Search Results (14)

Although the application of biochar to soils has been proposed as a method of carbon sequestration for climate mitigation while improving crop yields, losses of biochar carbon (BC) through mineralization may reduce these benefits. However, few field studies have been conducted that control for biochar migration so that the rates and processes of BC remineralization from soils, as well as the effects of biochar on native soil organic carbon, can be accurately determined. Here, biochar made from different biomass types (oak, pine wood, and grass) and temperatures (lightly charred at 250 °C and pyrolyzed at 400 and 650 °C) were added to fine sandy Entisol in an open agricultural field and Spodosol in a shaded forested site in North Central Florida. After 15 months, BC losses, determined by the Kurth–Mackenzie–Deluca chemical–thermal oxidation method, ranged from 17.5 to 93.3% y⁻¹ (14.0–51.5% y⁻¹ for the 650 °C biochar). These losses were correlated with but much greater than the 0.4–3% y⁻¹ BC losses recorded in a one-year laboratory study using the same biochars and those of several previous field studies (1–14% y⁻¹). The losses of non-BC native carbon stocks (i.e., positive priming) also varied with biochar and soil type and ranged from 1.5 to 15.8% y⁻¹. The high BC losses observed in this study may be attributed to the subtropical and temporally variable climate conditions at the study site. Greater efforts should be made to base BC long-term stability estimates on field studies that monitor or control for biochar migration rather than reliance only upon laboratory incubations. Full article

Prokaryotes play a key role in particulate organic matter’s decomposition and remineralization processes in the vertical scale of seawater, and prokaryotes contribute to more than 70% of the estimated remineralization. However, little is known about the microbial community and metabolic activity of the vertical distribution in the trenches. The composition and distribution of prokaryotes in the water columns and benthic boundary layers of the Kermadec Trench and the Diamantina Trench were investigated using high-throughput sequencing and quantitative PCR, together with the Biolog Ecoplate^TM microplates culture to analyze the microbial metabolic activity. Microbial communities in both trenches were dominated by Nitrososphaera and Halobacteria in archaea, and by Alphaproteobacteria and Gammaproteobacteria in bacteria, and the microbial community structure was significantly different between the water column and the benthic boundary layer. At the surface water, amino acids and polymers were used preferentially; at the benthic boundary layers, amino acids and amines were used preferentially. Cooperative relationships among different microbial groups and their carbon utilization capabilities could help to make better use of various carbon sources along the water depths, reflected by the predominantly positive relationships based on the co-occurrence network analysis. In addition, the distinct microbial metabolic activity detected at 800 m, which was the lower boundary of the twilight zone, had the lowest salinity and might have had higher proportions of refractory carbon sources than the shallower water depths and benthic boundary layers. This study reflected the initial preference of the carbon source by the natural microbes in the vertical scale of different trenches and should be complemented with stable isotopic tracing experiments in future studies to enhance the understanding of the complex carbon utilization pathways along the vertical scale by prokaryotes among different trenches. Full article

The East Siberian Sea (ESS) is one of the least studied seas in terms of ostracod fauna. Ostracods are sensitive organisms to environmental changes, and detailed information on their ecology is still required. To fill this knowledge gap, we studied 33 meiobenthic dredge samples collected from the western part of the ESS and the Chaun Bay together with 17 grab samples taken from the eastern part of the sea. Quantitative analyses of the ostracod assemblages demonstrate that the river-influenced western part of the ESS is inhabited by low diverse and impoverished fauna consisting of the taxa which are able to adapt to different environmental conditions. In the isolated Chaun Bay sheltered from significant riverine influence, the ostracod assemblages contain species that prefer more stable conditions. The predominance of living specimens over dead ones and individual valves points to strong carbonate dissolution that is more pronounced in the western ESS than in the Chaun Bay. The formation of such conditions might be related to the high content of dissolved carbon dioxide resulting from bacterial remineralization of in situ produced and land-derived organic matter in the bottom sediments and low pH near the seabed. Numerous ferromanganese crusts were found on the ostracod valve surfaces and inside the shells from the Chaun Bay. Full article

Fungi have long been known to be dynamic in coastal water columns with multiple trophic modes. However, little is known about their interactions with abiotic and biotic components, contribution to the biological carbon pump (BCP), and organic matter remineralization in the oceanic water column. In this study, we investigated how fungi vary spatially and how their variations relate to that of bacteria in the water column of the South China Sea (SCS). Fungi were about three orders less prevalent than bacteria, and the main factors influencing their distribution were depth, temperature, and distance from the sites of riverine inputs. The decline in the abundance of fungi with depth was less steep than that of bacteria. Correlation tests revealed a strong positive association between the abundance of fungi and bacteria, especially in the twilight (r = 0.62) and aphotic (r = 0.70) zones. However, the co-occurrence network revealed mutual exclusion between certain members of fungi and bacteria. The majority of fungi in the water column were saprotrophs, which indicated that they were generally involved in the degradation of organic matter, particularly in twilight and aphotic zones. Similar to bacteria, the involvement of fungi in the metabolism of carbohydrates, proteins, and lipids was predicted, pointing to their participation in the turnover of organic carbon and the biogeochemical cycling of carbon, nitrogen, and sulfur. These findings suggest that fungi play a role in BCP and support their inclusion in marine microbial ecosystem models. Full article

Despite recent studies suggesting that marine fungi are ubiquitous in oceanic systems and involved in organic matter degradation, their role in the carbon cycle of the oceans is still not characterized and fungal respiration and production are understudied. This study focused on determining fungal growth efficiencies and its susceptibility to temperature differences and nutrient concentration. Hence, respiration and biomass production of three fungal isolates (Rhodotorula mucilaginosa, Rhodotorula sphaerocarpa, Sakaguchia dacryoidea) were measured in laboratory experiments at two temperatures and two nutrient concentrations. We found that fungal respiration and production rates differed among species, temperature, and nutrient concentration. Fungal respiration and production were higher at higher temperatures, but higher fungal growth efficiencies were observed at lower temperatures. Nutrient concentration affected fungal respiration, production, and growth efficiency, but its influence differed among species. Altogether, this study provides the first growth efficiency estimates of pelagic fungi, providing novel insights into the role of fungi as source/sink of carbon during organic matter remineralization. Further research is now needed to unravel the role of pelagic fungi in the marine carbon cycle, a topic that gains even more importance in times of increasing CO₂ concentrations and global warming. Full article

In the marine environment, bacteria and viruses play a significant role in carbon fluxes, remineralization processes, and the infection of various organisms. We performed a survey in the northeastern Barents Sea, a region adjacent to the Arctic Ocean, to investigate spatial patterns of microbial plankton, after the main productive period, in October 2020. Two main water masses occurred in the study region—colder Arctic Water and warmer Barents Sea Water, representing transformed Atlantic Water. Multivariate analyses detected patchiness in the horizontal distribution of bacteria and viruses, and their abundances showed no clear association with the water masses. There was an obvious vertical pattern in microbial concentration, with the highest estimates in the upper layers. Surface viral and bacterial abundance varied in a wide range (2.20 × 10⁵–10.7 × 10⁵ cells·mL⁻¹ and 0.86 × 10⁶–14.98 × 10⁶ particles·mL⁻¹, respectively) and were correlated with each other. Bacterioplankton was dominated by small-sized cells (<2 μm, 0.04–0.06 µm³), and the average volume of bacterial cells tended to increase toward the seafloor. The ratio of viral to bacterial abundance (VBR) was 11 ± 1 and did not differ between water masses and depth layers. VBR were higher, compared to summer values, suggesting a strong impact of viruses on bacterioplankton, after the main productive season. Redundancy and correlation analyses showed that inorganic nutrients (nitrate and phosphate) and organic carbon from zooplankton were most responsible for the total variability in the microbial parameters. Water temperature and salinity, also, had a measurable impact, but their influence was lower. Bacterial abundance was lower than in other seasons and regions of the Barents Sea, while viral abundance was comparable, suggesting a stronger viral impact on Arctic marine bacteria in the autumn season. Full article

We characterized the biogeochemical organic carbon (C_org) cycles in the surface sediment layer of the Ulleung Basin (UB) of the East Sea. The total oxygen uptake (TOU) rate and the diffusive oxygen uptake (DOU) rate of the sediment were measured using an autonomous in situ benthic lander equipped with a benthic chamber (KIOST BelcII) and a microprofiler (KIOST BelpII). The TOU rate was in the range of 1.51 to 1.93 mmol O₂ m⁻² d⁻¹, about double the DOU rate. The high TOU/DOU ratio implies that the benthic biological activity in the upper sediment layer is one of the important factors controlling benthic remineralization. The in situ oxygen exposure time was about 20 days, which is comparable to the values of other continental margin sediments. The sedimentary C_org oxidation rates ranged from 6.4 to 6.5 g C m⁻² yr⁻¹, which accounted for ~2% of the primary production in UB. The C_org burial fluxes ranged from 3.14 ± 0.12 to 3.48 ± 0.60 g C m⁻² yr⁻¹, corresponding to more than 30% of the deposited C_org buried into the inactive sediment deep layer. Full article

Antarctic sea-ice is exposed to a wide range of environmental conditions during its annual existence; however, there is very little information describing the change in sea-ice-associated microbial communities (SIMCOs) during the changing seasons. It is well known that during the solar seasons, SIMCOs play an important role in the polar carbon-cycle, by increasing the total photosynthetic primary production of the South Ocean and participating in the remineralization of phosphates and nitrogen. What remains poorly understood is the dynamic of SIMCO populations and their ecological contribution to carbon and nutrient cycling throughout the entire annual life of Antarctic sea-ice, especially in winter. Sea ice at this time of the year is an extreme environment, characterized by complete darkness (which stops photosynthesis), extremely low temperatures in its upper horizons (down to −45 °C) and high salinity (up to 150–250 psu) in its brine inclusions, where SIMCOs thrive. Without a permanent station, wintering expeditions in Antarctica are technically difficult; therefore, in this study, the process of autumn freezing was modelled under laboratory conditions, and the resulting ‘young ice’ was further incubated in cold and darkness for one month. The ice formation experiment was primarily designed to reproduce two critical conditions: (i) total darkness, causing the photosynthesis to cease, and (ii) the presence of a large amount of algae-derived organic matter. As expected, in the absence of photosynthesis, the activity of aerobic heterotrophs quickly created micro-oxic conditions, which caused the emergence of new players, namely facultative anaerobic and anaerobic microorganisms. Following this finding, we can state that Antarctic pack-ice and its surrounding ambient (under-ice seawater and platelet ice) are likely to be very dynamic and can quickly respond to environmental changes caused by the seasonal fluctuations. Given the size of Antarctic pack-ice, even in complete darkness and cessation of photosynthesis, its ecosystem appears to remain active, continuing to participate in global carbon-and-sulfur cycling under harsh conditions. Full article

Teeth are unique and complex anatomical organs that can provide relevant data about a person's health, and play an important role in forensic medicine. Teeth are exposed to food, drinks, and the microbiota of the oral cavity; therefore, they have developed a high resistance to localized demineralization. Nevertheless, the continuous demineralization–remineralization cycle present in the oral environment can be influenced by stress, medication, mineralization agents, and other factors such as individual habits, especially diet. In this study, based on attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) spectra from tooth samples of 36 patients, several parameters were estimated: the crystallinity index (CI), the phosphate/amide I ratio, and the carbonate/phosphate ratio. In addition, in eight representative samples (six of the root of the tooth and two of the enamel area of the crown), additional characterization by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) was conducted. From the FTIR data, it was observed that the highest CI values were found in patients who smoked. Further, in both root and crown samples, the intensity of the absorption band corresponding to PO₄^3- increased in patients undergoing treatment with psychotherapeutic drugs. On the other hand, the intensity of the absorption band of the amide I group decreased with medical treatment and with the patient's biological age. Moreover, it was found that the remineralization process was more active in enamel than in the root due to direct contact with saliva. Regarding the results obtained from the X-ray powder diffractograms, exposure to psychotherapeutic drugs affected the definition of the peaks corresponding to hydroxyapatite, both in the crown and root samples. Concerning SEM results, qualitative differences in the stratification process in demineralized surfaces were observed, and EDS analyses showed some differences in the Ca/P ratio between pathological samples and control ones, but without clear patterns. The above techniques, in particular ATR-FTIR, showed promise for the investigation of the effect of changes produced in the hydroxyapatite structure in teeth and, consequently, to determine possible strategies in the diagnostic protocol. Full article

Oral biofilms will build up within minutes after cleaning of the dental hard tissues. While the application of remineralizing agents is a well-known approach to prevent dental caries, modern oral care products offer also additional active agents to maintain oral health. Human saliva contains many different organic and inorganic compounds that help to buffer organic acids produced by cariogenic microorganisms. However, most oral care products only contain remineralizing agents. To improve the benefit of those products, further active ingredients are needed. Books, review articles, and original research papers were included in this narrative review. Putting all these data together, we give an overview of oral biofilms and active compounds used in modern oral care products to interact with them. The special focus is on inorganic compounds and their interaction with oral biofilms. While organic compounds have several limitations (e.g., cell toxicity), inorganic compounds based on calcium and/or phosphate (e.g., sodium bicarbonate, hydroxyapatite, calcium carbonate) offer several advantages when used in oral care products. Calcium release can inhibit demineralization, and the release of hydroxide and phosphate ions might help in the buffering of acids. Therefore, the focus of this review is to summarize the scientific background of further active ingredients that can be used for oral care formulations. Full article

Sediment oxygen demand (SOD) and benthic nutrient fluxes (BNFs) were measured using an in situ benthic chamber at a fish farm (FF), oyster farm (OF), and controls (FF-C and OF-C) to assess the impact of aquaculture activities on organic carbon (OC) and nutrients cycles in coastal waters of Korea. The SOD at FF and OF ranged from 60 ± 2 to 157 ± 3 mmol m⁻² d⁻¹ and from 77 ± 14 to 84 ± 16 mmol m⁻² d⁻¹, respectively, more than five times those of the control sites. The SOD at farm sites is highly correlated with fish stock and food input, suggesting that excess feed input is an important control factor for OC remineralization. The combined analysis of sediment trap and SOD indicates that most of the deposited OC oxidized in the sediment and/or was laterally transported by the current before being buried in the sediment. The benthic nutrient fluxes at farms ranged from 5.45 to 8.95 mmol N m⁻² d⁻¹ for nitrogen and from 0.51 to 1.67 mmol P m⁻² d⁻¹ for phosphate, respectively, accounting for 37–270% and 52–804% of the N and P required for primary production in the water column. These results indicate that aquaculture farming may profoundly impact biogeochemical cycles in coastal waters. Full article

This study investigates the spatial and temporal variability of chromophoric-dissolved organic matter (CDOM) in the Mediterranean Sea. The analysis is carried out using a state-of-the-art 3D biogeochemical model. The model describes the plankton dynamics, the cycles of the most important limiting nutrients, and the particulate and dissolved pools of carbon. The source of CDOM is directly correlated to the dynamics of dissolved organic carbon (DOC) by a fixed production quota. Then CDOM degrades by photobleaching and remineralization. The main innovation of the system is the inclusion of a bio-optical radiative transfer model that computes surface upwelling irradiance, and therefore simulates remotely sensed reflectance (Rrs). Simulation results of three model configurations are evaluated using satellite Rrs, particularly at 412 nm, 443 nm, and 490 nm. All simulations show a winter minimum in Rrs for the considered bands. However, different parameterizations of DOC-release induce a different accumulation of CDOM, especially in the eastern Mediterranean, and a different Rrs signature: a more active microbial loop during summer implies a decrease of Rrs at 412 nm. We demonstrate how the usage of a bio-optical model allows us to corroborate hypotheses on CDOM-cycling based on blue–violet Rrs data, supporting the importance of this complementary data stream with respect to satellite-derived chlorophyll. Full article

Groundwater is the primary drinking water source on most oceanic islands, including Tutuila, American Samoa. Drinking water quality on Tutuila is impacted by anthropogenic pollution sources such as on-site sewage disposal systems, piggeries, and agricultural leachate, particularly across the densely populated Tafuna–Leone Plain. The remineralization of anthropogenically sourced organic matter produces nitrate and dissolved inorganic carbon, which, according to previously published studies, have the potential to mobilize naturally occurring metals. This study provides further evidence that nutrients and dissolved inorganic carbon, along with naturally sourced metal concentrations, become elevated along pollution gradients and show correlation with each other. Across the Tafuna–Leone Plain, nitrate concentrations have a moderately positive correlation with uranium and vanadium. Dissolved inorganic carbon also positively correlate with nitrate, uranium, and vanadium. Similar studies elsewhere suggest that, in addition to nitrate, organic matter remineralization associated with carbonate create conditions to favor natural metal mobilization. Correlation analysis results imply that, while the surveyed trace metals are likely naturally sourced, some become soluble and more mobile in the presence of anthropogenically sourced nitrate and dissolved inorganic carbon, which alters redox conditions in the aquifer. Full article

The achievement of carbon neutrality till 2050 will require the deployment of negative carbon emission technologies like the production and soil incorporation of biochar, produced from pyrolyzed plant-based residues. The carbon sequestration potential of biochar (BC) from hazelnut (Corylus avellana L.) shells (HNS) and sunflower (Helianthus annuus L.) husks (SFH) was evaluated when the biomass was carbonized in a fixed bed reactor, in a rotary kiln and in a screw reactor. In all tested reactors, higher temperatures (>500 °C) and longer retention times increased the C concentration and stability of the biochar, with negligible effects of the reactor type and feedstock. A national case study was developed for Austria concerning the potential use of SFH- and HNS-BC in combination with compost for reaching the “4 per mille” objective. An annual soil organic carbon increase of 2.5 Mt C would be needed, requiring amendment rates of 2.2 Mt C a⁻¹ for all annual crop areas and 0.3 Mt C a⁻¹ for all vineyards and orchards. If compost only were used, the annual cost would be about 200 EUR ha⁻¹ but short-term re-mineralization would have to be considered. If the more recalcitrant biochar were used only, about 2.3 t BC ha⁻¹ would be needed at a cost of 1400–1870 EUR ha⁻¹. The study shows in principle the feasibility of applying compost–biochar mixtures for achieving the “4 per mille” objective but in practice, supplemental soil management strategies for sequestering C will be required. Full article