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Issue 3, 2011
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Monitoring fluvial water chemistry for trend detection: hydrological variability masks trends in datasets covering fewer than 12 years

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Abstract

This paper sub-samples four 35 year water quality time series to consider the potential influence of short-term hydrological variability on process inference derived from short-term monitoring data. The data comprise two time series for nitrate (NO3-N) and two for DOC (using water colour as a surrogate). The four catchments were selected not only because of their long records, but also because the four catchments are very different: upland and lowland, agricultural and non-agricultural. Multiple linear regression is used to identify the trend and effects of rainfall and hydrological ‘memory effects’ over the full 35 years, and then a moving-window technique is used to subsample the series, using window widths of between 6 and 20 years. The results suggest that analyses of periods between six and eleven years are more influenced by local hydrological variability and therefore provide misleading results about long-term trends, whereas periods of longer than twelve years tend to be more representative of underlying system behaviour. This is significant: if such methods for analysing monitoring data were used to validate changes in catchment management, a monitoring period of less than 12 years might be insufficient to demonstrate change in the underlying system.

Graphical abstract: Monitoring fluvial water chemistry for trend detection: hydrological variability masks trends in datasets covering fewer than 12 years

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Publication details

The article was received on 28 Nov 2010, accepted on 12 Jan 2011 and first published on 23 Feb 2011


Article type: Paper
DOI: 10.1039/C0EM00722F
J. Environ. Monit., 2011,13, 514-521

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    Monitoring fluvial water chemistry for trend detection: hydrological variability masks trends in datasets covering fewer than 12 years

    N. J. K. Howden, T. P. Burt, F. Worrall and M. J. Whelan, J. Environ. Monit., 2011, 13, 514
    DOI: 10.1039/C0EM00722F

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