Ruidera Pools Natural Park, Spain, constitutes one of the most representative systems of carbonate precipitation in Europe. The prokaryotic community of a dry modern stromatolite recovered from the ...park has been analyzed by molecular techniques that included denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library analysis, together with microscopic observations from the sample and cultures. Ribosomal RNA was directly extracted to study the putatively active part of the microbial community present in the sample. A total of 295 16S rRNA gene sequences were analyzed. Libraries were dominated by sequences related to
Cyanobacteria, most frequently to the genus
Leptolyngbya. A diverse and abundant assemblage of non-cyanobacterial sequences was also found, including members of
Firmicutes,
Bacteroidetes,
Proteobacteria,
Actinobacteria,
Acidobacteria,
Planctomycetes and
Chloroflexi groups. No amplification was obtained when using archaeal primers. The results showed that at the time of sampling, when the pool was dry, the bacterial community of the stromatolites was dominated by groups of highly related
Cyanobacteria, including new groups that had not been previously reported, although a high diversity outside this phylogenetic group was also found. The results indicated that part of the
Cyanobacteria assemblage was metabolically active and could thus play a role in the mineralization processes inside the stromatolites.
In this study, the deterioration effects of lichens and other lithobionts in a temperate mesothermal climate were explored. We examined samples of dolostone and limestone rocks with visible signs of ...biodeterioration taken from the exterior wall surfaces of four Romanesque churches in Segovia (Spain):
San Lorenzo,
San Martín,
San Millán and
La Vera Cruz. Biofilms developing on the lithic substrate were analyzed by scanning electron microscopy. The most common lichen species found in the samples were recorded. Fungal cultures were then obtained from these carbonate rocks and characterized by sequencing Internal Transcribed Spacers (ITS). Through scanning electron microscopy in back-scattered electron mode, fungi (lichenized and non-lichenized) were observed as the most frequent microorganisms occurring at sites showing signs of biodeterioration. The colonization process was especially conditioned by the porosity characteristics of the stone used in these buildings. While in dolostones, microorganisms mainly occupied spaces comprising the rock's intercrystalline porosity, in bioclastic dolomitized limestones, fungal colonization seemed to be more associated with moldic porosity. Microbial biofilms make close contact with the substrate, and thus probably cause significant deterioration of the underlying materials. We describe the different processes of stone alteration induced by fungal colonization and discuss the implications of these processes for the design of treatments to prevent biodeterioration.
The kinetics of capillary imbibition into porous rocks is studied experimentally and theoretically. The Washburn law is modified by introducing various corrections relating to the microstructure of ...the rocks, such as tortuosity, pore shape (obtained experimentally), and applying the effective medium approximation (EMA) in order to calculate the effective radius that defines the hydraulic conductance and the topology of the capillary imbibition. The application of the EMA shows that capillary imbibition is mainly produced in 1-D, and the pore structure is constituted by different pore throats in series, linked by chamber pores. The capillary process has been discussed as a function of their petrography and pore structure. Our study of the Washburn equation and the addition of correction factors for the pore structure allows a very accurate prediction of the weight rate.
The rates of exclusive breastfeeding at 6 months in Spain are far from recommended by the World Health Organization, which is 50% by 2025. Evidence of the effectiveness of group interventions in late ...postpartum is limited. The objective of this study was to evaluate the effectiveness of the PROLACT group educational intervention for increasing the proportion of mother-child dyads with exclusive breastfeeding at 6 months compared to the usual practice in primary care.
Multicentre cluster randomized clinical trial. A total of 434 mother-child dyads who breastfed exclusively in the first 4 weeks of the children's life and agreed to participate were included. The main outcome was exclusive breastfeeding at 6 months. Secondary variables were type of breastfeeding, reasons for abandonment, degree of adherence and satisfaction with the intervention. To study the effectiveness, the difference in the proportions of dyads with exclusive breastfeeding at 6 months was calculated, and the relative risk (RR) and number needed to treat (NNT) were calculated with their 95% CIs. To study the factors associated with the maintenance of exclusive breastfeeding at 6 months, a multilevel logistic regression model was fitted. All analyses were performed to intention to treat.
The percentage of dyads with exclusive breastfeeding at 6 months was 22.4% in the intervention group and 8.8% in the control group. PROLACT intervention obtained an RR =2.53 (95% CI: 1.54-4.15) and an NNT = 7 (95%CI: 5-14). The factors associated with exclusive breastfeeding at 6 months were the PROLACT intervention, OR = 3.51 (95%CI: 1.55-7.93); age > 39 years, OR = 2.79 (95%CI: 1.02-7.6); previous breastfeeding experience, OR = 2.61 (95%CI: 1.29-5.29); income between 500 and 833.33 €, OR = 3.52 (95%CI 1.47-8.47).); planning to start work before the infant was 6 months old, OR = 0.35 (0.19-0.63) .
The PROLACT intervention in primary care is more effective than the usual practice for maintaining exclusive breastfeeding at 6 months, and can therefore be considered evidence-based practice for implementation in standard practice.
The trial was registered with ClinicalTrials.gov under code number NCT01869920 (03/06/2013).
► 102 Samples of carbonate rocks were tested during 100 cycles of freeze–thaw. ► Decay evolution was characterized at micro/meso-scale and petrophysically. ► Ultrasonic attenuation is the most useful ...parameter for studying damage evolution. ► Strength, porosity and weight decrease are not useful for damage quantification. ► Standard procedures are revealed as not effective for rock durability diagnostics.
This paper studies the resistance of rocks to freeze–thaw and their petrophysical evolution during weathering. Moreover, the accuracy of existing standards regarding frost durability is discussed. A long-term test was established with these purposes, in which 102 samples of six different dimension stone types were tested (carbonates).
Samples were divided into five groups and each group was tested after 0, 12, 24, 48 and 96 freeze–thaw cycles. At the end of the cycles several properties were measured: volume loss, open porosity variation, visual damage, mechanical properties evolution (measuring strength and elastic modulus) and ultrasonic propagation (quantifying both P-wave velocity and spatial attenuation). The micro-textural evolution was also studied using SEM in polished samples.
Results display that the rocks with the highest open porosity values (>10%) are the least durable. These rocks show a non-linear decay pattern, with long periods of apparent stability followed by rapid and catastrophic decay. Microscopic observation reveals that during the stable period, isolated microcracks appear from where new ones nucleate and grow as the test progresses. When a critical threshold is exceeded, microcracks turn into cracks and grow rapidly, causing rock breakdown after a low number of cycles. Most of the measured petrophysical parameters do not predict the ultimate breakdown of rocks. However, spatial attenuation of ultrasonic waves reveals as the most sensitive parameter, detecting the critical decay threshold of rocks and their imminent breakdown. Results suggest an important review of standardized durability tests since they do not reflect the reality of frost weathering of rocks: to increase the number of freeze–thaw cycles and to monitoring the weathering process of samples by means ultrasonic measurements.
► This research is approached from Sedimentary Petrology and Petrophysics fields. ► This work analyse texture and structure of a wide range of travertines and tufas. ► A rock classification is ...elaborated according to textural/structural aspects. ► An exhaustive petrophysical characterisation of all rock varieties is presented. ► Petrologic differences are related to different mechanical and water transport responses.
This paper establishes relationships between the structures of travertine and calcium carbonate tufa used as building stones and their physical properties. The most characteristic features of these kinds of rocks are the macropores in both stone types and the bedding planes and laminations in travertines. Large vuggy macropores have little influence on capillary water absorption, strength, elastic modulus or ultrasonic wave propagation, whereas microporosity is a much more determining factor. With travertines, the bedding planes and laminations give petrophysical anisotropy to rocks, where the highest capillary transport is reached parallel to the structure. However, rock strength and elasticity depend on both structure orientation and the predominant rock facies. The strongest and stiffest behaviour is found perpendicular to structure in low-porous banded samples, but in a parallel direction when the rock is highly porous.
Upper Pliocene dolomites (‘white earth’) from La Roda, Spain, offer a good opportunity to evaluate the process of dolomite formation in lakes. The relatively young nature of the deposits could allow ...a link between dolomites precipitated in modern lake systems and those present in older lacustrine formations. The La Roda Mg‐carbonates (dolomite unit) occur as a 3·5‐ to 4‐m‐thick package of poorly indurated, white, massive dolomite beds with interbedded thin deposits of porous carbonate displaying root and desiccation traces as well as local lenticular gypsum moulds. The massive dolomite beds consist mainly of loosely packed 1‐ to 2‐μm‐sized aggregates of dolomite crystals exhibiting poorly developed faces, which usually results in a subrounded morphology of the crystals. Minute rhombs of dolomite are sparse within the aggregates. Both knobbly textures and clumps of spherical bodies covering the crystal surfaces indicate that bacteria were involved in the formation of the dolomites. In addition, aggregates of euhedral dolomite crystals are usually present in some more clayey (sepiolite) interbeds. The thin porous carbonate (mostly dolomite) beds exhibit both euhedral and subrounded, bacterially induced dolomite crystals. The carbonate is mainly Ca‐dolomite (51–54 mol% CaCO3), showing a low degree of ordering (degree of ordering ranges from 0·27 to 0·48). Calcite is present as a subordinate mineral in some samples. Sr, Mn and Fe contents show very low correlation coefficients with Mg/Ca ratios, whereas SiO2 and K contents are highly correlated. δ18O‐ and δ13C‐values in dolomites range from −3·07‰ to 5·40‰ PDB (mean=0·06, σ=1·75) and from −6·34‰ to −0·39‰ PDB (mean=−3·55, σ=1·33) respectively. Samples containing significant amounts of both dolomite and calcite do not in general show significant enrichment or depletion in 18O and 13C between the two minerals. The correlation coefficient between δ18O and δ13C for dolomite is extremely low and negative (r=−0·05), whereas it is higher and positive (r=0·47) for calcite. The lacustrine dolomite deposit from La Roda is interpreted mainly as a result of primary precipitation of dolomite in a shallow, hydrologically closed perennial lake. The lake was supplied by highly saturated HCO3−/CO32− groundwater that leached dolomitic Mesozoic formations. Precipitation of dolomite from alkaline lake waters took place under a semi‐arid to arid climate. However, according to our isotopic data, strong evaporative conditions were not required for the formation of the La Roda dolomite. A significant contribution by bacteria to the formation of the dolomites is assumed in view of both petrographic and geochemical evidence.
This paper provides an ancient analogue for biologically mediated celestite and barite formation in dolomite precipitating microbial mats developed in lacustrine environments during the Miocene. ...Barite and celestite occurrences were studied in three temporally and spatially separated sedimentary successions: S1 and S2 in the Madrid Basin and S3 in the Duero Basin. In S1, macrocrystalline selenite gypsum occurs as laterally continuous beds; in the two other successions (S2 and S3), calcite pseudomorphs of lenticular gypsum aggregates are hosted in dolomite beds as evidence for the former presence of this evaporite. In S1, only celestite is associated with dolomite. Celestite crystals occur as both intergrown clusters, concentrated in pockets likely created by the dissolution of intrasedimentary anhydrite precursors, and as single precipitates associated with dolomite masses that replace selenite gypsum. Celestite crystals are nucleated commonly on organic substances that are pervasively associated with them. In S2 and S3, scarce single celestite crystals are restricted to calcite pseudomorphs after gypsum, whereas barite is the sulphate precipitated in the pseudomorphs' surroundings. Barite is commonly present as patchy poikilotopic crystals which include microbial structures and is embedded in organic matter. Additionally, barite is found as a secondary precipitate within Ba-bearing feldspars. Feldspar weathering is, thus, envisaged as a major source of barium at these sites.
Petrographical, isotopic and compositional observations point out that the barite and celestite formation was not caused by abiological processes only. Rather, the patchy distribution of the sulphates, close links to organic matter with biogenic isotope signatures, and inclusion of microbial structures, such as biologically mediated dolomite, provides evidence for the involvement of microbes in the formation of the sulphates. The coprecipitation of barite and celestite with dolomite entails complex interactions between different microorganisms and reinforces the biological formation of dolomite in saline lakes.
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