Species point records from 1985 University of Bristol upper Severn Estuary survey

This study was commissioned to extend the sparse information on the ecology of the Upper Severn Estuary in relation to the feasibility study to place a tidal energy barrage at English Stones. The report is in 3 parts: literature survey, field survey and a discussion of possible changes due to barrage construction. The literature survey examines published information (44 papers) on algae, saltmarshes, fish, birds and invertebrates and discusses the findings. A field survey concentrated on the invertebrates occuring in the major habitats (rock, shingle, sand, mud and saltmarsh) in 5 sectors of the upper estuary from Avonmouth to the riverine stretches above Gloucester. The major conclusion is that tidal scour and its effects together with the different sediment types are equally important to reduced and varying salinity in controlling invertebrate distribution. As expected, major ecological changes are predicted if a barrage were constructed. Increased stability of the system due, in particular, to the reduction in current strength and scour could lead to increases in both the diversity and absolute number of invertebrates. There would also be an increase in the area occupied by Spartina marsh. The report concludes with recommendations for further research required necessary to properly evaluate the consequences of barrage construction. In addition, many samples of saltmarsh invertebrates from the present study still require examination. It seems clear from the engineering and economic studies of the English Stones barrage that the project would not be viable as rapid silting of the upper basin would prevent efficient operation.本研究受委托开展，旨在补充有关上塞文河口（Upper Severn Estuary）生态的现有稀疏信息，以配合在英吉利石（English Stones）处修建潮汐能拦河坝的可行性研究。本报告分为三个部分：文献调研、野外调查，以及针对拦河坝建设可能引发的生态变化的探讨。文献调研部分梳理了已发表的44篇关于藻类、盐沼（saltmarshes）、鱼类、鸟类及无脊椎动物（invertebrates）的相关文献，并对研究结果进行了系统讨论。野外调查聚焦于上河口从埃文茅斯（Avonmouth）至格洛斯特以上河流河段的5个区域内，主要生境（岩石、砾石、沙质、泥质及盐沼）中栖息的无脊椎动物群落。核心结论为，潮汐冲刷及其影响，结合不同的沉积物类型，与盐度的降低和波动在调控无脊椎动物分布方面同等重要。正如预期，若修建拦河坝，该生态系统将出现显著变化：尤其由于流速与冲刷作用减弱，系统稳定性提升，这将导致无脊椎动物的物种多样性与种群绝对数量均有所增长，米草属（Spartina）盐沼的分布面积也将随之扩大。本报告最后提出了后续研究建议，以全面评估拦河坝建设可能带来的生态后果。此外，本研究采集的大量盐沼无脊椎动物样本仍有待进一步分析。从英吉利石拦河坝的工程与经济研究结果来看，该项目显然不具备可行性，因为上游流域的快速淤积将阻碍其高效运行。