Levin, Jonathan Chaim2024-10-222024-10-222024Levin, Jonathan Chaim. (2024). Tracing multiple aquatic ecosystem stressors across a land-use intensification gradient: A multi-tooled environmental forensic approach[PhD thesis, University of the Witwatersrand, Johannesburg]. WireDSpace.https://hdl.handle.net/10539/41802https://hdl.handle.net/10539/41802A thesis submitted to the Faculty of Science in the fulfillment of the requirements for the degree of Doctor of Philosophy in Ecohydrology In the School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg 2024South Africa requires advanced freshwater management approaches to address complex catchment stressors acting on aquatic ecosystems. An environmental forensics toolbox could help disentangle pollution sources, informing stressor-focused adaptive management. Existing national, spatial resource strategies that define aquatic resource objectives, overlook modelling different aquatic stressor-linked components across spatio-temporal scales to disentangle individual stressor effects along land-use intensification gradients. This thesis investigated how spatio-temporal, physico-chemical water quality parameters, dissolved and sediment-bound trace metals as well as fish tissue δ34S all collected from 15 river sites in the tributaries of the Gwathle River Catchment, positioned in the Platinum Belt of South Africa across a land-use intensification gradient, can be used to disentangle aquatic stressors. Through using a spatio-temporal generalised linear mixed effects model (GLMM) approach, the importance of employing a multi-hydrological-spatial (sub-basin, cumulative basin and riparian buffer) scale approach to link stressors (drivers) to changes in key catchment water quality parameters as opposed to a single scale approach was identified. At the sub-basin scale, ammonium concentrations were best explained by urban stress through wastewater effluent, Cu increased with mining via leaching from pollution control dams and mineral discharges, while turbidity increased with higher agricultural coverage, following greater tillage practices and irrigation. River pH was positively predicted for by slope heterogeneity at the cumulative-basin scale, while sulfate increased with mining at the cumulative 100 m riparian buffer, from leaching and discharges. Dissolved inorganics, including trace metals, are routinely assessed in national aquatic resource assessments, yet metals in sediments demonstrating legacy effects, are yet to be integrated. Using geo-spatial models across seasons, dissolved and sediment Cr concentrations were found to be driven primarily by mining both at the sub-basin scale, while dissolved Zn concentrations reflected sub-basin lithology and sediment-bound Zn reflected cumulative basin scale urban stress and lithology. Concordance correlation indicated that the Cr had a substantial positive stress-tracking agreement between the two media, with both tracking Cr land-use intensification gradient inputs while Zn displayed negligible concordance. While fish tissue δ15N has been used to trace nutrient pollution, no local or international research has assessed time-integrated fish tissue δ34S as a sulfur stress-tracer from interacting urban, agricultural and mining stressors. Using a spatio- temporal GLMM modelling approach, it was found to be possible to distinguish key agricultural and mining stressors on aquatic ecosystems, with δ34S being relatively enriched following sub-basin scale agriculture and relatively depleted following cumulative basin scale mining activities. The outcomes of this research expands our knowledge base on using aquatic physico-chemical parameters, inorganic media indicators, and biotic tracers, towards the development of a potential environmental forensic toolbox to elucidate complex pollution sources and pathways for enhanced catchment management and freshwater governance in South Africa.en© 2024 University of the Witwatersrand, Johannesburg. All rights reserved. The copyright in this work vests in the University of the Witwatersrand, Johannesburg. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of University of the Witwatersrand, Johannesburg.Geographic information systemsBiogeochemistryTrace metalsStable isotopesPollution tracingStatistical modellingManagement toolboxEcohydrologyUCTDSDG-15: Life on landThesisUniversity of the Witwatersrand, Johannesburg