Rivers and streams

Context

In their natural state rivers are dynamic systems, continually modifying their form. The mosaic of features found in rivers and streams supports a diverse range of plants and animals. For example, riffles and pools support aquatic species, and exposed sediments such as shingle beds and sand bars are important for a range of invertebrates, notably ground beetles, spiders and craneflies. Marginal and bankside vegetation support an array of wild flowers and animals. Rivers and streams often provide a wildlife corridor link between fragmented habitats in intensively farmed areas.

However in many cases their ability to rejuvenate and create new habitat has been reduced or arrested by flood defence structures and impoundments. Few rivers in the UK have not been physically modified by man and such rivers represent a very valuable resource. Erosion of banks has also been caused by canalisation and the removal of tree cover in historic times. Such activities have resulted in changes in the frequency and magnitude of flooding, altering seasonal patterns of flows and hydrograph form. In addition, flow regulation has altered patterns of sediment transport and nutrient exchange in river systems. Any resulting eutrophication can have detrimental effects on floodplain habitat which still retains some connection with the main stream.

The plant and animal assemblages of rivers and streams vary according to their geographical area, underlying geology and water quality. Swiftly-flowing upland, nutrient-poor rivers support a wide range of mosses and liverworts and relatively few species of higher plants. The invertebrate fauna of upland rivers is dominated by stoneflies, mayflies and caddisflies, while fish such as salmon Salmo salar and brown trout Salmo trutta are often present. In contrast, lowland nutrient-rich systems are dominated by higher plants, and coarse fish such as chub Leuciscus cephalus, dace Leuciscus leuciscus and roach Rutilus rutilus. Where nutrient levels are artificially raised, the occurrence of algae increases.

Adjacent semi-natural wetland habitats such as unimproved floodplain grasslands, marshy grassland, wet heath, fens, bogs, flushes, swamps and wet woodland, although intimately linked with the river, are covered in other reporting categories.

SSSIs can be notified if they qualify under criteria outlined in Section 6 of Chapter 6 Freshwater habitats of the Guidelines for Selection of Biological SSSIs. In Northern Ireland, ASSIs are selected on a very similar basis – the Guidelines for the Selection of Biological ASSIs in Northern Ireland is an addendum to the SSSI guidelines rather than an alternative.

Summary statistics

	SAC	A/SSSI	Total
Favourable condition	8%	32%	28%
Main monitoring coverage	E, W	E
Reported assessments	13	76	89
Completeness of assessments	54%	unknown
Distribution of features			UK

Number of assessments reported by country and site type

Country	SAC	SSSI/ASSI
England	12	72
Scotland	0	4
Wales	1	0
Northern Ireland	0	0
United Kingdom	13	76

Natura features

List of Natura 2000 interest features within this reporting category

Interest feature name
Formal name	Informal name	No. of assessments reported	Total no. of features	% assessed
Water courses of plain to montane levels with the Ranunculion fluitantis and Callitricho-Batrachion vegetation	Rivers with floating vegetation often dominated by water-crowfoot	13	24	54%

Natura 2000 comprises Special Protection Areas (under the Birds Directive) and Special Areas for Conservation (under the Habitats and Species Directive). The list presented here includes all of the qualifying interest features under these Directives, and shows the proportion of these features for which a condition assessment has been made.

SSSI features

List of SSSI and ASSI interest features in this reporting category

Interest feature name
Formal name	Informal name	No. of assessments reported
Mesotrophic river/stream	Mesotrophic river/stream	1
Oligotrophic river/stream	Oligotrophic river/stream	3
Rivers and streams	Rivers and streams	72

This list has not been fully standardised at a UK level yet. It is intended to show the principal constituent "feature types" for this reporting category.

Maps - distribution

UK distibution of reported interest features

Distribution of reported interest features.

Map showing the locations of the 10km squares in which at least one condition assessment has been reported. It does not show features that have not yet been assessed.

Maps - Natura

Current condition of SAC features
Distribution of SAC features showing assessments of favourability (where unfavourable-recovering is counted as unfavourable).

Condition of SAC features, with those currently reported as unfavourable-recovering shown as favourable
The implication of the unfavourable-recovering condition assessments is that at some point in the future these features should become favourable. This map shows the effect of that recovery by counting the favourable and unfavourable-recovering assessments together.

IMPORTANT NOTE: we do not have information on the timescale of the predicted recovery, which may be influenced by many past, natural and human related factors. A sustained sympathetic management regime is more likely to result in favourable condition being attained.

Key: Proportion of assessed features on 10km squares that are favourable:

Natura map legend - Key: proportion of assessed features on 10km squares that are favourable

Details of how these maps were produced

Maps - SSSI

Current condition of SSSI/ASSI features
Distribution of SSSI/ASSI features showing assessments of favourability (where unfavourable-recovering is counted as unfavourable).

Condition of SSSI/ASSI features, with those currently reported as unfavourable-recovering shown as favourable
The implication of the unfavourable-recovering condition assessments is that at some point in the future these features should become favourable. This map shows the effect of that recovery by counting the favourable and unfavourable-recovering assessments together.

Key: Proportion of assessed features on 10km squares that are favourable:

SSSI map legend - Proportion of assessed features on 10km squares that are favourable

Details of how these maps were produced

Condition summary

This lists the 10 different condition assessments and presents a bar chart showing the number of features within the SSSI series and the Natura 2000 series (either SPA for bird features or SAC for features other than birds). Note that for Natura 2000 we are able to estimate the number of features that have not been assessed during the 6 year reporting period - we are unable to do this for SSSI/ASSI because we do not have an overall list of notified interest features for these designations.

NB favourable unclassified and unfavourable unclassified have been used in this first six year cycle to get around difficulties in identifying trends in condition as common standards monitoring is implemented. It is expected that these categories will not be used for subsequent assessments of a feature.

Condition assessment - Natura 2000 features

The number and proportion of assessments for Natura 2000 (SAC and SPA) interest features falling into each of the condition categories. Note that the �unfavourable� category includes all reports of unfavourable condition except �unfavourable recovering� which is shown as a separate segment.

Condition assessment - SSSI features

The number and proportion of assessments for SSSI/ASSI interest features falling into each of the condition categories. Note that the �unfavourable� category includes all reports of unfavourable condition except �unfavourable recovering� which is shown as a separate segment.

Adverse activities

The number of interest features where an activity has been reported as being implicated in the "unfavourable" condition of a feature. More than one adverse activity may be reported for each feature.

Management measures

For each "measure" the chart shows the number of interest features where that measure has been taken on a site to improve or maintain the condition of an interest feature. More than one measure may be reported for each feature assessed.

Interpretation

28% of river and stream features reported are in favourable condition. River and stream features are generally in poor condition compared to other habitats, freshwater or otherwise. This is well below the average for all feature types combined. 32% of A/SSSI features and 8% of SAC features reported are in favourable condition. A further 11% of A/SSSI features reported are unfavourable-recovering.

Pollution and water quality issues are the main reasons for rivers and streams being considered in unfavourable condition. Many rivers have also been physically modified, often more than a century ago. Diffuse pollution is becoming increasingly recognised as a problem. In order to tackle this, the water companies' investment programmes will include the installation of phosphorus removal at most of the relevant sewage treatment works by 2010. In 2004 pilot schemes were launched to tackle diffuse pollution in four English river SAC catchments (Cumbrian Derwent, Clun, Wensum, and Hampshire Avon).

Other impacts on river SSSIs include abstraction, particularly from chalk aquifers, and invasive species such as the American signal crayfish Pacifastacus leniusculus. This species has not only ousted the native white-clawed crayfish Austropotamobius pallipes from many rivers, but is undermining banks causing their collapse, as well as siltation of gravels on chalk rivers such as the Lambourn SAC.

For some rivers, there are pressures causing concern adjacent to these sites. For example, invasive plant species such as giant hogweed Heracleum mantegazzianum and Japanese knotweed Fallopia japonica outside the site boundary. In some cases management action is already in place to forestall potential future problems, for example to address problems of nutrient enrichment from agriculture.