Agriculture has greatly influenced water quality, habitats, and fish assemblages in streams of the Mississippi Alluvial Plain (MAP) ecoregion. However, MAP streams have historically been understudied compared to streams in other agricultural regions of the USA. In this study, water quality, habitat, and fish assemblage composition were assessed seasonally (spring, summer, and fall) in eight representative MAP streams located across three U.S. states. The study design included four streams containing highly agricultural watersheds (herein termed “agriculture” streams) and four streams containing mostly forested watersheds (herein termed “forest” streams), which were intended to represent reference conditions for MAP streams. In general, forest streams contained significantly better instream and riparian habitats than agriculture streams (P = 0.010–0.040) whereas agriculture streams contained significantly greater levels of primary nutrients (P < 0.001–0.010). Differences between agriculture and forest streams with respect to other physical and chemical variables were intermittent and season dependent. Fish assemblages in agriculture and forest streams were structured primarily along an environmental gradient reflecting instream habitat conditions, water nutrient concentrations, and benthic chlorophyll-a production. Structurally, fish assemblages in both stream types contained many regionally common species, though some species appeared to exhibit affinities for a particular stream type. Functionally, fish assemblages in agriculture streams contained more tolerant species, more omnivores, and fewer insectivores compared to forest stream assemblages, which were nearly all insectivores. Overall, one-third of the fish specimens collected in forest streams classified as intolerant species. Our results suggested that stream water quality, habitat, and fish assemblages differed between agriculture and forest streams in the MAP, with fish assemblages exhibiting both structural and functional differences. Results were consistent with a larger body of literature from smaller, headwater streams whereby land-use changes (e.g., row-crop agriculture) impacted the physical, chemical, and biological characteristics of stream ecosystems. Results further highlight the importance of land use management and its effects on habitat diversity in stream ecosystems, and that protecting the few remaining undisturbed or less-disturbed streams should be a priority.

中文翻译：

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密西西比冲积平原中序农业和森林溪流的水质、生境和鱼类组合关系

农业极大地影响了密西西比冲积平原 (MAP) 生态区溪流中的水质、栖息地和鱼类组合。然而，与美国其他农业地区的溪流相比，MAP 溪流历来未被充分研究。在这项研究中，对位于美国三个州的八个代表性 MAP 溪流的水质、栖息地和鱼类组合组成进行了季节性（春季、夏季和秋季）评估。研究设计包括四个包含高度农业流域的溪流（本文称为“农业”溪流）和四个包含大部分森林覆盖的流域的溪流（本文称为“森林”溪流），其旨在代表 MAP 溪流的参考条件。一般来说，森林溪流的河​​内和河岸生境明显好于农业溪流（P = 0.010–0.040），而农业溪流含有明显更高水平的主要养分（P < 0.001–0.010）。农业和森林溪流在其他物理和化学变量方面的差异是间歇性的并且依赖于季节。农业和森林溪流中的鱼类组合主要沿着反映溪流栖息地条件、水养分浓度和底栖叶绿素-a 生产的环境梯度构建。从结构上讲，两种河流类型中的鱼类组合都包含许多区域常见物种，尽管某些物种似乎表现出对特定河流类型的亲和力。从功能上讲，与几乎全是食虫动物的森林溪流组合相比，农业溪流中的鱼类组合包含更多的耐受物种、更多的杂食动物和更少的食虫动物。总体而言，在森林溪流中采集的鱼类标本中有三分之一被归类为不耐受物种。我们的结果表明，MAP 中农业溪流和森林溪流的溪流水质、栖息地和鱼类组合不同，鱼类组合表现出结构和功能差异。结果与较小的源头河流的大量文献一致，其中土地利用变化（例如中耕作物农业）影响了河流生态系统的物理、化学和生物特征。结果进一步强调了土地利用管理的重要性及其对溪流生态系统栖息地多样性的影响，并且保护少数剩余的未受干扰或干扰较少的溪流应成为优先事项。