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4. CLASSIFYING SURFACE WATER BODIES
4.1 Overview
The WFD requires each surface water body to be classified in terms of ecological and chemical quality. For those water bodies not designated as heavily modified or artificial, this ecological quality is described in terms of ' ecological status'. This is an expression of the quality of the structure and functioning of surface water ecosystems as indicated by the condition of a number of 'quality elements'. The WFD uses the term 'quality elements' to refer to the different indicators of ecological quality making up its ecological status classification schemes.
There are five classes of ecological status, defined in terms of how much the ecological quality deviates from natural conditions. These are high, good, moderate, poor or bad. High status means that the water body is unaffected or virtually unaffected by human activity. A good status water body shows some signs of damage, such as slight alterations in the balance of aquatic species (biological quality elements) that would be expected in a water body unaffected by human activity.
The quality elements used to assess ecological status are:
- biological quality elements;
- chemical and physicochemical elements; and
- hydromorphological quality elements.
The ecological status of a water body is determined by combining assessment results for biological, chemical and physicochemical quality elements; with the quality element most severely affected by human activity determining the overall ecological status. This is called the ' one out - all out principle'3.
For a water body to achieve good ecological status, the biological quality elements must show only slight signs of disturbance caused by human activity. Among other things, this requires the chemical, physicochemical and hydromorphological quality of the water body to achieve the standards and conditions necessary to support the biological quality elements at good status.
Chemical status is either 'good' or 'failing to achieve good'. 'Good' means that none of the environmental quality standards established for priority substances and other dangerous substances identified at EU-level is being exceeded.
Ecological status and chemical status are then combined to provide an assessment of overall surface water status. The following diagram illustrates how these various elements are combined and how the 'one-out all-out' principle is applied.
Surface water status is determined by the poorer of ecological and chemical status; thus if chemical status is good but ecological status is failing to achieve good, then overall surface water status class is "moderate".
The classification of surface water bodies which are designated as heavily modified or artificial is described in Section 6.
4.2 Monitoring issues
Each surface water body will be classified by determining the impacts of the pressures to which it is subject using data collected by monitoring and, where relevant, the results of modelling. It is not possible to monitor accurately every stretch of water across Scotland at all times. It is therefore essential that SEPA's monitoring programmes are targeted on the basis of risk. For water bodies judged to be at risk of failing to achieve good status, SEPA will be expected to focus its assessments on those quality elements sensitive to the pressures placing the water bodies at risk.
SEPA must design a risk-based monitoring programme appropriately and collect sufficient data to inform its classification decisions. SEPA will be expected to provide information on its confidence in its classification (see Section 8 below).
SEPA may discount monitoring results which are influenced by one-off, unrepresentative and transient incidents, provided that the condition of each affected water body is adversely affected for only a short period of time, and recovers within a short period of time without the need for any restoration measures (i.e. there is only a transient blip in the condition of the water body).
4.3 The classification process
4.3.1 Assessing relevant quality elements
Standards and condition limits are used to define the class boundaries applicable to the different quality elements. To classify the ecological or chemical status of a surface water body, the determined values for parameters indicative of the relevant quality elements in a water body have to be compared with the corresponding standards and condition limits to be included in Ministers' 2008 Directions 4. The relevant quality elements depend on whether the water body concerned is a river, loch, transitional water or coastal water body. These are illustrated in Tables A1 to A5 at Annex A.
4.3.2 Update on biological assessment methods
In its report on surface water classification, UKTAG set out summary details of a range of biological methods recommended for use in the classification of surface water bodies. Full descriptions of those methods are currently being developed and are expected to be published on UKTAG's website in the autumn. SEPA will be expected to use these methods in carrying out the classification of Scotland's water bodies.
At present, the range of methods developed by UKTAG does not include systems for directly measuring:
(i) the impact of acidification on biological quality elements in rivers; or
(ii) the condition of fish communities in rivers or freshwater lochs
Methods to fill these gaps are being developed by UKTAG but will not be available in time to use in producing classifications for the river basin management plans in 2009.
Thus we are proposing to use the interim methods described in the following sections.
- River invertebrates and acidification
Given the significance of acidification impacts in parts of Scotland, we are proposing that SEPA uses the benthic invertebrate method described in Annex B for the purposes of assessing the ecological impact of acidification on rivers. This method will serve in the interim before a UK method becomes available and will ensure the first classification results reflect the impacts of acidification on river ecosystems.
There is currently limited data available on fish in lochs and so it is not practicable for SEPA to use an interim method to directly assess the condition of fish in freshwater lochs. However, we expect risks to fish communities to be indirectly reflected in the classification results. This is because impacts on other quality elements in lochs resulting from pressures that also affect fish, such as acidification, nutrient enrichment and hydromorphological alterations, will be assessed using the monitoring and assessment methods proposed for those other quality elements.
There is much more data on fish in rivers and we think it is appropriate that SEPA takes account of any such data available to it when making classification decisions. Consequently, where it has suitable data, we are proposing that SEPA use the interim criteria set out in Table C1 in Annex C when assessing the condition of fish communities in rivers. These criteria will apply until a UK monitoring and assessment method for fish is available.
We also expect SEPA to apply the standards specified in Table C2 in Annex C and developed by UKTAG for the purpose of assessing whether or not physical alterations affecting the hydromorphological quality element 'river continuity' are having significant adverse impacts on fish movements.
4.3.3 Alien species assessment
It is important to ensure that the impact of alien species is properly reflected in the classification process. Where significant adverse impacts are causing the ecological status of a water body to be moderate, poor or bad, we expect these to be reflected through the normal application of the proposed biological monitoring and assessment methods.
However these biological monitoring and assessment methods are not expected to be able to reliably detect impacts resulting from the introduction of alien species, such as to enable SEPA to differentiate between the high and good status classes.
In the absence of such tools, we expect SEPA to consider the impact of those 'high impact' species listed in Annex B of the UKTAG report on surface water classification. Where there is evidence that a listed species has become established over a significant spatial extent of a water body, SEPA should not classify the water body as being at high ecological status.
4.3.4 Spatial considerations
An important factor in assessing the status of a water body is the spatial extent of any adverse impact on a water body. Small, localised impacts are unlikely on their own to affect the ecological quality of a water body. In contrast, adverse impacts that extend over a significant area or length of a water body should be reflected in the classification results.
To ensure that classification results reflect impacts on the ecological quality of the water environment that are of sufficient spatial extent to affect ecological status, we expect SEPA to take account of the spatial criteria set out in the UKTAG report on surface water classification.
To do this, SEPA should aim to ensure that the monitoring data and modelling results it uses in classification are representative of the appropriate spatial extents of water bodies as defined by the UKTAG spatial criteria.
4.3.5 Overall surface water body status
SEPA must classify the overall status of each surface water body as high, good, moderate, poor or bad.
A detailed step-by-step approach to classifying the ecological status, chemical status and overall surface water status is set out in Annex D.
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