Aquatic Ecosystem Research, Faculty of Biology, University of Duisburg-Essen, Essen, Germany.
Aquatic Microbiology, Environmental Microbiology and Biotechnology, Faculty of Chemistry, University of Duisburg-Essen, Essen, Germany.
Sci Total Environ. 2024 May 20;926:171849. doi: 10.1016/j.scitotenv.2024.171849. Epub 2024 Mar 25.
Urban streams are exposed to a variety of anthropogenic stressors. Freshwater salinization is a key stressor in these ecosystems that is predicted to be further exacerbated by climate change, which causes simultaneous changes in flow parameters, potentially resulting in non-additive effects on aquatic ecosystems. However, the effects of salinization and flow velocity on urban streams are still poorly understood as multiple-stressor experiments are often conducted at pristine rather than urban sites. Therefore, we conducted a mesocosm experiment at the Boye River, a recently restored stream located in a highly urbanized area in Western Germany, and applied recurrent pulses of salinity along a gradient (NaCl, 9 h daily of +0 to +2.5 mS/cm) in combination with normal and reduced current velocities (20 cm/s vs. 10 cm/s). Using a comprehensive assessment across multiple organism groups (macroinvertebrates, eukaryotic algae, fungi, parasites) and ecosystem functions (primary production, organic-matter decomposition), we show that flow velocity reduction has a pervasive impact, causing community shifts for almost all assessed organism groups (except fungi) and inhibiting organic-matter decomposition. Salinization affected only dynamic components of community assembly by enhancing invertebrate emigration via drift and reducing fungal reproduction. We caution that the comparatively small impact of salt in our study can be due to legacy effects from past salt pollution by coal mining activities >30 years ago. Nevertheless, our results suggest that urban stream management should prioritize the continuity of a minimum discharge to maintain ecosystem integrity. Our study exemplifies a holistic approach for the assessment of multiple-stressor impacts on streams, which is needed to inform the establishment of a salinity threshold above which mitigation actions must be taken.
城市溪流受到各种人为压力源的影响。淡水盐化是这些生态系统的一个关键压力源，预计气候变化将进一步加剧这一问题，因为气候变化会同时改变水流参数，可能对水生生态系统产生非加性影响。然而，由于多压力源实验通常在原始而非城市地点进行，因此，盐度和流速对城市溪流的影响仍知之甚少。因此，我们在 Boye 河进行了一个中观实验，Boye 河是一条位于德国西部高度城市化地区的新近恢复的溪流，并沿着梯度（NaCl，每天 9 小时，+0 至+2.5 mS/cm）施加反复的盐度脉冲，同时结合正常和降低的流速（20 cm/s 与 10 cm/s）。我们使用跨多个生物群（大型无脊椎动物、真核藻类、真菌、寄生虫）和生态系统功能（初级生产、有机物质分解）的综合评估，表明流速降低具有普遍影响，导致几乎所有评估的生物群（除真菌外）发生群落转移，并抑制有机物质分解。盐度仅通过通过漂移增强无脊椎动物迁徙和减少真菌繁殖来影响群落组装的动态成分。我们警告说，在我们的研究中，盐的相对较小的影响可能是由于 30 多年前煤炭开采活动造成的过去盐污染的遗留效应。尽管如此，我们的结果表明，城市溪流管理应优先考虑最小流量的连续性，以维持生态系统的完整性。我们的研究例证了一种综合方法，用于评估对溪流的多压力源影响，这对于确定必须采取缓解措施的盐度阈值非常重要。
