Mark Cuthbert | Cardiff University (original) (raw)
Papers by Mark Cuthbert
Quarterly Journal of Engineering Geology and Hydrogeology, 2010
Water Resources Research, 2013
ABSTRACT [1] The use of inverse one-dimensional (1-D) analytical methods for estimating vertical ... more ABSTRACT [1] The use of inverse one-dimensional (1-D) analytical methods for estimating vertical stream-aquifer exchange flux is now commonplace. However, the application of such simple models can lead to significant errors in estimates of vertical exchange flux where the model assumptions are violated in real systems. An idea that is gaining acceptance in the literature is that the presence of nonvertical flow is such a violation. However, it is shown here that nonvertical flow by itself will not necessarily lead to errors in vertical flux estimation but rather that significant errors can stem from nonuniform (convergent/divergent) flow fields and/or hydrodynamic dispersion even within uniform flow fields. Nonuniform flow may also be expected, in some cases, to create discrepancies between flux estimates made on the basis of vertical head gradient measurements and those made using 1-D analytical heat tracer methods. Significant differences are observed in the estimates of heat-derived fluxes obtained by the amplitude ratio and phase-shift time-series methods when convergent and divergent flows are apparent. Such differences may potentially be used to infer that convergent or divergent flow is occurring and that a 1-D analysis is inappropriate.
Quarterly Journal of Engineering Geology and Hydrogeology - Q J ENG GEOL HYDROGEOL, 2009
ABSTRACT The way in which superficial deposits affect groundwater recharge is often a significant... more ABSTRACT The way in which superficial deposits affect groundwater recharge is often a significant source of uncertainty in groundwater resources and vulnerability assessments. A study of a small catchment in Shropshire, UK, shows how electrical resistivity tomography (ERT), with a degree of borehole control, can be an effective tool for defining the geometry of superficial deposits for purposes of inferring the hydraulic processes controlling groundwater recharge. Major lithological units were mapped to within c. 0.5 m vertically and 5 m horizontally using ERT surveys with a minimum electrode spacing of 2 m. Interpretation was aided by the strong contrast in resistivity between till and glaciolacustrine deposits (20-40 Omega m) and glaciofluvial deposits (generally >100 Omega m) that overlie the Permo-Triassic sandstone aquifer (saturated resistivity 60-145 Omega m) in the study area. A range of local-scale (tens to hundreds of metres) recharge models are presented, based on the findings of the field surveys, and it is shown how existing mapping misses key features of the superficial geology that may be very significant in enhancing or restricting aquifer recharge.
Understanding processes that control flow and chemical contaminant exchanges between groundwater ... more Understanding processes that control flow and chemical contaminant exchanges between groundwater and surface water in urban environments is important from water resource and ecological habitat perspectives. Achieving field-scale understanding, even over reaches just spanning tens of metres, is challenging. Spatial variability can cause process and parameter variation over centimetre scales and temporal influences may be important over event, seasonal and
ABSTRACT The natural attenuation of pollutants by biogeochemical processes in the hyporheic zone ... more ABSTRACT The natural attenuation of pollutants by biogeochemical processes in the hyporheic zone is recognized by the scientific community. Nevertheless, the different factors controlling these processes, especially the influence of hydrodynamic conditions on biodegradation, are not fully understood. An innovative experiment is described in which controlled long-term extraction from a bank-side well installed adjacent to the River Tame, Birmingham, UK, is used to modify the hydrodynamic conditions locally within the hyporheic zone. Extraction induces a decrease in the vertical components of flows from groundwater to surface water increasing their residence time within this interface as well as, potentially, increasing the river / groundwater mixing depths. The resulting temporal evolution of hydrodynamic and chemical conditions is monitored using a network of riverbed minipiezometers and multilevel samplers. This allows a better understanding to be gained of the processes involved in surface water / groundwater mixing and the conditions causing changes in biodegradation. Both the field measurements and the 3D hydrogeological model results show a coupled influence of the river levels and of the extraction test on the hydraulic heads within the hyporheic zone. It has been nevertheless difficult with this approach to investigate the real impact of the long term extraction tests on the vertical distribution of major ions within the riverbed, apparently strongly influenced by short-term variations of the river level.
Quaternary Science Reviews, 2015
Hydrogeology Journal, 2016
Quaternary Science Reviews, 2015
Geochimica et Cosmochimica Acta, 2015
Organic characterisation of cave drip water by LC-OCD and fluorescence analysis, Geochimica et Co... more Organic characterisation of cave drip water by LC-OCD and fluorescence analysis, Geochimica et Cosmochimica Acta (2015), doi: http://dx.Abstract 20 Cathedral Cave, Wellington, Australia, is a natural laboratory for studying water movement 21 and geochemical processes in the unsaturated zone by using artificial irrigation to activate 22 drip sites within the cave. Water sampled from two drip sites activated by irrigations carried 23 out in summer 2014 was analysed for dissolved inorganic ions and fluorescent organic 24 matter. The analysis allowed the development of a conceptual flow path model for each drip 25 site. DOM analysis was further complemented by liquid chromatography with organic carbon 26 detection (LC-OCD), applied for the first time to karst drip waters, allowing the 27 characterisation of six organic matter fractions. The differences in organic matter fractions at 28 each drip site are interpreted as a signature of the proposed flow paths. LC-OCD was also 29 compared with parallel factor analysis (PARAFAC) of the fluorescence and good correlations 30 were observed for high molecular weight organic matter. Strong positive correlations were 31 also observed for high molecular weight matter and Cu and Ni. This is suggestive of colloidal 32 transport of Cu and Ni by organic matter with high molecular weight, while small molecular 33 weight colloids were not efficient transporters. LC-OCD uniquely provides information on 34 2 non-fluorescent organic matter and can be used to further quantify drip water organic matter 35 composition. 36 37 65 impurities in water. The qualitative analysis is based on size exclusion chromatography 66 where large molecules have different degrees of interaction with the pores on the column 67 material resulting in different retention times for different molecular size fractions.
Hydrogeology Journal, 2014
The long-term monitoring records of hydraulic heads frequently contain fluctuations originating f... more The long-term monitoring records of hydraulic heads frequently contain fluctuations originating from different cyclic drivers. Fourier analysis applied to these records can reveal connected surface-water/groundwater system characteristics. The various components of the atmospheric tides, the earth tides and the presence of diurnal responses to evapotranspiration are identified and isolated through band-pass filtering of data recorded from both vented and absolute gauge transducers. The signature of the different cyclic drivers is contained in amplitude and phase of the various signal components and can be used to determine the degree of system confinement. A methodology is described for the calculation of barometric efficiency in confined aquifers based upon the amplitude of the M 2 and S 2 components of the earth and atmospheric tides. It is demonstrated that Fourier analysis of waterlevel fluctuations is a simple but underused tool that can help to characterise shallow groundwater systems. Fig. 5 DFT pairs for atmospheric pressure observed at BH 8 and the elfin crossing surface water level gauge. The complete spectrum is shown in the frequency amplitude plot. a Time series of barometric pressure; b DFT of a; c time series of Elfin Crossing, and d DFT of c Hydrogeology Journal Fig. 9 Comparison of a corrected hydraulic heads and b atmospheric pressure, for BH 7.1 and BH 12.2. Note the inverted phase of the atmospheric pressure signal in BH 12.2 data and also the completely different phase and frequencies of the unconfined signal of BH 7.1 Hydrogeology Journal
ABSTRACT The natural attenuation of pollutants by biogeochemical processes in the hyporheic zone ... more ABSTRACT The natural attenuation of pollutants by biogeochemical processes in the hyporheic zone is recognized by the scientific community. Nevertheless, the different factors controlling these processes, especially the influence of hydrodynamic conditions on biodegradation, are not fully understood. An innovative experiment is described in which controlled long-term extraction from a bank-side well installed adjacent to the River Tame, Birmingham, UK, is used to modify the hydrodynamic conditions locally within the hyporheic zone. Extraction induces a decrease in the vertical components of flows from groundwater to surface water increasing their residence time within this interface as well as, potentially, increasing the river / groundwater mixing depths. The resulting temporal evolution of hydrodynamic and chemical conditions is monitored using a network of riverbed minipiezometers and multilevel samplers. This allows a better understanding to be gained of the processes involved in surface water / groundwater mixing and the conditions causing changes in biodegradation. Both the field measurements and the 3D hydrogeological model results show a coupled influence of the river levels and of the extraction test on the hydraulic heads within the hyporheic zone. It has been nevertheless difficult with this approach to investigate the real impact of the long term extraction tests on the vertical distribution of major ions within the riverbed, apparently strongly influenced by short-term variations of the river level.
Understanding processes that control flow and chemical contaminant exchanges between groundwater ... more Understanding processes that control flow and chemical contaminant exchanges between groundwater and surface water in urban environments is important from water resource and ecological habitat perspectives. Achieving field-scale understanding, even over reaches just spanning tens of metres, is challenging. Spatial variability can cause process and parameter variation over centimetre scales and temporal influences may be important over event, seasonal and historic timeframes. A key goal, nevertheless, is to reconcile both flow and chemical transport lines of evidence to allow a harmonized conceptualization of flow and chemical exchanges to emerge. We present field data and developing interpretation from a well characterised, strongly gaining reach of the urban River Tame, Birmingham, UK that seeks to meet this goal. Despite the apparent simplicity and almost innocuous canal-like appearance of the 50 m intensively studied (and wider 200 m less studied) reach, reconciling flow and chem...
Earth and Planetary Science Letters, 2014
Applied Geochemistry, 2014
ABSTRACT The development of microbially mediated technologies for subsurface remediation and rock... more ABSTRACT The development of microbially mediated technologies for subsurface remediation and rock engineering is steadily increasing; however, we are lacking experimental data and models to predict bacterial movement through rock matrices. Here, breakthrough curves (BTC) were obtained to quantify the transport of the ureolytic bacterium, Sporocarsina pasteurii, through sandstone cores, as a function of core length (1.8 to 7.5 cm), bacterial density (4 x 106 to 9 x 107 cells / ml) and flow rate (5.8 to 17.5 m / s). S. pasteurii was easily immobilised within the homogeneous sandstone matrix (> 80 %) in comparison to a packed sand column (< 20 %; under similar experimental conditions), and percentage recovery decreased almost linearly with increasing rock core length. Moreover, a decrease in bacterial density or flow rate enhanced bacterial retention. A numerical model based on 1D advection dispersion models used for unconsolidated sand was fitted to the BTC data obtained here for sandstone. Good agreement between data and model was obtained at shorter rock core lengths (< 4 cm), suggesting that physicochemical filtration processes are similar in homogeneous packed sand and sandstones at these lengths. Discrepancies were, however observed at longer core lengths and with varying flow rates, indicating that the attributes of consolidated rock might impact bacterial transport progressively more with increasing core length. Implications of these results on microbial mineralisation technologies currently being developed for sealing fluid paths in subsurface environment is discussed.
Results are presented of a detailed study into the vadose zone and shallow water table hydrodynam... more Results are presented of a detailed study into the vadose zone and shallow water table hydrodynamics of a field site in Shropshire, UK. A conceptual model is presented and tested using a range of numerical models, including a modified soil moisture balance model (SMBM) for estimating groundwater recharge in the presence of both diffuse and preferential flow components. Tensiometry reveals that the loamy sand topsoil wets up via preferential flow and subsequent redistribution of moisture into the soil matrix. Recharge does not occur until near-positive pressures are achieved at the top of the sandy glaciofluvial outwash material that underlies the topsoil, about 1 m above the water table. Once this occurs, very rapid water table rises follow. This threshold behaviour is attributed to the vertical discontinuity in preferential flow pathways due to seasonal ploughing of the topsoil and to a lower permeability plough/iron pan restricting matrix flow between the topsoil and the lower outwash deposits. Although the wetting process in the topsoil is complex, a SMBM is shown to be effective in predicting the initiation of preferential flow from the base of the topsoil into the lower outwash horizon. The rapidity of the response at the water table and a water table rise during the summer period while flow gradients in the unsaturated profile were upward suggest that preferential flow is also occurring within the outwash deposits below the topsoil. A variation of the source-responsive model proposed by Nimmo shown to reproduce the observed water table dynamics well in the lower outwash horizon when linked to a SMBM that quantifies the potential recharge from the topsoil. The results reveal new insights into preferential flow processes in cultivated soils and provide a useful and practical approach to accounting for preferential flow in studies of groundwater recharge estimation.
Licensed abstraction well data collected during 1986-2008 from a total of 77 wells mainly located... more Licensed abstraction well data collected during 1986-2008 from a total of 77 wells mainly located at industrial sites combined with historic land use data from 1975 has allowed insight into the legacy of chlorinated solvent contamination in the Birmingham aquifer that underlies the UK&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s second largest city. This legacy, expected to be reasonably symptomatic of those occurring in other urban aquifers, was characterised by: dominance of parent solvents, particularly TCE (trichloroethene) that widely exceeded drinking-water quality criteria; greater TCE occurrence in wells in proximity to increased historic land use by the metal/engineering solvent-user industry (the relationship providing a first-pass indicator of future resource development potential); regional groundwater vulnerability controls; well abstraction changes (over months to decades) influential of observed concentration transients and anticipated plume capture or release; persistence of contamination over decades (with less soluble PCE (perchloroethene) showing increased persistence relative to TCE) that was reasonably ascribed to slow contaminant release from DNAPL (dense non-aqueous phase liquid) sources and, or low permeability layers; presence of dechlorination products arising from solvent (bio)degradation, although this key attenuation process appeared to have moderate to weak influence regionally on plumes; and, inadvertent, but significant solvent mass removal from the aquifer by industrial abstractions. Key challenges to realising future urban groundwater development were identified based on the observed legacy and well capture zone simulations. Despite the extensive contamination of the aquifer, it should still be possible to develop wells of high (several megalitres per day) capacity for drinking water supply (or other lower grade uses) without the requirement for solvent treatment. In those areas with higher risk of contamination, our dataset, together with application of emergent risk assessment approaches (that our dataset may serve to validate), could be used to inform potential abstractors as to whether solvent treatment is likely to be required at a particular abstraction site with time. Challenges identified that were relevant to the future development of Birmingham and urban aquifers more generally include the adequacy of groundwater quality monitoring data and uncertainties in contaminant source terms, abstraction well capture zone predictions and plume natural attenuation, in particular degradation rates. The study endorses that despite significant solvent contamination encountered, strategies can, and need, to be increasingly found to reclaim urban aquifer resources and more sustainably meet urban water demands.
Environmental science & technology, Jan 17, 2014
A Serratia sp. bacterium manufactures amorphous calcium phosphate nanominerals (BHAP); this mater... more A Serratia sp. bacterium manufactures amorphous calcium phosphate nanominerals (BHAP); this material has shown increased sorption capacity for divalent radionuclide capture. When heat-treated (≥450 °C) the cell biomass is removed and the biominerals are transformed to hydroxyapatite (HAP). Using a multimethod approach, we have elucidated both the site preferences and stability of analogue radionuclide incorporation for Sr, Co, Eu, and U. Strontium incorporates within the bulk amorphous inorganic phase of BHAP; however, once temperature modified to crystalline HAP, bonding was consistent with Sr substitution at the Ca(1) and/or Ca(2) sites. Cobalt incorporation occurs within the bulk inorganic amorphous phase of BHAP and within the amorphous grain boundaries of HAP. Europium (an analogue for trivalent actinides) substituted at the Ca(2) and/or the Ca(3) position of tricalcium phosphate, a known component of HAP grain boundaries. Uranium was surface complexed with no secondary mineral...
Quarterly Journal of Engineering Geology and Hydrogeology, 2010
Water Resources Research, 2013
ABSTRACT [1] The use of inverse one-dimensional (1-D) analytical methods for estimating vertical ... more ABSTRACT [1] The use of inverse one-dimensional (1-D) analytical methods for estimating vertical stream-aquifer exchange flux is now commonplace. However, the application of such simple models can lead to significant errors in estimates of vertical exchange flux where the model assumptions are violated in real systems. An idea that is gaining acceptance in the literature is that the presence of nonvertical flow is such a violation. However, it is shown here that nonvertical flow by itself will not necessarily lead to errors in vertical flux estimation but rather that significant errors can stem from nonuniform (convergent/divergent) flow fields and/or hydrodynamic dispersion even within uniform flow fields. Nonuniform flow may also be expected, in some cases, to create discrepancies between flux estimates made on the basis of vertical head gradient measurements and those made using 1-D analytical heat tracer methods. Significant differences are observed in the estimates of heat-derived fluxes obtained by the amplitude ratio and phase-shift time-series methods when convergent and divergent flows are apparent. Such differences may potentially be used to infer that convergent or divergent flow is occurring and that a 1-D analysis is inappropriate.
Quarterly Journal of Engineering Geology and Hydrogeology - Q J ENG GEOL HYDROGEOL, 2009
ABSTRACT The way in which superficial deposits affect groundwater recharge is often a significant... more ABSTRACT The way in which superficial deposits affect groundwater recharge is often a significant source of uncertainty in groundwater resources and vulnerability assessments. A study of a small catchment in Shropshire, UK, shows how electrical resistivity tomography (ERT), with a degree of borehole control, can be an effective tool for defining the geometry of superficial deposits for purposes of inferring the hydraulic processes controlling groundwater recharge. Major lithological units were mapped to within c. 0.5 m vertically and 5 m horizontally using ERT surveys with a minimum electrode spacing of 2 m. Interpretation was aided by the strong contrast in resistivity between till and glaciolacustrine deposits (20-40 Omega m) and glaciofluvial deposits (generally >100 Omega m) that overlie the Permo-Triassic sandstone aquifer (saturated resistivity 60-145 Omega m) in the study area. A range of local-scale (tens to hundreds of metres) recharge models are presented, based on the findings of the field surveys, and it is shown how existing mapping misses key features of the superficial geology that may be very significant in enhancing or restricting aquifer recharge.
Understanding processes that control flow and chemical contaminant exchanges between groundwater ... more Understanding processes that control flow and chemical contaminant exchanges between groundwater and surface water in urban environments is important from water resource and ecological habitat perspectives. Achieving field-scale understanding, even over reaches just spanning tens of metres, is challenging. Spatial variability can cause process and parameter variation over centimetre scales and temporal influences may be important over event, seasonal and
ABSTRACT The natural attenuation of pollutants by biogeochemical processes in the hyporheic zone ... more ABSTRACT The natural attenuation of pollutants by biogeochemical processes in the hyporheic zone is recognized by the scientific community. Nevertheless, the different factors controlling these processes, especially the influence of hydrodynamic conditions on biodegradation, are not fully understood. An innovative experiment is described in which controlled long-term extraction from a bank-side well installed adjacent to the River Tame, Birmingham, UK, is used to modify the hydrodynamic conditions locally within the hyporheic zone. Extraction induces a decrease in the vertical components of flows from groundwater to surface water increasing their residence time within this interface as well as, potentially, increasing the river / groundwater mixing depths. The resulting temporal evolution of hydrodynamic and chemical conditions is monitored using a network of riverbed minipiezometers and multilevel samplers. This allows a better understanding to be gained of the processes involved in surface water / groundwater mixing and the conditions causing changes in biodegradation. Both the field measurements and the 3D hydrogeological model results show a coupled influence of the river levels and of the extraction test on the hydraulic heads within the hyporheic zone. It has been nevertheless difficult with this approach to investigate the real impact of the long term extraction tests on the vertical distribution of major ions within the riverbed, apparently strongly influenced by short-term variations of the river level.
Quaternary Science Reviews, 2015
Hydrogeology Journal, 2016
Quaternary Science Reviews, 2015
Geochimica et Cosmochimica Acta, 2015
Organic characterisation of cave drip water by LC-OCD and fluorescence analysis, Geochimica et Co... more Organic characterisation of cave drip water by LC-OCD and fluorescence analysis, Geochimica et Cosmochimica Acta (2015), doi: http://dx.Abstract 20 Cathedral Cave, Wellington, Australia, is a natural laboratory for studying water movement 21 and geochemical processes in the unsaturated zone by using artificial irrigation to activate 22 drip sites within the cave. Water sampled from two drip sites activated by irrigations carried 23 out in summer 2014 was analysed for dissolved inorganic ions and fluorescent organic 24 matter. The analysis allowed the development of a conceptual flow path model for each drip 25 site. DOM analysis was further complemented by liquid chromatography with organic carbon 26 detection (LC-OCD), applied for the first time to karst drip waters, allowing the 27 characterisation of six organic matter fractions. The differences in organic matter fractions at 28 each drip site are interpreted as a signature of the proposed flow paths. LC-OCD was also 29 compared with parallel factor analysis (PARAFAC) of the fluorescence and good correlations 30 were observed for high molecular weight organic matter. Strong positive correlations were 31 also observed for high molecular weight matter and Cu and Ni. This is suggestive of colloidal 32 transport of Cu and Ni by organic matter with high molecular weight, while small molecular 33 weight colloids were not efficient transporters. LC-OCD uniquely provides information on 34 2 non-fluorescent organic matter and can be used to further quantify drip water organic matter 35 composition. 36 37 65 impurities in water. The qualitative analysis is based on size exclusion chromatography 66 where large molecules have different degrees of interaction with the pores on the column 67 material resulting in different retention times for different molecular size fractions.
Hydrogeology Journal, 2014
The long-term monitoring records of hydraulic heads frequently contain fluctuations originating f... more The long-term monitoring records of hydraulic heads frequently contain fluctuations originating from different cyclic drivers. Fourier analysis applied to these records can reveal connected surface-water/groundwater system characteristics. The various components of the atmospheric tides, the earth tides and the presence of diurnal responses to evapotranspiration are identified and isolated through band-pass filtering of data recorded from both vented and absolute gauge transducers. The signature of the different cyclic drivers is contained in amplitude and phase of the various signal components and can be used to determine the degree of system confinement. A methodology is described for the calculation of barometric efficiency in confined aquifers based upon the amplitude of the M 2 and S 2 components of the earth and atmospheric tides. It is demonstrated that Fourier analysis of waterlevel fluctuations is a simple but underused tool that can help to characterise shallow groundwater systems. Fig. 5 DFT pairs for atmospheric pressure observed at BH 8 and the elfin crossing surface water level gauge. The complete spectrum is shown in the frequency amplitude plot. a Time series of barometric pressure; b DFT of a; c time series of Elfin Crossing, and d DFT of c Hydrogeology Journal Fig. 9 Comparison of a corrected hydraulic heads and b atmospheric pressure, for BH 7.1 and BH 12.2. Note the inverted phase of the atmospheric pressure signal in BH 12.2 data and also the completely different phase and frequencies of the unconfined signal of BH 7.1 Hydrogeology Journal
ABSTRACT The natural attenuation of pollutants by biogeochemical processes in the hyporheic zone ... more ABSTRACT The natural attenuation of pollutants by biogeochemical processes in the hyporheic zone is recognized by the scientific community. Nevertheless, the different factors controlling these processes, especially the influence of hydrodynamic conditions on biodegradation, are not fully understood. An innovative experiment is described in which controlled long-term extraction from a bank-side well installed adjacent to the River Tame, Birmingham, UK, is used to modify the hydrodynamic conditions locally within the hyporheic zone. Extraction induces a decrease in the vertical components of flows from groundwater to surface water increasing their residence time within this interface as well as, potentially, increasing the river / groundwater mixing depths. The resulting temporal evolution of hydrodynamic and chemical conditions is monitored using a network of riverbed minipiezometers and multilevel samplers. This allows a better understanding to be gained of the processes involved in surface water / groundwater mixing and the conditions causing changes in biodegradation. Both the field measurements and the 3D hydrogeological model results show a coupled influence of the river levels and of the extraction test on the hydraulic heads within the hyporheic zone. It has been nevertheless difficult with this approach to investigate the real impact of the long term extraction tests on the vertical distribution of major ions within the riverbed, apparently strongly influenced by short-term variations of the river level.
Understanding processes that control flow and chemical contaminant exchanges between groundwater ... more Understanding processes that control flow and chemical contaminant exchanges between groundwater and surface water in urban environments is important from water resource and ecological habitat perspectives. Achieving field-scale understanding, even over reaches just spanning tens of metres, is challenging. Spatial variability can cause process and parameter variation over centimetre scales and temporal influences may be important over event, seasonal and historic timeframes. A key goal, nevertheless, is to reconcile both flow and chemical transport lines of evidence to allow a harmonized conceptualization of flow and chemical exchanges to emerge. We present field data and developing interpretation from a well characterised, strongly gaining reach of the urban River Tame, Birmingham, UK that seeks to meet this goal. Despite the apparent simplicity and almost innocuous canal-like appearance of the 50 m intensively studied (and wider 200 m less studied) reach, reconciling flow and chem...
Earth and Planetary Science Letters, 2014
Applied Geochemistry, 2014
ABSTRACT The development of microbially mediated technologies for subsurface remediation and rock... more ABSTRACT The development of microbially mediated technologies for subsurface remediation and rock engineering is steadily increasing; however, we are lacking experimental data and models to predict bacterial movement through rock matrices. Here, breakthrough curves (BTC) were obtained to quantify the transport of the ureolytic bacterium, Sporocarsina pasteurii, through sandstone cores, as a function of core length (1.8 to 7.5 cm), bacterial density (4 x 106 to 9 x 107 cells / ml) and flow rate (5.8 to 17.5 m / s). S. pasteurii was easily immobilised within the homogeneous sandstone matrix (> 80 %) in comparison to a packed sand column (< 20 %; under similar experimental conditions), and percentage recovery decreased almost linearly with increasing rock core length. Moreover, a decrease in bacterial density or flow rate enhanced bacterial retention. A numerical model based on 1D advection dispersion models used for unconsolidated sand was fitted to the BTC data obtained here for sandstone. Good agreement between data and model was obtained at shorter rock core lengths (< 4 cm), suggesting that physicochemical filtration processes are similar in homogeneous packed sand and sandstones at these lengths. Discrepancies were, however observed at longer core lengths and with varying flow rates, indicating that the attributes of consolidated rock might impact bacterial transport progressively more with increasing core length. Implications of these results on microbial mineralisation technologies currently being developed for sealing fluid paths in subsurface environment is discussed.
Results are presented of a detailed study into the vadose zone and shallow water table hydrodynam... more Results are presented of a detailed study into the vadose zone and shallow water table hydrodynamics of a field site in Shropshire, UK. A conceptual model is presented and tested using a range of numerical models, including a modified soil moisture balance model (SMBM) for estimating groundwater recharge in the presence of both diffuse and preferential flow components. Tensiometry reveals that the loamy sand topsoil wets up via preferential flow and subsequent redistribution of moisture into the soil matrix. Recharge does not occur until near-positive pressures are achieved at the top of the sandy glaciofluvial outwash material that underlies the topsoil, about 1 m above the water table. Once this occurs, very rapid water table rises follow. This threshold behaviour is attributed to the vertical discontinuity in preferential flow pathways due to seasonal ploughing of the topsoil and to a lower permeability plough/iron pan restricting matrix flow between the topsoil and the lower outwash deposits. Although the wetting process in the topsoil is complex, a SMBM is shown to be effective in predicting the initiation of preferential flow from the base of the topsoil into the lower outwash horizon. The rapidity of the response at the water table and a water table rise during the summer period while flow gradients in the unsaturated profile were upward suggest that preferential flow is also occurring within the outwash deposits below the topsoil. A variation of the source-responsive model proposed by Nimmo shown to reproduce the observed water table dynamics well in the lower outwash horizon when linked to a SMBM that quantifies the potential recharge from the topsoil. The results reveal new insights into preferential flow processes in cultivated soils and provide a useful and practical approach to accounting for preferential flow in studies of groundwater recharge estimation.
Licensed abstraction well data collected during 1986-2008 from a total of 77 wells mainly located... more Licensed abstraction well data collected during 1986-2008 from a total of 77 wells mainly located at industrial sites combined with historic land use data from 1975 has allowed insight into the legacy of chlorinated solvent contamination in the Birmingham aquifer that underlies the UK&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s second largest city. This legacy, expected to be reasonably symptomatic of those occurring in other urban aquifers, was characterised by: dominance of parent solvents, particularly TCE (trichloroethene) that widely exceeded drinking-water quality criteria; greater TCE occurrence in wells in proximity to increased historic land use by the metal/engineering solvent-user industry (the relationship providing a first-pass indicator of future resource development potential); regional groundwater vulnerability controls; well abstraction changes (over months to decades) influential of observed concentration transients and anticipated plume capture or release; persistence of contamination over decades (with less soluble PCE (perchloroethene) showing increased persistence relative to TCE) that was reasonably ascribed to slow contaminant release from DNAPL (dense non-aqueous phase liquid) sources and, or low permeability layers; presence of dechlorination products arising from solvent (bio)degradation, although this key attenuation process appeared to have moderate to weak influence regionally on plumes; and, inadvertent, but significant solvent mass removal from the aquifer by industrial abstractions. Key challenges to realising future urban groundwater development were identified based on the observed legacy and well capture zone simulations. Despite the extensive contamination of the aquifer, it should still be possible to develop wells of high (several megalitres per day) capacity for drinking water supply (or other lower grade uses) without the requirement for solvent treatment. In those areas with higher risk of contamination, our dataset, together with application of emergent risk assessment approaches (that our dataset may serve to validate), could be used to inform potential abstractors as to whether solvent treatment is likely to be required at a particular abstraction site with time. Challenges identified that were relevant to the future development of Birmingham and urban aquifers more generally include the adequacy of groundwater quality monitoring data and uncertainties in contaminant source terms, abstraction well capture zone predictions and plume natural attenuation, in particular degradation rates. The study endorses that despite significant solvent contamination encountered, strategies can, and need, to be increasingly found to reclaim urban aquifer resources and more sustainably meet urban water demands.
Environmental science & technology, Jan 17, 2014
A Serratia sp. bacterium manufactures amorphous calcium phosphate nanominerals (BHAP); this mater... more A Serratia sp. bacterium manufactures amorphous calcium phosphate nanominerals (BHAP); this material has shown increased sorption capacity for divalent radionuclide capture. When heat-treated (≥450 °C) the cell biomass is removed and the biominerals are transformed to hydroxyapatite (HAP). Using a multimethod approach, we have elucidated both the site preferences and stability of analogue radionuclide incorporation for Sr, Co, Eu, and U. Strontium incorporates within the bulk amorphous inorganic phase of BHAP; however, once temperature modified to crystalline HAP, bonding was consistent with Sr substitution at the Ca(1) and/or Ca(2) sites. Cobalt incorporation occurs within the bulk inorganic amorphous phase of BHAP and within the amorphous grain boundaries of HAP. Europium (an analogue for trivalent actinides) substituted at the Ca(2) and/or the Ca(3) position of tricalcium phosphate, a known component of HAP grain boundaries. Uranium was surface complexed with no secondary mineral...