Hurunui River Dissolved Reactive Phosphorus Concentrations and Loads

1. Hurunui River • Dissolved Reactive Phosphorus Concentrations and Loads • A tool to manage periphyton growth ? • Review of Ecan & NIWA Dataset • of DRP measurements at SH1 • Samples taken between • 2004 to June 2014

2. Purpose of Presentation • What do the water quality samples in the Hurunui River tell us about Phosphorus Concentrations and Loads? • How relevant is an in-river load limit to achieving in-river water quality outcomes? • How should P Loads be measured relative to the 2005-2010 baseline? • Has the P Load Limit at SH1 really been exceeded? • Should “landuse change” be a “permitted activity” or a “non-complying activity” under Rule 10.2(b) of the HWRRP?

3. Background: Periphyton Accumulation • NIWA study in April 2014; • Study to determine if adding N and P to the Hurunui River results in additional growth of Periphyton; • Results      • Downstream of Balmoral forest: • the growth of Periphyton is limited by the low concentration of Phosphorus in the river; • the concentration of nitrates in the river can be increased without increasing the growth Periphyton.

4. DRP - Dissolved Reactive Phosphorus 12 Months of the Year Ignoring season and river flow … All year round DRP concentrations appear to be stable

5. DRP - Dissolved Reactive Phosphorus Summer Months at flows less then 60 cumecs Good news: DRP concentrations during the Summer months at flows less than 60 cumecs have declined.

6. DRP (Concentration and Load) relationships with River Flow • There is a weak positive relationship between DRP Concentration and River Flow; • There is a strong positive relationship between DRP Load and River Flow; • High flow events that remove Periphyton also have high DRP loads;

7. More Good News: Hurunui River Flows since 2005 have been increasing Average River Flows for the period 2009-2013 are 14% higher than for the period 2005-2009. But… Higher Flows = Higher DRP Loads

8. EXAMPLE - 2005 Low flows = Low DRP Load Low flows = limited flushing flows = lots of Periphyton accumulation = Low DRP Load  Change of land use remains a permitted activity !!!

9. EXAMPLE – 2013 High flows = High DRP Load High flows = flushing flows = Periphyton removal = DRP Load Limit exceeded Change of land use becomes a non-complying activity !!!

10. DRP – Modelled* Annual Load and 6 year Rolling Average Load ____ Using the Ecan method to calculate Load, the 6 year average DRP load is increasing. This is because river flows are increasing;

11. BUT....... DRP Concentrations appear to be in decline !!! Has the Schedule 1 DRP load limit really been exceeded ??? To answer this question, we should apply the 2009-2014 DRP concentrations to the 2005-2010 river flows to determine if the Schedule 1 DRP load (regulating water quality) has been exceeded.

12. DRP – Average DRP Concentrations at River Flows between 20 to 90 cumecs 25% less Statistically significant at 95% Confidence • Taking River flow into account, DRP concentrations over the period 2009-2014 are around 15% less than concentrations over the period 2005-2010; • After removing the impact river flows, we can conclude the 2009-2014 DRP load is around 15% less than the equivalent 2005-2010 DRP load;

13. DRP – Average DRP Concentrations : SUMMER River Flows (20 to 50 cumecs) Summer DRP concentrations are much lower than the 2005-2010 baseline

14. Load Limit - Conclusions The 2009-2014 DRP load is around 15% less than the equivalent average annual 2005-2010 DRP load. Landuse change under Rule 10.2(b) should remain a permitted activity. • An in-river Load Limit is a very poor tool to manage in-river water quality and regulate landuse change; • The HWRRP should replace “In-River Load Limits” with catchment wide: • On-Farm N Load limits (t/ha/yr); & • On-Farm Best Practice phosphorus management requirements.

15. Water Quality Management • Set Limits where they can be managed • On-Farm Cause-Effect-Consequence-Reward • Replace in-river Load limits with: • On-Farm (Catchment wide) N Load limit (t/ha/yr); & • Best practice phosphorus management requirements. Nitrate-Nitrogen &Phosphorus management Medium Limit: Effectiveness High Low Low Farmer: Response and Incentive High Medium FARM High On-Farm Load Limit N-Loss (kg/ha/yr) & P-Loss Management Requirements; Medium Concentration Limits Nitrate-Nitrogen Toxicity Limits & Low-flow Phosphorus Limits • Periphyton Objectives GROUNDWATER Low 1 Groundwater Quality Limit • Concentration Limits • Nitrate-Nitrogen • Toxicity Limits & • Low-flow Phosphorus Limits Periphyton Objectives Human Health & Consequential Lowland Stream, Tributary & Mainstem effects SPRINGS/TRIBUTARY 8 MAINSTEM 2 Invertebrate Toxicity & Periphyton effects Invertebrate Toxicity, Periphyton & toxic bloom effects

16. What is Ngai Tahu Property doing over the next 6 months... • A more comprehensive NIWA study this summer in the Hurunui River to measure the accumulation of Periphyton biomass over time, and in response to additional N & P; • A Lincoln Agritech research project on groundwater flows and in-river N & P concentrations impacting the Hurunui River; • Preparation of a “Best Practice Phosphorus Manual” specific to the Hurunui Catchment; • Based on the above information (April/May 2015), consider the implications for N & P management and the need for a Plan Change.