Data from: Combined effects of local habitat, anthropogenic stress, and dispersal on stream ecosystems: a mesocosm experiment

The effects of anthropogenic stressors on community structure and ecosystem functioning can be strongly influenced by local habitat structure and dispersal from source communities. Catchment land uses increase the input of fine sediments into stream channels, clogging the interstitial spaces of benthic habitats. Aquatic macrophytes enhance habitat heterogeneity and mediate important ecosystem functions, being thus a key component of habitat structure in many streams. Therefore, the recovery of macrophytes following in-stream habitat modification may be prerequisite for successful stream restoration. Restoration success is also affected by dispersal of organisms from the source community, with potentially strongest responses in relatively isolated headwater sites that receive limited amount of dispersing individuals. We used a factorial design in a set of stream mesocosms to study the independent and combined effects of an anthropogenic stressor (sand sedimentation), local habitat (macrophytes, i.e. moss transplants) and enhanced dispersal (two levels: high vs. low) on organic matter retention, algal accrual rate, leaf decomposition and macroinvertebrate community structure. Overall, all responses were simple additive effects with no interactions between treatments. Sand reduced algal accumulation, total invertebrate density and density of a few individual taxa. Mosses reduced algal accrual rate and algae-grazing invertebrates, but enhanced organic matter retention and detritus- and filter-feeders. Mosses also reduced macroinvertebrate diversity by increasing the dominance by a few taxa. Mosses also reduced leaf-mass loss, possibly because the organic matter retained by mosses provided an additional food source for leaf-shredding invertebrates and thus reduced shredder aggregation into leaf packs. The effect of mosses on macroinvertebrate communities and ecosystem functioning was distinct irrespective of the level of dispersal, suggesting strong environmental control of community structure. The strong environmental control of macroinvertebrate community composition even under enhanced dispersal suggests that re-establishing key habitat features, such as natural stream vegetation, could aid ecosystem recovery in boreal streams.人为胁迫因子（anthropogenic stressors）对群落结构与生态系统功能的影响，会显著受到局域生境结构以及源群落扩散过程的调控。流域土地利用方式会增加细颗粒沉积物向河道的输入量，进而堵塞底栖生境（benthic habitats）的间隙空间。水生大型植物（aquatic macrophytes）能够提升生境异质性并调控关键生态系统功能，因此是多数溪流生境结构的核心组成部分。因此，在河道生境改造完成后，水生大型植物的恢复或许是实现成功溪流修复的必要前提。修复成效同时还会受到源群落生物扩散过程的影响，在接收扩散个体数量有限的相对孤立的源头溪流生境中，群落响应的潜在强度最高。本研究依托一组溪流中型实验生态系统（stream mesocosms）采用析因设计，探究了单一人为胁迫因子（砂石沉积）、局域生境配置（水生大型植物，即苔藓移植体）以及强化扩散（两个水平：高扩散与低扩散）对有机质保留量、藻类积累速率、叶片分解过程以及大型无脊椎动物群落结构的独立与联合效应。整体而言，所有观测响应均表现为简单的加性效应，各处理间未出现交互作用。砂石沉积会降低藻类积累量、无脊椎动物总密度以及部分类群的个体密度。苔藓移植体则会降低藻类积累速率与藻食性无脊椎动物的丰度，但同时提升了有机质保留量以及碎屑食性与滤食性无脊椎动物的丰度。苔藓移植体还会通过提升部分类群的优势度，降低大型无脊椎动物的群落多样性。苔藓移植体同时也会降低叶片质量损失率，其潜在机制为苔藓截留的有机质为食碎性无脊椎动物提供了额外食物来源，进而减少了食碎者向叶片包的聚集行为。无论扩散水平高低，苔藓移植体对大型无脊椎动物群落与生态系统功能的影响均保持一致，这表明群落结构受到较强的环境调控作用。即便在强化扩散条件下，大型无脊椎动物群落组成仍受到强烈的环境调控，这表明重建自然溪流植被等关键生境特征，或可助力北方溪流的生态系统恢复。