Ligand conversion in nanocrystal synthesis: the oxidation of alkylamines to fatty acids by nitrate

Ligands are a fundamental part of nanocrystals. They control and direct nanocrystal syntheses and provide colloidal stability. Bound ligands also affect the nanocrystals’ chemical reactivity and electronic structure. Surface chemistry is thus crucial to understand nanocrystal properties and functionality. Here, we investigate the synthesis of metal oxide nanocrystals (CeO2-x, ZnO, and NiO) from metal nitrate precursors, in the presence of oleylamine ligands. Surprisingly, the nanocrystals are capped exclusively with a fatty acid instead of oleylamine. Analysis of the reaction mixtures with nuclear magnetic resonance spectroscopy revealed several reaction byproducts and intermediates that are common to the decomposition of Ce, Zn, Ni, and Zr nitrate precursors. Our evidence supports the oxidation of alkylamine and formation of a carboxylic acid, thus unraveling this counterintuitive surface chemistry.Postprint (published version

Biofilm growth and nitrogen uptake responses to increases in nitrate and ammonium availability

Nitrate (NO3 −) and ammonium (NH4 +) are the two major dissolved inorganic nitrogen (DIN) species available in streams. Human activities increase stream DIN concentrations and modify the NO3 −:NH4 + ratio. However, few studies have examined biofilm responses to enrichment of both DIN species. We examined biofilm responses to variation in ambient concentrations and enrichments in either NO3 − or NH4 +. We incubated nutrient diffusing substrata (NDS) bioassays with three treatments (DIN-free, +NO3 − and +NH4 +) in five streams. Biomass-specific uptake rates (U spec ) of NO3 − and NH4 + were then measured using in situ additions of 15N-labeled NO3 − and NH4 +. Biomass (estimated from changes in carbon content) and algal accrual rates, as well as U spec -NO3 − of biofilms in DIN-free treatments varied among the streams in which the NDS had been incubated. Higher ambient DIN concentrations were only correlated with enhanced biofilm growth rates. U spec -NO3 − was one order of magnitude greater and more variable than U spec -NH4 +, however similar relative preference index (RPI) suggested that biofilms did not show a clear preference for either DIN species. Biofilm growth and DIN uptake in DIN-amended NDS (i.e., +NO3 − and +NH4 +) were consistently lower than in DIN-free NDS (i.e., control). Lower values in controls with respect to amended NDS were consistently more pronounced for algal accrual rates and U spec -NO3 − and for the +NH4 + than for the +NO3 − treatments. In particular, enrichment with NH4 + reduced biofilm U spec -NO3 − uptake, which has important implications for N cycling in high NH4 + streams

Nitrogen processing and the role of epilithic biofilms downstream of a wastewater treatment plant

We investigated how dissolved inorganic N (DIN) inputs from a wastewater treatment plant (WWTP) effluent are processed biogeochemically by the receiving stream. We examined longitudinal patterns of NH4+ and NO3− concentrations and their 15N signatures along a stream reach downstream of a WWTP. We compared the δ15N signatures of epilithic biofilms with those of DIN to assess the role of stream biofilms in N processing. We analyzed the δ15N signatures of biofilms coating light- and dark-side surfaces of cobbles separately to test whether light constrains functioning of biofilm communities. We sampled during 2 contrasting periods of the year (winter and summer) to explore whether changes in environmental conditions affected N biogeochemical processes. The study reach had a remarkable capacity for transformation and removal of DIN, but the magnitude and relevance of different biogeochemical pathways of N processing differed between seasons. In winter, assimilation and nitrification influenced downstream N fluxes. These processes were spatially segregated at the microhabitat scale, as indicated by a significant difference in the δ15N signature of light- and dark-side biofilms, a result suggesting that nitrification was mostly associated with dark-side biofilms. In summer, N processing was intensified, and denitrification became an important N removal pathway. The δ15N signatures of the light- and dark-side biofilms were similar, a result suggesting less spatial segregation of N cycling processes at this microhabitat scale. Collectively, our results highlight the capacity of WWTP-influenced streams to transform and remove WWTP-derived N inputs and indicate the active role of biofilms in these in-stream processes

Consequences of an ecosystem state shift for nitrogen cycling in a desert stream

Cessation of cattle grazing has resulted in the reestablishment of wetlands in some streams of the U.S. Southwest. Decades of cattle grazing prevented vascular plant growth in Sycamore Creek (Arizona, U.S.A.), resulting in stream reaches dominated by diatoms and filamentous green algae. Establishment of vascular plants can profoundly modify ecosystem processes; yet, the effects on nitrogen (N) cycling remain unexplored. We examined the consequences of this ecosystem state shift on N cycling in this N-limited desert stream. We compared results from whole-reach ammonium-N stable isotope (15NH4+) tracer additions conducted before (pre-wetland state) and 13 yr after (wetland state) free-range cattle removal from the watershed. Water column estimations showed that in-stream N uptake and storage were higher in the pre-wetland than in the wetland state. N turnover was also higher in the pre-wetland state, indicating that assimilated N was retained for shorter time in stream biomass. In addition, N uptake was mostly driven by assimilatory uptake regardless of the ecosystem state considered. Water column trends were mechanistically explained by the fact that the dominant primary uptake compartments in the pre-wetland state (i.e., algae and diatoms) had higher assimilatory uptake and turnover rates than those in the wetland state (i.e., vascular plants). Overall, results show that the shift in the composition and dominance of primary producers induced by the cessation of cattle grazing within the stream-riparian corridor changes in-stream N processing from a dominance of intense and fast N recycling to a prevalence of N retention in biomass of primary producers

Dissolved organic carbon bioreactivity and DOC:DIN stoichiometry control ammonium uptake in an intermittent Mediterranean stream

1. Heterotrophic organisms in streams use dissolved organic carbon (DOC) and dissolved inorganic nitrogen (DIN) from the water column to meet their growth and energy requirements. However, the role of DOC availability in driving DIN uptake in headwater streams is still poorly understood. In this study, we focus on how DOC:DIN stoichiometry and DOC bioreactivity control ammonium (NH$_4$$^+$) uptake and heterotrophic aerobic respiration, and how this influence varies among seasons in a forested Mediterranean headwater stream. 2. We estimated in-stream NH$_4$$^+$ uptake rates seasonally by conducting whole-reach constant-rate additions of NH$_4$$^+$ with and without amendments of either lignin (recalcitrant DOC) or acetate (labile DOC). During each addition, we characterised microbial community composition by molecular analyses, stream metabolism with the single-station method, and heterotrophic aerobic respiration by adding a metabolic tracer (resazurin). 3. The stream was heterotrophic (net ecosystem production 800% higher during the co-additions of acetate than when adding NH$_4$$^+$ either alone or with lignin. 4. Our results indicate that in-stream NH$_4$$^+$ uptake was largely controlled by heterotrophic bacteria, and that the stoichiometric balance between organic resources and nutrients was key to explaining the variability of in-stream NH$_4$$^+$ uptake and heterotrophic aerobic respiration. Moreover, the observed increase in NH$_4$$^+$ uptake during acetate additions suggests that heterotrophic activity was limited by labile DOC availability. 5. Our study highlights that both DOC:DIN stoichiometry and DOC bioreactivity are relevant factors driving the seasonal pattern of in-stream N processing in this forested Mediterranean headwater stream

Revision acerca del tratamiento no farmacologico del trastorno límite de personalidad. Comparacion de dos tratamientos: terapia dialectica conductual y grupo analisis

Borderline personality disorder is one of the most common personality disorder. These patients involve a high cost, consume more services than others without benefit and stay unaffected by the various treatments tested. Over the last years, several therapies with different approach for treatment of this common disorder have been studied. We compare two techniques DBT and group analysis. We conclude that both techniques can be useful and that its focus of intervention being different, could be complementary, to be used in devices such Day Hospital .It is recommend to treat these patients, dimensional vision of the disorder, suggesting that at different times of the therapeutic process to treat some nuclear symptoms, performed with different techniques, with an eclectic approach.El Trastorno Límite de Personalidad es uno de los trastornos de personalidad más frecuentes. Dichos pacientes suponen un coste elevado, siendo los que más servicios consumen y los que menos se benefician de estos, permaneciendo inalterados por los diversos tratamientos ensayados. En los últimos años se han estudiado varios enfoques psicoterapéuticos para el tratamiento de dicho trastorno. Se comparan dos técnicas Terapia Dialéctica Conductual y Grupoanálisis. Se concluye que ambas técnicas, pueden ser útiles y que sus focos de intervención al ser diferentes, podrían ser complementarias, para ser utilizadas en dispositivos tipo Hospital de Día. Se considera necesario, para el tratamiento de estos pacientes, la visión dimensional del trastorno, planteando el tratamiento en diferentes momentos del proceso, para tratar algunos síntomas nucleares, realizándose con diferentes técnicas, adoptando así un enfoque ecléctico

Combined Effects of Leaf Litter Inputs and a Flood on Nutrient Retention in a Mediterranean Mountain Stream During Fall

This study examined the effect of increasing in-channel leaf standing stocks on hydrologic transient storage and nutrient retention in a Mediterranean mountain stream. A flood at the end of the leaf fall period provided the opportunity to examine the effect of abrupt removal of much of the leaf material. Twenty-one chloride additions were performed from October to December 2004. In 13 of these, we also added ammonium and phosphate to estimate nutrient uptake lengths and uptake velocities to assess nutrient retention. The one-dimensional transport with inflow and storage (OTIS) model was used to estimate transient water storage parameters. Although discharge remained constant during leaf fall, water residence time increased because of in-channel litter accumulation, as did nutrient uptake velocity. Flooding reduced leaf benthic standing stocks by 65% and dramatically altered hydraulic and nutrient retention properties of the channel. After recession, the stream rapidly recovered in terms of nutrient retention, especially for phosphate. Abrupt changes in discharge under flood conditions largely determined the variability in stream nutrient retention. However, leaf litter inputs played an important role in nutrient dynamics during constant flow. Because both the flood regime and the timing of leaf fall are being regionally altered by climate change, our results have implications for stream nutrient dynamics under climate change scenarios

Wastewater treatment plant effluent inputs influence the temporal variability of nutrient uptake in an intermittent stream

Wastewater treatment plant (WWTP) effluents alter water chemistry and in-stream nutrient uptake rates of receiving freshwaters, thus changing the magnitude and fate of the nutrients exported. In Mediterranean regions, the dilution capacity of receiving streams can vary strongly over time due to the seasonal occurrence of floods and droughts, causing temporal variability of nutrient uptake. We assessed the temporal patterns and the controlling factors of net nutrient uptake in an intermittent Mediterranean stream receiving WWTP effluent inputs. We compiled the longitudinal concentration profiles of ambient dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) along a 800 m reach on 47 sampling dates between 2001 and 2017, encompassing a wide range of hydrological conditions. We estimated net nutrient uptake in the receiving stream. In 72% of the dates, high rates of net ammonium uptake co-occurred with net releases of either nitrate or nitrite. This pattern suggests that the receiving stream has a high nitrification capacity. Conversely, 75% of the dates did not show any longitudinal pattern in SRP concentration, suggesting that uptake and release processes for this element were either counterbalanced or both occurred at very low rates. Finally, net ammonium uptake was low when the stream had a low dilution capacity (< 40%) and ammonium concentration was high. Overall, we demonstrate that consideration of the receiving stream’s dilution capacity is imperative to the management of freshwaters to guarantee an adequate dilution of WWTP effluent inputs and avoid saturation of in-stream nutrient uptake capacity under low flow conditions in urban landscapes

Los lixiviados de las helófitas promueven la desnitrificación en ríos receptores de efluentes de plantas de tratamiento

nicas de bioingeniería empleando plantas acuáticas son utilizadas en la restauración de cursos fluviales, ya que reducen el exceso de nitrógeno (N) de la columna de agua y retienen metales pesados. A su vez, los lixiviados de su hojarasca pueden servir como una fuente adicional de materia orgánica disuelta lábil (DOM), que puede promover la respiración aeróbica y la eliminación de N a través de la desnitrificación. Probamos los efectos de los lixiviados de hojarasca de Iris pseudacorus y Phragmites australis en la estructura y actividad de biofilms de agua dulce cultivadas en canales alimentados por efluentes de una planta de tratamiento de aguas residuales (PTAR). Todas las fuentes de DOM aumentaron significativamente la respiración aeróbica y la desnitrificación del biofilm en comparación con los controles. Los resultados sugieren que la limitación en la biodisponibilidad de DOM puede ser aliviada mediante la utilización de lixiviados de helófitas.Instituto de Limnología "Dr. Raúl A. Ringuelet

Ecosystem respiration increases with biofilm growth and bed forms: Flume measurements with resazurin

In a set of streamside mesocosms, stream ecosystem respiration (ER) increased with biofilm biomass and flow heterogeneity (turbulence) generated by impermeable bed forms, even though those bed forms had no hyporheic exchange. Two streamside flumes with gravel beds (single layer of gravel) were operated in parallel. The first flume had no bed forms, and the second flume had 10 cm high dune-shaped bed forms with a wavelength of 1.0 m. Ecosystem respiration was measured via resazurin reduction to resorufin in each flume at three different biomass stages during biofilm growth. Results support the hypothesis that ER increases with flow heterogeneity generated by bed forms across all biofilm biomass stages. For the same biofilm biomass, ER was up to 1.9 times larger for a flume with 10 cm high impermeable bed forms than for a flume without the bed forms. Further, the amount of increase in ER associated with impermeable bed forms was itself increased as biofilms grew. Regardless of bed forms, biofilms increased transient storage by a factor of approximately 4.Keywords: bed forms, respiration, transient storage, biofilm, metabolism, resazuri