Applying measurements of N and O isotopes to New Zealand’s nitrate issues: detailing soil sources

Troy Baisden and Andy Phillips (GNS Science) Major contributions from: Cedric Douence & Simon Stewart

Funded by FRST (2008-12), GNS GCT9, Dartmouth (USA) internship Thanks to Jocelyn Powelson, Horizons, GNS Stable Isotope Lab, Len Wassenaar, Bernhard Mayer, Holly Winton, Liz Keller, Paul Mudge, Greater Wellington Regional Council

GNS Science 2

2 Where the N & O isotopes in NO3 come from in most of New Zealand…

Urine spots

NH4 + ½ O2 + 2 H2O

NO3

Drivers of lower δ18O: •  Higher elevation nitrate production •  Winter nitrification •  Nitrate production on irrigated land •  Sewage treatment + photosynthetic O2 Sources of higher δ18O: •  Nitrification in summer/evaporation •  Nitrate-bearing fertilizer

Developed method for NZ δ15Ν and δ18O to <0.3‰ Blank ≤ 5 ppb

GNS Science

δ18O

δ15N

GNS Science

In NZ, δ15N reflects intensity & duration of agriculture 4

δ15N (‰)

Mudge et al 2013 SSSAJ Winchmore Archived Soil Samples

PhD student Paul Mudge

GNS Science

Upper Manawatu Catchment: Pasture Dominated

GNS Science

Upper Manawatu – Pasture Streams & Rivers

-6

-4

-2

0

2

4

6

8

10

-2 0 2 4 6 8 10 12 14

Nov-10 Mar-11 May-11 Jul-11

δ15N – NO3

δ18 O

– N

O3

GNS Science

Why the Mangatarere?

•  Ideally a smaller catchment was needed with: – Groundwater understanding –  Interesting sources of nitrate to streamwater – Closer to our institute – Ability to identify hidden sources in the field

using DO, EC, and temperature.

GNS Science 8

~140 km2 Mangatarere Catchment

Pastoral + Effluent Sources

Graphic: GWRC report

Headwaters

Carterton Fault Masterton Fault

Sewage & Landfill

Piggery Effluent

Town of Carterton

Mangatarere Stream

Larger N-limited Waiohine River

GNS Science

0.0

1.0

2.0

5 10 15 20

NO

3 (g

/m3 )

Distance d/s of Gorge (Km)

-4.0

-2.0

0.0

2.0

Loca

l δ18

O

Ano

m (

‰)

3.0

7.0

11.0

δ15 N

-NO

3 (‰

)

Masterton Fault

STP

Bend into GW flow

Piggery Effluent

13-17 February 2012 Mangatarere Low Flow Campaign

Carterton Fault

GNS Science

Mangatarere Stream: Seasonal Bifurcation?

!4.0%

!2.0%

0.0%

2.0%

4.0%

6.0%

8.0%

0.0% 5.0% 10.0% 15.0%

δ18O

%NO3(‰

)+

δ15N%NO3(‰)+

November%2010%

Winter%2011%

January%2011%

Jan%2012%Storm%

Summer%2012%

δ15N – NO3 (‰)

δ18 O

– N

O3 (

‰)

Large summer δ18O anomaly in upper catchment samples

GNS Science

Sewage Treatment

(Photosynthetic)

A useable tool to track sources and denitrification where impacts matter

δ15N – NO3 (‰)

δ18 O

– N

O3 (‰

)

Negl. Atmospheric NO3; Few Fertilizer NO3 Sources

-6

-4

-2

0

2

4

6

8

10

-2 0 2 4 6 8 10 12 14

From Local DAM Line: calculate

δ18O anomaly

Food Web

GNS Science

Summary?

-10

-5

0

5

10

15

20

-5 0 5 10 15

δ18 O

-NO

3 (‰

)

δ15N-NO3 (‰)

Area 1 Area 2 Effluent

Soil Water Effects

Nitrate Fertiliser

Typical Effluent & Septic Forest &

Pasture Streams

Water isotopes provide an important additional tracer.

GNS Science

A long process…

Targeted Basic

Science

Applied Science

Operational Monitoring

•  1+ PhD Students •  Initial Applications to Policy & Management •  Investigations