Extreme enrichment in atmospheric 15N15N.

Molecular nitrogen (N2) comprises three-quarters of Earth's atmosphere and significant portions of other planetary atmospheres. We report a 19 per mil (‰) excess of 15N15N in air relative to a random distribution of nitrogen isotopes, an enrichment that is 10 times larger than what isotopic equilibration in the atmosphere allows. Biological experiments show that the main sources and sinks of N2 yield much smaller proportions of 15N15N in N2. Electrical discharge experiments, however, establish 15N15N excesses of up to +23‰. We argue that 15N15N accumulates in the atmosphere because of gas-phase chemistry in the thermosphere (>100 km altitude) on time scales comparable to those of biological cycling. The atmospheric 15N15N excess therefore reflects a planetary-scale balance of biogeochemical and atmospheric nitrogen chemistry, one that may also exist on other planets

Thermodynamic Constraints on Nitrogen Transformations and Other Biogeochemical Processes at Soil-Stream Interfaces

There is much interest in biogeochemical processes that occur at the interface between soils and streams since, at the scale of landscapes, these habitats may function as control points for fluxes of nitrogen (N) and other nutrients from terrestrial to aquatic ecosystems. Here we examine whether a thermodynamic perspective can enhance our mechanistic and predictive understanding of the biogeochemical function of soil-stream interfaces, by considering how microbial communities interact with variations in supplies of electron donors and acceptors. Over a two-year period we analyzed \u3e1400 individual samples of subsurface waters from networks of sample wells in riparian wetlands along Smith Creek, a first-order stream draining a mixed forested-agricultural landscape in southwestern Michigan, USA. We focused on areas where soil water and ground water emerged into the stream, and where we could characterize subsurface flow paths by measures of hydraulic head and/or by in situ additions of hydrologic tracers. We found strong support for the idea that the biogeochemical function of soil-stream interfaces is a predictable outcome of the interaction between microbial communities and supplies of electron donors and acceptors. Variations in key electron donors and acceptors (NO3−,N2O,NH4+,SO42−,CH4 role= presentation \u3eNO3−,N2O,NH4+,SO42−,CH4 ,, and dissolved organic carbon [DOC]) closely followed predictions from thermodynamic theory. Transformations of N and other elements resulted from the response of microbial communities to two dominant hydrologic flow paths: (1) horizontal flow of shallow subsurface waters with high levels of electron donors (i.e., DOC, CH4, and NH4+),, and (2) near-stream vertical upwelling of deep subsurface waters with high levels of energetically favorable electron acceptors (i.e., NO3-,N2O, and SO42-).. Our results support the popular notion that soil-stream interfaces can possess strong potential for removing dissolved N by denitrification. Yet in contrast to prevailing ideas, we found that denitrification did not consume all NO3- that reached the soil-stream interface via subsurface flow paths. Analyses of subsurface N chemistry and natural abundances of δ 15N in NO3- and NH4+ suggested a narrow near-stream region as functionally the most important location for NO3- consumption by denitrification. This region was characterized by high throughput of terrestrially derived water, by accumulation of dissolved NO3- and N2O, and by low levels of DOC. Field experiments supported our hypothesis that the sustained ability for removal of dissolved NO3- and N2O should be limited by supplies of oxidizable carbon via shallow flowpaths. In situ additions of acetate, succinate, and propionate induced rates of NO3- removal (∼ 1.8 g N· m-2· d-1) that were orders of magnitude greater than typically reported from riparian habitats. We propose that the immediate near-stream region may be especially important for determining the landscape-level function of many riparian wetlands. Management efforts to optimize the removal of NO3- by denitrification ought to consider promoting natural inputs of oxidizable carbon to this near-stream region

Protocols for Assessing Transformation Rates of Nitrous Oxide in the Water Column

Nitrous oxide (N2O) is a potent greenhouse gas and an ozone destroying substance. Yet, clear step-by-step protocols to measure N2O transformation rates in freshwater and marine environments are still lacking, challenging inter-comparability efforts. Here we present detailed protocols currently used by leading experts in the field to measure water-column N2O production and consumption rates in both marine and other aquatic environments. We present example 15N-tracer incubation experiments in marine environments as well as templates to calculate both N2O production and consumption rates. We discuss important considerations and recommendations regarding (1) precautions to prevent oxygen (O2) contamination during low-oxygen and anoxic incubations, (2) preferred bottles and stoppers, (3) procedures for 15N-tracer addition, and (4) the choice of a fixative. We finally discuss data reporting and archiving. We expect these protocols will make 15N-labeled N2O transformation rate measurements more accessible to the wider community and facilitate future inter-comparison between different laboratories

Ratios of Community Respiration to Photosynthesis and Rates of Primary Production in Lake Erie Via Oxygen Isotope Techniques

ABSTRACT. To evaluate levels of primary production and community metabolism in Lake Eri

Hypoxia in the Northern Gulf of Mexico in 2010: was the Deepwater Horizon Oil Spill a Factor? (PowerPoint)

Environmental Economics and Policy,

Temporal and spatial variations in R:P ratios in Lake Superior, an oligotrophic freshwater environment

A study of respiration to photosynthesis (R:P) ratios in Lake Superior, based on the fraction of O2 saturation and the isotopic composition of O2, was undertaken to evaluate spatial and temporal variations in the trophic status of a large oligotrophic freshwater environment. The lake was predominantly net heterotrophic from April to October 2000 (R:P ratios: 1.2 2.5). Uniform R:P ratios of ∼1.5 with depth and across the lake in April 2000 and 2001 revealed the homogeneity of the water column during spring. A brief period of net autotrophy was observed during summer thermal stratification in 2000 and 2001, and surveys showed this condition to be prevalent and lake-wide in August 2001 (R:P ratios: 0.5-0.9). Strong net autotrophy (R:P ratios: 0.6) was found near Duluth, Minnesota, and suggested the potential for the formation of mesotrophic conditions within areas of increased nutrient loadings from urbanization. Respiration and photosynthesis were shown to exert a strong control on O2 gas exchange within Lake Superior, as evidenced by significant correlations between R:P ratios and O2 gas exchange during periods of net heterotrophy and autotrophy. This observation was unexpected since [O2] in the lake appears to be dominated by atmospheric O2 gas exchange, given that the fraction of O2 saturation is continuously near levels expected for equilibration with the atmosphere. Furthermore, the relationship between the biological and physical O 2 fluxes may enable the use of R:P ratios to calculate O2 gas exchange and ultimately estimate CO2 fluxes between lakes and the atmosphere. Copyright 2004 by the American Geophysical Union

Variation in immune-related gene expression provides evidence of local adaptation in Porites astreoides (Lamarck, 1816) between inshore and offshore meta-populations inhabiting the lower Florida Reef Tract, USA

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Haslun, J. A., Hauff-Salas, B., Strychar, K. B., Cervino, J. M., & Ostrom, N. E. Variation in immune-related gene expression provides evidence of local adaptation in Porites astreoides (Lamarck, 1816) between inshore and offshore meta-populations inhabiting the lower Florida Reef Tract, USA. Water, 13(15), (2021): 2107, https://doi.org/10.3390/w13152107.Coral communities of the Florida Reef Tract (FRT) have changed dramatically over the past 30 years. Coral cover throughout the FRT is disproportionately distributed; >70% of total coral cover is found within the inshore patch reef zone (5 km from shore). Coral mortality from disease has been differentially observed between inshore and offshore reefs along the FRT. Therefore, differences between the response of inshore and offshore coral populations to bacterial challenge may contribute to differences in coral cover. We examined immune system activation in Porites astreoides (Lamarck, 1816), a species common in both inshore and offshore reef environments in the FRT. Colonies from a representative inshore and offshore site were reciprocally transplanted and the expression of three genes monitored biannually for two years (two summer and two winter periods). Variation in the expression of eukaryotic translation initiation factor 3, subunit H (eIF3H), an indicator of cellular stress in Porites astreoides, did not follow annual patterns of seawater temperatures (SWT) indicating the contribution of other stressors (e.g., irradiance). Greater expression of tumor necrosis factor (TNF) receptor associated factor 3 (TRAF3), a signaling protein of the inflammatory response, was observed among corals transplanted to, or located within the offshore environment indicating that an increased immune response is associated with offshore coral more so than the inshore coral (p < 0.001). Corals collected from the offshore site also upregulated the expression of adenylyl cyclase associated protein 2 (ACAP2), increases which are associated with decreasing innate immune system inflammatory responses, indicating a counteractive response to increased stimulation of the innate immune system. Activation of the innate immune system is a metabolically costly survival strategy. Among the two reefs studied, the offshore population had a smaller mean colony size and decreased colony abundance compared to the inshore site. This correlation suggests that tradeoffs may exist between the activation of the innate immune system and survival and growth. Consequently, immune system activation may contribute to coral community dynamics and declines along the FRT.We thank the Annis Water Resources Institute for both a graduate fellowship and research funding associated with this project, and Grand Valley State University for a Presidential Research Grant. We thank Michigan State University RTSF and the Integrative Biology Department at Michigan State University (Graduate Fellowship), and the Coastal Preservation Network (Award 250542). We also thank Erich Bartels and the Mote Marine Tropical Research Laboratory staff for their help with field and laboratory help and Jeff Landgraf for qRT-PCR help. This work could not have been completed without the help of the staff at Florida Keys National Marine Sanctuary (FKNMS) for providing permit number FKNMS-2011-10 allowing this research to take place

Unexpectedly high degree of anammox and DNRA in seagrass sediments: description and application of a revised isotope pairing technique

Understanding the magnitude of nitrogen (N) loss and recycling pathways is crucial for coastal N management efforts. However, quantification of denitrification and anammox by a widely-used method, the isotope pairing technique, is challenged when dissimilatory NO3−reduction to NH4+ (DNRA) occurs. In this study, we describe a revised isotope pairing technique that accounts for the influence of DNRA on NO3− reduction (R-IPT-DNRA). The new calculation procedure improves on previous techniques by (1) accounting for N2O production, (2) distinguishing canonical anammox from coupled DNRA-anammox, and (3) including the production of 30N2 by anammox in the quantification of DNRA. This approach avoids the potential for substantial underestimates of anammox rates and overestimates of denitrification rates in systems where DNRA is a significant NO3− reduction pathway. We apply this technique to simultaneously quantify rates of anammox, denitrification, and DNRA in intact sediments adjacent to a seagrass bed in subtropical Australia. The effect of organic carbon lability on NO3− reduction was also addressed by adding detrital sources with differing C:N (phytoplankton- or seagrass-derived). DNRA was the predominant pathway, contributing 49–74% of total NO3− reduction (mean 0.42 µmol N m−2 h−1). In this high C:N system, DNRA outcompetes denitrification for NO3−, functioning to recycle rather than remove N. Anammox exceeded denitrification (mean 0.18 and 0.04 µmol N m−2 h−1, respectively) and accounted for 64–86% of N loss, a rare high percentage in shallow coastal environments. Owing to low denitrification activity, N2O production was ∼100-fold lower than in other coastal sediments (mean 7.7 nmol N m−2 h−1). All NO3− reduction pathways were stimulated by seagrass detritus but not by phytoplankton detritus, suggesting this microbial community is adapted to process organic matter that is typically encountered. The R-IPT-DNRA is widely applicable in other environments where the characterization of co-existing NO3− reduction pathways is desirable