The nitrate time bomb: a numerical way to investigate nitrate storage and lag time in the unsaturated zone
The nitrate time bomb: a numerical way to investigate nitrate storage and lag time in the unsaturated zone
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DOI：
10.1007/s10653-013-9550-y
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发表时间：
2013-10-01
影响因子：
4.2
通讯作者：
Bloomfield, J. P.
中科院分区：
文献类型：
--
作者：
Wang, L.;Butcher, A. S.;Bloomfield, J. P.
地下水中的硝酸盐污染主要来自农业活动，仍然是一个国际问题。它威胁着环境、经济和人类健康。英国许多地下水体的硝酸盐浓度呈上升趋势。研究表明，由于硝酸盐的“储存”及其在不饱和和饱和区域的潜在传播时间较长，从土壤中浸出的硝酸盐可能需要数十年的时间才能排入地下水和地表水。然而，在当前的水硝酸盐管理和政策制定中很少考虑这一时间滞后。本研究的目的是开发一种流域规模的综合数值方法来研究地下水系统中硝酸盐的滞后时间，并选择英国伊甸谷作为案例研究区域。该方法涉及三个模型，即硝酸盐定时炸弹——模拟非饱和区（USZ）硝酸盐迁移的基于过程的模型、GISGroundwater——GIS地下水流模型和N-FM——模拟饱和区硝酸盐迁移的模型。这项研究回答了目前地下水中的硝酸盐何时进入不饱和区域并最终达到地下水位的科学问题；是历史硝酸盐负荷引起的研究区域地下水硝酸盐浓度的上升；是什么原因导致研究区地下水硝酸盐浓度分布不均匀；历史峰值硝酸盐负荷是否已达到该地区的地下水位。该地区地下水硝酸盐主要集中在1980年代至2000年代，而大部分水源保护区的地下水硝酸盐在1940年代至1970年代淋滤进入系统；超临界带厚度大且空间变化大是研究区地下水硝酸盐浓度分布不均匀的主要原因之一； 1983 年左右的硝酸盐峰值负荷影响了大部分研究区域。对于 Bowscar、Beacon Edge、Low Plains、Nord Vue、Dale Springs、Gamblesby、Bankwood Springs 和 Cliburn 周边地区，硝酸盐峰值负荷将在未来 34 年内达到地下水位；统计分析表明，8.7%的Penrith砂岩和7.3%的St Bees砂岩没有受到硝酸盐峰值的影响。该研究可以提高对地下水系统中硝酸盐过程的科学认识，为研究区地下水硝酸盐污染的有效管理提供支持。由于参数数量有限，本研究开发的方法和模型可以很容易地转移到其他领域。
Nitrate pollution in groundwater, which is mainly from agricultural activities, remains an international problem. It threatens the environment, economics and human health. There is a rising trend in nitrate concentrations in many UK groundwater bodies. Research has shown it can take decades for leached nitrate from the soil to discharge into groundwater and surface water due to the 'store' of nitrate and its potentially long travel time in the unsaturated and saturated zones. However, this time lag is rarely considered in current water nitrate management and policy development. The aim of this study was to develop a catchment-scale integrated numerical method to investigate the nitrate lag time in the groundwater system, and the Eden Valley, UK, was selected as a case study area. The method involves three models, namely the nitrate time bomb-a process-based model to simulate the nitrate transport in the unsaturated zone (USZ), GISGroundwater-a GISGroundwater flow model, and N-FM-a model to simulate the nitrate transport in the saturated zone. This study answers the scientific questions of when the nitrate currently in the groundwater was loaded into the unsaturated zones and eventually reached the water table; is the rising groundwater nitrate concentration in the study area caused by historic nitrate load; what caused the uneven distribution of groundwater nitrate concentration in the study area; and whether the historic peak nitrate loading has reached the water table in the area. The groundwater nitrate in the area was mainly from the 1980s to 2000s, whilst the groundwater nitrate in most of the source protection zones leached into the system during 1940s-1970s; the large and spatially variable thickness of the USZ is one of the major reasons for unevenly distributed groundwater nitrate concentrations in the study area; the peak nitrate loading around 1983 has affected most of the study area. For areas around the Bowscar, Beacon Edge, Low Plains, Nord Vue, Dale Springs, Gamblesby, Bankwood Springs, and Cliburn, the peak nitrate loading will arrive at the water table in the next 34 years; statistical analysis shows that 8.7 % of the Penrith Sandstone and 7.3 % of the St Bees Sandstone have not been affected by peak nitrate. This research can improve the scientific understanding of nitrate processes in the groundwater system and support the effective management of groundwater nitrate pollution for the study area. With a limited number of parameters, the method and models developed in this study are readily transferable to other areas.