The Water Resources Sector (Phase 1 report to the National Climate Change Risk Assessment)

[摘要] This technical report describes methods and results from the headwater streams component of Countryside Survey. Countryside Survey (CS) consists of a field-based survey of 591 1km x 1km sample squares spread across England, Scotland and Wales, undertaken approximately every eight years. Around 60% of these squares contain at least one linear water feature such as a stream or ditch. Surveys of a headwater stream or ditch/drain site have been undertaken as part of Countryside Survey in 1990, 1998 and 2007. Since 1998, the survey has consisted of three elements: the macroinvertebrates (small aquatic animals visible to the naked eye which live on the stream bed), the macrophytes (larger aquatic plants) and the habitats (the structure of the channel and riparian zone). A single water chemistry sample is taken for supporting information. In 1990, only the macroinvertebrate component of the survey was undertaken. Compared with larger rivers, headwater streams are relatively poorly covered by the monitoring of national agencies. The data collected in Countryside Survey allow for an integrated description of the changes in ecological status and biodiversity of headwater streams through time, and the description of these changes is the main aim of this report. Additionally, for macroinvertebrates, their status against a minimally-impacted reference condition may be assessed. The vast amount of data available for the terrestrial survey component of Countryside Survey allows many potential linkages to be examined between human activities and stream ecological response. In this report, we detail some of these linkages, which will be elaborated further as part of the Countryside Survey Integrated Assessment to be published later in 2010. Results show many areas of improvement over the period 1998 to 2007. Notable improvements have occurred to macroinvertebrate status indicators in England, although south east England in particular is starting from a lower baseline of headwater stream biological quality when compared to other parts of Great Britain. Numbers of sites at good or high macroinvertebrate status in south east lowland England are still relatively low (30%). Increases in the number of macrophyte species and habitat quality appear to have occurred throughout Great Britain. Finally, improvements to trophic (nutrient) status, as indicated by the macrophyte communities, have occurred in Scotland. Substantial improvements in macroinvertebrate indicators occurred between 1990 and 1998 for all parts of Great Britain, however part of this observed improvement may be due to drought conditions in 1990. Declines have been observed in macroinvertebrate status for the Scottish Highlands, which had the highest proportion of sites at good or high status in 1998, but in 2007 this proportion has dropped to a level comparable to that of the rest of Scotland and upland England. Unfortunately it is not currently possible to pinpoint causes of this decline. There is an indication of increased extent of resectioning (engineering of the channel to widen, deepen and straighten), particularly in lowland Scotland, however this may be due to this feature being better recorded in 2007 compared to 1998. The example from Scotland is unusual in that for other indices and countries, there is no evidence for differences in trends between Environmental Zones. Quantification of changes in Wales is limited by the smaller sample size. A provisional integrated assessment has linked land management characteristics taken from the Countryside Survey square containing each headwater streams site, to an indicator of stream biological quality based on the mean stress sensitivity score of the macroinvertebrate taxa present. This has indicated logical negative relationships between intensive land uses such as arable and improved grassland and ecological status. Indicators of management of the river channel, such as the extent of resectioning (for land drainage and flood defence purposes), are also negatively associated with ecological status. Characteristics of the riparian zone, such as the amount of woody cover, are positively associated with ecological status. Overall, the headwater streams component of Countryside Survey is now beginning to build up a picture of the changes occurring to the ecological status of headwater streams. The changes are broadly positive, although some negative changes will need further investigation. The Headwater Streams Report was produced by the Centre for Ecology and Hydrology CEH), with contributions by Queen Mary University of London (QMUL), and Bournemouth University (BU).

[发布机构] Defra

[效力级别] Hydrology