Factors Controlling Sediment Denitrification Rates in Grassland and Forest Streams

Sediment denitrification is an important nitrate (NO3-) removal process from agricultural streams. The direct and indirect factors that control denitrification rates in tributary sediments can vary depending on the types of agricultural activities and vegetation. Our research investigated (1) tributary sediment denitrification rates in a grassland stream affected by pasture ecosystems and a forest stream affected by N fertilization; and (2) the environmental factors that determine denitrification rates in tributary sediments. The denitrification enzyme activity (DEA) in grassland stream sediments is positively correlated with precipitation likely due to the increased nutrient exchange rates between stream water and sediments, and was higher than in forest stream sediments, leading to a decrease in NO3- concentration ([NO3-]) in stream sediments. The DEA in riparian sediments was regulated by carbon concentrations and did not contribute to NO3- removal from the riparian sediment in grassland and forest streams. Thus, environmental factors affected by different types of agricultural activities and vegetation might regulate denitrification rates and [NO3-] in agricultural stream ecosystems

Input of terrestrial organic matter linked to deglaciation increased mercury transport to the Svalbard fjords

Deglaciation has accelerated the transport of minerals as well as modern and ancient organic matter from land to fjord sediments in Spitsbergen, Svalbard, in the European Arctic Ocean. Consequently, such sediments may contain significant levels of total mercury (THg) bound to terrestrial organic matter. The present study compared THg contents in surface sediments from three fjord settings in Spitsbergen: Hornsund in the southern Spitsbergen, which has high annual volume of loss glacier and receives sediment from multiple tidewater glaciers, Dicksonfjorden in the central Spitsbergen, which receives sediment from glacifluvial rivers, and Wijdefjorden in the northern Spitsbergen, which receive sediments from a mixture of tidewater glaciers and glacifluvial rivers. Our results showed that the THg (52 +/- 15 ng g(-1)) bound to organic matter (OM) was the highest in the Hornsund surface sediments, where the glacier loss (0.44 km(3) yr(-1)) and organic carbon accumulation rates (9.3 similar to 49.4 g m(-2) yr(-1)) were elevated compared to other fjords. Furthermore, the delta C-13 (-27 similar to -24 parts per thousand) and delta S-34 values (-10 similar to 15 parts per thousand) of OM indicated that most of OM were originated from terrestrial sources. Thus, the temperature-driven glacial melting could release more OM originating from the meltwater or terrestrial materials, which are available for THg binding in the European Arctic fjord ecosystems.11Ysciescopu

Environmental Characteristics and Macrobenthic Community Structure of Yubu Island, a UNESCO-Designated Migratory Bird Sanctuary in the South Korea

This study investigated the environmental characteristics and macrobenthic community structures of an intertidal flat located on Yubu Island in the western coastal area of the Yellow Sea of South Korea. The study site has been well known for the migratory bird protection designated by UNESCO. We collected the samples of surface and depth core sediments and macrobenthos from the unused saltern and the area surrounding it in July 2017. Our results demonstrated that the means of mud, total carbon, and total nitrogen contents were 50%, 0.35% and 0.05%, respectively, and the origin of sediment composed of marine sources. The sedimentation rate ranged from 0.99 to 1.66 cm y−1, which was higher than other tidal flats in the Yellow Sea. The result of a topographic analysis indicated that the area in the unused saltern was 289.489 m2, and the length and width were 625 m and 500 m, respectively. A total of 13 species occurred with a mean density of 92 ind. m−2 and a mean biomass of 58.6 gWWt m−2. The Heteromastus filiformis (23.1%, 21 ind. m−2) was the most dominant species, followed by Perinereis linea (19.2%, 18 ind. m−2) and Tubuca arcuata (17.3%, 16 ind. m−2). Thus, this environmental information will help to establish policies to protect migratory birds in the future

The complete mitochondrial genome of blue-lined octopus Hapalochlaena fasciata (Hoyle, 1886) (Octopodiformes; Octopoda; Octopodidae)

The complete mitochondrial genome of the highly venomous blue-lined octopus, Hapalochlaena fasciata (Hoyle, 1886), was analyzed by the primer walking method. Its mitogenome was 15,479 bp in total length, comprising 13 protein-coding genes, 2 ribosomal RNA genes, and 23 transfer RNA genes. In the phylogenetic tree, the gene content and order were congruent with those of typical octopodiform species. The mitogenomic sequence presented could be very useful as the first record of the complete mitogenome for the genus Hapalochlaena

Enhancement of volcanic eruption in mid-ocean ridge during the last deglaciation: New sedimentary evidence in the middle part of Central Indian Ridge

Sedimentary evidence for enhanced volcanic eruption during the glacial/interglacial transition in the volcanically active mid-ocean ridges is still lacking. Here, we present the sedimentary records of enhanced deglacial volcanic activity in a well-dated sediment core from the middle part of Central Indian Ridge (CIR), which can provide clue for comprehensively understanding of the temporal relation of increase in submarine volcanism relative to glacial/interglacial transition. Notably, the 35-kyr sediment core used in this study contains continuous, discernible pyroclastic deposit layers (0.5–5 cm thick), which are composed mainly of angular and curved fluidal shards with vesicles, possibly suggesting volatile-rich ridge eruptions. High-resolution elemental profiles of the core provide definite records of at least 17 volcanic eruptions during the past 35 kyr. Interestingly, volcanism was sparse during the Last Glacial Maximum (LGM), but increased significantly during the last deglaciation after ~18 kyr BP. The last deglaciation-associated volcanic eruptions in the CIR may be linked to decompression melting during the LGM sea-level lowstand, reaffirming an influence of sea level variability on global ocean ridge magmatism. Combining the previous results, furthermore, simultaneous strengthening of submarine and subaerial volcanic eruptions during the last deglaciation could have accelerated the rise of atmospheric CO2, with the ensuing warming constituting positive feedback upon deglaciation. Highlights • A succession of pyroclastic records in a well-dated sediment core from the CIR was identified. • The morphologies of the pyroclasts are consistent with volatile-rich submarine eruption. • Deglaciation-associated enhanced volcanism seems robust in the mid-ocean ridges. • Tentative support for a link between ridge volcanism and climate change is provided

The spatial distribution of exoenzyme activities across the soil micro-landscape, as measured in micro- and macro-aggregates, and ecosystem processes

International audienceThe spatial ecology of soil microbial communities and their functioning is an understudied aspect of soil microbial ecology. Much of our understanding of the spatial organisation of microbial communities has been obtained at scales that are inappropriate for identifying how microbial functioning and spatial patterns are related. In order to reveal the spatial strategies of soil microorganisms, we measured the microscale spatial distribution of 6 exoenzyme activities (EEA) and related them to the catalytic potential of three soils. The relationship between EEA profiles and microbial community structure was also measured in soil aggregates. All the EEA exhibited scale-invariant spatial clustering. The extent of spatial clustering varied significantly among EEA, suggesting that microbial communities employ different spatial strategies when foraging for different elements. The dispersed distribution of alkaline phosphatase suggests that microorganisms invest more heavily in the acquisition of P. The EEA associated with the C and N cycles, but not the P cycle, were significantly affected by management practices in the loamy soil. A significant negative relationship between the extent of spatial clustering of EEA and the overall intensity of the EEA was identified in the two loamy soils, indicating that the microscale spatial ecology of microbial activity may have a significant impact on biogeochemical cycles. No relationship was found between microbial community structure and EEA profiles in aggregates. However, a number of negative relationships between the relative abundance of certain taxa and the most dispersed EEA (alkaline phosphatase and P-glucosidase) were found, suggesting that these taxa make the EEA products available by means other than the production of exoenzymes (e.g. solubilisation of phosphate through the production of organic acids)

Stable nitrogen isotope dynamics in the South China Sea

2

Microbial alteration in marine sediments: Insights from compound-specific isotopic compositions of amino acids in subseafloor environments

The proportion of amino acids (AAs) in sediment can be used as an indicator of microbial degradation, which is primarily the product of benthic prokaryote activity. The microbial activity would be reflected with the stable isotope ratio of nitrogen (δ15N) at the time of mineralization and resynthesis of AAs. In this study, the compound-specific isotope analysis of individual AAs was used to investigate δ15N variation associated with microbial processes in marine sediment samples. Our results showed a decrease in AA concentrations in core-top sediment was accompanied by an increase in δ15N values, suggesting large 15N enrichment in buried AAs. Phenylalanine displayed an increase in δ15N from the surface to depths greater than 2 cm, whereas relatively constant δ15N values at depths below 2 cm, suggesting that microbial utilization of phenylalanine varies with depth. Glycine showed the highest relative molar contribution (from 12.1 to 36.4%), with the largest δ15N increase (from 0.8 to 8.7) in deep sediment, implying that such information can serve as a measure of AA diagenesis in sedimentary environments. Our results also indicated that the δ15N values of individual AAs in sediment reflected the microbial alteration of organic matter at water-sediment interfaces and in sub-surface environments. These findings form an important basis for interpreting the δ15N values of AAs in sediment. Copyright © 2022 Choi, Choi, Chikaraishi, Takano, Kim, Lee, Lim and Shin.11Ysciescopu

Increase in anthropogenic mercury in marginal sea sediments of the Northwest Pacific Ocean

2