Aquatic communities across the Eurasian steppe face increasing anthropogenic pressures due to rapid population growth, catchment‐wide land‐use changes, and climate change. The particular type, intensity, overlay, and legacy of impacts along longitudinal gradients of Eurasian river networks provide a unique setting to investigate ecological responses in identifiable multiple stressor environments. We studied macroinvertebrate communities along the Kharaa River, Mongolia, which display a distinct, downstream gradient of moderate nutrient enrichment, disturbed bank morphology, reduced riparian vegetation, elevated turbidity, increased fine sediment substrate proportions, and fine sediment intrusion into the hyporheic zone. Within the encountered ranges of physical and chemical environmental factors (TP 0.02–0.09 mg/L, TN 0.33–0.96 mg/L, conductivity 167–322 µS/cm, formazin nephelometric units 0.62–5.43) and hyporheic fine sediment intrusion (0.9–1.6 g dry weight [DW]·L⁻¹·day⁻¹) the population densities and biomass of macroinvertebrates were high (5,313 ± 410 individuals/m² and 2,656 ± 152 mg DW/m²) and notably stable. In contrast, macroinvertebrate community structure showed strong and statistically significant negative linear relationships (Pearson's r) with turbidity, that is, for taxa richness (r = −.83), Shannon index of diversity (r = −.89), Evenness (r = −.86), the relative abundance of Ephemeroptera, Plecoptera, and Trichoptera (EPT) individuals (r = −.93) and relative biomass of hard substrate colonizers (r = −.86). The relative biomasses of fine substrate colonizers, as well as Chironomidae and Oligochaeta (both r = .76), were positively correlated with mean turbidity values. In addition, the Proportion of Sediment‐sensitive Invertebrates (PSI) methodology was adjusted for local application and the resulting index scores followed a similar pattern, with PSI also being significantly correlated (r = .66) with the relative abundance of EPT individuals, the latter being the most sensitive macroinvertebrate community index. We conclude that fine sediment load is the key factor for shaping macroinvertebrate community structure in the multistressor setting of the Kharaa River followed by hydromorphological habitat complexity determined by shear stress, substrate, and grain size distributions. We suggest that the implementation of effective regional management strategies aiming at the reduction of fine sediment pollution should be given the highest priority.

中文翻译：

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精细沉积物增加在欧亚草原河流域（蒙古卡拉河）沿多重应力梯度形成大型无脊椎动物群落中的关键作用

由于人口的快速增长，集水区范围内的土地利用变化和气候变化，整个欧亚草原的水生社区面临着越来越大的人为压力。沿欧亚河网纵向坡度的影响的特定类型，强度，覆盖范围和遗产，为研究可识别的多重压力环境中的生态响应提供了独特的环境。我们研究了蒙古喀拉拉河沿岸的大型无脊椎动物群落，这些群落表现出明显的下游梯度，适度的养分富集，扰乱的河岸形态，河岸植被减少，浊度升高，细沉积物底物比例增加以及细沉积物侵入到低河带。在遇到的物理和化学环境因素范围内（TP 0.02–0.09 mg / L，TN 0.33–0.96 mg / L，^-1 ·天^-1）大型无脊椎动物的种群密度和生物量较高（5,313±410个/ m ²和2,656±152 mg DW / m ²）并且非常稳定。相比之下，大型无脊椎动物群落结构与浊度之间显示出强烈的且具有统计学意义的负线性关系（Pearson's r），即，对于分类单元丰富度（r  = -.83），香农多样性指数（r  = -.89），均匀度（r  = -.86），E翅目，鞘翅目和毛鳞翅目（EPT）个体的相对丰度（r  = -.93）和硬质底物定居者的相对生物量（r = −.86）。优良的底物定居者，Chironomidae和Oligochaeta（r  = 0.76）的相对生物量与平均浊度值呈正相关。此外，对沉积物敏感无脊椎动物的比例（PSI）方法进行了本地化调整，所得指数得分遵循相似的模式，PSI也显着相关（r = 0.66），而EPT个体相对丰富，后者是最敏感的大型无脊椎动物群落指数。我们得出的结论是，良好的沉积物负荷是在Kharaa河多应力环境中塑造大型无脊椎动物群落结构的关键因素，其次是由剪切应力，基质和粒度分布决定的水文形态生境复杂性。我们建议，应优先执行旨在减少细沙沉积物污染的有效区域管理策略。