Burt T P, Howden N J K, Worrall F, Whelan M J
Department of Geography, Durham University, Durham, DH1 3LE, UK.
J Environ Monit. 2010 Jan;12(1):71-9. doi: 10.1039/b913003a. Epub 2009 Sep 17.
Long records of river water quality are invaluable for helping to understand the biogeochemistry of hydrological systems. They allow relationships to be established between changes in water quality (including seasonal cycles, episodic responses and long-term trends) and potential drivers, such as climatic forcing or human activity; they can act as a stimulus for process-oriented experimental research; they can be used to help to make predictions about future temporal and spatial patterns; and they can help to guide management options to mitigate water pollution. In this paper we present the case in favour of maintaining some long records of river water nitrate concentration at "benchmark" sites, in terms of enhancing process understanding and identifying system lags. Many long-term time series of nitrate concentration data share similar features including a pronounced seasonality characterised by a clear winter maximum, an upward trend in the post-war period followed by a levelling off, or even a decline in the last 20 years, and unusually high concentrations following drought years. Concentrations in any one year are often dependent on conditions in previous years; relationships can be established between concentrations and hydrological drivers (such as rainfall) with different lag periods which can yield information about supply or transport limitations to nitrate transfers. The interpretation of any record is dependent on its length: short records have a high potential for misinterpretation. Often, the value of long records only becomes apparent when analysed in retrospect, perhaps yielding insight into processes and phenomena for which the data collection programme was not originally designed. We, therefore, urge monitoring agencies to devise a strategy for maintaining long records--at least for a few benchmark stations.
长期的河流水质记录对于帮助理解水文系统的生物地球化学具有极高价值。它们有助于建立水质变化（包括季节性循环、偶发响应和长期趋势）与潜在驱动因素（如气候强迫或人类活动）之间的关系；可以激发以过程为导向的实验研究；可用于预测未来的时空模式；还能帮助指导减轻水污染的管理方案。在本文中，我们阐述了支持在“基准”站点维持一些河流水体硝酸盐浓度长期记录的理由，这有助于增强对过程的理解并识别系统滞后现象。许多硝酸盐浓度数据的长期时间序列具有相似特征，包括明显的季节性，以冬季明显最高值为特点；战后时期呈上升趋势，随后趋于平稳，甚至在过去20年出现下降；干旱年份后浓度异常高。任何一年的浓度往往取决于前几年的情况；浓度与水文驱动因素（如降雨）之间可建立不同滞后期的关系，这能提供有关硝酸盐转移的供应或运输限制的信息。对任何记录的解读都取决于其长度：短记录极易被误解。通常，长期记录的价值只有在事后分析时才会显现，或许能洞察到数据收集计划最初并未设计涵盖的过程和现象。因此，我们敦促监测机构制定一项维持长期记录的策略——至少针对一些基准站点。
