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The role of soil biotic communities has received increasing attention in relation to global climate change management and, particularly, greenhouse gas dynamics. Soil CO 2 fluxes are regulated by several physical, chemical and biological properties, and diatoms constitute a relevant component of the soil microbiological community. This study tests experimentally the effect of CO 2 leakages and soil texture on soil diatom communities. Our results show profound changes associated to both factors, namely an increase in species richness in CO 2 -added treatments containing sandy-loam soils, and a segregation of diatom assemblages according to CO 2 fluxes, irrespective of soil typology, as revealed by multivariate analysis. These effects seem to result from changes in soil pH since communities growing on alkaline plots show higher abundances but lower taxa numbers. No differences were found, however, when the two CO 2 fluxes tested were compared. Finally, soil texture is revealed as an important factor explaining structural differences in the observed diatom assemblages. The findings described here may help to develop accurate CO 2 leakage surveillance methods for geological storage sites. [ABSTRACT FROM AUTHOR]

Natural CO 2 vents have received growing interest in the last years due to their relation to CO 2 capture and storage (CCS) risk assessment studies. Despite the increasing body of knowledge, mostly focused on microbial communities, scarce information is available on how geological CO 2 affects mesofauna and microfauna, and their interactions. We studied microorganisms, microfauna i.e. protists and nematodes, and mesofauna communities, i.e. collembola and mites and their relationships in a natural CO 2 vent at La Sima (Spain). Four CO 2 flux intensities from Control (7–19 g m −2 d −1 ) to low (40–55 g m −2 d −1 ) and high fluxes (260–1600 g m −2 d −1 ), including extreme emissions (more than 10 4 g m −2 d −1 ) were studied. We found that increasing CO 2 emissions from Control to high fluxes strongly affected biota abundances and richness, cascading from microorganisms to mesofauna, and resulting in reduced and less diverse populations in each of the groups levels assayed. Nevertheless, at extreme fluxes edaphic biota biomass recovered in most of the communities, suggesting that the extreme CO 2 conditions are associated with high abundances of well adapted communities, although with very low diversity. Increases in abundance of bacteria, fungi and amoebae, but not ciliates, were related to increases in mesofauna richness and nematode and mesofauna abundances. Our results help to indicate the CO 2 threshold from which accidental losses from CCS operations can be detected in the long-term. [ABSTRACT FROM AUTHOR]

This paper evaluates the effect of CO 2 on protozoan communities, a neglected group in CO 2 related studies, despite their potential role in influencing bacterial communities, and vegetation growth. For this purpose, the effect of increased CO 2 in the soil upon the abundance of protozoa (amoebae, flagellates, and ciliates) and diversity of ciliates was experimentally studied in two soils. Twelve mesocosms were created with 8 m 2 cells filled with the upper layer of one of the two soils. The cells were equipped with systems that controlled injection of CO 2 at different depths. Two different flows of CO 2 (20 and 40 l/h) were studied simulating a potential CO 2 leakage from early CSS sites. Water content and pH levels were measured by continuous monitoring systems. There were no clear patterns in the abundance of amoebae, ciliates, or flagellates in response to the injection of CO 2 . The analysis used to evaluate the community structure of ciliates, such as Equitability, Margalef index, or the Colpodea to Polyhymenophorea ratio showed significant differences with increases in CO 2 . The results of this study indicate that controlled increments of CO 2 in the soil influence the composition of the ciliate community, but have no effect on their total abundance. This paper supports the use of ciliates as promising biological indicators of CO 2 effects in Carbon Capture and Storage operations. [ABSTRACT FROM AUTHOR]

The effects of artificial increments in soil carbon dioxide (CO 2 ) on microbial communities were studied in an experimental plant in Cubillos del Sil (León, Spain). The impact of two fluxes of CO 2 (20 and 40 l/h) influencing microbial communities and their relationships in two different soils (Cubillos and Hontomín) was evaluated by using three different approaches: community structure by DGGE, qPCR quantification of Bacteria , Archaea and Fungi domains and community-level physiological profile (CLPP). Soil type was the most important determinant factor in microbial activity and abundance: Cubillos soil showed a significantly higher qPCR copy numbers (58.68, 275.92 and 375.4%, for Bacteria , Archaea and Fungi , respectively) with a richer metabolism than Hontomín soil. No significant changes were observed in relation to CO 2 increase with any of the methods employed. Soil microbial communities proved to be resilient to short-term below-ground low CO 2 emissions. Short-term studies are useful for developing methods to detect possible leakages and assessing the likelihood of undesirable consequences on soil ecosystem. [ABSTRACT FROM AUTHOR]

The effect of controlled sub-surface CO 2 emissions on edaphic ciliate communities was examined in experimental mesocosms and then compared with the effect of natural CO 2 emissions from natural vents on edaphic ciliate communities to analyse the potential of ciliates as bioindicators of soil CO 2 increments. The relative abundance of each taxonomic family formed the basis for developing the metrics of the ciliate assemblages in order to obtain a quantitative soil quality bioassessment, the edaphic ciliate bioindex. Twenty-four mesocosms filled with soil and equipped with controlled CO 2 injection were built for the experiment. To evaluate the potential of soil ciliates as bioindicators, the same CO 2 fluxes were analyzed in both study conditions, from 0 to more than 150 ml CO 2 d −1 . Several diversity indices and other group ratios and percentages of community structure were calculated. Biodiversity of ciliates (Equitability, Margalef and Shannon indices) decreased with the increase in CO 2 fluxes, and Colpodid/Polyhymenophorean ratio increased. This indicated adverse conditions for the ciliates in the soil. There was a positive significant relationship between the observed CO 2 values measured in the test set and the values expected according to their inhabiting ciliate community. The weighted averaging of taxonomic group indicator method supported the experimental results attesting to the potential of edaphic ciliates as bioindicators of CO 2 flux increments. The ecological profiles estimated within the training test, based on the taxonomic level of family, were reliable and provided a basis for the use of ciliates to monitor soil CO 2 flux increments in a wide range of ecological conditions. [ABSTRACT FROM AUTHOR]