Influence of waste calcareous rock powder on concrete transmission performance

Reuse of stone powder formed in the production of manufactured sand is of great significance to environmental protection and resource utilization. In this paper, the waste calcareous rock powder formed in the manufactured sand production line was added into the concrete by 6%, 9%, 12% and 15%, and the total weight of manufactured sand and rock powder was controlled to be constant to prepare C30 and C40 environment-friendly manufactured sand concrete. The influence of rock powder on the compressive strength and transmission performance of concrete was analyzed. It was found that with the increase of stone powder content, the compressive strength of fresh paste and C30 concrete first increased and then decreased, while the concrete transmission performance and the compressive strength of C40 concrete continued to decline. It was suggested that the content of rock powder should not exceed 9%.

The challenge of managing the commercial harvesting of the sea urchin Paracentrotus lividus: advanced approaches are required

Sea urchins act as a keystone herbivore in marine coastal ecosystems, regulating macrophyte density, which offers refuge for multiple species. In the Mediterranean Sea, both the sea urchin Paracentrotus lividus and fish preying on it are highly valuable target species for artisanal fisheries. As a consequence of the interactions between fish, sea urchins and macrophyte, fishing leads to trophic disorders with detrimental consequences for biodiversity and fisheries. In Sardinia (Western Mediterranean Sea), regulations for sea urchin harvesting have been in place since the mid 90s. However, given the important ecological role of P. lividus, the single-species fishery management may fail to take into account important ecosystem interactions. Hence, a deeper understanding of population dynamics, their dependance on environmental constraints and multispecies interactions may help to achieve long-term sustainable use of this resource. This work aims to highlight how sea urchin population structure varies spatially in relation to local environmental constraints and species interactions, with implications for their management. The study area (Sinis Peninsula, West Sardinia, Italy) that includes a Marine Reserve was divided into five sectors. These display combinations of the environmental constraints influencing sea urchin population dynamics, namely type of habitat (calcareous rock, granite, basalt, patchy and continuous meadows of Posidonia oceanica), average bottom current speed and predatory fish abundance. Size-frequency distribution of sea urchins under commercial size (<5 cm diameter size) assessed during the period from 2004 to 2007, before the population collapse in 2010, were compared for sectors and types of habitat. Specific correlations between recruits (0–1 cm diameter size) and bottom current speeds and between middle-sized sea urchins (2–5 cm diameter size) and predatory fish abundance were assessed. Parameters representing habitat spatial configuration (patch density, perimeter-to-area ratio, mean patch size, largest patch index, interspersion/juxtaposition index) were calculated and their influence on sea urchin density assessed. The density of sea urchins under commercial size was significantly higher in calcareous rock and was positively and significantly influenced by the density and average size of the rocky habitat patches. Recruits were significantly abundant in rocky habitats, while they were almost absent in P. oceanica meadows. The density of middle-sized sea urchins was more abundant in calcareous rock than in basalt, granite or P. oceanica. High densities of recruits resulted significantly correlated to low values of average bottom current speed, while a negative trend between the abundance of middle-sized sea urchins and predatory fish was found. Our results point out the need to account for the environmental constraints influencing local sea urchin density in fisheries management.

Biological and geological characterization of modern biofilms and microbial mats and comparison with similar lithified structures in Colombian Cretaceous formations

Microorganisms may play an important role in the aggregation of sediments and the formation of sedimentary structures. Biofilms are microbial aggregates that, in a mature stage, can develop into microbial mats, fibrillar networks that irreversibly bind filaments of cyanobacteria and sediments, inside which it has been identified a stratification with functional groups of microorganisms that coexist, generate symbiotic relationships and potentially modify the characteristics of sediments and sedimentary rocks, particularly in extreme environments. In this work, filamentous cyanobacteria from biofilms of a lacustrine environment with intervals of flooding/desiccation and a saline environment, and a microbial mat from the Agua Caliente Thermal, El Rosal, Cundinamarca, are identified. In the biofilms, most cyanobacteria were found to belong to the Orden Oscillatoriales, while in the microbial mat cyanobacteria of the order Orden Nostocales were also recognized. Two rock samples isolated from the thermal which genesis was possibly influenced by the activity of cyanobacteria are described and classified. One of them, named R-1, is a calcareous rock inside which it was possible to differentiate biolaminations and an apparent dominance of biomineralization processes. This sample was both classified as a travertine and a microbial framestone with stromatolitic and thrombolytic texture. The second one, called R-2, is a siliciclastic rock classified as a mudstone and a microbial boundstone. Finally, a comparison between the sedimentary structures identified in those rocks with similar structures in the formations La Luna, Paja and Tetuán and the microbially-induced sedimentary structures (MISS) described in the literature is performed. Based on morphological resemblance, fibrillar networks identified locally in those formations are interpreted as possible biolaminations originated from the activity of cyanobacteria.

Nitrogen and phosphorus fertilization of sunflower crop in alkaline Cambisol

ABSTRACT Sunflower is a crop that has aroused the interest of farmers because of its adaptability to wide climatic conditions and for its use in biodiesel production. However, there are only a few studies on sunflower fertilization in alkaline soils. This study aimed to evaluate nitrogen (N) and phosphorus (P) fertilization in sunflower (Helianthus annuus L.) cultivated in alkaline soil. A field experiment was carried out in Baraúnas-RN, Brazil, in a Haplic Cambisol derived from calcareous rock, where the sunflower H-251 hybrid was cultivated. The treatments were a combination of four doses of N (30, 60, 90 and 120 kg ha-1) and four doses of P2O5 (30, 60, 90 and 120 kg ha-1). Sunflower growth and yield increased with the doses of N and P2O5. Doses of 30 kg ha-1 of N and 30 kg ha-1 of P2O5 were more economical, corresponding to grain yield of 2378 kg ha-1. Critical levels associated with these doses of N and P2O5 were 28.2 g kg-1 for N leaf content, 2.84 for P leaf content, and 6.75 mg dm-3 for soil available P extracted by Mehlich-1.

A new leprose Leprocaulon (Ascomycota, Leprocaulales) from Great Britain

Leprocaulon calcicola is described as new from walls in SE England; it is leprose, pale to mid blue-grey, and contains zeorin and usnic acid. It differs from L. knudsenii from North America in its habitat on mortared walls rather than non-calcareous rock and in its ITS sequence. ‘Lecanora’ ecorticata differs in the yellower colour, and the presence of unidentified fatty acids and traces of unknown terpenoids (but not zeorin) by thin-layer chromatography. Leprose lichens with usnic acid are still poorly known and sequencing must be used to support morphological and chemical studies.

Substrate type affects the abundance and size of a coral-reef sponge between depths

Substrate stability could influence abundance and size patterns of benthic organisms and thus affect community structure. Sponges on coral reefs are often found growing on calcareous rock and rubble that vary in stability, with loose rubble more easily moved by water flow, which is typically strongest in shallower water. Using the common Indo-Pacific sponge, Coscinoderma matthewsi (Lendenfeld, 1886), the present study examines the interaction of substrate type and depth (6 and 12m) on sponge abundance, size, morphology and skeletal properties (i.e. spongin fibres). Coscinoderma matthewsi was three times less common at 6m, with most sponges at this depth attached to rock, even though rubble had higher percentage cover. Mean sponge length, width and height were all greatest at 12m, with sponges growing largest on rock, probably because it is a more stable substrate for survival and growth. Morphology varied between depths, with most C. matthewsi individuals at 6m having a massive shape, whereas many sponges at 12m grew large lobes; this increases their surface area and possibly promotes filtration. Spongin density, length and width varied greatly among individuals; however, there was no consistent pattern across depth.