Using LANDSAT 8 and VENµS Data to Study the Effect of Geodiversity on Soil Moisture Dynamics in a Semiarid Shrubland

Soil moisture content (SMC) is a limiting factor to ecosystem productivity in semiarid shrublands. Long-term droughts due to climatic changes may increase the water stress imposed on these lands. Recent observations demonstrate positive relations between geodiversity—expressed by the degree of soil stoniness—and SMC in the upper soil layers. This suggests that areas of high geodiversity can potentially provide a haven for plant survival under water scarcity conditions. The objective of this study was to assess the effect of geodiversity on the dynamics of SMC in semiarid environments, which so far has not been fully investigated. The optical trapezoid model (OPTRAM) applied to six-year time series data (November 2013–July 2018), obtained from LANDSAT 8 and highly correlated with field measurements (R2 = 0.96), shows here that the SMC in hillslopes with high geodiversity is consistently greater than that in hillslopes with low geodiversity. During winter periods (December–March), the difference between the two hillslope types was ~7%, while during summer periods (June–September) it reduced to ~4%. By using the high-resolution spectral-spatiotemporal VENµS data, we further studied the geodiversity mechanism during summertime, and at a smaller spatial scale. The VENµS-based Crop Water Content Index (CWCI) was compared with the OPTRAM measurements (R2 = 0.71). The Augmented Dickey–Fuller test showed that water loss in the high-geodiversity areas during summers was very small (p-value > 0.1). Furthermore, the biocrust index based on the VENµS data showed that biological crust activity in the high-geodiversity hillslopes during summers is high and almost stationary (ADF p-value > 0.1). We suggest that the mechanism responsible for the high SMC in the high-geodiversity areas may be related to lower evaporation rates in the dry season and high runoff rates in the wet season, both of which are the combined result of the greater presence of developed biocrusts and stoniness in the areas of higher geodiversity.

Changes of the Microbial Community in Corn Soil Due to the Synergism Zeolite-Mineral Fertilizers

Microbial communities in agricultural ecosystems are characterized by a strong dynamic and radical change due to technological inputs applied. Corn is cultivated on large areas with high requirements for nutrients and an increased potential for activation of specific microbial groups. The aim of this study was to assess the unilateral and synergic effect of zeolite and mineral fertilizers on the development and transformation of microbial functional groups in the rhizosphere of corn. Physiological profile assessment of microbial communities has been carried out on the basis of substrate induced respiration, monitored over a period of 6 hours of incubation. The amount of CO2 registered in Microresp plates represents the activity of functional groups in decomposition of each type of substrate applied. Characteristic groups of microorganisms in maize rhizosphere are capable of decomposing acids: citric, L-malic, oxalic and α-Ketoglutaric. These substrates indicate the presence of high concentrations of organic matter in soil and the existence of a biological crust on the surface (citric acid), respectively the existence of powerful processes for the decomposition of organic material by actinomycetes (α-Ketoglutaric acid). The highest microbial activities were observed in groups of bacteria involved in processes of plant growth promotion and microbial groups with an important role in the processes of denitrification (oxalic acid). For the application of urea a triple value of activity of this type of microflora is observed. Functional groups codominant in soils cultivated with corn are specialized in efficient degradation of organic matter and biological crust, zeolite providing the complex substrate necessary for the development of these microorganisms.

Comparison between Methods of Biological Crust Removal on Granite

This paper presents the evaluation of the efficacy of the removal of biological crust from ornamental granites. The removal was made applying different procedures and the efficiency was evaluated by means of optic and scanning electron microscopy (SEM), Fourier Transformed Infrared spectrometry (FTIR) and colour measures (CIE-L*a*b* colour spaces). Among the cleaning procedures, an abrasive cleaning method, several chemicals-based methods applied by brush in aqueous media (using acids, bleach, benzalkonium chloride, ethanol and others) and laser (Nd:YVO4 at 355 nm) were used. This last method was previously found very efficient in removing graffiti and biological crusts in other granites. The present study was conducted on a granite of great commercial value from Galicia (NW Spain) and traditionally used on construction of historical buildings in this region and abroad. Slabs of this granite with an intense biological crust were used. Before the cleaning procedures, the biological crust was characterized by the same techniques to establish the comparison between Pre and Post cleaning. The efficacy in the crust removal was evaluated with optic and electronic microscopy; the best cleaning methods were the acid-based methods and laser. In both cases, no biological remains were found on the cleaning surfaces. Hydrogommage (the abrasive cleaning method) obtained intermediate results, and benzalkonium chloride cleaning showed the worst effectiveness. FTIR technique helped to identify the presence of organic signals of biological crust; and also, it provided useful information on the contaminant remains on the stone after cleaning and on mineral damages. Colour differences after cleaning gave additional information about the efficiency of the cleaning.