Overriding water table control on managed peatland greenhouse gas emissions.

Global peatlands store more carbon than is naturally present in the atmosphere1,2. However, many peatlands are under pressure from drainage-based agriculture, plantation development and fire, with the equivalent of around 3 per cent of all anthropogenic greenhouse gases emitted from drained peatland3-5. Efforts to curb such emissions are intensifying through the conservation of undrained peatlands and re-wetting of drained systems6. Here we report eddy covariance data for carbon dioxide from 16 locations and static chamber measurements for methane from 41 locations in the UK and Ireland. We combine these with published data from sites across all major peatland biomes. We find that the mean annual effective water table depth (WTDe; that is, the average depth of the aerated peat layer) overrides all other ecosystem- and management-related controls on greenhouse gas fluxes. We estimate that every 10 centimetres of reduction in WTDe could reduce the net warming impact of CO2 and CH4 emissions (100-year global warming potentials) by the equivalent of at least 3 tonnes of CO2 per hectare per year, until WTDe is less than 30 centimetres. Raising water levels further would continue to have a net cooling effect until WTDe is within 10 centimetres of the surface. Our results suggest that greenhouse gas emissions from peatlands drained for agriculture could be greatly reduced without necessarily halting their productive use. Halving WTDe in all drained agricultural peatlands, for example, could reduce emissions by the equivalent of over 1 per cent of global anthropogenic emissions.

Small artificial waterbodies are widespread and persistent emitters of methane and carbon dioxide.

Inland waters play an active role in the global carbon cycle and emit large volumes of the greenhouse gases (GHGs), methane (CH4 ) and carbon dioxide (CO2 ). A considerable body of research has improved emissions estimates from lakes, reservoirs and rivers but recent attention has been drawn to the importance of small, artificial waterbodies as poorly quantified but potentially important emission hotspots. Of particular interest are emissions from drainage ditches and constructed ponds. These waterbody types are prevalent in many landscapes and their cumulative surface areas can be substantial. Furthermore, GHG emissions from constructed waterbodies are anthropogenic in origin and form part of national emissions reporting, whereas emissions from natural waterbodies do not (according to Intergovernmental Panel on Climate Change guidelines). Here, we present GHG data from two complementary studies covering a range of land uses. In the first, we measured emissions from nine ponds and seven ditches over a full year. Annual emissions varied considerably: 0.1-44.3 g CH4  m-2  year-1 and -36-4421 g CO2  m-2  year-1 . In the second, we measured GHG concentrations in 96 ponds and 64 ditches across seven countries, covering subtropical, temperate and sub-arctic biomes. When CH4 emissions were converted to CO2  equivalents, 93% of waterbodies were GHG sources. In both studies, GHGs were positively related to nutrient status (C, N, P), and pond GHG concentrations were highest in smallest waterbodies. Ditch and pond emissions were larger per unit area when compared to equivalent natural systems (streams, natural ponds). We show that GHG emissions from natural systems should not be used as proxies for those from artificial waterbodies, and that artificial waterbodies have the potential to make a substantial but largely unquantified contribution to emissions from the Agriculture, Forestry and Other Land Use sector, and the global carbon cycle.

Effect of restoration on saltmarsh carbon accumulation in Eastern England.

Wetland soils are globally important carbon stores, and natural wetlands provide a sink for atmospheric carbon dioxide (CO2) through ongoing carbon accumulation. Recognition of coastal wetlands as a significant contributor to carbon storage (blue carbon) has generated interest into the climate change mitigation benefits of restoring or recreating saltmarsh habitat. However, the length of time a re-created marsh will take to become functionally equivalent to a natural (reference) system, or indeed, whether reference conditions are attainable, is largely unknown. Here, we describe a combined field chronosequence and modelling study of saltmarsh carbon accumulation and provide empirically based predictions of changes in the carbon sequestration rate over time following saltmarsh restoration. Carbon accumulation was initially rapid (average 1.04 t C ha-1 yr-1 during the first 20 years), slowing to a steady rate of around 0.65 t C ha-1 yr-1 thereafter. The resulting increase in C stock gave an estimated total C accumulation of 74 t C ha-1 in the century following restoration. This is approximately the same as our observations of natural marsh C content (69 t C ha-1), suggesting that it takes approximately 100 years for restored saltmarsh to obtain the same carbon stock as natural sites.

Critical review of the impacts of grazing intensity on soil organic carbon storage and other soil quality indicators in extensively managed grasslands.

Livestock grazing intensity (GI) is thought to have a major impact on soil organic carbon (SOC) storage and soil quality indicators in grassland agroecosystems. To critically investigate this, we conducted a global review and meta-analysis of 83 studies of extensive grazing, covering 164 sites across different countries and climatic zones. Unlike previous published reviews we normalized the SOC and total nitrogen (TN) data to a 30 cm depth to be compatible with IPCC guidelines. We also calculated a normalized GI and divided the data into four main groups depending on the regional climate (dry warm, DW; dry cool, DC; moist warm, MW; moist cool, MC). Our results show that taken across all climatic zones and GIs, grazing (below the carrying capacity of the systems) results in a decrease in SOC storage, although its impact on SOC is climate-dependent. When assessed for different regional climates, all GI levels increased SOC stocks under the MW climate (+7.6%) whilst there were reductions under the MC climate (-19%). Under the DW and DC climates, only the low (+5.8%) and low to medium (+16.1%) grazing intensities, respectively, were associated with increased SOC stocks. High GI significantly increased SOC for C4-dominated grassland compared to C3-dominated grassland and C3-C4 mixed grasslands. It was also associated with significant increases in TN and bulk density but had no effect on soil pH. To protect grassland soils from degradation, we recommend that GI and management practices should be optimized according to climate region and grassland type (C3, C4 or C3-C4 mixed).

Use of dynamic soil-vegetation models to assess impacts of nitrogen deposition on plant species composition: an overview.

Field observations and experimental data of effects of nitrogen (N) deposition on plant species diversity have been used to derive empirical critical N loads for various ecosystems. The great advantage of such an approach is the inclusion of field evidence, but there are also restrictions, such as the absence of explicit criteria regarding significant effects on the vegetation, and the impossibility to predict future impacts when N deposition changes. Model approaches can account for this. In this paper, we review the possibilities of static and dynamic multispecies models in combination with dynamic soil-vegetation models to (1) predict plant species composition as a function of atmospheric N deposition and (2) calculate critical N loads in relation to a prescribed protection level of the species composition. The similarities between the models are presented, but also several important differences, including the use of different indicators for N and acidity and the prediction of individual plant species vs. plant communities. A summary of the strengths and weaknesses of the various models, including their validation status, is given. Furthermore, examples are given of critical load calculations with the model chains and their comparison with empirical critical N loads. We show that linked biogeochemistry-biodiversity models for N have potential for applications to support European policy to reduce N input, but the definition of damage thresholds for terrestrial biodiversity represents a major challenge. There is also a clear need for further testing and validation of the models against long-term monitoring or long-term experimental data sets and against large-scale survey data. This requires a focused data collection in Europe, combing vegetation descriptions with variables affecting the species diversity, such as soil acidity, nutrient status and water availability. Finally, there is a need for adaptation and upscaling of the models beyond the regions for which dose-response relationships have been parameterized, to make them generally applicable.

The lamin B receptor of the nuclear envelope inner membrane: a polytopic protein with eight potential transmembrane domains.

The lamin B receptor is a previously identified integral membrane protein in the nuclear envelope of turkey erythrocytes that associates with the nuclear intermediate filament protein lamin B (Worman, H. J., J. Yuan, G. Blobel, and S. D. Georgatos. 1988. Proc. Natl. Acad. Sci. USA. 85:8531-8534). In the present report, we use cell fractionation and antibodies against the lamin B receptor to localize it to an 8-M urea-extracted membrane fraction of chicken liver nuclei, supporting an inner nuclear membrane localization. We deduced the amino acid sequence of the chicken lamin B receptor from overlapping clones obtained by screening cDNA libraries with a probe generated by the polymerase chain reaction with primers based on the partial protein sequence of the isolated protein. The mature lamin B receptor has a calculated molecular mass of 73,375 D and eight segments of hydrophobic amino acids that could function as transmembrane domains as determined by hydropathy analysis. Preceding the first putative transmembrane segment is a highly charged 204-residue-long amino terminal region that contains two consensus sites for phosphorylation by protein kinase A. Since the lamin B receptor has been shown to be phosphorylated by protein kinase A in vitro and in vivo and this phosphorylation affects lamin B binding (Applebaum, J., G. Blobel, and S. D. Georgatos. 1990. J. Biol. Chem. 265:4181-4185), it is likely that this amino terminal region faces the nucleoplasm. The amino terminal region also contains three DNA-binding motifs that are found in gene regulatory proteins and histones, suggesting that the lamin B receptor may additionally play a role in gene regulation and/or chromatin organization.

Thermal conductivity effect of carrier gases on flame-ionization detector sensitivity.

Data for six carrier gases of different thermal conductivities show a linear correlation between the logarithm of thermal conductivity and detector response. Carbon dioxide with a lower thermal conductivity than helium gives a ninefold increase in detector response.

Chromatographic silica gel: surface area determined by adsorption.

The surface area of silicic acid, a form of silica gel, has been determined by adsorption of methanol from a benzene solvent. The method is straightforward, uses inexpensive apparatus, and should be applicable to other particulate adsorbents.

Groundwater nitrogen composition and transformation within a moorland catchment, mid-Wales.

The importance of upland groundwater systems in providing a medium for nitrogen transformations and processes along flow paths is investigated within the Afon Gwy moorland catchment, Plynlimon, mid-Wales. Dissolved organic nitrogen (DON) was found to be the most abundant form of dissolved nitrogen (N) in most soils and groundwaters, accounting for between 47 and 72% of total dissolved nitrogen in shallow groundwater samples and up to 80% in deeper groundwaters. Groundwater DON may also be an important source of bio-available N in surface waters and marine systems fed by upland catchments. A conceptual model of N processes is proposed based on a detailed study along a transect of nested boreholes and soil suction samplers within the interfluve zone. Shallow groundwater N speciation reflects the soilwater N speciation implying a rapid transport mechanism and good connectivity between the soil and groundwater systems. Median nitrate concentrations were an order of magnitude lower within the soil zone (<5-31 microg/L) than in the shallow groundwaters (86-746 microg/L). Given the rapid hydrostatic response of the groundwater level within the soil zone, the shallow groundwater system is both a source and sink for dissolved N. Results from dissolved N(2)O, N(2)/Ar ratios and dissolved N chemistry suggests that microbial N transformations (denitrification and nitrification) may play an important role in controlling the spatial variation in soil and groundwater N speciation. Reducing conditions within the groundwater and saturated soils of the wet-flush zones on the lower hillslopes, a result of relatively impermeable drift deposits, are also important in controlling N speciation and transformation processes.

Balancing macronutrient stoichiometry to alleviate eutrophication.

Reactive nitrogen (N) and phosphorus (P) inputs to surface waters modify aquatic environments, affect public health and recreation. Source controls dominate eutrophication management, whilst biological regulation of nutrients is largely neglected, although aquatic microbial organisms have huge potential to process nutrients. The stoichiometric ratio of organic carbon (OC) to N to P atoms should modulate heterotrophic pathways of aquatic nutrient processing, as high OC availability favours aquatic microbial processing. Heterotrophic microbial processing removes N by denitrification and captures N and P as organically-complexed, less eutrophying forms. With a global data synthesis, we show that the atomic ratios of bioavailable dissolved OC to either N or P in rivers with urban and agricultural land use are often distant from a "microbial optimum". This OC-deficiency relative to high availabilities of N and P likely overwhelms within-river heterotrophic processing. We propose that the capability of streams and rivers to retain N and P may be improved by active stoichiometric rebalancing. Although autotrophic OC production contributes to heterotrophic rates substantial control on nutrient processing from allochthonous OC is documented for N and an emerging field for P. Hence, rebalancing should be done by reconnecting appropriate OC sources such as wetlands and riparian forests that have become disconnected from rivers concurrent with agriculture and urbanisation. However, key knowledge gaps require research prior to the safe implementation of this approach in management: (i) to evaluate system responses to catchment inputs of dissolved OC forms and amounts relative to internal production of autotrophic dissolved OC and aquatic and terrestrial particulate OC and (ii) evaluate risk factors in anoxia-mediated P desorption with elevated OC scenarios. Still, we find stoichiometric rebalancing through reconnecting landscape beneficial OC sources has considerable potential for river management to alleviate eutrophication, improve water quality and aquatic ecosystem health, if augmenting nutrient source control.

Modelling impacts of atmospheric deposition and temperature on long-term DOC trends.

It is increasingly recognised that widespread and substantial increases in Dissolved organic carbon (DOC) concentrations in remote surface, and soil, waters in recent decades are linked to declining acid deposition. Effects of rising pH and declining ionic strength on DOC solubility have been proposed as potential dominant mechanisms. However, since DOC in these systems is derived mainly from recently-fixed carbon, and since organic matter decomposition rates are considered sensitive to temperature, uncertainty persists over the extent to which other drivers that could influence DOC production. Such potential drivers include fertilisation by nitrogen (N) and global warming. We therefore ran the dynamic soil chemistry model MADOC for a range of UK soils, for which time series data are available, to consider the likely relative importance of decreased deposition of sulphate and chloride, accumulation of reactive N, and higher temperatures, on soil DOC production in different soils. Modelled patterns of DOC change generally agreed favourably with measurements collated over 10-20years, but differed markedly between sites. While the acidifying effect of sulphur deposition appeared to be the predominant control on the observed soil water DOC trends in all the soils considered other than a blanket peat, the model suggested that over the long term, the effects of nitrogen deposition on N-limited soils may have been sufficient to raise the "acid recovery DOC baseline" significantly. In contrast, reductions in non-marine chloride deposition and effects of long term warming appeared to have been relatively unimportant. The suggestion that future DOC concentrations might exceed preindustrial levels as a consequence of nitrogen pollution has important implications for drinking water catchment management and the setting and pursuit of appropriate restoration targets, but findings still require validation from reliable centennial-scale proxy records, such as those being developed using palaeolimnological techniques.

Modelling nitrogen saturation and carbon accumulation in heathland soils under elevated nitrogen deposition.

A simple model of nitrogen (N) saturation, based on an extension of the biogeochemical model MAGIC, has been tested at two long-running heathland N manipulation experiments. The model simulates N immobilisation as a function of organic soil C/N ratio, but permits a proportion of immobilised N to be accompanied by accumulation of soil carbon (C), slowing the rate of C/N ratio change and subsequent N saturation. The model successfully reproduced observed treatment effects on soil C and N, and inorganic N leaching, for both sites. At the C-rich upland site, N addition led to relatively small reductions in soil C/N, low inorganic N leaching, and a substantial increase in organic soil C. At the C-poor lowland site, soil C/N ratio decreases and N leaching increases were much more dramatic, and soil C accumulation predicted to be smaller. The study suggests that (i) a simple model can effectively simulate observed changes in soil and leachate N; (ii) previous model predictions based on a constant soil C pool may overpredict future N leaching; (iii) N saturation may develop most rapidly in dry, organic-poor, high-decomposition systems; and (iv) N deposition may lead to significantly enhanced soil C sequestration, particularly in wet, nutrient-poor, organic-rich systems.

Modelling the effect of climate change on recovery of acidified freshwaters: relative sensitivity of individual processes in the MAGIC model.

The MAGIC model was used to evaluate the relative sensitivity of several possible climate-induced effects on the recovery of soil and surface water from acidification. A common protocol was used at 14 intensively studied sites in Europe and eastern North America. The results show that several of the factors are of only minor importance (increase in pCO(2) in soil air and runoff, for example), several are important at only a few sites (seasalts at near-coastal sites, for example) and several are important at nearly all sites (increased concentrations of organic acids in soil solution and runoff, for example). In addition changes in forest growth and decomposition of soil organic matter are important at forested sites and sites at risk of nitrogen saturation. The trials suggest that in future modelling of recovery from acidification should take into account possible concurrent climate changes and focus specially on the climate-induced changes in organic acids and nitrogen retention.

Altered topoisomerase II alpha in a drug-resistant small cell lung cancer cell line selected in VP-16.

The H209/V6 cell line was derived from the H209 small cell lung cancer cell line by selection in etoposide (VP-16). Cytogenetic analysis indicates that the sensitive and resistant cell lines share 20 marker chromosomes and thus are clearly related. However, the H209/V6 cell line has four additional structurally altered chromosomes and a 2 N-modal chromosome number, while the H209 cell line is hypotetraploid (4 N-). H209/V6 cells are cross-resistant to some drugs that interact with topoisomerase II but not mitoxantrone. H209/V6 cells are also not cross-resistant to vincristine, trimetrexate, or cisplatin. The rates of VP-16 efflux are the same in the resistant and sensitive cell lines, which is consistent with the observation that P-glycoprotein mRNA is not detectable in either cell line. Fewer VP-16-induced DNA-protein complexes are observed in H209/V6 cells, and immunoblot analysis shows that levels of topoisomerase II alpha are reduced in H209/V6 cells compared to the sensitive H209 cells. Furthermore, the topoisomerase II alpha-related protein in H209/V6 cells has an increased electrophoretic mobility, with an apparent M(r) of 160,000. The levels of the topoisomerase II alpha 6.1-kilobase mRNA in H209/V6 cells are reduced > 10-fold. In addition, a second topoisomerase II alpha-related mRNA of approximately 4.8 kilobases is observed in H209/V6 cells but not in H209 cells. The quantity and electrophoretic mobility of the M(r) 180,000 topoisomerase II beta protein and its 6.1-kilobase mRNA are the same in the sensitive and resistant cell lines. The topoisomerase II strand-passing activity in H209/V6 nuclear extracts is reduced about 2-fold, but this activity is not more resistant to inhibition by VP-16 than the activity in H209 cells. However, band depletion immunoblot experiments show that the topoisomerase II alpha-related M(r) 160,000 protein in H209/V6 cells is not bound to DNA in the presence of concentrations of VP-16 that deplete the M(r) 170,000 topoisomerase II alpha in H209 cells and the M(r) 180,000 topoisomerase II beta in both the resistant and sensitive cells. We conclude that quantitative and qualitative alterations in topoisomerase II alpha have occurred in H209/V6 cells and are likely to contribute to its resistance phenotype.

Rapid isolation of bovine interphotoreceptor retinol-binding protein.

A large retinol-binding protein, interphotoreceptor retinol-binding protein, is found only in the interphotoreceptor matrix of the eye, and may function in vitamin A transport for the visual cycle. Interphotoreceptor retinol-binding protein is the major glycoprotein of this matrix, and can be isolated rapidly by affinity-adsorption onto concanavalin A-Sepharose. The yield is approx. 0.25 mg per bovine eye. Its apparent Mr is 250000 by gel-filtration chromatography, and 225000 by native polyacrylamide-gradient gel electrophoresis; this protein band displays endogenous retinol fluorescence on such gels. As measured by SDS-polyacrylamide gel electrophoresis, the apparent Mr is 140000. In the interphotoreceptor matrix most vitamin A-binding sites on this retinol-binding protein are unoccupied; however, addition of exogenous all-trans-retinol can saturate these sites. The apparent dissociation constant for retinol is 10(-6) M, as measured by fluorimetric titration.

The United Kingdom Acid Waters Monitoring Network: a review of the first 15 years and introduction to the special issue.

The United Kingdom Acid Waters Monitoring Network (AWMN) was established in 1988 to determine the ecological impact of acidic emissions control policy on acid-sensitive lakes and streams. AWMN data have been used to explore a range of causal linkages necessary to connect changes in emissions to chemical and, ultimately, biological recovery. Regional scale reductions in sulphur (S) deposition have been found to have had an immediate influence on surface water chemistry, including increases in acid neutralising capacity, pH and alkalinity and declines in aluminium toxicity. These in turn can be linked to changes in the aquatic biota which are consistent with "recovery" responses. A continuation of the current programme is essential in order to better understand apparent non-linearity between nitrogen (N) in deposition and runoff, the substantial rise in organic acid concentrations, and the likely impacts of forecast climate change and other potential constraints on further biological improvement.

Long-term increases in surface water dissolved organic carbon: observations, possible causes and environmental impacts.

Dissolved organic carbon (DOC) concentrations in 22 UK upland waters have increased by an average of 91% during the last 15 years. Increases have also occurred elsewhere in the UK, northern Europe and North America. A range of potential drivers of these trends are considered, including temperature, rainfall, acid deposition, land-use, nitrogen and CO2 enrichment. From examination of recent environmental changes, spatial patterns in observed trends, and analysis of time series, it is suggested that DOC may be increasing in response to a combination of declining acid deposition and rising temperatures; however it is difficult to isolate mechanisms based on monitoring data alone. Long-term DOC increases may have wide-ranging impacts on freshwater biota, drinking water quality, coastal marine ecosystems and upland carbon balances. Full understanding of the significance of these increases requires further knowledge of the extent of natural long-term variability, and of the natural "reference" state of these systems.

Trends in surface water chemistry of acidified UK freshwaters, 1988-2002.

Analysis of water chemistry data from 15 years of monitoring at 22 acid-sensitive lakes and streams in the UK reveals coherent national chemical trends indicative of recovery from acidification. Excess sulphate and base cations exhibit significant decline, often accompanied by an increase in an alkalinity-based determination of acid neutralising capacity (AB-ANC) and, at fewer sites, a decline in hydrogen and labile aluminium. Acid neutralising capacity determined by "charge-balance" (CB-ANC) exhibits few trends, possibly due to compound errors associated with its determination. Trend slopes in excess sulphate correlate with those for base cations, hydrogen ion and AB-ANC, with between-site variability linked to catchment hydrology, sea-salt inputs and forestry. Nitrate concentrations have not changed significantly but show high sensitivity to varying climate. Trends in AB-ANC are influenced by significant increases in dissolved organic carbon, the cause of which it is vital to establish before trends in the former can definitively be attributed to decreasing acidic deposition.

Nitrate leaching as a confounding factor in chemical recovery from acidification in UK upland waters.

Over the period 1988-2002, data from 18 of the 22 lakes and streams in the UK Acid Waters Monitoring Network (AWMN) show clear trends of declining excess sulphate concentrations in response to reductions in sulphur deposition, but fewer trends in increasing pH or alkalinity. There has been no significant decline in the deposition of total nitrogen over the same period, and no sites show a trend in nitrate concentration. Peak nitrate concentrations have already surpassed excess sulphate on occasion in half of the AWMN sites. Furthermore, current understanding of terrestrial N saturation processes suggests that nitrate leaching from soils may increase, even under a constant N deposition load. Best-case projections indicate that nitrate will overtake sulphate as the major excess acid anion in many sites within 10 years, while worst-case predictions with steady-state models suggest that in the longer-term, nitrate could become the dominant excess acid anion in most of the UK.