Megumu Fujibayashi

Global climate change driven by soot at the K-Pg boundary as the cause of the mass extinction

The mass extinction of life 66 million years ago at the Cretaceous/Paleogene boundary, marked by the extinctions of dinosaurs and shallow marine organisms, is important because it led to the macroevolution of mammals and appearance of humans. The current hypothesis for the extinction is that an asteroid impact in present-day Mexico formed condensed aerosols in the stratosphere, which caused the cessation of photosynthesis and global near-freezing conditions. Here, we show that the stratospheric aerosols did not induce darkness that resulted in milder cooling than previously thought. We propose a new hypothesis that latitude-dependent climate changes caused by massive stratospheric soot explain the known mortality and survival on land and in oceans at the Cretaceous/Paleogene boundary. The stratospheric soot was ejected from the oil-rich area by the asteroid impact and was spread globally. The soot aerosols caused sufficiently colder climates at mid–high latitudes and drought with milder cooling at low latitudes on land, in addition to causing limited cessation of photosynthesis in global oceans within a few months to two years after the impact, followed by surface-water cooling in global oceans in a few years. The rapid climate change induced terrestrial extinctions followed by marine extinctions over several years.

Feedback of threshold via estimating sources and composition of sedimentary organic matter across trophic gradients in freshwater lakes

The quantity and quality of sedimentary organic matter (SOM) in relation to material and energy flows are crucial for understanding the current state and future development of lake systems, yet, characterization of organic matter sources and assessment of their relative contributions in different trophic-state lakes caused by anthropogenic impacts are scarcely known. In this study, for obtaining information concerning the source of SOM and its compositional diversity along different trophic gradients, a total of thirty-one sampling sites from four freshwater lakes located in China and Japan were performed by the molecular level analysis using source-specific fatty acid biomarkers. Results indicated that SOM in these lakes was composed of microalgae-, aquatic plant-, terrestrial plant- and bacteria-derived organic matters based on their fatty acid profiles. The scatter plot matrix exhibited correlations between these sources, however, only terrestrial plant-derived organic carbon was a well predictor for sediment TOC with strong, spatiotemporal dynamics. The source and composition of SOM were evidently influenced by lake trophic state with redundancy analysis. Moreover, increase of lake trophic state led to the relatively higher contribution of aquatic organic matter sources to SOM pool compared with terrigenous sources, as evidenced by significant correlations between the trophic state index [TSI (TP)] and the ratio of terrigenous to aquatic fatty acids (TARFA ratio). Yet, this changing trend became more gradual with higher trophic state and prevented the occurrence of regime shift from allochthonous to autochthonous dominant state by a threshold (0.683) of TARFA ratio. Together, a conceptual diagram was proposed, which highlighted the prevailing state of allochthonous source and implicated sedimentary organics in biogeochemistry cycle within freshwater lakes.

Lead removal efficiency using biosorbents as alternative materials for permeable reactive barriers

As alternative materials for heavy metal removal, this study investigated biosorbents to determine their suitability for permeable reactive barriers. The lead removal efficiencies of brown seaweed (Undaria pinnatifida) and reed (Phragmites australis) were determined under different conditions (batch and column system). The experimental results for these biomaterials fitted the Langmuir isotherm with high correlation values. It was verified that the influence of temperature on affinity was higher than that on adsorption capacity. While the lead removal efficiency of U. pinnatifida was higher than of P. australis in the batch experiments, lead removal efficiency decreased for both materials at approximately the same time in the column experiments. This indicates that the dominance of the chemical and physical adsorption mechanisms could result in differences in these systems.

Comparison of four kinds of coagulants for the removal of picophytoplankton

Abstract The purpose of this study was to investigate the efficiency of the coagulation process for the removal of picophytoplankton from drinking water and, in addition, to investigate the performance of simple coagulants such as alum and ferric chloride, and polymer coagulants such as PAC and PSI, in picophytoplankton removal. Two simple coagulants such as alum (Al2(SO4)3·16H2O) and ferric chloride (FeCl3·6H2O) and two polymer coagulants such as poly-silicate iron (PSI) and poly-aluminum chloride (PAC) were used in both raw water including picophytoplankton and synthetic water samples prepared by Synechococcus sp. Analyses included a picophytoplankton count, an assessment of the turbidity, dissolved organic carbon, UV254, and zeta potential and the settling time measurements. The removal efficiency of picophytoplankton during the coagulation–flocculation–sedimentation process was determined using simple and polymer coagulants. Water samples with lower coagulation pH had better picophytoplankton removal ...

Influence of velocity gradient and rapid mixing time on flocs formed by polysilica iron (PSI) and polyaluminum chloride (PACl)

ABSTRACT The aim of this investigation was to evaluate the effect of different velocity gradient and rapid mixing time on coagulation and floc properties, using polysilica iron (PSI) and polyaluminum chloride (PACl) with different rapid mixing speeds and times. The growth, breakage, and re-growth of flocs were monitored by a particle-size analyzer during the rapid mixing, in order to determine the underlying mechanisms. For PSI and PACl, three different zones were found to depending on the G value in the coagulation process. At low G values (G   546 s−1 for PSI flocs and G > 390 s−1 for PACl flocs), breakup dominated over floc formation. Broken flocs did not fully re-grow after breakage, probably as a result of a change...

Evaluation of Food Sources Assimilated by Unionid Mussels Using Fatty Acid Trophic Markers in Japanese Freshwater Ecosystems

ABSTRACT Freshwater unionid bivalves play an important role in nutrient cycling and organic matter transportation and provide hard substrates for other benthic animals in freshwater ecosystems. Therefore, the conservation of unionid bivalves is considered essential for maintaining aquatic biodiversity. In this study, the assimilated food sources of six species of freshwater bivalves, Unio douglasiae, Unio douglasiae nipponensis, Unio biwae, Anodonta japonica, Pronodularia japonensis, and Lanceolaria grayana, were investigated using fatty acid trophic markers. The contribution (percentage of total identified fatty acids) of the trophic markers showed a similar tendency in all the bivalve species, even though they were sampled from various habitats. Fatty acid trophic markers of diatoms (20:5n3) and green algae and/or cyanobacteria (18:2n6 + 18:3n3) were dominant in all bivalve samples, ranging from 4.8% to 10.2% and 7.3% to 10.6%, respectively. Bacterial fatty acids were also detected in large amounts, ranging from 1.7% to 5.4%. In this study, all unionid bivalves contained diatom, green algal/cyanobacterial, and bacterial markers in substantial proportions, and no individual depended on a single food source, stressing the importance of ingesting and assimilating various food types.

The role of rapid mixing condition on picophytoplankton floc growth

AbstractThis work aims to evaluate the effect of different velocity gradient and rapid mixing time on floc properties of picophytoplankton, using polyaluminum chloride (PACl) and polysilicato-iron (PSI) as coagulant. The growth, breakage, and re-growth of flocs were followed by a particle size analyzer in order to investigate the underlying mechanisms. Three different zones were found to be depending on G value in coagulation process. At low G value (G   250 s−1for Synechococcus sp.-PSI flocs and G > 546 s−1 for kaolin-PSI flocs; G > 200 Synechococcus sp.-PACl flocs and G > 390 s−1 for kaolin-PACl flocs), breakup dominated over floc formation. Broken flocs did not fully re-grow after breakage; ...

Approach deliberation for source identification of sedimentary organic matters via comparing freshwater lakes with multi-ecotypes

Despite of the importance of understanding the sediment quality for lacustrine management, the source evaluation of sedimentary organic matter (SOM) in freshwater lakes is still insufficient. In this study, two shallow eutrophic lakes of Lake Taihu, China and Lake Izunuma, Japan were systematically investigated. Results of fatty acid profiles demonstrated that a wide range of organic matters, varying ecotypically, was inputted into the sediments of both lakes. Interestingly, there was a strong contribution from terrestrial plants to the sediments across ecotypes, with an approximate input from bacteria, and a relatively minor input from microalgae mainly included cyanobacteria, green algae, diatom and dinoflagellates. In addition, isotopic mixing model depicted a complementary picture that a significant, but spatially variable, amount of organic matter was derived from emergent and floating-leaf plants of Phragmites, Nelumbo, Nymphoides and Trapa L in Lake Izunuma. A general indicator selection procedure for the source assignments of SOM in freshwater ecosystems was therefore proposed: fatty acids could be a valid biomarker when the potential sources are unknown or unavailable; stable isotopes could be an effective supplement approach when assessing the special or defined organic sources.

Transfer of cyanobacterial carbon to a higher trophic-level fish community in a eutrophic lake food web: fatty acid and stable isotope analyses

The dietary utilization of cyanobacterial carbon by fish communities is poorly understood. We examined the transfer of cyanobacterial carbon to fish in a eutrophic lake using fatty acid biomarkers and measuring the stable carbon isotope ratios of fatty acid and bulk nitrogen. We collected five species of fish (Hypomesus nipponensis, Carassius sp., Cyprinus carpio, Tridentiger brevispinis, and Gymnogobius castaneus) as well as the seston from June to November 2016 from Lake Hachiro, Japan. Cyanobacterial blooms were observed from August to October. From June to August, cyanobacterial fatty acid biomarkers (18:2ω6 and 18:3ω3) accounted for only 1.4–4.3% of total fatty acids in these fish species, indicating a low contribution of cyanobacteria to fish diets during this period. However, the contribution of the cyanobacterial fatty acid biomarkers in these fish species increased sharply in September (10.5–17.1%), except in second-year H. nipponensis. In September, the stable carbon isotope ratios of 18:3ω3 in these fish species were almost equivalent to those in the seston, which was primarily composed of cyanobacteria. The trophic positions of the collected fish species ranged from 1.6 to 3.4, based on their stable nitrogen isotope values, indicating that some fish ingested cyanobacteria directly, while others acquired cyanobacteria indirectly, through the food chain. These findings indicate that cyanobacterial carbon is transferred up the food chain in eutrophic lake ecosystems with cyanobacterial blooms.

Spatio-temporal characteristics of the fatty acid compositions of two macrobenthos (Nuttallia olivacea and Hediste sp.) in the Nanakita River estuary, Japan

This study examined species-specific, dietary responses of two benthic macroinvertebrate species, Nuttllia olivacea and Hediste sp., to spatial and seasonal variations of resource composition in an estuarine tidal flat system of north-eastern Japan. This study measured fatty acid (FA) composition of sedimentary organic matter and macroinvertebrate tissue to estimate relative contributions of organic matter originating from different sources. N. olivacea and Hediste sp. are predominated in macrobenthos communities of sandy and muddy sediments in the studied estuary, respectively. The total FA of sedimentary organic matter was significantly related positively to the total organic carbon (TOC) content of sediment. FAs of diatom, bacteria, and terrestrial–plant origins were found higher values in the sediments with higher TOC. The dietary composition of N. olivacea showed both spatial and seasonal variations, but was consistently linked with diatom, bacteria and dinoflagellates in the sediments. Meanwhile, the FA composition of Hediste sp. demonstrated that the diets of this species depended heavily on diatom, bacteria and terrestrial plant. From these results it was revealed that Hediste sp. was more tightly linked with sedimentary organic matter composition compared with N. olivacea. This result indicates that Hediste sp. has a euryphagic diet and is possible to feed on sedimentary organic matter of various sources in natural environments. Both macroinvertebrate species showed different characteristics in terms of using of food resources and its spatial and seasonal variation. It is considered that the difference in feeding dietary habit of macroinvertebrates is one of the important factors which decide the sediment suitability for macrobenthos.