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首页> 外文期刊>Freshwater science >Invertebrate distribution across nested geomorphic features in braided-river landscapes
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Invertebrate distribution across nested geomorphic features in braided-river landscapes

机译：辫状河景观中嵌套地貌特征的无脊椎动物分布

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摘要

River landscapes are increasingly viewed as a collection of nested geomorphic features, the hydrological effects of which juxtapose to create a mosaic of aquatic habitat conditions. We examined how the combined hydrological influences of stream reaches and gravel bars affect the composition of hyporheic invertebrate assemblages along the longitudinal and vertical dimensions of river landscapes. We worked in 12 braided-river valley segments of tributaries to the Rh?ne River, France. Valley segments were bounded downstream by geological knickpoints so that bedform-induced exchange flows beneath gravel bars and riffles were predictably embedded in exchange flows occurring at the valley-segment scale. In upstream reaches (UR) and downstream reaches (DR) of each valley segment, we collected invertebrates at the heads and tails of gravel bars in the hyporheic zone and at the upstream and downstream ends of riffles in surface channels adjacent to the bars. Patterns of vertical hydraulic gradient and specific conductance and the resulting spatial heterogeneity of temperature, dissolved O_2, and particulate organic C suggested that DR were points of flow convergence and water mixing. Specific conductance increased and temperature decreased more steeply along gravel bars in DR, indicating that water from long hyporheic flow paths or lateral aquifers was discharging at the tails of bars in DR. Density hotspots for insect larvae corresponded to hyporheic patches at the heads of bars in DR, which received the highest organic matter inputs from localized downwelling of surface water and were not affected by inputs of cold water from hyporheic flow paths or lateral aquifers. Density of epigean taxa at the tails of bars decreased more steeply with depth in DR than in UR, and density of hypogean taxa increased more steeply. Viewing local hyporheic assemblages as the outcome of a series of environmental filters operating over multiple exchange flows induced by nested geomorphic features provides a general framework that may foster our understanding of biodiversity patterns in river landscapes.
机译：河流景观越来越多地被看作是嵌套的地貌特征的集合，其水文效应并列形成水生栖息地条件的马赛克。我们研究了河流到达和砾石坝的综合水文影响如何影响沿河景观的纵向和垂直维度的低变无脊椎动物组合的组成。我们曾在法国罗纳河的12条辫状河谷支流中工作过。谷地段被地质拐点限制在下游，因此，可预测地层诱发的砾石条和浅滩下方的交换流嵌入在谷类分段规模的交换流中。在每个谷段的上游河段（UR）和下游河段（DR）中，我们在流变区的砾石条的头和尾以及邻近条的表面通道的浅滩的上游和下游端收集了无脊椎动物。垂直水力梯度和比电导的模式以及由此产生的温度，溶解的O_2和颗粒状有机碳的空间异质性表明DR是流动收敛和水混合的点。沿DR的砾石条，电导率增加且温度下降更陡，表明来自长的水流路径或侧向含水层的水在DR的条尾处排出。昆虫幼虫的密度热点对应于DR的条状顶端的流变斑块，其从地表水的局部下降流中获得了最高的有机物输入，并且不受来自流变流动路径或侧向含水层的冷水输入的影响。与UR相比，DR深度下条形尾部的Epigean分类单元的密度下降幅度更大，而UR中，gegegan分类单元的密度增长幅度更大。将局部水流组合视为一系列环境过滤器的结果，这些环境过滤器是在嵌套地貌特征引起的多个交换流上运行的，这提供了一个总体框架，可以增进我们对河流景观中生物多样性模式的理解。

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