Long-term monitoring (1960-2008) of the river-sediment transport in the Red River Watershed (Vietnam): Temporal variability and dam-reservoir impact

The Red River (China/Vietnam, A = 155,000 km²) is a typical humid tropics river originating from the mountainous area of Yunnan Province in China. Based on information on daily discharge (Q) and suspended particulate matter (SPM) concentration between 1960-2008 for the SonTay gauging station (outlet of the River and entry to the Delta) provided by the National Institute IMHE-MONRE, the mean annual SPM flux was estimated at 90 Mt/yr, corresponding to a sediment yield of 600 t/km²/yr. The temporal variability of annual SPM fluxes (ranging from 24 to 200 Mt/yr) is strongly related to the interannual hydrological conditions. However, some years of high water flow were not associated with high sediment fluxes, especially after 1989 when the HoaBinh dam came into operation. Therefore, the median discharge pre- (3389 m³/s) and post 1989 (3495 m³/s) are similar indicating there was little or no change between both periods. Sediment rating curves (power law-type; SPM = aQ^b) were fitted for both periods (1960-1989; 1990-2008). The analysis of the pre- and post-1989 sediment rating parameters (a, b) suggests a downshift of b-parameter values after 1989, attributed to a decrease of the sediment supply due to the commissioning of the HoaBinh dam. A single sediment rating curve derived from 1960-1989 data was used to simulate the annual variability of former sediment delivery, generating excellent cumulative flux estimates (error ~ 1%). In contrast, applying the same rating curve to the 1990-2008 data resulted in systematic and substantial (up to 109%) overestimation. This suggests that the HoaBinh dam reduces annual SPM delivery to the delta by half, implying important metal/metalloid storage behind the HoaBinh dam.     

Quantitative multimolecular marker approach to investigate the spatial variability of the transfer of pollution from the Fensch River to the Moselle River (France)

The lipidic fraction from 8 sediments sampled at the confluence between the Fensch River (FR) and the Moselle River (MR) have been analyzed by gas chromatography-mass spectrometry (GC-MS) in order to investigate the transfer of organic micropollutants from the FR to the MR. Molecular markers have been quantified and classified into five categories: natural, petrogenic, pyrogenic and sewage water markers and non-specific molecules. This classification coupled with the quantification of the molecules allows the comparison between anthropogenic and natural inputs and the source apportionment of anthropogenic molecules that are not covalently bound to sedimentary organic macromolecules. The transfer and the fate of organic micropollutants in river sediments seem to be controlled by the water flow. Low water flow conditions induce the settling of fine particles, which could limit the biodegradation. This leads to the preservation of the original anthropogenic fingerprint that is rich in low molecular weight molecules. In high water flow conditions, sediments are mainly composed of coarse particles, limiting the preservation of organic matter, which leads to a persistent anthropogenic fingerprint, mainly composed of high molecular weight compounds.     

Three-dimensional pollutant transport model for the Pearl River Estuary

In this paper, the development and implementation of a three-dimensional, numerical pollutant transport model, which is based on an orthogonal curvilinear coordinate system in the horizontal direction and a sigma coordinate system in the vertical direction, is delineated. An efficient as well as simple open boundary condition is employed for pollutant transport in this mathematical model. It is then applied to model the distribution and transport of Chemical Oxygen Demand in the Pearl River Estuary. The results from the numerical simulations illustrate that the transboundary or inter-boundary effects of pollutants, between the Guangdong Province and the Hong Kong Special Administrative Region due to the wastewater discharged from the Pearl River Delta Region, are quite strong.     

Organic matter transport and degradation in the river Seine (France) after a combined sewer overflow

The impact of a combined sewer overflow (CSO) upon receiving waters has been studied in the river Seine during Summers 1995 and 1996. Three main events have been monitored with special attention paid to the computation of oxygen, carbon and suspended solids budgets. Bacterial biomass and bacterial production rates have been measured to provide a more accurate understanding of the carbon cycle of the river Seine. Oxygen consumption inside the polluted water masses was totally due to the activity of large bacteria discharged into the river by the CSO, the activity of native small bacteria did not significantly increase after CSOs. Suspended solids issued from the CSO very quickly settles in this deep, slowly flowing river. However, discharged dissolved organic carbon (DOC) cannot account for the observed oxygen depletions, the additional carbon source could be phytoplankton or deflocculated/degraded particulate organic matter.     

Temporal variability of nitrate transport through hydrological response during flood events within a large agricultural catchment in south-west France

The temporal variability of nitrate transport was monitored continuously in a large agricultural catchment, the 1110 km² Save catchment in south-west France, from January 2007 to June 2009. The overall aim was to analyse the temporal transport of nitrate through hydrological response during flood events in the catchment. Nitrate loads and hysteresis were also analysed and the relationships between nitrate and hydro-climatological variables within flood events were determined. During the study period, 19 flood events were analysed using extensive datasets obtained by manual and automatic sampling. The maximum NO₃⁻ concentration during flood varied from 8.2 mg l⁻¹ to 41.1 mg l⁻¹ with flood discharge from 6.75 m³ s⁻¹ to 112.60 m³ s⁻¹. The annual NO₃⁻ loads in 2007 and 2008 amounted to 2514 t and 3047 t, respectively, with average specific yield of 2.5 t km⁻¹² yr⁻¹. The temporal transport of nitrate loads during different seasonal flood events varied from 12 t to 909 t. Nitrate transport during flood events amounted to 1600 t (64% of annual load; 16% of annual duration) in 2007 and 1872 t (62% of annual load; 20% of annual duration) in 2008. The level of peak discharge during flood events did not control peak nitrate concentrations, since similar nitrate peaks were produced by different peak discharges. Statistically strong correlations were found between nitrate transport and total precipitation, flood duration, peak discharge and total water yield. These four variables may be the main factors controlling nitrate export from the Save catchment. The relationship between nitrate and discharge (hysteresis patterns) investigated through flood events in this study was mainly dominated by anticlockwise behaviour.     

Assessment quality of a nonuniform suspended sediment transport model under unsteady flow condition (case study: Aras River)

This study presents a one‐dimensional, fully coupled numerical model for nonequilibrium suspended sediment transport that can be applied to channels and alluvial rivers. The accuracy of calculations was enhanced using a nonuniform size distribution, and evaluating probability of hiding and exposure effect of particles. This model is also capable of calculating the flocculation and temperature effect on sediment transport. In addition, the BOD and its influence on suspended sediment transport have been discussed. The study was conducted on the Aras River, Iran's third major river with a relatively high sediment concentration. To verify the model, water depth and sediment concentration of measured field data are compared with simulated data. Comparisons show a regression coefficient of more than 95% and mean computational error is less than 5%. The agreement of the data shows that the model is capable of predicting flow and suspended sediment transport with a correlation coefficient higher than 98%.     

Hydrochemical processes controlling arsenic and selenium in the Changjiang River (Yangtze River) system

The hydrochemistry of arsenic and selenium in the Changjiang (Yangtze River) was studied, based on continuously monitored data at Nantong station (i.e. 180 km inland from river mouth), the main Changjiang channel and 10 major tributaries. The dissolved inorganic arsenic (DIAs) and selenium (DISe) concentrations of the Changjiang are related to water discharge, rock type of drain basin, anthropogenic influences etc. The DIAs and DISe levels vary over an order of magnitude throughout the basin (i.e. 6.95-68.9 nmol/L for DIAs, 1.16-9.92 nmol/L for DISe). Source rock composition is the primary control on the concentrations of DIAs and DISe in the Changjiang. Several tributaries (e.g. Xiangjiang River, Minjiang River and Tuojiang River) are contaminated by human activities. Flux calculations from hydrographic data at Datong (the most downstream main channel station without tidal influence) indicate that the Changjiang transports 234.8 x 10(5) mol/yr of DIAs and 49.6 x 10(5) mol/yr of DISe to the East China Sea.     

Fate of arsenic-bearing phases during the suspended transport in a gold mining district (Isle river Basin, France)

Arsenic-rich (~ 140-1520 mg.kg^− 1) suspended particulate matter (SPM) was collected daily with an automatic sampler in the Upper Isle River (France) draining a former gold mining district in order to better understand the fate of arsenic during the suspended transport (particles smaller than 50 μm). Various techniques at a micrometric scale (EPMA, quantitative SEM-EDS with an automated particle counting including classification system and μXRD) were used to directly characterize As-bearing phases. The most frequent ones were aggregates of fine clay particles. Their mineralogy varied with particle sources involved. These aggregates were formed by chlorite-phlogopite-kaolinite assemblages during the high flow and chlorite-illite-montmorillonite during the low flow. Among all the observed As-carriers in SPM, these clay assemblages were the least As-rich (0.10 up to 1.58 wt.% As) and their median As concentrations suggested that they were less concentrated during the high flow than during the low flow. Iron oxyhydroxides were evidenced by μXRD in these clay aggregates, either as micro- to nano-sized particles and/or as coating.(Mn, Fe)oxyhydroxides were also present as discrete particles. Manganese oxides (0.14-1.26 wt.% As) transport significantly more arsenic during the low flow than during the high flow (0.16-0.79 wt.% As). The occurrence of Fe oxyhydroxide particles appeared more complex. During the low flow, observations on banks and in wetlands of freshly precipitated Fe hydroxides (ferrihydrite-type) presented the highest As concentrations (up to 6.5 wt.% As) but they were barely detected in SPM at a microscale. During the high flow, As-rich Fe-oxyhydroxides (0.10-2.80 wt.% As) were more frequent, reflecting mechanical erosion and transport when the surface water level increased.Arsenic transfers from SPM to corresponding aqueous fraction mostly depend on As-carrier stability. This study shows the temporal occurrence of each type of As-bearing phases in SPM, their As concentrations at a particle scale and abundance according to hydrological periods.     

Influence of anthropogenic sources on total gaseous mercury variability in Grenoble suburban air (France)

Total gaseous mercury (TGM) has been monitored at Champ sur Drac, a suburban site of Grenoble in southern east France. TGM measurements have been made over 4 periods of approximately 10 days throughout 1999-2000 using cold vapour atomic fluorescence absorption technique. The first monitoring campaign was initiated on November 4, 1999, followed by three other campaigns respectively on January 12, 2000, April 10, 2000 and July 17, 2000. Concurrent monitoring of O3, NO, NO2, SO2 and of meteorological parameters have also been performed. The mean TGM concentration was 3.4 ng m(-3) with maximum hourly mean concentration of 37.1 ng m(-3). Although mean TGM concentration was not greatly different from those previously measured in the troposphere, the greater TGM variability as well as the occurrence of high TGM concentration linked to particular wind conditions suggested the strong influence of anthropogenic sources. The chlor-alkali plant located nearby, the others chemical industries using fuel combustion and the municipal waste incinerator were thought to contribute to mercury pollution events.     

Historical perspective of heavy metals contamination (Cd, Cr, Cu, Hg, Pb, Zn) in the Seine River basin (France) following a DPSIR approach (1950-2005)

The Driver-Pressures-State-Impact-Response approach is applied to heavy metals in the Seine River catchment (65,000 km(2); 14 million people of which 10 million are aggregated within Paris megacity; 30% of French industrial and agricultural production). The contamination pattern at river mouth is established on the particulate material at different time scales: 1930-2000 for floodplain cores, 1980-2003 for suspended particulate matter (SPM) and bed-sediments, 1994-2003 for atmospheric fallout and annual flood deposits. The Seine has been among the most contaminated catchments with maximum contents recorded at 130 mg kg(-1) for Cd, 24 for Hg, 558 for Pb, 1620 for Zn, 347 for Cu, 275 for Cr and 150 for Ni. Today, the average levels for Cd (1.8 mg kg(-1)), Hg (1.08), Pb (108), Zn (370), Cu (99), Cr (123) and Ni (31) are much lower but still in the upper 90% of the global scale distribution (Cr and Ni excepted) and well above the natural background values determined on pre-historical deposits. All metal contents have decreased at least since 1955/65, well before metal emission regulations that started in the mid 1970's and the metal monitoring in the catchment that started in the early 1980's. In the last 20 y, major criteria changes for the management of contaminated particulates (treated urban sludge, agricultural soils, dredged sediments) have occurred. In the mid 1990's, there was a complete shift in the contamination assessment scales, from sediment management and water usage criteria to the good ecological state, now required by the 2000 European Directive. When comparing excess metal outputs, associated to river SPM, to the average metal demand within the catchment from 1950 to 2000, the leakage ratios decrease exponentially from 1950 to 2000 for Cd, Cr, Cu, Pb and Zn, meanwhile, a general increase of the demand is observed: the rate of recycling and/or treatment of metals within the anthroposphere has been improved ten-fold. Hg environmental trajectory is very specific: there is a marked decontamination from 1970 to 2000, but the leakage ratio remains very high (10 to 20%) during this period. Drivers and Pressures are poorly known prior to 1985; State evolution since 1935 has been reconstructed from flood plain cores analysis; Impacts were maximum between 1950 and 1970 but remained unknown due to analytical limitation and lack of awareness. Some Responses are lagging 10 y behind monitoring and have much evolved in the past 10 y.     

Phosphorus load estimation in the Saginaw River, MI using a Bayesian hierarchical/multilevel model

We propose the use of Bayesian hierarchical/multilevel ratio approach to estimate the annual riverine phosphorus loads in the Saginaw River, Michigan, from 1968 to 2008. The ratio estimator is known to be an unbiased, precise approach for differing flow-concentration relationships and sampling schemes. A Bayesian model can explicitly address the uncertainty in prediction by using a posterior predictive distribution, while in comparison, a Bayesian hierarchical technique can overcome the limitation of interpreting the estimated annual loads inferred from small sample sizes by borrowing strength from the underlying population shared by the years of interest. Thus, by combining the ratio estimator with the Bayesian hierarchical modeling framework, long-term loads estimation can be addressed with explicit quantification of uncertainty. Our study results indicate a slight decrease in total phosphorus load early in the series. The estimated ratio parameter, which can be interpreted as flow-weighted concentration, shows a clearer decrease, damping the noise that yearly flow variation adds to the load. Despite the reductions, it is not likely that Saginaw Bay meets with its target phosphorus load, 440 tonnes/yr. Throughout the decades, the probabilities of the Saginaw Bay not complying with the target load are estimated as 1.00, 0.50, 0.57 and 0.36 in 1977, 1987, 1997, and 2007, respectively. We show that the Bayesian hierarchical model results in reasonable goodness-of-fits to the observations whether or not individual loads are aggregated. Also, this modeling approach can substantially reduce uncertainties associated with small sample sizes both in the estimated parameters and loads.     

Nitrogen flux and sources in the Mississippi River Basin

Nitrogen from the Mississippi River Basin is believed to be at least partly responsible for the large zone of oxygen-depleted water that develops in the Gulf of Mexico each summer. Historical data show that concentrations of nitrate in the Mississippi River and some of its tributaries have increased by factors of 2 to more than 5 since the early 1900s. We have used the historical streamflow and concentration data in regression models to estimate the annual flux of nitrogen (N) to the Gulf of Mexico and to determine where the nitrogen originates within the Mississippi Basin. Results show that for 1980-1996 the mean annual total N flux to the Gulf of Mexico was 1,568,000 t/year. The flux was approximately 61% nitrate as N, 37% organic N, and 2% ammonium as N. The flux of nitrate to the Gulf has approximately tripled in the last 30 years with most of the increase occurring between 1970 and 1983. The mean annual N flux has changed little since the early 1980s, but large year-to-year variations in N flux occur because of variations in precipitation. During wet years the N flux can increase by 50% or more due to flushing of nitrate that has accumulated in the soils and unsaturated zones in the basin. The principal source areas of N are basins in southern Minnesota, Iowa, Illinois, Indiana, and Ohio that drain agricultural land. Basins in this region yield 800 to more than 3100 kg total N/km2 per year to streams, several times the N yield of basins outside this region. Assuming conservative transport of N in the Mississippi River, streams draining Iowa and Illinois contribute on average approximately 35% of the total N discharged by the Mississippi River to the Gulf of Mexico. In years with high precipitation they can contribute a larger percentage.     

Spatial and temporal variability in VOC levels within a commercial retail building

A study was performed to characterize the concentration of dozens of volatile organic compounds (VOCs) at 10 locations within a single large building and track these concentrations over a 2-year period. The study was performed at a shopping center (strip mall) in New Jersey. A total of 130 indoor air samples were collected from 10 retail stores within the shopping center and analyzed for 60 VOCs by US EPA Method TO-15. Indoor concentrations of up to 55,100 microg/m(3) were measured for individual VOCs. The indoor/outdoor ratio (I/O) was as high as 1500 for acetone and exceeded 100 at times for various compounds, indicating that significant indoor air sources were present. A large degree of spatial variability was observed between stores within the building, with concentrations varying by three to four orders of magnitude for some compounds. The spatial variability was dependent on the proximity of the sampling locations to the indoor sources. A large degree of temporal variability also was observed for compounds emitted from indoor sources, but the temporal variability generally did not exceed two standard deviations (sigma). For compounds not emitted from indoor sources at significant rates, both the spatial and temporal variability tended to range within an order of magnitude at each location. PRACTICAL IMPLICATIONS: Many cross-sectional studies have been published where the levels of volatile organic compounds (VOCs) were measured in indoor air at one or two locations for houses or offices. This study provides longitudinal data for a commercial retail building and also addresses spatial variability within the building. The data suggest that spatial and temporal variability are important considerations for compounds emitted from indoor sources. Elevated concentrations were found in retail spaces with no apparent emission sources due to their proximity to other retail spaces with emission sources.     

Biomonitoring of the genotoxic potential (micronucleus assay) and detoxifying activity (EROD induction) in the River Dadou (France), using the amphibian Xenopus laevis

Within the framework of a general survey of the water quality of the river Dadou (Tarn, France), different physico-chemical parameters were measured and an inventory of the fish population was made along the water course, around the Rassisse dam. With the aim of monitoring the potential genotoxic effects and the detoxifying activities induced in organisms exposed to the river water, two in vivo bioassays were performed in laboratory experiments, using larvae of the amphibian Xenopus laevis. The first was the micronucleus test, using red blood cells, and the second the assay of ethoxyresorufin-O-deethylase (EROD) induction in the liver of exposed animals. Eight water samples were taken from the river and at outlet points from the two major industrial activities of the studied section of the water course: a spar-fluor mine and a water treatment plant. Genotoxic impact and EROD induction were measured in the larvae. The effluent of the filter-washing process from the water treatment plant was found to be particularly genotoxic, even after dilution in pure reconstituted water, but no particular genotoxicity was found, either in Dadou river water, or in the effluents from the mine. On the other hand, most of the water samples tested produced a clear induction of EROD activity compared to the level of enzymatic activity found in the liver of larvae reared in the river water sampled upstream of the industrial activities. These results were interpreted taking into account (i) the high concentrations of pollutants (fluorine and manganese) measured in the river water, (ii) the very low population levels inventoried in the downstream section of the river and (iii) the possible interactions between the substances present in the river water, particularly the classical EROD inducers PAHs and PCBs.     

Spatial and temporal evolution of the levels of tritium in the Tagus River in its passage through Caceres (Spain) and the Alentejo (Portugal)

This work is the result of a collaboration between Spanish and Portuguese laboratories. The specific objective was to quantify the time evolution during 1994, 1995 and 1996 of the radioecological impact of the liquid releases of 3H from the Almaraz Nuclear Power Plant (ANPP) in the section of the Tagus River corresponding to Cáceres province in Spain and the Alentejo region in Portugal. We found that the temporal evolution of the levels of tritium depends on the management of the water held in the cooling reservoir of the ANPP and the presence of the dams that exist along the river. This management regime has a 12-month period. Also the movement of the mass of tritiated water (HTO) downriver was much faster during 1996 than 1995 or 1994 due to the hydrological differences between those years and consequently to the different amounts of water transferred between the reservoirs of the dams. From the hypothesis that hydrodynamically it is impossible to differentiate tritiated water from non-tritiated water, a model was constructed that satisfactorily reproduces the temporal evolution of the 3H in the zone of the Tagus River in which the exchange of water takes place, with the cooling reservoir of the Almaraz Nuclear Power Plant.     

Sources, distribution and variability of hydrocarbons and metals in atmospheric deposition in an urban area (Paris, France)

Total atmospheric deposition, i.e., both wet and dry deposition, was sampled during 11 months in the "Ile-de-France" region, France. Monthly fluxes of aliphatic hydrocarbons (AHs), polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) were studied at three representative sites (two urbanised and one semiurban). A combination of spatial and temporal variability of total fluxes and pollutant fingerprints allows a better understanding of atmospheric pollutant dynamics over this region. In the whole studied area, aggregated total atmospheric fluxes of AHs, PAHs and HMs range from 19 to 33 mg m(-2) y(-1), 99 to 161 mug m(-2) y(-1) and 48 to 103 mg m(-2) y(-1), respectively. The highest values are observed in Paris centre, reflecting the importance of the urban centre as a source of pollutants, with a decline in many atmospheric deposits when moving away from urban areas. The seasonal distribution of these pollutants suggests the impact of residential heating on urban atmospheric deposition of hydrocarbons and the increase of dust loads containing HMs during summer. The qualitative study performed on atmospheric deposition data highlights the main sources of pollutants. Aliphatic fingerprints suggest a marked contribution of biogenic inputs to aliphatic contamination in the whole Ile-de-France region and slight petroleum inputs in urban areas. Aromatic fingerprints, characterised by the great predominance of phenanthrene, fluoranthene and pyrene, associated with some specific ratio values, suggest the mixture of petrogenic and pyrolytic contaminations of atmospheric deposition in the whole "Ile-de-France" region. HM distribution shows the presence of anthropogenic sources of Al and Fe in this area and the stationary sources (incinerators and plants) as a significant source of Si, S and Sb in the urban atmosphere. Moreover, a pollutant mix phenomenon, occurring in such an urban atmosphere, shows a significant influence on atmospheric deposition at the semiurban site.     

The spatial and temporal trends of Cd, Cu, Hg, Pb and Zn in Seine River floodplain deposits (1994-2000)

Fresh floodplain deposits (FD), from 11 key stations, covering the Seine mainstem and its major tributaries (Yonne, Marne and Oise Rivers), were sampled from 1994 to 2000. Background levels for Cd, Cu, Hg, Pb, and Zn were established using prehistoric FD and actual bed sediments collected in small forested sub-basins in the most upstream part of the basin. Throughout the Seine River Basin, FD contain elevated concentrations of Cd, Cu, Hg, Pb and Zn compared to local background values (by factors>twofold). In the Seine River Basin, trace element concentrations display substantial downstream increases as a result of increasing population densities, particularly from Greater Paris (10 million inhabitants), and reach their maxima at the river mouth (Poses). These elevated levels make the Seine one of the most heavily impacted rivers in the world. On the other hand, floodplain-associated trace element levels have declined over the past 7 years. This mirrors results from contemporaneous suspended sediment surveys at the river mouth for the 1984-1999 period. Most of these temporal declines appear to reflect reductions in industrial and domestic solid wastes discharged from the main Parisian sewage plant (Seine Aval).     

Spatial and temporal variations of plutonium isotopes (238Pu and 239,240Pu) in sediments off the Rhone River mouth (NW Mediterranean)

The dispersion and fate of the Rhone River inputs to the Gulf of Lions (Northwestern Mediterranean Sea) have been studied through the spatial and temporal distributions of plutonium isotopes in continental shelf sediments. Plutonium isotopes ((238)Pu and (239,240)Pu) are appropriate tracers to follow the dispersion of particulate matter due both to their high affinity for particles and their long half-lives. In the Rhone River valley, plutonium isotopes originate from both the weathering of the catchment basin contaminated by global atmospheric fallout, and the liquid effluents released from the Marcoule reprocessing plant since 1961. This work presents a first detailed study on (238)Pu and (239,240)Pu distributions in sediments from the Rhone prodelta to the adjacent continental shelf, since the decommissioning of Marcoule in 1997. The vertical distribution of Pu isotopes has been analysed in a 4.75 m long core sampled in 2001 at the Rhone mouth. Despite this length, plutonium is found at the last 10 cm, manifesting the high sedimentation rate of the prodeltaic area and its ability for trapping fine-grained sediments and associated contaminants. The highest (238)Pu and (239,240)Pu concentrations reached 1.26 and 5.97 Bq kg(-1) respectively and were found within the layer 280-290 cm. The (238)Pu/(239,240)Pu activity ratios (AR) demonstrated an efficient and huge trapping of the Pu isotopes derived from Marcoule. The fresh sediments, located on the top of the core, show lower plutonium activity concentrations and lower (238)Pu/(239,240)Pu ratios. This decrease is in close relation with the shut down of the Marcoule reprocessing plant in 1997. In 2001, plutonium isotopes were also analysed in 21 surface sediments located offshore and concentrations ranged from 0.03 to 0.17 Bq kg(-1) for (238)Pu and from 0.33 to 1.72 Bq kg(-1) for (239,240)Pu. The (238)Pu/(239,240)Pu AR ranged from 0.24 close to the river mouth to 0.06 southwards, indicating the decreasing influence of the Marcoule releases (global fallout AR 0.03-0.05 and Marcoule AR 0.30). This is in good agreement with the main direction spread of the Rhone River plume and the bottom current. This dataset has been compared to those obtained in the same area in 1984 and 1990 in order to follow the time trend in Pu concentrations. This comparison highlights the decrease with time in plutonium concentrations close to the Rhone River mouth, but further away this reduction is not so evident.     

A model approach for evaluating effects of remedial actions on mercury speciation and transport in a lake system

This paper provides a model approach for understanding mercury cycling in aquatic systems. The information gained is then used for evaluating three remedial actions, namely, natural attenuation, dredging and capping. Onondaga Lake, NY was used as a model aquatic system. Mercury transport and speciation in both the water column and the benthic sediment were simulated by using a Water Quality Analysis Simulation Program. Model predictions for the water column generally agreed with the measured values reported in literature for Onondaga Lake. Sensitivity analyses of the model were conducted for determining the impact of transport mechanisms and speciation mechanisms. Advection, sorption and settling were important mechanisms of Hg transport in the water column. In the benthic sediment, settling of Hg from the water column was the most important input source of Hg. Reduction, methylation and demethylation were important mechanisms of Hg speciation in both the water column and the benthic sediment. Assuming that Hg loading is steady, natural attenuation showed no positive impact for remediation of Hg-contaminated aquatic systems as compared with dredging and capping.     

Numerical estimation and sensitivity analysis of the energy demand for six industrial buildings in France

When it comes to dealing with energy savings in buildings, studies almost systematically focus on the residential and tertiary building stocks while the industrial building stock is ignored. This study comes as a first step to move forward on this topic and its objectives are threefold: first to develop a simple methodology suitable for various industrial activities, then to analyse the distribution of the energy demand by use for six different cases and, finally, to carry out a sensitivity analysis. A first observation was that the energy demands for HVAC and lighting systems and the heat loads were of the same order of magnitude. The energy demand for heating and cooling was normally distributed, and the uncertainty on the results lay between ±20% and ±40% for most cases. The influence of six weather conditions was estimated for all of the six buildings and found to be significant, yet not uniformly.