Bech Tina B, Hellal Jennifer, Badawi Nora, Jakobsen Rasmus, Aamand Jens
Department of Geochemistry, Geological Survey of Denmark and Greenland, GEUS, Øster Voldgade 10, Copenhagen DK-1350, Denmark; Rambøll Danmark A/S, Hannemanns Allé 53, Copenhagen 2300, Denmark.
BRGM, Orléans F-45071, France.
Water Res. 2023 Aug 15;242:120174. doi: 10.1016/j.watres.2023.120174. Epub 2023 Jun 4.
Contamination of rivers by nitrate and pesticides poses a risk for aquatic ecosystems in lowland catchments that are often intensively used for agriculture. Here, the hyporheic zone, the streambed underneath the stream, plays a vital role due to its efficient self-purification capacity. The present study aims to evaluate the denitrification and transformation potential of 14 pesticides and three transformation products in the hyporheic sediment from a lowland stream with a high N load and by comparing an agricultural straightened section to a natural meandering part of the stream influenced by different groundwater discharges. Batch experiments were set up to evaluate the denitrification and pesticide transformation potentials in hyporheic sediment from two depths (5-15 cm (a) and 15-25 cm (b)). Our results revealed that (i) differences between the agricultural and natural sections of the river did not influence pollutant attenuation, (ii) both the nitrate and pesticide attenuation processes were more rapid in the upper "a" layer compared to the "b" layer due to higher microbial abundance, (iii) high groundwater discharge reduced the denitrification potential while pesticide transformation was unaffected, (iv) denitrification correlated with denitrifier abundance (nirK) in the "b" layer, while this correlation was not seen in the "a" layer, and (v) a microbial community with low diversity can explain limited transformation for the majority of tested pesticides. Overall, our results suggest that high groundwater discharge zones with reduced residence time in the hyporheic zone can be an important source of pesticides and nitrate to surface water.
硝酸盐和农药对河流的污染给低地集水区的水生生态系统带来了风险，这些集水区通常被密集用于农业生产。在这里，河底潜流带，即溪流下方的河床，因其高效的自我净化能力而发挥着至关重要的作用。本研究旨在评估来自一个氮负荷高的低地溪流的河底潜流沉积物中14种农药和三种转化产物的反硝化和转化潜力，并通过比较农业拉直段与受不同地下水排放影响的溪流自然蜿蜒段来进行评估。设置了批次实验来评估两个深度（5 - 15厘米（a）和15 - 25厘米（b））的河底潜流沉积物中的反硝化和农药转化潜力。我们的结果表明：（i）河流农业段和自然段之间的差异不影响污染物的衰减；（ii）由于微生物丰度较高，与“b”层相比，上层“a”层中的硝酸盐和农药衰减过程更快；（iii）高地下水排放降低了反硝化潜力，而农药转化不受影响；（iv）反硝化与“b”层中的反硝化菌丰度（nirK）相关，而在“a”层中未观察到这种相关性；（v）多样性低的微生物群落可以解释大多数测试农药的有限转化。总体而言，我们的结果表明，在河底潜流带停留时间缩短的高地下水排放区可能是地表水农药和硝酸盐的重要来源。
