A Paleolimnological Investigation of Agricultural Intensification, Water Quality and Ecosystem Change
Total Page：16
File Type：pdf, Size：1020Kb
A paleolimnological investigation of agricultural intensification, water quality and ecosystem change at Lake Nganoke, southern Wairarapa, NZ By Jakob Ethan Parrish A thesis submitted to Victoria University of Wellington in partial fulfilment of the requirements for the degree of Master of Science 2020 II ABSTRACT Decreasing water quality of lakes as a result of anthropogenic landuse and specifically agricultural intensification is well documented in New Zealand. However, monitoring records of lake health are typically short, only commencing once signs of lake deterioration are observed. The shortness of the instrumental record precludes a detailed understanding of the relationship between landuse change, lake ecosystem trajectories and the effectiveness of mitigation strategies such as riparian planting. Paleolimnological reconstruction from sediment cores has the potential to develop high-resolution time series that may extend lake monitoring centuries into the past. This thesis uses paleoenvironmental reconstruction to investigate lake ecosystem change and water quality in Lake Nganoke, Wairarapa, New Zealand as a result of landuse intensification. The primary aim of this thesis is to reconstruct the past environment of Lake Nganoke from a pre-human reference state to the current day to assess: 1) how increased nutrient fluxes associated with landuse intensification have impacted the lake ecosystem; and 2) the ability of riparian zones to buffer these fluxes. The reconstruction was achieved using a multi proxy approach with pre and post-human environments of Lake Nganoke characterised using Palynology, geochemistry, eDNA and hyperspectral scanning. Māori land clearance was identified at ~AD 1450 (95% CI: AD 1417-1551). The appearance of Pinus pollen and increases in fertilisation and stocking rates placed European arrival at ~AD 1850 (95% CI: 1809 - 1870), while intensification of agricultural landuse occurred post ~AD 1950 (95% CI: 1948 - 1964). The prehuman environment of Lake Nganoke experienced little change, with the catchment dominated by tall trees and likely heavily forested. The lake ecosystem and water quality during this time showed little to no change, with algal productivity likely driven by a constant input of natural nutrients. Post Māori arrival, algal productivity was reduced suggesting an increase in water quality likely driven by added lake marginal plants providing a riparian buffer to terrestrially derived nutrients. Lake productivity increased dramatically post European arrival ~AD 1850, coeval with an increase in sediment Cd, suggesting that fertilisation may have driven a decline in water quality. Further increases in fertilisation and stocking rates indicate additional agricultural nutrient fluxes entering Lake Nganoke in AD 1950 when agriculture intensified. Abundances in denitrifying Gammaproteobacteria indicate increases in nutrient loading while bloom forming Cyanobacteria peak ~AD 2000 before declining till present. Riparian planting following Māori arrival appears sufficient to buffer the lake against increased terrestrial nutrient fluxes associated with land clearing. III However, a riparian zone that covers the majority of the catchment post European settlement was inadequate in altering the lake’s degrading ecosystem and water quality trajectory. IV ACKNOWLEDGMENTS First and foremost, I would like to thank my supervisors, Jamie Howarth and Andrew Rees. Jamie, thank you for your guidance, extensive knowledge and high standards that have enabled me to elevate my work. Andrew, thank you for your support, patience and being the good cop to Jamie’s bad cop. You both have been amazing to work with and have helped shape myself and this thesis into the quality it has become. Secondly, I would like to acknowledge Marcus, Susie and the Lakes 380 team who have supported this thesis. Georgia, Maïlys and the wider Cawthron group, who helped carry out the DNA analysis and John, who put up with my multiple questions about ‘r’ coding. Claire, Lizette and the staff at GNS, who’s work ethic and lab skills are second to none and helped with the initial sampling and hyperspectral scanning of Lake Nganoke cores. Thank you, Xun Li who carried out the pollen analysis and Sean Waters who first pioneered the idea of phosphorous fractionation downcore. A massive appreciation must go towards the office crew, Laura, Pip, Steph, Maia and Megan who put up with my insistent questions and lack of foundation in geology. Lastly, I would like to thank my family and Tyler for their support and encouragement. Thank you - for this would not have been possible without you. V VI TABLE OF CONTENTS ABSTRACT ................................................................................................................ III ACKNOWLEDGMENTS .............................................................................................. V TABLE OF CONTENTS .............................................................................................. VII LISTS OF FIGURES ..................................................................................................... X LISTS OF TABLES ......................................................................................................XII LISTS OF EQUATIONS ..............................................................................................XII 1 CHAPTER 1: INTRODUCTION .............................................................................. 1 1.1 MOTIVATION AND RATIONALE ............................................................................ 1 1.2 THESIS OVERVIEW ............................................................................................... 2 2 CHAPTER 2: LITERATURE REVIEW ....................................................................... 3 2.1 FRAMING THE PROBLEM ..................................................................................... 3 2.2 CHANGING LANDUSE........................................................................................... 3 2.3 FRESH WATER DEGRADATION ............................................................................. 7 2.4 AGRICULTURAL POLLUTANT MITIGATION: RIPARIAN PLANTING ........................... 9 2.5 USE OF PALEOLIMNOLOGY ................................................................................ 12 2.5.1 DRIVERS OF LAKE ECOSYSTEM AND WATER QUALITY CHANGE ......................................... 13 2.5.2 MEASURES OF LAKE WATER QUALITY AND ECOSYSTEM CHANGE..................................... 14 2.5.3 THE IMPORTANCE OF DATING LAKE SEDIMENTS ............................................................... 17 3 CHAPTER 3: RESEARCH HYPOTHESES AND OBJECTIVES ..................................... 19 3.1 RESEARCH HYPOTHESES .................................................................................... 19 3.2 OBJECTIVES ....................................................................................................... 19 4 CHAPTER 4: STUDY SITE ................................................................................... 21 4.1 PHYSIOGRAPHIC PROPERTIES ............................................................................ 21 4.2 SOUTHERN PLAINS ............................................................................................ 24 4.3 HUMAN SETTLEMENT AND AGRICULTURAL DEVELOPMENT ............................... 25 4.4 LAKE NGANOKE ................................................................................................. 27 5 CHAPTER 5: METHODOLOGY AND METHODS ................................................... 29 5.1 METHODOLOGY ................................................................................................ 29 5.2 CORE RETRIEVAL AND SUBSAMPLING ................................................................ 30 5.2.1 CORE RETRIEVAL ................................................................................................................. 30 5.2.2 SUBSAMPLING .................................................................................................................... 31 5.3 AGE-DEPTH MODEL ........................................................................................... 32 5.3.1 DATING ............................................................................................................................... 32 5.3.2 AGE MODELS ...................................................................................................................... 33 5.4 LANDUSE RECONSTRUCTION ............................................................................. 33 5.4.1 PALYNOLOGY ...................................................................................................................... 33 5.4.2 CHARCOAL .......................................................................................................................... 34 5.4.3 ANALYSIS OF ENVIRONMENTAL DNA USING DROPLET DIGITAL PCR ................................. 34 5.4.4 GEO-CHEMICAL ANALYSIS – CADMIUM, TOTAL NITROGEN AND TOTAL CARBON ............ 36 5.4.5 AERIAL PHOTOGRAPHY ...................................................................................................... 37 VII 5.5 LAKE ECOSYSTEM AND WATER QUALITY RECONSTRUCTION ............................... 37 5.5.1 HYPERSPECTRAL IMAGING ................................................................................................. 37 5.5.2 BACTERIAL METABARCODING (16S rRNA) ......................................................................... 37 5.5.3 STATISTICAL TESTING – NONMETRIC