The amount of pollutants and nutrients entering rivers via point sources is increasing along with human population and activity. Although wastewater treatment plants (WWTPs) greatly reduce pollutant loads into the environment, excess nutrient loading is a problem in many streams. Using a Community and Ecosystem Function (CEF) approach, we quantified the effects of WWTP effluent on the performance of microbes and detritivores associated to organic matter decomposition, a key ecosystem process. We measured organic matter breakdown rates, respiration rates and exo-enzymatic activities of aquatic microbes. We also measured food consumption and growth rates and RNA to body-mass ratios (RNA:BM) of a dominant amphipod Echinogammarus berilloni. We predicted responses to follow a subsidy-stress pattern and differences between treatments to increase over time. To examine temporal effects of effluent, we performed a laboratory microcosm experiment under a range of effluent concentrations (0, 20, 40, 60, 80 and 100%), taking samples over time (days 8, 15 and 30; 4 and 10 replicates to assess microbe and detritivore performance respectively, per treatment and day). This experiment was combined with a field in situ Before-After Control-Impact Paired (BACIP) experiment whereby we added WWTP effluent poured (10 L s⁻¹ during 20–40 min every 2 h) into a stream and collected microbial and detritivore samples at days 8 and 15 (5 and 15 replicates to assess the microbe and detritivore performance respectively, per period, reach and sampling day). Responses were clearer in the laboratory experiment, where the effluent caused a general subsidy response. Field measures did not show any significant response, probably because of the high dilution of the effluent in stream water (average of 1.6%). None of the measured variables in any of the experiments followed the predicted subsidy-stress response. Microbial breakdown, respiration rates, exo-enzymatic activities and invertebrate RNA:BM increased with effluent concentrations. Differences in microbial respiration and exo-enzymatic activities among effluent treatments increased with incubation time, whereas microbial breakdown rates and RNA:BM were consistent over time. At the end of the laboratory experiment, microbial respiration rates increased 156% and RN:BM 115% at 100% effluent concentration. Detritivore consumption and growth rates increased asymptotically, and both responses increased with by incubation time. Our results indicate that WWTP effluent stimulates microbial activities and alters detritivore performance, and stream water dilution may mitigate these effects.

通过点源进入河流的污染物和养分的数量随着人口和活动的增加而增加。尽管废水处理厂（WWTP）大大减少了进入环境的污染物负荷，但过多的养分负荷在许多河流中仍然是一个问题。使用社区和生态系统功能（CEF）方法，我们量化了污水处理厂污水对微生物和与有机物分解（一个关键的生态系统过程）相关的有害生物的性能的影响。我们测量了水生微生物的有机物分解速率，呼吸速率和外酶活性。我们还测量了食物消耗量和增长率，以及主要的两足动物棘皮E虫的RNA与身体质量比（RNA：BM）。我们预测响应将遵循补贴-压力模式，并且治疗之间的差异会随着时间的推移而增加。为了检查废水的时间效应，我们在一定范围的废水浓度（0％，20％，40％，60％，80％和100％）下进行了实验室微观实验，并随时间（第8、15和30天； 4和10个重复样品）进行了采样分别评估每个治疗和每天的微生物和有害微生物表现）。该实验与原位对照-对照前后配对（BACIP）实验相结合，在该实验中，我们添加了WWTP废水倾倒（10 L s ^-1在每2 h的20–40分钟内）流入溪流，并在第8天和第15天收集微生物和有害微生物样本（重复5和15次，分别评估每个时期，每个采样日和采样日的微生物和有害微生物表现）。在实验室实验中，废水产生了普遍的补贴反应，因此反应更加清晰。现场测量未显示出任何明显的响应，这可能是由于废水在河水中的高度稀释（平均为1.6％）所致。在任何实验中，没有一个测量变量遵循预测的补贴-压力响应。微生物分解，呼吸速率，外酶活性和无脊椎动物RNA：BM随着废水浓度的增加而增加。污水处理中微生物呼吸和外酶活性的差异随孵育时间的增加而增加，而微生物分解率和RNA：BM随时间变化是一致的。在实验室实验结束时，在100％的废水浓度下，微生物的呼吸速率增加了156％，RN：BM的增加了115％。枯草芽孢杆菌的消耗量和生长速率逐渐增加，并且两种反应都随着孵育时间的增加而增加。我们的结果表明，污水处理厂的污水刺激了微生物活动并改变了除草剂的性能，溪水稀释可能减轻了这些影响。