Evaporative losses from soils covered by physical and different types of biological soil crusts

Evaporation of soil moisture is one of the most important processes affecting water availability in semiarid ecosystems. Biological soil crusts, which are widely distributed ground cover in these ecosystems, play a recognized role on water processes. Where they roughen surfaces, water residence time and thus infiltration can be greatly enhanced, whereas their ability to clog soil pores or cap the soil surface when wetted can greatly decrease infiltration rate, thus affecting evaporative losses. In this work, we compared evaporation in soils covered by physical crusts, biological crusts in different developmental stages and in the soils underlying the different biological crust types. Our results show that during the time of the highest evaporation (Day 1), there was no difference among any of the crust types or the soils underlying them. On Day 2, when soil moisture was moderately low (11%), evaporation was slightly higher in well-developed biological soil crusts than in physical or poorly developed biological soil crusts. However, crust removal did not cause significant changes in evaporation compared with the respective soil crust type. These results suggest that the small differences we observed in evaporation among crust types could be caused by differences in the properties of the soil underneath the biological crusts. At low soil moisture (<6%), there was no difference in evaporation among crust types or the underlying soils. Water loss for the complete evaporative cycle (from saturation to dry soil) was similar in both crusted and scraped soils. Therefore, we conclude that for the specific crust and soil types tested, the presence or the type of biological soil crust did not greatly modify evaporation with respect to physical crusts or scraped soils.

This work has been supported by several research projects: PROBASE (CGL2006–11619/HID) and BACARCOS (CGL2011-29429) funded by the Ministerio de España de Ciencia e Innovación, including funds of the European Union European Regional Development Fund and COSTRAS (RNM–3614) funded by the Consejería de Innovación, Ciencia y Empresa de la Junta de Andalucía, also including funds of the European Union European Regional Development Fund. The first author is funded by a Formación de Personal Investigador fellowship from the Spanish Government (BES–2007–15218). We thank Roberto Lázaro, Isabel Miralles and Mónica Ladrón de Guevara for their help in the field work, Emilio Rodríguez for his assistance with the laser scanner and the use of the software SAGA and Hilda Smith for her help in the laboratory analyses. The authors are grateful to anonymous reviewers for constructive comments of this manuscript. The Cautivo site's owner, the Viciana family, is thanked for ceding their land as a ‘scientific experimental site’.

Peer reviewed