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Sensitivity of river eutrophication to multiple stressors illustrated using graphical summaries of physics-based river water quality model simulations

Hutchins, Michael G.; Hitt, Olivia E.. 2019 Sensitivity of river eutrophication to multiple stressors illustrated using graphical summaries of physics-based river water quality model simulations. Journal of Hydrology, 577, 123917. 11, pp. https://doi.org/10.1016/j.jhydrol.2019.123917

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Abstract/Summary

The severity of river eutrophication is influenced by multiple stressors which reflect a wide-ranging variety of drivers encompassing land management, population growth and climatic effects. Experimental studies have successfully identified response to single or paired stressors under controlled conditions in small streams but have limited capability to characterise larger systems influenced by a wider variety of stressors. Here, a physics-based water quality model of the River Thames (UK) is used to explore the impacts of water temperature, phosphate concentration, river flow, urbanisation and riparian shading on indicators of chlorophyll and dissolved oxygen concentration by way of a sensitivity analysis. To understand the impact of model structural uncertainty, results are presented from two alternative formulations of the biological response. All outputs from each unique combination of stressors are presented in one graphic comprising multiple sub-plots that display the results of thousands of model runs simultaneously. Consequently, graphical analysis allows us to pinpoint under what circumstances reductions in key variables representing management-related stressors (i.e. lowering phosphorus concentrations and establishing riparian shading) may act synergistically, antagonistically or simply in an additive manner. Furthermore, we identify how these relationships may vary under different river flow and water temperature regimes and changes in abstraction and effluent discharge rates, to indicate the likely influence of future climate and population growth. Response can vary markedly depending on the choice of biological model and also changes considerably downstream along the river system. Chlorophyll indicators consistently show antagonistic responses to reduction in stressors whereas dissolved oxygen indicators show varied and complex responses. As expected, increases in phosphorus loading are detrimental, but so too are large decreases. Whilst the analysis suggests that urbanisation impacts are in general not expected to be large, changes in water demand brought about by population growth have disproportionate effects at low flows. These may result in increased incidence of very low dissolved oxygen concentrations which damage the health of the ecosystem.

Item Type: Publication - Article
Digital Object Identifier (DOI): https://doi.org/10.1016/j.jhydrol.2019.123917
UKCEH and CEH Sections/Science Areas: Pollution (Science Area 2017-)
Water Resources (Science Area 2017-)
ISSN: 0022-1694
Additional Keywords: eutrophication, river water quality model, River Thames, graphical analysis, multi-stressors
NORA Subject Terms: Ecology and Environment
Date made live: 15 Jul 2019 11:32 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/524300

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