Anthropogenic increases in nitrogen (N) and phosphorus (P) concentrations can strongly influence the structure and function of ecosystems. Even though lotic ecosystems receive cumulative inputs of nutrients applied to and deposited on land, no comprehensive assessment has quantified nutrient-enrichment effects within streams and rivers. We conducted a meta-analysis of published studies that experimentally increased concentrations of N and/or P in streams and rivers to examine how enrichment alters ecosystem structure (state: primary producer and consumer biomass and abundance) and function (rate: primary production, leaf breakdown rates, metabolism) at multiple trophic levels (primary producer, microbial heterotroph, primary and secondary consumers, and integrated ecosystem). Our synthesis included 184 studies, 885 experiments, and 3497 biotic responses to nutrient enrichment. We documented widespread increases in organismal biomass and abundance (mean response = +48%) and rates of ecosystem processes (+54%) to enrichment across multiple trophic levels, with no large differences in responses among trophic levels or between autotrophic or heterotrophic food-web pathways. Responses to nutrient enrichment varied with the nutrient added (N, P, or both) depending on rate versus state variable and experiment type, and were greater in flume and whole-stream experiments than in experiments using nutrient-diffusing substrata. Generally, nutrient-enrichment effects also increased with water temperature and light, and decreased under elevated ambient concentrations of inorganic N and/or P. Overall, increased concentrations of N and/or P altered multiple food-web pathways and trophic levels in lotic ecosystems. Our results indicate that preservation or restoration of biodiversity and ecosystem functions of streams and rivers requires management of nutrient inputs and consideration of multiple trophic pathways.

中文翻译：

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实验性氮和磷富集刺激了藻类和碎屑食物网的多个营养级：来自溪流和河流的全球荟萃分析

人为增加的氮 (N) 和磷 (P) 浓度会强烈影响生态系统的结构和功能。尽管流水生态系统接受了施用和沉积在土地上的养分的累积输入，但没有综合评估量化溪流和河流内的养分富集效应。我们对已发表的研究进行了荟萃分析，这些研究通过实验增加了溪流和河流中 N 和/或 P 的浓度，以检查富集如何改变生态系统结构（状态：初级生产者和消费者的生物量和丰度）和功能（比率：初级生产、叶分解率、代谢）在多个营养级（初级生产者、微生物异养、初级和次级消费者以及综合生态系统）。我们的综合包括 184 项研究、885 项实验、和 3497 种对营养丰富的生物反应。我们记录了生物量和丰度的广泛增加（平均响应 = +48%）和生态系统过程速率（+54%）在多个营养级富集，营养级之间或自养或异养食物之间的响应没有大的差异。网络途径。对养分富集的反应因添加的养分（N、P 或两者）而异，这取决于比率与状态变量和实验类型的关系，并且在水槽和全流实验中比在使用养分扩散基质的实验中更大。一般来说，营养丰富的效果也随着水温和光照而增加，并在无机 N 和/或 P 的环境浓度升高的情况下降低。总体而言，N 和/或 P 浓度的增加改变了 Lotic 生态系统中的多种食物网途径和营养水平。我们的研究结果表明，河流和河流的生物多样性和生态系统功能的保护或恢复需要管理养分输入并考虑多种营养途径。