Although the term ‘wetlands in drylands’ sounds like a contradiction, many drylands host a range of ephemeral wetlands. Pans, for example, are widespread features in many drylands, representing topographic depressions of varying size and shape that host ephemeral, sometimes saline, bodies of shallow water following infrequent precipitation or river flooding events. Pans are included in many wetland classifications, and are the most ubiquitous wetland types in many drylands. Pans are ‘hotspots’ of biological activity and their hydrology, geochemistry and distinctive soil microbial communities mean that they may sequester and store substantial amounts of organic and inorganic carbon (C). The C cycle on pans is unusual in that in the absence of vascular plant cover, C is sequestered by autotrophic organisms, such as cyanobacteria, in biological soil crusts (BSCs). BSC organisms can also facilitate biomineralization and the formation of carbonates, which effectively lock up C in stable, inorganic, long-term stores.
Our understanding of dryland cyanobacterial photosynthesis and C sequestration is hampered by a fundamental lack of information on: 1) the nature and spatial distribution of soil microbial communities; 2) the relative importance and synergistic effects of the diverse controls on photosynthetic activity and respiration; and 3) the fate of C sequestered by cyanobacteria and its longevity in sediment and soils. This prevents us from knowing where, why and how much C is sequestered and how this might be affected by future climatic changes. Without an improved conceptual understanding and quantification of these factors, changes to the wider C cycle within and beyond drylands will remain uncertain and difficult to predict. Here we present data on C stores, CO2 fluxes and microbial composition of sediment and soils on pans from the Kalahari in Botswana and the Monegros region of northeast Spain. Our data go some way towards demonstrating the importance of dryland pans for local and regional C cycles.
Oral presentation given by Andrew Thomas @ADThomas_1970
Meeting book available here.