An update to the decision framework to attribute atmospheric nitrogen deposition as a threat to, or cause of, unfavourable habitat conditions on protected sites

Perring, Michael P. ORCID: https://orcid.org/0000-0001-8553-4893; Deacon, Alice ORCID: https://orcid.org/0009-0006-1122-0924; Rowe, Ed ORCID: https://orcid.org/0000-0003-4784-7236; Jones, Laurence ORCID: https://orcid.org/0000-0002-4379-9006. 2024 An update to the decision framework to attribute atmospheric nitrogen deposition as a threat to, or cause of, unfavourable habitat conditions on protected sites. Natural England, 74pp. (Unpublished)

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Abstract/Summary

The Nitrogen Decision Framework (NDF) is a tool to assess the likelihood of damage to a site from atmospheric nitrogen (N), based on information about N deposition, the degree of sensitivity of features/habitats on the site to N deposition, any evidence of existing adverse impacts, and uncertainty in all these parameters. The Factor 1 spreadsheet of the NDF assesses the risk that N deposition is impacting features on a site. The original Factor 1 spreadsheet (see Jones et al. 2016) accounts for three main sources of uncertainty in a systematic manner: (i) the reliability of critical load ranges and the consistency of UK evidence with those ranges; (ii) the cross match between the EUNIS habitats for which there is a critical load and the EUNIS habitat that encompasses the habitat feature of interest; and (iii) the cross match between the EUNIS habitat for the feature of interest and the habitat description in the Common Standards Monitoring (CSM) Guidance. When new data become available, the systematic form of the NDF Factor 1 spreadsheet allows for updates. A revision of the spreadsheet is now timely: (i) The empirical critical loads for N have recently been updated (Bobbink et al. 2022), providing revised estimates for critical load ranges, and their associated reliability, for a variety of EUNIS habitats. These revised critical load estimates mean the consistency of UK evidence with them needs assessment. (ii) EUNIS habitat hierarchical classifications and associated habitat descriptions have been updated (see the EUNIS website ). These updates may affect the closeness of the match between CSM Guidance habitat descriptions and the most relevant EUNIS habitat class, and thence the match between the EUNIS habitat class and the EUNIS habitat class for which a critical load is available. All these revisions have the potential to affect exceedance scores for given habitats under uncertain amounts of N deposition. UKCEH have updated, and quality assured, the Factor 1 spreadsheet accounting for these new data and their associated uncertainty. UKCEH have updated and cross-checked the Lookup tables which allow exceedance factors to be quantified for all habitats of interest, not just those for which critical loads have been defined. We have further considered the certainty of the match between the revised empirical critical loads for N, and the UK evidence, updating the procedure to reflect the congruence in timing between this update and the empirical revision of critical loads. In essence, we asked whether UK evidence is involved in the setting of the critical load for a given EUNIS critical load habitat. UKCEH have provided two spreadsheet versions: (i) A ‘clean’ version that maintains the same format as the original Factor 1 spreadsheet; and, (ii) A ‘commented’ version that provides different coloured text, and comments boxes, with associated ReadMe tabs, to highlight changes from the original sheet (Jones et al. 2016) that may have a material impact on exceedance factors. This report accompanies the spreadsheet revisions, and they should be read in conjunction with each other to ease interpretation; for instance, the ReadMe sheet in the revised spreadsheet provides a link to this report and the original Factor 1 report. Key Results Many of the critical load minimum and maximum values have been revised downwards following the empirical critical loads revision. Additional minima and maxima have been added to Lookup tables that consider the certainty of the match between critical loads and the habitat guidance. Reductions in minima and maxima, in the absence of other changes, can lead to higher exceedances for habitat features for a given amount of N deposition. The revised procedure to assess UK evidence consistency suggests most EUNIS critical load habitats used in the Factor 1 spreadsheet incorporate some UK evidence. In several cases, for instance saltmarsh, revisions to the empirical critical load have led to new habitat sub-categories being included in the Factor 1 spreadsheet. There have been few changes to EUNIS habitat descriptions between the former and revised classifications. Some habitats do have revised descriptions, but the vast majority of these revisions did not have material implications for the match between the CSM Guidance habitat type (or sub-type) and the revised EUNIS habitat class. Wetland habitats do not have, at the date of this report, a published revised hierarchical classification on the EUNIS website. However, Bobbink et al. (2022) includes revised habitat codes in the Wetlands chapter. Following discussions with the chapter’s lead author (Dr. Chris Field), it became apparent that these codes were supplied based on Chytrý et al. (2020). We have informed our revisions through reference to Chytrý et al. (2020) and its associated Supplementary Material. Until the hierarchical classification has been confirmed, care should be taken in the use of the updated Factor 1 spreadsheet for all Wetland habitats, especially those where revisions have been implemented (e.g. 39. Soakway and sump (upland); 40b. Upland calcareous springs). Apart from E4.2, all previous EUNIS habitats where critical loads were provided were matched to a new code from the revised hierarchy. We provide worked examples to indicate how the types of changes highlighted above can have material implications for exceedance factors in specific habitats. This report also provides, as an Annex, full descriptions of the changes implemented, including any revisions to uncertainty scores, across all forty seven habitat types included in the Factor 1 spreadsheet, together with sub-types where relevant. Conclusion Overall, these updates bring the Factor 1 spreadsheet into line with the latest understanding of sensitivity of UK terrestrial habitats to N deposition. We recommend the EUNIS website is checked at a later date for when the Wetlands hierarchical classification is released. We also recommend developing Lookup tables between CSM guidance (sub)-habitat types, NVC classifications, Annex 1 habitats and EUNIS habitat codes with notes as to the certainty of the match. The Factor 1 spreadsheet should be checked, and revised if necessary, at that time. Revisions to the spreadsheet will also need considering if CSM Guidance changes, if there are any further updates to the EUNIS hierarchical classifications and/or descriptions, and at any future revision to the empirical critical loads for nitrogen. Consideration could be given to further updates if new evidence, relevant to the UK context, comes to light in between revisions to the European-scale empirical critical load report.

Item Type:	Publication - Report (Project Report)
UKCEH and CEH Sections/Science Areas:	Soils and Land Use (Science Area 2017-)
Funders/Sponsors:	Natural England
NORA Subject Terms:	Ecology and Environment
Date made live:	25 Jun 2024 10:11 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/537617

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