Modeling reactive transport with chemical equilibrium reactions requires solution of coupled partial differential and algebraic equations. In this work, two formulations are developed to combine the method of lines (MOL) with the global implicit approach. The first formulation has a non-conservative form and leads to a nonlinear system of ordinary differential equations with a reduced number of unknowns. The second formulation presents better conservation properties but leads to a nonlinear system of differential algebraic equations with a large number of unknowns. In both formulations, the resulting systems are integrated in time using the DLSODIS time solver which adapts both the order of the time integration and the time step size to provide the necessary accuracy. Numerical experiments show that higher-order time integration is effective for solving the non-conservative formulation and point out the high benefit of the MOL for solving reactive transport problems.

The goal of this project was to develop a method to measure the total gaseous mercury (TGM) concentrations in unsaturated soils. Existing methods did not allow for easy replication, were costly, and were more suited for other gases, such as CO2, that do not react with collection surfaces. To overcome these problems, we developed a method that simultaneously collects up to ten soil pore air samples. We used a single mass flow controller, one pump, and two banks of rotameters to draw soil air out of the ground at 25 smL min−1 onto gold-coated quartz traps. Analysis of the gold traps was performed with a Tekran 2500 CVAFS mercury detector. The system was field tested at the Piney Reservoir Ambient Air Monitoring Station in western Maryland. Our system was relatively precise and accurate. For example, replicate TGM concentrations differed by less than 25% and recovery of known amounts of mercury were greater than 95%. Field measurements showed that the maximum soil pore air TGM concentrations, between 3 and 4 ng m−3, occurred at the Oe–A soil horizon interface. At all other depths, the total mercury concentrations were lower than the ambient air concentrations of 1.8 ng m−3. We believe our new method can be used to precisely and accurately measure the TGM concentrations in unsaturated soils at multiple locations simultaneously.

Soils are an important sink for persistent organic pollutants (POPs), and high mountain soils are considered a stable reservoir for many compounds due to their high organic matter content. This study focuses on the small-scale variability on the environmental distribution of dichlorodiphenyltrichloroethane (DDT) in mountain soils. Several soil samples taken from May 2007 to June 2008 in a small area at around 1,900 m a.s.l. (Italian Central Alps) were analyzed for DDT compounds. Pedological analyses were done as well. Organic matter content, soil layer, differences in solar radiation, and sampling period were considered as possible variability factors. Organic matter content can account for a DDT concentration difference of a factor 3 among different sites, soil layer can account for a concentration difference of a factor near 2, differences in solar radiation values do not seem to affect DDT concentrations, whereas the sampling period has the greatest influence with a difference factor of three to four among different sampling dates. Summing all these variability factors together, even though operating on such a small scale, we obtain a predicted spatial variability depending on the considered variables near to one order of magnitude. In particular, it was surprising that seasonal variations could be so great. If this conclusion is to be confirmed in the future, this element must be considered very carefully by scientists and environmental agencies during monitoring campaigns.

Sediment profiles from ten excessively limed lakes were used to study the occurrence of lime residues as a result of incomplete lime dissolution and the influence of treatment with very high lime doses on the sequestration of metals in lake sediments. The sediment profiles were subjected to multi-element analysis and compared to sediment profiles from previous studies of lakes limed with normal lime doses and untreated reference lakes. The high lime doses were found to result in large lime residues in the sediment, with lime concentrations of up to 70% of the dry sediment in the studied lakes. Excessive liming, like liming with normal doses, was found to cause increased sequestration in sediments of, e.g. Cd, Co, Ni and Zn, metals where the mobility is known to be highly pH dependent, compared to non-limed reference lakes. No effect of liming on the sequestration of Cu, Cr, Pb and V could be shown. The size of the lime dose did not seem to influence the metal sequestration in the sediment, since no difference between the excessively limed lakes and lakes limed with normal doses was found. On the contrary, the large lime residues were found to cause a dilution of the metal concentrations in the sediments, since lime products used for lake liming generally have lower metal concentrations compared to the sediments.

Riparian wetlands are subject to nitrogen enrichment from upgradient agricultural and urban land uses and also from flooding by nitrogen-enriched surface waters. The effects of this N enrichment on wetland soil biogeochemistry may be mediated by both the presence of plants and the presence of redox-active compounds, specifically iron oxides in the soil. Despite the extensive research on wetland N cycling, the relative importance of these two factors on nitrogen is poorly known, especially for forested wetlands. This study evaluates the responses of the N and the Fe cycles to N enrichment in a riparian forested wetland, contrasting vegetated field plots with plots where the vegetation was removed to test the role of plants. Furthermore, in vitro anaerobic incubations of the experimental soils were performed to track Fe chemical changes over time under anoxic or flooded conditions. Wetland soils treated with N in form of urea, as expected, had significantly higher amounts inorganic nitrogen. In the soils where vegetation was also removed, in addition to inorganic nitrogen pool, increase in organic nitrogen pool was also observed. The results demonstrate the role of vegetation in limiting the effects excess urea has on different soil nitrogen pools. Results from anaerobic incubation of the experimental soils demonstrated the effects of N enrichment on the wetland Fe cycle. The effects of excess nitrogen and the role of vegetation on the Fe cycle in riparian wetland soil became more evident during anaerobic incubation experiments. At the end of the field experiment, Fe concentrations in the soils under the treatments were not significantly different from the control soils at the 5% confidence level. However, during the anaerobic incubation experiment of soils collected at the end of the experiment from these plots, the N-enriched soils and the unvegetated soils maintained significantly elevated concentrations of reducible Fe(III) for the initial 2-week period of incubation, and the soils collected from the plots with both the treatments had the highest Fe(III) concentrations. After 20 days of incubation, however, the Fe(III) concentrations decreased to the similar concentrations in all the incubated soils. The study clarifies the roles vegetation play in mediating the effects of N enrichment and also demonstrates that N enrichment does affect wetland redox cycle, which has strong implications on ecosystem services such as water quality improvement.

Radon levels in two old mines in San Luis, Argentina, are reported and analyzed. The radiation dose and environmental health risk of 222Rn concentrations to both guides and visitors were estimated. CR-39 nuclear track detectors were used for this purpose. The values for the 222Rn concentration at each monitoring site ranged from 0.43 ± 0.04 to 1.48 ± 0.12 kBq m−3 in the Los Cóndores wolfram mine and from 1.8 ± 0.1 to 6.0 ± 0.5 kBq·m−3 in the La Carolina gold mine, indicating that, in this mine, the radon levels exceed up to four times the action level of 1.5 kBq m−3 recommended by the International Commission on Radiological Protection. The patterns of the radon transport process revealed that the La Carolina gold mine can be interpreted as a gas confined into a single tube with constant cross-section and air velocity. Patterns of radon activity, taking into account the chimney-effect winds, were used to detect tributary currents of air from shafts or larger fissures along the main adit of the Los Cóndores mine, showing that radon can be used as an important tracer of tributary air currents stream out from fissures and smaller voids in the rock of the mine.

The recovery potential of stream acidification from years of acidic deposition is dependent on biogeochemical processes and varies among different acid-sensitive regions. Studies that investigate long-term trends and seasonal variability of stream chemistry in the context of atmospheric deposition and watershed setting provide crucial assessments on governing biogeochemical processes. In this study, water chemistries were investigated in Noland Divide watershed (NDW), a high-elevation watershed in the Great Smoky Mountains National Park (GRSM) of the southern Appalachian region. Monitoring data from 1991 to 2007 for deposition and stream water chemistries were statistically analyzed for long-term trends and seasonal patterns by using Seasonal Kendall Tau tests. Precipitation declined over this study period, where throughfall (TF) declined significantly by 5.76 cm year−1. Precipitation patterns play a key role in the fate and transport of acid pollutants. On a monthly volume-weighted basis, pH of TF and wet deposition, and stream water did not significantly change over time remaining around 4.3, 4.7, and 5.8, respectively. Per NDW area, TF SO4 2- flux declined 356.16 eq year−1 and SO4 2- concentrations did not change significantly over time. Stream SO4 2- remained about 30 μeq L−1 exhibiting no long-term trends or seasonal patterns. SO4 2- retention was generally greater during drier months. TF monthly volume-weighted NH4 + and NO3 - concentrations significantly increased by 0.80 μeq L−1 year−1 and 1.24 μeq L−1 year−1, respectively. TF NH4 + fluxes increased by 95.76 eq year−1. Most of NH4 + was retained in the watershed, and NO3 - retention was much lower than NH4 +. Stream monthly volume-weighted NO3 - concentrations and fluxes significantly declined by 0.56 μeq L−1 year−1 and 139.56 eq year−1, respectively. Overall, in NDW, inorganic nitrogen was exported before 1999 and retained since then, presumably from forest regrowth after Frazer fir die-off in the 1970s from balsam wooly adelgid infestation. Stream export of NO3 - was greater during winter than summer months. During the period from 1999 to 2007, stream base cations did not exhibit significant changes, apparently regulated by soil supply. Statistical models predicting stream pH, ANC, SO4 2-, and NO3 - concentrations were largely correlated with stream discharge and number of dry days between precipitation events and SO4 2- deposition. Dependent on precipitation, governing biogeochemical processes in NDW appear to be SO4 2- adsorption, nitrification, and NO3 - forest uptake. This study provided essential information to aid the GRSM management for developing predictive models of the future water quality and potential impacts from climate change.

Poorly constructed wells (leaky or without a gravel pack) and abandoned wells can behave as conduits for the interconnection of aquifers at different depths and facilitate the transfer of contaminants between these aquifers. This is the case with Campo de Cartagena (SE Spain) where the primary land use is intensive irrigated agriculture, along with a high density of wells. The unconfined aquifer is heavily impacted by a high concentration of nitrate associated with agricultural activities. The present work provides a methodological approach to evaluate the impact of the unconfined aquifer on the water quality of the confined aquifer caused by leaky wells in high-density areas of production wells. The research approach included the use of geochemical and isotopic tools; specifically, nitrate was used as a tracer for evaluating the impact, and the code MIX_PROGRAM was used for mixing calculations. Results show an increase of the impact of the unconfined aquifer on the confined aquifer along the groundwater flow direction toward the coast, although this general pattern is controlled by local factors (pumping, intensity of agricultural practices, density of wells, and groundwater residence time).

As a new approach, urban air pollution was characterised by the variation of columnar content of the pollutants. Columnar content (CC) was estimated as the product of the pollutant’s mixing ratio and the mixing height. Mixing ratio data of the Metropolitan Air Quality Monitoring Network of Budapest were used, whilst mixing height was calculated by the meteorological AERMET model code. Time variation of CC refers to the real pollution exchange in the atmosphere that allows direct investigation of the emissions as well as post-emission modifications of the pollutants (such as chemical degradation or production). The diurnal urban CO cycle was found to be determined by two or three main influx peaks according to the traffic pattern of the site. The diurnal variation of NOx level was found to be driven by traffic emission as well. Variant ratios of NOx to CO influxes obtained for the different locations of the city range from 0.12 to 0.23, probably according to the vehicle composition of the traffic. The daily balance of photochemical production, chemical degradation and deposition of ozone yielded negative or positive depending on the location. Negative balances imply that the polluted urban atmosphere is a net ozone neutraliser source. Entrainment from the free troposphere yielded the major contributor to the diurnal ozone level at each site. The diurnal urban PM10 cycle was found to be determined by traffic emission during the morning and evening rush hours whilst secondary aerosol formation around noon. In the evening, high PM10 level rise was observed due to direct traffic emission as well as rapid conversion of the fine aerosol fraction to the coarse fraction.

Environmentally safe disposal of sulfide-rich reactive mine tailings is one of the major challenges facing the mining industry in Canada, Scandinavia, USA, and many other parts of the world. Placing tailings under a water cover is one of the effective methods to reduce the influx of oxygen to the tailings. Wind-induced turbulence and subsequent resuspension of the tailings, however, are major concerns with this approach. In this paper, a study of wind-induced resuspension at the Shebandowan tailings storage facility, northwestern Ontario, Canada, is discussed. The study compares computer modeling of required water cover depths and resuspended tailings concentrations to observed field data. The calculated minimum water cover depths required to eliminate resuspension were found to be higher than the existing implemented water cover depths in each cell. The predicted resuspended tailings concentrations for the west cell were 6-22 mg/l with an average value of 15 mg/l and, for the east cell, 1-10 mg/l, with an average of 6.0 mg/l. In comparison, optical backscatter sensors, deployed in situ, recorded average resuspended tailings concentration up to 25 mg/l, indicating that the model results were similar to the field-measured values. Results from sediment trap measurements did not show any correlation between the amount of resuspended tailings and water cover depth. Sediment traps collect not only sediments eroded and suspended at the location of deployment but also those that have been transported from elsewhere and redeposited at the trap location. The amount of resuspension occurring at Shebandowan does not raise a major concern because discharge from the tailings area is collected and managed before it reports to the final effluent.