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.

Change

Water Body ID

Water Body Name

SAC

Phosphorus target (µg l-1)

Water body removed

GB110064048730

Mawddach - middle

Afon Eden - Cors Goch Trawsfynydd

n/a

Water body removed

GB110065053960

Glaslyn – upstream Colwyn

Coedydd Derw a Safleoedd Ystlumod Meirion

n/a

Additional water body

GB111067051980

Tryweryn - Mynach to Llyn Celyn

Afon Dyfrdwy a Llyn Tegid

10

Additional water body

GB110064048740

Wen (Mawddach)

Afon Eden - Cors Goch Trawsfynydd

10

Additional water body

GB110064054610

Crawcwellt South

Afon Eden - Cors Goch Trawsfynydd

5

Additional water body

GB109056040000

Grwyne Fawr - source to conf Grwyne-Fechan

River Usk

7

Phosphorus target tightened

GB111067051610

Ceiriog - upstream of Teirw

Afon Dyfrdwy a Llyn Tegid

10 (previously 28)

Phosphorus target tightened

GB111067051910

Ceiriog - confluence Dee to Teirw

Afon Dyfrdwy a Llyn Tegid

25 (previously 28)

Phosphorus target tightened

GB110064048750

Eden - lower

Afon Eden - Cors Goch Trawsfynydd

5 (previously 10)

Phosphorus target tightened

GB109056039960

Grwyne-Fechan - source to conf Grwyne Fawr

River Usk

15 (previously 28)

Phosphorus target tightened

GB110064048710

Mawddach lower

Afon Eden - Cors Goch Trawsfynydd

10 (previously 13)

Phosphorus target reduced

GB110061030690

Deepford Brook - headwaters to conf with Syfynwy

Afonydd Cleddau

40 (previously 39)

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.

Change

Water- body ID

Waterbody Name

Site

Target µg l-1

Sample point ID

Additional water body

GB111067051980

Tryweryn - Mynach to Llyn Celyn

Afon Dyfrdwy a Llyn Tegid

10

288

Additional water body

GB110064048740

Wen (Mawddach)

Afon Eden - Cors Goch Trawsfynydd

10

20228

Additional water body

GB110064054610

Cracwellt South

Afon Eden - Cors Goch Trawsfynydd

5

28902

Additional water body

GB109056040000

Grwyne Fawr - source to conf Grwyne-Fechan

River Usk

7

Phosphorus target tightened

GB111067051610

Ceiriog - upstream of Teirw

Afon Dyfrdwy a Llyn

10

28038

Phosphorus target tightened

GB111067051910

Ceiriog - confluence Dee to Teirw

Afon Dyfrdwy a Llyn Tegid

25

578

Phosphorus target tightened

GB110064048750

Eden - lower

Afon Eden - Cors Goch Trawsfynydd

5

20064

Phosphorus target tightened

GB109056039960

Grwyne-Fechan - source to conf Grwyne Fawr

River Usk

15

Phosphorus target tightened

GB110064048710

Mawddach lower

Afon Eden - Cors Goch Trawsfynydd

10

20003

Phosphorus target relaxed

GB110061030690

Deepford Brook - headwaters to conf with Syfynwy

Afonydd Cleddau

40

86005

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

Waterbody Name

Target µg l-1

No. samples annual

Annual Mean µg l-1

No. samples growing season

Growing Season Mean µg l-1

Previous Status 2021

Result Status 2022

Tryweryn - Mynach to Llyn Celyn

10

26

8.55

18

9.57

not included

pass

Wen (Mawddach)

10

no data

-

no data

-

not included

not assessed

Cracwellt South

5

21

2.34

14

2.78

not included

pass

Grwyne Fawr - source to conf Grwyne-Fechan

7

no data

-

no data

-

not included

not assessed

Ceiriog - upstream of Teirw

10

no data

-

no data

-

not assessed

not assessed

Ceiriog - confluence Dee to Teirw

25

31

22.25

19

25.9

pass

fail

Eden - lower

5

21

0.77

14

0.86

pass

pass

Grwyne-Fechan - source to conf Grwyne Fawr

15

no data

-

no data

-

not assessed

not assessed

Mawddach lower

10

28

0.85

18

0.74

pass

pass

Deepford Brook - headwaters to conf with Syfynwy

40

28

44.25

17

50.2

fail

fail

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).

Assessment

Pass

Fail

Total

Not assessed

Grand Total

Number of water bodies

43

66

109

18

127

% of water bodies assessed

39.4

60.6

85.8

14.2

100

% by length (km) of water bodies assessed

44

56

88.1

11.9

100

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

 

SAC River

Pass (no. water bodies)

Pass (% of water bodies assessed)

Fail (no water bodies)

Fail (% of water bodies assessed)

Total no. water bodies

Not assessed

Grand Total

River Dee & Llyn Tegid

4

50

4

50

8

1

9

Afon Eden - Cors Goch Trawsfynydd

4

100

0

0

4

1

5

Afon Gwyrfai a Llyn Cwellyn

2

100

0

0

2

0

2

Afon Teifi

8

50

8

50

16

2

18

Afon Tywi

2

100

0

0

2

1

3

Afonydd Cleddau

5

33

10

67

15

4

19

Meirionnydd Oakwoods and Bat Sites

2

100

0

0

2

0

2

River Usk / Afon Wysg

2

12

15

88

17

7

24

River Wye / Afon Gwy

14

33

29

67

43

2

45

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.

 

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