Water characteristics and retention in Angkor sandstone monuments and their linkage with microorganisms responsible for ammonia oxidation and nitrate accumulation

Water availability in built environment, including heritage, plays a fundamental role in microbial colonization and subsequent biodeterioration. However, it is uncertain about the relationship between specific water characteristics and microbial development. Here, we applied water intrusion gravimetry (WIG) to quantify water distribution and then linked it to microbial growth by combining molecular biology techniques and petrophysical and mineralogical analyses. Porosity as well as capillary, gravitational, and saturation waters were distinctly increased in the monument stones compared to the adjacent quarry fresh sandstone. Archaea and bacteria, responsible for ammonia-oxidizing archaea (AOA), nitrite-oxidizing bacteria (NOB) and Comammox species were enriched with increasing capillary water mainly, and intriguingly, the copies of bacterial 16S rRNA and Comammox amoA genes were positively correlated with capillary water significantly (r² = 0.73, p < 0.001) and inversely correlated with gravitational water (r² = 0.60, p < 0.01). An important finding for the enlargement of the pores in the monuments was the dissolution of calcite and oxides from the sandstone by HNO₃ erosion simulation. Collectively, these findings advance our understanding of water status in the pores of monuments and provide new insights into mechanisms of biofilm formation and preventive measures against microbial issues and biodeterioration.