Recent observations have shown that many sandstone buildings, including important components of the UK’s cultural heritage, are becoming covered with green algal growths. This is likely to result from recent changes in air quality and the impacts of a changing climate. The precise influences of these growths on the stone surface and sub-surface are under considerable debate. The underlying question is whether they are benign and indeed bioprotective, or conversely if they are detrimental and biodeteriorative. To approach this question, there is a need for interdisciplinary studies linking geomorphological expertise with that of molecular microbiology and climatology.
The ‘Green Walls’ project contributes to this question by drawing together state of the art methods from each of these disciplines, as part of a larger project on sandstone heritage and climate change. The overall aim is to form a multi-faceted analysis of the current and future nature of algal greening on sandstone heritage in north-west Britain.
In order to better understand the interplay between climate change and the growth and impacts of green algae (chlorophyta), three phases of study have been adopted within an integrated overall methodology. Linked field and laboratory experiments, microbial species identification as well as impact and bioreceptivity analyses of sandstone contribute towards achievement of the project aim.
Northern Ireland has an abundance of sandstone heritage and given the likelihood of warmer, wetter winters; algal growth on vulnerable monuments is likely to become a primary conservation concern in the next 50 years. It thus makes an ideal major field location for the project. As a point of comparison, a satellite study is being conducted at Sheffield Cathedral. This will form an interesting comparison given the difference in climatic conditions and pollution history. Key foci for study are the impacts of stone aspect and angle of inclination on degree of algal colonisation.
Phase One of the study involves sampling from purpose-built test walls in Derrygonnelly, Northern Ireland as well as sandstone buildings in central Belfast and Sheffield. Novel, non-destructive biological sampling is conducted twice yearly, alongside measurements of moisture movements within stone facades. The rate, extent and composition of biological coverage is and will be closely monitored over the 3-year assessment period.
Phase Two encompasses laboratory analysis of these samples; standard gene profiling and sequencing techniques are used to establish community composition and abundance.
In order to contextualise this information, Phase Three involves laboratory simulations of algal growth on sandstones under likely, future climatic conditions. Composition and growth rates of algal biofilms and their impacts on sandstone will be compared to results from field studies. In effect, this allows for a comparative simulation-based study between present and future climatic conditions.
Investigation of the nature and impacts of algal soiling, as provided by this project, will supply invaluable information for those managing our sandstone cultural heritage. This will enable more informed decisions to be made over appropriate management and conservation strategies for the future.