The relevance of wastewater treatment plant (WWTP) effluents in fluvial networks is increasing as urbanization grows in catchments. Urban-sourced fine particles from WWTP effluents deposit and accumulate in the streambed sediment of receiving streams over time and can fuel respiration rates, which can thus potentially increase rates of biogeochemical reactions and CO₂ emissions to the atmosphere. We aimed to provide a quantitative assessment of the influence of WWTP-sourced fine particles deposited in the streambed sediment on stream metabolic activity for 1 year in an intermittent Mediterranean stream. More nutrient-rich and metabolically active fine particle standing stocks were observed downstream of the WWTP, propagating to the end of the 820 m study reach, especially during the dry period (i.e., when the dilution capacity of the stream to WWTP inputs is <40%). Based on the longitudinal patterns of fine particle standing stocks and their metabolic activity, we estimated that the in-stream bioreactive capacity associated with these fine particles could potentially lead to substantial carbon dioxide emissions to the atmosphere (3.1 g C/m²/d). We show the importance of incorporating fine particle standing stocks downstream of point source inputs, particularly WWTPs in intermittent streams, into carbon budgets.

中文翻译：

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河流水文控制城市来源细颗粒的纵向生物反应足迹

随着流域城市化的发展，污水处理厂 (WWTP) 流出物在河流网络中的相关性正在增加。随着时间的推移，来自 WWTP 流出物的城市来源的细颗粒在接收河流的河床沉积物中沉积和积累，并且可以促进呼吸速率，因此可能会增加生物地球化学反应的速率和 CO ₂排放到大气中。我们旨在定量评估沉积在河床沉积物中的 WWTP 来源的细颗粒对间歇性地中海溪流中 1 年的溪流代谢活动的影响。在污水处理厂下游观察到更多营养丰富和代谢活跃的细颗粒立存，一直传播到 820 米研究河段的末端，特别是在干旱时期（即，当流向 WWTP 输入的稀释能力小于 40% 时）。根据细颗粒常备种群的纵向模式及其代谢活动，我们估计与这些细颗粒相关的流内生物反应能力可能导致大量二氧化碳排放到大气中（3.1 g C/m ² /d） . 我们展示了将点源输入下游的细颗粒常备存量，特别是间歇性流中的污水处理厂纳入碳预算的重要性。