Temporal and spatial analysis of nitrate concentrations from the Frome and Piddle catchments in Dorset (UK) for water years 1978 to 2007: Evidence for nitrate breakthrough?
Temporal and spatial analysis of nitrate concentrations from the Frome and Piddle catchments in Dorset (UK) for water years 1978 to 2007: Evidence for nitrate breakthrough?
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DOI：
10.1016/j.scitotenv.2008.08.042
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发表时间：
2008-12-15
影响因子：
9.8
通讯作者：
Burt, T. P.
中科院分区：
文献类型：
--
作者：
Howden, N. J. K.;Burt, T. P.
本文分析了 1978 年至 2007 年期间英格兰南部弗罗姆和皮德尔流域 35 个地点的硝酸盐浓度时间序列。皮德尔流域完全位于其上游的白垩含水层内，而弗罗姆河的源头是白垩和其他岩性的混合物；两条河流流经下游的古近纪沙子和粘土，然后注入普尔港。在每个站点，观察到的变化来源源于样本月份（季节性）和年份（基本趋势）之间的差异。考虑到水年平均浓度，除两个地点外，所有地点都与年份存在强烈且高度显着的正相关性。皮德尔河的年增长率往往高于弗罗姆河，而在这两个流域中，年增长率往往在下游下降；这两种影响都与地下水影响的程度有关。除了强劲的上升趋势外，大多数站点硝酸盐浓度还存在明显的季节周期；振幅通常在下游增加。抛开线性假设，溶质突破曲线（S 曲线）适合 36 个硝酸盐时间序列中的 34 个。结果表明，S 曲线的应用可以恰当地描述年平均浓度随时间的变化，并且在大多数情况下比线性模型有所改进。对这些以地下水为主的流域中硝酸盐浓度上升的解释从统计基础转向水文过程基础，为了解低地流域功能提供了宝贵的见解。 (C) 2008 Elsevier B.V. 保留所有权利。
This paper analyses time series of nitrate concentration for 35 sites throughout the Frome and Piddle catchments in southern England for the period 1978-2007. The Piddle catchment lies wholly within the Chalk aquifer in its upper reaches, whereas the headwaters of the Frome are a mixture of Chalk and other lithologies; both rivers flow across Palaeogene sands and clays in their lower reaches, before discharging into Poole Harbour. At each site sources of observed variation arise from differences between sample month (seasonality) and year (underlying trend). Considering water year mean concentrations, there is a strong and highly significant positive correlation with year for all but two sites. The annual rate of increase tends to be higher in the Piddle than the Frome, and in both catchments the annual rate of increase tends to decrease downstream; both these effects relate to the degree of groundwater influence. In addition to the strong upward trend, there is also a clear seasonal cycle in nitrate concentration at most sites; amplitude generally increases downstream. Laying aside the assumption of linearity, solute breakthrough curves (S-curves) are fitted to 34 of the 36 nitrate time series. Results show that application of S-curves is an appropriate description of changes in annual mean concentrations over time and provides improvements over linear models in most cases. The interpretation of rising nitrate concentrations in these groundwater-dominated catchments moves from a statistical to a hydrological process base, providing valuable insight into lowland catchment function. (C) 2008 Elsevier B.V. All rights reserved.