Describing trophic structure within freshwater food webs can be a useful tool for understanding relationships to make ecological inferences and to inform management action. A complementary analysis examining both stable isotope (SI) and biomass community components may be useful, because these two responses may be influenced differently by habitat factors and perturbations (e.g. flooding disturbance). To test this, stable isotope-derived trophic height and biomass were characterised, as was coarse allochthonous, periphyton, invertebrate and fish components, for 27 stream communities in Canterbury, New Zealand. Using piecewise structural equation modelling to test relationships between components, it was found that increased catchment agricultural land cover was associated with increased periphyton biomass and δ¹⁵N (trophic height) in stream invertebrates and invertivorous fishes, likely due to nitrate runoff, but did not affect piscivorous fishes. Additionally, native forest land cover was associated with increased instream allochthonous biomass. Increased discharge (i.e. larger habitat size) did not affect the trophic height or biomass per-unit-area of large-bodied piscivorous fishes (non-native trout and native eels), although it did result in decreased biomass of small-bodied invertivorous fishes (primarily native benthic taxa), likely due to high water velocities in larger habitats rendering habitat less suitable for small-bodied fishes. Finally, flooding disturbance negatively affected both trophic height and biomass of large-bodied fishes, but did not affect small-bodied invertivorous fishes. Overall, describing stream trophic structure with complementary SI and biomass structural equation models appears to be a useful approach for constructing an integrative picture of how abiotic and biotic habitat factors affect freshwater communities. Our findings indicate that land cover, stream size and flooding disturbance should be taken into consideration by stream managers when conducting habitat restoration efforts or setting fish harvest regulations.

中文翻译：

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牧区和原生林地覆盖、洪水干扰和溪流大小对新西兰溪流营养生态的影响

描述淡水食物网内的营养结构可以成为理解关系以进行生态推断和为管理行动提供信息的有用工具。检查稳定同位素 (SI) 和生物量群落成分的互补分析可能是有用的，因为这两种响应可能会受到栖息地因素和扰动（例如洪水干扰）的不同影响。为了测试这一点，对新西兰坎特伯雷的 27 个溪流群落的稳定同位素衍生的营养高度和生物量进行了表征，以及粗的外来生物、附生生物、无脊椎动物和鱼类成分。使用分段结构方程模型来测试组件之间的关系，发现流域农业土地覆盖的增加与附生生物生物量和 δ ^{15 的}增加有关N（营养高度）在溪流无脊椎动物和食肉鱼类中，可能是由于硝酸盐径流造成的，但对食鱼鱼类没有影响。此外，原生林地覆盖与河内异地生物量增加有关。排放量的增加（即更大的栖息地面积）不会影响大型鱼类（非本地鳟鱼和本地鳗鱼）的营养高度或单位面积的生物量，尽管它确实导致小型反身鱼类的生物量减少（主要是原生底栖类群），可能是由于较大栖息地的高水速导致栖息地不太适合小型鱼类。最后，洪水扰动对大型鱼类的营养高度和生物量都有负面影响，但对小型反身鱼类没有影响。全面的，用互补的 SI 和生物量结构方程模型描述河流营养结构似乎是构建非生物和生物栖息地因素如何影响淡水群落的综合图景的有用方法。我们的研究结果表明，河流管理者在进行栖息地恢复工作或制定鱼类捕捞规定时应考虑土地覆盖、河流大小和洪水干扰。