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Tufa classification

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{{OR/17/020}}
==Aims and scope of project==
The primary aim was to undertake an active survey to identify sites within Gloucestershire that could be described as the Habitats Directive Annex 1 habitat ‘''H7220 Petrifying springs with tufa formation (Cratoneurion)''’ with the details being added to an inventory of all known H7220 habitats in England to support the GIS inventories for Biodiversity Action Plan (BAP) Priority Habitats ([http://www.natureonthemap.org.uk/ www.natureonthemap.org.uk]).

==Definition of petrifying springs with tufa formation==
The habitat ‘H7220 Petrifying springs with tufa formation ''(Cratoneurion'')’ is defined in the Interpretation Manual of European Union Habitats (European Commission, 2013<ref name="European Commission 2013">

EUROPEAN COMMISSION, 2013. Interpretation Manuel of European Union Habitats EUR28. European Commission DG Environment Nature ENV B.3.</ref>) as;
* Hard water springs with active formation of tufa. These formations are found in such diverse environments as forests or open countryside. They are generally small (point or linear formations) and dominated by bryophytes (''Cratoneurion commutati'').
* Confirms that this vegetation type corresponds (in the UK) to the UK National Vegetation Classification (NVC) types ‘M37 ''Cratoneuron commutatum-Festuca rubra ''spring community’ and ‘M38 ''Cratoneuron commutatum-Carex nigra ''spring community’ as described by Rodwell (1998)<ref name="Rodwell 1998">RODWELL, J S. 1998. British plant communities volume 2 — Mires & Heaths. Cambridge University Press.</ref>.
* Lists the following plant species: ''Arabis soyeri, Pinguicula vulgaris, Saxifraga aizoides; Cochlearia pyrenaica ''(in sites with heavy metals); ''Carex appropinquata, Epilobium davuricum, Juncus triglumis ''(in the Boreal region). Mosses: ''Catoscopium nigritum, Palustriella commutata, Palustriella falcata'', ''Cratoneuron filicinum, Eucladium verticillatum, Hymenostylium recurvirostrum ''and ''Hamatocaulis vernicosus, Philonotis calcarea, Scorpidium revolvens, S. cossonii, Palustriella decipiens, Bryum pseudotriquetum ''(in the Boreal region).
* For the purposes of this report, the habitat ‘H7220 Petrifying springs with tufa formation ''(Cratoneurion'')’ is defined as spring vegetation dominated by either/or both of the pleurocarpous mosses ''Palustriella commutata, Palustriella falcata ''(formerly treated as the single species ''Cratoneuron commutatum''). Both these mosses are often, but not exclusively associated with tufa. For more details on the definition and interpretation of H7220 Petrifying springs with tufa formation ''(Cratoneurion'')’ in the UK, refer to Graham and Farr (2014)<ref name="Graham 2014">GRAHAM and FARR. 2014. Petrifying springs in Wales. Field Bryology (112). 19–29. Open Access http://nora.nerc.ac.uk/508972/ </ref>.

==Tufa formation==
Tufa formation occurs after dissolution by water of rocks rich in calcium carbonate (Banks & Jones, 2012). Once the groundwater emerges at the surface, via a spring or seepage or as river base flow, interactions with the atmosphere cause the loss or evasion of CO2 and the resultant precipitation of calcium carbonate, as tufa:

Ca2+ + 2 HCO3-↔ CaCO3 + CO2 + H2O

The principal sources of calcium carbonate for the sites within this study are the calcareous bedrock aquifers of the Jurassic Oolites, Carboniferous Limestone, Devonian sandstones and Lower Lias mudstones. Tufa can precipitate with varying success rates over a variety of substrates. Tufa can precipitate both on dead (leaves, twigs and logs) and living organic material (bryophytes, liverworts, tree roots etc.) and inorganic material such as stones. Figure 1-1 provides an illustration of rapid tufa formation on Beech leaves at Cranham Wood.

[[Image:OR17020fig1-1.jpg|thumb|center|400px| '''Figure 1-1'''    Rapid tufa deposition on Beech leaves at Cranham Wood. ]]

==Tufa classification==
Tufa can occur in two broad geochemical categories. The first is associated with thermal waters (thermogene) and the second associated with meteoric waters (meteogene). Meteogene tufas are the most widely distributed (Pentecost and Viles, 1994<ref name="Pentecost 1994">PENTECOST, A, and VILES, H C. 1994. A review and reassessment of travertine classification. Geographie physique et Quaternaire 48:305–314.</ref>) and cover all the examples within this report. Tufa fabric can be visible with the naked eye (mesofabric) or in more detail under the microscope (microfabric). There are many factors that influence tufa fabrics including; temperature, flow rate, CO2 evasion rate, supersaturation with respect to calcite, ion transport mechanisms, plant growth and animal burrows (Pentecost, 2005<ref name="Pentecost 2005">PENTECOST, A. 2005. Travertine. Springer-Verlag, Berlin and Heidelberg. 445 pp.</ref>). Fabrics have also been the basis of several classification schemes which emphasize the influence of plants (Pentecost and Viles, 1994<ref name="Pentecost 1994">PENTECOST, A, and VILES, H C. 1994. A review and reassessment of travertine classification. Geographie physique et Quaternaire 48:305–314.</ref>) on the formation of a variety of tufa fabrics. Bryophytes and algae can influence tufa fabrics through the trapping and binding of calcite (Pentecost, 1993). Tufa morphologies, unlike most erosional or destructive land surface processes are frequently constructive in nature (Pentecost, 2005<ref name="Pentecost 2005"></ref>) and their morphologies are defined in ‘British travertines: a review’ (Pentecost, 1993), summarised in Table 1 and Figure 1-2.

<center>
{| class="wikitable"
|+ Table 1    Classification of tufa deposits described in this report, after Pedley (1990) and Pentecost & Viles (1994)<ref name="Pentecost 1994">PENTECOST, A, and VILES, H C. 1994. A review and reassessment of travertine classification. Geographie physique et Quaternaire 48:305–314.</ref>.
| ! scope="col" style="width: 150px;" | '''Classification'''
| ! scope="col" style="width: 100px;" | '''Setting'''
| ! scope="col" style="width: 100px;" | '''Type'''
| ! scope="col" style="width: 400px;" | '''Description'''
|- style="vertical-align:top;"
| rowspan="2" | Deposits on gentle slopes (''c''. <10°)
| Marsh
| Paludal
| Surface coatings of tufa on vegetation, marshy locations or alluvial valley bottoms (e.g. Cranham Wood, Alder Carr, Midger Wood).
|- style="vertical-align:top;"
| Lake
| Laucustrine crusts
| e.g. Malham Tarn (no lacustrine sites identified in this study).
|- style="vertical-align:top;"
| rowspan="5" | Deposits on steep slopes (''c''. >10°)
| Cliffs
| Cascades (cliffs)
| Very slow seepage of calcareous water on cliff faces (e.g. Aust and Sedbury Cliff).
|- style="vertical-align:top;"
| rowspan="4" | River
| Cascades (river)
| On waterfalls and steep ground (e.g. Strawberry Bank Cascade, Bathurst Estate, Alder Carr, Cranham Wood).
|- style="vertical-align:top;"
| Barrages
| Spanning streams or rivers and forming back fill barrages, ponds and pools (including: Slade Brook, Dowdeswell, Strawberry Bank, Kingscote & Horsley Wood, Woodchester Park and Workmans Wood).
|- style="vertical-align:top;"
| Fluvial Crusts
| Formed in running water in small and larger rivers, smooth and sheet like or nodular and coralloid (includes most of the alluvial sites mentioned in this study).
|- style="vertical-align:top;"
| Springheads
| Dominated by bryophytes and often forming headwaters to river systems with cascades, barrages and fluvial crusts (includes the springheads and seepages that supply most sites within this study).
|}
</center>

[[Image:OR17020fig1-2.jpg|thumb|center|300px| '''Figure 1-2'''    Common tufa morphologies in the UK, not to scale (Modified from Pentecost & Viles, 1994<ref name="Pentecost 1994"></ref>). ]]

==Recent european work on H7220==
Recent research into the H7220 habitat includes; Heery, 2007<ref name="Heery 2007">HEERY, S. 2007. A survey of tufa-forming (petrifying) springs in the Slieve Bloom, Ireland.</ref> & Heery et al, 2014 (Ireland)<ref name="Heery 2014">HEERY, S, MOORKENS, E, and CAMPBELL. 2014. An account of tufa-forming (Petrifying Spring Habitats in the Slieve Bloom Mountains, Ireland. In Biology and Environment: Proceedings of the Royal Irish Academy. Vol. 114B, No. 1 p1–11.DOI:10.3318/bioe.2013.26 </ref>; Farr, Graham and Stratford, 2014 (Wales, UK)<ref name="Farr 2014">FARR, G, GRAHAM, J, and STRATFORD, C S. 2014. Survey, characterisation and condition assessment of Palustriella dominated springs 'H7220 petrifying springs with tufa formation (Cratoneurion) in Wales Report for Natural Resources Wales. BGS Reference OR/14/043. Open Access Link http://nora.nerc.ac.uk/512109/ </ref>; Graham & Farr, 2014 (Wales)<ref name="Graham 2014">GRAHAM and FARR. 2014. Petrifying springs in Wales. Field Bryology (112). 19–29. Open Access http://nora.nerc.ac.uk/508972/ </ref>; Lyons, 2015 (Ireland)<ref name="Lyons 2015">LYONS, M D. 2015. The flora and conservation status of petrifying springs in Ireland. Thesis submitted for the degree of Doctor of Philosophy. Department of Botany, University of Dublin, Trinity College. </ref>; Lyons and Kelly, 2016 (monitoring guidelines in Ireland)<ref name="Lyons 2016">LYONS, M D, and KELLY, D L. 2016. Monitoring guidelines for the assessment of petrifying springs in Ireland. Irish Wildlife Manuals, No. 94. National Parks and Wildlife Service, Department of Arts, Heritage, Regional, Rural and Gaeltacht Affairs, Ireland. </ref>; Couvreur et al., 2016 (Belgium)<ref name="Couvreur 2016">COUVREUR, J M, SAN MARTIN, G S, and SOTIAUX, A. 2016. Factors Affecting the Presence and the Diversity of Bryophytes in the Petrifying Sources Habitat (7220) in Wallonia and the Brussels-Capital Region, Belgium. International Journal of Agronomy. http://dx.doi.org/10.1155/2016/5365412</ref>; Royal Hoskoning DHV, 2016<ref name="Royal 2016">ROYAL HOSKONING DHV, 2016. Towards threshold values for nutrients. Petrifying springs in South-Limburg (NL) in a Northwest European context.</ref> (nitrate and phosphate threshold values). There is an active EU LIFE project called ‘Springday; Conservation and restoration of petrifying spring habitats (H7220) in Estonia’, due for completion in May 2018 (NAT/EE/000860 [http://www.loodushoid.ee/SPRINGDAY_348.htm/ www.loodushoid.ee/SPRINGDAY_348.htm]).

==Invertebrates asociated with calcareous springs and seepages==
The present survey included only a botanical and hydrogeological assessment of sites. However, the broad habitats present (calcareous springheads and associated seepages, streams in both open habitat and woodland) are very important for invertebrates and therefore warrant the brief assessment below based on a literature review.

Woodland seepages are probably the most widespread, and yet little known seepage habitat in Britain for invertebrates (Boyce, 2012<ref name="Boyce 2012">BOYCE, D C. 2012. English Nature Research Report Number 452: A review of seepage invertebrates in England.</ref>). The woodland seepages included in this survey have great variation in form including: open seepages dominated by tall stands of Pendulous Sedge ''Carex pendula ''with other wetland species such as Hemp-agrimony ''Eupatorium cannabinum'', Water Mint ''Mentha aquatica ''and Greater Horse-tail ''Equisetum telmateia''; open rocky spring heads (often with tufa); open ‘mossy’ cascades (dominated by bryophytes such as ''Palustriella commutata, Pellia endiviifolia, Conocephalum conicum'') with tufa dams and shallow pools; seepages with significant fallen deadwood and exposed tree roots (often with tufa); heavily shaded seepages with bare mud, detritus and little or no vegetation.

Woodland seepages that are heavily shaded and have a poorly developed ground flora (with much open mud and detritus) are frequently considered, with perhaps the exception of some shade tolerant fern and bryophyte species, to be of low conservation value. However, Boyce (2012)<ref name="Boyce 2012"></ref> draws particular attention to the perils of relying too heavily on botanical criteria in assessing invertebrate communities of seepages. Two groups, in particular (crane flies and soldier flies) are associated with such shaded and open habitats and include many species of conservation concern.

Boyce (2012)<ref name="Boyce 2012"></ref> lists invertebrates of conservation concern for woodland seepages of which 62% are crane flies (''Tipulidae ''and ''Ptychopteridae''). Crane flies generally have soft-bodied larvae that thrive in cool, saturated, shaded conditions. Although they occur in seepages with a wide range of chemistry, some rare species (such as ''Gonomyia abbreviata, Gonomyia bifida, Molophilus corniger, Orimarga virgo, Paradelphomyia ecalcarata, Ptychoptera longicauda ''and ''Ptychoptera scutellaris) ''are clearly associated with calcareous seepages (Boyce, 2012<ref name="Boyce 2012"></ref>). In addition, Godfrey (2012<ref name="Godfrey 2012"> GODFREY, A. 2012. Springs and Seepages of Wessex (Blackdown Hills Invertebrate Survey).</ref>; 2014<ref name="Godfrey 2014">GODFREY, A. 2014. Springs and Seepages of Wessex (Mendips Invertebrate Survey). </ref>) surveyed calcareous seepages in Somerset and recorded the UK BAP species ''Lipsothrix nervosa'', Red Data Book species ''Ellipteroides alboscutellata ''(a species requiring constant flushing of base-rich waters with most records coming from tufa-rich seepages in woodland) and the Red Data Book species ''Gonomyia abbreviata ''(restricted to small shaded streams in woods on calcareous soils).

Soldier flies (''Stratiomyidae'') also mostly occur in open habitats with many species of conservation concern occurring within seepages with ''Oxycera analis ''and ''Oxycera leonina ''appearing to be restricted to calcareous seepages in woodland and at woodland edges (Boyce 2012<ref name="Boyce 2012"></ref>).

Neutral to calcareous seepages are associated with several molluscs of conservation concern. Four rare species (''Acicula fusca, Leiostyla anglica, Spermodea lamellate, Phenacolimax major'') are closely associated with seepages dominated by Opposite-leaved Golden-saxifrage ''Chrysosplenium oppositifolium ''(found amongst ''Chrysosplenium ''plants and in saturated leaf litter) while three rare species ''(Catinella arenaria, Vertigo genesii, Vertigo geyeri'') are associated with more strongly calcareous seepages (Boyce 2012<ref name="Boyce 2012"></ref>). The rare Gloucestershire snails ''Ena montana'', ''Phenacolimax major, Acicula fusca ''and ''Macrogastra rolphii ''are noted as being associated with wet bryophyte-rich flushes within Cotswold Commons and Beechwoods Site of Special Scientific Interest (SSSI).

A number of rare water beetles are also associated with calcareous springs including ''Hydroporus ferrugineus, Hydroporus longulus, Hydroporus marginatus, Agabus biguttatusis ''(Boyce 2012<ref name="Boyce 2012"></ref>). ''Hydroporus ferrugineus ''is semi-subterranean occurring in springs, groundwater-fed trickles, ''H. longicornis ''is known from woodland flushes and ''Agabus biguttatusis ''occurs under stones or amongst gravel in springs (Hammond, 2017<ref name="Hammond 2017">HAMMOND, M. 2017. The water beetles of Yorkshire. YHEDT Publishing. </ref>). In addition, the rare riffle beetle ''Riolus subviolaceus ''occurs on the underside of tufa-encrusted stones (Hammond, 2017<ref name="Hammond 2017"></ref>) and is recorded from calcareous woodland springs in Somerset (Godfrey, 2014<ref name="Godfrey 2014"></ref>).

The shallow calcareous and rocky water courses that frequently occur close to springs over limestone continue to be an important habitat for the survival of relict populations of the native White-clawed Crayfish ''Austropotamobius pallipes''.

==Site selection==
Sites were selected by Iain Diack (Natural England), Chris Uttly (Stroud Council) and Richard Spyvee (Gloucestershire Wildlife Trust) from both a selection of designated and non-designated sites. Figure 1-3 shows the location and geological setting for each site.

[[Image:OR17020fig1-3.jpg|thumb|center|500px| '''Figure 1-3'''    Location of tufa forming sites described in this report (''Includes mapping data licensed from Ordnance Survey. © Crown Copyright and/or database right 2017. Licence number 100021290 EUL'' and British Geological Survey Data 1:50 000). ]]
==References==
<References/>
[[Category: OR/17/020 Survey, characterisation and condition assessment of Palustriella dominated springs 'H7220 Petrifying springs with tufa formation (Cratoneurion)' in Gloucestershire, England | 04]]

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