Howden Nicholas J K, Burt Tim P, Worrall Fred, Whelan Michael J
Department of Civil Engineering, University of Bristol, Queen's Building, University Walk, Bristol, BS8 1TR, UK.
J Environ Monit. 2011 Mar;13(3):514-21. doi: 10.1039/c0em00722f. Epub 2011 Feb 23.
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 (NO(3)-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.
本文对四个35年的水质时间序列进行子采样，以考虑短期水文变异性对从短期监测数据得出的过程推断的潜在影响。数据包括两个硝酸盐（NO(3)-N）时间序列和两个溶解性有机碳（使用水色作为替代指标）时间序列。选择这四个集水区不仅是因为它们有长期记录，还因为这四个集水区差异很大：有高地和低地的，有农业和非农业的。使用多元线性回归来确定整个35年期间降雨和水文“记忆效应”的趋势及影响，然后使用移动窗口技术对序列进行子采样，窗口宽度在6到20年之间。结果表明，6到11年期间的分析受局部水文变异性影响更大，因此会给出关于长期趋势的误导性结果，而超过12年的时期往往更能代表潜在的系统行为。这很重要：如果使用此类分析监测数据的方法来验证集水区管理的变化，那么少于12年的监测期可能不足以证明潜在系统的变化。
