Assessing the Hydraulics of Water Heaters by Adding Fluoride as a Tracer to Inform its Overall Effect on Water Quality

As residential water heaters are the primary source of waterborne disease outbreaks in the U.S. there is a need to better understand how they are contributing to decreased water quality in buildings. Previous work has indicated that intermittent stagnation, low disinfection residual and operation temperatures promote the growth of pathogens in water heaters. The overall effect of hydrodynamics of water heaters on these factors remains unclear. Therefore, a tracer study was performed to determine the effect of and characterize hydraulics of the typical residential water heater on water quality. Controlling temperature and flow rate, a pilot-scale hot water system (50 gal) with specially adapted fittings was used. The fittings allowed for injection of fluoride as a tracer. 4.40 mg/L fluoride solution was injected at room temperature into the inlet line, set at 2.50 gal/min, to derive a step input fluoride concentration. Samples were obtained at the outlet of the tank, then fluoride concentration was measured by ion chromatography. A model was derived numerically in Matlab to validate if the experimental data reflected the behavior of a continuous stirred tank reactor. The data was consistent with the model but deviated at high flow rate and temperature conditions indicating that dispersion effects may be a factor. Additional tests with this tracer can help to better evaluate hydrodynamics of the system and thus its impact on water quality before it reaches the point of use

Transport Contaminant in Flowing Water for Improving Water Quality

Clean freshwater is fundamental to sustain human activities and the aquatic life. However, cities, industries, and agriculture wastes deteriorate water quality. For example, released fertilizer induces excess algal growth. This leads to major ecological problems such as eutrophication of freshwater ecosystems which has not only a great environmental cost impact, but can also affect the health and sustenance living of the people. This project investigates the transport of nitrate, a major plant fertilizer, in flowing freshwater. Streams and rivers can transform nitrate, thus mitigating its impact. Most of the biogeochemical reactions involved in nitrate removal take place where microorganisms usually thrive, at the sediment or water interfaces. We propose to study how the riverbed sediment influences nitrate transport and transformation. At Notre Dame University, our group conducted tracer experiments in artificial streams at the Linked Ecosystem Experimental Facility (LEEF). The experiment was conducted by co-injecting a conservative tracer (NaCl) and a nitrate salt (KNO3) and measuring their concentration over time at a downstream station. The data shows how their behavior differs as a function of time. Because water flowing through the sediment is much slower than the surface flow, we can make a space for time substitution and attribute longer timescales to travel in the hyporheic zone. As a result, we can attribute reaction rates to specific reactive zones in the stream. Our results show that benthic and hyporheic nitrate uptakes were reflected in the shape of the nitrate breakthrough curves. The benthic zone induced an exponentially decreasing nitrate signal at early times, while the hyporheic uptake was reflected by the truncation of the late time power law tail. We suggest that our analysis should be useful to scientists and managers alike, as we provide a new, spatially explicit, understanding of nitrate fate in flowing systems

Fractal Patterns in Riverbed Morphology Produce Fractal Scaling of Water Storage Times

River topography is famously fractal, and the fractality of the sediment bed surface can produce scaling in solute residence time distributions. Empirical evidence showing the relationship between fractal bed topography and scaling of hyporheic travel times is still lacking. We performed experiments to make high-resolution observations of streambed topography and solute transport over naturally formed sand bedforms in a large laboratory flume. We analyzed the results using both numerical and theoretical models. We found that fractal properties of the bed topography do indeed affect solute residence time distributions. Overall, our experimental, numerical, and theoretical results provide evidence for a coupling between the sand-bed topography and the anomalous transport scaling in rivers. Larger bedforms induced greater hyporheic exchange and faster pore water turnover relative to smaller bedforms, suggesting that the structure of legacy morphology may be more important to solute and contaminant transport in streams and rivers than previously recognized

Dynamic spatio-temporal patterns of metapopulation occupancy in patchy habitats

Spatio-temporal dynamics in habitat suitability and connectivity among mosaics of heterogeneous wetlands are critical for biological diversity and species persistence in aquatic patchy landscapes. Despite the recognized importance of stochastic hydroclimatic forcing in driving wetlandscape hydrological dynamics, linking such effects to emergent dynamics of metapopulation poses significant challenges. To fill this gap, we propose here a dynamic stochastic patch occupancy model (SPOM), which links parsimonious hydrological and ecological models to simulate spatio-temporal patterns in species occupancy in wetlandscapes. Our work aims to place ecological studies of patchy habitats into a proper hydrologic and climatic framework to improve the knowledge about metapopulation shifts in response to climate-driven changes in wetlandscapes. We applied the dynamic version of the SPOM (D-SPOM) framework in two wetlandscapes in the US with contrasting landscape and climate properties. Our results illustrate that explicit consideration of the temporal dimension proposed in the D-SPOM is important to interpret local- A nd landscape-scale patterns of habitat suitability and metapopulation occupancy. Our analyses show that spatio-temporal dynamics of patch suitability and accessibility, driven by the stochasticity in hydroclimatic forcing, influence metapopulation occupancy and the topological metrics of the emergent wetlandscape dispersal network. D-SPOM simulations also reveal that the extinction risk in dynamic wetlandscapes is exacerbated by extended dry periods when suitable habitat decreases, hence limiting successful patch colonization and exacerbating metapopulation extinction risks. The proposed framework is not restricted only to wetland studies but could also be applied to examine metapopulation dynamics in other types of patchy habitats subjected to stochastic external disturbances

Hydrogeomorphology of the Hyporheic Zone: Stream Solute and Fine Particle Interactions With a Dynamic Streambed

Hyporheic flow in streams has typically been studied separately from geomorphic processes. We investigated interactions between bed mobility and dynamic hyporheic storage of solutes and fine particles in a sand-bed stream before, during, and after a flood. A conservatively transported solute tracer (bromide) and a fine particles tracer (5 μm latex particles), a surrogate for fine particulate organic matter, were co-injected during base flow. The tracers were differentially stored, with fine particles penetrating more shallowly in hyporheic flow and retained more efficiently due to the high rate of particle filtration in bed sediment compared to solute. Tracer injections lasted 3.5 h after which we released a small flood from an upstream dam one hour later. Due to shallower storage in the bed, fine particles were rapidly entrained during the rising limb of the flood hydrograph. Rather than being flushed by the flood, we observed that solutes were stored longer due to expansion of hyporheic flow paths beneath the temporarily enlarged bedforms. Three important timescales determined the fate of solutes and fine particles: (1) flood duration, (2) relaxation time of flood-enlarged bedforms back to base flow dimensions, and (3) resulting adjustments and lag times of hyporheic flow. Recurrent transitions between these timescales explain why we observed a peak accumulation of natural particulate organic matter between 2 and 4 cm deep in the bed, i.e., below the scour layer of mobile bedforms but above the maximum depth of particle filtration in hyporheic flow paths. Thus, physical interactions between bed mobility and hyporheic transport influence how organic matter is stored in the bed and how long it is retained, which affects decomposition rate and metabolism of this southeastern Coastal Plain stream. In summary we found that dynamic interactions between hyporheic flow, bed mobility, and flow variation had strong but differential influences on base flow retention and flood mobilization of solutes and fine particulates. These hydrogeomorphic relationships have implications for microbial respiration of organic matter, carbon and nutrient cycling, and fate of contaminants in streams

Benthic Biofilm Controls on Fine Particle Dynamics in Streams

Este artículo contiene 15 páginas, 7 figuras, 3 tablas.Benthic (streambed) biofilms metabolize a substantial fraction of particulate organic matter and nutrient inputs to streams. These microbial communities comprise a significant proportion of overall biomass in headwater streams, and they present a primary control on the transformation and export of labile organic carbon. Biofilm growth has been linked to enhanced fine particle deposition and retention, a feedback that confers a distinct advantage for the acquisition and utilization of energy sources. We quantified the influence of biofilm structure on fine particle deposition and resuspension in experimental stream mesocosms. Biofilms were grown in identical 3 m recirculating flumes over periods of 18–47 days to obtain a range of biofilm characteristics. Fluorescent, 8 mm particles were introduced to each flume, and their concentrations in the water column were monitored over a 30 min period. We measured particle concentrations using a flow cytometer and mesoscale (10 mm to 1 cm) biofilm structure using optical coherence tomography. Particle deposition-resuspension dynamics were determined by fitting results to a stochastic mobile-immobile model, which showed that retention timescales for particles within the biofilm-covered streambeds followed a power-law residence time distribution. Particle retention times increased with biofilm areal coverage, biofilm roughness, and mean biofilm height. Our findings suggest that biofilm structural parameters are key predictors of particle retention in streams and rivers.This study was funded by a Marie Curie Intra- European Fellowship to WRH (FP7- PEOPLE-2011-IEF-302297) and an Austrian Science Fund grant to T.J.B. (START Y420-B17). K.R.R. was supported by a CUAHSI Pathfinder fellowship and U.S. NSF Graduate Research Fellowship. J.D.D. was supported by a Fulbright-Spain fellowship. The modeling effort was supported by U.S. NSF grants EAR- 1215898 and EAR-1344280 to AIP. Supporting data are provided at doi:10.6084/m9.figshare.4252193.Peer reviewe

Impacts of water level on metabolism and transient storage in vegetated lowland rivers: insights from a mesocosm study

Transient storage zones for water represent potential hot spots for metabolic activity in streams. In lowland rivers, the high abundance of submerged vegetation can increase water transient storage, bioreactive surface areas and, ultimately, in-stream metabolic activity. Changes in flow resulting from climatic and anthropogenic factors that influence the presence of aquatic vegetation can also, thereby, impact in-stream metabolism and nutrient cycling. We investigated the effects of water column depth on aquatic vegetation cover and its implications on water transient storage and associated metabolic activity in stream mesocosms (n=8) that represent typical conditions of lowland streams. Continuous injections of metabolically reactive (resazurin-resorufin) tracers were conducted and used to quantify hydraulic transport and whole-mesocosm aerobic respiration. Acetate, a labile carbon source, was added during a second stage of the tracer injection to investigate metabolic responses. We observed both higher vegetation coverage and resazurin uptake velocity, used as a proxy of mesocosm respiration, with increasing water column depth. The acetate injection had a slight, positive effect on metabolic activity. A hydrodynamic model estimated the water transport and retention characteristics and first-order reactivity for three mesocosms. These results suggest that both the vegetated surface water and sediments contribute to metabolically active transient storage within the mesocosms, with vegetation having a greater influence on ecosystem respiration. Our findings suggest that climate and external factors that affect flow and submerged vegetation of lowland rivers will result in changes in stream respiration dynamics and that submerged vegetation are a particularly important and sensitive location for stream respiration

Fibrinolyse intraveineuse des infarctus cérébraux (expérience de l'unité neurovasculaire du CHU de Rouen)

Objectifs. Le traitement par fibrinolyse intraveineuse des infarctus cérébraux est utilisé au CHU de Rouen depuis 2004. L'objectif de ce travail est de reprendre les bases scientifiques de ce traitement, d'évaluer les pratiques du service de neurologie du centre hospitalo-universitaire (CHU) de Rouen et de les comparer aux données de la littérature. Patients et méthodes. Les données ont été recueillies de manière rétrospective par étude des dossiers médicaux des patients traités par fibrinolyse entre le le 1er octobre 2004 et le 31 décembre 2008. Un recueil de données épidémiologiques, cliniques, radiologiques et biologiques a été effectué. Le déficit neurologique a été calculé par un score NIH. Le devenir fonctionnel des patients a été évalué grâce au score de Rankin modifié. Les délais de prise en charge pré et intra- hospitaliers ont été mesurés et analysés. Résultats. Cinquante-trois patients ont reçu un traitement fibrinolytique par rt-PA à la suite d'un infarctus cérébral dans le service de neurologie du CHU de Rouen pendant cette période soit 1.48 % des patients ayant un infarctus cérébral pris en charge dans ce service. Ils avaient un âge moyen de 58 ans. Leur déficit initial médian était de 15 au score NIH. Le délai moyen de prise en charge pré hospitalière était de 94 minutes. Le délai de prise en charge intra-hospitalière était de 83 minutes. Ces délais étaient corrélés négativement. A 24 heures post-traitement, 51 % des patients étaient améliorés d'au moins 4 points au score NIH. A distance du traitement, 51 % des patients étaient indépendants dans les activités de la vie quotidienne (score de Rankin <= 2). Le taux d'hémorragie symptomatique était de 11 % et le taux de décès à 3 mois de 13 %. Un taux de 37,7 % de violations de protocole a été enregistré, essentiellement du fait de dépassements de délai. Ces patients n'ont pas eu plus de complications hémorragiques. Seule la présence de leucoaraïose sur le scanner initial était associée à un risque accru de complications hémorragiques cérébrales. Conclusion. Nous avons pu montrer que nos résultats issus de l'activité en pratique courante d'une unité neurovasculaire sont comparables à ceux des grands essais randomisés et des autres études observationnelles. Bien que l'on observe au cours des années un nombre croissant de patients qui peuvent recevoir ce traitement, il est nécessaire de poursuivre l'effort d'information et d'organisation indispensable à la réalisation de ce traitement compte tenu du délai imparti.ROUEN-BU Médecine-Pharmacie (765402102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Stochastic dynamics of wetlandscapes: Ecohydrological implications of shifts in hydro-climatic forcing and landscape configuration

Wetlands play an important role in watershed eco\u2010hydrology. The occurrence and distribution of wetlands in a landscape are affected by the surface topography and the hydro\u2010climatic conditions. Here, we propose a minimalist probabilistic approach to describe the dynamic behaviour of wetlandscape attributes, including number of inundated wetlands and the statistical properties of wetland stage, surface area, perimeter, and storage volume. The method relies on two major assumptions: (a) wetland bottom hydrologic resistance is negligible; and (b) groundwater level is parallel to the mean terrain elevation. The approach links the number of inundated wetlands (depressions with water) to the distribution of wetland bottoms and divides, and the position of the shallow water table. We compared the wetlandscape attribute dynamics estimated from the probabilistic approach to those determined from a parsimonious hydrologic model for groundwater\u2010dominated wetlands. We test the reliability of the assumptions of both models using data from six cypress dome wetlands in the Green Swamp Wildlife Management Area, Florida. The results of the hydrologic model for groundwater\u2010dominated wetlands showed that the number of inundated wetlands has a unimodal dependence on the groundwater level, as predicted by the probabilistic approach. The proposed models provide a quantitative basis to understand the physical processes that drive the spatiotemporal hydrologic dynamics in wetlandscapes impacted by shallow groundwater fluctuations. Emergent patterns in wetlandscape hydrologic dynamics are of key importance not only for the conservation of water resources, but also for a wide range of eco\u2010hydrological services provided by connectivity between wetlands and their surrounding uplands