La Croix, Andrew D.Greaves, Nicole2026-06-022026-06-022025https://hdl.handle.net/10289/18311The nuances of the dynamic changes in the water chemistry and sediment deposition within the fluvial to marine transition zone (FMTZ) are difficult and time consuming to capture within water samples as due to the constantly changing nature. Marine water intrusion up rivers changes along short time scales of minutes, hours, and days to months and years. To be able to accurately capture the extent and changes that occur along the FMTZ would provide vital environmental and depositional information regarding river health, temporal variations and forming depositional environments. The use of geochemical sediment proxies as a measure of marine water intrusion upstream is an ongoing topic of research with many potential proxies investigated throughout literature. However, the identification of proxies that represent not only the general movement from fresh to brackish to marine conditions but can also be used to distinguish a gradient along river position as recording the finer changes in water chemistry have yet to be demonstrated within literature. This study aims to identify whether the dynamics of marine water intrusion are recorded through sediment geochemistry or physical properties along a gradient and to assess the uses for the proxies identified, creating an assemblage of proxies to be utilised within future study. Sediment proxies of grainsize, percentage mud (%mud), loss on ignition (LOI), strontium and barium ratios (Sr/Ba), carbon isotopes of delta thirteen carbon (δ13C) and carbon and nitrogen ratios (C/N), X-Ray diffraction (XRD) minerology, and X-ray fluorescence (XRF) elements, will be investigated as potential proxies for marine water intrusion up the FMTZ of the lower Waihou River, Aotearoa, New Zealand. This research finds that whilst varying levels of success were demonstrated within literature, many of the tested proxies fail to identify the fluvial to marine transition let alone distinguish a gradient of change through river position. Strontium/Barium ratios are the only proxy to identify a clear relationship with river distance, presenting with a weak to moderate relationship, finding a lack of small scale precision but the larger scale transition was observed. The carbon isotope results presented a negligible relationship but indicated it may have potential use as a proxy, which prompts the need for further study of the usage of this method as a proxy for marine water intrusion. Whilst this study does not claim to disregard the usefulness of these proxies nor their potential for identifying the hydrodynamics of the FMTZ within the sediment, it does stand that little evidence of it has been found within this research and prompts the thorough investigation of the potential held by these proxies both within the Waihou River and various other river systems of varying size and type where processes vary. Consideration to the type of river environments literature seems to focus on is also prompted as to whether these proxies may only be viable under certain conditions.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.Thesis