Non-rainfall Water Inputs Research Articles

Non-rainfall water inputs are controlled by aspect in a semiarid ecosystem

Differences in vegetation pattern between slope aspects in semiarid environments are well known, with shaded aspects presenting a higher biomass. The micrometeorological and soil conditions involved in non-rainfall water inputs (NRWI), comprising dew and water vapour adsorption (WVA) were compared between two contrasted slopes and different environmental conditions (wet and dry periods). Changes in natural soil surfaces were measured using automated microlysimeters, and the partial contributions of dew and WVA to the total NRWI were clarified. Dew amounts were higher on the northeast facing slope and were directly related to dew durations. Differences in dew deposition between slopes were mainly driven by insolation patterns, which controlled the surface temperatures, the soil water content and, in turn, dew duration. Apart from spatial variation in microclimate, WVA deposition was higher in the southwest facing slope due to its higher clay content and electric conductivity and because of its lower soil water content. Water vapour adsorption was directly governed by the relative humidity amplitude in summer (with dry soil) but not in winter. A significant amount of water evaporation was satisfied by NRWI, reaching 100% in dry periods and being WVA the main input.

Comment on “Microlysimeter station 1 for long term non-rainfall water input and evaporation studies” by Uclés et al.

Comment on “Microlysimeter station 1 for long term non-rainfall water input and evaporation studies” by Uclés et al.

Simulated climate change reduced the capacity of lichen-dominated biocrusts to act as carbon sinks in two semi-arid Mediterranean ecosystems

The importance of biological soil crusts (biocrusts) for the biogeochemistry of drylands is widely recognized. However, there are significant gaps in our knowledge about how climate change will affect these organisms and the processes depending on them. We conducted a manipulative full factorial experiment in two representative dryland ecosystems from central (Aranjuez) and southeastern (Sorbas) Spain to evaluate how precipitation, temperature and biocrust cover affected the assimilation and net C balance of biocrusts. Chlorophyll fluorescence, net photosynthesis and dark respiration were measured in situ bimonthly during a year. We also conducted daily cycle measurements of net photosynthesis in winter and at the end of spring. In Sorbas, warming reduced the fixation of atmospheric C in biocrust-dominated microsites throughout the year. In Aranjuez, there was an interaction between the three factors evaluated; during winter, net photosynthesis was significantly greater in high biocrust cover plots under natural conditions and in the rainfall exclusion treatment. During the daily surveys, rainfall exclusion and warming reduced C fixation in Sorbas and in Aranjuez respectively. The effects of the treatments evaluated varied with the rainfall and non-rainfall water inputs (NRWIs) registered before the measurements. Our results suggest that changes in NRWI regimes as consequence of warming could have a greater impact on the C balance of biocrusts than changes in rainfall amounts. They also indicate that climate change may reduce the photosynthetic ability of lichens, with a consequent reduction of their dominance in biocrust communities at the mid to long term. This could reduce the ability of dryland ecosystems to fix atmospheric C.

Microlysimeter station for long term non-rainfall water input and evaporation studies

Non-rainfall atmospheric water input (NRWI), which is comprised of fog, dew and soil water vapour adsorption (WVA), has been proven to be an important water source in arid and semiarid environments. Its minor contribution to the water balance and the difficulty in measuring it have resulted in a wide variety of measurement methods (duration and quantification), especially for dew. Microlysimeters seem to be the most realistic method for dew measurement on natural surfaces and they can also detect WVA. This paper presents an automated microlysimeter that enables accurate studies of NRWI and evaporation on soil and small plants. Furthermore, we have developed a field strategy for their long term placement and installation which prevents damage from rainfall, soil movement or other field conditions, keeping the microlysimeters balanced and dry. This design allows the measurement of evaporation and NRWI on different cover types, including small plants. By monitoring the surface temperatures, dewfall and water vapour adsorption can be distinguished and the relative contribution of dew and WVA on the NRWI can also be found. Our automated microlysimeter design, construction and field installation have proven to be an useful and effective tool in an NRWI study.