1. 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 2 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 3 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 4 12 Months of the Year Ignoring season and river flow … All year round DRP concentrations appear to be stable

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

6. DRP (Concentration and Load) relationships with River Flow 6 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 7 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 8 Low flows = limited flushing flows = lots of Periphyton accumulation = Low DRP Load  Change of land use remains a permitted activity !!!

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

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

11. BUT....... 11 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 12 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; 25% less Statistically significant at 95% Confidence

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

14. Load Limit - Conclusions 14 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. 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.

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

16. What is Ngai Tahu Property doing over the next 6 months... 16 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.