Controls upon biomass losses and char production from prescribed burning on UK moorland.

Prescribed burning is a common management technique used across many areas of the UK uplands. However, there are few data sets that assess the loss of biomass during burning and even fewer data on the effect of burning on above-ground carbon stocks and production of char. During fire the production of char occurs which represents a transfer of carbon from the short term bio-atmospheric cycle to the longer term geological cycle. However, biomass is consumed leading to the reduction in litter formation which is the principal mechanism for peat formation. This study aims to solve the problem of whether loss of biomass during a fire is ever outweighed by the production of refractory forms of carbon during the fire. This study combines both a laboratory study of char production with an assessment of biomass loss from a series of field burns from moorland in the Peak District, UK. The laboratory results show that there are significant effects due to ambient temperature but the most important control on dry mass loss is the maximum burn temperature. Burn temperature was also found to be linearly related to the production of char in the burn products. Optimisation of dry mass loss, char production and carbon content shows that the production of char from certain fires could store more carbon in the ecosystem than if there had been no fire. Field results show that approximately 75% of the biomass and carbon were lost through combustion, a figure comparable to other studies of prescribed fire in other settings. Char-C production was approximately 2.6% of the carbon consumed during the fire. This study has shown that there are conditions (fast burns at high temperatures) under which prescribed fire may increase C sequestration through char production and that these conditions are within existing management options available to practitioners.

Monitoring fluvial water chemistry for trend detection: hydrological variability masks trends in datasets covering fewer than 12 years.

This paper sub-samples four 35 year water quality time series to consider the potential influence of short-term hydrological variability on process inference derived from short-term monitoring data. The data comprise two time series for nitrate (NO(3)-N) and two for DOC (using water colour as a surrogate). The four catchments were selected not only because of their long records, but also because the four catchments are very different: upland and lowland, agricultural and non-agricultural. Multiple linear regression is used to identify the trend and effects of rainfall and hydrological 'memory effects' over the full 35 years, and then a moving-window technique is used to subsample the series, using window widths of between 6 and 20 years. The results suggest that analyses of periods between six and eleven years are more influenced by local hydrological variability and therefore provide misleading results about long-term trends, whereas periods of longer than twelve years tend to be more representative of underlying system behaviour. This is significant: if such methods for analysing monitoring data were used to validate changes in catchment management, a monitoring period of less than 12 years might be insufficient to demonstrate change in the underlying system.

Charcoal production in a UK moorland wildfire--how important is it?

Wildfires are a common feature of peatland environments, but the carbon balance of these wildfires is often not considered and the production of refractory black carbon in these wildfires could be an important addition to carbon accumulation and mitigate losses of biomass during the fire. This study investigates the biomass and carbon losses during a moorland wildfire. Changes in above-ground carbon stocks were calculated using a combination of field data, laboratory measurements and literature values. The results show that approximately 14% of the carbon in the original above-ground biomass remained on the site after the burn. Black carbon production was approximately 6 gC m(-2) which constituted 4.3% of the biomass lost. The survival of biomass and black carbon may help to mitigate the loss of carbon during the fire.

Dynamic baselines for the detection of water quality impacts - the case of shale gas development.

There is a need for the development of effective baselines against which the water quality impacts of new developments can be assessed. The specific conductance of flowback water from shale gas operations is typically many times the specific conductance of surface water and near-surface groundwater. This contrast in specific conductance means that specific conductance could be the ideal determinand for detecting water quality impacts from shale gas extraction. If specific conductance is to be used for detecting the impacts of shale gas operations, then a baseline of specific conductance in water bodies is required. Here, Bayesian hierarchical modelling of specific conductance was applied across English groundwater. The modelling used existing, spot-sampled data from the years 2000 to 2018 from 537 unique borehole locations. When the differences between boreholes was considered, then the approach was sufficiently sensitive to detect 1% mixing of fracking fluid in groundwater at a 95% confidence interval. The Bayesian hierarchical modelling maximises the return on public investment and provides a means by which future observations can be judged.

The need to integrate legacy nitrogen storage dynamics and time lags into policy and practice.

Increased fluxes of reactive nitrogen (Nr), often associated with N fertilizer use in agriculture, have resulted in negative environmental consequences, including eutrophication, which cost billions of dollars per year globally. To address this, best management practices (BMPs) to reduce Nr loading to the environment have been introduced in many locations. However, improvements in water quality associated with BMP implementation have not always been realised over expected timescales. There is a now a significant body of scientific evidence showing that the dynamics of legacy Nr storage and associated time lags invalidate the assumptions of many models used by policymakers for decision making regarding Nr BMPs. Building on this evidence, we believe that the concepts of legacy Nr storage dynamics and time lags need to be included in these models. We believe the biogeochemical research community could play a more proactive role in advocating for this change through both awareness raising and direct collaboration with policymakers to develop improved datasets and models. We anticipate that this will result in more realistic expectations of timescales for water quality improvements associated with BMPs. Given the need for multi-nutrient policy responses to tackle challenges such as eutrophication, integration of N stores will have the further benefit of aligning both researchers and policymakers in the N community with the phosphorus and carbon communities, where estimation of stores is more widespread. Ultimately, we anticipate that integrating legacy Nr storage dynamics and time lags into policy frameworks will better meet the needs of human and environmental health.

A spatial total nitrogen budget for Great Britain.

Understanding nutrient budgets makes it possible to predict where and by how much nutrients are accumulating in the environment. Previous studies have considered this problem for nitrogen (N) but have limited themselves to reactive N species (i.e. excluding N2) or have considered total N (including N2) but have been limited to regional or national scales. In this study the spatially-distributed total nitrogen (N) budget of Great Britain (GB) was estimated at a 1 km2 grid scale. The inputs of N considered were: biological N fixation; atmospheric deposition; food and feed transfer; and inorganic synthetic fertilizer. The outputs of N considered were: atmospheric emission; terrestrial denitrification; fluvial loss from the soil; gaseous emissions from sewage treatment plants; direct sewage flux loss; and groundwater loss. All pathways were considered over a number of years. This study constructed a spatially-differentiated total N budget for GB, which not only includes all major N pathways but also distributes the N budget to various land uses with a 1 km2 spatial resolution. The results showed that both sink and source areas exist across GB, although the majority of 1 km2 grid squares were identified as sources. Based on a mass balance model calculated for 2015, total N exhibited a net flux of a source of -1045 (±244) ktonnes N/year. The spatial N budget across GB ranged from -21 (±3) tonnes N/year to 34 (±5) tonnes N/year, where 66% of grid squares were source areas and 34% were sink areas. Urban and arable land use were predominantly source areas: 97% of total urban land use and 98.5% of total arable land use. 65% of grassland was a sink area. The total amount of N released to the environment by human activity in 2015 was -16.65 kg N/ca/yr.

Assessing fugitive emissions of CH4 from high-pressure gas pipelines in the UK.

Natural gas pipelines are an important source of fugitive methane emissions in lifecycle greenhouse gas assessments but limited monitoring has taken place of UK pipelines to quantify fugitive emissions. This study investigated methane emissions from the UK high-pressure pipeline system (National Transmission System - NTS) for natural gas pipelines. Mobile surveys of CH4 emissions were conducted across four areas in the UK, with routes bisecting high-pressure pipelines (with a maximum operating pressure of 85bar) and separate control routes away from the pipelines. A manual survey of soil gas measurements was also conducted along one of the high-pressure pipelines using a tunable diode laser. For the pipeline routes, there were 26 peaks above 2.1ppmv CH4 at 0.23peaks/km, compared with 12 peaks at 0.11peaks/km on control routes. Three distinct thermogenic emissions were identified on the basis of the isotopic signal from these elevated concentrations with a peak rate of 0.03peaks/km. A further three thermogenic emissions on pipeline routes were associated with pipeline infrastructure. Methane fluxes from control routes were statistically significantly lower than the fluxes measured on pipeline routes, with an overall pipeline flux of 627 (241-1123 interquartile range) tonnes CH4/km/yr. Soil gas CH4 measurements indicated a total flux of 62.6ktCH4/yr, which equates to 2.9% of total annual CH4 emissions in the UK. We recommend further monitoring of the UK natural gas pipeline network, with assessments of transmission and distribution stations, and distribution pipelines necessary.

Organic matter properties of Fennoscandian ecosystems: Potential oxidation of northern environments under future change?

The oxidative ratio (OR) of an ecosystem, which reflects the ratio of O2:CO2 associated with ecosystem gas exchanges, is an important parameter in understanding the sink of CO2 represented by the terrestrial biosphere. There is a growing body of ecosystem-based approaches to understand OR; however, there are still a number of unknowns. This study addressed two gaps in our understanding of the oxidation of the terrestrial biosphere: (1) What is the oxidation state of Arctic ecosystems, and in particular permafrost soils? (2) Will coupled climate and land use change cause the terrestrial organic matter oxidation state to change? The study considered eight locations along a transect from southern Sweden to northern Norway and sampled different organic matter types (soil, litter, trees, and herbaceous vegetation) as well as different soil orders (Inceptisols, Spodosols, Histosols, and Gelisols). The study showed that although there was no difference between soil orders, there was a significant effect due to location with OR increasing from 1.03 at the southernmost location to 1.09 in the northernmost location; this increase is independent of soil order or type of organic matter. The pattern of post hoc differences in the OR with latitude suggests that the increase in OR is correlated with the northern limit of arable agriculture. The study suggests that the combined effects of climate and land use change could lead to a decrease in terrestrial organic matter OR and an increase in its oxidation state.

Novel granular materials with microcrystalline active surfaces: waste water treatment applications of zeolite/vermiculite composites.

The application of zeolites as adsorbents for waste water management is limited by the facts that only synthetic zeolites have sufficient capacity and only natural zeolites can be manufactured in practical sizes for application, i.e. synthetic zeolites have too small a grain size to be used and natural zeolites have low adsorption capacities. This study seeks to resolve this problem by the manufacture of synthetic zeolites upon an expanded lamella matrix (vermiculite). The synthesized composite was tested to show whether it combined the useful properties of both natural and synthetic zeolites. The study compared: hydraulic conductivity, adsorption capacity and rate of attainment of equilibrium of the synthetic composite in comparison to both a natural and a synthetic zeolite. The results demonstrate that the vermiculite-based composite shows the same hydraulic properties as a natural clinoptilolite with similar grain size (2-5mm), however, the rate of adsorption and maximum coverage were improved by a factor of 4.

Novel low density granular adsorbents - properties of a composite matrix from zeolitisation of vermiculite.

This paper reports the preparation and properties of a new low density granular absorbent material based on a zeolite/vermiculite composite. The composite prepared addresses a number of important issues relating to the use of zeolites in environmental and waste management applications. The material prepared has large particle size due to binderless adhesion of zeolite crystals within the protective lamellar matrix provided by the vermiculite granule. Additionally, the porous nature of new material ensures that it outperforms natural zeolite grains in ion-exchange tests. The material was shown to have a low bulk density (0.75 g cm(-3)) adding the benefit that the majority of grains float on water for over 15 h. The conclusion of the study is that the use of composite matrices enable the preparation of materials which show the physical properties of the host, (e.g., granular and low density), whilst maintaining the powder-like properties (e.g., high ion-exchange and small crystal size) of the active component. The resulting material can be easily handled and separated from aqueous waste streams using either flotation or exploiting its granular nature.

Towards a mechanistic understanding of carbon stabilization in manganese oxides.

Minerals stabilize organic carbon (OC) in sediments, thereby directly affecting global climate at multiple scales, but how they do it is far from understood. Here we show that manganese oxide (Mn oxide) in a water treatment works filter bed traps dissolved OC as coatings build up in layers around clean sand grains at 3%w/wC. Using spectroscopic and thermogravimetric methods, we identify two main OC fractions. One is thermally refractory (>550 °C) and the other is thermally more labile (<550 °C). We postulate that the thermal stability of the trapped OC is due to carboxylate groups within it bonding to Mn oxide surfaces coupled with physical entrapment within the layers. We identify a significant difference in the nature of the surface-bound OC and bulk OC . We speculate that polymerization reactions may be occurring at depth within the layers. We also propose that these processes must be considered in future studies of OC in natural systems.

Can climate change explain increases in DOC flux from upland peat catchments?

Long-term increases in DOC concentration in rivers draining areas of upland peat are a ubiquitous phenomenon in the UK. Several hypotheses have been proposed to explain these increases, but one compelling explanation is the observed long-term increase in temperature in UK uplands causing increases in peat decomposition rates, and increasing the depth of oxidation as evaporation increases depth to the water table. The study constructed an empirical model for water table depth and decomposition rate calibrated against observations from the Environmental Change Network monitoring site at Moor House in the North Pennines, UK. The study shows: (i) Depth of the water table has not changed significantly over a 30-year period, reflecting the fact that blanket peat is well buffered against climate change. (ii) Increases in temperature are responsible for a 12% increase in DOC production while an approximate 78% increase in DOC production has been observed. (iii) Overall DOC production is predicted to rise by 6% but observation suggests increases on the scale of 97%. (iv) The model inadequately represents changes in production and supply of DOC during periods of severe drought. The study shows that temperature change alone is insufficient to explain observed increases in DOC production. Alternative explanations for large increases in DOC production could include changes in land management, but an enzymic latch mechanism, i.e. derepression of anaerobic degradation, causing increased decomposition rates in response to severe drought is preferred.

Carbon budget for a British upland peat catchment.

This study describes the analysis of fluvial carbon flux from an upland peat catchment in the North Pennines. Dissolved organic carbon (DOC), pH, alkalinity and calcium were measured in weekly samples, with particulate organic carbon (POC) measured from the suspended sediment load from the stream outlet of an 11.4-km(2) catchment. For calendar year 1999, regular monitoring of the catchment was supplemented with detailed quasi-continuous measurements of flow and stream temperature, and DOC for the months September through November. The measurements were used to calculate the annual flux of dissolved CO(2), dissolved inorganic carbon, DOC and POC from the catchment and were combined with CO(2) and CH(4) gaseous exchanges calculated from previously published values and the observations of water table height within the peat. The study catchment represents a net sink of 15.4+/-11.9 gC/m(2)/yr. Carbon flows calculated for the study catchment are combined with values in the literature, using a Monte Carlo method, to estimate the carbon budget for British upland peat. For all British upland peat the calculation suggests a net carbon sink of between 0.15 and 0.29 MtC/yr. This is the first study to include a comprehensive study of the fluvial export of carbon within carbon budgets and shows the size of the peat carbon sink to be smaller than previous estimates, although sensitivity analysis shows that the primary productivity rather than fluvial carbon flux is a more important element in estimating the carbon budget in this regard.

Quantum vs. topological descriptors in the development of molecular models of groundwater pollution by pesticides.

Using monitoring observations from two, independent studies of US groundwater comprising a total of 61 pesticide compounds, this study has shown that those compounds found in groundwater can be distinguished from those that cannot be found in groundwater on the basis of semi-empirical, quantum chemical and empirical molecular descriptors. For the semi-empirical descriptors, logistic regression models have been developed and validated against the dataset based on the semi-empirical and quantum chemical descriptors. Logistic regression models, based on the Debye dipole moment (mu), the hydration energy (DeltaHhyd), and van der Waals volume (VvdW), resulted in a maximal explained variation in the data of 74%. When topological indices were also included the explained variance in data increased to 91%, with 86% of the variation being explained by the rule that a compound will be found in groundwater if: 0.28mu < 6chip(v) where 6chip(v) is the sixth-order molecular path connectivity and mu is the dipole moment of the compound. The significance of the dipole moment and hydration energy (or van der Waals volume) indicates that it is water solubility that controls mobility, with the inclusion of topological descriptors representing structural factors limiting the solubility. The dependence of leaching potential on the descriptors that control solubility indicates that predictions of environmental fate based on this approach may represent a strong alternative to the use of adsorption and degradation parameters.

The impact of sheep grazing on the carbon balance of a peatland.

Estimates of the greenhouse gas (GHG) fluxes resulting from sheep grazing upon upland peat soils have never been fully quantified. Previous studies have been limited to individual flux pathways or to comparing the presence to the absence of sheep grazing. Therefore, this study combines a model of the physical impact of grazing with models of: biomass production; energy usage in sheep; and peat accumulation. These combined modelling approaches enabled this study to consider the indirect and direct impacts of sheep upon the carbon and greenhouse gas balance of a peatland at different grazing intensities as well as the changes between grazing intensities. The study considered four vegetation scenarios (Calluna sp., Molinia sp.; reseeded grasses, and Agrostis-Festuca grassland) and a mixed vegetation scenario based upon the vegetation typical of upland peat ecosystems in northern England. Each scenario was considered for altitudes between 350 and 900 m above sea level and for grazing intensities between 0.1 and 2 ewes/ha. The study can show that the total GHG flux at the vegetative carrying capacity tended to decline with increasing altitude for all vegetation scenarios considered except for Molinia sp. The average total GHG flux for all scenarios was 1505 kg CO(2)eq/ha/yr/(ewe/ha), and on average 89% of the fluxes were directly from the sheep and not from the soil, and are therefore not unique to a peat soil environment. The study suggests that emission factors for upland sheep have been greatly underestimated. By comparing the total flux due to grazers to the flux to or from the soil that allows the study to define a GHG carry capacity, i.e. the grazing intensity at which the flux due to grazing is equal to the sink represented by the peat soils, this GHG carrying capacity varies between 0.2 and 1.7 ewes/ha with this capacity declining with increasing altitude for all model scenarios.

The multi-annual nitrogen budget of a peat-covered catchment--changing from sink to source?

Only a few studies have considered the N budget of peat soils and this in turn has limited the ability of studies to consider the impact of changes in climate and atmospheric deposition upon the N budget of a peat soil. This study considered the total N budget of an upland peat-covered catchment over the period 1993 to 2009. The study has shown: i) Over the period of study the total N atmospheric deposition declined from 3.5 to 0.7 tonnes N/km2/yr. ii) The total fluvial export of N at soil source varied from 0.41 to 1.85 tonnes N/km2/yr with the fluvial flux being greater than the atmospheric input in 3 years of the study, implying significant internal processing. iii) Measuring the C:N ratio of organic matter pools in the ecosystem shows that gross primary productivity and litter decomposition represent outputs of N from the soil while DOC production and humification represent inputs of N. iv) Overall, the total N budget of the peat ecosystem varies from − 1.0 to + 2.5 tonnes N/km2/yr, i.e. in some years the ecosystem is a net source of N. The time series of the total N budget suggests that the ecosystem is responding to the occurrence of severe droughts with a long-term decline in N storage that could be interpreted as a response to long-term high N deposition rates, even if those rates have now diminished.

The flux of dissolved nitrogen from the UK--evaluating the role of soils and land use.

Fluvial dissolved nitrogen (dissolved organic nitrogen [DON], nitrate and ammonium) fluxes from the terrestrial biosphere of the UK to surrounding oceans are explained on the basis of combined predictions of soil to water transfer and in-stream loss. The flux of different nitrogen species from land to surface waters is estimated using an export coefficient model employing catchment soil, land use and hydroclimatic characteristics, fitted to flux estimates derived from the Harmonised Monitoring Scheme between 2001 and 2007 for 169 UK catchments. In-stream losses of DON, nitrate and ammonium were estimated using a transit time filter in the fluvial network. Comparisons of modelled land to water N flux (2125 ktonnes N yr(-1)) with estimates of N fluxes to estuarine and ocean systems at the tidal limit (791 ktonnes N yr(-1)) suggest that significant in-channel N losses occur. These in transit losses are equivalent to up to 55 kg N ha(-1) yr(-1).

Can carbon offsetting pay for upland ecological restoration?

Upland peat soils represent a large terrestrial carbon store and as such have the potential to be either an ongoing net sink of carbon or a significant net source of carbon. In the UK many upland peats are managed for a range of purposes but these purposes have rarely included carbon stewardship. However, there is now an opportunity to consider whether management practices could be altered to enhance storage of carbon in upland peats. Further, there are now voluntary and regulated carbon trading schemes operational throughout Europe that mean stored carbon, if verified, could have an economic and tradeable value. This means that new income streams could become available for upland management. The 'Sustainable Uplands' RELU project has developed a model for calculating carbon fluxes from peat soils that covers all carbon uptake and release pathways (e.g. fluvial and gaseous pathways). The model has been developed so that the impact of common management options within UK upland peats can be considered. The model was run for a decade from 1997-2006 and applied to an area of 550 km2 of upland peat soils in the Peak District. The study estimates that the region is presently a net sink of -62 ktonnes CO2 equivalent at an average export of -136 tonnes CO2 equivalent/km2/yr. If management interventions were targeted across the area the total sink could increase to -160 ktonnes CO2/yr at an average export of -219 tonnes CO2 equivalent/km2/yr. However, not all interventions resulted in a benefit; some resulted in increased losses of CO2 equivalents. Given present costs of peatland restoration and value of carbon offsets, the study suggests that 51% of those areas, where a carbon benefit was estimated by modelling for targeted action of management interventions, would show a profit from carbon offsetting within 30 years. However, this percentage is very dependent upon the price of carbon used.

Regional lead isotope study of a polluted river catchment: River Wear, Northern England, UK.

High precision, lead isotope analyses of archived stream sediments from the River Wear catchment, northeast England (1986-88), provide evidence for three main sources of anthropogenic lead pollution; lead mining, industrial lead emissions and leaded petrol. In the upper catchment, pollution is totally controlled and dominated by large lead discharges from historic mining centres in the North Pennine Orefield ((208)Pb/(206)Pb, (207)Pb/(206)Pb ratios range from 2.0744-2.0954 and 0.8413-0.8554 respectively). In the lower catchment, co-extensive with the Durham Coalfield and areas of high population density, pollution levels are lower and regionally more uniform. Isotope ratios are systematically higher than in the upper catchment ((208)Pb/(206)Pb, (207)Pb/(206)Pb ratios range from 2.0856-2.1397 and 0.8554-0.8896 respectively) and far exceed values determined for the geogenic regional background. Here, the pollution is characterised by the atmospheric deposition of industrial lead and petrol lead. Lead derived from the combustion of coal, although present, is masked by the other two sources. Recent sediments from the main channel of the River Wear are isotopically indistinguishable from older, low order stream sediments of the North Pennine Orefield, indicating that contamination of the river by lead mining waste (up to several 1000 mg/kg Pb at some locations) continues to pose an environmental problem; a pattern that can be traced all the way to the tidal reach. Using within-catchment isotope variation and sediment lead concentrations, estimates can be made of the discharges from discrete mines or groups of mines to the overall level of lead pollution in the River Wear. As well as providing information pertinent to source apportionment and on-going catchment remediation measures, the database is a valuable resource for epidemiologists concerned with the health risks posed by environmental lead.