Solute, suspended sediment and bedload transportation in a pristine temperate forest, Silver Stream, New Zealand. Amanda Louise Fountain A thesis submitted in fulfilment of the requirements for the degree of Masters of Science, in Geography, at the University of Otago, Dunedin, New Zealand December 2012 Abstract Solutes, suspended sediment and bedload calculations are important for understanding the dynamic processes of flow pathways and geomorphic change. Large amounts of solute and sediment studies have focused on alpine environments within New Zealand with little attention given to temperate forests, an important and valued component of the New Zealand’s land use. This aims of this study is to quantify all three loads (solute, suspended sediment and bedload) for a pristine temperate forest, suitable as a future reference catchment. Over the ten-month study, 14 event flows were evaluated utilising 15-minute stage, specific conductivity and turbidity data as well as grab samples and post event reach surveys. Annual solute load was 14.85 t km-2 yr-1 (53% of total load), slightly higher than the annual suspended sediment load of 12.79 t km-2 yr-1 (45%). Bedload was a smaller proportion of total load with 0.57 t km-2 yr-1 (2%), 4% of suspended sediment. The chemical composition demonstrated a schist-dominated catchment with calcium bicarbonate waters travelling through subsurface pathways. Hysteresis analysis suggests that solutes do not respond to initial flushing of old water and are, therefore, completely dominated by dilution effects of incoming new water for each event. Suspended sediment hysteresis, however, showed variation over events. Clockwise hysteresis was dominant, which indicated the majority of events showed mobilisation of in-stream sediment. Anti-clockwise hysteresis was also evident in following peaks coupled with reduced sediment loads indicating temporary catchment exhaustion of fine sediment. Seasonality effects were observed for solute loads whereby winter showed the lowest rate of solute accumulation and autumn the highest. Sediment loads were in comparison purely dominated by event flows. Bedload surveys showed evidence of deposition and erosion over the study period. Deposition was attributed to sediment build up behind upstream large woody debris which was subsequently removed and sediment deposited within the reach. Erosion occurred due to prior catchment stress and through threshold discharge evacuating sediment. ii Acknowledgements I would like to thank the following people who have helped me throughout the year in the completion of this thesis: Dr. Sarah Mager for the guidance and support on this project and Masters. I have learnt a lot from continuing onto Masters and I am glad I did it, but most of all you have help me realise that I truly enjoy studying and teaching other about rivers. Julie Clark for all the teaching of methods and laboratory work you helped me with and not being too fazed by the many “floods” I caused in the lab. Dave and Nigel for again getting used to the late notice H&S forms and equipment grabs as well as teaching me how to use lots of interesting equipment. The Otago Regional Council and the Dunedin City Council Waste Water Business unit for land access, permission to install the gauging station and the data exchanges. To all the staff and residential leader team at Salmond College, you guys are the best and it would not feel like home without you. My mum and sister for always being supportive, you guys never fail to amaze me. Kane, for looking after me when it rains, coming to the sandfly central, late night laboratory dates and encouraging me all the way. iii Table of Contents Abstract .............................................................................................................................. ii Acknowledgements ........................................................................................................... iii Table of Contents ............................................................................................................. iv List of Tables ................................................................................................................... vii List of Figures ................................................................................................................... ix Chapter 1 Introduction ..................................................................................................... 1 Chapter 2 Solute, suspended sediment and bedloads: A theoretical review ............... 5 2.1 Hydro-chemistry, understanding solute loads ...................................................... 5 2.1.1 International and New Zealand solutes ........................................................ 5 2.1.2 Flow pathways and solute chemistry ............................................................ 7 2.1.3 Identification of solute sources ................................................................... 12 2.2 Fluvial geomorphology, understanding suspended sediment and bedload ........ 18 2.2.1 International and New Zealand suspended sediment and bedload ............. 18 2.2.2 Influences on river channel morphology ..................................................... 22 2.2.3 Sources and supply of sediments ................................................................. 25 2.2.4 Uncertainty around bedload measurement ................................................. 26 2.3 Research questions and expected outcomes ....................................................... 28 Chapter 3 Methods .......................................................................................................... 31 3.1 Research strategy ................................................................................................ 31 3.2 Field site description ........................................................................................... 33 3.2.1 Catchment characteristics ........................................................................... 33 3.2.2 Local climatological and hydrological patterns ......................................... 36 iv 3.3 Field equipment and methods ............................................................................. 38 3.3.1 Discharge .................................................................................................... 38 3.3.2 Surface water continuous measurements .................................................... 40 3.3.3 Surface water samples ................................................................................. 41 3.3.4 Total reach surveys ..................................................................................... 41 3.4 Laboratory analysis ............................................................................................ 42 3.4.1 Total dissolved solids analysis .................................................................... 42 3.4.2 Total suspended solids analysis .................................................................. 44 3.5 Data analysis ....................................................................................................... 45 3.5.1 Time series smoothing ................................................................................. 45 3.5.2 Total yearly and specific catchment loads .................................................. 46 3.5.3 Principal component analysis ..................................................................... 46 3.5.4 Hysteresis and chemo-graphs ..................................................................... 47 3.5.5 Ion analysis ................................................................................................. 47 3.5.6 Morphometric bedload calculation ............................................................. 47 3.5.7 Channel change 3D surface maps ............................................................... 49 Chapter 4 Results ............................................................................................................ 50 4.1 Silver Stream hydro-chemistry overview ........................................................... 50 4.2 Temporal trends and variation ............................................................................ 51 4.3 Factors influencing solutes and sediments ......................................................... 57 4.4 Solute and sediment loads .................................................................................. 58 4.5 Event flow hysteresis .......................................................................................... 62 4.6 Chemical composition ........................................................................................ 71 4.7 Bedload and geomorphic change ........................................................................ 75 4.8 Results summary ................................................................................................ 85 v Chapter 5 Discussion ....................................................................................................... 87 5.1 Solute chemistry ................................................................................................. 87 5.2 Suspended sediment dynamics ........................................................................... 93 5.3 Changes in channel reach form .......................................................................... 99 5.4 Collaboration of solutes, suspended sediments and Bedload ........................... 105 5.5 Limitations and future research