Stable isotopic evidence of nitrogen sources and C4 metabolism driving the world’s largest macroalgal green tides in the Yellow Sea

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 17437, doi:10.1038/s41598-018-35309-3.During recent years, rapid seasonal growth of macroalgae covered extensive areas within the Yellow Sea, developing the world’s most spatially extensive “green tide”. The remarkably fast accumulation of macroalgal biomass is the joint result of high nitrogen supplies in Yellow Sea waters, plus ability of the macroalgae to optionally use C4 photosynthetic pathways that facilitate rapid growth. Stable isotopic evidence shows that the high nitrogen supply is derived from anthropogenic sources, conveyed from watersheds via river discharges, and by direct atmospheric deposition. Wastewater and manures supply about half the nitrogen used by the macroalgae, fertiliser and atmospheric deposition each furnish about a quarter of the nitrogen in macroalgae. The massive green tides affecting the Yellow Sea are likely to increase, with significant current and future environmental and human consequences. Addressing these changing trajectories will demand concerted investment in new basic and applied research as the basis for developing management policies.This work was supported by the State Key Project of Research and Development Plan (2016YFC1402106)

DNA methylation dynamics of the human preimplantation embryo

In mammals, cytosine methylation is predominantly restricted to CpG dinucleotides and stably distributed across the genome, with local, cell type-specific regulation directed by DNA binding factors1-3. This comparatively static landscape dramatically contrasts the events of fertilization, where the paternal genome is globally reprogrammed. Paternal genome demethylation includes the majority of CpGs, though methylation is maintained at several notable features4-7. While these dynamics have been extensively characterized in the mouse, only limited observations are available in other mammals, and direct measurements are required to understand the extent to which early embryonic landscapes are conserved8-10. We present genome-scale DNA methylation maps of human preimplantation development and embryonic stem cell (ESC) derivation, confirming a transient state of global hypomethylation that includes most CpGs, while sites of persistent maintenance are primarily restricted to gene bodies. While most features share similar dynamics to mouse, maternally contributed methylation is divergently targeted to species-specific sets of CpG island (CGI) promoters that extend beyond known Imprint Control Regions (ICRs). Retrotransposon regulation is also highly diverse and transitions from maternally to embryonically expressed, species-specific elements. Together, our data confirm that paternal genome demethylation is a general attribute of early mammalian development that is characterized by distinct modes of epigenetic regulation

Methane Emissions Above and Below a Ditch Plug, Sprague River Marsh, Phippsburg, ME

This study investigates methane emissions behind a ditch plug installation in the Sprague River Marsh, Phippsburg, Maine. Ditch plugs are common man-made tidal restrictions that inhibit tidal flow in salt marshes. Previous work has shown that higher methane emissions are associated with lower salinities. However, the effects of ditch plugs on methane emissions are previously unknown. Understanding the potential release of carbon in the form of methane on salt marshes is important for the overall carbon budget as salt marshes are one of the most effective carbon sinks. Static gas chambers were used to collect air samples above and below the ditch plug for 5 months during the summer of 2016. The samples were analyzed using a GC-FID and the data showed no statistical significant difference in methane emissions above or below the ditch plug. This concludes that the presence of the ditch plug in this particular location did not result in an increase of methane emissions on the marsh due to the high salinity levels in the area. This may not always true for ditch plugs everywhere, as these results are only considering a particular salinity regime. Vegetation and elevation were also surveyed in order to get a baseline for potential future studies

An example of accelerated changes in current and future ecosystem trajectories: Unexpected rapid transitions in salt marsh vegetation forced by sea level rise

Accelerated sea level rise has forced greater changes in the vegetation of Great Sippewissett Marsh during the recent few years than were recorded in the previous half century. Even with conservative estimates of sea level rise, accretion in the salt marsh platform would be insufficient to match submergence, but in addition, a new set of cascading changes seem to be accelerating the transformation of the Great Sippewissett Marsh vegetation mosaic, including conversion of cover by short to taller Spartina alterniflora, leading to lowering below-ground biomass and weakening of sediment columns, while the greater above-ground biomass increases wrack that strands and smothers high marsh vegetation. In addition, a salt-tolerant variant of Phragmites australis has begun to aggressively invade upper elevations of Great Sippewissett Marsh, replacing high marsh species cover, as well as dominating adjoining low-lying areas that might have allowed salt marsh landward migration as sea level effects increase. In many parts of Great Sippewissett Marsh, area of high marsh is steadily diminishing, taller S. alterniflora has extended upwards in areas previously supporting high marsh species, but its landward progress is now impeded by competition and shading by the phalanx of P. australis that has extended down-slope. The vegetation gradient in Great Sippewissett Marsh—and other salt marshes—is in rapid transition, and its decadal future seems in doubt

Salt marsh sediments act as sinks for microplastics and reveal effects of current and historical land use changes

Microplastic particles are widespread in marine sediments and the abundance of the different types of particles vary widely. In this paper we demonstrate that salt marshes effectively capture microplastics in their sediments, and that microplastic accumulations increase with the level of urbanization of the land surrounding estuarine areas. We extracted microplastics from sediment cores in salt marshes of SE New England estuaries at different degrees of urbanization and land use intensity. Microplastics were present everywhere, but their abundances increased markedly with the degree of urbanization of the land. Microplastic fragment counts were linked to nearby urbanization and their abundances seemed to be linked to more local, within-watershed inputs. The number of fibers was similar across all sites suggesting that fiber accumulation in these sediments is likely influenced by effective long-distance transport from large-scale areas. The sedimentary record confirmed that microplastics have been accumulating in these estuaries since the early 1950s, and their abundances have increased greatly in more recent years in response to the progressive urbanization of the watersheds and intensification of land uses. Our results highlight the role of salt marsh sediments as sinks for microplastics in the marine environment