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1. Effects of external recirculation on a two‐stage mainstream anaerobic‐anammox treatment system

   https://doi.org/10.1002/wer.1019  

   Li, Xiaojin ; He, Zhen ( February 2019 , Water Environment Research)

   Nitritation‐anammox treatment can be a potentially energy‐ and resource‐efficient technology for treating mainstream wastewater. However, the issue of nitrate residue from anammox treatment remains to be addressed. Herein, external recirculation of the anammox effluent to a hybrid anaerobic reactor (HAR), which was also to provide a continuous flow with lowCOD/N for the nitritation‐anammox reactor, was employed to decrease the residue compounds. The recirculation ratio of 50% was observed to be the optimal to achieve the best overall performance with potential savings in energy demand. Specifically, in the operation scenario ofR = 50%, the highestCODremoval of ~90% by theHARwas achieved. Meanwhile, the lowestCOD/NH₄⁺‐N ratio of ~2.0 in theHAReffluent ensured the lowest observedNO₃⁻‐N/NH₄⁺‐N ratio of ~14% in the nitritation‐anammox reactor. These results have demonstrated the feasibility of applying external recirculation for nitrate residue removalviadenitrification in the anaerobic pretreatment stage.

   Nitritation‐anammox treatment is an attractive method for mainstream wastewater treatment.

   Nitrate residue from anammox processes contributes to total nitrogen in the final effluent.

   Recirculation of anammox effluent to an anaerobic reactor can decrease nitrate residue.

   A recirculation ratio of 50% results in a low COD/NH₄⁺ratio of 2 that benefits the subsequent anammox.

    

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2. Estimating the effects of non‐native species on nutrient recycling using species‐specific and general allometric models

   https://doi.org/10.1111/fwb.13092  

   Fritschie, Keith J. ; Olden, Julian D. ( February 2018 , Freshwater Biology)

   Non‐native species are now common in community assemblages, but the influence of multiple introductions on ecosystem functioning remains poorly understood. In highly invaded systems, one promising approach is to use functional traits to scale measured individuals’ effects on ecosystem function up to the community level. This approach assumes that functional traits provide a common currency among species to relate individuals to ecosystem functioning.

   The goals of this study were to (i) test whether the relationship between body size and ecosystem functioning (per capita nutrient recycling) was best described by general or species‐specific scaling models; (ii) relate community structure (total biomass, average body size, non‐native dominance) to aggregated, community‐level nutrient recycling rates and ratios; and (iii) determine whether conclusions regarding the relationships between community structure and aggregate ecosystem functioning differed between species‐specific and general scaling approaches.

   By combining experimental incubations and field surveys, we compare consumer‐mediated nutrient recycling of fish communities along a non‐native dominance gradient in the Verde River watershed of central Arizona,USA. Data from ˜340 field‐sampled freshwater fish demonstrated support for general allometric relationships predicted by the metabolic theory of ecology (NH₄‐N scaling coefficient = 0.72 [0.64–0.80];PO₄‐P = 0.67 [0.47–0.86]). However, the best‐fit models for N and P included species‐specific random effects for both allometric slopes and intercepts.

   According to species‐specific models, stream fish communities recycled 1–12 mmolNH₄‐N/hr (median = 2.8 mmol/hr) and 0.02–0.74 mmolPO₄‐P/hr (median = 0.07 mmol/hr) at N:P ratios between 13.3 and 83.5 (median = 28.8). General models generated similar estimates forNH₄‐N recycling but less accurate estimates forPO₄‐P. Stochastic simulations that incorporated error around allometric parameter estimates led to qualitatively similar but larger differences between general and species‐specific results.

   Community structure influenced aggregate nutrient recycling, but specific conclusions depended on the scaling approach. Total biomass explained much of the among‐community variation in aggregateNH₄‐N andPO₄‐P for both model types, whereas non‐native dominance alone best predicted variation in aggregate N:P. Surprisingly, species‐specific and general models both reached significant yet quantitatively opposing conclusions regarding the relationship between N:P supply and non‐native dominance.

   Study results indicate that shifting fish community structure can substantially alter ecosystem functioning in this river system. However, some inferred relationships between community structure and aggregate nutrient recycling varied depending on whether general or species‐specific scaling approaches were taken. Although trait‐based approaches to link environmental change, community structure and ecosystem function hold much promise, it will be important to consider when species‐specific versus general models are necessary to scale from individuals to ecosystems.

    

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3. Higher fat stores contribute to persistence of little brown bat populations with white‐nose syndrome

   https://doi.org/10.1111/1365-2656.12954  

   Cheng, Tina L. ; Gerson, Alexander ; Moore, Marianne S. ; Reichard, Jonathan D. ; DeSimone, Joely ; Willis, Craig K. R. ; Frick, Winifred F. ; Kilpatrick, Auston Marm ; Tate, ed., Ann ( February 2019 , Journal of Animal Ecology)

   The persistence of populations declining from novel stressors depends, in part, on their ability to respond by trait change via evolution or plasticity. White‐nose syndrome (WNS) has caused rapid declines in several North America bat species by disrupting hibernation behaviour, leading to body fat depletion and starvation. However, some populations ofMyotis lucifugusnow persist withWNSby unknown mechanisms.

   We examined whether persistence ofM. lucifiguswithWNScould be explained by increased body fat in early winter, which would allow bats to tolerate the increased energetic costs associated withWNS. We also investigated whether bats were escaping infection or resistant to infection as an alternative mechanism explaining persistence.

   We measured body fat in early and late winter during initialWNSinvasion and 8 years later at six sites where bats are now persisting. We also measured infection prevalence and intensity in persisting populations.

   Infection prevalence was not significantly lower than observed in declining populations. However, at two sites, infection loads were lower than observed in declining populations. Body fat in early winter was significantly higher in four of the six persisting populations than duringWNSinvasion.

   Physiological models of energy use indicated that these higher fat stores could reduceWNSmortality by 58%–70%. These results suggest that differences in fat storage and infection dynamics have reduced the impacts ofWNSin many populations. Increases in body fat provide a potential mechanism for management intervention to help conserve bat populations.

    

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4. Matrix methods for stochastic dynamic programming in ecology and evolutionary biology

   https://doi.org/10.1111/2041-210X.13291  

   Reimer, Jody R. ; Mangel, Marc ; Derocher, Andrew E. ; Lewis, Mark A. ; Ergon, ed., Torbjørn ( September 2019 , Methods in Ecology and Evolution)

   Organisms are constantly making tradeoffs. These tradeoffs may be behavioural (e.g. whether to focus on foraging or predator avoidance) or physiological (e.g. whether to allocate energy to reproduction or growth). Similarly, wildlife and fishery managers must make tradeoffs while striving for conservation or economic goals (e.g. costs vs. rewards). Stochastic dynamic programming (SDP) provides a powerful and flexible framework within which to explore these tradeoffs. A rich body of mathematical results on SDP exist but have received little attention in ecology and evolution.

   Using directed graphs – an intuitive visual model representation – we reformulated SDP models into matrix form. We synthesized relevant existing theoretical results which we then applied to two canonical SDP models in ecology and evolution. We applied these matrix methods to a simple illustrative patch choice example and an existing SDP model of parasitoid wasp behaviour.

   The proposed analytical matrix methods provide the same results as standard numerical methods as well as additional insights into the nature and quantity of other, nearly optimal, strategies, which we may also expect to observe in nature. The mathematical results highlighted in this work also explain qualitative aspects of model convergence. An added benefit of the proposed matrix notation is the resulting ease of implementation of Markov chain analysis (an exact solution for the realized states of an individual) rather than Monte Carlo simulations (the standard, approximate method). It also provides an independent validation method for other numerical methods, even in applications focused on short‐term, non‐stationary dynamics.

   These methods are useful for obtaining, interpreting, and further analysing model convergence to the optimal time‐independent (i.e. stationary) decisions predicted by an SDP model. SDP is a powerful tool both for theoretical and applied ecology, and an understanding of the mathematical structure underlying SDP models can increase our ability to apply and interpret these models.

    

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5. Multireference exciplex binding energies: Basis set convergence and error

   https://doi.org/10.1002/qua.25819  

   Krueger, Rachel A. ; Blanquart, Guillaume ( October 2018 , International Journal of Quantum Chemistry)

   In multichromophore systems, characterization of electronic structure requires characterization of exciplexes, electron‐hole pairs delocalized over multiple molecules. Computing exciplex binding energy requires an accurate description of both the noncovalent interactions between the chromophores and their excited electronic states. The critical role of basis set selection for accurate description of noncovalent interactions is well known, but for some of the most accurate excited‐state methods, basis set dependence is incompletely understood. In this work, the impact of basis set size and diffuseness on CASSCF/NEVPT2 binding energies is determined for three systems in their lowest singlet excited states: the benzene excimer, thecis‐butadiene‐benzene exciplex, and the benzene‐naphthalene exciplex. We demonstrate that excellent CBS binding energies may be obtained using the moderately‐sized jun‐cc‐pV(D + d)Z and jun‐cc‐pV(T + d)Z basis sets and a simpleN⁻³model. Repeating this procedure with theN = 3, 4basis sets from the most diffuse basis set family applied to each system yields a binding energy of 56.6 ± 1.2 kJ/mol for the benzene excimer and binding energies of 11.1 ± 0.5 kJ/mol and 19.2 ± 1.7 kJ/mol for thecis‐butadiene‐benzene exciplex and the benzene‐naphthalene exciplex, respectively.

    

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