Timothy G. Jones

Atmospheric nitrogen deposition promotes carbon loss from peat bogs

Peat bogs have historically represented exceptional carbon (C) sinks because of their extremely low decomposition rates and consequent accumulation of plant remnants as peat. Among the factors favoring that peat accumulation, a major role is played by the chemical quality of plant litter itself, which is poor in nutrients and characterized by polyphenols with a strong inhibitory effect on microbial breakdown. Because bogs receive their nutrient supply solely from atmospheric deposition, the global increase of atmospheric nitrogen (N) inputs as a consequence of human activities could potentially alter the litter chemistry with important, but still unknown, effects on their C balance. Here we present data showing the decomposition rates of recently formed litter peat samples collected in nine European countries under a natural gradient of atmospheric N deposition from ≈0.2 to 2 g·m−2·yr−1. We found that enhanced decomposition rates for material accumulated under higher atmospheric N supplies resulted in higher carbon dioxide (CO2) emissions and dissolved organic carbon release. The increased N availability favored microbial decomposition (i) by removing N constraints on microbial metabolism and (ii) through a chemical amelioration of litter peat quality with a positive feedback on microbial enzymatic activity. Although some uncertainty remains about whether decay-resistant Sphagnum will continue to dominate litter peat, our data indicate that, even without such changes, increased N deposition poses a serious risk to our valuable peatland C sinks.

Deep instability of deforested tropical peatlands revealed by fluvial organic carbon fluxes.

Tropical peatlands contain one of the largest pools of terrestrial organic carbon, amounting to about 89,000 teragrams (1 Tg is a billion kilograms). Approximately 65 per cent of this carbon store is in Indonesia, where extensive anthropogenic degradation in the form of deforestation, drainage and fire are converting it into a globally significant source of atmospheric carbon dioxide. Here we quantify the annual export of fluvial organic carbon from both intact peat swamp forest and peat swamp forest subject to past anthropogenic disturbance. We find that the total fluvial organic carbon flux from disturbed peat swamp forest is about 50 per cent larger than that from intact peat swamp forest. By carbon-14 dating of dissolved organic carbon (which makes up over 91 per cent of total organic carbon), we find that leaching of dissolved organic carbon from intact peat swamp forest is derived mainly from recent primary production (plant growth). In contrast, dissolved organic carbon from disturbed peat swamp forest consists mostly of much older (centuries to millennia) carbon from deep within the peat column. When we include the fluvial carbon loss term, which is often ignored, in the peatland carbon budget, we find that it increases the estimate of total carbon lost from the disturbed peatlands in our study by 22 per cent. We further estimate that since 1990 peatland disturbance has resulted in a 32 per cent increase in fluvial organic carbon flux from southeast Asia—an increase that is more than half of the entire annual fluvial organic carbon flux from all European peatlands. Our findings emphasize the need to quantify fluvial carbon losses in order to improve estimates of the impact of deforestation and drainage on tropical peatland carbon balances.

Contrasting vulnerability of drained tropical and high‐latitude peatlands to fluvial loss of stored carbon

Carbon sequestration and storage in peatlands rely on consistently high water tables. Anthropogenic pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of pressures including drainage, burning, land conversion for agriculture, timber, and biofuel production, cause loss of peat-forming vegetation and exposure of previously anaerobic peat to aerobic decomposition. This can shift peatlands from net CO2 sinks to large CO2 sources, releasing carbon held for millennia. Peatlands also export significant quantities of carbon via fluvial pathways, mainly as dissolved organic carbon (DOC). We analyzed radiocarbon (14C) levels of DOC in drainage water from multiple peatlands in Europe and Southeast Asia, to infer differences in the age of carbon lost from intact and drained systems. In most cases, drainage led to increased release of older carbon from the peat profile but with marked differences related to peat type. Very low DOC-14C levels in runoff from drained tropical peatlands indicate loss of very old (centuries to millennia) stored peat carbon. High-latitude peatlands appear more resilient to drainage; 14C measurements from UK blanket bogs suggest that exported DOC remains young ( 500 year) carbon in high-latitude systems. Rewetting at least partially offsets drainage effects on DOC age.

Methane indicator values for peatlands: a comparison of species and functional groups

Previous studies have shown a correspondence between the abundance of particular plant species and methane flux. Here, we apply multivariate analyses, and weighted averaging, to assess the suitability of vegetation composition as a predictor of methane flux. We developed a functional classification of the vegetation, in terms of a number of plant traits expected to influence methane production and transport, and compared this with a purely taxonomic classification at species level and higher. We applied weighted averaging and indirect and direct ordination approaches to six sites in the United Kingdom, and found good relationships between methane flux and vegetation composition (classified both taxonomically and functionally). Plant species and functional groups also showed meaningful responses to management and experimental treatments. In addition to the United Kingdom, we applied the functional group classification across different geographical regions (Canada and the Netherlands) to assess the generality of the method. Again, the relationship appeared good at the site level, suggesting some general applicability of the functional classification. The method seems to have the potential for incorporation into large-scale (national) greenhouse gas accounting programmes (in relation to peatland condition/management) using vegetation mapping schemes. The results presented here strongly suggest that robust predictive models can be derived using plant species data (for use in national-scale studies). For trans-national-scale studies, where the taxonomic assemblage of vegetation differs widely between study sites, a functional classification of plant species data provides an appropriate basis for predictive models of methane flux.

Methodologies for Extracellular Enzyme Assays from Wetland Soils

Measurement of extracellular enzymic activity in wetland soils can give an indication of the ecosystems biogeochemical processes, and rates of nutrient and carbon cycling. Analysis of these have allowed researchers to gain an understanding of the ecosystems’ microbial ecology and how it can be affected by environmental factors. Here we give a detailed description of the assays necessary to determine the activity of a suite of key hydrolase enzymes and phenol oxidases. These enzymes control the rates of decomposition and consequently the production of biogenic greenhouse gases. Knowing the processes responsible for the breakdown of organic matter is therefore essential if it becomes necessary to curb these emissions. Our protocols allow for cost effective analysis of a large number of samples and provide sufficient accuracy to determine differences between soil types. When coupled with contemporary microbial techniques these enzyme assays permit entire biochemical pathways to be determined, giving unparalleled knowledge on the processes involved in wetland ecosystems.

Transformations in DOC along a source to sea continuum; impacts of photo-degradation, biological processes and mixing

Peatlands export significant amounts of dissolved organic carbon (DOC) to freshwaters, but the quantity of DOC reaching marine environments is typically less than the input to the fluvial system due to processing within the water column. Key removal processes include photo-chemical degradation, and heterotrophic bacterial respiration. In this study we examined these processes using 14C-labelled DOC to quantify the extent of DOC breakdown and to determine its fate following irradiation under controlled laboratory conditions. We examined the influence of microbial processes occurring within the water column, the potential role of stream-bed biofilms, and the possible modifying effects of downstream mixing, as DOC in water from the peatland encounters runoff from upland mineral soils (“Mountain”), nutrient-rich runoff from agricultural soils, and seawater in an estuary. Our results demonstrated conservative mixing of DOC from Peatland and Mountain waters but interactive effects when Peatland water was mixed with Agricultural and Estuary waters and exposed to solar radiation. The mixing of Peatland and Agricultural waters led to net DOC production, suggesting that DOC was only partially degraded by solar radiation and that the products of this might have fuelled autotrophic microbial growth in the samples. The mixing of Peatland water with saline estuary water resulted in net DOC loss following irradiation, suggesting a role for sunlight in enhancing the flocculation of DOC to particulate organic carbon (POC) in saline environments.

Influence of habitat on the quantity and composition of leachable carbon in the O2 horizon: Potential implications for potable water treatment

Abstract Organic material leached from the organic (O) horizon of soils is a major source of natural organic matter (NOM) in surface waters. Dissolved organic carbon (DOC) is a known precursor for the formation of disinfection by-products (DBPs), including trihalomethanes (THMs), formed during chlorination. In this study the concentration and composition of leachable O2 horizon DOC from 5 habitats within a United Kingdom upland reservoir catchment (beech, spruce, larch, and pine forests and blanket peat) were compared with an emphasis on potential treatment implications using XAD fractionation and THM formation potential (THMFP) tests. Statistically significant differences were found between habitats, with pine and larch leachates yielding particularly high DOC concentrations (mean 19.3 and 13.4 mg/L, respectively) and THMFP7d values (mean 1306 and 1527 μg/L, respectively). The interspecies variation observed suggests that the typical distinction made between deciduous and coniferous species in previous studies is overly simplistic. Interestingly, peat leachate exhibited a surprisingly low DOC concentration (mean 9.0 mg/L), suggesting that the high DOC flux associated with these habitats may be the result of other factors such as depth of organic matter and mineral content. Averaged across all habitats, mean standardized THMFP (STHMFP) was highest in the hydrophobic acid (HPOA) fraction, although substantial differences in the relative reactivities of fractions were found between habitats. Synergistic effects are also likely to complicate the relationship between fractional character and STHMFP.

Heavy Rainfall Impacts on Trihalomethane Formation in Contrasting Northwestern European Potable Waters

There is emerging concern over the impact of extreme events such as heavy rainfall on the quality of water entering the drinking water supply from aboveground sources, as such events are expected to increase in magnitude and frequency in response to climate change. We compared the impact of rainfall events on streamwater quality in four contrasting upland (peatland and mineral soil) and lowland agricultural catchments used to supply drinking water in France (Brittany) and the United Kingdom (North Wales) by analyzing water samples collected before, during, and after specific events. At all four streams, heavy rainfall led to a considerable rise in organic matter concentration ranging from 48 to 158%. Dissolved organic carbon (DOC) quality, as determined using specific ultraviolet absorbance, changed consistently at all sites during rainfall events, with a greater proportion of aromatic and higher molecular weight compounds following the onset of rainfall. However, the change in DOC quality and quantity did not significantly alter the trihalomethane formation potential. We observed small increases in trihalomethane (THM) generation only at the Welsh peatland and agricultural sites and a small decrease at the Brittany agricultural site. The proportion of brominated THMs in chlorinated waters was positively correlated with bromide/DOC ratio in raw waters for all sites and hydrological conditions. These results provide a first indication of the potential implications for surface-based drinking water resources resulting from expected future increases in rainfall event intensity and extension of dry periods with climate changes.

A Decision Support System for Drinking Water Production Integrating Health Risks Assessment

The issue of drinking water quality compliance in small and medium scale water services is of paramount importance in relation to the 98/83/CE European Drinking Water Directive (DWD). Additionally, concerns are being expressed over the implementation of the DWD with respect to possible impacts on water quality from forecast changes in European climate with global warming and further anticipated reductions in north European acid emissions. Consequently, we have developed a decision support system (DSS) named ARTEM-WQ (AwaReness Tool for the Evaluation and Mitigation of drinking Water Quality issues resulting from environmental changes) to support decision making by small and medium plant operators and other water stakeholders. ARTEM-WQ is based on a sequential risk analysis approach that includes consideration of catchment characteristics, climatic conditions and treatment operations. It provides a holistic evaluation of the water system, while also assessing human health risks of organic contaminants potentially present in treated waters (steroids, pharmaceuticals, pesticides, bisphenol-a, polychlorobiphenyls, polycyclic aromatic hydrocarbons, petrochemical hydrocarbons and disinfection by-products; n = 109). Moreover, the system provides recommendations for improvement while supporting decision making in its widest context. The tool has been tested on various European catchments and shows a promising potential to inform water managers of risks and appropriate mitigative actions. Further improvements should include toxicological knowledge advancement, environmental background pollutant concentrations and the assessment of the impact of distribution systems on water quality variation.

Plant Species Effects on the Carbon Storage Capabilities of a Blanket bog Complex

Plants are known to influence peatland carbon fluxes both i) directly through respiration and ii) by the production of litter and root exudates, which are then broken down by microbes within the peat matrix. In this study we investigated whether three different plant species typical of a UK blanket bog complex - Calluna vulgaris, Juncus effusus and mixed Sphagnum species - influence the carbon sequestering abilities of the peat that they grow in. To quantify this we measured fluxes of soil derived CO2 and CH4, and extractable levels of dissolved organic carbon (DOC) and phenolics, from peat samples taken from areas dominated by one of the three plant communities. It was found that there were significant differences between the carbon fluxes from the different sites, which we attributed to changes brought about by the vegetation on the pH, phenolic concentrations and extracellular enzyme activities found in the peat matrix. Peat taken from Sphagnum-dominated areas emitted less CO2 than the other two sample groups, and had lower overall DOC concentrations and phenol oxidase activities. Conversely, Juncus-peat had the highest CO2 and CH4 fluxes, along with the greatest phenol oxidase activities. Taking all the results into consideration the plants were ranked in order of their ability to reduce the loss of carbon from the peat soil within which they were growing: Sphagnum > Calluna > Juncus. These results suggest that plant community structures could be altered in order to maximise a peatland’s ability to be used as a carbon store should they need to be managed as part of a carbon stewardship scheme or a geoengineering project – if this was to be the sole management interest in an area of peatland.