Monitoring of methane in groundwater from the Vale of Pickering, UK: temporal variability and source discrimination

Groundwater abstracted from aquifers in the Vale of Pickering, North Yorkshire, UK and monitored over the period 2015–2022, shows evidence of variable but commonly high concentrations of dissolved CH4. Sampled groundwater from the Jurassic organic-rich Kimmeridge Clay Formation (boreholes up to 180 m depth) has concentrations up to 57 mg/L, and concentrations up to 59 mg/L are found in groundwater from underlying confined Corallian Group limestone (borehole depths 50–227 m). The high concentrations are mainly from boreholes in the central parts of the vale. Small concentrations of ethane (C2H6, up to 800 μg/L) have been found in the Kimmeridge Clay and confined Corallian groundwaters, and of propane (C3H8, up to 160 μg/L) in deeper boreholes (110–180 m) from these formations. The concentrations are typically higher in groundwater from the deeper boreholes and vary with hydrostatic pressure, reflecting the pressure control on CH4 solubility. The occurrences contrast with groundwater from shallow Quaternary superficial deposits which have low CH4 concentrations (up to 0.39 mg/L), and with the unconfined and semi-confined sections of the Corallian aquifer (up to 0.7 mg/L) around the margins of the vale. Groundwater from the Quaternary, Kimmeridge Clay formations and to a small extent the confined Corallian aquifer, supports local private-water supplies, that from the peripheral unconfined sections of Corallian also supports public supply for towns and villages across the region. Dissolved methane/ethane (C1/C2) ratios and stable-isotopic compositions (δ13C-CH4, δ2H-CH4 and δ13C-CO2) suggest that the high-CH4 groundwater from both the Kimmeridge Clay and confined Corallian formations derives overwhelmingly from biogenic reactions, the methanogenesis pathway by CO2 reduction. A small minority of groundwater samples shows a more enriched δ13C-CH4 composition (−50 to −44 ‰) which has been interpreted as due to anaerobic or aerobic methylotrophic oxidation in situ or post-sampling oxidation, rather than derivation by a thermogenic route. Few of the existing groundwater sites are proximal to abandoned or disused conventional hydrocarbon wells that exist in the region, and little evidence has been found for an influence on groundwater dissolved gases from these sites. The Vale of Pickering has also been under recent consideration for development of an unconventional hydrocarbon (shale-gas) resource. In this context, the monitoring of dissolved gases has been an important step in establishing the high-CH4 baseline of groundwaters from Jurassic deposits in the region and in apportioning their sources and mechanisms of genesis

Molecular investigations into cambium differentiation in tree stems

© 2010 Emma CrewdsonInvestigations into the molecular control of the production of secondary vascular tissue from the cambium lag behind research into the production of cells from other meristematic tissue types in plants. The majority of research into secondary growth in plants has either been conducted using the herbaceous Arabidopsis thaliana as a model species or has focussed on expression studies, with only a few transgenic experiments carried out in trees. The recent development of a new approach for generating transgenic cambial sectors in tree stems (ISSA) provided an opportunity for further study of molecular regulation of secondary growth. Polarity determination and meristem maintenance are two important processes that occur in the cambial zone of trees and allow for the correct development of secondary tissues. Therefore, genes believed to be involved in these processes were selected for use in the two experiments of this study. The HD-ZIP III family of genes are well-known to play a role in the determination of vascular polarity in Arabidopsis, and so the REV gene from this family was over-expressed in some transgenic sectors. The microRNA miR166 was over-expressed in other sectors, in order to down-regulate the expression of members of the HD-ZIP III gene family. In contrast to the dramatic phenotypes observed in Arabidopsis mutants with perturbed REV expression, no strong phenotypes were observed following manipulation of REV expression in poplar transgenic sectors. It is possible that the tight regulation of polarity within vascular tissue, combined with intercellular signals from adjacent non-transgenic cells, may have contributed to this result. Other possibilities are that the determination of polarity in secondary growth occurs in a different fashion to that of primary growth, or that polarity is already irreversibly fixed by the time that secondary growth begins. ARK1, a poplar homologue of the Arabidopsis meristem maintenance gene STM, was over-expressed in transgenic sectors using the ISSA method. Phenotypes obtained in this experiment were comparable to those of previously published whole plant over-expression of ARK1. It appeared that ARK1 had an effect of delaying xylem cell differentiation for a short period of time following division from the cambium, effectively promoting the maintenance of cells in a more meristematic state. A further phenotype was observed in two transgenic sectors in which immature partially-differentiated fibre cells were surrounded by mature fully-differentiated cells. This could also be the result of delayed differentiation caused by ARK1 over-expression, or may reflect an effect of ARK1 on dormancy. This project has allowed for the further characterisation of the ARK1 meristem maintenance gene and raises questions about the polarity determination of secondary tissues which could be examined in future investigations