Over the last decades, arsenic (As) contamination of soil-plant-water systems has become a major concern for Bangladesh and West Bengal, India. The geochemistry of the sediment depositional environment which subsequently, on sediment burial, give rise to elevated As in Holocene groundwater’s of Southeast Asia, may provide clues to unravelling the mechanistic basis and spatial heterogeneity of this phenomenon. The Sundarbans mangrove ecosystem, Bangladesh, is a modern analogue, and indeed forms a continuum with, the Holocene sediments of concern and thus studying As cycling in surface Sundarbans sediments. Similarly, rice paddy fields in many regions of the Bengal Basin form a continuum with Holocene sediments. Sediment cores were collected from a wide range of locations within the Sundarbans to study surface spatial, as well as down the profile (~1 m), As distribution and it’s association with other geochemical parameters. Pore and surface water, and Diffusive Gradients in Thin films (DGT) were sampled from 4 different interlocked sub-habitats over 0.29 km2: major river bank, main tributary, forest floor and minor tributary. Further experiments were conducted to observe As dynamics in mangrove surface sediments on application of mangrove detritus. Finally 3 interlinked experiments (field manuring, soil batch culture, greenhouse growth trials) were conducted to assess the effect of farm-yard manure (FYM) and rice straw, at a field application rate practised in Bangladesh (5 t/ha), on As mobilization in soil and subsequent assimilation by rice. As concentration in mangrove sediment down the profile was found to be more associated with elevated Fe and Mn than with organic matter (OM), with significant spatial variations among the locations. Sediment particle size was an important factor determining As retention and mobilization, which is also true for deeper Bengal Bay sediments. Proximity to mangrove vegetation and to water bodies was found to have significant effect on As dynamics. Porewaters from coarse textured, low OM riverbank sediment were high in As, but with only a small pool of As for resupply from the solid phase, showing similarities with grey aquifer sediments compared to fine textured and high OM content forest floor sediments. The As column dynamics study showed that As release into porewater was strongly associated with Fe release, indicating the strong association of the 2 elements, with OM playing a major role in their dissolution. The desorption studies also showed OM driving As mobilization within short time. Due to strong redox cycling very little evidence of As methylation was observed in biologically active mangrove porewaters. But we found 10-fold increase in dimethylarsinic acid (DMA) production compared to a non-amended control using the same sediments treated with mangrove detritus in the laboratory. OM amendments lead to considerable mobilization of As into both soil porewaters and standing surface waters in rice paddy. In a greenhouse rice cultivation experiment, flooding initially caused greatly enhanced As mobilization in porewater (< 24 d), but the effects of flooding on As mobilization decreased during later rice growth, particularly at grain fill. However, OM amendment did not cause significant As accumulation in grain and straw compared to control. It was noted in field trials and greenhouse studies that OM fertilization greatly enhanced As mobility to surface waters, which may have major implications for fate of As in paddy agronomic ecosystems.

The water stored in and flowing through the subsurface is fundamental for sustaining human activities and needs, feeding water and its constituents to surface water bodies and supporting the functioning of their ecosystems. Quantifying the changes that affect the subsurface water is crucial for our understanding of its dynamics and changes driven by climate change and other changes in the landscape, such as in land-use and water-use. It is inherently difficult to directly measure soil moisture and groundwater levels over large spatial scales and long times. Models are therefore needed to capture the soil moisture and groundwater level dynamics over such large spatiotemporal scales. This thesis develops a modeling framework that allows for long-term catchment-scale screening of soil moisture and groundwater level changes. The novelty in this development resides in an explicit link drawn between catchment-scale hydroclimatic and soil hydraulics conditions, using observed runoff data as an approximation of soil water flux and accounting for the effects of snow storage-melting dynamics on that flux. Both past and future relative changes can be assessed by use of this modeling framework, with future change projections based on common climate model outputs. By direct model-observation comparison, the thesis shows that the developed modeling framework can reproduce the temporal variability of large-scale changes in soil water storage, as obtained from the GRACE satellite product, for most of 25 large study catchments around the world. Also compared with locally measured soil water content and groundwater level in 10 U.S. catchments, the modeling approach can reasonably well reproduce relative seasonal fluctuations around long-term average values. The developed modeling framework is further used to project soil moisture changes due to expected future climate change for 81 catchments around the world. The future soil moisture changes depend on the considered radiative forcing scenario (RCP) but are overall large for the occurrence frequency of dry and wet events and the inter-annual variability of seasonal soil moisture. These changes tend to be higher for the dry events and the dry season, respectively, than for the corresponding wet quantities, indicating increased drought risk for some parts of the world.

No description available.

Distributions of water transit times (TTDs), and related storage-selection (SAS) distributions, are spatially integrated metrics of hydrological transport within landscapes. Recent works confirm that the form of TTDs and SAS distributions should be considered time variant-possibly depending, in predictable ways, on the dynamic storage of water within the landscape. We report on a 28 day periodic-steady-state-tracer experiment performed on a model hillslope contained within a 1 m3 sloping lysimeter. Using experimental data, we calibrate physically based, spatially distributed flow and transport models, and use the calibrated models to generate time-variable SAS distributions, which are subsequently compared to those directly observed from the actual experiment. The objective is to use the spatially distributed estimates of storage and flux from the model to characterize how temporal variation in water storage influences temporal variation in flow path configurations, and resulting SAS distributions. The simulated SAS distributions mimicked well the shape of observed distributions, once the model domain reflected the spatial heterogeneity of the lysimeter soil. The spatially distributed flux vectors illustrate how the magnitude and directionality of water flux changes as the water table surface rises and falls, yielding greater contributions of younger water when the water table surface rises nearer to the soil surface. The illustrated mechanism is compliant with conclusions drawn from other recent studies and supports the notion of an inverse-storage effect, whereby the probability of younger water exiting the system increases with storage. This mechanism may be prevalent in hillslopes and headwater catchments where discharge dynamics are controlled by vertical fluctuations in the water table surface of an unconfined aquifer. Plain Language Summary Volumes of water reside within landscapes for varying amounts of time before they are discharged to a stream. That length of time determines how long the water has to interact chemically with soil and rock, and therefore influences the chemistry of water that ends up in stream channels. Quantifying the full range and variability of those travel times remains a challenge. We built an experimental hillslope, which allows us to keep track of all the water that enters and exits the soilsomething that is difficult to accomplish in open environmental systems. We introduced chemically distinct water into the hillslope at specific points in time and followed the movement of that water within, and upon exit from the soil. We discovered that the water being discharged from the hillslope tends to have resided in the landscape for shorter lengths of time when the hillslope is very wet (like a wetted sponge) than when it is very dry (like a dry sponge). This insight helps us understand how different rainfall regimes, and the associated wetness of the landscape, can potentially influence water transit times through the landscape, and their relationship with stream chemistry.

No description available.

Thesis advisor: Rudolph Hon / Groundwater in the Shepley's Hill Landfill (SHL) area had a high arsenic concentration for at least 20 years. This study is aimed at understanding the migration pathways of arsenic in the SHL area and postulating the possible sources and mechanisms for the mobilization of arsenic. A direct-push sampling technique (DPT) was applied in the summer of 2010 within the SHL and its downgradient area, which provided groundwater samples from various depths and locations. A long-term monitoring dataset from 1998 to 2009 was utilized as a subsidiary source for temporal analysis. Spatial distributions of arsenic and other major dissolved compositions were analyzed. Extremely high arsenic concentrations (up to ~ 15000 µg/L) were detected in the deep glacial sand deposits close to a peat layer within the SHL. Arsenic concentrations decrease dramatically in the downgradient area north of the SHL. The transport of arsenic in the SHL area is similar to that of iron. The source of arsenic is likely to been within the boundary of the SHL. The glacial sand overburden within the SHL provides enough source for the arsenic mobilization. A possible mechanism of arsenic mobilization in the SHL area is that the reductive dissolution/desorption of arsenic from iron bearing minerals under a lasting reducing environment created by decompositions of organic matter in waste and peat. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Thesis advisor: Rudolph Hon / In the northeast United States, arsenic (As) contamination in groundwater is frequently associated with historical landfill leachate plumes. Based on the history of Shepley's Hill Landfill (SHL) in Devens, MA, solid waste disposal activities spanned nearly a century of landfilling with little or no documentation of when or what waste material was disposed. Past geochemical investigations proved the presence of high levels of As in groundwaters within and around the SHL region. A total of 114 samples were collected from the SHL region and analyzed for their hydrogeochemistry and isotopic signature. Since the isotopic ratios of äD and ä18O can potentially be influenced by the mobilization process of As, this study attempts to identify any correlations between the stable isotopic ratios and the hydrogeochemistry of SHL waters. The results of the groundwater hydrogeochemical analysis show multiple relationships between metal concentrations and As concentration levels, typical of groundwater undergoing redox reactions. The result of the stable isotope analysis show significant fractionation of stable isotope ratios away from the meteoric water line. However, the role of strong redox gradients and various redox ladder reactions involving water did not produce a significant correlation with the isotopic fractionations present within different zones of the landfill. In most cases, the fractionations stand independent of the increase/decrease in As concentration and can be attributed to either unrelated chemical reactions within groundwater or evaporation. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Thesis advisor: Rudolph Hon / The application of road de-icers has lead to increasing solute concentrations in surface and ground water across the northern US, Canada, and northern Europe. In a public water supply well field in southeastern Massachusetts, USA, chloride concentrations in ground water from an unconfined aquifer have steadily risen for the past twenty years. The objectives of this study are to understand spatial and temporal trends in road salt concentrations in order to identify contamination sources and fate. To this end, the methods of this project include field and lab work. Water samples were collected from surface, near-surface, and ground water from March 2012 to March 2013. The other major field data are specific conductance measurements from probes located in three piezometers. In the lab, all samples were analyzed for major ions with ion chromatography analysis. Additionally, trace elements were measured by inductively coupled plasma analysis on a subset of samples. The results of these hydrogeochemical procedures showed several important trends. First, the highest concentrations of sodium and chloride from near-surface samples were located near to roadways. Second, ground water samples taken from glacial sediments contained relatively high concentrations throughout the water column, whereas ground water samples from wetlands had high concentrations only near the surface. Third, there was no clear relationship between pH and cation concentrations. Finally, specific conductance data showed strong seasonal trends near to the surface, whereas values taken from deeper in the aquifer were steadily increasing. Based on these results, it is highly probable that road salt application is the dominate contamination source. The pathways of road salt in the watershed include runoff into surface water and infiltration into the vadose zone and ground water. Road salt appears to preferentially travel through glacial features rather than floodplain features. It is possible that sodium from road salt is sorbed to aquifer sediment and displaces other cations. However, the low values of trace metals suggest that cation exchange is not mobilizing heavy metals. Finally, the increasing specific conductance values deep in the aquifer suggest that road salt is retained within the aquifer and concentrations will likely increase in the future if the current road salt application procedures are continued. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

A crescente importância da questão do uso sustentável da água e a conseqüente necessidade de se diminuir a poluição e o desperdício desse reservatório terrestre, impulsionaram esse estudo. O objetivo principal do trabalho é avaliar a aplicação de indicadores isotópicos ambientais, como Sr, Pb, O e D, para estudos da origem e qualidade da água de recarga de um aqüífero, bem como do impacto da impermeabilização da superfície da cidade sobre esses indicadores. Para isso foram escolhidas duas áreas na Bacia do Alto Tietê, na Cidade de São Paulo, uma na Zona Oeste (área 1 - USP) e outra na Zona Leste (área 2 - VE), onde foram coletadas amostras de água da SABESP, de água de chuva e de poços de monitoramento, por um ano, além de sedimentos. Foram realizadas análises químicas em 390 amostras de água e 62 de solos, além de 413 análises isotópicas de H e O e 122 de Sr e Pb em água, além de 34 de Sr e Pb em sedimento. A determinação de procedimentos químicoanalíticos, para análises isotópicas de Pb e Sr em águas com baixas concentrações destes elementos, foi o primeiro resultado deste trabalho e definiu que as amostras devem ser filtradas e acidificadas, antes da evaporação, e seus resíduos devem ser dissolvidos com HCl, HNO3 e HF, para depois a amostra ser purificadas por resina de troca iônica. Todas as amostras de água subterrânea apresentaram alguma contaminação antrópica. Os poços da VE apresentaram contaminação caracterizada por altas concentrações de cloreto, sulfato e nitrato e a USP de cloreto, sulfato, amônio, sódio e fluoreto, além de elevada alcalinidade. Os lixiviados de Pb em sedimentos mostraram que há pouca interação destes com a água subterrânea e esses não foram utilizados como membros finais da mistura. As análises isotópicas (H e O) das chuvas indicaram que as precipitações da Cidade de São Paulo sofrem influência tanto do efeito quantidade, quanto das diferentes origens de massas de ar em diferentes períodos do ano. A estimativa de recarga utilizando os isótopos mostrou que a VE, mais impermeável, apresentou uma contribuição antrópica 10% (H e O) a 20% (Pb) maior do que a USP. Na USP, a recarga natural calculada por isótopos de H e O possui uma média de 70%, enquanto na VE esse valor cai para 59%. Os isótopos de Pb forneceram médias de 53% e 35%, respectivamente para USP e VE, de recarga natural. Diante dos cálculos efetuados e análises (químicas e isotópicas) concluiu-se que os isótopos de Sr não são indicados para traçar a recarga de áreas contaminadas, já que mostram pouca interação entre a rocha e a água. Os isótopos estáveis não apresentaram muita diferença entre as assinaturas de água da SABESP e das amostras mais contaminadas por esgoto e não são bons diferenciadores dessas duas fontes. Já os isótopos de Pb são bons indicadores de recarga para áreas contaminadas, porque conseguem discriminar as águas oriundas de fugas da rede da SABESP e do esgoto. / The importance of a sustainable use of water and its resultant necessity of reducing groundwater pollution and waste is the driving force of this study. The main subject is to evaluate the application of environmental isotopes, as H, O, Sr and Pb, for studying the groundwater recharge sources and its quality, as well as the impact of the surface sealing on these indicators, due to urbanization. Two areas with different occupation in São Paulo City, within the Upper Tietê Watershed, one in west zone (area 1) and other in the east zone (area 2) were chosen to do this study. In both areas, water samples were collected for a year from: monitoring wells, supply agency and rain. Sediments were also sampled during drilling. Chemical analyses were carried out in 390 water samples and 62 sediments, whereas H and O isotopic analyses were performed on 413 water samples and Pb and Sr isotopic analyses on 122 water samples and 34 sediments. This work also determined that analytical procedures for Pb and Sr isotopic analyses of groundwater samples with low Sr and Pb concentration should filter and acidify water samples prior to evaporate it, their residue should be dissolved with HCl, HNO3 and HF, before purification by ionic exchange resin. All groundwater samples showed some anthropogenic contamination. Groundwater contamination in VE is characterized by high concentrations of Cl-, SO42- and NO3-, whereas in USP of Cl-, SO42-, NO3-, Na+ and F- besides high alkalinity. The Pb leaching isotopic technique applied on sediments showed that there is low water-rock interaction and they were not used as end members for the mixing calculation. The H and O isotopic analyses indicated that precipitation in São Paulo are dependent of the amount effect and the different sources of air masses in different climate periods. The isotopic estimate of recharge indicated that VE, which has a more impermeable surface, has approximately 10% (H e O) to 20% (Pb) more anthropogenic recharge than USP. At USP the natural recharge calculated by H and O isotopes has mean value of 70%, whereas in VE this value drops to 59%. The Pb isotopes indicated a natural recharge of 53% and 35% for USP and VE, respectively. The conclusions made with the isotopic and chemical results are that: Sr isotopes are not good recharge tracers for contaminated areas with low residence time; O and H isotopes do not present significant differences between isotopic signatures from water distributed by the public supply company and most contaminated samples by sewage; Pb isotopes are good indicators of recharge tracers for contaminated areas, as they can discriminate waters from sewer leakage and public supply company waters.

Este trabalho estabeleceu cenários típicos para o Estado de São Paulo, a partir de dados de investigações ambientais de empreendimentos que armazenam, manipulam ou comercializam combustíveis derivados de petróleo (posto de combustíveis, TRR - transportador retalhista e revendedor, garagem e bases). As plumas de contaminação em fase dissolvida foram caracterizadas a partir de dados levantados em campo e dos resultados obtidos com o modelamento das plumas, usando o modelo Domenico. Desse modo, foi possível comparar as características das plumas reais com as calculadas e posteriormente discutir sobre os perímetros de proteção de poços de abastecimento (PPP). Uma das conclusões é de que não existe correlação entre a extensão das plumas de fase dissolvida (benzeno) real e a calculada. E ao comparar as extensões das plumas calculadas (Domenico) com os PPP calculados por modelo numérico, pode-se notar que somente em 3 cenários houve alguma correlação. Uma das principais recomendações é a reavaliação dos PPP, considerando os dados deste trabalho. / The current work has aimed to establish typical hydrogeological scenarios within the boundaries of São Paulo state, Brazil, based on environmental assessment data obtained at sites that store, manipulate or commercialize petroleum originated fuel (gas stations, TRR and fuel distribution plants). The dissolved phase contamination plumes were characterized based on field obtained data and numeric modeling, adopting Domenico model. In this way, it was possible to analyze the features of the real contamination plumes, compared with the modeled ones, and establish a discussion about production wells protection perimeter (PPP). One of the main conclusions is that there is no correlation between the extension of the real dissolved plumes (benzene) and the modeled ones. While comparing the extension of the modeled plumes (Domenico) with the PPP calculated by numeric modeling, it is possible to observe that only 3 of the analyzed scenarios have presented some identifiable correlation. One of the main recommendations is to perform a reevaluation of the PPP methodology, taking into account the data obtained in the current work.