Low flow and heatwaves alter ecosystem functioning in a stream mesocosm experiment.
Low flow and heatwaves alter ecosystem functioning in a stream mesocosm experiment.
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DOI：
10.1016/j.scitotenv.2021.146067
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发表时间：
2021-02
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影响因子：
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通讯作者：
Raquel Arias Font;K. Khamis;A. Milner;G. S. Sambrook Smith;M. Ledger
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作者：
Raquel Arias Font;K. Khamis;A. Milner;G. S. Sambrook Smith;M. Ledger
预计气候变化将加剧环境压力对河流生态系统的影响。极端事件，如低流量和热浪，可能对河流生态系统功能产生深远的影响，但对这些压力源的影响及其在多个过程中的相互作用的研究仍然很少。在这里，我们报告了一个为期两个月的溪流围隔实验的结果，该实验测试了低流量（水位下降66%，没有砾石暴露）和热浪（三个8天的事件，高于环境温度+5 °C，每个事件之间的恢复时间为10-15天）对一系列生态系统过程（即碎屑分解，生物膜积累，生态系统代谢和DOC数量和质量）的影响。低流量降低了整个系统的代谢，抑制了总初级生产力（GPP）和生态系统呼吸（ER）的速率，但DOC浓度升高。总体而言，栖息地收缩的主要驱动力减少生态系统功能的低流量处理。相比之下，热浪增加分解，藻类的积累，和腐殖类DOC，但降低叶分解效率。净生态系统生产力（NEP）在整个实验中普遍下降，但最明显的低流量和热浪时，独立发生。NEP对三次连续热浪事件的反应评估显示，序列中较晚的反应更少（即与对照组更相似），表明生物膜群落可能适应秋季热浪。然而，当热浪与低流量同时发生时，观察到ER和GPP的强烈降低，表明微生物死亡率增加和驯化减少。我们的研究表明，秋季热浪可能会延长初级生产者的生长季节，并刺激分解者。随着气候变化，河流生态系统可能变得更加异养，更快地处理可再生碳。需要进一步研究，以确定对较高营养水平的影响、元群落动态以及连续低流量和热浪产生的潜在遗留影响。
Climate change is expected to intensify the effect of environmental stressors on riverine ecosystems. Extreme events, such as low flow and heatwaves, could have profound consequences for stream ecosystem functioning, but research on the impact of these stressors and their interaction across multiple processes, remains scarce. Here, we report the results of a two-month stream mesocosm experiment testing the effect of low flow (66% water level reduction, without gravel exposure) and heatwaves (three 8-d episodes of +5 °C above ambient with 10–15 days recovery between each episode) on a suite of ecosystem processes (i.e. detrital decomposition, biofilm accrual, ecosystem metabolism and DOC quantity and quality). Low flow reduced whole system metabolism, suppressing the rates of gross primary production (GPP) and ecosystem respiration (ER), but elevated DOC concentration. Overall, habitat contraction was the main driver of reduced ecosystem functioning in the low flow treatment. By contrast, heatwaves increased decomposition, algal accrual, and humic-like DOC, but reduced leaf decomposition efficiency. Net ecosystem production (NEP) generally decreased across the experiment but was most pronounced for low flow and heatwaves when occurring independently. Assessment of NEP responses to the three successive heatwave events revealed that responses later in the sequence were more reduced (i.e. more similar to controls), suggesting biofilm communities may acclimate to autumn heatwaves. However, when heatwaves co-occurred with low flow, a strong reduction in both ER and GPP was observed, suggesting increased microbial mortality and reduced acclimation. Our study reveals autumn heatwaves potentially elongate the growth season for primary producers and stimulate decomposers. With climate change, river ecosystems may become more heterotrophic, with faster processing of recalcitrant carbon. Further research is required to identify the impacts on higher trophic levels, meta-community dynamics and the potential for legacy effects generated by successive low flows and heatwaves.