文献分享 | WR：富营养化河流集水区沉积物磷衰减和释放的时空动力学研究

沉积物可以减少上覆水中的磷(P)，并降低零级和一级沟渠和溪流的营养状况。如果沉积物中化学磷释放的风险很小，这些特征可以被视为从陆地动员磷和继续输送到河流系统之间的中间缓解特征。然而，风险评估很少基于时间尺度动态，尤其是沉积物和水体环境中的精细尺度。很少关注化学磷缓冲过程、沉积物的磷不稳定/难降解以及河流/水体中磷在较长季节性时间尺度上的水文动力学的精细时间组合的研究。本文利用BlackwaterTRACE（社区和环境跨界行动—2004年至2010年）有关的研究数据集（一项关于爱尔兰跨境地区分散和点源污染的研究和行动倡议），旨在填补受富营养化高度影响集水区沉积物-水-磷相互作用动态特征的知识空白。目标是，1) 研究作为营养物质迁移连续体中季节性中间过程的精细时间尺度下磷衰减和释放过程，2) 将这些结果纳入现有或改进的床层沉积物磷风险/效用概念模型中，以应用于富营养化管理。

Fig. 1. Catchment maps for Co. Monaghan (M) and Co. Armagh (A), and location in the Irish border area. Solid black lines indicate the stream network and inverted black triangles indicate sample sites. Sites MK and A8 at the catchment outlets are where synchronous hydrological and water quality (P) data were captured at high resolution. Sites MM, MB, MC and A8, A7, A4 are where bed sediment and water column P data were gathered.

Table 1 

Method used for sequential P fractionation of bed sediments based on a spectrum from labile to recalcitrant fractions. 

where published synchronous hydrological and water quality data could be combined with unpublished sediment P fractionation and EPC0 measurements at three sites in each of two of the study catchments (Co. Monaghan and Co. Armagh, Fig. 1). 

Fig. 2. Normalised discharge for the period 01/04/08 to 31/03/09 period in the Co. Monaghan (a) and Co. Armagh (b) catchments. Rainfall was measured within the Co. Monaghan catchment. Co. Armagh rainfall was taken from records covering the whole Blackwater River catchment.

Fig. 3. Time-series of P load and accumulated loads for the Co. Monaghan (a) and Co. Armagh (b) catchments, respectively.

Fig. 4. Discharge percentiles and the median P concentration (TP black circles; TRP white circles) in each percentile for Co. Monaghan (a) and Co. Armagh (b) catchments, respectively. Data are fitted with orthogonal polynomial regressions (TP black; TRP grey). Black arrows indicate a potential change-point between diffuse (right of arrow) and point (left of arrow) source pressures. White arrows indicate a further change point where point sources become disconnected (left of white arrow) at extreme low flows. 

Fig. 5. Scatter plots of EPC0 and DRP concentration, against 1:1 lines for the Co. Monaghan (a) and Co. Armagh (b) catchment sites. These data are also collated by catchment site as box-whisker plot ranges (c) indicating a mostly sedimentary P sink over the one year sampling period. Whiskers are calculated as 1.5 * interquartile ranges, and outliers (circles) are greater than these values.

Fig. 6. Phosphate Exchange Potential (PEP) in bed sediments (with stream TP concentration as context), with PEP trends shown as LOESS regressions in the Co. Monaghan (a) and Co. Armagh (b) catchment. More negative PEP values indicate a higher magnitude of P attenuation, and vice versa. 

Fig. 7. Box-whisker plots of Psenner P fractions at all catchment sites shown as a proportion contribution to the sum of fractions. 

Fig. 8. The development of total and labile to recalcitrant sediment P fractions shown alongside the accumulating P load as measured at the catchment outlets (MM – Fig. 8a) and at upstream sites (MB and MC, Fig. 8b and c) in the Co. Monaghan catchment. 

Fig. 9. The development of total and labile to recalcitrant sediment P fractions shown alongside the accumulating P load as measured at the catchment outlet (A8 – Fig. 9a) and at upstream sites (A7 and A4, Fig. 9b and c) in the Co. Armagh catchment. For legend see Fig. 8.

本研究利用沉积物磷酸盐交换势(PEP，常用来反映平衡态磷浓度EPC0和溶解态反应磷DRP之间的浓度差异，即当EPC0>DRP时，床层沉积物是缓冲层，限制DRP向上覆水中的移动)、河流/沟渠沉积物中的磷组分以及受影响流域的磷质量负荷的同步数据集，表明了沉积物磷在时间和空间上的瞬态变化特征。河流沉积物中磷的增加和损失是动态变化的且和不同磷组分相关。PEP强度是动态变化，尽管存在高度不稳定的沉积磷部分，但很少达到饱和状态，即并没有表明沉积物中化学磷释放的潜力（大部分分布低于或接近于零）。PEP结果表明空间和时间变化很可能是由暴雨事件期间源断开/重新连接和沉积物流动引起的，从高衰减潜力时期转变为接近饱和时期。然而，这本身可能是一种误导性的风险评估，因为由物理原因导致的磷释放，尤其是沉积物中不稳定的碳酸氢盐-连二亚硫酸盐(B-D)P部分，是暴雨事件期间磷迁移的更主要的过程，尤其在连续的夏季暴雨事件过程中减少了84%；并且在风暴之后更容易重新积累，这种积累可能是由于化学过程造成的。监测到离开集水区的总磷和总反应磷负荷与这些变化一致。这种间歇性磷释放的具体下游营养效应需要根据其生物利用度并结合其他更受关注的分散和点磷源过程进行评估。

  文章信息

S. Lia, J. Arnscheidta, R. Cassidyb, R.W. Douglasa, H.J. McGrogana, P. Jordan. The spatial and temporal dynamics of sediment phosphorus attenuation and release in impacted stream catchments [J]. Water Research, 2023, 245, 120663.

  DOI:

https://doi.org/10.1016/j.watres.2023.120663

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郭晨茜 | 供稿

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