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Over the past decade, neutral theory has gained attention and recognition for its capacity to explain bacterial community structure (BCS) in addition to deterministic processes. However, no clear consensus has been drawn so far on their relative importance. In a metacommunity analysis, we explored at the regional and local scale the effects of these processes on the bacterial community assembly within the water column of 49 freshwater lakes. The BCS was assessed using terminal restriction fragment length polymorphism (T-RFLP) of the 16S rRNA genes. At the regional scales, results indicated that the neutral community model well predicted the spatial community structure (R(2) mean = 76%) compared with the deterministic factors - which explained only a small fraction of the BCS total variance (less than 14%). This suggests that the bacterial compartment was notably driven by stochastic processes, through loss and gain of taxa. At the local scale, the bacterial community appeared to be spatially structured by stochastic processes (R(2) mean = 65%) and temporally governed by the water temperature, a deterministic factor, even if some bacterial taxa were driven by neutral dynamics. Therefore, at both regional and local scales the neutral community model appeared to be relevant in explaining the bacterial assemblage structure.

ABSTRACT:The suitability of a commonly used accumulation and wash-off model for continuous modelling of urban runoff contamination was evaluated based on 11-month turbidity and flow-rate records from an urban street. Calibration and uncertainty analysis were performed using a Markov Chain Monte-Carlo sampling method for both suspended solids loads (discharge rates) and concentration modelling. Selected models failed at replicating suspended solids concentration over the complete monitoring period. The studied dataset indeed suggests that the accumulation process is rather unpredictable and cannot be satisfactorily represented with usual accumulation models unless short periods are considered. Regarding suspended solid loads modelling, noticeably better performance was achieved, but similar results could as well be obtained with much simpler constant concentration models. Unless providing very accurate estimates of concentrations in runoff, accounting for their temporal variability during rain events may therefore not always be necessary for pollutant loads modelling, as loads are in fact mostly explained by runoff volumes.

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This study aims at evaluating the influence of a heavily urbanized area such as the Paris city area on receiving water contamination by bisphenol A (BPA) and alkylphenol ethoxylate by-product (APE). Firstly, concentrations in urban sources were investigated. Therefore, in addition to wastewater treatment plant effluents commonly studied, wet-weather urban sources including combined sewer overflows, urban runoff and total atmospheric fallout were considered. The first results highlight significant contaminations of all urban sources (from few ng/L in atmospheric fallout to several µg/L in other sources) with clearly distinguishable distribution patterns.Secondly, the concentration changes along the Seine River from upstream to downstream of Paris conurbation were investigated. While concentrations of BPA and nonylphenoxy acetic acid (NP1EC) significantly increase because of urban sources, 4-nonylphenol concentrations are homogeneous along the Seine River. These results suggest a global dissemination of 4-nonylphenol at the scale of the Seine River basin. Finally, the relationship between pollutant concentrations and Seine river flow were studied upstream and downstream of the Parisian conurbation. As a result, the clear decrease of NP1EC dissolved concentrations according to Seine River flow underlines the influence of punctual urban pollution on Seine River contamination.Conversely, 4-nonylphenol dissolved concentrations reinforce the hypothesis of its widespread at the scale of the Seine River basin. Keywords: Nonylphenol, bisphenol A, urban sources, Seine River, atmospheric fallout, heavily urbanized area 2 IntroductionAmong the pollutants commonly pointed out in the literature for their endocrine disrupting properties, alkylphenol ethoxylates (APE) and the 2,2-(4,4 hydroxydiphenyl) propane commonly named bisphenol A (BPA) deserve special attention because of their global spread in the environment (Staples et al. 1998; Vethaak et al. 2005). APE, mainly composed of nonylphenol ethoxylate (NPE: 80%) and octylphenol ethoxylate (OPE: 20%), are widely used for industrial and domestic applications, such as lubricating, oil additives, detergents and antistatic agents (Ying et al. 2002). A reasonable estimate of the world annual production of NPE is around 500,000 tons (Ying et al. 2002). BPA is mainly used as a monomer in the manufacture of polycarbonate plastics known for its high resistance to shocks and temperature (plastic windows or greenhouses, car bumpers, baby bottles), and in epoxy resins used as food contact lacquer for cans and tin cans. Due to its uses, the world production of BPA was evaluated at about 3,000,000 tons (Vandenberg et al. 2007)While BPA is recognized as an endocrine disrupting chemical (Wetherill et al. 2007), NPE and OPE have been of rising concern because of their biodegradation by-products. Indeed, in urban or natural environment NPE can be biodegraded through oxidative or non-oxidative pathways (John and White 1998;Jonkers et al. 2001). Under oxidative biodegradation pathway, NPE turn i...