Purpose

Engineering and dredging strategies to manage sediment, along with river-scouring, can reveal older sediments. These present a unique opportunity to assess past sources of phosphorus (P) inputs into river sediments. We used the sediment concentrations of P, lead (Pb) and ^206/207Pb isotopes to produce ‘first-order’ estimates of the source (diffuse agricultural or sewage treatment) of phosphorus.

Materials and methods

Sediment cores (n = 30) were collected from the length of the non-tidal River Nene, a lowland river in eastern England. Cores were analysed for sediment elemental concentrations and Pb isotopes. Principal component analysis and linear regression modelling were used to assess the relationships between P, Pb and Pb isotopes. Monte-Carlo simulations and boot-strapping were undertaken to estimate, with 95% confidence intervals, the source of P in these sediments.

Results and discussion

Analysis of the relationships between P_Total, Pb_Total and ^206/207Pb isotope ratios suggested that sediments were deposited largely prior to the phasing out of tetra-ethyl Pb (Pb_BHT) from petrol. Regression models showed positive correlations between P_Total and Pb_Total (R² = 0.85). Principal component analysis suggested a strong sewage treatment signal for Pb and P enrichment. In the rural upper three water bodies, little sewage treatment work (STW)-derived P was found in the sediment, a consequence of limited STW input and greater sediment transport. In the more urbanised water bodies 4–6, ‘first-order estimates’ of STW P suggest that median concentrations were 30–40% of P_Total.

Conclusions

The strong relationships between Pb and P concentrations in river water provided the opportunity to use ^206/207Pb isotope ratios to calculate ‘first-order’ estimates of the proportion of P released from STWs in the historical sediment. Understanding the sources of historical sediment P can be used to assess the success of current sediment management strategies and to base further mitigation measures. Results suggest that whilst much recent sediment P is removed, the legacy sediment remains to contribute P to the water body. Thus, options regarding the practical removal of these sediments and the extent to which this would improve water P status need to be assessed and balanced against options such as further decreasing soil P or STW P stripping.

中文翻译：

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使用206/207 Pb同位素比估算低地河流系统历史沉积物中的磷源

目的

工程和疏strategies管理泥沙的策略，以及对河道的冲刷，可以揭示较旧的泥沙。这些为评估过去向河流沉积物中输入的磷（P）来源提供了独特的机会。我们使用了P，铅（Pb）和^206/207 Pb同位素的沉积物浓度对磷的来源（农业或污水处理的扩散）进行了“一级”估算。

材料和方法

沉积岩心（n  = 30）是从非潮汐河内内河（英格兰东部的低地河流）的长度收集的。分析岩心的沉积物元素浓度和Pb同位素。主成分分析和线性回归模型用于评估P，Pb和Pb同位素之间的关系。进行了蒙特卡洛模拟和引导分析，以95％的置信区间估算了这些沉积物中的P来源。

结果和讨论

对P _Total，Pb _Total和^206/207 Pb同位素比之间的关系进行分析表明，沉积物主要是在从汽油中逐步淘汰四乙基Pb（Pb _BHT）之前沉积的。回归模型显示P _Total和Pb _Total（R ² = 0.85）。主成分分析表明，Pb和P富集具有很强的污水处理信号。在农村上游三个水体中，在沉积物中发现的污水处理工作（STW）来源的P很少，这是由于STW输入受限和更大的泥沙输送量的结果。在城市化程度更高的水域4–6中，STW P的“一级估算”表明中值浓度为P _Total的30–40％。

结论

河流水中铅和磷浓度之间的紧密关系为利用^206/207铅同位素比计算历史沉积物中STW释放出的P的比例提供了“一级”估计。了解历史沉积物P的来源可用于评估当前沉积物管理策略的成功，并为进一步的缓解措施提供依据。结果表明，尽管去除了许多近期的沉积物P，但剩余的沉积物仍然可以为水体贡献P。因此，需要评估有关实际去除这些沉积物的选择方案以及在多大程度上可以改善水磷状况的方案，并与诸如进一步减少土壤磷或污水处理厂污水剥离等方案进行权衡。