Dataset for: Resilience of natural lake phytoplankton communities to pulse disturbances from micropollutant exposure and vertical mixing

Freshwaters are increasingly exposed to complex mixtures of pharmaceutical and personal care products (PPCPs) from municipal wastewater. PPCPs are known to alter freshwater communities' structure and functioning, however, their interaction with other disturbances and whether their combined effects can impact ecological resilience (i.e. the ability of a system to tolerate disturbances without altering the system's original structure and processes) remain unexplored. Using in situ mesocosms in two lakes with different nutrient levels (mesotrophic and eutrophic), we assessed whether a pulse exposure to sub-lethal concentrations of 12 PPCPs affects the ecological resilience of natural phytoplankton communities that experienced an abrupt environmental change involving the destabilization of the water column through mixing. Such mixing events are predicted to increase as the effects' climate change unfold, leading to more frequent storms, which disrupt stratification in lakes and force communities to restructure. We assessed their combined effects on community metrics (biomass, species richness and composition) and their relative resilience using four indicators (cross-scale, within scale, aggregation length and gap length), inferred from phytoplankton communities by discontinuity analysis. The mixing disturbance alone had negligible effects on the community metrics, but when combined with chemical contaminants significant changes were measured: reducing total biomass, species richness and altered community composition of phytoplankton. Once these changes occurred, they persisted until the end of the experiment (day 20) where the communities' structures from the two highest exposure levels diverged from the controls. The resilience indicators were not affected by PPCPs, but differed significantly between lakes, with lower resilience found in the eutrophic lake. PPCPs can significantly alter community structures and reinforce mechanisms that maintain ecosystems in a “degraded state”.

淡水生态系统正日益暴露于市政废水排放的复杂药物与个人护理用品（pharmaceutical and personal care products, PPCPs）混合污染物中。已知PPCPs会改变淡水群落的结构与功能，但其与其他干扰因素的交互作用，以及二者的联合效应是否会影响生态弹性（即生态系统在不改变原有结构与过程的前提下耐受干扰的能力），目前仍未得到探索。本研究依托两个不同营养水平（中营养型与富营养型）湖泊的原位中型生态系统（in situ mesocosms），探究了12种PPCPs以亚致死浓度（sub-lethal concentrations）进行脉冲暴露（pulse exposure），对经历了因水体混合导致水柱不稳定这一突发环境变化的自然浮游植物群落的生态弹性的影响。随着气候变化加剧，此类水体混合事件的发生频率预计会上升：极端风暴愈发频繁，会破坏湖泊水体分层，迫使群落重新构建。本研究通过间断性分析（discontinuity analysis）从浮游植物群落中推导得到四项指标（跨尺度（cross-scale）、尺度内（within scale）、聚集长度（aggregation length）与间隙长度（gap length）），以此评估二者对群落指标（生物量、物种丰富度与群落组成）及其相对弹性的联合效应。仅水体混合干扰对群落指标的影响可忽略不计，但当与化学污染物联合作用时，则会产生显著变化：降低浮游植物总生物量与物种丰富度，并改变其群落组成。此类变化一旦发生，会持续至实验结束（第20天），此时两个最高暴露浓度组的群落结构与对照组已出现显著分化。四项弹性指标未受PPCPs的显著影响，但在两个湖泊间存在显著差异：富营养化湖泊的弹性水平更低。PPCPs可显著改变群落结构，并强化将生态系统维持在「退化状态」的机制。