DOCSLIB.ORG

Waikato Shallow Lakes Modelling

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Waikato Shallow Lakes Modelling ISSN 2463-6029 (Print) ISSN 2350-3432 (Online) Waikato Shallow Lakes Modelling 2017 ERI Report 94 Client report prepared for DairyNZ, Waikato River Authority, Waikato Regional Council, DOC/Fonterra Living Waters Partnership and Waipa District Council By Moritz K. Lehmann, David P. Hamilton, Kohji Muraoka, Grant W. Tempero, Kevin J Collier and Brendan J Hicks Environmental Research Institute University of Waikato, Private Bag 3105 Hamilton 3240, New Zealand Waikato Shallow Lakes Modelling Cite report as: Lehmann, M. K., Hamilton, D. P., Muraoka, K., Tempero, G. W., Collier, K. J., Hicks, B. J. 2017. Waikato Shallow Lakes Modelling. ERI Report 94. Environmental Research Institute, University of Waikato, Hamilton, New Zealand. 223 pp. Cover photo: Lake Ngāroto on a calm day in November 2015. Disclaimer: The information and opinions provided in this Report have been prepared for the Client and its specified purposes. Accordingly, any person other than the Client, who uses the information and opinions in this report, does so entirely at their own risk. The Report has been provided in good faith and on the basis that reasonable endeavours have been made to be accurate, not mislead in any way, and to exercise reasonable care, skill and judgment in providing information and opinions contained therein. Neither the University of Waikato, nor any of its employees, officers, contractors, agents or other persons acting in its behalf or under its control, accepts any responsibility or liability to third parties in respect of any information or opinions provided in the Report. Report reviewed by: Approved for release by: Marnie Campbell John Tyrrell University of Waikato University of Waikato 2 Waikato Shallow Lakes Modelling Executive Summary The principal aim of this study is to apply a modelling approach to identify, evaluate and prioritise specific in-lake and catchment restoration options which could be applied to improve the water quality and ecological health of peat and riverine lake types across the Waikato Region. Four representative lakes have been selected as case studies for this work based on their social, cultural and ecological significance, as well as the availability of historical monitoring data and the potential transferability of the study findings to similar lake systems. The lakes include Rotomānuka, Ngāroto, Waahi and Waikare. This study comprises the following six objectives for each lake: 1. Define baseline water quality and ecological health based on existing monitoring data and knowledge. 2. Determine the key pressures, drivers and processes governing lake water quality and ecological health. 3. Define, evaluate and rank the likely effectiveness of a range of in-lake and catchment management strategies to improve existing water quality and biodiversity values. 4. Evaluate the level of certainty around the suggested restoration strategies that meet the desired outcomes, as well as the timeframes implementation and longevity. 5. Identify an achievable end state for water quality and ecological health, taking into consideration existing trophic state, legacies and catchment land use. 6. Provide an expert assessment on whether the strategies identified are also likely to be effective when applied to other similar Waikato lake types. Process-based dynamic modelling was chosen for this study because it can be used to test the plausibility of conceptual models of lake ecosystem function, to shed light on the importance of various processes contributing to observed system behaviour, and to extrapolate to future scenarios that fall outside the range of historical observations. This report consists of a main body of text with an Extended Conclusions section that goes into detail about processes in the lakes that are relevant to understanding management, as well as 7 appendices. For modelling of one-dimensional (1-D) lake hydrodynamics and ecological processes, we chose the one-dimensional, coupled hydrodynamic-ecological model DYRESM-CAEDYM as the tool for 3 Waikato Shallow Lakes Modelling assessing effects of altered hydrology, nutrient and sediment loads, and climate on physical and biogeochemical processes in Lakes Ngāroto, Waahi and Rotomānuka. Modelling of three- dimensional (3-D) hydrodynamics of Lake Waikare was initiated using Delft3D-FLOW but not progressed to the point of presenting simulations given the time constraints of the present study. Catchment boundary conditions consisting of time series of discharges and contaminant loads for each of the lakes were generated using either the process-based INtegrated CAtchments model (INCA), the TopNet hydrological model or mass-balance calculations from known water level and outflow data, with measured data used to check the veracity of assumptions and model outputs. Multiple lake management scenarios were conceptualised with a project working group and these were simulated using a DYRESM-CAEDYM model calibrated to each lake application (Ngāroto, Waahi and Rotomānuka). The management approaches assessed can be broadly considered as belonging to three categories: 1. External nutrient load reduction: associated with land use change or other nutrient loss reductions from improved management practices and/or targeted interventions, e.g., erosion control, denitrification beds; 2. Hydrological modifications: diversion of inflows away from the lake or increasing the water level to alter wind-driven resuspension of sediments; 3. Geochemical engineering: by using sediment capping to reduce internal loading and/or continuous low-dosage alum treatment to reduce dissolved P and increase flocculation in the water column. The base model and each scenario simulation are presented and compared using metrics which describe the water quality in terms of summary statistics, for example, attribute bands (A, B, C or D) from the National Objectives Framework (NOF) of the National Policy Statement for Freshwater Management (NPS-FM, MfE 2015a). Lake Ngāroto Lake Ngāroto is the largest of the Waipa peat lakes (surface area of 108 ha) and is important for its cultural history and for recreational activities. Its current mean depth is c. 2 m and maximum depth 4 m. The Lake Ngāroto catchment is predominantly dairy pasture, resulting in high external nutrient loads to the lake. The high nutrient load, shallow depth, loss of submerged macrophytes and reduced lake volume (compared with historical levels) have collectively led to resuspension of bottom sediments, high water column turbidity and high levels of internal nutrient loading. Lake Ngāroto has recurrent algal blooms, hosts large populations of invasive fish including catfish, rudd, 4 Waikato Shallow Lakes Modelling gambusia, goldfish and koi carp, but also has valuable native fish populations including common bullies, shortfin eels and common smelt. Isotope data from this study indicate that the food base is dominated by organic matter, most likely primarily of terrestrial origin but with some seasonal variability, and large eels are at the top of the food web but with potential for some overlap of diet with catfish and koi carp. The lake model for Ngāroto showed an acceptable match to observations of temperature, surface and bottom dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS) and chlorophyll a, though observed data were quite sparse for deriving input data to the lake model and for comparisons with model outputs. In-lake data were repeated over a five-year period from one year of measured data for the purpose of model comparisons. There was also limited data on inflow composition to derive a daily inflow file consisting of discharges and concentrations of TSS and nutrient species. The model was most sensitive to parameters relating to the density of particulate organic matter, reinforcing that it would be useful to quantify the size and nature of suspended material in the water column of Lake Ngāroto, as well as establishing setting velocities. Parameters affecting the dynamics of cyanobacteria and temperature responses were also particularly sensitive. Fourteen simulations were carried out for Lake Ngāroto to examine water quality effects of changes in external (catchment) loads, internal (bottom-sediment) loads, water level changes and an inflow (Ngārotoiti) diversion. Despite reductions in internal and external nutrient loads of up to 50%, no scenario resulted in NOF status of the lake improving from the D band. The scenario most effective at reducing median total phosphorus (TP), total nitrogen (TN) and chlorophyll a (TCHLA) was N14 (50% external reduction for P and 50% anoxic release reduction for P). This simulation might equate to some land use change and improved land management practices, as well as geochemical engineering to reduce the internal (bottom-sediment) nutrient load. Comparisons between scenarios which combine internal and external load reductions in N and P in various combinations (e.g., N3, N7, N13 and N14) suggest that chlorophyll a concentration is driven reasonably evenly by external and internal nutrient loading, with much of the internal loading occurring during summer when phytoplankton growing conditions are most suitable (i.e., warmer water temperature and higher irradiance). For Lake Ngāroto to meet the bottom line in the NOF within the next 3-4 decades will require intensive catchment actions that will ultimately reduce the level of nutrient enrichment in the bottom sediments. Perhaps more importantly, however, and with a much higher risk in terms of
Load more

Recommended publications
  • Section 32AA Evaluation Report
    Section 32AA Evaluation Report Rezoning Proposal Puketirini, Huntly Terra Firma Resources Ltd Date: 17 February 2021 Terra Firma Resources Limited PO Box 67, Ngaruawahia 3742 New Zealand Tel. +64 274 336 585 Section 32AA Evaluation Report Rezoning Proposal, Puketirini, Huntly PREPARED FOR: Craig Smith Director Terra Firma Resources Ltd PROJECT: Section 32AA Evaluation Report Residential Zoning at Puketirini, Huntly DATE: 17 February 2021 ……………………………………. Lucy Smith Page 2 Section 32AA Evaluation Report Rezoning Proposal, Puketirini, Huntly Contents Executive Summary 1. Introduction .................................................................................................................................... 5 2. Section 32 of the Resource Management Act 1991 ....................................................................... 6 3. Section 32AA Report Scope and Format ......................................................................................... 7 4. Assessment of Environmental Effects ............................................................................................. 7 5. Outline of Rezoning Proposal ........................................................................................................ 10 6. Relevant PDP Objectives and Policies ........................................................................................... 14 7. Alignment with Higher Order Documents .................................................................................... 20 8. Scale and Significance ..................................................................................................................
    [Show full text]
  • 2016 Pilot Waikato River Report Card: Methods and Technical Summary
    2016 Pilot Waikato River Report Card: Methods and Technical Summary Prepared for Waikato River Authority March 2016 2016 Pilot Waikato River Report Card: Methods and Technical Summary Prepared by: Bruce Williamson (Diffuse Sources) John Quinn (NIWA) Erica Williams (NIWA) Cheri van Schravendijk-Goodman (WRRT) For any information regarding this report please contact: National Institute of Water & Atmospheric Research Ltd PO Box 11115 Hamilton 3251 Phone +64 7 856 7026 NIWA CLIENT REPORT No: HAM2016-011 Report date: March 2016 NIWA Project: WRA14203 Quality Assurance Statement Reviewed by: Dr Bob Wilcock Formatting checked by: Alison Bartley Approved for release by: Bryce Cooper Photo: Waikato River at Wellington Street Beach, Hamilton. [John Quinn, NIWA] 2016 Pilot Waikato River Report Card: Methods and Technical Summary Contents Summary ............................................................................................................................ 9 Reflections from the Project Team ..................................................................................... 12 1 Introduction ............................................................................................................ 18 1.1 Report Cards ........................................................................................................... 18 1.2 2015 Pilot Waikato River Report Cards .................................................................. 20 1.3 Purpose of this Technical Summary .......................................................................
    [Show full text]
  • Age and Growth of Wild-Caught Grass Carp in the Waikato River Catchment
    Age and growth of wild-caught grass carp in the Waikato River catchment Cindy Baker and Joshua Smith DOC RESEARCH & DEVELOPMENT SERIES 238 Published by Science & Technical Publishing Department of Conservation PO Box 10–420 Wellington, New Zealand DOC Research & Development Series is a published record of scientific research carried out, or advice given, by Department of Conservation staff or external contractors funded by DOC. It comprises reports and short communications that are peer-reviewed. Individual contributions to the series are first released on the departmental website in pdf form. Hardcopy is printed, bound, and distributed at regular intervals. Titles are also listed in our catalogue on the website, refer www.doc.govt.nz under Publications, then Science and Research. © Copyright April 2006, New Zealand Department of Conservation ISSN 1176–8886 ISBN 0–478–14077–0 This is a client report commissioned by Waikato Conservancy and funded from the Science Advice Fund. It was prepared for publication by Science & Technical Publishing; editing and layout by Ian Mackenzie. Publication was approved by the Chief Scientist (Research, Development & Improvement Division), Department of Conservation, Wellington, New Zealand. In the interest of forest conservation, we support paperless electronic publishing. When printing, recycled paper is used wherever possible. CONTENTS Abstract 5 1. Introduction 6 2. Methods 6 3. Results 7 4. Discussion 9 5. Conclusions 10 6. Acknowledgements 10 7. References 11 Age and growth of wild-caught grass carp in the Waikato River catchment Cindy Baker and Joshua Smith National Institute of Water & Atmospheric Research Ltd, PO Box 11-115, Hamilton, New Zealand ABSTRACT Two relatively small grass carp (Ctenopharyngodon idellus) were captured in the lower Waikato River basin, New Zealand: one from Lake Whangape (1.65 kg, 435 mm fork length (FL)), and one from Pungarehu Canal, below the floodgates to Lake Waikare (3.1 kg, 570 mm FL).
    [Show full text]
  • 2031 Auckland/Waikato Fish & Game 15
    SPORTS FISH AND GAME MANAGEMENT PLAN FOR AUCKLAND/WAIKATO FISH AND GAME REGION 2021 – 2031 AUCKLAND/WAIKATO FISH & GAME 156 BRYMER RD, RD 9, HAMILTON PH: 07 849 1666 [email protected] www.fishandgame.org.nz Contents: PART 1 BACKGROUND AND RESOURCE SUMMARY How To Use this Plan ...................................................................................................................... 5 1.1. Operation of Plan .................................................................................................................... 5 1.2. Plan Review ............................................................................................................................. 5 1.3. Organisational management .................................................................................................. 5 2. Introduction .................................................................................................................................... 6 2.1. Fish and Game New Zealand ................................................................................................... 6 2.2. The Auckland/Waikato Fish and Game ................................................................................... 6 3. Legal Context................................................................................................................................... 9 3.1. Conservation Act 1987 ............................................................................................................ 9 3.2. Wildlife Act 1953 ....................................................................................................................
    [Show full text]
  • Agenda for a Meeting of the Strategy & Finance Committee to Be Held Via
    1 Agenda for a meeting of the Strategy & Finance Committee to be held via Audio Visual Conference on MONDAY, 6 SEPTEMBER 2021 commencing at 9.30am. 1. APOLOGIES AND LEAVE OF ABSENCE 2. CONFIRMATION OF STATUS OF AGENDA 3. DISCLOSURES OF INTEREST 4. CONFIRMATION OF MINUTES Meeting held on Monday, 26 July 2021 5 5. ACTIONS REGISTER 12 6. STRATEGY REPORTS 6.1 Climate Action Progress – August 2021 14 6.2 Hamilton & Waikato Tourism Annual Report to Waikato District Council – 1 July 2020 40 – 30 June 2021 6.3 Changes to Default Growth – High Growth Projection from Waikato Projections 2018- 65 2068 6.4 Economic and Community Development Work Programme Update – August 2021 72 7. FINANCE REPORTS 7.1 Approved Counterparty Review 78 7.2 General Rate Position 80 8. EXCLUSION OF THE PUBLIC 84 GJ Ion CHIEF EXECUTIVE Waikato District Council Strategy & Finance Committee 1 Agenda: 6 September 2021 2 TERMS OF REFERENCE AND DELEGATION Reports to: The Council Chairperson: Cr Janet Gibb Deputy Chairperson: Cr Aksel Bech Membership: The Mayor, all Councillors and Mrs Maxine Moana-Tuwhangai (Maangai Maaori) Meeting frequency: Six-weekly Quorum: Majority of members (including vacancies) Purpose: The Strategy & Finance Committee is responsible for: 1. Monitoring of Council’s strategy, and performance (both financial and non-financial) against the Long Term Plan and Annual Plan. 2. Setting the broad vision and direction of the District, determine specific outcomes that need to be met to deliver on that vision, and develop and monitor strategies to achieve those goals. 3. Determining financial matters within its delegations and Terms of Reference and making recommendations to Council on financial matters outside its authority.
    [Show full text]
  • Pdf Huntly Domain and Lake Hakanoa Reserve Management Plan Pdf, 979 KB Download
    HUNTLY DOMAIN AND LAKE HAKANOA RESERVE MANAGEMENT PLAN Prepared for Waikato District Council by Boffa Miskell Ltd Approved by Council on 28 August 2012 Contents Introduction ......................................................... 1 Purpose of the Reserve Management Plan 1 Reserve Management Plan Procedure 4 Strategic Context 1 How to Use this Reserve Management Plan 6 Context ................................................................ 7 Location 7 Natural Physical Features 10 Historical Context 10 Community Consultation 13 Issues and Opportunities 13 Core Community Values 13 Vision and Objectives for Huntly Domain and Lake Hakanoa ................................................... 20 Development of the Vision 20 The Vision 20 Objectives 20 Reserve Management ....................................... 21 Objective 1 – To maintain existing facilities and resources for active recreation 21 Objective 2 – To provide for a range of passive recreational activities and for community events 23 Objective 3 – To manage and enhance safe access for pedestrians and vehicles 26 Objective 4 – To progressively improve Lake Hakanoa‟s water quality 27 Objective 5 – To actively manage and enhance lakeside and lake margin vegetation and wetland areas 30 Objective 6 – To manage and enhance passive recreation opportunities at Lake Hakanoa 32 Objective 7 – To provide integrated management of the Reserve. 35 Landscape Concept Plan .................................. 38 Landscape Concept Statement 38 Introduction Purpose of the Reserve Management Plan Huntly
    [Show full text]
  • Lakeside Te Kauwhata Private Plan Change Ecological Report Prepared for Lakeside Developments 2017 Ltd
    Lakeside Te Kauwhata Private Plan Change Ecological Report Prepared for Lakeside Developments 2017 Ltd 6 March 2017 Document Quality Assurance Bibliographic reference for citation: Boffa Miskell 2016. Lakeside Te Kauwhata: Private Plan Change Ecological Report. Report prepared by Boffa Miskell for Lakeside Developments Ltd. Prepared by: Dave Slaven Status: FINAL Revision / version: D Issue date: 6 March 2017 Use and Reliance This report has been prepared by Boffa Miskell Limited on the specific instructions of our Client. It is solely for our Client’s use for the purpose for which it is intended in accordance with the agreed scope of work. Boffa Miskell does not accept any liability or responsibility in relation to the use of this report contrary to the above, or to any person other than the Client. Any use or reliance by a third party is at that party's own risk. Where information has been supplied by the Client or obtained from other external sources, it has been assumed that it is accurate, without independent verification, unless otherwise indicated. No liability or responsibility is accepted by Boffa Miskell Limited for any errors or omissions to the extent that they arise from inaccurate information provided by the Client or any external source. Template revision: 20150331 0000 File ref: 16241 SECTION ONE - CONTEXT 1 Executive Summary Lakeside Developments 2017 Ltd has contracted to purchase a current dairy farm to the south of Te Kauwhata and converting it into a residential subdivision. While shelter belts and copses of planted exotic trees are present throughout the farm it is largely devoid of native vegetation, with the exception of a narrow riparian fringe on the margins of two lakes that border the farm to the west and east.
    [Show full text]
  • 4380 Whangamarino Gates Diagrama3
    IN THE MATTER of the Resource Management Act 1991 (“RMA” or “the Act”) AND IN THE MATTER of a submission in respect of the PROPOSED WAIKATO DISTRICT PLAN by AMBURY PROPERTIES LIMITED pursuant to Clause 6 of Schedule 1 of the Act EVIDENCE OF AJAY DESAI ATTACHMENTS ATTACHMENT A COMMUNITY GATE OPERATION PROCEDURES DIAGRAM Whangamarino TE ONETEA GATE OPERATION Control Gate Action is determined primarily by the relationship between the Waikato River level at the gate and the Lake W ha n g Waikare level. am ar in o Situation Action R iv er Waikato River level is below Lake Waikare Levels Te Onetea gate will be closed Waikato River level is above Lake Waikare Level but below Te Onetea gate will be open RL . metres Waikato River level is above Lake Waikare Level and Te Onetea gate will be closed above RL . metres WAIKARE GATE OPERATION Whangamarino Wetland Action is determined by the relationship between the Lalce Level and the appropriate seasonal Target Level. Season Action W a April to September Gate opening/closing levels and apertures are to be set i k a RL . metres with the objective of keeping the Lake level between RL’s t o . and . metres. R i v er October to December Gate opening/closing levels and apertures are to be set RL . metres with the objective of keeping the Lake level between RL’s . and . metres. SH January to March Gate opening/closing levels and apertures are to be set RL . metres with the objective of keeping the Lake level between RL’s .
    [Show full text]
  • Waikato River Water Take Proposal
    WAIKATO RIVER WATER TAKE PROPOSAL Lower Waikato River Bathymetry Assessment Changes Consequent to Development for Watercare Services Ltd December 2020 R.J.Keller & Associates PO Box 2003, Edithvale, VIC 3196 CONTENTS EXECUTIVE SUMMARY ....................................................................................................................... 4 1. INTRODUCTION ........................................................................................................................ 5 2. SUMMARY AND CONCLUSIONS ................................................................................................ 8 2.1 INTRODUCTION .......................................................................................................................... 8 2.2 “NATURAL” VARIABILITY IN FLOW RATES ........................................................................................ 8 2.3 HISTORICAL CHANGES IN BATHYMETRY ........................................................................................... 9 2.4 HYDRO DAM DEVELOPMENT ........................................................................................................ 9 2.5 SAND EXTRACTION ..................................................................................................................... 9 2.6 LOWER WAIKATO FLOOD PROTECTION ......................................................................................... 10 2.7 LAND USE CHANGES ................................................................................................................
    [Show full text]
  • Hydrodynamic Modelling of Lake Whangape and Lake Waahi
    Hydrodynamic modelling of Lake Whangape and Lake Waahi Lake Whangape (Austin Zhang) February 2014 ERI Report 31 Prepared for Waikato Regional Council By Hannah F. E. Jones and David P. Hamilton Environmental Research Institute Faculty of Science and Engineering University of Waikato, Private Bag 3105 Hamilton 3240, New Zealand Cite report as: Jones, H. F. E., Hamilton D. P., 2014. Hydrodynamic modelling of Lake Whangape and Lake Waahi. Prepared for Waikato Regional Council. Environmental Research Institute Report No. 31, University of Waikato, Hamilton. 33 pp. Disclaimer: This report was prepared by scientists from the Environmental Research Institute, University of Waikato. The authors have used the best available information and made use of all data provided in preparing this report, and have interpreted this information exercising all reasonable ability and caution. Furthermore, the accuracy of information and model simulations presented in this document is entirely reliant on the accuracy and completeness of supplied information. The authors do not accept any liability, whether direct, indirect or consequential, arising out of the provision of information in this report. Reviewed by: Approved for release by: Chris McBride John Tyrrell Advanced Technical Officer Business Manager Environmental Research Institute Environmental Research Institute University of Waikato University of Waikato ii Executive Summary The University of Waikato was contracted by Waikato Regional Council to develop hydrodynamic models for Lake Whangape and Lake Waahi. The models are intended to provide a basis for future water quality modelling to inform the restoration of habitat for native fish and the management of pest fish populations. Lakes Whangape and Waahi are shallow, highly eutrophic lakes in the lower Waikato River basin.
    [Show full text]
  • Waikato and Waipā River Restoration Strategy Isbn 978-0-9922583-6-8
    WAIKATO AND WAIPĀ RIVER RESTORATION STRATEGY ISBN 978-0-9922583-6-8 ISBN 978-0-9922583-7-5 (online) Printed May 2018. Prepared by Keri Neilson, Michelle Hodges, Julian Williams and Nigel Bradly Envirostrat Consulting Ltd Published by Waikato Regional Council in association with DairyNZ and Waikato River Authority The Restoration Strategy Project Steering Group requests that if excerpts or inferences are drawn from this document for further use by individuals or organisations, due care should be taken to ensure that the appropriate context has been preserved, and is accurately reflected and referenced in any subsequent spoken or written communication. While the Restoration Strategy Project Steering Group has exercised all reasonable skill and care in controlling the contents of this report, it accepts no liability in contract, tort or otherwise, for any loss, damage, injury or expense (whether direct, indirect or consequential) arising out of the provision of this information or its use by you or any other party. Cover photo: Waikato River. WAIKATO AND WAIPĀ RIVER RESTORATION STRATEGY TE RAUTAKI TĀMATA I NGĀ AWA O WAIKATO ME WAIPĀ RESTORATION STRATEGY FOREWORD HE KUPU WHAKATAKI MŌ TE RAUTAKI TĀMATA FROM THE PARTNERS MAI I TE TIRA RANGAPŪ Tooku awa koiora me oona pikonga he kura tangihia o te maataamuri. The river of life, each curve more beautiful than the last. We are pleased to introduce the Waikato and Waipā River Restoration Strategy. He koanga ngākau o mātou nei ki te whakarewa i te Rautaki Tāmata i ngā Awa o Waikato me Waipā. This document represents an exciting new chapter in our ongoing work to restore and protect the health and wellbeing of the Waikato and Waipā rivers as we work towards achieving Te Ture Whaimana o Te Awa o Waikato, the Vision & Strategy for the Waikato River.
    [Show full text]
  • Ecological Modelling of Water Quality Management Options in Lake Waahi to Support Hauanga Kai Species: Technical Report
    Ecological modelling of water quality management options in Lake Waahi to support Hauanga Kai species: Technical report 2018 ERI report number: 108 Citation Allan M 2018. Ecological modelling of water quality management options in Lake Waahi to support Hauanga Kai species: Technical report. ERI report no. 108, Environmental Research Institute, The University of Waikato, Hamilton. Cover photo Landsat seven image captured 28/5/2015 Reviewed by: Approved for release by: Dr Kevin Collier Dr John Tyrell Associate Professor Research Developer Environmental Research Institute Environmental Research Institute The University of Waikato The University of Waikato Hamilton Hamilton Availability Available on a Creative Commons Attribution 3.0 New Zealand Licence Executive Summary This report describes a numerical modelling approach for Lake Waahi to assess the effects of various future scenarios on water quality attributes known to affect the appearance of the lake’s multiple hauanga kai species across differing spatial scales. Hauanga kai refers to customary gathering and use of naturally occurring and cultivated foods. Numerical models were used to support shared learning and development of future scenarios in response to different management options and environmental pressures. The shallow lakes of the Waikato region have been particularly impacted by anthropogenic eutrophication. This is due to the fact that many of these lakes have already undergone a degree of natural eutrophication due to their geomorphic properties, such as their low elevation and shallow depth. The main contributing factors to water quality decline in shallow Waikato lakes have been identified as: high external nutrient and sediment loads, internal loading exacerbated by high sediment resuspension and bioturbation from pest fish (carp), reduced water depth due to installation of water control structures, reduction in wetland filtering potential due to draining, and stock access to wetlands.
    [Show full text]