Countryside Survey 2000. Module 2: Freshwater studies.  Module 2 final report

by
M.T. Furse and 29 co-authors
Contact: Mike Furse (mtf@ceh.ac.uk). CEH Dorset, Winfrith Technology Centre, Dorchester, Dorset, DT2 8ZD, UK

Contents

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Executive Summary

The overall objectives of Countryside Survey 2000 were:

• to record the stock of countryside features associated with the wider countryside, including information on land cover, landscape features, terrestrial and freshwater habitats and species, in 1998
• to determine change by comparison with earlier surveys
• to maintain and refine the base line set down in 1990 to ensure the survey data continue to be relevant to current policy needs
• to develop the data-base of countryside information following the 1990 Survey so that a range of data outputs, relevant to the reporting frameworks used by Central Government and its Agencies and the needs of research and the academic community, can be derived, with the first results available in 2000

Within these overall objectives, a sub-set of more detailed objectives have been developed for the survey of freshwater habitats. These are as follows:

• to provide information on the status, distribution and recent changes in freshwater habitats in Great Britain: to include assessments of freshwater biota, river habitats and water chemistry. The survey work will be integrated with the survey of widespread habitats and landscape and will be compatible with the survey and monitoring procedures used by the Environment Agency
• to provide information on the status and distribution of the macro-invertebrate fauna of streams and rivers in Great Britain.
• to determine and evaluate change by comparison with 1990 survey data relating to the same sites
• to determine the habitat structure and degree of modification of river corridors
• to undertake a limited diagnostic survey of the chemical character of the watercourses to help interpret the results of macro-invertebrate and river habitat surveys
• to investigate the relationship between the habitat quality and modification of river corridors, the ecological quality of the watercourse and the condition of the surrounding countryside
• to derive indicators relating to status and change in watercourse and river habitat quality

In order to meet these objectives, aquatic macro-invertebrate fauna and habitat quality of river corridors of a single watercourse were surveyed in each 1km square in which an appropriate watercourse was present. Single chemical samples were also taken at each site. Opportunistic surveys of diatoms, macrophytes and chironomid pupal exuviae were also undertaken but these samples have not yet been analysed. A total of 425 watercourses were surveyed for their river habit quality, of which 404 were flowing at the time of visit and were also sampled biologically and chemically. All surveys were undertaken in 1998.

The biological condition of each sampling point was assessed using the same standard quality indices widely applied by the water industry. Two further indices, the Habitat Quality Assessment (HQA) and Habitat Modification Index (HMI) were used to assess the condition of the river corridor.

Macro-invertebrate samples collected during CS2000 were compared with samples collected from 354 matched sites also sampled during CS1990. Comparisons showed a widespread increase in taxon richness, with an average of 24.3 taxa (mainly species) per sample in 1998, compared with 16.5 in 1990. Mean gains were greater in the uplands than the lowlands and greater in Scotland than England and Wales. However, the mean number of taxa per site remained slightly higher in England and Wales than in Scotland.

The increase in mean taxa per site was accompanied by an increase in the frequency of distribution of most taxa. Of the 473 taxa recorded in 1998, 329 (70%) were more frequent in that year than in 1990, 106 (22%) were less frequent and 38 (8%) showed no change. These 473 taxa included a total of three that had Red Data Book status and 30 that were categorised as being Nationally Scarce.

There was a tendency for the greatest gains in frequency to be made by taxa associated with fast flow conditions. Conversely, taxa making the least increase or the greatest decrease in frequency tended to be those associated with slow-flow conditions or standing water. The changes in frequency of individual taxa were significantly correlated with their known flow preferences, as categorised in the Lotic invertebrate Index for Flow Evaluation (LIFE).

Increases in number of taxa also occurred at family level. The number of relevant families is present in a sample (NTaxa) is one of the two indices of biological condition of sites derived from the Biological Monitoring Working Party (BMWP) Score system for the purposes of this study. The other is the Average Score Per Taxon (ASPT). ASPT is a measure of the average organic pollution tolerance of the taxa present in a sample.

A general increase in the number of scoring taxa per site and of ASPT values led to apparent improvement in the biological condition of Countryside Survey sites in 1998 compared to their condition in 1990. These improvements occurred in all six Environmental Zones recognised in Countryside Survey 2000 but were most marked in Scotland.

RIVPACS (River Invertebrate Prediction and Classification) was used to compare the grades of biological condition of sites in 1990 and 1998. Analyses showed that 25.1% of sites in GB showed a significant increase in their biological grade between 1990 and 1998, whilst only 2.0% showed a significant decline. The respective figures for Scotland were 33.0% (significant improvement) and 1.1% (significant decline). In England and Wales the corresponding values were 17.2% and 2.9%. The general improvement in biological condition of Countryside Survey streams was matched but an equivalent annual rate of improvement between the National Rivers Authority’s 1990 River Quality Assessment and their 1995 General Quality Assessment.

Values of the Habitat Quality Assessment were, on average, higher in Scotland than in England and Wales, where the lowest mean value per Environmental Zone was recorded in the “Easterly lowlands”. However, the highest recorded mean value was in the “Uplands” of England and Wales.

Conversely, Habitat Modification Scores were lower in the uplands than the lowlands and in Scotland rather than England and Wales. Low values signify little channel management and are considered desirable. The lowest mean value of this index was in the “True uplands” of Scotland, indicating minimal management practices. Conversely, the highest mean value was in the “Easterly lowlands” of England and Wales, where channel straightening and dredging are commonplace.

In all Environmental Zones, except the “Uplands” of England and Wales, one or both of the biotic index values derived from the BMWP Score system were significantly correlated with one or both of the two indices of habitat quality and modification derived from River Habitat Survey. This confirms expectations that the biological condition of streams tends to be highest in stretches that are of good habitat quality and subject to little channel management.

Strong significant relationships were also observed between riparian Broad Habitat type and indices of river corridor condition. Some significant relationships between Broad Habitat type and the biological condition were also recorded, although these were fewer and weaker than with the RHS indices. In particular, corridor and in-stream biological condition were negatively correlated with the frequency of the “Arable and horticulture” Broad Habitat. Positive correlations were strongest with “Broadleaved, mixed and yew woodland” and, to a lesser extent, with “Coniferous woods”.

The extent of habitat modification was significantly and positively correlated (p<0.001) with the extent of “Arable and horticulture”, “Improved grassland” and “Built up areas & gardens”. Significant negative correlations (p<0.001) between extent of individual Broad Habitats and Habitat Modification Score occurred with “Acid grassland” and “Bog. At the p<0.05 level, additional negative correlations were with “Broadleaved, mixed and yew woodland”, “Coniferous woods”, “Dwarf shrub heath and “Fenland, marsh and swamp”.

Possible explanations for the improvement in the biological condition of the CS2000 watercourses between 1990 and 1998 were considered. The possibility that they resulted from the differential performance of the field surveyors was discounted. The previous experience of the 1990 and 1998 field teams and the pre-survey training that each group received were well matched. Other possible explanations included:

• differences in flow conditions
• improved water chemistry
• reduction in pollution incidents
• increase in the development of vegetated riparian strips (buffer zones), managed separately from the rest of the adjacent field

Whilst the presence of unmanaged, tall vegetation was correlated with good in-stream biological condition, results from other modules of CS200 suggest that this form of vegetated riparian strip is also associated with reduction of botanical diversity. Management procedures for “buffer zones” that consolidate the improvement of in-stream conditions, without reducing the diversity of streamside vegetation, are desirable.

Three research programmes are proposed, in order to examine the results of CS200 in more detail. These are:

• How is the improvement in the quality of freshwater habitats related to management, use and structure of the river corridor and adjacent catchment land cover?
• How can the multiple sources of ecological information collected during CS2000 be best used to indicate the nutrient status of small watercourses?
• How are changes in the biological condition of upland streams related to changes in land management and climate?