Determining historic ecological conditions in lowland rivers: applying palaeoecological techniques to river restoration planning

人们普遍认识到，人类活动已导致全球河流生态系统的水文地貌(水流特征和河流地貌)和生态发生重大变化，在许多情况下，可能需要恢复河流的形态多样性。然而，在英格兰低地的大部分地区，由于历史上的河道改变，已经失去或处于不利地位的河流动植物的性质和数量仍然存在重大问题。这些河流中的许多经过了许多世纪的广泛修改，以达到各种目的。一些最重大的修改发生在第二次世界大战后的几十年里，目的是通过改善土地排水和相关的洪水管理来提高粮食安全。河道化，包括拉直、加深、加宽和重新定位，导致栖息地异质性大大降低，对河流和泛滥平原的生物多样性造成严重影响。需要更好地了解受损或丧失的地貌、水文，特别是生物多样性要素，以便确定恢复和恢复河道形态和功能的计划措施的益处。为了在自然过程在大空间尺度上受到影响的环境中产生这种理解，提出了一种创新的古生态方法，该方法将提供一个了解过去河流状况的窗口，以便在修复之前可以测量当代河道和居住在其中的社区。该项目将结合现代河流形态和生态学的分析与古生态技术(通过研究河岸和与河流相关的泛滥平原沉积)来探索英格兰选定的低地河流的近代历史。我们假设，由于历史上的管理做法，河道形态和河流动物群落的自然要素已经丢失或受到损害。该项目将通过对毛翅目昆虫(毛翅目幼虫)化石和当代毛翅目昆虫和水生鞘翅目昆虫(甲虫)组合的研究，描述一些经过改造的重要栖息地特征，并通过使用古生态技术来表征动物群落的变化。研究地点是从指定为特殊科学价值地点(SSSI)的英国河流网络中挑选出来的。该网络包括在英格兰发现的不同河流类型的代表性实例，研究将集中在六条河流上，包括：博尔特河(肯特)、R.Eye(莱斯特郡)、R.Hull(东约克郡)和R.Wensum(诺福克)都表现出不同程度的拉直和过度加宽，R.Mease(斯塔福德郡)和R.Blythe(W.Mids)。其具有基本上未修改的频道形式。从战后河道改造时代开始，人们就发现了潜在的古河道所在地。这些包括旧的河道特征(包括河道拉直或天然牛弓后被切断的弯道)，或者在经过大幅修改的河道内的沉积物，这些沉积物没有受到干扰。详细的地点识别将包括检查历史地图、河流地貌评估、研究航空照片以及咨询当地自然英格兰和环境局工作人员。将按照拉夫堡大学制定的程序收集和分析大型无脊椎动物亚化石(毛翅目和鞘翅目)的沉积物岩芯和/或切片。这些数据将与当代修改后的航道中记录的群落进行比较，以便直接评估可能因地貌变化而产生的变化。

It is widely recognised that anthropogenic activities have resulted in significant changes to the hydromorphology (flow characteristics and fluvial geomorphology) and ecology of riverine ecosystems globally and that to reinstate morphological diversity physical river restoration may be required in many instances. However, significant questions remain regarding the nature and number of riverine flora and fauna that have been lost or disadvantaged by historic channel modifications across much of lowland England. Many of these rivers have been extensively modified for many centuries for a variety of purposes. Some of the most significant modification took place in the decades following World War II, in a drive to increase food security through improved land drainage and associated flood management. Channelisation, involving straightening, deepening, widening and reprofiling resulted in greatly reduced habitat heterogeneity, with serious implications for riverine and floodplain biodiversity. A better understanding of the geomorphological, hydrological and particularly the biodiversity elements that have been compromised or lost is required in order to characterise the benefits of planned measures to restore and reinstate channel form and function. To generate this understanding in an environment where natural processes have been impacted over large spatial scales, an innovative palaeoecological approach is proposed that will provide a window on past riverine conditions so that the contemporary channel and community inhabiting it can be gauged prior to restoration. This project will combine analysis of contemporary river morphology and ecology with palaeoecological techniques (via examination of instream and floodplain deposits associated with the river) to explore the recent history of selected lowland rivers in England. We hypothesise that natural elements of channel morphology and the instream faunal community have been lost or compromised due to historic management practices. The project will characterise some of the critical habitat features that have suffered from modifications and through the use of palaeoecological techniques characterise the changes in the faunal community through examination of fossil and contemporary Trichoptera (caddis fly larvae) and aquatic Coleoptera (beetles) assemblages. Study sites have been selected from the English network of rivers designated as Sites of Special Scientific Interest (SSSIs). This network includes representative examples of different river types found in England and research will focus on six rivers comprising: the River Beult (Kent), R. Eye (Leicestershire), R. Hull (EastYorkshire) and R. Wensum (Norfolk) all exhibiting straightening and over-widening to varying degrees, and the R. Mease (Staffordshire) with significantly less modification and the R. Blythe (W. Mids.) which has a largely unmodified channel form. Potential palaeochannel localities have been identified dating from the post-war era of channel modification. These include old channel features (including meanders cut off following channel straightening or natural ox-bows) or sediments within largely modified channels that have escaped disturbance. Detailed site identification will involve examination of historical maps, geomorphological appraisals of the rivers, study of aerial photos and consultation with local Natural England and Environment Agency staff. Sediment cores and/or sections will be collected and analysed for sub-fossil macroinvertebrates (Trichoptera and Coleoptera) following the procedures developed at Loughborough University. This data will be compared with the communities recorded in the contemporary modified channel, in order to directly evaluate changes likely to have resulted from the altered geomorphology.