OR/17/020 Methods

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Farr, G, and Graham, J. 2017. Survey, characterisation and condition assessment of Palustriella dominated springs 'H7220 Petrifying springs with tufa formation (Cratoneurion)' in Gloucestershire, England. British Geological Survey Internal Report, OR/17/020.

Twenty two sites were surveyed between 18th and 29th January 2017 by Gareth Farr (hydrogeologist) and Jonathan Graham (botanist) working in partnership at all times.

Botanical survey methods

A complete plant species list (flowering plants and bryophytes) was obtained for each site including precise habitat notes on the occurrence of individual species within flushes (such as whether species occurred on stone, dead wood, living tree roots, within or beside channels etc.). In addition, notes were made on species groups occurring at different parts of sites (such as those associated with open springheads or wooded cascades etc.). Flowering plants, bryophytes and lichens were identified (where possible) in the field but where there was uncertainty, specimens were collected and determined microscopically. The location of species of note or species occurring locally within a site or species occurring in discrete locally dominant patches were more precisely noted. A detailed map was drawn in the field for each site noting locations of individual springheads, runnels and tufa, and particular effort was made to accurately delimit areas of Palustriella dominated vegetation. A particular study was made of species associated with (or appearing to be actively associated with the formation of) tufa. Nomenclature adopted follows Stace (2010) for most flowering plants; Cope & Gray (2009)[1] for grasses; M O, Hill, T H, Blackstock, D G, Long and G P, Rothero, (2018)[2] for bryophytes and The British Lichen Society (2017) for lichens.

Elevation and orientation

Elevations as maOD (meters above ordnance datum) were measured from 10 m DTM (digital terrane model) LiDAR, using ARC map and the dominant orientation (NW, NE, SE or SW) of each site was recorded. For the larger sites that form down a slope, a maximum and minimum elevation were recorded and average for the site produced.

Geology and hydrogeology

At each site the principal source of water, mainly springs or seepages were identified. Springs and seepages were attributed to mapped geological units using the published British Geological Survey 1:50 000 Bedrock and Superficial maps. Where there was more than one potential aquifer (e.g. two concurrent formations that are likely to be in hydraulic continuity) then both units have been attributed. Future site specific investigation may refine the knowledge of the source aquifers, residence time of groundwater and hydrogeological conceptual models. Fieldwork was undertaken in January (winter), and the visual flow estimates (to the nearest 1 l/s) are likely to represent the higher end of flow at each site. Due to the timing of the survey it was not possible to provide evidence for either minimum or maximum (drought — flood/winter–summer) flow conditions.

Water chemistry

Water samples were collected at each site for inorganic chemical analysis. Each sample was collected as close to the source of water, often a springhead or seepage face, as possible. Care was taken to only collect samples that represented water associated with tufa formation and supply to the main tufa forming bryophytes. Field parameters for pH, electrical conductivity and temperature were measured on ‘Metter Toldeo — SevernGo’ field meters. The meters were calibrated each day for both pH and electrical conductivity, using a two point calibration of pH 4 and 7 and 760 and 1413 µscm respectively. The samples were filtered using a 0.45 µm filter into two separate 35 ml plastic bottles. The water samples were frozen on the day of collection and sent to the UCAS accredited British Geological Survey Inorganic Laboratory (Nottingham) for ICP-MS and IC analysis of major ions, nutrients, alkalinity and trace elements. An ionic balance was performed on each analysis. In addition to the field readings a Lab electrical conductivity, pH and alkalinity were measured. The data set with limits of detection for each parameter are included in the Appendix.

Atmospheric deposition

We assigned a value for nitrogen deposition to each of the sites in this study using UK atmospheric deposition 5 x 5 km modelled data based on the CBED (concentration based estimated deposition) methodology. Data for Annex 1 habitats and designated sites in the UK can be accessed on APIS (air pollution information systems) www.apis.ac.uk. Using the 5 x 5 km modelled data we report values for average, NH3, NOX and total Nitrogen as kg N ha-1 year-1 for each of the study sites. Critical loads, agreed in a UNECE (European Nature Information System) workshop in 2010 (Hall et al 2015[3], set values for each EUNIS class where data exists. Values for UK habitats can also be viewed on the APIS website at www.apis.ac.uk/indicative-critical-load-values. Methods for calculating critical loads and their exceedances in the UK are reported in Hall et al 2015[3]. However in the UK there are no specific critical loads for the H7220 Petrifying springs habitat, so for the current Annex 1 assessments the EUNIS class D4.2 critical loads are applied. The current critical load range for this habitat is 15–25 kg N/ha/yr, with a recommended value of 15 kg N/ha/yr for site-based assessments (pers. com. Jane Hall, Centre for Ecology and Hydrology 14/3/17). We report the modelled nitrogen deposition values for each site and undertake a broad assessment, to see how many of the petrifying springs sites exceed the recommended site relevant critical load of 15 kg N/ha/yr.

References

  1. COPE, T, and GRAY, A. 2009. Grasses of the British Isles (BSBI Handbook No. 13). Botanical Society of Britain and Ireland.
  2. HILL, M.O. BLACKSTOCK, T.H. LONG, D G, and ROTHERO, G P. 2018. Check-list and Census Catalogue of British and Irish bryophytes updated 2008.
  3. 3.0 3.1 HALL, J, CURTIS, C, DORE, T, and SMITH, R. 2015. Methods for the calculation of critical loads and their exceedances in the UK. Report to DEFRA, prepared under contract AQ0826. https://www.cldm.ceh.ac.uk/sites/cldm.ceh.ac.uk/files/MethodsReport_Updated_July2015_WEB.pdf>