Impact of Young Biocrust on Dryland Surface Albedo

More than 40% of the Earth’s surface is covered by drylands. Due to limited availability of water, less surface area is covered by vascular plants. Instead, this space is occupied by microbial communities that exist in close contact with mineral soil, creating a living aggregate on the upper soil layer and are known collectively as biological soil crusts or “biocrusts”. Biocrusts play a vital role in ecosystem functioning in drylands specifically through their influence on hydrological processes (e.g., water retention, infiltration). However, the impact of biocrusts on evaporation is not well understood. Biocrusts have been reported to either increase or decrease evaporation. One mechanism by which biocrusts can affect evaporation is through changes in surface albedo. Mature biocrusts are known to decrease the surface albedo via microbial sunscreen pigments, leading to higher surface temperatures and evaporation rates. To further explore this under-researched topic, we measured albedo at two lysimeter facilities: Landscape Evolution Observatory at Biosphere 2 in Oracle, AZ, operated by the University of Arizona, and SEPHAS weighing lysimeters in Boulder City, NV, operated by the Desert Research Institute. At both locations, the soil surface is partially covered by young (order of 10 years) biocrust. We measured the albedo of the lysimeter soil surfaces at locations with and without biocrust. Preliminary analysis of data from both facilities indicates higher surface albedo in the presence of young biocrust compared to soil surfaces without biocrusts, which contrasts with the expected lower albedo found for mature biocrusts compared to soil surfaces without biocrust.