Michael J. Spence

Processes controlling the distribution and natural attenuation of dissolved phenolic compounds in a deep sandstone aquifer

Processes controlling the distribution and natural attenuation (NA) of phenol, cresols and xylenols released from a former coal-tar distillation plant in a deep Triassic sandstone aquifer are evaluated from vertical profiles along the plume centerline at 130 and 350 m from the site. Up to four groups of contaminants (phenols, mineral acids, NaOH, NaCl) form discrete and overlapping plumes in the aquifer. Their distribution reflects changing source history with releases of contaminants from different locations. Organic contaminant distribution in the aquifer is determined more by site source history than degradation. Contaminant degradation at total organic carbon (TOC) concentrations up to 6500 mg l(-1) (7500 mg l(-1) total phenolics) is occurring by aerobic respiration NO3-reduction, Mn(IV)-/Fe(III)-reduction, SO4-reduction, methanogenesis and fermentation, with the accumulation of inorganic carbon, organic metabolites (4-hydroxybenzaldehyde, 4-hydroxybenzoic acid), acetate, Mn(II), Fe(II), S(-II), CH4 and H2 in the plume. Aerobic and NO3-reducing processes are restricted to a 2-m-thick plume fringe but Mn(IV)-/Fe(II)-reduction, SO4-reduction, methanogenesis and fermentation occur concomitantly in the plume. Dissolved H2 concentrations in the plume vary from 0.7 to 110 nM and acetate concentrations reach 200 mg l(-1). The occurrence of a mixed redox system and concomitant terminal electron accepting processes (TEAPs) could be explained with a partial equilibrium model based on the potential in situ free energy (deltaGr) yield for oxidation of H2 by specific TEAPs. Respiratory processes rather than fermentation are rate limiting in determining the distribution of H2 and TEAPs and H2 dynamics in this system. Most (min. 90%) contaminant degradation has occurred by aerobic and NO3-reducing processes at the plume fringe. This potential is determined by the supply of aqueous O2 and NO3 from uncontaminated groundwater, as controlled by transverse mixing, which is limited in this aquifer by low dispersion. Consumption to date of mineral oxides and SO4 is, respectively, <0.15% and 0.4% of the available aquifer capacity, and degradation using these oxidants is <10%. Fermentation is a significant process in contaminant turnover, accounting for 21% of degradation products present in the plume, and indicating that microbial respiration rates are slow in comparison with fermentation. Under present conditions, the potential for degradation in the plume is very low due to inhibitory effects of the contaminant matrix. Degradation products correspond to <22% mass loss over the life of the plume, providing a first-order plume scale half-life >140 years. The phenolic compounds are biodegradable under the range of redox conditions in the aquifer and the aquifer is not oxidant limited, but the plume is likely to be long-lived and to expand. Degradation is likely to increase only after contaminant concentrations are reduced and aqueous oxidant inputs are increased by dispersion of the plume. The results imply that transport processes may exert a greater control on the natural attenuation of this plume than aquifer oxidant availability.

Isotopic modelling of the significance of bacterial sulphate reduction for phenol attenuation in a contaminated aquifer

A Triassic sandstone aquifer polluted with a mixture of phenolic hydrocarbons has been investigated by means of high-resolution groundwater sampling. Samples taken at depth intervals of 1 m have revealed the presence of a diving pollutant plume with a sharply defined upper margin. Concentrations of pollutant phenols exceed 4 g/l in the plume core, rendering it sterile but towards the diluted upper margin evidence for bacterial sulphate reduction (BSR) has been obtained. Groundwaters have been analysed for both delta34S-SO4 and delta18O-SO4. Two reservoirs have been identified with distinct sulphate oxygen isotope ratios. Groundwater sulphate (delta18O-SO4 = 3-5/1000) outside the plume shows a simple linear mixing trend with an isotopically uniform pollutant sulphate reservoir (delta18O-SO4 = 10-12/1000) across the plume margin. The sulphur isotope ratios do not always obey a simple mixing relation, however, at one multilevel borehole, enrichment in 34SO4 at the plume margin is inversely correlated with sulphate concentration. This and the presence of 34S-depleted dissolved sulphide indicate that enrichment in 34SO4 is the result of bacterial sulphate reduction. Delta34S analysis of trace hydrogen sulphide within the plume yielded an isotope enrichment factor (epsilon) of -9.4/1000 for present-day bacterial sulphate reduction. This value agrees with a long-term estimate (-9.9/1000) obtained from a Rayleigh model of the sulphate reduction process. The model was also used to obtain an estimate of the pre-reduction sulphate concentration profile with depth. The difference between this and the present-day profiles then gave a mass balance for sulphate consumption. The organic carbon mineralisation that would account for this sulphate loss is shown to represent only 0.1/1000 of the phenol concentration in this region of the plume. Hence, the contribution of bacterial sulphate reduction to biodegradation has thus far been small. The highest total phenolic concentration (TPC) at which there is sulphur isotope evidence of bacterial sulphate reduction is 2000 mg/l. We suggest that above this concentration, the bactericidal properties of phenol render sulphate-reducing bacteria inactive. Dissolved sulphate trapped in the concentrated plume core will only be utilised by sulphate reducers when toxic phenols in the plume are diluted by dispersion during migration.

Impacts of pollutant loading, climate variability and site management on the surface water quality of a lowland raised bog, Thorne Moors, E. England, UK

Variations in surface water S chemistry were investigated at a waterlogged raised peatland in the NE of England from 1994 to 2000. While S inputs were important, below-ground cycling of S, dependent upon water table height, played a dominant role in affecting SO4 concentration of the surface waters. Evaporative concentration of SO4 during drought played only a subordinate role in increasing SO4 concentrations. At Thorne Moors SO4 in surface water shows a clear and statistically significant trend: (i) high concentrations (relative to pristine bogs) (mean 18 mg L−1) under high pollutant loadings before drought; (ii) extremely elevated concentrations (mean 52 mg L−1) under declining pollutant loadings during drought in 1996 and lowered water tables; (iii) recovery to significantly lower concentrations (mean 4.3 mg L−1) as water tables recovered (due to increased rain and site management) whilst pollutant loadings continued to fall. The increase in surface water SO4 in 1996 was accompanied by a significant rise in the S content of Sphagnum moss growing on the surface of the pools. As such the S content of Sphagnum may act as a proxy for variations in surface water S chemistry and thus environmental change.

Denitrification and phenol degradation in a contaminated aquifer.

A natural groundwater system modified by pollutant phenols and agricultural nitrate has been modelled in the laboratory by a series of sacrificial microcosm experiments. Samples of aquifer sediment and groundwater from the margin of the phenol plume were used to inoculate anaerobic microcosms enriched in nitrate and pollutant phenols. Rapid degradation of phenol and p-cresol was observed over a 35-day period leading to the generation of inorganic carbon and a number of transient intermediates. O-cresol proved to be recalcitrant on the experimental time-scale. A mass balance calculation shows that, during degradation, carbon was conserved in the aqueous phase. Groundwater-sediment interactions were monitored using carbon stable isotope data. A mass balance for solution TIC indicates thatp-cresol degradation stimulated the dissolution of sedimentary carbonate phases due to the formation of carbonic acid. Compound-specific carbon isotope analysis (GC-IRMS) was used to search for 13C enrichment in residual p-cresol. A slight enrichment trend (epsilon = -2.5/1000) was tentatively identified. The potential of this fractionation effect for obtaining in situ degradation rates is discussed. Results from the microcosm experiments help to explain the observed distribution of nitrate and phenols within the polluted aquifer.

Assessment of the use of fluorescent tracers in a contaminated Chalk aquifer

Abstract Field tracer tests and parallel laboratory experiments were performed to establish tracer performance and solute transport velocity in a contaminant plume arising from an unleaded fuel spill in the Chalk aquifer of the southern UK. An initial forced gradient test between injection and pumped wells 24 m apart largely failed for practical reasons; subsequently other down-gradient wells were periodically monitored for tracer breakthrough under natural gradient conditions over the next 10 months, giving tracer velocities of 37–51 m a−1, consistent with plume development and implying significant retardation of the tracer by fracture–matrix diffusion. Amino-G Acid concentrations fell rapidly during the field tests and laboratory experiments, and indicated that this tracer was susceptible to biodegradation under model plume conditions. Sodium Fluorescein was more strongly sorbed to aquifer materials than Amino-G Acid and exhibited some suppression of fluorescence in the presence of contaminants, but was resistant to biodegradation. Elevated background fluorescence produced an effective detection limit for Sodium Fluorescein of 1.8 μg l−1 in the most contaminated part of the plume.

Biodegradation potential of MTBE in a fractured chalk aquifer under aerobic conditions in long-term uncontaminated and contaminated aquifer microcosms

The potential for aerobic biodegradation of MTBE in a fractured chalk aquifer is assessed in microcosm experiments over 450 days, under in situ conditions for a groundwater temperature of 10 degrees C, MTBE concentration between 0.1 and 1.0 mg/L and dissolved O2 concentration between 2 and 10 mg/L. Following a lag period of up to 120 days, MTBE was biodegraded in uncontaminated aquifer microcosms at concentrations up to 1.2 mg/L, demonstrating that the aquifer has an intrinsic potential to biodegrade MTBE aerobically. The MTBE biodegradation rate increased three-fold from a mean of 6.6+/-1.6 microg/L/day in uncontaminated aquifer microcosms for subsequent additions of MTBE, suggesting an increasing biodegradation capability, due to microbial cell growth and increased biomass after repeated exposure to MTBE. In contaminated aquifer microcosms which also contained TAME, MTBE biodegradation occurred after a shorter lag of 15 or 33 days and MTBE biodegradation rates were higher (max. 27.5 microg/L/day), probably resulting from an acclimated microbial population due to previous exposure to MTBE in situ. The initial MTBE concentration did not affect the lag period but the biodegradation rate increased with the initial MTBE concentration, indicating that there was no inhibition of MTBE biodegradation related to MTBE concentration up to 1.2 mg/L. No minimum substrate concentration for MTBE biodegradation was observed, indicating that in the presence of dissolved O2 (and absence of inhibitory factors) MTBE biodegradation would occur in the aquifer at MTBE concentrations (ca. 0.1 mg/L) found at the front of the ether oxygenate plume. MTBE biodegradation occurred with concomitant O2 consumption but no other electron acceptor utilisation, indicating biodegradation by aerobic processes only. However, O2 consumption was less than the stoichiometric requirement for complete MTBE mineralization, suggesting that only partial biodegradation of MTBE to intermediate organic metabolites occurred. The availability of dissolved O2 did not affect MTBE biodegradation significantly, with similar MTBE biodegradation behaviour and rates down to ca. 0.7 mg/L dissolved O2 concentration. The results indicate that aerobic MTBE biodegradation could be significant in the plume fringe, during mixing of the contaminant plume and uncontaminated groundwater and that, relative to the plume migration, aerobic biodegradation is important for MTBE attenuation. Moreover, should the groundwater dissolved O2 concentration fall to zero such that MTBE biodegradation was inhibited, an engineered approach to enhance in situ bioremediation could supply O2 at relatively low levels (e.g. 2-3 mg/L) to effectively stimulate MTBE biodegradation, which has significant practical advantages. The study shows that aerobic MTBE biodegradation can occur at environmentally significant rates in this aquifer, and that long-term microcosm experiments (100s days) may be necessary to correctly interpret contaminant biodegradation potential in aquifers to support site management decisions.

Fountains Abbey and the Acquisition of Bordley-In-Craven: Anglo-Scandinavians, Scots and Monastic Flocks

This article is based on material from the surviving manuscripts of Fountains Abbey. For reasons discussed below, this material was omitted from the only published version of early charters from th...

Bayesian Inference on Individual-Based Models by Controlling the Random Inputs

Complex models are becoming increasingly popular in ecological modelling. However, quantifying uncertainty, estimating parameters and so on for a model of this sort are complicated by the fact that their probabilistic behaviour is often implicit in its rules or programs rather than made explicit as in a more conventional statistical or stochastic model. In a complex stochastic model, the output is dependent on both the parameters and the random inputs, i.e. the random numbers used to resolve decisions or generate stochastic quantities within the model. By treating these random inputs as nuisance parameters, often we can turn the model into a deterministic model where small movements in the parameter space result in small changes in the model output. When this is the case it will allow us to use Approximate Bayesian Computation methods with MCMC in order to perform parameter estimation. Controlling the random inputs allows us to move better in the parameter space and improves the mixing of the Markov chain. We will use these methods to estimate parameters in an individual-based model which is used to model the population dynamics of a group-living bird, the woodhoopoe.

Religion, time and memorial culture in late medieval Ripon

The Wakefield manorial court rolls are a significant and remarkable historical resource. Beginning in 1274, they provide a record of the proceedings of the manor court down to the abolition of copyhold tenure in 1925, with a further number of registers dealing with the administration of this property in the decades following. Although relatively few of the court rolls have survived up until 1322, from that year on there is an almost continuous, and very rich, record of the court’s proceedings contained in more than 670 substantial court rolls. Throughout its history, the Wakefield manor court met every three weeks, like most manorial courts; but the manor was unusual for its exceptional size. On average a typical manor would comprise roughly six square miles (approximately 1500 hectares) whereas the manor of Wakefield encompassed an area of well over a hundred (almost 39,000 hectares) and occupied a great swathe of the West Riding of Yorkshire containing a range of agricultural, industrial and mercantile interests. In recognition of the international significance of these records the Wakefield manorial court rolls were enrolled on the UNESCO Memory of the World register in 2011. The archive was deposited with the Yorkshire Archaeological and Historical Society by the Earl of Yarborough, as Lord of the Manor, in 1943 and since 2015 it has been held for the Society by the Special Collections department of the Brotherton Library, University of Leeds. Since 1901 the Yorkshire Archaeological and Historical Society has been engaged in a project to publish the court rolls. Initially focussing on the rolls for the Middle Ages, a new series was established in the mid 1970s to publish a wider chronological range and engage modern historians unfamiliar with the court rolls as a source. To date the new series has published eight Religion, time and memorial culture in late medieval Ripon, by Stephen Werronen, Woodbridge, Boydell & Brewer (for the Royal Historical Society), 2017, 212 pp., 4 b&w illus, £50 (hardback), ISBN 978-0-86193-345-7