scholarly journals Fluxes and <sup>13</sup>C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought

2008 ◽  
Vol 5 (2) ◽  
pp. 1319-1360 ◽  
Author(s):  
K.-H. Knorr ◽  
B. Glaser ◽  
C. Blodau
Keyword(s):  
Soil Heterogeneity ◽  
Free Energies ◽  
Dissolved Carbon ◽  
Hydrogenotrophic Methanogenesis ◽  
13C Isotope ◽  
Drying And Rewetting ◽  
Labelling Experiment ◽  
Aerobic Soil ◽  
The Impact ◽  
Chamber Measurements

Abstract. The impact of drought and rewetting on carbon cycling in peatland ecosystems is currently debated. We studied the impact of experimental drought and rewetting on intact monoliths from a temperate fen over a period of ~300 days, using a permanently wet treatment and two treatments undergoing drought for 50 days. In one of the mesocosms vegetation had been removed. Net production of CH4 was calculated from mass balances in the peat and emission using static chamber measurements and results compared to 13C isotope budgets of CO2 and CH4 and energy yields of acetoclastic and hydrogenotrophic methanogenesis. Drought retarded methane production after rewetting for days to weeks and promoted methanotrophic activity. Based on isotope and flux budgets, aerobic soil respiration contributed 32–96% in the wet and 86–99% in the other treatments. Drying and rewetting did not shift methanogenic pathways according to δ 13C ratios of CH4 and CO2. Although δ13C ratios indicated a prevalence of hydrogenotrophic methanogenesis, free energies of this process were small and often positive on the horizon scale, suggesting that methane was produced very locally. Fresh plant-derived carbon input apparently supported respiration in the rhizosphere and sustained methanogenesis in the unsaturated zone according to a 13C-CO2 labelling experiment. The study documents that drying and rewetting in a rich fen soil may have little effect on methanogenic pathways but result in rapid shifts between methanogenesis and methanotrophy. Such shifts may be promoted by roots and soil heterogeneity, as hydrogenotrophic methanogenesis occurred locally even when conditions were not conducive for this process in the bulk peat.

scholarly journals Fluxes and <sup>13</sup>C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought

2008 ◽  
Vol 5 (5) ◽  
pp. 1457-1473 ◽  
Author(s):  
K.-H. Knorr ◽  
B. Glaser ◽  
C. Blodau
Keyword(s):  
Soil Heterogeneity ◽  
Free Energies ◽  
Dissolved Carbon ◽  
Hydrogenotrophic Methanogenesis ◽  
13C Isotope ◽  
Drying And Rewetting ◽  
Labelling Experiment ◽  
Global Concern ◽  
Aerobic Soil ◽  
The Impact

Abstract. Peatlands contain a carbon stock of global concern and significantly contribute to the global methane burden. The impact of drought and rewetting on carbon cycling in peatland ecosystems is thus currently debated. We studied the impact of experimental drought and rewetting on intact monoliths from a temperate fen over a period of ~300 days, using a permanently wet treatment and two treatments undergoing drought for 50 days. In one of the mesocosms, vegetation had been removed. Net production of CH4 was calculated from mass balances in the peat and emission using static chamber measurements. Results were compared to 13C isotope budgets of CO2 and CH4 and energy yields of acetoclastic and hydrogenotrophic methanogenesis. Drought retarded methane production after rewetting for days to weeks and promoted methanotrophic activity. Based on isotope and flux budgets, aerobic soil respiration contributed 32–96% in the wet treatment and 86–99% in the other treatments. Drying and rewetting did not shift methanogenic pathways according to δ13C ratios of CH4 and CO2. Although δ13C ratios indicated a prevalence of hydrogenotrophic methanogenesis, free energies of this process were small and often positive on the horizon scale. This suggests that methane was produced very locally. Fresh plant-derived carbon input apparently supported respiration in the rhizosphere and sustained methanogenesis in the unsaturated zone, according to a 13C-CO2 labelling experiment. The study documents that drying and rewetting in a rich fen soil may have little effect on methanogenic pathways, but result in rapid shifts between methanogenesis and methanotrophy. Such shifts may be promoted by roots and soil heterogeneity, as hydrogenotrophic methanogenesis occurred locally even when conditions were not conducive for this process in the bulk peat.

scholarly journals Computational Insight into the Rope-Skipping Isomerization of Diarylether Cyclophanes

Symmetry ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 2127
Author(s):  
Thomas J. Summers ◽  
Hrishikesh Tupkar ◽  
Tyler M. Ozvat ◽  
Zoë Tregillus ◽  
Kenneth A. Miller ◽  
...  
Keyword(s):  
Asymmetric Catalysis ◽  
Room Temperature ◽  
Chemical Bonds ◽  
Chiral Molecules ◽  
Free Energies ◽  
Design And Synthesis ◽  
The Impact ◽  
Rope Skipping ◽  
Temperature Factors ◽  
Insight Into

The restricted rotation of chemical bonds may lead to the formation of stable, conformationally chiral molecules. While the asymmetry in chiral molecules is generally observed in the presence of one or more stereocenters, asymmetry exhibited by conformational chirality in compounds lacking stereocenters, called atropisomerism, depends on structural and temperature factors that are still not fully understood. This atropisomerism is observed in natural diarylether heptanoids where the length of the intramolecular tether constrains the compounds to isolable enantiomers at room temperature. In this work, we examine the impact tether length has on the activation free energies to isomerization of a diarylether cyclophane substructure with a tether ranging from 6 to 14 carbons. Racemization activation energies are observed to decay from 48 kcal/mol for a 7-carbon tether to 9.2 kcal/mol for a 14-carbon tether. Synthetic efforts to experimentally test these constraints are also presented. This work will likely guide the design and synthesis of novel asymmetric cyclophanes that will be of interest in the catalysis community given the importance of atropisomeric ligands in the field of asymmetric catalysis.

Nitrogen process in stormwater bioretention: The impact of alternate drying and rewetting on nitrogen migration and transformation

2021 ◽  
Author(s):  
Yao Chen ◽  
Renyu Chen ◽  
Zhen Liu ◽  
Xuehua Yu ◽  
Shuang Zheng ◽  
...  
Keyword(s):  
Pore Water ◽  
Laboratory Experiments ◽  
Reductase Activity ◽  
Nitrogen Transformation ◽  
Transformation Mechanism ◽  
Dry Period ◽  
Bioretention System ◽  
Plant Organ ◽  
Drying And Rewetting ◽  
The Impact

Abstract Abstract Nitrogen migration and transformation in the stormwater bioretention system were studied in laboratory experiments, in which the effects of drying-rewetting were particularly investigated. The occurrence and distribution of nitrogen in the plants, the soil, and the pore water were explored under different drying-rewetting cycles. The results clearly showed that bioretention system could remove nitrogen efficiently in all drying-rewetting cycles. The incoming nitrogen could be retained in the topsoil (0–10 cm) and accumulated in the planted layer. However, the overlong dry periods (12 and 22 days) cause an increase in nitrate in the pore water. In addition, nitrogen is mostly stored in the plants’ stem tissues. Up to 23.26% of the inflowing nitrogen can be immobilized in plant organ after a dry period of 22 days. In addition, the relationships between nitrogen reductase activity in the soil and soil nitrogen content were explored. The increase of soil TN content could enhance the activity of nitrate reductase. Meanwhile, the activity of hydroxylamine reductase (HyR) could be enhanced with the increase of soil NO3− content. These results provide a reference for the future development of nitrogen transformation mechanism and the construction of stormwater bioretention systems.

The impact of salinity on the microbial response to drying and rewetting in soil

2017 ◽  
Vol 108 ◽  
pp. 17-26 ◽  
Author(s):  
Kristin M. Rath ◽  
Arpita Maheshwari ◽  
Johannes Rousk
Keyword(s):  
Microbial Response ◽  
Drying And Rewetting ◽  
The Impact

The Impact of Soil Heterogeneity on Nitrate Dynamic and Losses in Tile-Drained Arable Fields

2016 ◽  
Vol 227 (10) ◽  
Author(s):  
Denise Bednorz ◽  
Nadine Tauchnitz ◽  
Olaf Christen ◽  
Holger Rupp ◽  
Ralph Meissner
Keyword(s):  
Soil Heterogeneity ◽  
Arable Fields ◽  
The Impact

Fire effects on the spatial patterns of soil resources in a Nicaraguan wet tropical forest

2005 ◽  
Vol 21 (4) ◽  
pp. 435-444 ◽  
Author(s):  
Brent C. Blair
Keyword(s):  
Leaf Litter ◽  
Tropical Forests ◽  
Forest Fires ◽  
Soil Heterogeneity ◽  
Fire Effects ◽  
Fire Intensity ◽  
Vegetative Cover ◽  
Soil Resources ◽  
In Fire ◽  
The Impact

Anthropogenic wildfires are becoming increasingly frequent in wet tropical forests. This trend follows that of other anthropogenic disturbances, which are now acute and widespread. Fires pose a potentially serious threat to tropical forests. However, little is known about the impact of unintended forest fires on below-ground resources in these ecosystems. This study investigated the influence of fires on the distribution and variability of soil resources on two sets of 50×50-m burned and unburned plots in a Nicaraguan rain forest. Samples were collected at 5-m intervals throughout each plot as well as subsamples at 50-cm intervals. Geostatistical techniques as well as univariate statistics were used to quantify the spatial autocorrelation and variability of selected nutrients (N, P and K), carbon and standing leaf litter. Most variability in this forest was spatially dependent at a scale of 30 m or less. However the average range of autocorrelations varied greatly between properties and sites. Burning altered soil heterogeneity by decreasing the range over which soil properties were autocorrelated. Overall the average patch size (range) for nitrogen was reduced by 7%, phosphorus by 52%, potassium by 60% and carbon by 43%. While phosphorus and leaf litter increased in the burned plots compared to unburned plots, potassium was not different. Nitrogen and carbon did not display a consistent pattern between burning regimes and this may be explained by variation in fire intensity. Leaf litter measurements did not correlate with measured soil nutrients within plots. Observed changes in the burned forest were likely a result of both the intensity of burning and change in vegetative cover between the time of the fires and soil sampling.

scholarly journals High soil solution carbon und nitrogen concentrations in a drained Atlantic bog are reduced to natural levels by 10 yr of rewetting

2013 ◽  
Vol 10 (10) ◽  
pp. 15809-15849 ◽  
Author(s):  
S. Frank ◽  
B. Tiemeyer ◽  
J. Gelbrecht ◽  
A. Freibauer
Keyword(s):  
Soil Solution ◽  
Water Table ◽  
Water Table Depth ◽  
Peat Layer ◽  
Deep Drainage ◽  
Dissolved Carbon ◽  
Total Dissolved Nitrogen ◽  
Natural Site ◽  
Nitrogen Concentrations ◽  
The Impact

Abstract. Artificial drainage of peatlands causes dramatic changes in the release of greenhouse gases and in the export of dissolved carbon (C) and nutrients to downstream ecosystems. Rewetting anthropogenically altered peatlands offers a possibility to reduce nitrogen (N) and C losses. In this study, we investigate the impact of drainage and rewetting on the cycling of dissolved C and N as well as on dissolved gases over a period of 1 yr and 4 month, respectively. The peeper technique was used to receive a high vertical sampling resolution. Within one Atlantic bog complex a near natural site, two drained grasslands sites with different mean water table positions, and a former peat cutting area rewetted 10 yr ago were chosen. Our results clearly indicate that drainage increased the concentration of dissolved organic carbon (DOC), ammonia, nitrate and dissolved organic nitrogen (DON) compared to the near natural site. Drainage depth further determined the release and therefore the concentration level of DOC and N species, but the biochemical cycling and therefore dissolved organic matter (DOM) quality and N species composition were unaffected. Thus, especially deep drainage can cause high DOC losses. In general, DOM at drained sites was enriched in aromatic moieties as indicated by SUVA280 and showed a higher degradation status (lower DOC to DON ratio) compared to the near natural site. At the drained sites, equal C to N ratios of uppermost peat layer and DOC to DON ratio of DOM in soil solution suggest that the uppermost degraded peat layer is the main source of DOM. Nearly constant DOC to DON ratios and SUVA280 values with depth furthermore indicated that DOM moving downwards through the drained sites remained largely unchanged. DON and ammonia contributed most to the total dissolved nitrogen (TN). The subsoil concentrations of nitrate were negligible due to strong decline in nitrate around mean water table depth. Methane production during the winter months at the drained sites moved downwards to areas which were mostly water saturated over the whole year (>40 cm). Above these depths, the recovery of the water table in winter months led to the production of nitrous oxide around mean water table depth at drained sites. 10 yr after rewetting, the DOM quality (DOC to DON ratio and SUVA280) and quantity were comparable to the near natural site, indicating the re-establishment of mostly pristine biochemical processes under continuously water logged conditions. The only differences occur in elevated dissolved methane and ammonia concentrations reflecting the former disturbance by drainage and peat extraction. Rewetting via polder technique seems to be an appropriate way to revitalize peatlands on longer timescales and to improve the water quality of downstream water bodies.

scholarly journals The importance of freeze/thaw cycles on lateral tracer transport in ice-wedge polygons

2021 ◽  
Author(s):  
Elchin Jafarov ◽  
Daniil Svyatsky ◽  
Dylan Harp ◽  
Brent Newman ◽  
David Moulton ◽  
...  
Keyword(s):  
Climate Models ◽  
Lateral Flow ◽  
The Arctic ◽  
Tracer Transport ◽  
Lateral Transport ◽  
Dissolved Carbon ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle ◽  
The Impact

Abstract. A significant portion of the Arctic coastal plain is classified as polygonal tundra and plays a vital role in soil carbon cycling. Recent research suggests that lateral transport of dissolved carbon could exceed vertical carbon releases to the atmosphere. However, the details of lateral subsurface flow in polygonal tundra have not been well studied. We incorporated a subsurface transport process into an existing state-of-art hydrothermal model. The model captures the physical effects of freeze/thaw cycles on lateral flow in polygonal tundra. The new modeling capability enables non-reactive tracer movement within subsurface. We utilized this new capability to investigate the impact of freeze/thaw cycle on lateral flow in the polygon polygonal tundra. Our study indicates the important role of freeze/thaw cycle and freeze-up effect on lateral tracer transport, suggesting that dissolved species could be transported from the middle of the polygon to the sides within a couple of thaw seasons. Introducing carbon lateral transport in the climate models could substantially reduce the uncertainty associated with the impact of thawing permafrost.

First-principles stability ranking of molecular crystal polymorphs with the DFT+MBD approach

2018 ◽  
Vol 211 ◽  
pp. 253-274 ◽  
Author(s):  
Johannes Hoja ◽  
Alexandre Tkatchenko
Keyword(s):  
First Principles ◽  
Structure Prediction ◽  
Molecular Crystal ◽  
Crystal Structure Prediction ◽  
Free Energies ◽  
Many Body ◽  
Dispersion Effects ◽  
Stability Ranking ◽  
Exact Exchange ◽  
The Impact

We discuss the impact of many-body dispersion effects, exact exchange, and vibrational free energies on a crystal structure prediction procedure applicable to pharmaceutically relevant systems. Furthermore, we show that this procedure is generally robust and the used approximations lead on average to changes of relative stabilities of only 1–2 kJ mol−1.

scholarly journals Model-aided quantification of dissolved carbon and nitrogen release after windthrow disturbance in an Austrian karst system

2016 ◽  
Vol 13 (1) ◽  
pp. 159-174 ◽  
Author(s):  
A. Hartmann ◽  
J. Kobler ◽  
M. Kralik ◽  
T. Dirnböck ◽  
F. Humer ◽  
...  
Keyword(s):  
Forest Disturbance ◽  
Inorganic Nitrogen ◽  
Climate Projections ◽  
Dissolved Carbon ◽  
Quality Of Water ◽  
Before And After ◽  
Doc Production ◽  
Hydrological System ◽  
Karst Systems ◽  
The Impact

Abstract. Karst systems are important for drinking water supply. Future climate projections indicate increasing temperature and a higher frequency of strong weather events. Both will influence the availability and quality of water provided from karst regions. Forest disturbances such as windthrow can disrupt ecosystem cycles and cause pronounced nutrient losses from the ecosystems. In this study, we consider the time period before and after the wind disturbance period (2007/08) to identify impacts on DIN (dissolved inorganic nitrogen) and DOC (dissolved organic carbon) with a process-based flow and solute transport simulation model. When calibrated and validated before the disturbance, the model disregards the forest disturbance and its consequences on DIN and DOC production and leaching. It can therefore be used as a baseline for the undisturbed system and as a tool for the quantification of additional nutrient production. Our results indicate that the forest disturbance by windthrow results in a significant increase of DIN production lasting  ∼  3.7 years and exceeding the pre-disturbance average by 2.7 kg ha−1 a−1 corresponding to an increase of 53 %. There were no significant changes in DOC concentrations. With simulated transit time distributions we show that the impact on DIN travels through the hydrological system within some months. However, a small fraction of the system outflow (< 5 %) exceeds mean transit times of > 1 year.

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