Spatial and temporal patterns of aquatic macrophyte biodiversity at the river catchment scale: the River Glaven, north Norfolk

过去200年来，农业景观中的淡水生物多样性主要受到人类活动的影响，特别是农业集约化。生物多样性的变化既发生在长的(几十个世纪)的时间尺度上，也发生在短的(几年)时间尺度上，其强度随时间和空间而变化。水生景观的物种数量减少，生态退化加剧，因此，调查河流流域尺度上生物多样性的格局和变化对于更好地了解生态和为保护提供信息是重要的。英国诺福克北部的Glaven河为以水生植物为指示组在流域尺度上调查生物多样性提供了独特的机会。自20世纪90年代末以来，对流域内的水体(包括湖泊、池塘、河段、沟渠和死水)进行了广泛的水生植物调查，本论文涉及75项新的大型植物调查，旨在填补空间和立地类型方面的空白，以创建一个包含250多个站点和大约750个单独调查的数据库，提供良好的集水区空间覆盖。这个数据库被用来解决三个关键问题：i)哪些水体类型拥有最稀有的物种和最多的生物多样性？二)如果集水区面积丧失，集水区规模的生物多样性是否会下降？和iii)现有的保护努力为流域规模的生物多样性做了什么？这项研究的另一个主要方面是对塞尔布里格湖和贝菲尔德湖两个关键湖址的沉积岩芯的大型化石和硅藻进行了古生态分析，以研究过去两个世纪的生态变化。这两个地点以前都表现出良好的生态条件，随后由于恢复工作而经历了一段富营养化时期和随后的恢复。该项目展示了如何在如此详细的空间覆盖范围内检查集水区的生物多样性，从而提出独特的问题，因此这种方法如何能够更好地为保护工作提供信息。

Freshwater biodiversity over the last 200 years in agricultural landscapes has been primarily influenced by human activities, particularly agricultural intensification. Biodiversity changes have occurred on both long (decades-centuries) and short (years) timescales, and their intensity varies over time and space. Aquatic landscapes have seen declines in species populations and increases in ecological degradation, therefore investigating patterns of and changes in biodiversity at the river catchment scale is important for better ecological understanding and informing conservation.The River Glaven, north Norfolk, UK, provides a unique opportunity to investigate biodiversity at the catchment scale using aquatic macrophytes as an indicator group. Waterbodies in the catchment including lakes, ponds, river sections, ditches, and backwaters, have been extensively surveyed for aquatic macrophytes since the late 1990s and this thesis involved 75 new macrophyte surveys, targeted to fill gaps spatially and in site type, to create a database of over 250 sites and approximately 750 individual surveys providing excellent spatial coverage of the catchment. This database was employed to address three key questions: i) which waterbody types hold the rarest species and the most biodiversity? ii) if areas of the catchment are lost will catchment scale biodiversity decline? and iii) what have existing conservation efforts done for catchment scale biodiversity? The other major strand of the research involved palaeoecological analysis of macrofossils and diatoms of two sediment cores from key lake sites, Selbrigg Pond and Bayfield Lake, to examine ecological change over the last two centuries. Both sites showed previously good ecological conditions, followed by a period of eutrophication and subsequent recovery due to restoration efforts.This project demonstrates how examining biodiversity at the catchment scale with such detailed spatial coverage allows for unique questions to be asked and therefore how the approach can better inform conservation efforts.