University of Almería

About: University of Almería is a education organization based out in Almería, Spain. It is known for research contribution in the topics: Population & Context (language use). The organization has 4674 authors who have published 10905 publications receiving 233036 citations. The organization is also known as: University of Almeria & Universidad de Almería.

Biological soil crust development affects physicochemical characteristics of soil surface in semiarid ecosystems

Abstract: Water and nutrients are scarce resources in arid and semiarid ecosystems. In these regions, biological soil crusts (BSCs) occupy a large part of the soil surface in the open spaces surrounding patches of vegetation. BSCs affect physicochemical soil properties, such as aggregate stability, water retention, organic carbon (OC) and nitrogen (N) content, associated with primary ecosystem processes like water availability and soil fertility. However, the way BSCs modify soil surface and subsurface properties greatly depends on the type of BSC. We hypothesised that physicochemical properties of soil crusts and of their underlying soils would improve with crust development stage. Physicochemical properties of various types of soil crusts (physical crusts and several BSC development stages) and of the underlying soil (soil layers 0–1 cm and 1–5 cm underneath the crusts) in two semiarid areas in SE Spain were analysed. The properties that differed significantly depending on crust development stage were aggregate stability, water content (WC) (at −33 kPa and −1500 kPa), OC and N content. Aggregate stability was higher under well-developed BSCs (cyanobacterial, lichen and moss crusts) than under physical crusts or incipient BSCs. WC, OC and N content significantly increased in the crust and its underlying soil with crust development, especially in the first centimetre of soil underneath the crust. Our results highlight the significant role of BSCs in water availability, soil stability and soil fertility in semiarid areas.

A model for light distribution and average solar irradiance inside outdoor tubular photobioreactors for the microalgal mass culture.

Abstract: A mathematical model to estimate the solar irradiance profile and average light intensity inside a tu- bular photobioreactor under outdoor conditions is pro- posed, requiring only geographic, geometric, and solar position parameters. First, the length of the path into the culture traveled by any direct or disperse ray of light was calculated as the function of three variables: day of year, solar hour, and geographic latitude. Then, the phenom- enon of light attenuation by biomass was studied con- sidering Lambert-Beer's law (only considering absorp- tion) and the monodimensional model of Cornet et al. (1900) (considering absorption and scattering phenom- ena). Due to the existence of differential wavelength ab- sorption, none of the literature models are useful for ex- plaining light attenuation by the biomass. Therefore, an empirical hyperbolic expression is proposed. The equa- tions to calculate light path length were substituted in the proposed hyperbolic expression, reproducing light inten- sity data obtained in the center of the loop tubes. The proposed model was also likely to estimate the irradi- ance accurately at any point inside the culture. Calcula- tion of the local intensity was thus extended to the full culture volume in order to obtain the average irradiance, showing how the higher biomass productivities in a Phaeodactylum tricornutum UTEX 640 outdoor chemo- stat culture could be maintained by delaying light limita- tion. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 701-714, 1997.