Experimental investigations into the influence of biofilms and environmental factors on short‐term microtopographic fluctuations of supratidal sandstone

Abstract

In this study laboratory experiments were used to explore the role of biofilms, formed by lithobiontic microorganism communities, in causing hourly surface changes of supratidal sandstone and the potential linkage to long‐term rock decay. To isolate the influence of individual environmental factors (temperature and humidity) on rock surface changes (expansion and contraction), a colonized (biofilm‐covered) and a non‐colonized sandstone block (biofilm‐free) underwent the same univariate microclimatic simulations closely controlled by an environmental chamber. Simulations were run under three different light conditions, with a natural light lamp on, on and off at 20‐min intervals and off, to investigate the impact of light on rock surface dynamics. Measured with a traversing micro‐erosion meter (TMEM), two‐hourly microtopographic fluctuations of these two sandstone blocks were compared in the same environment. Induced by microclimatic variations, surface movements of significantly higher magnitude (12–120% under varying tempeature and 121–154% under varying humidity) and different change patterns were observed on the colonized block, indicating the primary role of biofilm in driving microtopographic fluctuations of supratidal sandstone. However, thermally driven changes of similar magnitude and pattern were observed on both surfaces, suggesting other mechanisms also operating on the non‐colonized rock surface in this process. Due to the sensitivity of biofilm microorganism communities to light, the magnitude and pattern of surface changes was impacted by light condition. Because biofilms increased the magnitude and number of cycles of expansion and contraction of the experimental rock surface, we propose that lithobiontic biofilms facilitate the detachment of grains and granular disintegration on the rock surface, consequently contributing to rock decay and accelerating the rate of breakdown of supratidal rock. This short‐term episode therefore needs to be superimposed on longer term studies to fully understand the role of biofilms in rock surface change. © 2019 John Wiley & Sons, Ltd.

Biogeomorphology, quo vadis? On processes, time, and space in biogeomorphology

“…Neumeier and Amos, 2006; Turner et al ., 2006; Coleman and Kirwan, 2019; Schepers et al ., 2020), laboratory studies (e.g. Möller et al ., 2014; Spencer et al ., 2016; Lokhorst et al ., 2019; Yuan et al ., 2019), and numerical modelling (e.g. Fagherazzi et al ., 2012; D'Alpaos and Marani, 2016; Nardin et al ., 2018, 2020; Lera et al ., 2019).…”

“…Yuan et al . (2019) use an environmental chamber to simulate variable isolated environmental factors acting on rock surfaces of a supratidal sandstone colonized by biofilm. This not only allows investigation of processes separately, but also over a much shorter time period.…”

“…Microbial communities are often overlooked as biotic engineers. A study of Yuan et al (2019) finds that lithobiontic biofilms contribute to shoreline rock decay through intensified magnitude and an increased number of cycles of expansion and contraction.…”

“…These results could help to recreate diverse vegetation communities in flume experiments, mimicking real-world applications and hence facilitating upscaling of results from flume experiments. Yuan et al (2019) use an environmental chamber to simulate variable isolated environmental factors acting on rock surfaces of a supratidal sandstone colonized by biofilm. This not only allows investigation of processes separately, but also over a much shorter time period.…”