Primary source stable isotope signatures.

Terrestrial organic matter is believed to play an important role in promoting resilient estuarine food webs, but the inherent interconnectivity of estuarine systems often obscures the origins and importance of these terrestrial inputs. To determine the relative contributions of terrestrial (allochthonous) and aquatic (autochthonous) organic matter to the estuarine food web, we analyzed carbon, nitrogen, and sulfur stable isotopes from multiple trophic levels, environmental strata, and habitats throughout the estuarine habitat mosaic. We used a Bayesian stable isotope mixing model (SIMM) to parse out relationships among primary producers, invertebrates, and a pelagic and demersal fish species (juvenile Chinook salmon and sculpin, respectively). The study was carried out in the Nisqually River Delta (NRD), Washington, USA, a recently-restored, macrotidal estuary with a diverse habitat mosaic. Plant groupings of macroalgae, eelgrass, and tidal marsh plants served as the primary base components of the NRD food web. About 90% of demersal sculpin diets were comprised of benthic and pelagic crustaceans that were fed by autochthonous organic matter contributions from aquatic vegetation. Juvenile salmon, on the other hand, derived their energy from a mix of terrestrial, pelagic, and benthic prey, including insects, dipterans, and crustaceans. Consequently, allochthonous terrestrial contributions of organic matter were much greater for salmon, ranging between 26 and 43%. These findings demonstrate how connectivity among estuarine habitat types and environmental strata facilitates organic matter subsidies. This suggests that management actions that improve or restore lateral habitat connectivity as well as terrestrial-aquatic linkages may enhance allochthonous subsidies, promoting increased prey resources and ecosystem benefits in estuaries.陆地有机质（Terrestrial organic matter）被认为在维系河口食物网韧性方面发挥着关键作用，但河口生态系统固有的连通性往往会掩盖这类陆地输入物的来源与重要性。为厘清陆地（异源，allochthonous）有机质与水生（内源，autochthonous）有机质对河口食物网的相对贡献，我们对整个河口生境镶嵌体中多个营养级、环境层及生境的碳、氮、硫稳定同位素进行了分析。我们采用贝叶斯稳定同位素混合模型（SIMM）解析了初级生产者、无脊椎动物以及两种鱼类——中上层鱼类（奇努克鲑幼鱼）和底栖鱼类（杜父鱼）——之间的营养关系。本研究在美国华盛顿州的尼斯夸利河三角洲（Nisqually River Delta，NRD）开展，该区域为一处近期完成修复的强潮河口，拥有丰富多样的生境镶嵌体。大型藻类、大叶藻（Eelgrass）以及潮滩沼泽植物构成了尼斯夸利河三角洲食物网的主要基础营养组分。底栖杜父鱼的食物组成中约90%为底栖与浮游甲壳类，这些甲壳类的营养来源为水生植被产生的内源有机质。而奇努克鲑幼鱼的能量则来源于陆地、浮游与底栖三类猎物的混合，具体包括昆虫、双翅目动物以及甲壳类。因此，陆地异源有机质对奇努克鲑幼鱼的贡献占比显著更高，介于26%至43%之间。本研究结果揭示了河口生境类型与环境层之间的连通性如何促进有机质补给效应。这表明，通过改善或修复横向生境连通性以及陆-水联动关系的管理措施，可增强异源有机质补给效应，进而提升河口区域的猎物资源储量与生态系统服务效益。