Sediment stability is a critical component for the understanding of cohesive sediment dynamics. Traditionally, physico-chemical sediment conditions have been regarded as most important drivers of sediment stability. However, over the last decade, the stabilization of sediment by biological activity, particularly the influence of highly hydrated matrices of extracellular polymeric substances (EPS) has been given increasing attention. However, most studies have focused on the sediment/water interface and, usually, of marine systems. The present study exploits current knowledge of EPS dynamics from marine systems and applies it to freshwater habitats, also considering a wide range of biological and physico-chemical variables. Natural sediments were taken from a freshwater site with high levels of heavy metal pollution (Lauffen reservoir, River Neckar, Germany). Vertical profiles from the flocculent surface layer to depth of 50 cm within the sediment were investigated, monthly, over the course of year. Tubificidae and Chironomidae larvae constituted the majority of the macrofauna. Despite the turbidity of the water column, a highly diverse and abundant microphytobenthic community of diatoms (11-82 microg g(-1) DW) was found at the sediment surface closely associated with high numbers of bacteria (10(9) cells g(-1) DW). The concentrations of all EPS moieties were remarkably high (0.1-0.5, 1.7-3.8, 0.9-5.2 mg g(-1) DW, for colloidal and bound carbohydrates and proteins, respectively) and levels were comparable to those determined in intertidal studies. The microalgal and bacterial biomass both showed strong correlations with the colloidal and bound EPS carbohydrate fractions. The data suggested that the present macrofauna as well as the metabolic activities of microalgae and bacteria interact with sedimentological factors to influence the properties of the sediment by binding fine-grained sediment, changing water content and enhancing the organic content through secretion products. The colloidal and bound EPS moieties showed strong correlation with the critical shear stress for erosion over sediment depth. It is suggested that the cohesive strength of the sediment was controlled by a high number of active adsorption sites and higher charge densities in fine grained sediments. The EPS network may significantly enhance this by embedding particles and permeating the void space but also in offering additional ionic binding sites and cross-linkages.

中文翻译：

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细胞外聚合物对河流沉积物的微生物稳定作用。

沉积物稳定性是理解粘性沉积物动力学的重要组成部分。传统上，理化沉积物条件被认为是沉积物稳定性的最重要驱动因素。然而，在过去的十年中，人们越来越关注通过生物活性来稳定沉积物，特别是高度水合的细胞外聚合物（EPS）基质的影响。但是，大多数研究都集中在沉积物/水界面，通常是海洋系统。本研究利用了来自海洋系统的EPS动力学的当前知识，并将其应用于淡水生境，同时考虑了广泛的生物学和物理化学变量。天然沉积物取自重金属污染程度较高的淡水地点（劳芬水库，内卡河，德国）。在一年中，每月一次从絮状表面层到沉积物内50 cm的垂直剖面进行调查。大型动物的大部分是Tubificidae和Chironomidae幼虫。尽管水柱浑浊，但在沉积物表面发现了高度多样化和丰富的硅藻微藻类群落（11-82 microg g（-1）DW），与大量细菌（10（9）细胞g（ -1）DW）。所有EPS部分的浓度都非常高（对于胶体和结合的碳水化合物和蛋白质，分别为0.1-0.5、1.7-3.8、0.9-5.2 mg g（-1）DW），并且其水平与潮间研究中确定的水平相当。微藻和细菌生物量均与胶体和结合的EPS碳水化合物组分显示出很强的相关性。数据表明，目前的大型动物以及微藻类和细菌的代谢活动与沉积学因素相互作用，通过结合细颗粒沉积物，改变水含量和通过分泌产物提高有机含量来影响沉积物的性质。胶体和结合的EPS部分与在沉积深度范围内侵蚀的临界切应力具有很强的相关性。建议通过细颗粒状沉积物中大量的活性吸附位和较高的电荷密度来控制沉积物的内聚强度。EPS网络可以通过嵌入颗粒和渗透空隙空间来显着增强此功能，还可以提供其他离子结合位点和交联键。