Search

Elevated phosphorus (P) loading from the watersheds draining into Lake Erie, particularly from agricultural (53%) and urban (43%) sources, is identified as one of the main drivers of the severe eutrophication. In this study, we present a comprehensive evaluation of 11 process-based models to characterize the water cycle as well as nutrient fate and transport within a watershed context, and to find a robust and replicable way to optimize the modelling strategy for the Lake Erie watershed. Our primary objective is to review the conceptual/technical strengths and weaknesses of the individual models for reproducing surface runoff, groundwater, sediment transport, nutrient cycling, and channel routing, and to collectively guidethe management of theLakeErieBasin. Our analysis suggested that the availablemodels either opted for simpler approximations of the multifaceted, nonlinear dynamics of nutrient fate and transport, and instead placed more emphasis on the advanced representation of the water cycle or, introduced a greater degree of biogeochemical complexity but simplified their strategies to recreate the roles of critical hydrological processes. Notwithstanding its overparameterization problem, the MIKE SHE model provides the most comprehensive 3D representation of the interplay between surface and subsurface hydrological processes with a fully dynamic description, whereby we can recreate the solute transport that infiltrates from the surface to the unsaturated soil layer and subsequently percolates into the saturated layer. Likewise, the physically based submodels designed to represent the sediment detachment and erosion/removal processes (DWSM, HBV-INCA, HSPF, HYPE, and MIKE SHE), offer a distinct alternative to USLE-type empirical strategies. The ability to explicitly simulate the daily plant growth (SWAT and APEX) coupled with a dynamic representation of soil P processes can be critical when evaluating the long-term watershed responses to various agricultural management strategies. Drawing parallels with the (sub)surface and sediment erosion processes, a more complicated physically based approach, e.g., the dynamic wave model provided by MIKE SHE (coupled with MIKE URBAN or MIKE HYDRO) and SWMM may be more appropriate for realistically simulating the pressurized flow and backwater effects of water routing in both open channels and closed pipes. While our propositions seem to favor the consideration of complex models that may lack the commensurate knowledge to properly characterize the underlying processes, we contend this issue can be counterbalanced by the joint consideration of simpler empirical models under an ensemble framework, which can both constrain the plausible values of individual processes and validate macroscale patterns. Finally, our study discusses critical facets of the watershed modelling work in Lake Erie, such as the role of legacy P, the challenges in reproducing spring-freshet or event-flow conditions, and the dynamic characterization of water/nutrient cycles under the nonstationarity of a changing climate. Key words: best management practices, model ensemble, uncertainty analysis, adaptive management implementation, Lake Erie. La charge elevee de phosphore (P) provenant des bassins versants qui se deversent dans le lac Erie, en particulier du bassin versant de la riviere Maumee a predominance agricole, est identifiee comme l'un des principaux facteurs de gravite de l'eutrophisation. Dans cette etude, les auteurs presentent une evaluation complete de onze modeles fondes sur les processus pour caracteriser le cycle de l'eau, le devenir et le transport des nutriments dans un contexte de bassin versant, et pour trouver une facon robuste et reproductible d'optimiser la strategie de modelisation pour le bassin versant du lac Erie. Leur objectif principal consiste a examiner les forces et les faiblesses conceptuelles ou techniques des differents modeles pour reproduire le ruissellement de surface, les eaux souterraines, le transport des sediments, le cycle des nutriments, le trace des canaux et pour guider collectivement la mise en ceuvre de la gestion adaptative dans le lac Erie. Leur analyse suggere que les modeles disponibles ont soit opte pour des approximations plus simples de la dynamique complexe et non lineaire du devenir et du transport des nutriments et ont plutot mis l'accent sur la representation avancee du cycle de l'eau, soit introduit un plus grand degre de complexite biogeochimique, mais ont simplifie leurs strategies pour recreer le role des processus hydrologiques critiques. En depit de son probleme de surparametrage, MIKE SHE fournit la representation 3D la plus complete de l'interaction entre les processus hydrologiques de surface et de sous-surface avec une description pleinement dynamique, par laquelle il est possible de recreer le transport d'un solute qui s'infiltre de la surface a la couche de sol non saturee et percole ensuite dans la couche saturee. De meme, les sous-modeles fondes sur la physique concus pour representer le detachement des sediments et les processus d'erosion/ablation (DWSM, HBV-INCA, HSPF, HYPE et MIKE SHE) offrent une option distincte aux strategies empiriques de type USLE. La capacite de simuler explicitement la croissance quotidienne des plantes (SWAT et APEX) couplee a une representation dynamique des processus de P du sol peut etre critique lors de l'evaluation des reponses a long terme des bassins versants a diverses strategies de gestion agricole. En etablissant un parallele avec les processus d'erosion (sub)surface et sedimentaire, une approche physique plus complexe, par exemple le modele dynamique de vagues fourni par MIKE SHE (couple a MIKE URBAN ou MIKE HYDRO) et SWMM, peut etre plus appropriee pour simuler de maniere realiste les effets de l'ecoulement sous pression et du reflux de l'eau dans les canaux ouverts et les conduites fermees. Alors que leurs propositions semblent favoriser la prise en compte de modeles complexes qui peuvent manquer de connaissances adequates pour caracteriser correctement les processus sous-jacents, ils soutiennent que ce probleme peut etre contrebalance par la prise en compte conjointe de modeles empiriques plus simples, dans un cadre d'ensemble, qui peuvent a la fois contraindre les valeurs plausibles des processus individuels et valider les modeles a grande echelle. Enfin, cette etude aborde des aspects critiques du travail de modelisation des bassins versants du lac Erie, tels que le role du phosphore residuel, les difficultes a reproduire les conditions de crue printaniere ou d'ecoulement, et la caracterisation dynamique des cycles de l'eau et des nutriments dans le contexte de non-stationnarite d'un climat changeant. [Traduit par la Redaction] Mots-cles : meilleures pratiques de gestion, ensemble de modeles, analyse d'incertitude, mise en ceuvre de la gestion adaptative, lac Erie., Introduction Lake Erie, the shallowest of the Great Lakes, has been the most severely impacted by eutrophication-related issues, including excessive harmful algal blooms (HABs) (Stumpf et al. 2012; Bertani et [...]

Glucose is the most efficient energy source, and various cancer cells depend on glycolysis for energy production. For maintenance of survival and proliferation, glucose sensing and adaptation to poor nutritional circumstances must be well organized in cancer cells. While the glucose sensing machinery has been well studied in yeasts, the molecular mechanism of glucose sensing in mammalian cells remains to be elucidated. We have reported glucose deprivation rapidly induces AKT phosphorylation through PI3K activation. We assumed that regulation of AKT is relevant to glucose sensing and further investigated the underlying mechanisms. In this study, AKT phosphorylation under glucose deprivation was inhibited by galactose and fructose, but induced by 2-deoxyglucose (2-DG). Both 2-DG treatment and glucose deprivation were found to induce AKT phosphorylation in HepG2 cells. These findings suggested that glucose transporter may not be involved in the sensing of glucose and induction of AKT phosphorylation, and that downstream metabolic events may have important roles. A variety of metabolic stresses reportedly induce the production of reactive oxygen species (ROS). In the present study, glucose deprivation was found to induce intracellular hydrogen peroxide (H2O2) production in HepG2 cells. N-acetylcysteine (NAC), an antioxidant reagent, reduced both the increase in cellular H2O2 levels and AKT phosphorylation induced by glucose deprivation. These results strongly suggest that the glucose deprivation-induced increase of H2O2 in the cells mediated the AKT phosphorylation. RNA interference of NOX4, but not of NOX5, completely suppressed the glucose deprivation-induced AKT phosphorylation as well as increase of the intracellular levels of ROS, whereas exogenous H2O2 could still induce AKT phosphorylation in the NOX4-knockdown cells. In this study, we demonstrated that the ROS generated by NOX4 are involved in the intracellular adaptive responses by recognizing metabolic flux. [ABSTRACT FROM AUTHOR]