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Changing climate and nutrient transfers : evidence from high temporal resolution concentration-flow dynamics in headwater catchments.

Ockenden, M.C. and Deasy, C.E. and Benskin, C.McW.H. and Beven, K.J. and Burke, S. and Collins, A.L. and Evans, R. and Falloon, P.D. and Forber, K.J. and Hiscock, K.M. and Hollaway, M.J. and Kahana, R. and Macleod, C.J.A. and Reaney, S.M. and Snell, M.A. and Villamizar, M.L. and Wearing, C. and Withers, P.J.A. and Zhou, J.G. and Haygarth, P.M. (2016) 'Changing climate and nutrient transfers : evidence from high temporal resolution concentration-flow dynamics in headwater catchments.', Science of the total environment., 548-549 .


We hypothesise that climate change, together with intensive agricultural systems, will increase the transfer of pollutants from land to water and impact on stream health. This study builds, for the first time, an integrated assessment of nutrient transfers, bringing together a) high-frequency data from the outlets of two surface water-dominated, headwater (~ 10 km2) agricultural catchments, b) event-by-event analysis of nutrient transfers, c) concentration duration curves for comparison with EU Water Framework Directive water quality targets, d) event analysis of location-specific, sub-daily rainfall projections (UKCP, 2009), and e) a linear model relating storm rainfall to phosphorus load. These components, in combination, bring innovation and new insight into the estimation of future phosphorus transfers, which was not available from individual components. The data demonstrated two features of particular concern for climate change impacts. Firstly, the bulk of the suspended sediment and total phosphorus (TP) load (greater than 90% and 80% respectively) was transferred during the highest discharge events. The linear model of rainfall-driven TP transfers estimated that, with the projected increase in winter rainfall (+ 8% to + 17% in the catchments by 2050s), annual event loads might increase by around 9% on average, if agricultural practices remain unchanged. Secondly, events following dry periods of several weeks, particularly in summer, were responsible for high concentrations of phosphorus, but relatively low loads. The high concentrations, associated with low flow, could become more frequent or last longer in the future, with a corresponding increase in the length of time that threshold concentrations (e.g. for water quality status) are exceeded. The results suggest that in order to build resilience in stream health and help mitigate potential increases in diffuse agricultural water pollution due to climate change, land management practices should target controllable risk factors, such as soil nutrient status, soil condition and crop cover.

Item Type:Article
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Publisher statement:© 2019 This manuscript version is made available under the CC-BY-NC-ND 4.0 license
Date accepted:No date available
Date deposited:21 October 2019
Date of first online publication:2016
Date first made open access:21 October 2019

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