Zeug Steven C, Winemiller Kirk O
Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Texas 12208, USA.
Ecology. 2008 Jun;89(6):1733-43. doi: 10.1890/07-1064.1.
Algal carbon has been increasingly recognized as the primary carbon source supporting large-river food webs; however, many of the studies that support this contention have focused on lotic main channels during low-flow periods. The flow variability and habitat-heterogeneity characteristic of these systems has the potential to significantly influence food web structure and must be integrated into models of large-river webs. We used stable-isotope analysis and IsoSource software to model terrestrial and algal sources of organic carbon supporting consumer taxa in the main channel and oxbow lakes of the Brazos River, Texas, USA, during a period of frequent hydrologic connectivity between these habitat types. Standardized sampling was conducted monthly to collect production sources and consumer species used in isotopic analysis. Predictability of hydrologic connections between habitat types was based on the previous 30 years of flow data. IsoSource mixing models identified terrestrial C3 macrophytes (riparian origin) as the primary carbon source supporting virtually all consumers in the main channel and most consumers in oxbow lakes. Small-bodied consumers (<100 mm) in oxbow lakes assimilated large fractions of algal carbon whereas this pattern was not apparent in the main channel. Estimates of detritivore trophic positions based on delta15N values indicated that terrestrial material was likely assimilated via invertebrates rather than directly from detritus. High flows in the river channel influenced algal standing stock, and differences in the importance of terrestrial and algal production sources among consumers in channel vs. oxbow habitats were associated with patterns of flooding. The importance of terrestrial material contradicts the findings of recent studies of large-river food webs that have emphasized the importance of algal carbon and indicates that there can be significant spatial, temporal, and taxonomic variation in carbon sources supporting consumers in large rivers.
藻类碳已越来越被视为支持大型河流食物网的主要碳源；然而，许多支持这一观点的研究都集中在低流量时期的河流主河道。这些系统的流量变异性和栖息地异质性特征有可能显著影响食物网结构，必须将其纳入大型河流食物网模型。我们使用稳定同位素分析和IsoSource软件，对美国得克萨斯州布拉索斯河主河道和牛轭湖在这些栖息地类型频繁水文连通期间支持消费者类群的陆地和藻类有机碳来源进行建模。每月进行标准化采样，以收集用于同位素分析的生产源和消费者物种。栖息地类型之间水文连通的可预测性基于过去30年的流量数据。IsoSource混合模型确定陆地C3大型植物（河岸起源）是支持主河道几乎所有消费者和牛轭湖大多数消费者的主要碳源。牛轭湖中小体型消费者（<100毫米）吸收了大部分藻类碳，而这种模式在主河道中并不明显。基于δ15N值的碎屑食性动物营养级估计表明，陆地物质可能是通过无脊椎动物吸收的，而不是直接从碎屑中吸收的。河道中的高流量影响了藻类现存量，河道与牛轭湖栖息地消费者之间陆地和藻类生产源重要性的差异与洪水模式有关。陆地物质的重要性与最近关于大型河流食物网的研究结果相矛盾，这些研究强调了藻类碳的重要性，并表明在支持大型河流消费者的碳源方面可能存在显著的空间、时间和分类学差异。
