Indicative values within nutrient nitrogen critical load ranges for use in air pollution impact assessments

Critical load values for nutrient nitrogen deposition are provided as a range (e.g. 10-20 kgN/ha/yr for dry heaths).  The table below provides indicative values within the critical load range (by habitat type) for use in impact assessments (e.g. assessments that are part of planning applications or environmental permit applications).  Further explanation is provided in the document attached at the bottom of the table.

Note: A document has also been produced  to provide guidance on applying the critical load range for atmospheric nitrogen deposition to bog habitats in the UK.

Habitat type (EUNIS code)

Critical load (CL) range

 (kgN/ha/yr)

Recommended value to use at screening stage of assessment

(kgN/ha/yr)

Recommended value to use at detailed assessment stage

(kgN/ha/yr)

Marine habitats

 

 

 

Mid-upper saltmarshes (A2.53)

20-30

20

20

Pioneer & low-mid saltmarshes (A2.54 and A2.55) 

20-30

30

30

Coastal habitats

 

 

 

Shifting coastal dunes (B1.3)

10-20

10

10

Coastal stable dune grasslands (grey dunes) (B1.4)

8-15

8

Acid dunes = 8
Calcareous dunes = 10

Coastal dune heaths (B1.5)

10-20

10

10

Moist to wet dune slacks (B1.8) 

10-20

10

Low base availability = 10
High base availability = 15

Inland surface waters

 

 

 

Softwater lakes (permanent oligotrophic waters) (C1.1)

3-10

 

Seek site specific advice

Seek site specific advice

Dune slack pools (permanent oligotrophic waters) (C1.16) 

10-20

10

10

Permanent dystrophic lakes, ponds and pools (C1.4) 

3-10

Seek site specific advice

Seek site specific advice

Mire, bog and fen habitats

 

 

 

Raised & blanket bogs (D1)

5-10

5

Apply guidance

Valley mires, poor fens and transition mires (D2)

10-15

10

10

Rich fens (D4.1)

15-30

15

15

Montane rich fens (D4.2) 

15-25

15

15

Grasslands and tall forb habitats

 

 

 

Sub-atlantic semi-dry calcareous grassland (E1.26)

15-25

15

15

Non-Mediterranean dry acid and neutral closed grassland (E1.7)

10-15

10

10

Inland dune pioneer grasslands (E1.94)

8-15

8

Acid dunes = 8
Calcareous dunes = 10

Inland dune siliceous grassland (E1.95)

8-15

8

Acid dunes = 8
Calcareous dunes = 10

Low and medium altitude hay meadows (E2.2)

20-30

20

20

Mountain hay meadows (E2.3)

10-20

10

10

Moist & wet oligotrophic grasslands:

 

 

 

Molinia caerulea meadows (E3.51)

15-25

15

15

Heath (Juncus) meadows & humid (Nardus Stricta) swards (E3.52)

10-20

10

10

Moss & lichen dominated mountain summits (E4.2)

5-10

5

7

Alpine and subalpine acid grasslands (E4.3)

5-10

5

5

Alpine and subalpine calcareous grasslands (E4.4)

5-10

5

5

Heathland, scrub & tundra

 

 

 

Arctic, alpine and subalpine scrub habitats (F2)

5-15

 

5

5

 

Northern wet heaths (F4.11) 

 

 

 

  • U’ Calluna-dominated wet heath (upland moorland)

10-20

10

10

  • ‘L’ Erica tetralix dominated wet heath (lowland)

10-20

10

10

 Dry heaths (F4.2)

10-20

10

10

Forest habitats (general)

Use if not one of specific forests in section below

 

 

 

Broadleaved woodland (G1)

10-20

10

10

Coniferous woodland (G3)

5-15

5

10
(Use 5 if lichens/free-living algae important features of the site).  

Forest habitats (specific)

 

 

 

Fagus woodland (beech) (G1.6)

10-20

10

15

Acidophilous Quercus-dominated woodland (oak) (G1.8)

10-15

10

10

 Meso- and eutrophic Quercus woodland (G1.A) 

15-20

15

15

Pinus sylvestris woodland south of the taiga (G3.4)

5-15

5

12

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