age to quality Mosaic Chart for mrtclass by medclust2 medclust2 A: <5 0 to 10 years old 1A “Natural Fresh” 1B 2 “Natural Evolved” 11 to 40 yearsto 40 B: 5 old “Impacted” 41 to 100 C: 40-100 years old 100+ years>100 D: old GNS Science

DELINEATION METHODS - results Pemberton (MRT = 95 years) 8 7 Concentration (mg/l) 6 5 Nitrate-N 4 Chloride 3 2 1 0 1995 1998 2001 2004 2006 2009 Date GNS Science

Age and quality of groundwater in New Zealand - Chris Daughney

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Age and quality of groundwater in New Zealand - Chris Daughney — Presentation Transcript

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