Groundwater and Porewater as Major Sources of Alkalinity to a Fringing Coral Reef Lagoon (Muri Lagoon, Cook Islands)

To better predict how ocean acidification will affect coral reefs, it is important to understand how biogeochemical cycles on reefs alter carbonate chemistry over various temporal and spatial scales. This study quantifies the contribution of shallow porewater exchange (as quantified from advective chamber incubations) and fresh groundwater discharge (as traced by 222Rn) to total alkalinity (TA) dynamics on a fringing coral reef lagoon along the southern Pacific island of Rarotonga over a tidal and diel cycle. Benthic alkalinity fluxes were affected by the advective circulation of water through permeable sediments, with net daily flux rates of carbonate alkalinity ranging from −1.55 to 7.76 mmol m−2 d−1, depending on the advection rate. Submarine groundwater discharge (SGD) was a source of TA to the lagoon, with the highest flux rates measured at low tide, and an average daily TA flux of 1080 mmol m−2 d−1 at the sampling site. Both sources of TA were important on a reef-wide basis, although SGD acted solely as a delivery mechanism of TA to the lagoon, while porewater advection was either a sink or source of TA dependent on the time of day. This study describes overlooked sources of TA to coral reef ecosystems that can potentially alter water column carbonate chemistry. We suggest that porewater and groundwater fluxes of TA should be taken into account in ocean acidification models in order to properly address changing carbonate chemistry within coral reef ecosystems

Drivers of pCO2 Variability in Two Contrasting Coral Reef Lagoons: The Influence of Submarine Groundwater Discharge

The impact of groundwater on pCO2 variability was assessed in two coral reef lagoons with distinct drivers of submarine groundwater discharge (SGD). Diel variability of pCO2 in the two ecosystems was explained by a combination of biological drivers and SGD inputs. In Rarotonga, a South Pacific volcanic island, 222Rn‐derived SGD was driven primarily by a steep terrestrial hydraulic gradient, and the water column was influenced by the high pCO2 (5501 µatm) of the fresh groundwater. In Heron Island, a Great Barrier Reef coral cay, SGD was dominated by seawater recirculation through the sediments (i.e., tidal pumping), and pCO2 was mainly impacted through the stimulation of biological processes. The Rarotonga water column had a higher average pCO2 (549 µatm) than Heron Island (471 µatm). However, pCO2 exhibited a greater diel range in Heron Island (778 µatm) than in Rarotonga (507 µatm). The Rarotonga water column received 29.0 ± 8.2 mmol free‐CO2 m−2 d−1 from SGD, while the Heron Island water column received 12.1 ± 4.2 mmol free‐CO2 m−2 d−1. Over the course of this study, both systems were sources of CO2 to the atmosphere with SGD‐derived free‐CO2 most likely contributing a large portion to the air‐sea CO2 flux. Studies measuring the carbon chemistry of coral reefs (e.g., metabolism and calcification rates) may need to consider the effects of groundwater inputs on water column carbonate chemistry. Local drivers of coral reef carbonate chemistry such as SGD may offer more approachable management solutions to mitigating the effects of ocean acidification on coral reefs

Drivers of pCO2 Variability in Two Contrasting Coral Reef Lagoons: The Influence of Submarine Groundwater Discharge

The impact of groundwater on pCO2 variability was assessed in two coral reef lagoons with distinct drivers of submarine groundwater discharge (SGD). Diel variability of pCO2 in the two ecosystems was explained by a combination of biological drivers and SGD inputs. In Rarotonga, a South Pacific volcanic island, 222Rn‐derived SGD was driven primarily by a steep terrestrial hydraulic gradient, and the water column was influenced by the high pCO2 (5501 µatm) of the fresh groundwater. In Heron Island, a Great Barrier Reef coral cay, SGD was dominated by seawater recirculation through the sediments (i.e., tidal pumping), and pCO2 was mainly impacted through the stimulation of biological processes. The Rarotonga water column had a higher average pCO2 (549 µatm) than Heron Island (471 µatm). However, pCO2 exhibited a greater diel range in Heron Island (778 µatm) than in Rarotonga (507 µatm). The Rarotonga water column received 29.0 ± 8.2 mmol free‐CO2 m−2 d−1 from SGD, while the Heron Island water column received 12.1 ± 4.2 mmol free‐CO2 m−2 d−1. Over the course of this study, both systems were sources of CO2 to the atmosphere with SGD‐derived free‐CO2 most likely contributing a large portion to the air‐sea CO2 flux. Studies measuring the carbon chemistry of coral reefs (e.g., metabolism and calcification rates) may need to consider the effects of groundwater inputs on water column carbonate chemistry. Local drivers of coral reef carbonate chemistry such as SGD may offer more approachable management solutions to mitigating the effects of ocean acidification on coral reefs

The genomes of two key bumblebee species with primitive eusocial organization

Background: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. Results: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. Conclusions: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation

The neutron and its role in cosmology and particle physics

Experiments with cold and ultracold neutrons have reached a level of precision such that problems far beyond the scale of the present Standard Model of particle physics become accessible to experimental investigation. Due to the close links between particle physics and cosmology, these studies also permit a deep look into the very first instances of our universe. First addressed in this article, both in theory and experiment, is the problem of baryogenesis ... The question how baryogenesis could have happened is open to experimental tests, and it turns out that this problem can be curbed by the very stringent limits on an electric dipole moment of the neutron, a quantity that also has deep implications for particle physics. Then we discuss the recent spectacular observation of neutron quantization in the earth's gravitational field and of resonance transitions between such gravitational energy states. These measurements, together with new evaluations of neutron scattering data, set new constraints on deviations from Newton's gravitational law at the picometer scale. Such deviations are predicted in modern theories with extra-dimensions that propose unification of the Planck scale with the scale of the Standard Model ... Another main topic is the weak-interaction parameters in various fields of physics and astrophysics that must all be derived from measured neutron decay data. Up to now, about 10 different neutron decay observables have been measured, much more than needed in the electroweak Standard Model. This allows various precise tests for new physics beyond the Standard Model, competing with or surpassing similar tests at high-energy. The review ends with a discussion of neutron and nuclear data required in the synthesis of the elements during the "first three minutes" and later on in stellar nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic

The contribution of anammox and denitrification to sediment N\u3csub\u3e2\u3c/sub\u3e production in a surface flow constructed wetland

This study used anaerobic slurry assays and intact core incubations to quantify potential rates of anammox (anaerobic ammonia oxidation) in sediments along the flow path of a surface flow constructed wetland receiving secondary treated sewage effluent. Anammox occurred at two of the four sites assayed with a maximum rate of 199.4 ± 18.7 μmol N·m -2·hr-1 (24% of total N2 production) at the discharge end of the wetland. Denitrification was the major producer of N2, with a maximum rate of 965.3 ± 122.8 μmol N\u3c·m-2.hr-1 at site 2. Oxygen was probably the key regulator of anammox activity within the studied CW. In addition to anammox, we found evidence that nitrifier-denitrification was potentially responsible for the production of N2O. Total production of N2O was 15.1% of the total gaseous N produced. Limitations to the methodology for quantifying anammox in CW\u27s are outlined. This study demonstrated that denitrification is not the only pathway for gaseous production in constructed wetlands and that wetlands may be significant sources of greenhouse gases such as N2O

Temporal and spatial variability in the cycling of nitrogen within a constructed wetland: a whole-system stable-isotope-addition experiment

Constructed wetlands attenuate effluent nutrients, are hydrodynamically well defined, and are a useful proxy for the study of nitrogen (N) transformation in eutrophic natural systems. A whole-system stable-isotope addition was undertaken to describe the N cycling within a constructed wetland. Addition of 15NH4+ and particulate organic 15N (PO15N) and a conservative tracer (Li+) revealed that, initially, sedimentation of PO15N and assimilatory uptake of 15NH/ near the wetland inlet removed most of the added 15N. Denitrification Of NO3- dominated inorganic N dynamics and was higher upstream than downstream owing to the greater availability of NO5- upstream. More NH 4- was mineralized upstream where PON settlement was highest, and settled PON started being mineralized within 14 d. Nitrification was insignificant upstream but was an important process in the downstream region of the wetland in spite of low oxygen concentration. In the medium term (2-8 weeks), the PO15N initially removed to the sediments continued to be mineralized, releasing 15NH/ back to the water column. Remineralized 15N spiraled through sediment and then macrophyte pools. A dry-out period resulted in a minor washout of N during the subsequent inundation. After 157 d, 30.8% ± 7.3% of the added 15N was still in sediments, 7.4% ± 3.8% was in plants, 40.8% ± 8.3% had been lost most likely as 15N2, and the remainder had been released in the wetland outlet water. Internal recycling retards the flow of N through wetlands, and shortterm retention leads to eventual enhanced removal through denitrification

Dinitrogen (N2) fixation rates in a subtropical seagrass meadow measured with a direct 15N-N2 tracer method

This study used a direct 15N stable isotope labelling technique to measure rates of dinitrogen (N2) fixation within above- and belowground loci of a subtropical seagrass meadow (Zostera muelleri). The total rate of N2 fixation (i.e. sum of the above- and belowground rates) was ~38 µmol N2 m-2 h-1, similar to other rates measured in subtropical systems. Rates of N2 fixation were higher when the 15N-N2 label was added to the surface water compared to when it was added to the sediments. Furthermore, the lowest rates of N2 fixation were observed in the root/rhizome material regardless of whether the 15N-N2 label was added directly to the rhizosphere (0.12 µmol N2 m-2 h-1) or the overlying water column (7.3 µmol N2 m-2 h-1). These results suggest that there was active transport of fixed N from the leaves to the roots of the seagrass plants, in contrast to other studies in which N2 fixation was more active in the rhizosphere. Our study demonstrates the utility of the direct 15N-N2 tracer approach for quantifying the spatial heterogeneity of N2fixation in complex seagrass environments

Corrigendum to Inorganic nitrogen transformations within permeable carbonate sands [Continental Shelf Research, vol. 77, doi:10.1016/j.csr.2014.02.002]

Corrections: In this article the transformation of nitrogen within permeable carbonate sands is examined. Part of the study involved the addition of coral spawn material to a series of flow through reactor columns. The authors wish to correct the amount and nature of coral spawn material added to the columns. In the original manuscript the amount of carbon and nitrogen added as coral spawn material was quoted as 20 and 4 µmol respectively, giving a C:N ratio of 5. However, the amount of carbon and nitrogen added as coral spawn was 20.4 and 1.4 µmol respectively, giving a molar C:N ratio of 14.6

Nitrous oxide fluxes in estuarine environments: response to global change

Nitrous oxide is a powerful, long-lived greenhouse gas, but we know little about the role of estuarine areas in the global N2O budget. This review summarizes 56 studies of N2O fluxes and associated biogeochemical controlling factors in estuarine open waters, salt marshes, mangroves, and intertidal sediments. The majority of in situ N2O production occurs as a result of sediment denitrification, although the water column contributes N2O through nitrification in suspended particles. The most important factors controlling N2O fluxes seem to be dissolved inorganic nitrogen (DIN) and oxygen availability, which in turn are affected by tidal cycles, groundwater inputs, and macrophyte density. The heterogeneity of coastal environments leads to a high variability in observations, but on average estuarine open water, intertidal and vegetated environments are sites of a small positive N2O flux to the atmosphere (range 0.15–0.91; median 0.31; Tg N2O-N yr−1). Global changes in macrophyte distribution and anthropogenic nitrogen loading are expected to increase N2O emissions from estuaries. We estimate that a doubling of current median NO3− concentrations would increase the global estuary water–air N2O flux by about 0.45 Tg N2O-N yr−1 or about 190%. A loss of 50% of mangrove habitat, being converted to unvegetated intertidal area, would result in a net decrease in N2O emissions of 0.002 Tg N2O-N yr−1. In contrast, conversion of 50% of salt marsh to unvegetated area would result in a net increase of 0.001 Tg N2O-N yr−1. Decreased oxygen concentrations may inhibit production of N2O by nitrification; however, sediment denitrification and the associated ratio of N2O:N2 is expected to increase