Faculty of Science and Technology, the University of the Basque Country (UPV/EHU), PO Box 644, 48080 Bilbao, Spain.
Catalan Institute for Water Research (ICRA), Carrer Emili Grahit 101, 17003 Girona, Spain.
Ecotoxicol Environ Saf. 2019 Mar;169:960-970. doi: 10.1016/j.ecoenv.2018.11.103. Epub 2018 Dec 12.
Effluents from urban wastewater treatment plants (WWTP) consist of complex mixtures of substances that can affect processes in the receiving ecosystems. Some of these substances (toxic contaminants) stress biological activity at all concentrations, while others (e.g., nutrients) subsidize it at low concentrations and stress it above a threshold, causing subsidy-stress responses. Thus, the overall effects of WWTP effluents depend mostly on their composition and the dilution capacity of the receiving water bodies. We assessed the immediate and legacy effects of WWTP effluents in artificial streams, where we measured the uptake of soluble reactive phosphorus (SRP) by the biofilm, biomass accrual, benthic metabolism and organic matter decomposition (OMD). In a first phase (32 d), the channels were subjected to a gradient of effluent contribution, from pure stream water to pure effluent. WWTP effluent affected the ecosystem processes we measured, although we found no clear subsidy-stress patterns except for biofilm biomass accrual. Instead, most of the processes were subsidized, although they showed complex and process-specific patterns. Benthic metabolism and OMD were subsidized without saturation, as they peaked at medium and high levels of pollution, respectively, but they never fell below control levels. SRP uptake was the only process that decreased with increasing effluent concentration. In a second phase of the experiment (23 d), all channels were kept on pure stream water to analyse the legacy effects of the effluent. For most of the processes, there were clear legacy effects, which followed either subsidy, stress, or subsidy-stress patterns. SRP uptake capacity was stressed with increasing pollution legacy, whereas algal accrual and benthic metabolism continued being subsidized. Conversely, biofilm biomass accrual and OMD showed no legacy effects. Overall, the WWTP effluent caused complex and process-specific responses in our experiment, mainly driven by the mixed contribution of subsidizers and stressors. These results help improving our understanding of the effects of urban pollution on stream ecosystem functioning.
城市污水处理厂（WWTP）的废水由可影响受纳生态系统中过程的物质的复杂混合物组成。这些物质中的一些（有毒污染物）在所有浓度下都会对生物活性造成压力，而另一些物质（例如营养物）则在低浓度下支持生物活性，在超过阈值时对生物活性造成压力，从而导致补贴-压力反应。因此，WWTP 废水的总体影响主要取决于它们的组成和受纳水体的稀释能力。我们在人工溪流中评估了 WWTP 废水的即时和遗留影响，在那里我们测量了生物膜对可溶性反应性磷（SRP）的吸收、生物量积累、底栖代谢和有机物质分解（OMD）。在第一阶段（32 天），通道受到从纯溪流到纯废水的废水贡献梯度的影响。WWTP 废水影响了我们测量的生态系统过程，尽管我们没有发现明确的补贴-压力模式，除了生物膜生物量积累。相反，大多数过程都得到了补贴，尽管它们表现出复杂和特定于过程的模式。底栖代谢和 OMD 没有饱和而得到补贴，因为它们分别在中等和高水平的污染下达到峰值，但从未低于对照水平。只有 SRP 吸收随着废水浓度的增加而减少。在实验的第二阶段（23 天），所有通道都保持在纯溪流水中，以分析废水的遗留影响。对于大多数过程，都存在明显的遗留效应，这些效应遵循补贴、压力或补贴-压力模式。随着污染遗留物的增加，SRP 吸收能力受到压力，而藻类积累和底栖代谢继续得到补贴。相反，生物膜生物量积累和 OMD 没有遗留效应。总体而言，WWTP 废水在我们的实验中引起了复杂和特定于过程的反应，主要由补贴剂和压力源的混合贡献驱动。这些结果有助于提高我们对城市污染对溪流生态系统功能影响的理解。
