To assign relevant critical loads to habitat interest features on A/SSSIs it is necessary to:
- ascertain if the feature is potentially sensitive to N deposition or acidity and if so to
- apply a critical load by corresponding the interest feature with a EUNIS class for which a nutrient N critical load is set or a BAP broad habitat for which an acidity critical load is set.
The country conservation agencies notify A/SSSIs and provide information on the sites through their websites: Northern Ireland-EA; SNH; Natural England & CCW. Since APIS covers the whole of the UK, it has been necessary to use a common nomenclature for habitat interest features in the site relevant critical loads search tool. Therefore, the reporting categories used by JNCC in the 2006 A/SSSI Common Standards Monitoring 6 Year Report have been used (JNCC, 2006), with some modifications. A list of the reporting categories, and any modifications, is given below and their relationship with BAP broad and priority habitats shown.
The A/SSSI habitat interest features were supplied for the site relevant critical loads project in 2007 by the country conservation agencies. Sites notified between 2007 and 2009 have since been added. However, the process of identifying A/SSSI interest features is ongoing in some agencies and the lists of interest features may be subject to change. The official A/SSSI citations can be found on the links given above.
The reporting categories used to define habitat interest features are fairly broad and may contain habitats with a range of sensitivity to nitrogen deposition and/or acidity. The SRCL search tool, therefore, prompts the user refine the habitat definition so that the relevant critical load can be chosen. The user is asked to define a BAP Priority Habitat, if one is applicable, or a BAP Broad Habitat which corresponds with the habitat at the site [linkages between UKBAP broad habitat and UK Priority habitats can be found on the UKBAP table]. Then, if there is more than one critical load which could apply to that Priority or Broad habitat, the user is asked to define the relevant EUNIS class. Many users will not be familiar with this European classification. Further information is available here (EUNIS) and JNCC has published a correspondence table relating all habitat classifications including EUNIS. If you do not have details of the habitat at a site, beyond Broad or Priority Habitat, then it is recommended that you select the most sensitive critical load for the initial screening assessment.
We have been unable to match species interest features at A/SSSI to critical loads. However, some species may be very sensitive to nitrogen deposition or acidity, often with effects mediated through habitat changes. An assessment of nitrogen deposition/acidity impacts on an A/SSSI should also consider species interest features. The site relevant critical loads tool will provide deposition estimates for the site to help with this. Table 1. Relationship between reporting category used in APIS SRCL and BAP Broad and Priority Habitats.
| Reporting category - used in APIS | BAP Broad Habitat (pp = part only) | BAP Priority Habitat |
| Acid grassland - lowland | Acid grassland pp | Lowland dry acid grassland |
| Acid grassland - upland | Acid grassland pp | none |
| Blanket bogs | Bogs pp | Blanket bog |
| Bogs* | Bogs | Lowland Raised Bog, Blanket Bog |
| Broadleaved and mixed woodland | Broadleaved, Mixed and Yew Woodland | Wood-Pasture & Parkland, Upland Oakwood, Lowland Beech and Yew Woodland, Upland Mixed Ashwoods, Wet Woodland, Lowland Mixed Deciduous Woodland, Upland Birchwoods |
| Calcareous grassland - lowland | Calcareous Grassland pp | Lowland Calcareous Grassland |
| Calcareous grassland - upland | Calcareous Grassland pp | Upland Calcareous Grassland |
| Coniferous woodland | Coniferous woodland pp | Native pine woodlands |
| Dunes, shingle and machair | Supralittoral sediment | Coastal Vegetated Shingle, Machair, Coastal Sand Dunes |
| Dwarf shrub heath* | Dwarf Shrub Heath | Lowland heathland, Upland Heathland |
| Fen, marsh and swamp* | Fen, Marsh and Swamp pp | Upland Flushes, Fens and Swamps, Lowland fens. Purple moor grass and rush pasture |
| Fens and marshes - lowland | Fen, Marsh and Swamp pp | Lowland fens + Purple moor grass and rush pasture |
| Fens and marshes - upland | Fen, Marsh and Swamp pp | Upland Flushes, Fens and Swamps |
| Heathlands - lowland | Dwarf Shrub Heath pp | Lowland heathland |
| Heathlands - upland | Dwarf Shrub Heath pp | Upland heathland |
| Limestone pavement, inland cliffs and screes | Inland rock pp | Inland Rock Outcrop and Scree Habitats, Calaminarian Grasslands, Open Mosaic Habitats on Previously Developed Land, Limestone Pavements |
| Lowland raised bogs | Bogs pp | Lowland Raised Bog |
| Montane grasslands and heaths | Montane habitats | Mountain heaths and willow scrub |
| Neutral grassland lowland | Neutral grassland | Lowland meadows |
| Neutral grassland upland | Neutral grassland | Upland hay meadows |
| Neutral Grassland* | Neutral grassland | Lowland meadows, Upland hay meadows |
| Rivers and streams | Rivers and Streams | Rivers |
| Saltmarsh | Littoral sediment pp | Coastal saltmarsh |
| Sea cliffs | Supralittoral rock pp | Maritime cliff and slope |
| Standing open water - not including oligotrophic or dystrophic types** | Standing waters and canals pp | Ponds , Mesotrophic Lakes, Eutrophic Standing Waters, Aquifer Fed Naturally Fluctuating Water Bodies |
| Standing Open Water - Dystrophic ** | Standing waters and canals pp | Oligotrophic and Dystrophic Lakes |
| Standing open water - oligotrophic ** | Standing waters and canals pp | Oligotrophic and Dystrophic Lakes |
| Upland assemblages | various: very broad category, upland heath and blanket bog are main components | various |
| * = additional category used in APIS where country conservation agency unable to confirm if feature was upland or lowland |
| ** = Reporting category "Standing Open Water" has been split to differentiate oligotrophic and dystrophic types for which N CLs have been set |