A modelagem da dinâmica de solutos no solo tem se mostrado uma ferramenta essencial, pois permite simular cenários e prever impactos ao meio ambiente associados ao manejo inadequado de fertilizantes agrícolas. Na zona radicular das culturas a parametrização do transporte de solutos, bem como a parametrização física do solo, são de difícil determinação tornando a sua modelagem onerosa e imprecisa. Portanto, a presente pesquisa teve como objetivo avaliar a performance do modelo SWAP (Soil, Water, Atmosphere and Plant), em simular a extração da solução do solo pela cultura do milho, em ambiente protegido. O ambiente de estudo ficou restrito à rizosfera da cultura do milho ao longo de seu ciclo de desenvolvimento, mediante a aplicação de uma solução de nitrato de potássio via água de irrigação. Para isso, conduziu-se um experimento em ambiente protegido, cujo cultivo do milho foi feito em 18 lisímetros de drenagem de 500L com plantio de duas covas por lisímetro (plantio em 22/11/2014 e colheita em 22/02/2015). Os valores de umidade volumétrica do solo e de condutividade elétrica da solução do solo foram registrados pela TDR (Time Domain Reflectometry), sendo monitorados em 4 profundidades ao longo da secção transversal das raízes (5, 15, 25 e 35 cm). Também foram monitoradas variáveis agrometeorológicas a fim de se descrever as condições experimentais. Os valores simulados pelo modelo SWAP foram confrontados com os dados observados, registrados pela TDR. A avaliação da performance do modelo foi feita pelo emprego do índice de concordância (Id), índice de avaliação de modelos (E), raíz quadrada média do erro (RMSE) e coeficiente de determinação. Diante dos resultados obtidos, percebeu-se pelo monitoramento agrometeorológico que o ciclo da cultura se deu em condições de anomalias climáticas, isso de certa forma influenciou na extração de água pela cultura. A simulação da extração de água na rizosfera do milho pelo modelo SWAP demonstrou uma satisfatória performance do modelo, o qual apresentou resultado pelos índices de avaliação valores superiores a 0,7 e índices de concordância superiores a 0,9 para todas as camadas monitoradas. O erro quadrático médio foi inferior a 0,009 cm3 cm-3 para todas as camadas, apesar de ter nas camadas mais profundas uma atenuação qualitativa na simulação. O movimento da extração da solução do solo na rizosfera, em especial, nas camadas superficiais apresentaram resultados satisfatórios com índices de avaliação de modelos de 0,659 e 0,596 e índices de concordância de 0,913 e 0,834, respectivamente, para as camadas de 5 e 15 cm de profundidade. Já para as camadas mais profundas não se observou boa aderência do valor simulado aos dados. O coeficiente de extração relativa da solução do solo pelo milho apresentou valor de 16%. Assim, o modelo SWAP mostrou-se satisfatório na simulação do movimento da solução do solo na zona radicular da cultura do milho, mesmo sob condições atmosféricas extremas. Não obstante, seu desempenho foi prejudicado para as simulações em camadas inferiores, onde foi observada uma baixa variação do conteúdo de água e concentração de sais no solo. / The modeling of solute dynamics in soil is an essential tool for simulating scenarios and predicting environment impacts associated with inadequate management of fertilizers. Solute transport parameter and soil physical parameters in the vadose zone are difficult to determine, causing modeling to be expensive and imprecise. This research, therefore, was set up to evaluate the effectiveness of the SWAP (Soil, Water, Atmosphere and Plant) model to simulate soil solution uptake by corn under controlled environmental conditions. The study consisted of applying a potassium nitrate solution in irrigation water to maize rhizosphere throughout its development cycle. The experiment was conducted in a greenhouse, in which maize was planted on 11/22/2014 and harvested on 02/22/2015 in eighteen 500L drainage lysimeters.The soil moisture values and electrical conductivity of soil solution were registered by TDR (Time Domain Reflectometry) at four depths (5, 15, 25 and 35 cm) along the cross-section of the root. Environmental variables were also monitored in order to characterize the experimental conditions. Values simulated by the SWAP model were compared with observed data recorded by the TDR. Model performance was evaluated by the use of the Concordance Index (Id), the Model Assessment Index (E), Root Mean Square Error (RMSE), and Coefficient of Determination. As the experiment was conducted under controlled conditions, the water uptake patterns might not be reflective of uptake patterns under normal weather conditions. The simulation of water extraction in the rhizosphere of corn by SWAP model matched observed values, with indices greater than 0.7 and concordance rates of over 0.9, for all monitored layers. The RMSE was less than 0.009 cm3 cm-3 for all layers. The concentration of extracts of the soil solution in the rhizosphere, in particular in the top two layers, were satisfactorily simulated with model evaluation indexes of 0.659 and 0.596, and concordance rates of 0.913 and 0.834, respectively, for the 5 and 15 cm layers. For the deeper layers, there was little correlation between the observed and simulated value. The relative extraction coefficient of soil solution for corn was 16%. Thus, the SWAP model satisfactorily simulated soil solution movement in the upper layers of the vadose zone of maize, even under extreme weather conditions. However, the model did not perform as well in the lower layers performance was impaired for the simulations in lower layers, which had low variation in the observed water content and salt concentration in the soil.

No description available.

La zone non saturée joue un rôle clé sur le transfert des pesticides et la qualité des eaux souterraines. Les connaissances sur les processus d’écoulement et de rétention dans les matériaux géologiques de la zone non saturée au-delà des sols sont toutefois parcellaires. Le transfert du glyphosate et du S-métolachlore (SMOC), et de leurs métabolites AMPA, ESA-métolachlore (MESA) et OXA-métolachlore (MOXA) est étudié en colonne pour deux matériaux fluvio-glaciaires issus d’un aquifère de l’Est lyonnais : un sable, S-x, et un mélange bimodal de graviers et de sables, Gcm,b. Pour des conditions de non-saturation en eau, l’écoulement dans les colonnes est fractionné en deux zones, eau mobile et eau immobile, d’importance variable suivant le solide. La sortie du SMOC est retardée par rapport au traceur de l’eau ; son bilan de masse déficitaire traduit une rétention de la molécule lors de son transfert. A l’inverse, le MESA et le MOXA se comportent comme le traceur de l’eau. Le glyphosate et l’AMPA sont très peu mobiles dans la colonne de Gcm,b (seul matériau étudié) avec des quantités éluées inférieures à 1% de la quantité appliquée. La modélisation montre que le transfert des molécules est affecté de manière variable suivant le matériau par la cinétique physique d’échange entre les zones d’eau mobile et immobile et par la cinétique chimique des molécules. Cette cinétique chimique est décrite par des expérimentations complémentaires de sorption en batch. La caractérisation des matériaux révèle la présence d’oxydes et de minéraux argileux qui pourrait expliquer leur forte réactivité, qui s’avère parfois supérieure à celle des sols de la zone d’étude. / Vadose zone play a key role in pesticides transfer and groundwater quality. Knowledge’s about leaching and retention processes in the vadose zone below the shallow soil zone are still poorly understood. Transfer of glyphosate, S-metolachlor (SMOC), and their metabolites AMPA, ESA-metolachlor (MESA) and OXA-metolachlor (MOXA) is studied in unsaturated columns filled with two glaciofluvial materials collected in the East of Lyon: a sand, S-x, and a bimodal gravel, Gcm,b. Experiments show water fractionation into mobile and immobile compartments with variable importance according to material column. SMOC outflow is delayed compared to the conservative tracer. SMOC mass balance is in deficit revealing retention in columns. At the opposite, complete mass elution associated with retardation factors close to unity shows that there is no adsorption of MESA and MOXA in either lithofacies. Glyphosate and AMPA mobility is very low in the one Gcm,b column studied with amounts in leachates inferior to 1% of applied. Modelling show pesticides and metabolites transfer is affected by both flow regionalisation and non-equilibrium sorption. Chemical kinetic of sorption mechanisms is studied with complementary batch experiments. The high glaciofluvial materials reactivity, in some cases upper than soil reactivity from the study site, could be attributed to oxides and clay minerals.

>Magister Scientiae - MSc / Aquifer vulnerability assessment is increasingly becoming a very significant basis in order to fulfil the water demands in South Africa. Knowledge of soil hydraulic properties that consists of the soil water retention and hydraulic conductivity functions is a prerequisite for predicting solution transport in soils. The overall objective of the study is to develop a database of hydraulic properties for collected undisturbed samples and to test selected models by making use of this database. Studies of the vadose zone are generally restricted to the top 1.2 meters; therefore this study aims at essentially improving the lack of measurements and modelling in the vadose zone. There exist several methods to determine hydraulic properties of soil that make use of hydraulic conductivity (K) determination in the vadose zone. The most accurate estimates of hydraulic conductivity are possible through direct measurements or measurements of the water retention curve. For this study, the drilling and sampling of five boreholes (maximum depth 20 m) proceeded during March and April 2005 at two typical sites in the Western Cape, namely the Berg river site (Riebeek West) and Ithemba site (Cape Flats). In total, 76 undisturbed core samples were collected from which the detailed borehole log descriptions were made. The determination of the soil water retention curves of the collected samples was based on laboratory techniques using Eijkelkamp drying and suction equipment (sand box and clay box). When modelling groundwater vulnerability, it is essential to look at the soil water retention curves with increased importance, as they provide graphical and mathematical confirmation of porosity, preferential flows, volumetric water content and unsaturated hydraulic conductivity. Therefore, a numerical model called RETC was used to determine soil hydraulic properties. The RETC model uses equations of Van Genuchten (Van Genuchten, 1980) and Brooks-Corey (Brooks and Corey, 1966) to determine parameters for soil water retention and the methods of Mualem (1976) and Burdine (1953) to determine unsaturated hydraulic conductivity functions. Saturated hydraulic conductivity values were estimated by using RETC soil database based on textural descriptions of collected samples. Using the soil hydraulic estimates obtained from RETC, sensitivity analyses were run with a one dimensional transport model, Macro 5.0 for two sites at iThemba and in the Berg river.

Of the many toxic chemicals released into the Hanford vadose zone over the decades of nuclear weapons production, uranium has emerged as a contaminant of significant interest. The ammonia gas injection remediation method has been identified as a promising approach towards mitigating the risks to the ecosystem by limiting the mobility of the radionuclide in the vadose zone. The remediation method was replicated using synthetic porewater solutions with a range of constituent concentrations equal to that of the Hanford 200 Area vadose zone. The uranium-bearing products of the remediation method were characterized using kinetic phosphorescence analysis for aqueous uranium, scanning electron microscopy with energy dispersive spectroscopy and electron microprobe for imaging and elemental analysis, and a sequential extraction procedure modified for the sample precipitates. Evaluation revealed that the resultant uranium-bearing solids likely took the form of uranium-silicates and uranium carbonates, with the latter being precipitated primarily in mid-to-high bicarbonate samples.

No description available.

An investigation to assess the anthropogenic pollutant loads, transport and impact on shallow groundwater in one of Kampala’s peri-urban areas (Bwaise III Parish) was undertaken. Bwaise III is a densely populated informal settlement with a high water table (<1.5 m) and inadequate basic social services infrastructure (e.g, sanitation, safe water supply, roads, etc). Field surveys were undertaken to identify, locate and quantify various pollutant sources. Information on the usability and operational aspects of the excreta and solid waste management systems was obtained from consultations with the residents. Water from installed monitoring wells and one operational protected spring and wastewater (sullage) characteristics (quality, discharges for drains and spring, water levels for the wells) as well as soil characteristics (soil stratigraphy, physical and chemical) were determined through field and laboratory measurements. Laboratory batch experiments were undertaken to estimate phosphorus sorption potential of the soils. The results reveal that excreta disposal systems, solid waste and sullage are the major contributors to shallow groundwater contamination. High contaminant loads from these sources accumulate within the area resulting in widespread contamination. The water table responds rapidly to short rains (48hr) due to the pervious and shallow (<1 m) vadose zone, which consists of mostly organic fill material. Rapid water quality deterioration (increased thermotolerant coliforms, organic content in the form of total kjedahl nitrogen, phosphorus) following rains potentially follows from leaching, desorption and macropore flow. Spatial variation of the water quality in the area is largely related to anthropogenic activities within the vicinity of the well sources. Animal rearing, solid waste dumps and latrines are seen to result in increased localised microbial and organic content during the rains. The spring discharge with high nitrate levels does not respond to short rains suggesting that this source is fed by regional baseflow. The corresponding high microbial contamination in this case is a result of observed poor maintenance of the protection structure leading to direct ingress of contaminated surface runoff. Natural attenuation of contaminants is very limited. Estimated bacteria die-off rates are very low, about 0.01hr-1, suggesting a high risk for microbial contamination. The soils still have potential to retain additional phosphorus, whose sorption is largely a function of iron, available phosphorus and moisture content of the soils. This is also seen with the model results in which the phosphorus contaminant plume sticks to the surface irrespective of the rainfall infiltration rates. Simulation results show that continuous heavy intense rains (> 0.25mm/min) result in rapid flooding occurring within 1hr to 2 days. With lower rains, the water table does not rise to the surface, and no flooding takes place. Protection of the shallow groundwater in the area requires socio-technical measures targeting reduction of pollutant loads within the area as well as a wider spring catchment. Re-protection of the spring, coupled with awareness creation, should be immediately addressed so as to reduce microbial contamination. Community participation in solidwaste management should be encouraged. Resource recovery systems such as composting of the mostly organic waste and use of ecological sanitation toilet systems should be piloted in the area. Successful operation of the systems however depends on continuous sensitisation of the communities. / QC 20101207

Mining of uranium ore and its extraction using the milling process generates solid and liquid waste, commonly termed uranium mine tailings. Uranium mine tailings is radioactive, as it consists of residual uranium, thorium, and radium, which amounts to 85% of the original ore’s radioactivity. Due to the extensively long half-lives of uranium (4.5x109 years), thorium (75,400 years), and radium (1,620 years) and their harmful radioactive, it is imperative to isolate uranium mine tailings from the environment for a longer period. Containment of uranium mine tailings in dam-like structures, called uranium mine tailings dam (UMTD), is the most followed disposal and storage method. Like a conventional water retention dam, UMTDs are also susceptible to failure, mainly due to adverse weather conditions. Once the UMTD fails, a fraction of the radioactive tailings infiltrates and migrate through the vadose zone contaminating the groundwater sources underlying it. Radionuclide behavior and migration in the subsurface are affected by several environmental factors. To minimize the uncertainty and improve current radionuclide fate and transport models, it is vital to study these factors and any interdependence existing between them. This study aims to understand these environmental factors by i) enlisting the factors affecting subsurface radionuclide migration through scoping review of articles and reports, and ii) analyzing the interdependence existing between the factors using the complex network theory (CNT) approach and identifying the dominant factors among them. Factors such as chemical and biological characteristics of soil stratigraphy, groundwater, and radioactive tailings plume, meteorological, and hydrogeological are found to influence radionuclide behavior and transport mechanisms in the vadose zone. CNT approach described soil microorganisms, fraction of organic carbon, infiltration rate of the soil, transmissivity, clay fraction in the soil, particulates in groundwater, and infiltrating rainwater as dominant factors in the NoF based on their centrality measures and sensitivity analysis of the network of factors (NoF). Any uncertainty associated with these factors will affect and propagate through the model. Hence, sufficient resources should be directed in the future to characterize these factors and minimize their uncertainty, which will lead to developing reliable fate and transport models for radionuclides. / Thesis / Master of Applied Science (MASc) / Waste products from uranium mining and milling operations are called uranium mine tailings, which are radioactive. Generally, uranium mine tailings are disposed of and isolated in dam-like structures referred to as uranium mine tailings dams (UMTD). One of the most common causes of UMTD failure is extreme weather conditions. When a UMTD fails, a part of tailings, consisting of radionuclides uranium, thorium, and radium, infiltrate into the subsurface through the vadose zone. Radionuclide behavior and transport in the subsurface is influenced by several environmental factors. The objective of the present study is to understand the factors affecting radionuclide migration by i) conducting a scoping review on radionuclide migration in the subsurface to describe the factors studied in the literature, and ii) understanding and analyzing any relation among the factors and deriving the most dominant factors based on their relation. This study can be used further to develop accurate and reliable radionuclide fate and transport models with minimal uncertainty.

<p dir="ltr">Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic chemicals known for their persistence in the environment and potential health risks. PFAS are linked to several adverse effects in human and wildlife health. The detection of PFAS in biosolids has raised concerns about their use in agricultural and land application practices. This is because some PFAS are known to enter the food system through plant uptake and some leach into groundwater. The purpose of this study was to examine the PFAS profile in soils and porewater with depth at an agricultural site with historical biosolids applications. The site selected has received biosolids at agronomic rates for corn for approximately four decades. This study utilized a total of six lysimeters, three “shallow” at 60 cm and three “deep” at 120 cm, to monitor PFAS leaching in soil. Porewater samples were collected within 1-3 days after rain events based on rainfall amount and response of the moisture sensor installed at the site. For each of five porewater sampling events, PFAS and supplemental water parameters like total organic carbon (TOC) and pH were measured. Soil cores, taken in one-foot increments before and after the 3-month study, were analyzed for PFAS, soil OC, moisture, and grain size. All samples were analyzed using high resolution mass spectrometry for 54 PFAS and in line with EPA 1633 method. Soil characteristics such as texture, moisture, and soil OC significantly influence PFAS transport and sorption capacity within the soil profile, impacting PFAS distribution across soil depths. PFAS in the soil profile decreased with increasing depth and directly correlated with soil OC. Long chain PFAS were strongly retained in the top 60 cm and minimally distributed to the porewater. Short-chain PFAS proportionally dominated porewater samples, with elevated concentrations observed in shallow porewater driven by increased saturation (perched water) from a low permeability clay layer. Unsaturated conditions enhance PFAS retardation through air-water interface partitioning in addition to soil particle sorption mechanisms. In this study, less than 0.1% of PFAS leach from the vadose zone of a biosolid impacted plot annually, underscoring the longevity of PFAS in the soil profile and importance of understanding PFAS transport dynamics for effective environmental management.</p>

Nonpoint source (NPS) pollution is possibly the greatest form of contamination to our nation's waters. Nutrient pollutants, such as nitrate and ammonium, often enter aquatic ecosystems through surface and subsurface hydrological transport that drain agricultural watersheds. The over-abundance of nitrogen within these watersheds is easily transported to receiving stream and rivers, and result in aquatic ecosystem degradation. In response to the problem of nutrient loading to aquatic ecosystems, ecosystems scientists and federal and state governments have recommended the use of streamside management zones (SMZ) to reduce the amount of NPS pollutants. A small agricultural watershed in southwestern North Carolina was utilized to quantify subsurface transport of nitrate and ammonium to a naturally developing riparian area along Cartoogechaye Creek. Vertical and lateral transport of nitrate and ammonium were measured along three transect perpendicular to the stream. Transects were instrumented with time domain reflectometry (TDR) and porous cup tension lysimeters to monitor soil water and nutrient flux through the pasture and riparian area located at the base of the watershed. The HYDRUS 2-D flow and transport model was used to predict and simulate subsurface flow. Predicted flow was coupled with observed field nutrient data to quantify nutrient flux as a function of slope location. HYDRUS 2-D was capable of simulating subsurface flow (saturated and unsaturated) as a function of observed soil physical properties (bulk density, saturated hydraulic conductivity, particle size distribution, water retention characteristics) and climatic data (precipitation, air temperature, wind speed, etc.). The riparian area was effective in reducing the amount of nonpoint source pollution to a naturally developing riparian area from an agricultural watershed. Dramatic decreases in both NO3- -N and NH4+ -N in upland pasture water were observed within the riparian area. Seasonal percent reductions of NO3- from the pasture to riparian area in subsurface water within the study watershed are as follows: summer (2002) = 456%; fall (2002) = 116%; winter (2003) = 29%; spring = 9%, pasture and riparian, respectively. / Master of Science