Presentation: Scales and Balances: The use of dimensionless numbers to characterize transport, reaction and ecohydraulic connectivity.
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Biographical Information: Carolyn Oldham is Winthrop Professor at the University of Western Australia in the School of Environmental Systems Engineering. She earned a BSc with Honors in Chemistry and a PhD in Environmental Engineering for an investigation into the effects of turbulence on oxygen patchiness in a lake. Since 1994, Carolyn has worked to integrate her cross-disciplinary research interests in transport processes, environmental chemistry and spatial and temporal patchiness. This focus on cross-disciplinary integration, i.e. trans-disciplinary research, has led Carolyn to collaborate with hydrologists, oceanographers, estuarine and groundwater scientists. She has led a diverse range of research projects on arsenic contamination of wetlands, rivers and ground waters, fate and transport of decomposing seagrass wrack in coastal waters, groundwater nitrogen plumes into coastal waters, prediction of contaminant dynamics after mine closure, and acidification dynamics in surface and ground waters. While the context of Carolyn’s research has been, and remains, extremely diverse, she has worked to integrate approaches and frameworks across multiple disciplines and has maintained her core interest in the interactions between transport and biogeochemical transformation processes, with a focus on patchiness and connectivity dynamics at system, local and micro scales.
Assessing the potential for transfer or export of biogeochemicals or pollutants from aquatic systems is of primary importance under changing land use and climatic conditions. Over the past decade the connectivity/disconnectivity dynamics of aquatic systems and catchments have been related to their potential to export material, however we continue to use multiple definitions of connectivity, and most have focused strongly on physical (hydrologicaly or hydraulic) connectivity. In this presentation we define ecohydraulic connectivity as the ability of matter and organisms to transfer within and between elements of the hydrological cycle while undergoing biogeochemical transformation. The connectivity/disconnectivity dynamic must take into account the opportunity for a given reaction to occur during transport and/or isolation. Using this definition, we propose three distinct regimes: I) which is ecohydraulically connected and diffusion dominated; II) which is ecohydraulically connected and advection dominated and III) which is both hydraulically and ecohydraulically disconnected. Within each regime we propose the use of a new non-dimensional number, NE, to compare exposure timescales with reactions timescales. NE is reaction-specific and allows the estimation of relevant spatial scales over which the reactions of interest are taking place. Case studies provide examples of how NE can be used to gain insight into the biogeochemical processes that are significant under the specified conditions. Finally, we explore the implications of this framework for improved water management, for our understanding of biodiversity, resilience and biogeochemical competitiveness under specified conditions.