Solution to Pollution – 11th February 2013, Massey University

Land use, nutrients and periphyton in the Tukituki River – the TRIM model

Kit Rutherford NIWA, 82 Ford Rd, Napier

Acknowledgements NIWA: John Quinn, Bob Wilcock, Niall Broekhuizen HBRC: Adam Uytendaal, Husam Baalousha, Dougal Gordon, Ian Millner, Barry Lynch , Rob Waldron, Monique Benson Cawthron: Roger Young GNS-Science: Mike Toews, Maksym Gusyev …and uncle Tom Cobbley

Management questions Can LU intensification be N/P neutral or better?

Can on-farm mitigation be done cost-effectively? Can WWTP upgrades be done cost-effectively? Are there other mitigations (eg dam releases)?

Do we need to control N or P, or both? Etc…….

Scientific challenge – quantify the links between

• on-farm & in-city practices • river nutrients, plants and health?

Farms OVERSEER (annual)

SPASMO & APSIM (daily)

Streams QUAL2e, RIVMOD

Periphyton Guidelines SPASM, SAL (daily) Groundwater

Tritium ageing MODFLOW (flow)

FEM-WATER (flow, nitrogen)

Catchment BNZ, GLEAMS

E2 INCA SWAT CLUES

ROTAN

TRIM_STREAM (daily) • Dilution, scour, advection • Nutrient spiraling • Periphyton growth

TRIM_CATCHMENT • AGRIBASE (land use) • OVERSEER (annual N/P losses)

• Drainage – slow flow • Runoff – quick flow

Daily inflows statistical estimates based on monthly monitoring

1994-2012

TRIM_CATCHMENT Slow flow • MODFLOW groundwater catchments, lags • Groundwater attenuation Quick flow • Nearest stream – no lags • Attenuation Annual N and P stream inflows

Enter the TRIM model…

y = 2240x-1.155

R² = 0.94

y = 2130x-1.164

R² = 0.93

0

0.5

1

1.5

2

0 500 1000 1500PE

T/Ra

infa

ll

Rainfall (mm/y)

Penman PET

Priestley Taylor PET

𝐴𝐴𝐴𝐴𝐴𝐴𝑅𝑅𝐴𝐴𝑅𝑅𝑅𝑅

=1 + 𝑤𝑤 𝑃𝑃𝐴𝐴𝐴𝐴

𝑅𝑅𝐴𝐴𝑅𝑅𝑅𝑅

1 + 𝑤𝑤 𝑃𝑃𝐴𝐴𝐴𝐴𝑅𝑅𝐴𝐴𝑅𝑅𝑅𝑅 + 𝑅𝑅𝐴𝐴𝑅𝑅𝑅𝑅

𝑃𝑃𝐴𝐴𝐴𝐴

𝑃𝑃𝐴𝐴𝐴𝐴𝑅𝑅𝐴𝐴𝑅𝑅𝑅𝑅

= 𝑎𝑎𝑅𝑅𝐴𝐴𝑅𝑅𝑅𝑅−𝑏𝑏

0

5

10

15

20

25

30

1960 1970 1980 1990 2000 2010 2020

Flow

(m3/

s)

Waipawa at RDS

TRIM

observed

0

5

10

15

20

25

30

1960 1970 1980 1990 2000 2010 2020

Flow

(m3/

s)

Tukituki at Tapairu Rd

TRIM

observed

0

20

40

60

80

100

1960 1970 1980 1990 2000 2010 2020

Flow

(m3/

s)

Tukituki at Red Bridge

TRIM

observed

𝐴𝐴𝐴𝐴𝐴𝐴𝑅𝑅𝐴𝐴𝑅𝑅𝑅𝑅

=1 + 𝑤𝑤 𝑃𝑃𝐴𝐴𝐴𝐴

𝑅𝑅𝐴𝐴𝑅𝑅𝑅𝑅

1 + 𝑤𝑤 𝑃𝑃𝐴𝐴𝐴𝐴𝑅𝑅𝐴𝐴𝑅𝑅𝑅𝑅 + 𝑅𝑅𝐴𝐴𝑅𝑅𝑅𝑅

𝑃𝑃𝐴𝐴𝐴𝐴

w = 2

Mean 12.5 years

Max >400 years

OVERSEER kgN/y, kgP/y

MODFLOW MRT

Quick flow

Slow flow

Quick flow attenuation /km

Slow flow attenuation /year

Stre

am a

ttenu

atio

n /k

m

0

0.2

0.4

0.6

0.8

1

1.2

1994 1999 2004 2009 2014

TN (g

N/m3

)Tukituki at SH50

SOE

TRIM

0.002

0.02

0.2

1994 1999 2004 2009 2014

TP (g

P/m3

)

Tukituki at SH50

SOE

TRIM

0

2

4

6

8

10

1994 1999 2004 2009 2014

TN (g

N/m3

)

Porangahau at OruawharaRd

SOE

TRIM

0

0.1

0.2

0.3

0.4

0.5

0.6

1994 1999 2004 2009 2014

TP (g

P/m3

)

Porangahau at OruawharaRd

SOE

TRIM

0

0.5

1

1.5

2

1994 1999 2004 2009 2014

TN (g

N/m3

)

Makaretu at SH50

SOE

TRIM

0.005

0.05

0.5

1994 1999 2004 2009 2014TP

(gP/

m3)

Makaretu at SH50

SOE

TRIM

0

1

2

3

1994 1999 2004 2009 2014

TN (g

N/m3

)

Tukituki at SH2

SOE

TRIM

0

0.05

0.1

0.15

1994 1999 2004 2009 2014

TP (g

P/m3

)

Tukituki at SH2

SOE

TRIM

So N and P gets into the river – so what?

Aesthetics

Mayflies, stoneflies => midges, worms, snails Fish food quality decreases

Oxygen and pH problems

Fish kills? Toxic algae?

Plant biology 101

Biomass = Growth – Loss

Loss = low at low flows Growth = high in summer (temperature, sunlight)

Growth = high when N/P supply is high

TRIM_STREAM needs to use a DAILY time step but

TRIM_CATCHMENT predicts annual N & P inputs

Monthly monitoring

concentrations

Resampled daily

concentrations

Current annual load

Future annual load

0.0001

0.001

0.01

0.1

1

1/01/1994 1/01/1999 1/01/2004 31/12/2008

lookup

DRP

0.0001

0.001

0.01

0.1

1

10

1/01/1994 1/01/1999 1/01/2004 31/12/2008

lookup

TP

0.0001

0.001

0.01

0.1

1

1 10 100 1000

lookup

DRP

0.0001

0.001

0.01

0.1

1

10

1 10 100 1000

lookup

TP

Future daily concentrations

Increased N/P inputs => higher growth rate

High growth rate => biomass accumulates faster between floods

=> Biomass is high more often => maximum biomass is Higher

NB Long periods of low flow => high biomass

even if N/P inputs are low

Calibration January 2011

P controls plant growth and biomass Evidence of P recycling or release

periphyton

Questions addressed using TRIM_STREAM 1. How far from a source do nutrients elevate biomass? 2. Is N or P the limiting nutrient in the Tukituki?

distance

nutrient

WWTP

Case 1: no nutrient recycling (Thomann 1970)

periphyton

distance

nutrient

WWTP

Case 2: nutrient recycling (Chapra pers. comm.)

Plant growth can’t explain N loss Denitrification? Confirmed by 2012 survey

Top reach – P limited Bottom reach – N limited Denitrification? Sediment P release?

0

0.01

0.02

0.03

0.04

0.051/

01/2

010

11/0

4/20

10

20/0

7/20

10

28/1

0/20

10

5/02

/201

1

16/0

5/20

11

DR

P (g

/m3)

prd 74km

Tukituki @ Red Bridge

0

5

10

15

20

25

30

35

1/01

/201

0

11/0

4/20

10

20/0

7/20

10

28/1

0/20

10

5/02

/201

1

16/0

5/20

11

Biom

ass

(gC

/m2)

prd 74km

Tukituki @ Red Bridge

Observed and predicted time series

Predicted benefits of reducing P inputs from the WWTP

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

1/01/1

989

20/07

/1989

5/02/1

990

24/08

/1990

12/03

/1991

28/09

/1991

DRP

(g/m3

)

Tapairu Rd Consent

Current

0

10

20

30

40

50

60

70

1/01/1

989

20/07

/1989

5/02/1

990

24/08

/1990

12/03

/1991

28/09

/1991

Bioma

ss (g

C/m2

)

Tapairu Rd Consent

Current

Effects of intensification – no P mitigation

TRIM1 study (Rutherford et al. 2011)

Frequency of compliance with guidelines

TRIM1 study (Rutherford et al. 2011)

Problem • High plant biomass in summer low flows is not a new problem in cobble-bed East Coast rivers

• Biomass = Growth - Loss

• Increasing N/P supply increases growth rate • High biomass occurs more frequently • Higher maximum biomass occurs

• Decreasing flow reduces dilution and loss

Solutions • On-farm N/P loss control/reduction

Stock exclusion, Riparian buffers and wetlands, Critical source area control Improved effluent irrigation etc

• Practical methods are available (e.g., AgResearch toolbox)

• Adoption is patchy – Cost, Availability of information/technology

• Improved management of wastewater discharges

– Cost for small municipalities

• Flushing flows – possible with a dam • Riparian shade – small streams only

• No magic bullet • Combinations of measures required

Challenge Agree/implement combinations of mitigation measures so we can have…

…but not this (…too often)