Physiographics of Southland Part 1: Delineation of key drivers of regional hydrochemistry and water quality Technical Report June 2016 Rissmann, C., Rodway, E., Beyer, M., Hodgetts, J., Snelder, Ta., Pearson, L., Killick, M., Marapara, T.R., Akbaripasand, A., Hodson, R., Dare, J., Millar, R., Ellis, T., Lawton, M., Ward, N., Hughes, Ba., Wilson, Kb., McMecking, J., Horton, Tc., May, D., Kees, L. aLWP Ltd, bLandpro Ltd, cGeological Sciences, University of Canterbury Publication No. 2016/3 Version 2 ‐ Preliminary Document Quality Control Environment Environmental Information Southland Division: Title: Physiographics of Southland Part 1: Delineation of key drivers of regional No: 2016/3 Report reference: hydrochemistry and water quality Rissmann, C., Rodway, E., Beyer, M., Hodgetts, J., R., Snelder, T., Pearson, L., Killick, M., Marapara, T. R., Akbaripasand, A., Hodson, R., Dare, J., Millar, R., Ellis, T., Lawton, M., Ward, N., Hughes B., Prepared by: Wilson K., McMecking, J., Horton, T., May, D., Kees, L. Illustrations by: Hodgetts, J. Maps produced by: Rodway, E., Beyer, M. Peter Almond1, Troy Baisden2, Vincent Bidwell3, Chris Daughney2, Bill Dyck4, Allan Hewitt5, Clive Howard‐Williams6, Scott Larned6, Matthew Leybourne7, Mike Scarsbrook8, Hanspeter Schreier9, Ranvir Singh10, Trevor Webb5, Jenny Webster‐Brown11; Southland Science Technical Advisory Group12. 1. Soils and Physical Sciences, Lincoln University 2. GNS Science 3. Vincent Bidwell Consulting 4. Bill Dyck Ltd 5. Landcare Research 6. NIWA Reviewed by: 7. Department of Earth Sciences, Laurentian University 8. Dairy New Zealand 9. Professor Emeritus, Land and Water Systems, University of British Columbia 10. Massey University, Institute of Natural Resources 11. Waterways Centre for Freshwater Management, University of Canterbury and Lincoln University 12. Southland Science Technical Advisory Group comprised of National and International Experts advising on the Southland Science Programme. Members: Dr Clive Howard‐ Williams, NIWA; Dr Chris Daughney, GNS; Dr Murray Close, ESR; Dr Cath Moore, GNS/ESR; Dr Liz Wedderburn, AgResearch; Prof. Jenny Webster‐Brown, University of Canterbury; Associate Prof. Peter Almond, Lincoln University; Dr Mike Scarsbrook, DairyNZ; Dr Vince Bidwell (independent consultant); Bill Dyck, Envirolink Coordinator. Approved for issue Graham Sevicke‐Jones by: Director, Science and Information Date issued: 1 June 2016 Project Code: 4065.1446 2 Physiographics of Southland Part 1: Delineation of key drivers of regional hydrochemistry and water quality. Version 2 - Preliminary Document History Version: 1 Status: Preliminary Date: June 2016 Doc ID: This report has been prepared in good faith within time and budgetary limits. Due to time Disclaimer: constraints we have not been able to incorporate all review feedback. These limitations will be addressed in a later review and a subsequent version published. Version: 2 Status: Preliminary November Date: Doc ID: 2016 Text and figure amended on page 15 to reflect the fact that the previous Physiographics of Notes: Southland Part 2 and Part 3 reports have been combined into a new single Part 2 report. This report has been prepared in good faith within time and budgetary limits. Due to time Disclaimer: constraints we have not been able to incorporate all review feedback. These limitations will be addressed in a later review and a subsequent version published. 3 Physiographics of Southland Part 1: Delineation of key drivers of regional hydrochemistry and water quality. Version 2 - Preliminary Environment Southland Physiographics of Southland copyright © Unless otherwise stated, this copyright work is licensed for re-use under a Creative Commons Attribution 4.0 International License. Except for any photographs, in essence, you are free to copy, distribute and adapt the work, as long as you attribute the work to Environment Southland and abide by the other license terms. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ . To reuse a photograph please seek permission by sending a request to the stated image owner. Attribution to Environment Southland should be in written form and not by reproduction of any logo. If you adapt this work in any way, or include it in a collection, and publish, distribute, or otherwise disseminate that adaptation or collection to the public, the following attribution statement should be used: This work uses material sourced from the Physiographics of Southland project, which is licensed by Environment Southland for re-use under the Creative Commons Attribution 4.0 International License. Disclaimer Environment Southland uses reasonable endeavours but does not warrant that this information is current, complete or accurate. Professional or specialist advice should be obtained before taking or refraining from taking any action on the basis of this information. To the extent permitted by law, Environment Southland will not be liable for any loss, liability or costs suffered or incurred as a result of any reliance placed on this information. Citation of documents should be in the form: Physiographics of Southland (2016). Part 1: Delineation of key drivers of regional hydrochemistry and water quality. Environment Southland publication number: 2016/3 ISBN: 978-0-909043-16-2 (online) Physiographics of Southland (2016): Development and application of a classification system for managing land use effects on water quality in Southland. Environment Southland publication number: 2016/11 ISBN: 978-0-909043-17-9 (online) Abstract The key aim of this work was to better understand and estimate spatial variation in freshwater hydrochemistry at a regional scale in Southland, New Zealand using a physiographic approach. We developed a semi‐quantitative, mechanistic conceptual model to estimate the hydrochemical variation in ground‐ and surface waters and shallow, soil influenced groundwater on the basis of four key drivers: (i) precipitation source; (ii) recharge mechanism and water source; (iii) combined soil and geological redox potential, and; (iv) the combination of geomorphic setting and substrate (rock or biological sediment) composition. We applied a multi‐element, multi‐isotope approach to 28,548 individual samples to identify critical characteristics of existing spatial frameworks (for soil, geology, topography, hydrology and hydrogeology) to resolve key spatial drivers over the hydrochemical variation of surface water and shallow, soil influenced groundwater. The model was validated through stratification of hydrochemical data using maps spatially depicting variance in key drivers, and independent empirical modelling. Empirical testing indicated a strong estimation capacity for surface water hydrochemistry, but was weaker for groundwater. Nonetheless, the patterns of hydrochemical response for groundwater were still consistent with the model. Furthermore, given a regional, median base flow index of 0.47 the strong performance of the model for surface water indicates the characterisation of young, soil zone influenced groundwater across Southland is robust. We conclude that the conceptual model is a sound platform for understanding and explaining the spatial controls over hydrochemistry outcomes in Southland. This work provides a spatially resolved platform for the development of a risk based framework for regional landuse. Future work will look at the use of the key drivers as a basis for modelling of transient water and nutrient flux. 4 Physiographics of Southland Part 1: Delineation of key drivers of regional hydrochemistry and water quality. Version 2 - Preliminary Executive Summary Why is the delineation of key drivers of hydrochemistry important? The controls over and signatures of Southland’s freshwater were studied to help understand the setting and suite of key drivers that govern regional scale variation in freshwater hydrochemistry, including water quality. Specifically, this work focuses on characterising the controls (key drivers) over surface and shallow soil zone influenced groundwater composition based on a physiographic approach. It makes no attempt to estimate exact compositions but rather estimate general trends, magnitudes and patterns in regional freshwater composition. Further, this study makes no attempt to theorise the composition and/or water quality of deeper groundwaters associated with semi‐ confined or confined aquifers that are poorly coupled to the soil zone (Figure 1). The latter is an important frame of reference for this work as surface water is by definition a mix of soil water and groundwater drainage. The ability to estimate surface water composition is therefore considered a robust test of the performance of our approach. Figure 1: Diagram depicting what constitutes shallow, hydrologically connected ground- and surface water in this study (green ticks are included, red crosses are excluded). How were the key drivers delineated? To identify and explain the drivers of spatial variation, data for precipitation (rain, hail and snow), soil, soil water, ground‐ and surface water were analysed and cross‐referenced against existing 5 Physiographics of Southland Part 1: Delineation of key drivers of regional hydrochemistry and water quality. Version 2 - Preliminary spatial frameworks of topography, geomorphology, hydrology, hydrogeology and soils. This included classifying waters with common origins and identification of the controls or ‘drivers’ over hydrochemical variation. The drivers specific to the Southland context were identified