Riparian management affects instream habitat condition in a dairy stream catchment

Using a space-for-time substitution design, we investigated the response of structural instream habitat and fish populations to different riparian management practices throughout a Dairy Best Practice Catchment. We found a significant negative correlation between the upstream area of stock exclusion fencing and deposited instream fine sediment cover. Furthermore, we determined that this relationship emerges when ≥300 m lengths of upstream riparian area were included in the analysis, indicating the scale at which stock exclusion fencing results in a positive instream habitat response. Specifically, for this historically degraded spring-fed stream, our findings indicate that riparian segments with 5 m wide stock exclusion fences (both banks) are required to achieve instream fine sediment cover below 20% in downstream reaches. Fish were sparse and evenly spread throughout the catchment. Fish distributions were not correlated with reach-scale riparian or instream habitat variables, possibly because the available habitat quality gradient was too narrow.

本研究采用空间替代时间法（space-for-time substitution），在乳业最佳实践流域（Dairy Best Practice Catchment）内探究了河流结构生境与鱼类种群对不同河岸带管理措施的响应。研究发现，牲畜禁入围栏（stock exclusion fencing）上游区域与河流内沉积细泥沙覆盖率之间存在显著负相关关系。进一步分析表明，当分析纳入不小于300米的上游河岸带长度时，该相关关系方才显现，这指明了牲畜禁入围栏可产生正向河流生境响应的空间尺度。针对这条历史退化型泉水补给河流，本研究结果显示，需在两岸设置宽度为5米的牲畜禁入围栏的河岸带片段，方能使下游河段的河流内细泥沙覆盖率降至20%以下。研究区内鱼类种群稀少且分布均匀，鱼类分布与河段尺度的河岸带或河流生境变量均无显著相关性，这可能是因为可用生境的质量梯度过于狭窄。