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The effects of lichen cover upon the rate of solutional weathering of limestone
... Erosion, however, is the process in which rock particles are carried away from the original rock volume [6]. Usually, weathering precedes the rock erosion, but it does not unequivocally involve the consecutive erosion of a weathered surface [10][11][12][13][14]. ...
... All these conclusions reveal the influence of rock properties and exposition conditions on the weathering of rocks, and validate the new proposed methodology as a helpful and rapid tool for measuring rock Table 4 Erosion rates measured in Nueva Tabarca island (published in [13] ...
A novel methodology is presented for measuring weathering microrates after one-year of direct exposure of rocks to environment. The study focuses on building materials used in the cultural heritage exposed to semiarid coastal Mediterranean climate (SE Spain). Three different carbonate rocks, with significant differences in porosity and texture, were studied in two different exposition orientations (north and south). Results are interpreted according to local microenvironmental conditions and petrologic aspects (porosity, pore size distribution and mineralogy). South-facing rock blocks show the highest weathering microrates (9130 mm/ky and 18750 mm/ky for fine and coarse-grained porous limestones, respectively). They are 1.55 and 1.92 times higher than rates obtained in north-facing rock samples. Physical and chemical decay mechanisms overlap in the weathering process. On the one hand, physical processes are more evident in porous limestones, being predominant in south exposure samples. On the other hand, chemical corrosion is the main weathering mechanism in massive limestones as well as in porous limestones with unstable components. Dissolution prevails in northern exposure. Obtained weathering rates are two to three magnitude orders higher than the erosion rates measured in the same rocks, highlighting the conceptual differences between both parameters.
... BRCs have been noted to play a crucial role in the functioning of arid and hyper-arid environments because of the limited activity of plants and soil (Pointing and Belnap, 2012). A range of geobiological roles have been suggested for BRCs, including rock weathering (Garcia-Pichel, 2006;Warscheid and Braams, 2000), soiling effect (Viles and Gorbushina, 2003), deterioration of architectural heritage sites (Cabello-Briones and Viles, 2017) and mitigating geomorphic processes (Mcllroy de la Rosa et al., 2014). BRCs have also gained attention from astrobiologists, who point out that such communities, when located in deserts, may act as analogues for possible life on Mars (Corenblit et al., 2019). ...
... However, they require large amounts of sample material, which is destructive and, therefore, unsuitable when dating archaeological sites or monuments. Lichenometry, which has been used extensively as a chronological tool in Arctic settings, is inapplicable for studying hot-desert geomorphology since deserts lack the moisture needed for lichen development (Dorn, 2009;Mcllroy de la Rosa et al., 2014). To overcome these obstacles, we used a well-preserved archaeological site built of stones that exhibit developed BRCs, marking the upper limit of the time frame needed for such processes to occur. ...
Biological rock crusts (BRCs) are ubiquitous features of rock surfaces in drylands composed of slow-growing microbial assemblages. BRC presence is often correlated with rock weathering, soiling effect or mitigating geomorphic processes. However, their development rate is still unknown. In this work, we characterised and dated BRCs in an arid environment, under natural conditions, by integrating archaeological, microbiological and geological methods. To this end, we sampled rocks from a well-documented Byzantine archaeological site and the surrounding area located in the central Negev, Israel. The archaeological site, which is dated to the fourth to seventh centuries CE, was constructed from two lithologies, limestone and chalk. BRC started developing on the rocks after being carved, and its age should match that of the site. Using stable carbon and oxygen isotope ratios, we confirmed the biogenic nature of the crusts. The BRC samples showed mild differences in the microbial community assemblages between the site and its surroundings, irrespective of lithology, confirming the dominance of aeolian inoculation sources. All BRCs were dominated by Actinobacteria, Cyanobacteria and Proteobacteria. We further measured the BRC thickness on 1700-year-old building stone blocks and determined it to be 0.1–0.6 mm thick. Therefore, a BRC growth rate was estimated, for the first time, to be 0.06–0.35 mm kyr-1. Our dating method was then validated on a similar archaeological site located ca. 20 km away, giving comparable values. We propose that BRC growth rates could be used as an affordable yet robust dating tool in archaeological sites in arid environments.
... A weathering role of lichens, as pioneer colonizers of natural rock surfaces, has long been recognized (Jones, 1988). Lichen deterioration of stone in cultural heritage has also been widely characterized (reviewed by St. Clair and Seaward, 2004;Gazzano et al., 2009;Seaward, 2015), although evidence of protective effects has also been unveiled (McIlroy de la Rosa et al., 2012Rosa et al., , 2014, with references therein). Biogeophysical and biogeochemical processes at the rock surface have been ascribed to the attachment and penetration of epilithic and endolithic lichens, and their release of primary and secondary metabolites with acidic and chelating functions, respectively (Adamo and Violante, 2000;Chen et al., 2000;Favero-Longo et al., 2011;Salvadori and Casanova Municchia, 2016). ...
... Epilithic lichens, in particular Verrucaria nigrescens, have been shown to retain moisture on limestone (Saint Quentin) surfaces (Carter and Viles, 2003) and have been suggested to play an umbrella-like protection with respect to deteriogenic endolithic species, such as Bagliettoa baldensis (Carter and Viles, 2005). By contrast, occurrence of Bagliettoa baldensis on Burren limestone has been shown to reduce dissolution processes if compared with bare surfaces (McIlroy de la Rosa et al., 2014). Similarly, a surface-sealing effect of the lithocortex of Verrucaria rubrocincta, anatomically similar to the LI of the examined species, has also been hypothesized on Sonoran caliche limestone (Bungartz and Garvie, 2004). ...
Hyphal penetration, mineral dissolution and neoformation at the lichen–rock interface have been widely characterized by microscopic and spectroscopic studies, and considered as proxies of lichen deterioration of stone substrates. However, these phenomena have not been clearly related to experimental data on physical properties related to stone durability, and the physical consequences of lichen removal from stone surfaces have also been overlooked. In this study, we combine microscopic and spectroscopic characterization of the structural organization of epi- and endolithic lichens (Caloplaca marina (Wedd.) Du Rietz, Caloplaca ochracea (Schaer.) Flagey, Bagliettoa baldensis (A.Massal.) Vězda, Porina linearis (Leight.) Zahlbr., Verrucaria nigrescens Pers.) at the interface with limestones of interest for Cultural Heritage (Portland Limestone, Botticino Limestone), with analysis of rock properties (water absorption, surface hardness) relevant for durability, before and after the removal or scraping of lichen thalli. Observations using reflected-light and electron microscopy, and Raman analyses, showed lichen–limestone stratified interfaces, differing in the presence/absence and depth of lichen anatomical layers (lithocortex, photobiont layer, pervasive and sparse hyphal penetration component) depending on species and lithology. Specific structural organizations of lichen–rock interface were found to be associated with differential patterns of water absorption increase, evaluated by Karsten tube, in comparison with surfaces with microbial biofilms only, even more pronounced after the removal or scraping of the upper structural layers. Equotip measurements on surfaces bearing intact thalli showed lower hardness in comparison with control surfaces. By contrast, after the removal or scraping procedures, Equotip values were similar to or higher than those of controls, suggesting that the increasing open porosity may be related to a biogenic hardening process. Such counterposed patterns of porosity increase and hardening need to be considered when models relating lichen occurrence on limestones and biogeomorphological surface evolution are proposed, and to evaluate the consequences of lichen removal from stone-built cultural heritage. Copyright
... Recent exposure trials conducted by McIlroy de la Rosa et al. (2014) suggest that lichen communities (predominantly endolithic) on exposed clint surfaces in the Burren induce net bioprotection relative to lichen-free surfaces. During a 12 month exposure of lichen-colonized and lichen-free Carboniferous limestone surfaces from the Burren, average dissolutional losses of calcium were greater from the lichenfree limestone surface by approximately 1.25 times. ...
... Even when limestone is apparently directly exposed to subaerial weathering, close inspection of clints in the Burren reveals a fairly ubiquitous cover of endolithic and epilitihic lichens (McCarthy, 1983;McCarthy and Mitchell, 1985) as well as cyanobacterial patinas, which acting as a buffer between the rock surface and the atmosphere, can influence the overall rate of karstification (McIlroy de la Rosa et al., 2014) and contribute to the development of micro-and meso-scale bioweathering features (Moses and Smith, 1993;McIlroy de la Rosa et al. 2012). Additionally, the littoral karren of the Burren, which have not been considered in this text, are also known to be largely the product of marine bioerosion (Simms, 1990;Drew, 2009;Coombes, 2014). ...
The term glaciokarst describes a landscape where both glacial and karstic processes have contributed to geomorphological evolution and has been applied to a range of environments from the high arctic to the alpine Mediterranean. Nevertheless, glaciokarstic environments globally often exhibit significant variation in geomorphological processes and landforms due to these geographical differences. The Burren, County Clare, Republic of Ireland, is often quoted as a quintessential glaciokarstic landscape. However, the Burren and other similar environments would appear to lean towards one end of the glaciokarst spectrum, where solutional and biological processes have been dominant throughout the Holocene, in contrast to ice‐dominated glaciokarsts where karstic and biokarstic processes are temperature‐limited and cryospheric processes remain the principal geomorphological agents.
Holocene landscape evolution and the development of a range of meso‐, micro‐ and nano‐scale karren features on limestone surfaces appears to be largely biokarstic in origin. Karstification of many glacially scoured limestone pavements would have begun under acidic soil cover, with biological soil processes contributing to smooth, rounded cryptokarstic surface forms. Holocene soil erosion is attributed to anthropogenic activity, climatic fluctuations and the evolution of the karstic groundwater system leading to vertical soil loss through widening grikes. Exposed limestone pavements subject to subaerial conditions often exhibit extensive lichen colonization which has been shown to influence the overall rate of karstification and contribute to the development of micro‐ and meso‐scale bioweathering features. Where cryptokarstic features have been exhumed from beneath soil cover, their evolution under subaerial conditions leads to intermediate, polygenetic karren features.
In light of our current understanding of the Burren landscape, it is proposed that the term glaciobiokarstic may be a better expression to encompass the biological processes that have played a fundamental role in the evolution of the Burren and similar landscapes, without neglecting the contribution of glacial and inorganic karstic processes. Copyright © 2016 John Wiley & Sons, Ltd.
... Lichens have been associated with several ecosystem services such as soil fertility, nutrient cycling, biocontrol, mineral production and soil formation (de Bello et al., 2010). Lichen contribution to this latter ecosystem service is particularly evident on calcium carbonate surfaces, where epilithic and endolithic organisms regulate the processes of both biophysical and biochemical weathering of rocks, which is a preliminary step in soil formation (Jie and Blume, 2002;McIlroy de la Rosa et al., 2014). The former effects include physical weakening of the rocks as a consequence of desiccation and re-hydration processes, whereas the biochemical action is due to the production of metabolites which can enhance the weathering (Ascaso et al., 1998). ...
... As a consequence of massive alteration of communities, e.g. due to a fire event, the decay of lichen hyphae may expose weakened rocks to dissolution, triggering relatively rapid surface lowering due to weathering processes (McIllroy de la Rosa et al., 2013Rosa et al., , 2014. The approach for measuring functional diversity is basically the same as for taxonomic diversity, and information can be retrieved both within (i.e. ...
Epilithic lichen communities in dry grasslands on calcareous substrata play important functional roles, which may be compromised by the impact of fire. Lichens are involved in both rock weathering and rock stabilization, these processes being directly related to soil formation. In this paper, we examined the hypothesis that the functional and the taxonomic diversity of epilithic lichen communities in Mediterranean dry grassland is influenced by both time since fire and fire frequency. These disturbances produced different effects on the functional richness and on the taxonomic diversity of the communities. Our findings revealed that: (1) a drastic reduction of biodiversity was caused by frequent fires in the same area; (2) that resulting lichen communities in burned sites were merely an impoverishment of unburned areas; and (3) that in the case of infrequent fires, lichen communities can recover functional diversity even if a reduction of taxonomic diversity occurs.
... Erosion, however, is the process in which material components are carried away from the original rock surface, and consequently, the eroded rock volume is lower than the original one [16]. Usually, weathering precedes the erosion, but it does not unequivocally involve the consecutive erosion of a weathered surface [8,[17][18][19][20]. The objectives of this study focus on three main points: 1. ...
... It is also important to investigate to what extent the presence of biofilm can reduce the loss of material from the surface over time and to understand to what extent the presence of biofilm prevents the surface recession. Only a few studies have tried to investigate this aspect (McIlroy de la Rosa et al., 2014), mainly by quantifying the concentration of calcium ions by ion chromatography in collected of run-off rainwater from outdoor exposed colonised and uncolonised carbonate stone substrates. Difference in surface roughness and loss of material may also be investigated by exploiting the confocal microscope, 3D optical profilometry, optical interferometry or atomic force microscopy. ...
... Erosion, however, is the process in which material components are carried away from the original rock surface, and consequently, the eroded rock volume is lower than the original one [16]. Usually, weathering precedes the erosion, but it does not unequivocally involve the consecutive erosion of a weathered surface [8,[17][18][19][20]. The objectives of this study focus on three main points: 1. ...
... Williams' research has not yet identified the pioneer organisms of pedogenesis, which involves weathering of parent rock to form parent material and the process by which parent material forms soil. In searching for pioneer organisms, researchers in the area of biokarst study have started rigorous discussions about fungi, algae, lichens, and other organisms living in karst environment, mainly focusing on the weathering process and the roles they play in this process (Danin and Gerson, 1983;Cao et al., 1993;Katja, 2000;Smith et al., 2000;McIlroy de la Rosa et al., 2014;Cao et al., 2020). ...
The formation of soil in karst ecosystem has always been a scientific problem of great concern to human beings. Algae can grow on the exposed and non-nutrition carbonate surface, inducing and accelerating weathering of rock substrates, thus promoting soil formation. Yet the actual contribution of algae to solutional weathering intensity remains unclear. In this study, we performed weathering simulation experiment on two algae species (Klebsormidium dissectum (F.Gay) H.Ettl & G.Gärtner and Chlorella vulgaris Beijerinck), which were screened from carbonated rock surfaces from a typical karst region in South China. The results showed: (1) both algae have solutional weathering effect on carbonate rock, (2) there is no difference of solutional intensity observed, yet the solutional modes are different, suggesting different ecological adaptative strategies, (3) algae on carbonate rocks have higher carbonic anhydrase activity (CAA) and secrete more extracellular polysaccharide (EPS), accelerating rock weathering. (4) The absolute dissolution amount of carbonate rock with algae participation is 3 times of that of without algae. These results indicate the significant impact of terrestrial algae on carbonate rock solutional weathering and provides quantitative evidence that terrestrial algae are pioneer species. It also contributes to our further understanding of soil formation in karst ecosystems in South China.
... Lichens can provide bioprotection for stone surfaces, acting as a barrier against weathering, retaining moisture, increasing waterproofing, reducing thermal stress and erosion, and absorbing pollutants [11]. For the same species and lithologies, the balance between biodeterioration and bioprotection may change depending on (micro)-environmental conditions [12]. ...
This paper provides preliminary data for influence of gray and yellow lichens on archeological monuments in Stobi. Also was determinated the origin of the minerals which adhere to the rhizine/hyphae. According of the SEM results, in lichen are found small grains of minerals which originated from parent rocks or weathering. In the lichens on marble was determinated the present of the following minerals:calcite, dolomite, Fe carbonate, Ca silicate, Ca,Fe,Al silicate and Fe,Al silicate. Carbonate minerals come from marble while silicates are the result of weathering. In lichens on sandstone ware determined the following minerals: K,Al silicate, Ca carbonate quartz Fe,Mg silicate, Fe-oxide, zircon, and Na, Ca,Al silicate. Carbonate minerals are result of weathering while other determinated minerals originate from sandstone. Clay minerals are a result of the decomposition of feldspars.
... It has been noted by several authors Naylor 2005;Carter and Viles 2005;McIlroy de la Rosa et al., 2012;Favero-Longo and Viles 2020) that biodeterioration and bioprotection should not be viewed as conflicting, dichotomous, isolated positions; rather they are two ends of the same scale with both acting in tandem. The biodeteriorative effects inflicted by a given species may be outweighed by bioprotective effects that inhibit and retard more severe and faster acting weathering as observed with lichen (McIlroy de la Rosa et al., 2014) on Angkor temples in Cambodia by Bartoli et al. (2014). The hyphal penetration of lichen was deemed overall less deleterious than if the lichen was absent and the stone substrate was exposed to direct sunlight and weathering. ...
The deleterious effects (biodeterioration) and the protective benefits (bioprotection) of biological colonisation on manmade structures have long been debated. Lichens, biofilms, algae, bivalves and gastropods contribute both directly and indirectly to damaging substrata in the coastal zone which can enhance abiotic erosive forces that exploit biologically induced superficial damage. There is mounting evidence that these same species may also provide protective benefits. This debate often impacts approaches to managing fouling on concrete assets in the coastal environment. The net benefit or detriment a species or assemblage has on a structure is spatially and temporally dynamic and subject to the influence of various abiotic and biotic factors at different scales. However, the net outcome may be more pronounced under different contexts, particularly under warming and ocean acidifying climate change scenarios which is where further research should focus. Additionally, as bioprotection represents a potentially valuable ecosystem service, it supports the argument for increasing and improving habitat availability and biodiversity on artificial coastal structures via ecological enhancement. Quantifying bioprotection in useful metrics, such as monetary value or time added to serviceable life, would help demonstrate the benefits of bioprotective species in a meaningful way.
Outline:
... Once bedrock is not covered by soil, lichens progressively colonize its surface. Lichens are known to cause rock weathering (chemical and physical; Danin et al., 1982;Adamo and Violante, 2000), but they can also protect the rock from erosion by limiting the direct contact of the rock with erosional agents as well as preventing the disintegrated particles of bedrock to be detached (Seaward et al., 1989;Ariño et al., 1995;McIlroy de la Rosa et al., 2014). Lichens use rhizines to anchor themselves to the rock (Chen et al., 2000;Büdel and Scheidegger, 2008). ...
The development of a karst landscape results from complex interactions between lithology, climate, hydrology, soil, vegetation and tectonics. Weathering and erosion of carbonate rocks leads to denudation of karst landscapes. As dissolution of carbonate rocks is often considered to be the main process governing carbonate weathering, other processes are often overlooked. Here we present research done in the North Dalmatian Plain, a carbonate erosive surface located in the Dinaric karst region. Although the study site is composed of two different carbonate lithologies having different weathering style, there is no evident lithological impact on the topography of the erosive surface. Analyses of ³⁶Cl concentration were performed in ten proximal bedrock samples from both lithologies and resulted in long-term denudation rates ranging from 14.7 to 22.8 m/Ma. Since no statistical significance was found between samples from different lithologies (all samples belong to a single normal population) and they have the same geomorphological context and climate features, variable denudation rates are attributed to local (sample specific) differences. In the study site there are no large outstanding rock residuals or patches with deep soil profiles. Thus, to maintain the levelled erosive surface, local differential denudation rates have to vary with time. We hypothesize that lichens and pedogenic carbonates have a significant role in modulating local differences in denudation rates. Our study shows that even at outcrop scale those differences can be significant, and the study of sample populations is preferred to single or limited number of analyses. Thus, the long-term denudation rate of the North Dalmatian Plain, including its local variability is 18.91 ± 0.81 m/Ma. Despite classical studies on karst terrains assume that dissolution is the main process responsible for development of these landscapes, our research highlights the importance of physical weathering in combination with dissolution of carbonates as main controls on the denudation of karst landscapes.
... In contrast, our tests of Navajo Sandstone surficial cores did not show a significant difference in strength between lichen-covered and bare rock. These different test results can best be attributed to the much greater strength of Navajo Sandstone (mean = 280 kPa) compared to the highly friable, non-crusted samples tested bySlavik et al. (2017) (all mean values < 27 kPa).Filippi et al. (2021) also found that biocrusts had no significant effect on the tensile strength of sandstone, but emphasized that, by decreasing the entry of rainwater into rock, they greatly decrease the effects of weathering processes(Garcia-Valles et al., 2003;McIlroy de la Rosa, 2014;Mustoe, 2010). FollowingFilippi et al. (2021),Kurtz and Netoff (2001) andSlavik et al. (2017), we see lichens as protective veneers that bind grains and diminish entry of water into their substrate. ...
On many Navajo Sandstone outcrops in southern Utah, steep, decimetre‐high scarps (downslope‐facing margins of rock sheets) interrupt smooth slopes covered by crustose lichens. Scarps form where sheeting joints and water emerge at the land surface. Weathering at scarp faces causes upslope backwasting of rock sheets and leaves behind smooth, unweathered rock surfaces that become stabilized by lichens. We hypothesize that subsurface, low‐angle, open fractures in porous and permeable rocks are barriers to downward flux of water through the vadose zone. Runoff and lateral flow through the uppermost rock sheets deliver water to scarps, inducing backwasting. Monitoring of temperature and water/ice content within two surficial rock sheets revealed that, in the winter of 2020–2021, snowmelt that entered lichen‐covered surfaces persisted for 64 days and underwent 46 freeze/thaw cycles. Water gained from summer rains remained for a maximum of 11 days. Flaking rock and dangling lichen crusts that overhang scarps indicate backwasting is now active. We conclude that freeze/thaw cycles (rather than salt precipitation) drive backwasting at our study sites, all of which are located more than 1400 m above sea level where the climate is relatively cool, and snowfalls are frequent. Backwasting would likely be more rapid and extensive under a cooler, wetter (periglacial) climate. Although broad, gently sloping, lichen‐covered rock sheets dominate the land surface, they are not downwasting; weathering is instead restricted to the near‐vertical, lichen‐free, backwasting scarps.
... Rock outcrops and cobbles are often covered by lithic cyanobacteria and lichens, whether in wet areas (Porembski et al., 1994;Allan and Roulet, 1994;Tretiach and Pecchiari, 1975;Tretiach and Geletti, 1977;Mcllroy de la Rosa et al., 2014) or in deserts (Wessels, 1989;Palmer and Friedman, 1990;Bungartz et al., 2004;Garvie et al., 2008;Jung et al., 2019;Wierzchos et al., 2020;Gwizdala et al., 2021). This is also the case in the Negev, at the southern part of Israel where a sharp gradient of precipitation from north (200 mm at the city of Beer Sheva) to south (35 mm at the city of Eilat) occurs, and where cyanobacteria and especially chlorolichens (lichens having green algae as photobionts) abound (Friedmann and Galun, 1974;Danin and Garty, 1983;Kidron, 2000;Kidron et al., 2011;Temina, 2013, 2017). ...
While previous measurements in a small drainage basin in the Negev Desert (Sede Boqer) discovered dewless habitats (<0.03 mm of non-rainfall water, NRW), which are inhabited by lithic cyanobacteria, it is not clear whether these findings can be generalized to other locations in the Negev. The question is especially relevant for high elevation sites (1000 m above msl) where previous measurements recorded high amounts of dew and fog and lush cover of lichens. For this end, measurements along an elevational gradient were carried out, at Nizzana (NIZ), 250 m above msl, Sede Boqer (SB), 550 m above msl, and Har Harif (HH), 1000 m above msl. The measurements included (a) cover and biomass (chlorophyll a) of the cyanobacteria and lichens on bedrocks along a 30 m transect at the south-facing slopes, (b) simultaneous monitoring of the surface temperatures of bedrocks inhabited by cyanobacteria and lichens, and (c) periodic measurements of NRW at these habitats using the cloth-plate method (CPM) and cloths attached to rock surfaces inhabited by both lithobionts. A significant decrease in minimum temperatures and increase in NRW (as recorded by the CPM) with elevation was recorded following the pattern: NIZ (0.12 mm) < SB (0.20 mm) < HH (0.29 mm). A significant increase in NRW with elevation was also recorded at the lichen habitat (with NRW of up to 0.51 mm), but yet NRW at the cyanobacteria habitat was always <0.04 mm, i.e., below the necessary threshold required for their activation. The findings point to the fact that variability in rock temperatures dictates the amount of NRW, and regardless of the general increase in NRW with elevation, cyanobacteria are confined to dewless habitats. A prokaryote–eukaryote partition in accordance with NRW is thus apparent, with cyanobacteria serving as useful bioindicators for dewless habitats in the Negev.
... Adhesion and penetration of lichen structures, together with the release of acidic and chelating metabolites, have physical and chemical impacts, exerting mechanical stress and causing dissolution and/or neoformation of minerals (Salvadori & Casanova-Municchia, 2016). However, at least in some cases, lichen bioprotection has been also documented, due to their umbrella-like action against other weathering forces (Carter & Viles, 2004;McIlroy de la Rosa et al., 2014) or the sealing of rock discontinuities due to biomineralization (Lee & Parsons, 1999). ...
The balance between lichen biodeterioration and bioprotection processes on stone surfaces depends on many variables and is crucial to understanding the role of lichens in biogeomorphology and their threat to stone heritage conservation. However, stones colonized by lichens have still been mostly examined in terms of affected volumes and physico‐chemical modes of interactions, overlooking the overall effects on properties related to surface durability. In this study, the impact of lichen colonization patterns on Cortemilia sandstone was examined beneath thalli of three lichen species. Rock hardness, a proxy for rock durability, was measured at different depths from the surface using an Equotip hardness tester and compared to that of freshly cut surfaces and exposed surfaces uncolonized by lichens. Mineralogical analyses were performed by X‐ray powder diffraction on rock beneath lichen colonization, in comparison with unweathered rock. Equotip analyses quantified a differential, species‐specific decrease in stone hardness. This variability was related to differences in hyphal penetration patterns and, possibly, calcite (re‐)precipitation. In particular, in the case of the species most impacting rock hardness, X‐ray diffraction patterns of calcite showed a remarkable stability of crystallographic plane (01–12), known to be enhanced in the presence of organic chelants. These results confirm that decisions on lichen removal from stone surfaces should consider species‐specific behaviour. Moreover, the innovative approach of measuring stone hardness variation in association with the analysis of biomineralization processes contributes to unveil the extension of the sphere of lichen interaction within the stone substrate beyond the limit of the hyphal penetration.
... According to Morando et al. (2017) and Slavík et al. (2017), the BIRC reduces saturated hydraulic conductivity and capillary water absorption, which significantly alters the infiltration rate, thereby controlling most of the processes controlled by moisture. For example, the BIRC considerably decreases the entry of rainwater into the rock (Garcia-Vallès et al., 2003;Mustoe, 2010;McIlroy de la Rosa et al., 2014), which decreases the effects of the weathering processes related to water action (Hall, 1988;Paradise, 2002;Garcia-Vallès et al., 2003;Mol and Viles, 2012). Similarly, Wieler et al. (2019) suggested that the BIRC decreases evaporation rates, thereby attenuating salt crystallization pressure in the rock and reducing rock damage. ...
Weathering and disintegration of sandstone outcrops are a complex process involving loose material production, rockfall phenomena, and creation of picturesque natural sceneries. On historical monuments, they induce damage to building stone. Here we present a new look on sandstone weathering/recession the central aspect of which is rapid disintegration of portions of the rock massif, which are no longer physically connected with the main rock mass, though still in situ. A set of field and laboratory measurements including mechanical (tensile strength, drilling resistance) and hydraulic (permeability, surface moisture) methods were applied to compare the properties of the disconnected portions with those of the surrounding rock mass. Also, physical weathering experiments were performed to characterize the effect of confinement on the breakdown rate of several sandstone samples. The presence of disconnected portions is very common in dry climates where they are usually elongated parallel to horizontal surfaces. In humid temperate climates, however, they are less abundant, being elongated mostly vertically. The surfaces of detachment follow bedding planes, planar elements of other sedimentary structures, and subhorizontal fractures, and stress shadows on subvertical cliff faces. Weathered surfaces of the disconnected portions show reduced tensile strength and drilling resistance values, a faster capillary water absorption and a higher surface moisture compared to the much less weathered surfaces of the surrounding rock mass. Physical experiments demonstrated that a confinement by the surrounding rock mass may considerably delay the loosening of rock during weathering. The much faster disintegration rates of the disconnected portions of rock compared to their surroundings are explained by the fact that they are not confined and have a larger surface area. The recession rates of sandstone surfaces with disconnected portions are highly variable both in space and time and their genesis can be demonstrated by two suggested conceptual models.
... Such hypotheses were based on early macroscopic observations of differential erosion rates with and without lithobionts, suggesting an umbrella-like protective effect (Mottershead and Lucas 2000;Özvan et al. 2015). Such interpretations of lithobionts as forming a physical barrier against other weathering factors have been supported by the quantification of lower solutional weathering from lithobiont (lichen)-covered limestone slates in comparison with uncolonized controls after 1 year of exposure in the humid climate of Ireland (McIlroy de la Rosa et al. 2014). Although ivy (Hedera helix L.) can cause biodeterioration (Bartoli et al. 2017), in some cases it has been found to have an umbrella-like impact and protect historic limestone walls from pollutants (which can lead to soiling and deterioration) (Sternberg et al. 2010). ...
Lithobionts (rock-dwelling organisms) have been recognized as agents of aesthetic and physico-chemical deterioration of stonework. In consequence, their removal from cultural heritage stone surfaces (CHSS) is widely considered a necessary step in conservation interventions. On the other hand, lithobiontic communities, including microbial biofilms (‘biological patinas’), can help integrate CHSS with their environmental setting and enhance biodiversity. Moreover, in some cases bioprotective effects have been reported and even interpreted as potential biotechnological solutions for conservation. This paper reviews the plethora of traditional and innovative methodologies to characterize lithobionts on CHSS in terms of biodiversity, interaction with the stone substrate and impacts on durability. In order to develop the best management and conservation strategies for CHSS, such diagnosis should be acquired on a case-by-case basis, as generalized approaches are unlikely to be suitable for all lithobionts, lithologies, environmental and cultural contexts or types of stonework. Strategies to control biodeteriogenic lithobionts on CHSS should similarly be based on experimental evaluation of their efficacy, including long-term monitoring of the effects on bioreceptivity, and of their environmental safety. This review examines what is known about the efficacy of control methods based on traditional-commercial biocides, as well as those based on innovative application of substances of plant and microbial origin, and physical techniques. A framework for providing a balanced scientific assessment of the role of lithobionts on CHSS and integrating this knowledge into management and conservation decision-making is presented.
Graphic abstract
... In addition, biological mechanisms have been proposed to promote rock weathering through mechanisms such as flaking via 15 colony growth (Viles, 2012), acidification by bacterial extractions (Garcia-Pichel, 2006;Warscheid and Braams, 2000) or alkalization during photosynthesis by cyanobacteria (Büdel et al., 2004). In contrast, it was proposed that micro-and macroorganisms colonisation can mitigate weathering in temperate, coastal regions (McIlroy de la Rosa et al., 2014;Mustoe, 2010) through encrustation or protection from direct rain impact. Yet, it is not clear which of these mechanisms dominates or what is the relative contribution of chemical vs biological processes to weathering in arid environments. ...
In drylands, microbes that colonise rock surfaces were linked to erosion because water scarcity excludes traditional weathering mechanisms. We studied the origin and role of rock biofilms in geomorphic processes of hard lime and dolomitic rocks that feature comparable weathering morphologies though originating from arid and hyperarid environments, respectively. We hypothesised that weathering patterns are fashioned by salt erosion and mediated by the rock biofilms that originate from the adjacent soil and dust. We used a combination of microbial and geological techniques to characterise rocks morphologies and the origin and diversity of their biofilm. Amplicon sequencing of the SSU rRNA gene suggested that bacterial diversity is low and dominated by Proteobacteria and Actinobacteria. These phyla formed laminar biofilms only on rock surfaces that were exposed to the atmosphere and burrowed up to 6mm beneath the surface, protected by sedimentary deposits. Unexpectedly, the microbial composition of the biofilms differed between the two rock types and was also distinct from the communities identified in the adjacent soil and settled dust, showing a habitat-specific filtering effect. Moreover, the rock bacterial communities were shown to secrete extracellular polymeric substances that form an evaporation barrier, reducing water loss rates by 65–75%. The reduced water transport rates through the rock also limit salt transport and its crystallisation in surface pores, which is thought to be the main force for weathering. Concomitantly, the biofilm layer stabilises the rock surface via coating and protects the weathered front. Our hypothesis contradicts common models, which typically consider biofilms as weathering-promoting agents. In contrast, we propose the microbial colonisation of mineral surfaces acts to mitigate geomorphic processes in hot, arid environments.
... Several of these lichens form a crust on and/or beneath the rock surface and become fully integrated within the rock substrate (Chen et al., 2000;de los R ıos et al., 2002). Endolithic lichens have been shown to protect Carboniferous limestone surfaces from weathering by rainwater (McIlroy de laRosa et al., 2014). Pores in the limestone become filled with a network of hyphae which waterproof the stone and act as a barrier to sulfate ingress. ...
The growth of microbial biofilms and various biomineralization phenomena can lead to the formation of stable layers and veneers on rocks known as 'rock varnishes' that can stabilize surfaces and protect from further weathering. This article describes the potential application of fungal systems for bioprotection of rock and mineral-based substrates and the evidence to support this concept of utilizing natural or engineered colonization and metabolic properties of fungi, including lichens.
... Cámara et al. 2015) and v) developing methods to quantify the weathering rates induced by individual species or by a limited set of the most representative ones on the surface of interest (e.g. Aghamiri & Schwartzman 2002, Bartoli et al. 2014, Gazzano et al. 2009a, b, Mcllroy de la Rosa et al. 2014). The majority of work has been applied at characterizing the biodeterioration of a range of stonework in Europe and only sporadically in other regions of the globe. ...
Contradictory evidence from biogeomorphological studies has increased the debate on the extent of lichen contribution to differential rock surface weathering in both natural and cultural settings. This study, undertaken in Côa Valley Archaeological Park, aimed at evaluating the effect of rock surface orientation on the weathering ability of dominant lichens. Hyphal penetration and oxalate formation at the lichen-rock interface were evaluated as proxies of physical and chemical weathering, respectively. A new protocol of pixel-based supervised image classification for the analysis of periodic acid-Schiff stained cross-sections of colonized schist revealed that hyphal spread of individual species was not influenced by surface orientation. However, hyphal spread was significantly higher in species dominant on north-west facing surfaces. An apparently opposite effect was noticed in terms of calcium oxalate accumulation at the lichen-rock interface, detected by Raman spectroscopy and complementary X-ray microdiffraction on south-east facing surfaces only. These results suggest that lichen-induced physical weathering may be most severe on north-west facing surfaces by means of an indirect effect of surface orientation on species abundance, and thus dependent on the species, whereas lichen-induced chemical weathering is apparently higher on south-east facing surfaces and dependent on micro-environmental conditions, giving only weak support to the hypothesis that lichens are responsible for the currently observed pattern of rock-art distribution in Côa Valley. Assumptions about the drivers of open-air rock-art distribution patterns elsewhere should also consider the micro-environmental controls of lichen-induced weathering, to avoid biased measures of lichen contribution to rock-art deterioration. This article is protected by copyright. All rights reserved.
... Furthermore, erosion is understood to be the final step in a series of decay mechanisms resulting in the total loss of a material. However, there is strong evidence that several weathering mechanisms precede this loss stage, such as surface hardening (redeposition of solutional products) or softening (induced by both climate and biological activity), which lead to stone surface property alterations including increased porosity and the formation of superficial layers (Pope et al. 2002;Hoke and Turcotte 2004;Inkpen et al. 2012b;McIlroy de la Rosa et al. 2014). Erosion or surface recession can therefore be considered a relatively coarse measure of weathering, and an improved understanding of limestone breakdown relies on quantifying the entire weathering trajectory. ...
This study estimates stone weathering rates using in situ surface hardness testing. Surface hardness changes are precursors to erosion and may be utilized to describe stone weathering behaviour. The method proposed here complements previous approaches to determining stone weathering rates by surface loss/change. A time series covering 1–248 years of exposure is investigated using a sample of 12 headstones in two nearby cemeteries. Using an Equotip D surface hardness tester, rates of change in surface hardness for top and bottom sections of the headstones were determined and the data evaluated using robust, nonparametric statistical methods. When considering all headstones as one time series, nonlinear behaviour is observed with rates of decline in surface hardness slowing over time. However, breakpoint analysis shows a breakpoint at c. 100 years, with higher rates of surface hardness decline (as measured by QC
50—the regression coefficient for 0.50 quantile regression) up to that point and lower rates thereafter. Up to c. 100 years, surface hardness declines more rapidly in the top versus bottom sections. Possible explanations for the differing rates in surface hardness changes are: (a) inherent natural stone variability and/or different weathering-stress history; (b) the use of two different Portland limestone varieties; (c) synergistic effects of microclimates and lichen cover. In order to gain a deeper insight into stone weathering behaviour, future studies could combine surface hardness measurements with surface change methods such as micro-erosion meter and lead plug index over short- and long-term time series on architectural heritage under real-world conditions.
... Endolithic organic matter associated with lichens colonization can provide waterproofing to the stone and act as a sulfate contamination barrier [58]. Thus, endolithic lichen can induce bioprotection of carboniferous limestone by a passive 'umbrella' or 'thalline shielding' effect [55,59]: hyphal binding of the rock surface and subsurface appears only to retard, but do not prevent the dissolution of the calcareous substrate [60]. This bioprotection effect depends upon the metabolic activity of the microorganism and thus is subjected to seasonal variations. ...
Bacteria can live either as free planktonic cells in bulk solution, or as sessile cells attached to a surface. In addition to their attachment status, sessile bacteria are part of sessile communities termed biofilms. A biofilm can be defined as a microbial community attached to a solid surface composed of cells organised as microcolonies embedded in an organic polymer matrix of microbial origin. Thus, a biofilm is made of microbial cells and extracellular polymeric substances. The biofilm mode of life provides several advantages to microorganisms including resistance to environmental stresses, increased communication and genetic exchange between cells. Microbial biofilm development can be observed on virtually all kinds of stone monuments such as castles, caves, churches/cathedrals, fountains, temples, tombs/catacombs, etc., and can be associated with problems of conservation. Several types of autotrophic and heterotrophic microorganisms are usually observed on stone monuments such as bacteria, fungi, algae and lichens.
The European standard EN15898 defines the main general terms used in the field of conservation of cultural property such as alteration, deterioration, weathering, treatment and cleaning. The term biodeterioration is not defined in the EN15898 standard, but can be defined as “any undesirable change in the properties of a material caused by the vital activi-ties of organism”. The biodeterioration of stone materials corresponds to an aesthetic action (production of pigments), to a biochemical action (stone dissolution or salt cristallisation driven by cell metabolism) and to a physical action (mechani-cal pressure during growth).
This review has two main objectives: to summarise the actual knowledge about basics of microbial colonisation and bio-deterioration of stone monuments and to realise a quantitative and qualitative analysis of publications in scientific journals on this topic.
... The relative importance of bioprotection vs deterioration can also vary for a single species (e.g. Baglietotta baldensis) on a seasonal scale because of changes in metabolic activity (McIlroy de la Rosa et al., 2014). ...
While karst is not biogenic in the same sense as, say, coral reefs or peat bogs, and carbonate dissolution can occur abiotically, formation of karst landscapes would not occur in the absence of the biosphere. Seven levels of biogeomorphic biotic-abiotic interactions are identified, from indirect impacts to landforms as extended phenotypes. Karst is generally near the biogenic end of that spectrum, featuring reciprocal interactions and mutual adjustments between biota and landforms and interrelated geomorphological and ecological processes. Karst biogeomorphology may also involve niche construction. In many cases biogeomorphic ecosystem engineering in karst is contingent, in the sense that the engineer organisms may have no, or different, biogeomorphic impacts in non-karst environments. Several examples of contingent ecosystem engineering in karst are given, including biogeomorphic effects of chinkapin oak. Abiotic geomorphic features exist on Earth, but consideration of landform types lying between the biotic-abiotic extremes would likely yield broadly similar conclusions to those about karst. However, it is also clear that we know very little about niche construction and coevolution in karst biogeomorphology, and whether karst or any specific karst features can be considered an extended (composite) phenotype is still an open question. Thus far, most work on biogeomorphology and ecosystem engineering has focused on what might be called obligate engineers—organisms whose engineering effects are at least inevitable, if not necessary to their survival. However, in some cases contingent ecosystem engineers have substantial geomorphic impacts.
... En las últimas décadas, numerosos autores han demostrado la participación de bacterias, hongos, algas, líquenes, musgos y plantas vasculares en el biodeterioro de las superficies rocosas de monumentos antiguos (Eckardt, 1985;1990;Krumbein, 1998;Piervittori, Favero-Longo & Gazzano, 2009;Warscheid, Petersen & Krumbein, 1988;Warscheid, Oetling & Kumbrein, 1991;Warscheid & Krumbein, 1994). Dichas comunidades se desarrollan asociadas a los sustratos de roca, ocasionando el deterioro químico y físico de la misma, y alterando a través de diferentes mecanismos la apariencia estética y la integridad física del material (Favero-Longoa et al., 2011;McIlroy, Warke & Smith, 2014;Palinska & Krumbein, 1998;Scarciglia et al., 2012), con la consecuente formación y transformación de minerales. La excreción de enzimas y ácidos inorgánicos y orgánicos disuelve los componentes estructurales del sustrato mineral, contribuyendo a los procesos de deterioro (Eckardt, 1985;Guglielmin, Favero-Longo, Cannone, Piervittori & Strini, 2011;Warscheid et al., 1988;Warscheid & Braams, 2000). ...
In this paper we present the deterioration processes that exert lichen communities in siliceous sandstones of two historical monuments of the nineteenth and twentieth Centuries of the Guanajuato city (steps of the Guanajuato University and the School of Music at the Guanajuato University). In addition to contributing to the knowledge of deterioration, data on the lichen species found, is provided, the causes of its growth and its role in the deterioration of the stone material, in order to implement measures of protection and prevention. The lichen-rock interface was observed using complementary techniques such as, optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Inductively Coupled Plasma) (ICP), and energy dispersive spectroscopy X-ray (EDS). Were identified five species of lichens: Xanthoparmelia mexicana, Xanthoparmelia tasmanica; Caloplaca aff. brouardii, Caloplaca aff. ludificans and Aspicilia sp. These lichens penetrate 0.5 µm to 50 µm on the substrate through its rhizines, causing disintegration of minerals in the rock surface (plagioclase, quartz and feldspar). The disintegration of minerals along with the changes in chemical composition in the lichen-rock interface shows a negative action on the rocky surface, (the decrease in SiO2, Al2O3, Zn, and K2O and the presence of a high percentage in CaO, Fe2O3, and MgO
Cultural heritage sites worldwide are increasingly threatened by deterioration due to natural erosion and the intensified effects of climate change. Soft capping, an environmentally friendly approach for protecting built heritage using plants, has been underexplored from a biological perspective. This article aims to review studies on soft capping applied to earthen and masonry heritage from the 1980s to the present. The findings categorise soft capping into four types: Phototropic biofilms- and Lichen-capping, Bryophyte-capping, Spermatophyte-capping and Mixed plants-capping. The selection of soft capping type depends on the site's microclimates, building materials and the structure's geometry. Soft capping helps to regulate the microclimates of affected structures, slowing deterioration and enhancing their long-term sustainability. Additionally, it offers flexible adaptation to individual cases for optimal protection. Despite the considerable benefits of soft capping, further research and expanded databases are necessary to better understand factors such as type selection, composition, protective efficacy and limitations. This knowledge will enable more informed conservation strategies for applying soft capping to heritage sites in the future.
Fungi are ubiquitous and important biosphere inhabitants, and their abilities to decompose, degrade, and otherwise transform a massive range of organic and inorganic substances, including plant organic matter, rocks, and minerals, underpin their major significance as biodeteriogens in the built environment and of cultural heritage. Fungi are often the most obvious agents of cultural heritage biodeterioration with effects ranging from discoloration, staining, and biofouling to destruction of building components, historical artifacts, and artwork. Sporulation, morphological adaptations, and the explorative penetrative lifestyle of filamentous fungi enable efficient dispersal and colonization of solid substrates, while many species are able to withstand environmental stress factors such as desiccation, ultra-violet radiation, salinity, and potentially toxic organic and inorganic substances. Many can grow under nutrient-limited conditions, and many produce resistant cell forms that can survive through long periods of adverse conditions. The fungal lifestyle and chemoorganotrophic metabolism therefore enable adaptation and success in the frequently encountered extremophilic conditions that are associated with indoor and outdoor cultural heritage. Apart from free-living fungi, lichens are a fungal growth form and ubiquitous pioneer colonizers and biodeteriogens of outdoor materials, especially stone- and mineral-based building components. This article surveys the roles and significance of fungi in the biodeterioration of cultural heritage, with reference to the mechanisms involved and in relation to the range of substances encountered, as well as the methods by which fungal biodeterioration can be assessed and combated, and how certain fungal processes may be utilized in bioprotection.
This study investigated the poorly known phenomenon of Centimetric circular areas Uncolonized by Microbial Biofilms (CUMBs) which is frequently observed on natural and heritage stone surfaces displaying widespread lithobiontic colonization. In order to unveil a possible relationship with past lichen colonization, analyses were carried out on the distribution, morphometry, physical and mineralogical properties, and microscopic features of CUMBs on the marble surfaces of a balustrade in the Garden of a Savoy residence in Torino (Italy; UNESCO-WHS 823bis) and in its original quarry site in the W-Alps. Image analyses of CUMBs displayed a distributional and dimensional compatibility with lichen thalli (re-)colonizing surfaces in their vicinity. Invasive analyses on quarry materials displayed similar microscopic modifications in marble layers beneath CUMBs and lichens, associated to a higher stabilization of the calcite {01–12} form, which is favoured by the presence of organic substances. These findings support the hypothesis of a lichen origin for some CUMBs, which may derive from the modification of physical stone properties and/or a long-lasting allelopathic effect affecting surface bioreceptivity.
Rock weathering is a key process in global elemental cycling. Life participates in this process with tangible consequences observed from the mineral interface to the planetary scale. Multiple lines of evidence show that microorganisms may play a pivotal—yet overlooked—role in weathering. This topic is reviewed here with an emphasis on the following questions that remain unanswered: What is the quantitative contribution of bacteria and fungi to weathering? What are the associated mechanisms and do they leave characteristic imprints on mineral surfaces or in the geological record? Does biogenic weathering fulfill an ecological function, or does it occur as a side effect of unrelated metabolic functions and biological processes? An overview of efforts to integrate the contribution of living organisms into reactive transport models is provided. We also highlight prospective opportunities to harness microbial weathering in order to support sustainable agroforestry practices and mining activities, soil remediation, and carbon sequestration.
Culture and cultural heritage are the imprints of human civilization and architectural depiction of society and cultures. Antique documents and cultural heritages such as historic buildings, monuments, manuscripts and paintings are brittle and undergo physical, chemical and biological deterioration during the course of time. Escalating air pollution and global warming are the main cause of deterioration of stone monuments and artworks. The deterioration process can be restored by employing various microbiological tools such as biocleaning, biomineralization, biocementation and biofilm formation. This chapter summarizes eco-friendly microbiological approaches used to restore cultural heritages, archaeological sites and wall paintings.
This paper reviews studies on the Quaternary tectonics and geomorphic processes of the Ryukyu arc, southwestern Japan. The Ryukyu arc lies along the subduction zone between the Eurasia and Philippine sea plates. Many islands of the Ryukyu arc are classified into volcanic islands, accretionary complex islands and uplifted coral reef islands. The Quaternary tectonics forms many strike-slip and normal faults in the Pleistocene limestone (Ryukyu group) originating from coral reef sediments. Mountains and hills consisting of metamorphic and sedimentary rocks are eroded, reflecting the rate of weathering controlled by various environmental conditions. Previous physiographic studies considered several landforms as tropical and subtropical landscapes, whereas such landforms should be reconsidered in terms of geological factors as well as climatic ones. The authors suggest that future studies require a more comprehensive and integrated understanding of the geomorphic processes involving both the climatic and geological factors.
In drylands, microbes that colonize rock surfaces have been linked to erosion because water scarcity excludes traditional weathering mechanisms. We studied the origin and role of rock biofilms in geomorphic processes of hard lime and dolomitic rocks that feature comparable weathering morphologies, although these two rock types originate from arid and hyperarid environments, respectively. We hypothesized that weathering patterns are fashioned by salt erosion and mediated by the rock biofilms that originate from the adjacent soil and dust. We used a combination of microbial and geological techniques to characterize rock morphologies and the origin and diversity of their biofilms. Amplicon sequencing of the SSU rRNA gene suggested that bacterial diversity is low and dominated by Proteobacteria and Actinobacteria. These phyla only formed laminar biofilms on rock surfaces that were exposed to the atmosphere and burrowed up to 6 mm beneath the surface, protected by sedimentary deposits. Unexpectedly, the microbial composition of the biofilms differed between the two rock types and was also distinct from the communities identified in the adjacent soil and settled dust, showing a habitat-specific filtering effect. Moreover, the rock bacterial communities were shown to secrete extracellular polymeric substances (EPSs) that form an evaporation barrier, reducing water loss rates by 65 %–75 %. The reduced water transport rates through the rock also limit salt transport and its crystallization in surface pores, which is thought to be the main force for weathering. Concomitantly, the biofilm layer stabilizes the rock surface via coating and protects the weathered front. Our hypothesis contradicts common models, which typically consider biofilms to be agents that promote weathering. In contrast, we propose that the microbial colonization of mineral surfaces acts to mitigate geomorphic processes in hot, arid environments.
In drylands, microbes that colonise rock surfaces were linked to erosion because water scarcity excludes traditional weathering mechanisms. We studied the origin and role of rock biofilms in geomorphic processes of hard lime and dolomitic rocks that feature comparable weathering morphologies though originating from arid and hyperarid environments, respectively. We hypothesised that weathering patterns are fashioned by salt erosion and mediated by the rock biofilms that originate from the adjacent soil and dust. We used a combination of microbial and geological techniques to characterise rocks morphologies and the origin and diversity of their biofilm. Amplicon sequencing of the SSU rRNA gene suggested that bacterial diversity is low and dominated by Proteobacteria and Actinobacteria. These phyla formed laminar biofilms only on rock surfaces that were exposed to the atmosphere and burrowed up to 6 mm beneath the surface, protected by sedimentary deposits. Unexpectedly, the microbial composition of the biofilms differed between the two rock types and was also distinct from the communities identified in the adjacent soil and settled dust, showing a habitat-specific filtering effect. Moreover, the rock bacterial communities were shown to secrete extracellular polymeric substances that form an evaporation barrier, reducing water loss rates by 65-75%. The reduced water transport rates through the rock also limit salt transport and its crystallisation in surface pores, which is thought to be the main force for weathering. Concomitantly, the biofilm layer stabilises the rock surface via coating and protects the weathered front. Our hypothesis contradicts common models, which typically consider biofilms as weathering-promoting agents. In contrast, we propose the microbial colonisation of mineral surfaces acts to mitigate geomorphic processes in hot, arid environments.
Microbial biofilms frequently cause the esthetic and biological deterioration of stone monuments. Chichén Itzá, designated as a UNESCO World Heritage Site and as one of the seven new wonders of the world, is one Maya archeological site affected by biofilms. In the present study, we analyzed the biofilms at three different building complexes of Chichén Itzá: the Lower Temple of the Jaguars, the Temple of the Warriors, and Tzompantli. Samples of biofilms and detached rocks were taken from walls with abundant white-, green-, black-, and orange-colored biofilms. The morphology of rock fragments and dust was analyzed by electron and optical microscopy and was structurally characterized by X-ray diffraction. An HCl treatment (5% v/v) was subsequently applied to eliminate carbonates. The morphological analysis evidenced the presence of cyanobacteria, algae, and lichens. Some algae formed small nodules on orange- or black-colored rocks. Lichens were associated with a distinct mineral content on the inner surface of rocks versus on the outer surface. The presence of calcium oxalates such as weddellite (C2CaO4·2H2O) and whewellite (C2CaO4·H2O) and other minerals, including quartz and feldspars, was confirmed by X-ray diffraction. The lichens collected from the Lower Temple of the Jaguars and Tzompantli were therefore confirmed to disintegrate rock surfaces through biomineralization and the formation of oxalate crystals. At sites with greater solar radiation, a higher quantity of weddellite and a lower quantity of whewellite were observed. In conclusion, the establishment of microorganisms on the stone surfaces of Chichén Itzá causes esthetic damage and also leads to the biomineralization of these rock surfaces.
It is difficult to estimate weathering rates of rocks based on actual landforms. However, using stone-built architectures, artifacts, and traces of human activity on rock surfaces, weathering rates of rocks under weathering-limited conditions can be obtained easily because stone-built heritages, in general, have a geometrical shape and zero-datum levels. In addition, it is possible to estimate weathering rates of a millennium-scale and changes of rates up to a millennium scale. Many studies on weathering rates of rocks use stone-built heritages. This study reviews recent geomorphological studies that estimate weathering rates, and summarizes their trends. Most of the studies analyze gravestones and churches built since the 19th and 11th centuries, respectively. Such stone-built heritages are more commonly located in humid temperate areas. Weathering rates are estimated mainly from surface recession or surface loss of gravestones and church-building stones. The major three building stones—carbonate rocks (rate: 2-90 mm/ka), sandstone (8-100 mm/ka), and granite (5-65 mm/ka)—have different ranges of weathering rates. Among these stones, the rates for carbonate rocks are sensitive to climatic conditions and atmospheric sulfur dioxide concentrations. The results of the studies reveal that weathering rates show an obvious dependence on aspects. North-facing surfaces tend to have lower rates than surfaces facing other cardinal directions because each surface has different temperature and moisture conditions due to insolation. Moreover, the studies reveal that temporal changes in weathering rates rarely fit a simple linear model. Changes in atmospheric acidity, landform development, and vegetation cover rapidly affect the intensity of weathering processes and cause fluctuations in weathering rates.
Environmental geomicrobial studies offer insights into the structure and function of the built environment microbiome.
A typical Seljukian town of Ahlat, located between the north-western shores of the Lake Van and the Nemrud and Suphan volcanoes of the Eastern Turkey is hosting rich and colorful cultural heritage sites. Among these, famous Seljukian Cemetery is a major archeological district with monumental tombstones (stelae). Excessive deterioration, erosion and lichen colonization can be observed in these cultural artifacts. The main objective of this study is the investigation of stones’ physical characterization and evaluation of the microstructural features. A degradation model was outlined starting with the capillary water uptake from the bottom section and lichen colonization starting from the top and covering these tombstones upto their mid sections. This paper provides some information about the historical town of Ahlat and its tombstones. Some physical and microstructural characterization of the gravestones and the results of chemical and physical analysis are also presented along with some recommendations.
Studies demonstrate the active and passive capability of lichens to inhibit or retard the weathering of calcareous surfaces. Lichen coverage may actively protect a surface through shielding by the thallus and the binding and waterproofing of the rock surface and subsurface by fungal hyphae. Passive protection of rock surfaces may be induced by the formation of an insoluble encrustation, such as calcium oxalate, at the lichen-rock interface. Recent research suggests that the decay of hyphae, induced by changes in microenvironmental conditions, necrosis, parasitism or the natural physiological traits of particular lichen species, may expose a chemically and physically weakened substrate to dissolution, triggering relatively rapid weathering-related surface lowering. Consequently, certain epilithic crustose and endolithic lichens may induce a period of surface stability throughout the course of their lifespan, followed by a phase of instability and rapid episodic microtopographical evolution after death and decay. A series of conceptual models is proposed to illustrate this idea over short (single lichen lifespan) and long (multiple lichen lifespans) timescales. The models suggest that the microscale biogeomorphological system of lichen-rock interaction is underpinned by non-linear dynamical system theory as it exhibits dynamical instability and is consequently difficult to predict over a long timescale. Dominance by biodeterioration or bioprotection may be altered by changes in lichen species or in environmental conditions over time.
Laboratory salt decay simulations are a well established method to assess the relative durability of stone. There is still, however, very much scope to implement improved monitoring techniques to investigate the changes experienced by the materials during these experiments. Non-destructive techniques have acquired over recent decades a preferential status for monitoring change samples during salt decay tests, as they allow cumulative tests on each sample. The development of HD laser scanning permits detailed mapping of surface changes and, therefore, constitutes an effective technique to monitor non-destructively surface changes in tested samples as an alternative to other monitoring techniques such as traditional weight loss strategies that do not permit any degree of spatial differentiation that can be related, for example, to underlying stone properties.
Several different limestone lithologies are present. Topography and microtopography vary among these, and since they are all exposed to the same climate, the differences must relate to properties of the rocks themselves. Detailed surveys of solution flutes were made at five sites, in order to assess quantitively the degree of such rock-induced variation. It is possible to group the sites according to whether the host rocks are fine-textured sparites or more coarsely-textured recrystallised limestones. The sparites displaying larger solution flutes developed on steeper rock faces. Solution flutes at the Royal Arch site are significantly different from all others in terms of width, sectional area, sectional shape, and rock face slope. -from English summary
An update of the account in Technical Bulletin 5 which describes a traversing model of MEM capable of making more readings per station than the standard model, and also improvements in the design of reference studs.-K.Clayton
Data are reported demonstrating the potential role of microscale morphologies, induced by endolithic lichen communities, specifically Verrucaria baldensis, in the initiation and development of mesoscale solution basin formation on limestone in the Burren, County Clare. A biophysical model is proposed outlining the different microscale stages leading to solution basin initiation with a progression from initial lichen colonization and growth, associated perithecial biopitting followed by biopit coalescence to form biotroughs, their subsequent enlargement and eventual incipient solution basin formation. This model provides one explanation for solution basin development as this end state may also be achieved through simple solutional means without biological input. The complexity of interactions at the lichen–rock interface are identified with emphasis on the spatial and temporal variability of these underlining the point that, as with macrotopographies at the landscape scale, rock surface microtopographies also reflect historical weathering legacies.
This study was undertaken to gain a better understanding of karst hydrology. To do this, the present day hydrology and the paleohydrology were determined in three karst basins. The basins chosen were the Swago, Locust and Spring Creek basins in Pocahontas and Greenbrier Counties, West Virginia. A number of conventional field techniques were used successfully in this study, including the following: current meter and dye dilution gauging; dye and lycopodium stream tracing; geological and cave mapping; the setting up of stage recorders; geochemistry; and limestone erosion measurements. The climate of the region was investigated to obtain realistic precipitation, temperature and potential evaporation data over the study basins.
It was found that the mean precipitation over two of the basins was 30% higher than recorded data in the valleys. The karst development of the basins was found to take place in four major stages. These were: A) initial surficial flow, B) strike controlled drainage, C) major piracies from one sub-basin to another, and D) shortening of the flow routes. The major controls on the karst development were found to be: A) the Taggard shale, B) the strike direction, which controlled early basin development, and C) the hydraulic gradient from the sink to rising, which controlled later basin development.
To better assess the quantitative hydrology, and to assist in determining the type of unexplorable flow paths, a watershed model was developed. This modelled the streamflow from known climatic inputs using a number of measured or optimized parameters. The simulation model handled snowmelt, interception, infiltration, interflow, baseflow, overland flow, channel routing, and evaporation from the interception, soil water, ground water, snowpack and channel water. The modelled basin could be split up into 20 segments, each with different hydrological characteristics, but a maximum of 3 segments was used in this study.
A total of 29 parameters was used in the model although only 10 (other than those directly measurable) were found to be sensitive in the three basins. The simulated streamflow did not match the real flows very well due to errors in the data input and due to simplifications in the model. It was found, however, that as the proportion of the limestone in a segment increased the overland flow decreased, the interflow increased, the baseflow and interflow recessions were faster, the soil storages were smaller and the infiltration rate was higher, than in segments with a larger proportion of exposed clastics. The flow characteristics of the inaccessible conduits were inferred from the channel routing parameters and it was postulated that the majority of the underground flow in the karst basins was taking place under vadose conditions.
We review the contribution made to understanding landform evolution through the use of the micro-erosion meter (MEM) and the variant, the traversing micro-erosion meter (TMEM). The MEM has allowed the direct measurement of bedrock erosion in terrestrial and coastal settings as well as of building stone. As recorded in MEM measurements, world wide the average rate of surface lowering on shore platforms is 1.486 mm a− 1, and on terrestrial rock surfaces, measured lowering rates are on average 0.903 mm a− 1. Reported means obscure significant variation in rates from a range of environmental settings and lithologies. The MEM has in a number of examples allowed the identification of the contribution of individual processes in polygenetic settings, particularly in shore platform studies. The dynamic nature of rock weathering has been highlighted, where the TMEM has revealed rock surfaces swelling and contracting at time scales ranging from hours to years. The MEM will continue to provide useful data on erosion rates and processes but the most fruitful investigations will be those that combine the T/MEM with other techniques that transcend time and space scale issues in erosion and process measurement.
Phytokarst is a distinctive landform resulting from a curious type of biologic erosion. Filamentous algae bore their way into limestone to produce black-coated, jagged pinnacles marked by delicate, lacy dissection that lacks any gravitational orientation. Ordinary rainfall-produced karst and littoral karst are characterized by flat-bottomed pans and vertically oriented flutes, thus differing from phytokarst. Algae attack by dissolving calcite preferentially to dolomite.
The lichen vegetation of a limestone pavement in the Burren region of western Ireland is described. Species are distributed in relation to gradients of moisture, nutrient-availability and insolation; these in turn may be related to the range of geomorphological micro-features associated with karst. The majority of the 136 stands are dominated by endolithic and foliose cyanophilic lichens. Epilithic, non-cyanophilic crusts grow best on surfaces subjected to occasional bird-manuring. A successional sequence from bare rock through endolithic communities to ones dominated by epilithic, noncyanophilic species does not occur in the Burren.
Knowledge of the long-term rates of erosion of shore platforms are needed to assist modeling platform development, understand rates and modes of development and decipher issues of inheritance from former sea level. Few studies report rates from more than 2 years of monitoring. We report decadal scale erosion rates using both a micro-erosion meter and a traversing micro-erosion meter with measurements from 30 years and 10 years, respectively. Gross mean surface lowering rates measured over 10 years with a traversing micro-erosion meter were 0.901 (S.E.=0.116) mm/yr compared with 1.130 (S.E.=0.217) mm/yr over two years. Over thirty years (1973–2003) 12 micro-erosion meter sites provide a mean surface lowering rate of 1.09 (S.E.=0.126) mm/yr compared to 1.43 (S.E. 0.128) mm/yr calculated over twenty years (1973–1993) from 15 bolt sites and 1.53 (S.D.=1.45) mm/yr from 31 bolt sites. Rates calculated over longer time periods are reduced compared to short-term rates as a result of faster eroding bolt sites being removed from the data set. Comparison of means between short and long time periods for existing bolts show no significant difference. That is, short-term measurements over two years are representative of decadal scale erosion rates. In fact decadal scale rates may under represent rates of platform development because of the loss of faster eroding bolt sites. The loss of such bolts means that obtaining long-term erosion rates is problematic. Future modeling of shore platform development can use MEM rates with more certainty, but we recommend using higher rates from shorter term studies, unless longer records are complete.
Solution rates of four tablets made from limestone obtained in Slovenia, Guilin (China), Chichibu (Japan), and samples of limestone from each observation point were measured in seven limestone areas in Japan from 1993 to 1997. Solution rates in the air 1.5m above the ground show a high correlation between water surplus (WS) and water deficit (WD) by Thornthwaite's method. Solution rates of limestone tablets in soils show values 1.5 to 5 times higher than those in the air. The solution rates of limestone tablets in A1 and B2 horizons show high correlation coefficients with annual precipitation. High solution rates in soils may be related to high CO2 values under humid and warm periods.In 1993, when a cool and humid summer prevailed in almost all of Japan, the trend of solution rates increased with the WS-WD ratio showing the largest range during the five years. In 1994, which had an extremely hot and dry summer with a return period of about 100 years, the trend of the solution rates increased with the WS-WD ratio having the lowest range during five years. Solution rates of limestone tablets in the air at each point increased with the WS-WD ratio over the five year period.
This study presents characterizations of weathering forms of the same oolitic limestone from four quarries and eight monuments exposed on various environmental conditions focusing on the waterproofing effect of endolithic organic matter. Patinas were analyzed by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX), capillarity coefficient through weathered and unweathered sides, gypsum content and porous network morphology by epoxy resin molding. Study of weathering forms on old quarries indicates that lichens colonization (Verrucaria nigrescens and Caloplaca aurantia) can fill the superficial porous network with a dense network of lichenised fungal hyphae. Capillary coefficient measurement on natural and calcinated samples showed that endolithic organic matter can waterproof the stone and could act as a sulfate contamination barrier. Similar endolithic organic layer due to ancient lichens growth are found on some antique monuments of the Nîmes downtown and could explain their well-preserved state, unlike decayed 19th century churches that were never colonized by lichens.
Biokarst can be the result of processes related to both plants and animals, and can include both erosional and depositional forms. A tentative classification of biokarst forms is presented, and there is a section on process-form links. -K.Clayton
Laboratory simulations of salt weathering (using sodium sulphate) and freeze–thaw attack (using an Icelandic Cycle) on 19 different limestones indicate that the rocks do not respond in an identical way to the two processes. Resistance to salt is a poor predictor of resistance to frost. Moreover, Young's modulus of elasticity, which was determined by the Grindosonic method, appears not in itself to be a reliable indicator of resistance to frost attack. Copyright © 1999 John Wiley & Sons, Ltd.Des essais en laboratoire d'altération par le sel (avec du sulfate de sodium) et d'attaques par des alternances de gel-dégel (cycle islandais) sur 19 calcaires différents indiquent que les roches ne répondent pas d'une manière identique aux deux processus. La résistance au sel est un pauvre indicateur de la résistance au gel. En outre le module d'élasticité de Young qui a été déterminé avec un appareil Grindosonic, ne paraît pas être un indicateur fiable de la résistance au gel. Copyright © 1999 John Wiley & Sons, Ltd.
Measurements taken from 1979 up to the present by a micrometer in the Classical Karst of Trieste permit us to confirm that the average annual volume of lowering by the surface dissolution of limestones in our region is about 0.02 mm. However, each lithotype has its own typical surface degradation leve!, linked not only to clima tic con- ditions, but also to other geological factors.
A new census catalogue of Irish lichens, based on vice-county distribution, enumerates 957 taxa (including 6 subspecies, 14 varieties and 2 forms); a significant proportion of the data assembled is derived from earlier records, the present status of which has not been determined. Numerous taxa listed as occurring in the 1953 census catalogue have been omitted since they have proved to be incorrect, dubious, or difficult to assign current nomenclature in the absence of herbarium material. An appendix lists unconfirmed records, including 39 taxa which would be additional to the Irish lichen flora. Irish lichen records, going back to Caleb Threlkeld (1676-1728), occur sporadically throughout eighteenth century botanical literature, but the true foundations of Irish lichenology were laid in the nineteenth century by Thomas Taylor (c. 1787-1848), Theobald Jones (1790-1868), David Moore (1808-1879) and Isaac Carroll (1828-1880). In the first half of the twentieth century Matilda C. Knowles (1864-1933), Annie Lorrain Smith (1854-1937), Robert Lloyd Praeger (1865-1953), Robert A. Phillips (1866-1945), John Adams (1872-1948) and Lilian E. Porter (1885-1973) added considerably to our knowledge of the flora, their records being summarized by Walter Watson (1872-1960) in his Census Catalogue published in 1953. About this period, the Scandinavian lichenologists G. Degelius, E. Dahl and A. H. Magnusson collected in
Biodeterioration processes on three Spanish calcareous monuments (Scipio's Tower, Olèrdola Wall, and the Naveta d'Es Tudons) were investigated. Scipio's Tower and Olèrdola Wall, both located in Catalonia, were built with blocks of bioclastic pack‐stones (foraminifera, bivalves, gastropods, red algae, echinoderms) of the Langhian (Middle Miocene) Age. The Naveta d'Es Tudons, located on the island of Menorca, was constructed with blocks made up of bioclastic packstones, partially dolomitized and dedolomitized, and is of Miocene Age. The main organisms that inhabited these three monuments were lichens [mainly Dirina massiliensis Durieu et Mont, Verrucaria nigrescens Pers., Caloplaca aurantia (Pers.) Hellb., Caloplaca velana (Massal.) Du Rietz, Caloplaca erythrocarpa (Pers.) Zw., Petractis thelotremalla (Bagl.) Vezda, and Strigula calcarea Bricaud et Roux], which caused the main alteration of the rock. The distributions of these lichens were determined and their actions on the stone were studied by different techniques. From the samples studied, a general and complete alteration profile was proposed and described. In this profde from the external area of the stone to the unaltered substratum, five zones were distinguished: lichen thallus, microcorrosion surface, altered zone, transition zone, and finally the unaltered zone or substratum. A model of evolution of these zones was also developed. Some structures found in the different zones of these profiles were morphologically described and filaments and spheres were identified. In the same way, some diagenetic products found in these zones were described and related to the processes that originated them. An interpretation of these structures and products and their relation to organisms and microorganisms was attempted.
Soluble rocks undergo erosion by solution when rain falls on an unprotected rock surface. Lichens may act to protect the surface from such erosion, and the protected area may subsequently emerge from the surrounding lowering surface to form an area of higher relief. Specimens of Aspicilia calcarea and Diploschistes diacapsis act in this way on a gypsum surface, creating conical or rounded mounds up to 15 mm in height. In the case of Aspicilia, the lichen centre decays, re-exposing to surface solution the central area, which then corrodes to create a cratered gypsum cone. The gradient of the cone side-slopes is a function of the relative rates of lichen radial growth and rock surface lowering.
Karren landforms developing on limestone rocks are understood to be produced primarily by chemical dissolutional processes. Available data suggest that rainfall intensity, drop size, water temperature and viscosity play significant roles in the growth of the most simple of these features, which are termed rillenkarren. Nevertheless, chemical data and scanning electron microscopy provided by our study have shown that mechanical removal of small limestone particles is one of the principal processes involved in the growth of rillenkarren. This mode of detachment is caused by the impact of raindrops but their effect seems greatly increased when algal cells of Chroococcus minutus (Kütz.) Näg. have previously corroded the surface of the limestone, weakening its crystalline structure. These fragile micromorphologies of biokarstic origin are fundamental in the development of rillenkarren, complementing the wellknown physico-chemical controls that are involved.
A simulation was undertaken within a climatic chamber to investigate limestone dissolution under varied carbonic acid (H2CO3) strengths as a possible analogue for future increases in atmospheric CO2 arising from global warming. Twenty-eight samples cut from a block of Bath (Box Hill) limestone from Somerville College, Oxford, which had been removed during restoration after 150 years in an urban environment, were weighed and placed in closed bottles of thin plastic containing varying concentrations of H2CO3. Half of the stone samples were derived from exposed surfaces of the stone block (weathered) while the others were obtained from the centre of the block on unexposed surfaces (unweathered). The purpose of this was to compare dissolution of previously weathered versus unweathered surfaces in strong (pH 4.73) versus weak (pH 6.43) solutions of H2CO3. A temperature of c. 19 °C was maintained within the chamber representing a plausible future temperature in Oxford for the year 2200 given current warming scenarios. The simulation lasted 25 days with a few stone samples being removed midway. Stone samples show reduced weight in all cases but one. There was greater dissolution of stone samples in a strong H2CO3 solution as conveyed by higher concentrations of total hardness and Ca2+ in the water samples as well as enhanced microscopic dissolution features identified using SEM. The simulation confirms that enhanced atmospheric CO2 under global warming, given adequate moisture, will accelerate dissolution rates particularly of newly replaced limestone building stones. However, previously weathered surfaces, such as those on historical stone exposed for a century or more, appear to be less susceptible to the effects of such increased rainfall acidity. Conservation techniques which remove weathered surfaces, such as stone cleaning, may accelerate future decay of historical limestone structures by increasing their susceptibility to dissolution.
A vision technique system was implemented in order to highlight the deterioration developing on the surfaces of stone samples during an artificial ageing test with marine spray. The system, which employs a matrix CCD camera and a laser beam, provides various kinds of information about the decay suffered by the stone samples, by comparing two types of visual information at different times throughout the ageing test: the partial digital images of the sample surfaces and then the surface relief and laser light reflection obtained by casting a sheet of laser light on to the material. The accuracy of the laser camera scanner is evaluated in the first part of this paper. The methodology was successfully used to identify the degradation morphologies occurring on five types of limestone exposed to salt spray, and to quantify the deterioration using statistical parameters computed from digitized visual data.
On a prélevé des échantillons de calcaire carbonifère, de calcaire magnesien, du calcaire oolithique inférieur et du grand calcaire oolithique. On a determiné leurs poids spécifiques, leurs densités sèches et saturées et leurs porosités absolues et effectives. Les densités décroissent et les porosités augmentent selon le sens décroissant de l'âge du calcaire concerné. La perméabilité de ces échantillons était la plus grande quand la porosité augmentait. La résistance diminuait le plus quand la porosité était la plus grande. Cela veut dire que le calcaire carbonifére etait très résistant alors que le grand calcaire oolithique était relativement faible. Étant saturé, le calcaire le plus résistant montrait la plus petite réduction de résistance en pourcentage. Le calcaire plus résistant possèdait une dureté la plus grande; le calcaire le moins résistant montrait la dureté la moins grande. Le module de Young tendait à s'accroître avec la densité, avec la résistance et avec la dureté croissantes. Le calcaire carbonifère avait le module de Young le plus grand, pendant que celui du grand calcaire oolithique était le plus petit. On a aussi déterminé l'indice de Poisson et les propriétés élastiques qui y sont reliées.
This paper describes the effect of lichen colonization on the first century A.D. pavement of the forum at Baelo Claudia, a Roman city located in southern Spain. Lichen colonization is scarce, covering only 13% of the total surface. The rest of the flagstones are mostly uncovered but show strong physico-chemical weathering. The flagstones colonized by lichens do not show weathering. The distribution of the species is influenced by environmental factors, confirming the role of lichens as bioindicators of different habitats. The lichen/sandstone interface shows some weathering, but nevertheless, the protective role of lichens in an aggressive environment is noticeable.
Bioprotection is identified as an earth surface process. However, it has been little studied, little acknowledged and yet may have major implications for the operation and management of geomorphic systems. Key early observations are traced back to Darwin's ‘Voyage of the Beagle’, Geikie in the natural environment and Watson for the built environment. Recent field observations and experimental work examining bioprotection are reviewed, with a specific focus on lichens and the landscape, as are its complex interactions with other processes. A conceptual model of bioprotection is presented for the case of an epilithic lichen on a limestone surface.
British and Irish karst environments are of geomorphological and ecological conservation value. As illustrated by a simple conceptual model, future climate change is likely to influence three key aspects of karst geomorphology, i.e. hydrology, dissolution rates and the operation of other geomorphological processes such as mass movements. However, the response of an individual karst area to these changes will depend on the magnitude and nature of regional climate change, as well as the unique geomorphological characteristics of the area. In order to illustrate the range of potential responses, five contrasting karst areas are investigated in further detail (i.e. the Burren, Cuilcagh, the Mendip Hills, Assynt and the Yorkshire Dales). For each area, an assessment is made of the sensitive aspects of the geomorphology and detailed climate predictions given for the 2020s and 2050s (using the UKCIP 1998 scenarios downscaled to the bioclimatic classes identified by the MONARCH project). All areas show an increase in winter effective rainfall, and all but the Mendip Hills show at least a modest rise in mean annual effective rainfall. The Mendip Hills karst is predicted to experience a decline in mean annual effective rainfall (up to 54%) producing an allied reduction in dissolution rates and a possible increase in vulnerability of cave deposits. Turloughs in the Burren area are likely to experience more pronounced drying out in summer, but given the minor predicted alterations in effective rainfall in the Yorkshire Dales, fragile tufa deposits are unlikely to be seriously affected. The impacts of future climate change on British and Irish karst areas need to be considered alongside the already extensive human impacts in these areas, but are unlikely to cause major geomorphic change, although impacts on sensitive landforms and allied biota may have negative effects on conservation.
This study describes anatomy, ontogenesis and history of taxonomy of calcicolous endolitic species of the genus Verrucaria, which have been treated as Bagliettoa and Protobagliettoa (Verrucaria sect. Sphinctrina), and that are characterized by black, flat (lid-like) radiate crackling involucrellum, completely endolitic thallus and presence of macrosferoid cells formed by hy-phae in the lower part of the medullar layer. Most of the revised taxa were described by Servít (more than 100), and show alarge taxo-nomic heterogeneity. Consequently, adetailed study had to be done to unify the group again. The characteristic characters have been recognized as the size and shape of the involucrellum and the development of the cortex layer. Following diacritic characters were recognized just morphological variations that originate regularly during ontogenesis. After revision the num-ber of species reducedfrom more than twenty to four: V.baldensis, V.limborioides, V.marmorea and V.parmigerella. The genus Bagliettoa differs from the genus Verrucaria in different forming of involucrellum, other significant characters (ascus morphology and further structures of hymenium), usually used to define lichen genera are identical. Therefore, anew section Bagliettoa has been estab-lished within the genus Verrucaria, which is well defined by the way of opening and shape of involucrellum. The genus Protobagliettoa has been separated from the genus Bagliettoa artifi-cially for the absence of ascospores in 1955 by Servít. The separation of genera Bagliettoa and Protobagliettoa to the family Bagliettoaceae is formal too, because other families in Verrucariales have not been established afterwards on the base of different structure of involucrellum. There-fore, the revision disapproves such unjustified separation and recommends to keep all the studied species of genus Verrucaria (Verrucariaceae). From the practical point of view, the revi-sion can help to determine all of the mentioned species outside. Eleven species (Limboria sphinctrina Duf., Protobagliettoa lactea (Arnold) Servít, V.bosniaca Servít, V.dalmatica Servít, V.grummanni Servít, V.gyelnikii Servít, V.parmigera J. Steiner, V.serbica Servít, V.steineri Kuan, V.subconcentrica (J. Steiner) Servít and V.suzaeana Servít), and also other 75 varieties and forms, were synonymized with the species V.baldensis A. Massal. Two species (V. ceracea J. Steiner and V.quarnerica Zahlbr.) and 4 varieties or forms were restricted to synonyms of the V.limborioides (A. Massal.) Clauzade & Roux. The species V.cazzae Zahlbr., one of its varieties, and one of its forms were restricted to synonyms of the species V.marmorea (Scop.) Arnold. Two species (P. kutakiana Servít and V.sphinctrinella Zschacke) and 20 variet-ies or forms were restricted to the synonyms of the species V.parmigerella Zahlbr. A new neotype and an isoneotype of the species V.marmorea there have been established, 19 taxa have been lectotypified (Protobagliettoa lactea (Arnold) Servít var. ochracea Servít, Verrucaria bagliettoaeformis (Hazsl.) Servít var. caesia (Arnold) Servít, Verrucaria baldensis A. Massal., Verrucaria baldensis A.Massal. var. canici Servít f.bakonyensis Servít, Verrucaria baldensis A.Massal. var. spilomatica A.Massal., Verrucaria calciseda DC. f.alocyza Arnold, Verrucaria calciseda DC. var. lactea Arnold, Verrucaria cazzae Zahlbr., Verrucaria inaequata (Servít) Servít f.helvetica Servít, Verrucaria inaequata (Servít) Servít var. transsilvanica Servít, Verrucaria parmigera J.Steiner, Verrucaria parmigera J.Steiner var. calcivoroides J.Steiner, Verrucaria parmigera J.Steiner var. calcivoroides J.Steiner f.arnoldiana Servít, Verrucaria pinguis J.Steiner f.alocizoides J.Steiner, Verrucaria sphinctrina Ach. var. tiroliensis Servít, Verrucaria sphinctrinella Zschacke var. elevata Servít f.spermogonifera (Arnold) Servít, Verrucaria steineri Kuan f.scrobicularis Servít, Verrucaria subconcentrica (J. Steiner) Servít var. nigroaureolata (Servít) Servít f.limitata Servít and Verrucaria subconcentrica (J. Steiner) Servít var. nigroaureolata (Servít) Servít f.rauca Servít).
Supervisor: Dr Heather Viles. Thesis (D. Phil.)--University of Oxford, 2002. Includes bibliographical references.
The British National Materials Exposure Programme (N.M.E.P.) ran from 1987 to 1995 and involved exposure of a range of materials samples (including tablets of Monks Park and Portland Limestones) at over 20 sites around Britain for 1-, 2-, 4- and 8-year periods, under known climate and pollution conditions. Deterioration of the limestone tablets has previously been recorded in terms of weight change, contents of soluble salts, and visual soiling. In the present study samples from exposed and sheltered positions at Wells, Bolsover and Lough Navar have been studied using a spectrophotometer, optical microscopy and scanning electron microscopy (SEM) to investigate the distribution and nature of particulate material and its role in soiling and decay. Clearly, recognisable pollutant particles such as perforated cenospheres, are only rarely present. Organisms and organic remains, including filamentous microorganisms and pollen grains, are widely distributed. At each site, soiling has different characteristics in terms of composition and change over time related in part to differences in climate and pollution histories. There is no general link between degree of soiling and amount of decay (in terms of surface recession) as the nature of decay is a key influence on the relation between soiling and decay.
Smith Microscale biopitting by the endolithic lichen Verrucaria baldensis and its proposed role in mesoscale solution basin development on limestone Earth Surf
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New lichen records from the Burren and the Aran Islands (H9)
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