Search

Microorganisms play a role in the construction or modulation of various types of landforms. They are especially notable for forming microbially induced sedimentary structures (MISS). Such microbial structures have been considered to be among the most likely biosignatures that might be encountered on the martian surface. Twenty-nine algorithms have been tested with images taken during a laboratory experiment for testing their performance in discriminating mat cracks (MISS) from abiotic mud cracks. Among the algorithms, neural network types produced excellent predictions with similar precision of 0.99. Following that step, a convolutional neural network (CNN) approach has been tested to see whether it can conclusively detect MISS in images of rocks and sediment surfaces taken at different natural sites where present and ancient (fossil) microbial mat cracks and abiotic desiccation cracks were observed. The CNN approach showed excellent prediction of biotic and abiotic structures from the images (global precision, sensitivity, and specificity, respectively, 0.99, 0.99, and 0.97). The key areas of interest of the machine matched well with human expertise for distinguishing biotic and abiotic forms (in their geomorphological meaning). The images indicated clear differences between the abiotic and biotic situations expressed at three embedded scales: texture (size, shape, and arrangement of the grains constituting the surface of one form), form (outer shape of one form), and pattern of form arrangement (arrangement of the forms over a few square meters). The most discriminative components for biogenicity were the border of the mat cracks with their tortuous enlarged and blistered morphology more or less curved upward, sometimes with thin laminations. To apply this innovative biogeomorphological approach to the images obtained by rovers on Mars, the main physical and biological sources of variation in abiotic and biotic outcomes must now be further considered.

Additional file 1: Figure S1. Scanning electron microscopy images of a control sample, E5 sample and E25 sample after 28 day curing period at T = 20 °C, % RH = 75. Table S1. Sample variation, pre- and post-treatment with E5. Table S2. Sample variation, pre- and post-treatment with E25. Table S3. Temperature dependence, pre- and post-treatment with E5. Table S4. Temperature dependence, pre- and post-treatment with E25.

Water plays a vital role in the deterioration and conservation of built and rock-hewn heritage and it is generally agreed that climate change is significantly changing the environmental controls on stone decay. We here introduce the framework of heritage hydrology as a holistic way of conceptualising the flows and stores, processes and impacts of water interacting with building materials. We distinguish the basic types of stone-built buildings, ruins and free-standing walls, and rock-hewn sites. Analogous to catchment hydrology, heritage hydrology can be subdivided into water fluxes and water reservoirs, further subdivided into inputs (e.g. wind-driven rain, capillary rise), throughputs (e.g. runoff down façade), storages (moisture content) and outputs (evaporation and runoff). Spatial patterns of moisture are different between buildings and rock-hewn sites, both presenting hydrological complexities. The interaction between mean and short-term precipitation, wind, radiation and resulting evaporation may lead to very different impacts at different heritage sites. We here differentiate between the detail scale, the façade scale and the building or site scale. Patterns at different sites can be very variable on different scales due to the multitude of influencing parameters and it is not clear which scale of moisture variations is actually relevant for decay processes. Temporal patterns are equally scale-dependent and include short-term fluctuations in temperature and rainfall, high-magnitude episodic events such as floods and storms, and longer-term changes as a result of seasonality, interannual variability and secular trends or climate change. Based on the outlined framework we advocate a research agenda for heritage hydrology in the future. This should focus on (1) finding the best combinations of methods to measure and model spatio-temporal patterns in moisture; (2) researching the major factors controlling spatio-temporal patterns in moisture; (3) figuring out which spatio-temporal patterns are most important for driving deterioration and how their respective scales interact.

Additional file 1. Additional Figures S1â S5 and Tables S1, S2.

10 págnas.- 6 figuras.- 1 tabla.- referencias, 2020 marks 25 years since Olivier Guillitte defined the term ‘bioreceptivity’, to describe the ability of a building material to be colonised by living organisms. Although Guillitte noted in his 1995 paper that several issues required further investigation, to the best of our knowledge the bioreceptivity concept has not been restated, reviewed, reanalysed or updated since then. The present paper provides an opinionated exposition of the status and utility of the bioreceptivity concept for built heritage science and conservation in the light of current knowledge, aimed to stimulate further discussion. A bibliometric analysis highlights the key dimensions of the past 25 years of published research, showing that the term bioreceptivity has been widely used in the field of built cultural heritage. In our reanalysis of the concept, special attention is devoted to the six types of bioreceptivity (primary, secondary, tertiary, intrinsic, extrinsic and semi-extrinsic) articulated by Guillitte in 1995. We propose that field-based studies of bioreceptivity are urgently needed, and that the intrinsic, extrinsic and semi-extrinsic types of bioreceptivity should be dropped, and a new category (quaternary bioreceptivity) added. Additionally, we propose that bioreceptivity in submerged and subsoil environments should also be considered. Bioreceptivity remains an important concept for managing both new build and built heritage, as it provides the key to understanding the drivers and patterns of biological colonisation of building materials., P. Sanmartín and B. Prieto thank the financial support of Xunta de Galicia grant ED431C 2018/32. A.Z. Miller acknowledges the support from the CEECIND/01147/2017 contract funded by Fundação para a Ciência e a Tecnologia (Portugal).