Update to phosphorus targets for water bodies in Special Area of Conservation (SAC) rivers in Wales

As part of the focus on water quality in SAC Rivers in Wales, we have reviewed the waterbodies in scope for SAC targets, and also made changes to the phosphorus targets for six water bodies. This review is part of the water quality target setting process for SAC Rivers and implements recommendations in the Compliance Assessment of Welsh River SACs Against Phosphorus Targets (Hatton-Ellis and Jones 2021).

In the future the aim is to do a full review of all water quality targets for water bodies which are part of SAC rivers, therefore it was decided to implement these minor changes immediately rather than wait. The changes are detailed below (Table 1).  

As a result of the review, two water bodies have been removed and four have been added due to minor inconsistencies in mapping. This has largely been due to water bodies which do not align with the SAC boundary and also due to updated information about the location of the relevant SAC features.

In addition, targets for five water bodies have been tightened and for one water body the target has been relaxed. The phosphorus targets are based on a typology using thresholds for altitude, alkalinity and river size.  The changes are due to the water body having been assigned either an incorrect altitude, alkalinity or river size or incorrect phosphorus data used during the original target setting process.

Table 1. Changes to waterbodies and phosphorus targets  since the publication of the  Compliance Assessment of Welsh River SACs Against Phosphorus Targets (Hatton and Jones 2021).

Following these changes, there are now 127 water bodies within SAC rivers with a defined single  phosphorus target

Find a full list of phosphorus targets for each SAC river in Wales

Re-assessment of waterbodies following changes to the phosphorus targets

The additional water bodies and water bodies with revised targets have now been re-assessed for compliance, using data from the same time period as the original phosphorus compliance report (2017-2019) and the results are shown in Table 2 below.

One waterbody is now assessed as failing, which was previously assessed as passing, the ‘Ceiriog - confluence Dee to Teirw’ (GB111067051910) in the River Dee SAC. This is only failing for the growing season mean. Compliance assessment results for water bodies in the River Dee SAC in the 2021 report and with the revised targets (which cause the water body on the Ceiriog to fail) are shown in figures 1 and 2 respectively, below.

Table 2. Information about additional water bodies and water bodies with changed phosphorus target

Table 3. Phosphorus compliance for additional water bodies and water bodies with changed phosphorus target

Figure 1. Orthophosphate compliance map for the River Dee SAC from the 2021 Compliance assessment. Water bodies shaded green pass their target. Other colours fail the target with different colours representing the magnitude of failures in µg l-1^-1, expressed as the larger of annual means and growing season means. Greyed out water bodies could not be assessed due to lack of data.

Figure 2. Orthophosphate compliance map for the River Dee SAC based on the updated targets. Water bodies shaded green pass their target. Other colours fail the target with different colours representing the magnitude of failures in µg l-1^-1, expressed as the larger of annual means and growing season means. Greyed out water bodies could not be assessed due to lack of data.

Summary of phosphorus compliance for all 127 water bodies within SAC Rivers in Wales

A total of 109 water bodies in nine different SACs were assessed (Table 3 below). Overall, 43 (39.4%) water bodies passed their targets and 66 (60.6%) water bodies failed. This varied in each SAC river with no water bodies assessed as failing in the Afon Eden - Cors Goch Trawsfynydd, Afon Gwyrfai a Llyn Cwellyn, River Tywi and the Meirionnydd Oakwoods and Bat Sites SACs (Table 4 below).

Table 3. Summary of SAC river phosphorus compliance results expressed as number and length of water bodies.

Table 4. Summary of SAC river phosphorus compliance results for the nine SAC Rivers in Wales.

Sample point correction

In the  Compliance Assessment of Welsh  River SACs Against Phosphorus Targets  (Hatton-Ellis and Jones 2021), the report mentions an ‘additional sample point from near Waunfawr Sewage Treatment Works (STW) (55219 Waen STW)’ on page 34. This should read sample point 22519.