This study aimed to distinguish the contribution of stream fragmentation and poor habitat and water quality to the decline in riverine fish species. The species presence was related to the number of barriers between a specific lowland stream section and the main river and to the length of the stream section remaining between two barriers. To investigate the relationship between the absence of fish species and poor ecological water quality, the EQR and stream velocity indices were compared between accessible sites where the fish was either present or absent. 79% of the 1039 km lowland stream length was disconnected from the river Meuse by one or more barriers and 34% by more than 5 barriers, while 28% of all stream sections were shorter than 2.5 km. Only 2% of sites scored a very good water quality, while all study sites were characterized by (very) slow flowing waters (<0.15 m/s). As many fish passages are built to improve connectivity, fish passages do not improve habitat quality. Gudgeon and stone loach were hardly affected by stream fragmentation, and only slightly by too short stream sections. Ide was moderately affected, while the migratory species chub and dace were severely affected by stream fragmentation. Chub and dace were also sensitive to poor habitat and water quality. Distinguishing the effects of stream fragmentation, habitat deterioration, and poor water quality on lowland stream fish distribution increased the understanding of the reasons for the presence and absence of species and may aid effective management and restoration efforts.

中文翻译：

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通过大坝进入浑水：河流破碎、栖息地恶化和水质差对低地河流鱼类分布的综合影响

本研究旨在区分河流破碎化和恶劣的栖息地和水质对河流鱼类物种减少的贡献。物种的存在与特定低地河流部分和主要河流之间的障碍数量以及两个障碍之间剩余的河流部分的长度有关。为了研究鱼类物种缺失与生态水质差之间的关系，比较了鱼类存在或不存在的可访问地点之间的 EQR 和河流速度指数。1039 公里的低地溪流长度中有 79% 被一个或多个障碍与默兹河断开，34% 被超过 5 个障碍断开，而所有溪流段中的 28% 短于 2.5 公里。只有 2% 的站点获得了非常好的水质，而所有研究地点的特点是（非常）缓慢流动的水（<0.15 m/s）。由于建造了许多鱼道以改善连通性，鱼道并不能改善栖息地质量。Gudgeon 和石泥鳅几乎没有受到河流破碎的影响，对太短的河流断面影响很小。Ide 受到中度影响，而迁徙物种 chub 和 dace 受到河流破碎的严重影响。鲢鱼和鲱鱼对恶劣的栖息地和水质也很敏感。区分河流破碎、栖息地恶化和水质差对低地河流鱼类分布的影响，增加了对物种存在和不存在原因的理解，并可能有助于有效的管理和恢复工作。由于建造了许多鱼道以改善连通性，鱼道并不能改善栖息地质量。Gudgeon 和石泥鳅几乎没有受到河流破碎的影响，对太短的河流断面影响很小。Ide 受到中度影响，而迁徙物种 chub 和 dace 受到河流破碎的严重影响。鲢鱼和鲢鱼对恶劣的栖息地和水质也很敏感。区分河流破碎、栖息地恶化和水质差对低地河流鱼类分布的影响，增加了对物种存在和缺失原因的理解，并可能有助于有效的管理和恢复工作。由于建造了许多鱼道以改善连通性，鱼道并不能改善栖息地质量。Gudgeon 和石泥鳅几乎没有受到河流破碎的影响，对太短的河流断面影响很小。Ide 受到中度影响，而迁徙物种 chub 和 dace 受到河流破碎的严重影响。鲢鱼和鲢鱼对恶劣的栖息地和水质也很敏感。区分河流破碎、栖息地恶化和水质差对低地河流鱼类分布的影响，增加了对物种存在和缺失原因的理解，并可能有助于有效的管理和恢复工作。Ide 受到中度影响，而迁徙物种 chub 和 dace 受到河流破碎的严重影响。鲢鱼和鲢鱼对恶劣的栖息地和水质也很敏感。区分河流破碎、栖息地恶化和水质差对低地河流鱼类分布的影响，增加了对物种存在和缺失原因的理解，并可能有助于有效的管理和恢复工作。Ide 受到中度影响，而迁徙物种 chub 和 dace 受到河流破碎的严重影响。鲢鱼和鲢鱼对恶劣的栖息地和水质也很敏感。区分河流破碎、栖息地恶化和水质差对低地河流鱼类分布的影响，增加了对物种存在和缺失原因的理解，并可能有助于有效的管理和恢复工作。