QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe

Land-use intensity increases benthic N₂O emissions across three sub-tropical estuaries

Estuaries play an important role in regulating nitrous oxide (N₂O) fluxes to the atmosphere, but little is known about how catchment land-use changes influence benthic N₂O cycling. We measured seasonal benthic N₂O fluxes and constructed N₂O budgets in three sub-tropical estuaries draining catchments with contrasting levels of land-use intensity. Benthic habitats were a net N₂O sink in the minimally impacted Noosa River Estuary (−287 nmol m‾² h‾¹) and a net source of N₂O in the highly impacted Brisbane River Estuary (126 nmol m‾² h‾¹). Vegetated habitats can act as an important sink of N₂O with uptakes of −286 and −35 nmol m‾² h‾¹ in the Noosa and Maroochy River Estuaries, respectively. Benthic N₂O fluxes were significantly correlated with benthic NO₃− fluxes, suggesting NO₃− availability was an important control on benthic N₂O fluxes. Combining benthic flux data with surface water N₂O emissions measurements showed that increased benthic N₂O fluxes helped drive increasing water–air N₂O emissions over the land-use intensity gradient. Overall, our results show that land-use driven changes to both the diversity and sediment composition of benthic habitats play an important role in regulating N₂O dynamics in estuarine ecosystems. This highlights that both sediment quality and nitrogen loading need to be considered in order to reduce emissions of greenhouse gases in the coastal ecosystems

Effects of free nitrous acid treatment conditions on the nitrite pathway performance in mainstream wastewater treatment

© 2018 Elsevier B.V. Inline sludge treatment using free nitrous acid (FNA) was recently shown to be effective in establishing the nitrite pathway in a biological nitrogen removal system. However, the effects of FNA treatment conditions on the nitrite pathway performance remained to be investigated. In this study, three different FNA treatment frequencies (daily sludge treatment ratios of 0.22, 0.31 and 0.38, respectively), two FNA concentrations (1.35 mgN/L and 4.23 mgN/L, respectively) and two influent feeding regimes (one- and two-step feeding) were investigated in four laboratory-scale sequencing batch reactors. The nitrite accumulation ratio was positively correlated to the FNA treatment frequency. However, when a high treatment frequency was used e.g., daily sludge treatment ratio of 0.38, a significant reduction in ammonia oxidizing bacteria (AOB) activity occurred, leading to poor ammonium oxidation. AOB were able to acclimatise to FNA concentrations up to of 4.23 mgN/L, whereas nitrite oxidizing bacteria (NOB) were limited by an FNA concentration of 1.35 mgN/L over the duration of the study (up to 120 days). This difference in sensitivity to FNA could be used to further enhance nitrite accumulation, with 90% accumulation achieved at an FNA concentration of 4.23 mgN/L and a daily sludge treatment ratio of 0.31 in this study. However, this high level of nitrite accumulation led to increased N2O emission, with emission factors of up to 3.9% observed. The N2O emission was mitigated (reduced to 1.3%) by applying two-step feeding resulting in a nitrite accumulation ratio of 45.1%. Economic analysis showed that choosing the optimal FNA treatment conditions depends on a combination of the wastewater characteristics, the nitrogen discharge standards, and the operational costs. This study provides important information for the optimisation and practical application of FNA-based sludge treatment technology for achieving the mainstream stable nitrite pathway

Seasonal and spatial controls on N₂O concentrations and emissions in low-nitrogen estuaries: Evidence from three tropical systems

Nitrous oxide (N₂O) production and emissions are observed in estuary waters, yet little is known about estuary N₂O)fluxes under low dissolved inorganic nitrogen (DIN) conditions. We present high-resolution spatial surveys of N₂O) concentrations in three low-DIN (NO₃¯ < 30 μmol L¯¹) tropical estuaries in Queensland, Australia (Johnstone River, Fitzroy River, Constant Creek), during consecutive wet and dry seasons. Constant Creek had the lowest concentrations of dissolved inorganic nitrogen (DIN; 0.01 to 5.4 μmol L¯¹ of NO₃¯ and 0.09 to 13.6 μmol L¯¹ of NH₄⁺) and N₂O)(93–132% saturation), and associated low mean N₂O) emissions (0.02–3 μmol m¯²d¯¹). The Johnstone River Estuary had the highest N₂O) concentrations (97–245% saturation), with mean emissions of 4 to 6 μmol m¯²d¯¹, driven by upstream groundwater and riverine sources. In the Fitzroy River Estuary, N₂O) concentrations (100–204% saturation) and emissions (1–2 μmol m¯²d¯¹) were associated with wastewater inputs, which had a larger effect during the dry season. Estuary freshwater flushing time was an important factor: when freshwater was relatively stagnant, in-situ N₂O) emissions were larger than riverine N₂O) inputs. Conversely, fast freshwater flushing times diminished the role of in-situ emissions, and dissolved N₂O)largely flushed through the estuary directly to the ocean. Overall N₂O) emissions from the three tropical estuaries were low compared to previous studies, but were reasonably predicted by DIN concentrations: at low water column NO₃¯ concentrations (i.e. <5 μmol L¯¹ ) estuaries can exhibit negative water-air N₂O) fluxes

Estuaries as sources and sinks of N₂O across a land use gradient in subtropical Australia

Intensifying agricultural production and coastal urbanization are increasing nitrogen (N) loads to estuaries, potentially increasing emissions of the greenhouse gas nitrous oxide (N₂O). Here we present a first assessment of how changes in land use intensity affect estuarine N₂O fluxes. We measured N₂O concentrations over marine-freshwater transects in the wet and dry seasons in eight subtropical estuaries selected for differences in land use intensity. Daily estuary N loads ranged from 0.5 ± 0.4 kg N km¯² d¯¹ (minimally impacted) to 51 ± 30 kg N km¯² d¯¹ (highly impacted), corresponding to higher concentrations of all inorganic N species (nitrate, ammonium, and N₂O) in the highly impacted estuaries. Net N₂O fluxes from the eight estuaries ranged from −20 μg N₂O-N km¯² d¯¹ (sink) to +300 μg N₂O-N km¯² d¯¹(source). However, neither N concentrations nor N loads explained the variations in N₂O fluxes. Instead, seasonal differences in freshwater flushing times increased either N₂O uptake (minimally impacted systems) or N₂O efflux (moderately impacted systems) relative to N load. The lack of relationship between freshwater flushing times (kinetics) and N₂O fluxes from the highly impacted estuaries, combined with evidence for both low carbon quality and phosphorous limitation in those systems, suggests that N₂O emissions from highly impacted estuaries were controlled by stoichiometry rather than kinetics. This study shows that estuaries can shift from net sinks to sources of N₂O as land use intensity increases but that the magnitude of this switch cannot be predicted based on N loads alone

Land-use intensity alters both the source and fate of CO₂ within eight sub-tropical estuaries

Combined pressures from inland agricultural intensification and coastal development are dramatically altering estuaries’ structure and function. Despite the established global significance of estuarine carbon (C) cycling, the impact of growing anthropogenic stress on coastal C inputs and exports is unclear. To address this gap, we evaluated the magnitude and drivers of estuary C fluxes in eight sub-tropical estuaries at Low (n = 3), Moderate (n = 2), and High (n = 3) levels of nutrient enrichment. We measured changes in the concentration and isotopic composition (δ¹³C) of the major C pools (organic and inorganic) and gaseous product of C turnover (CO₂) over wet and dry seasons. Over both sampling periods estuaries classified Moderate and High emitted far more CO₂ (37 ± 10 mmol m¯² d¯¹) than those classified Low (6.3 ± 4 mmol m¯² d¯¹). However, estuaries with both high nutrients and high turbidity produced less CO₂, and thus exported more DIC, than expected from hydrodynamics (freshwater flushing time). Differences in estuary phytoplankton biomass (Chla concentrations) corresponded with differences in the biological CO₂ production (respiration) rates estimated from δ¹³C-DIC variations, although respiration rates were higher than predicted based on hydrodynamics (surface area/discharge) in high nutrient, low turbidity systems. Together these findings demonstrate that land-use intensification can alter both the source and the production of estuary CO₂, and suggest that the direction of this shift can depend on ancillary factors like turbidity as well as nutrient enrichment. Evidence that human alterations to coastal ecosystems can shift the balance between DIC downstream export and CO₂ emissions outside of the range predicted by hydrodynamic factors like residence time, surface area, and discharge has implications for global C models