Carbon isotope fractionation during aerobic biodegradation of trichloroethene by Burkholderia cepacia G4: a tool to map degradation mechanisms

The strain Burkholderia cepacia G4 aerobically mineralized trichloroethene (TCE) to CO2 over a time period of similar to20 h. Three biodegradation experiments were conducted with different bacterial optical densities at 540 nm (OD(540)s) in order to test whether isotope fractionation was consistent. The resulting TCE degradation was 93, 83.8, and 57.2% (i.e., 7.0, 16.2, and 42.8% TCE remaining) at OD(540)s of 2.0, 1.1, and 0.6, respectively. ODs also correlated linearly with zero-order degradation rates (1.99, 1.11, and 0.64 mumol h(-1)). While initial nonequilibrium mass losses of TCE produced only minor carbon isotope shifts (expressed in per mille delta C- 13(VPDB)), they were 57.2, 39.6, and 17.0parts per thousand between the initial and final TCE levels for the three experiments, in decreasing order of their OD(540)s. Despite these strong isotope shifts, we found a largely uniform isotope fractionation. The latter is expressed with a Rayleigh enrichment factor, E, and was -18.2 when all experiments were grouped to a common point of 42.8% TCE remaining. Although, decreases of epsilon to -20.7 were observed near complete degradation, our enrichment factors were significantly more negative than those reported for anaerobic dehalogenation of TCE. This indicates typical isotope fractionation for specific enzymatic mechanisms that can help to differentiate between degradation pathways

Hydrostratigraphic characterisation of shallow coastal aquifers of Eastern Dahomey Basin, S/W Nigeria using integrated hydrogeophysics; implication for saltwater intrusion

This study employed electrical resistivity tomography (ERT) in characterising the shallow groundwater aquifers of Eastern Dahomey basin in southwestern Nigeria to assess the possible occurrence and distribution of saltwater within the aquifers. Electrical resistivity tomography (ERT), induced polarization (IP) and borehole logging were carried in locations with relatively enhanced electrical conductivity (EC) within the coastal zone of the basin through 97 groundwater samples from shallow wells and boreholes; 500 m-length ERT and IP sections were carried out along three traverses A–B, C–D and E–F in directions perpendicular and parallel to the coastline. Three geoelectrical layers were identified along traverse line A–B which comprises cross-sections 1, 2, 3 and 4 located around Ugbonla, Aboto and Igbokoda with layers’ resistivity and chargeability values ranging from (1–1000, 33–200 and 1–1700 Ωm), and (−50–200 Ωm, −30–200 Ωm and −50–120 Ωm, respectively, from the top to the bottom layer. These values indicated unconsolidated sand/lateritic silty clay, underlain by a sandy/silty clay layer with underlying fine-grained sand with disseminated clay lenses. The average thickness of the first two layers was 16 and 53 m while that of the third layer was undetermined. Resistivity and chargeability results from ERT and IP cross-sections along profile C–D exhibited characteristics similar to that of profile A–B with unconsolidated sands which were underlain by intercalation of sandy/silty clay and fine-grained sands with suspected clay lenses saturated with saline water. Profile E–F revealed a geoelectrical layer with low resistivity which ranged from 1–30 Ωm with the corresponding chargeability between −150–400 ms. This indicated a saline water-saturated layer of fine-grained sand and silty clay which is overlaid by the unconsolidated unconfined freshwater aquifer. Correlation of selected ERT results with borehole logs further affirmed the suspected lithology from the sections. Two scenarios of saltwater intrusions into coastal freshwater aquifer were suggested which include the presence of trapped salt-saturated clay lenses within aquifer lithology and seawater incursion induced by over-drafting of groundwater in this basin.Therefore, it identified the need for further investigation which will involve a combination of hydrochemical and isotopes to further understand the paleowater hypothesis

Assessing the impact of climate change on groundwater quality of shallow coastal aquifer of eastern Dahomey basin, southwestern Nigeria

Despite the increasing interest in climate change and water security, research linking climate change and groundwater quality is still at an early stage. This study explores the seasonal effect of the change in biogeochemical process for the redox-sensitive ions and metals Fe 2+, Mn 2+, SO 4 2-, and NO 3 - to assess the groundwater quality of the shallow coastal aquifer of Eastern Dahomey Basin in southwestern Nigeria. Field physicochemical measurement of EC, pH TDS, Eh, salinity, temperature, and the static water level (SWL) was carried out on 250 shallow wells; 230 water samples were collected for analysis between June 2017 and April 2018. A spatial distribution map of these ions and metals showed an increasing concentration in the dry season water samples compared to those of the wet season. This higher concentration could be attributed to change in the intensity of hydrochemical processes such as evaporation, redox, and mineral precipitation. Results of linear regression modelling established significant relationships between SWL, SO 4 2-, NO 3 -, Fe, and Eh for both wet and dry seasons with the p-value falling between 75% and 95%, which can also be seen in the plots of Eh/ORP against Fe 2+, Mn 2+, SO 4 2-, and NO 3 -. These results revealed the influence of the redox process for both seasons, while also having a higher impact in the dry season while variation of concentration revealed decrease with increase in depth, which could be attributed to a decrease in well hydraulic properties and aeration. An Eh-pH geochemical diagram revealed NO 3 - as the controlling biogeochemical process over Fe in most of the sample wells. Concentrations of NO 3 -, Fe, and Mn are above the World Health Organization's (WHO) standard for drinking water in most water samples. This study has established the link between climate change and groundwater quality in shallow coastal aquifers and suggested the need for strategic groundwater management policy and planning to ameliorate groundwater quality deterioration

Evaluation of daily gridded meteorological datasets over the Niger Delta region of Nigeria and implication to water resources management

Hydro-climatological study is difficult in most of the developing countries due to the paucity of monitoring stations. Gridded climatological data provides an opportunity to extrapolate climate to areas without monitoring stations based on their ability to repli-cate the Spatio-temporal distribution and variability of observed datasets. Simple cor-relation and error analyses are not enough to predict the variability and distribution of precipitation and temperature. In this study, the coefficient of correlation (R2), Root mean square error (RMSE), mean bias error (MBE) and mean wet and dry spell lengths were used to evaluate the performance of three widely used daily gridded precipitation, maximum and minimum temperature datasets from the Climatic Research Unit (CRU), Princeton University Global Meteorological Forcing (PGF) and Climate Fore-cast System Reanalysis (CFSR) datasets available over the Niger Delta part of Nigeria. The Standardised Precipitation Index was used to assess the confidence of using grid-ded precipitation products on water resource management. Results of correlation, er-ror, and spell length analysis revealed that the CRU and PGF datasets performed much better than the CFSR datasets. SPI values also indicate a good association between station and CRU precipitation products. The CFSR datasets in comparison with the other data products in many years overestimated and underestimated the SPI. This indicates weak accuracy in predictability, hence not reliable for water resource man-agement in the study area. However, CRU data products were found to perform much better in most of the statistical assessments conducted. This makes the methods used in this study to be useful for the assessment of various gridded datasets in various hy-drological and climatic applications

Selection of CMIP5 GCM ensemble for the projection of spatio-temporal changes in precipitation and temperature over the Niger Delta, Nigeria

Selection of a suitable general circulation model (GCM) ensemble is crucial for effective water resource management and reliable climate studies in developing countries with constraint in human and computational resources. A careful selection of a GCM subset by excluding those with limited similarity to the observed climate from the existing pool of GCMs developed by different modeling centers at various resolutions can ease the task and minimize uncertainties. In this study, a feature selection method known as symmetrical uncertainty (SU) was employed to assess the performance of 26 Coupled Model Intercomparison Project Phase 5 (CMIP5) GCM outputs under Representative Concentration Pathway (RCP) 4.5 and 8.5. The selection was made according to their capability to simulate observed daily precipitation (prcp), maximum and minimum temperature (Tmax and Tmin) over the historical period 1980–2005 in the Niger Delta region, which is highly vulnerable to extreme climate events. The ensemble of the four top-ranked GCMs, namely ACCESS1.3, MIROC-ESM, MIROC-ESM-CHM, and NorESM1-M, were selected for the spatio-temporal projection of prcp, Tmax, and Tmin over the study area. Results from the chosen ensemble predicted an increase in the mean annual prcp between the range of 0.26% to 3.57% under RCP4.5, and 0.7% to 4.94% under RCP 8.5 by the end of the century when compared to the base period. The study also revealed an increase in Tmax in the range of 0 to 0.4 °C under RCP4.5 and 1.25–1.79 °C under RCP8.5 during the periods 2070–2099. Tmin also revealed a significant increase of 0 to 0.52 °C under RCP4.5 and between 1.38–2.02 °C under RCP8.5, which shows that extreme events might threaten the Niger Delta due to climate change. Water resource managers in the region can use these findings for effective water resource planning, management, and adaptation measures

Potential impacts of climate change on extreme weather events in the Niger Delta part of Nigeria

The Niger Delta is the most climate-vulnerable region in Nigeria. Flooding events are recorded annually in settlements along the River Niger and its tributaries, inundating many towns and displacing people from their homes. In this study, climate change impacts from extreme meteorological events over the period 2010-2099 are predicted and analyzed. Four coupled model intercomparison project phase 5 (CMIP5) global climate models (GCMs) under respectively concentration pathways (RCP4.5 and RCP8.5) emission scenarios were used for climate change predictions. Standardized precipitation indices (SPI) of 1-month and 12-month time steps were used for extreme event assessment. Results from the climate change scenarios predict an increase in rainfall across all future periods and under both emission scenarios, with the highest projected increase during the last three decades of the century. Under the RCP8.5 emission scenario, the rainfall at Port Harcourt and Yenagoa Stations is predicted to increase by about 2.47% and 2.62% while the rainfall atWarri Station is predicted to increase by about 1.39% toward the end of the century. The 12-month SPI under RCP4.5 and RCP8.5 emission scenarios predict an exceedance in the extreme wet threshold (i.e., SPI > 2) during all future periods and across all study locations. These findings suggest an increasing risk of flooding within the projected periods. The finding can be useful to policymakers for the formulation and planning of flood mitigation and adaptation measures

Controlling factors in the production of extracellular polysaccharides in phytoplankton : final report

Report examines the use Dictyosphaerium pulchellum in a flooded pit as a means to adsorb metal

Helium Porosity Formation in Vanadium Alloys of V-Ti-Cr, V-W-Zr and V-W-Ta Systems in Comparison with Binary Alloys

Vanadium alloys are considered candidates for use as structural materials of fusion reactors. A large amount of helium will be accumulated in such materials. The presence of helium in the materials may result in gas swelling. This paper presents the results on helium porosity formation researches in V–Ti–Cr, V–W–Zr and V–W–Ta alloys obtained by means of TEM. Samples were irradiated by 40 keV Не+ ions up to dose of 5 ⋅ 1020m−2 at 923 K. Alloy V–4%Ti–4%Cr has a smallest helium swelling among the ternary alloys and its swelling is significantly lower than swelling of dual V–Ti and V–Cr alloys. The swelling of the ternary V–2%W–1%Zr alloy is more than 3 times less than the swelling of vanadium, several times less than that of V–W alloys and slightly lower than the swelling of V– Zr alloys. Swelling increases by a factor of 1.5 with increasing of Zr content to 2% in the ternary V–2%W–1%Zr alloy. Similarly, gas swelling of ternary V–2%W–1%Ta alloy is significantly lower than that for binary V–W and V–Ta alloys. Assumptions are made about the possible mechanisms of the effect of alloying elements in vanadium on helium porosity formation. Keywords: vanadium alloys, swelling, helium, radiation resistance