Oblique aggradation: a novel explanation for sinuosity of low‐energy streams in peat‐filled valley systems

Low‐energy streams in peatlands often have a high sinuosity. However, it is unknown how this sinuous planform formed, since lateral migration of the channel is hindered by relatively erosion‐resistant banks. We present a conceptual model of Holocene morphodynamic evolution of a stream in a peat‐filled valley, based on a palaeohydrological reconstruction. Coring, ground‐penetrating radar (GPR) data, and ¹⁴C and OSL dating were used for the reconstruction. We found that the stream planform is partly inherited from the Late‐Glacial topography, reflecting stream morphology prior to peat growth in the valley. Most importantly, we show that aggrading streams in a peat‐filled valley combine vertical aggradation with lateral displacement caused by attraction to the sandy valley sides, which are more erodible than the co‐evally aggrading valley‐fill. Owing to this oblique aggradation in combination with floodplain widening, the stream becomes stretched out as channel reaches may alternately aggrade along opposed valley sides, resulting in increased sinuosity over time. Hence, highly sinuous planforms can form in peat‐filled valleys without the traditional morphodynamics of alluvial bed lateral migration. Improved understanding of the evolution of streams provides inspiration for stream restoration. Copyright © 2016 John Wiley & Sons, Ltd.     

Ageing of Dissolved Halogenated Humic Substances and the Microbiological Influence on this Process

The distribution of halogens in various fractions of humic substances (HS), separated by their molecular weight, was found to be different for the different halogens. This was demonstrated for chlorine, bromine, and iodine in sewage and brown water samples by applying inductively coupled plasma mass spectrometry coupled with size‐exclusion chromatography. Quantification of the different fractions of iodinated humic substances was obtained by quadrupole mass spectrometry in connection with the isotope dilution technique using an ¹²⁹I‐enriched spike solution. Quantitative analysis was not possible for the corresponding chlorine and bromine species because of spectrometric interferences in the quadrupole instrument. The ageing of HS/halogen species was followed with respect to possible transformations of these species in a ground and sewage water sample up to eight weeks. Even if a distinct structural variation of the humic substance was observed with time by measuring the UV absorption, chlorine remained in the same molecular weight fraction and only a small change was found for the HS/bromine species after eight weeks. In contrast to these findings a substantial transformation of HS/iodine compounds took place, which demonstrated that the transfer probability of halogens from one to another HS fraction is increased with decreasing strength of the halogen bond to carbon. By comparing the results of an original sewage water sample with a filtered one and with another one which was enriched by microorganisms cultivated from the same original sample, a strong microbiological influence on the transformation of HS/iodine species was found. A quantitative balance of the corresponding HS/iodine fractions was calculated for an ageing period of eight weeks showing that iodine was preferably transferred to newly formed UV active HS substances of high molecular weight. In total, no iodine was released from the humic substances.     

Optimizing radiocarbon chronologies in peat profiles with examples from Xinjiang,China

Reliable chronological frameworks are crucial to paleoenvironmental studies, and high precision ¹⁴C dating is the foundation, but many factors, such as dating materials, surficial deposition (influenced by nuclear bomb), and the ¹⁴C age plateau, will affect the reliability of the ¹⁴C ages and chronology frameworks. In this paper, we present 87 ¹⁴C dates of different peat fractions from three peat sites in Xinjiang, China. Plant macrofossils, rootlets, the fine fraction of <90 μm, the mid-size fraction of 90–250 μm and the coarse fraction of >250 μm from selected peat samples were measured to investigate the alternative suitable fraction for dating except for plant macrofossils. We discovered that the 90–250 μm component of peat can provide alternative and reliable results in case of plant macrofossils are not available. Additionally, more dating samples from surficial peat deposition were collected, and accurate surface chronological control points were produced by comparing ¹⁴C results of plant macrofossils with atmospheric ¹⁴C bomb data. Furthermore, multiple data sets with wiggle matching were used along the radiocarbon age plateau to minimize calibrated errors when dates on the ¹⁴C age plateau were shown. Finally, radiocarbon chronology frameworks in peat profiles were optimized. In conclusion, we not only focus on the reliable dating materials, but also highlight that the importance of surficial deposition (after 1950AD) and the anomalous ¹⁴C dates when establishing the dating framework in peat profiles. Furthermore, we propose that the obtaining chronological control points of surficial peat is an important part of the establishing and improving of peat chronological framework in future research.     

Surfactant‐Enhanced Electroosmotic Flushing in a Trichlorobenzene Contaminated Clayey Soil

Remediation of the sites contaminated with organic contaminants, such as chlorobenzenes, remains a challenging issue. Electroosmotic flushing can be a promising approach which is based on mechanism of electrokinetic remediation for removal of organic contaminants from fluids in low‐permeability soil. To select an optimum surfactant that can effectively enhance electroosmotic flushing, three common surfactants, Triton X‐100 (EK2), Tween 80 (EK3), and a mixture of sodium dodecyl sulfate and Triton X‐100 (EK4) buffered with Na₂HPO₄/NaH₂PO₄ solution, were tested. The efficiency of each kind of surfactant was evaluated using a three‐dimensional box filled with a clayey soil spiked with 1,2,4‐trichlorobenzene, and compared with a test (EK1) without surfactant. The results demonstrated that the buffer solutions efficiently neutralized H⁺ and OH^? produced by electrolysis. EK3 with Tween 80 added in the flushing solution reached the highest electroosmotic permeability of 10^?4 cm²/v/s and achieved a notably high cumulative electroosmotic flow (EOF) of 5067 mL within 6 d, which was 6.3, 3.4, and 4.2 times higher than that in EK1, EK2, and EK4, respectively. There were 420 mL more cumulative EOF obtained after 50 h of electrical application in EK4 than in EK2. The introduction of nonreactive ions can increase the current, thereby benefiting the EOF. Both the higher pH caused by the buffer and the application of nonionic surfactants can make the zeta potential more negative, thereby increasing the EOF. Tween 80 can be recommended as the best flushing solution for removing organic contaminants from sites when electrokinetic remediation is applied.     

Primordial noble gases in separated meteoritic minerals,II

Eight silicate samples from the Orgueil carbonaceous chrondrite were analyzed for He, Ne, Ar, and Xe by a stepwise heating technique. Six of the samples, including two etched with NaOH, were density fractions covering the following ranges: < 2.35, 2.35–2.45, 2.45–2.48, and > 2.48 g/cm³. Two others were grain-size fractions, separated according to their ability to form a colloid at pH 11.5.All fractions are grossly deficient in cosmogenic neon, having retained only 8–33% of their normal complement. Retentivity increases with density.All fractions give low²⁰Ne/²²Ne ratios above 950°C, suggestive of D.C. Black's exotic “Neon-E” component of²⁰Ne/²²Ne ≤ 3.4. The lowest ratios were found in the low-density and especially the non-colloidal fractions. This suggests that the host phase of Ne-E is a clay mineral of lower iron content and coarser grain size than the main silicates of Orgueil.The main fraction,ρ = 2.35–2.45g/cm³, is inhospitable to Xe; it contains less Xe and releases it more readily at low temperatures (30–35% in 1 hour at 550°C) than do any of the other fractions.     

Influence of pore size and geometry on peat unsaturated hydraulic conductivity computed from 3D computed tomography image analysis

In organic soils, hydraulic conductivity is related to the degree of decomposition and soil compression, which reduce the effective pore diameter and consequently restrict water flow. This study investigates how the size distribution and geometry of air‐filled pores control the unsaturated hydraulic conductivity of peat soils using high‐resolution (45 µm) three‐dimensional (3D) X‐ray computed tomography (CT) and digital image processing of four peat sub‐samples from varying depths under a constant soil water pressure head. Pore structure and configuration in peat were found to be irregular, with volume and cross‐sectional area showing fractal behaviour that suggests pores having smaller values of the fractal dimension in deeper, more decomposed peat, have higher tortuosity and lower connectivity, which influences hydraulic conductivity. The image analysis showed that the large reduction of unsaturated hydraulic conductivity with depth is essentially controlled by air‐filled pore hydraulic radius, tortuosity, air‐filled pore density and the fractal dimension due to degree of decomposition and compression of the organic matter. The comparisons between unsaturated hydraulic conductivity computed from the air‐filled pore size and geometric distribution showed satisfactory agreement with direct measurements using the permeameter method. This understanding is important in characterizing peat properties and its heterogeneity for monitoring the progress of complex flow processes at the field scale in peatlands. Copyright © 2010 John Wiley & Sons, Ltd.     

The Baker Creek Research Watershed: Streamflow data highlighting the behaviour of an intermittent Canadian Shield stream through a wet–dry–wet cycle

Baker Creek drains water from subarctic Canadian Shield terrain comprised of a mix of exposed Precambrian bedrock, lakes, open black spruce forest and peat filled depressions. Research in the catchment has focused on hydrological processes at the hillslope and catchment scales. Streamflow is gauged from several diverse sub-catchments ranging in size from 9 to 155 km². The period of record (2003–2019) of streamflow from these sub-catchments extends from 12 to 17 years, and these data are the focus of this note. Such data are unique in this remote region. 2003–2019 was a period that included both historic wet and dry conditions. Observations during such a diversity of conditions are helping to improve understanding of how stream networks that drain this landscape expand and contract in response to short and long hydroclimatic cycles. These data from a distinctly cold and dry region of low relief, thin soils, exposed bedrock and permafrost are a valuable contribution to the global diversity of research catchment data.     

Chemical and spectroscopic characterization of humic substances from sediment and riparian soil of a highly polluted urban river (Suquía River,Córdoba,Argentina)

The Suquia River,the largest urban river in Cordoba(Argentina),has been severely polluted for decades.Actions must be taken to restore its environmental quality by managing riparian zones for increased water-self purification.The current study aimed to characterize organic matter(OM) dynamics and humic substances(HS) spectrochemical properties along the lower-middle basin of the Suquia River.Riparian soil(0-20 cm) and sediment(0-10 cm) samples were collected from a reference location(S1)and four polluted sites(S2-S5) during a low-flow period.The contents of soil and sedimentary OM and HS fractions were analyzed by wet oxidation,as well as HS Fourier transform infrared(FT-IR) and ultraviolet-visible(UV-Vis) spectrochemical properties.The OM and HS fractions from riparian soil were high upstream of Cordoba City(S1 and S2,50.2-50.4 g/kg OM) and within a 50 km downstream location(S5,30.9 g/kg OM) owing to a surplus of fresh plant biomass-carbon(C) inputs.Highly heterogeneous sediment samples did not show any significant differences among sites(P 0.05).The lowest values of the ratio of absorbances at 465 and 665 nm(E4/E6)(1.78) and the Δ log K(0.15) coefficient(a measure of HS maturity degree) were obtained downstream of Cordoba City,for both riparian soil and sediment,indicating that HS were enriched by more condensed aromatic structures within highly degraded portions of the river.All samples exhibited similar IR spectra,implying overlapping recalcitrant-C structures at the functional group level,but with different absorbance intensity.Data from the current study constitute a baseline for understanding the chemical nature of HS from sediment and riparian soil along the Suquia River and can be used as a reference for future studies tracking OM compositional changes over time.     

Formation of Humic-like Substances in Mixed and Pure Cultures of Aquatic Microorganisms

A natural decay of plant and animal biomass in aquatic environments results in the release of different simple structured organic substances into water. In our laboratory experiments we investigated whether some of them, e.g., starch or peptone, and also a complex yeast biomass can be transformed into humic-like substances by natural assemblages and some pure cultures of aquatic microorganisms. After a 6 months incubation most of the cultural media enriched with those natural organic substrates turned dark in color and humic-like substances (HS) could be isolated. However, the original substrate organic carbon was mainly mineralized in microbial cultures, and only about 3 % C was converted into HS. Total yields of HS differed in dependence of the individual substrate used (peptone > yeast > starch), the origin of inoculum (river > lake > groundwater), and the incubation temperature (20°C > 10°C). According to their elemental composition, and their spectroscopical and electrophoretic characteristics the microbially formed HS resembled natural aquatic humic matter, but were higher in aliphatic constituents (carbohydrates, peptides) and lower in aromatic structures. HS-like substances were also obtained from pure cultures of a bacterium Bacillus sphaericus and a fungus Cladosporium cladosporioides. The ¹³C and ¹⁵N isotopic contents of the microbially produced HS differed in dependence on the microbial inoculum and the type of organic substrates used, but in general they indicated anabolic processes to be mainly responsible for the humification of the simple organic substrates used in our experiments.     

The construction of a reliable absolute chronology for the last two millennia in an anthropogenically disturbed peat bog: Limitations and advantages of using a radio-isotopic proxy and age–depth modelling

The main aim of this paper is to present the pitfalls connected with the construction of reliable chronologies for anthropogenically disturbed peatlands over the last two millennia based on ²¹⁰Pb and ¹⁴C dating, i.e. the period of the strongest human impact on these ecosystems. The following hypotheses have been formulated: i) parts of peatlands suspected to be affected by peat extraction may possess traces of mechanical disturbances undetectable using different analyses based on biota proxy; ii) failure to consider information included in radionuclide date inversions may contribute to the establishment of misleading chronologies. To test these hypotheses, different scenarios of chronology based on high resolution ²¹⁰Pb and ¹⁴C dating from a peat core retrieved from the Puścizna Krauszowska bog (southern Poland) have been analysed. Nowadays, this mire is intensively exploited by humans; however, it contains remains of dome considered undisturbed, from which the core presented in this paper was collected. The set of dates revealed the presence of marked ¹⁴C date inversions (mechanical disturbances) which, if inappropriately interpreted before the age–depth modelling process, may lead to the establishment of misleading chronologies, and thus an incorrect interpretation of biota proxy records, e.g. pollen. Those sections of peat profiles with prominent age inversions and/or strong discrepancies between the peat accumulation rate and bulk density should be rejected from age–depth modelling, even if interpretable chronologies can be obtained.     

The impact of pipe flow in riparian peat deposits on nitrate transport and removal

The effect of preferential flow in soil pipes on nitrate retention in riparian zones is poorly understood. The characteristics of soil pipes and their influence on patterns of groundwater transport and nitrate dynamics were studied along four transects in a 1‐ to >3‐m deep layer of peat and marl overlying an oxic sand aquifer in a riparian zone in southern Ontario, Canada. The peat‐marl deposit, which consisted of several horizontal layers with large differences in bulk density, contained soil pipes that were generally 0.1 to 0.2 m in diameter and often extended vertically for 1 to >2 m. Springs that produced overland flow across the riparian area occurred at some sites where pipes extended to the peat surface. Concentrations of NO₃^?–N (20–30 mg L^?1) and dissolved oxygen (DO) (4–6 mg L^?1) observed in peat pipe systems and surface springs were similar to values in the underlying sand aquifer, indicating that preferential flow transported groundwater with limited nitrate depletion. Low NO₃^?–N concentrations of <5 mg L^?1 and enriched δ¹⁵N values indicated that denitrification was restricted to small areas of the peat where pipes were absent. Groundwater DO concentrations declined rapidly to <2 mg L^?1 in the peat matrix adjacent to pipes, whereas high NO₃^?–N concentrations of >15 mg L^?1 extended over a larger zone. Low dissolved organic carbon values at these locations suggest that supplies of organic carbon were not sufficient to support high rates of denitrification, despite low DO conditions. These data indicate that it is important to develop a greater understanding of pipes in peat deposits, which function as sites where the transport of large fluxes of water with low biogeochemical reaction rates can limit the nitrate removal capacity of riparian zones. Copyright © 2011 John Wiley & Sons, Ltd.     

Dating basal peat: The geochronology of peat initiation revisited

Attributing the start of peat growth to an absolute timescale requires dating the bottom of peat deposits overlying mineral sediment, often called the basal peat. Peat initiation is reflected in the stratigraphy as a gradual transition from mineral sediment to increasingly organic material, up to where it is called peat. So far, varying criteria have been used to define basal peat, resulting in divergent approaches to date peat initiation. The lack of a universally applicable and quantitative definition, combined with multiple concerns that have been raised previously regarding the radiocarbon dating of peat, may result in apparent ages that are either too old or too young for the timing of peat initiation. Here, we aim to formulate updated recommendations for dating peat initiation. We provide a conceptual framework that supports the use of the organic matter (OM) gradient for a quantitative and reproducible definition of the mineral-to-peat transition (i.e., the stratigraphical range reflecting the timespan of the peat initiation process) and the layer defined as basal peat (i.e., the stratigraphical layer that is defined as the bottom of a peat deposit). Selection of dating samples is often challenging due to poor preservation of plant macrofossils in basal peat, and the representativity of humic and humin dates for the age of basal peat is uncertain. We therefore analyse the mineral-to-peat transition based on three highly detailed sequences of radiocarbon dates, including dates of plant macrofossils and the humic and humin fractions obtained from bulk samples. Our case study peatland in the Netherlands currently harbours a bog vegetation, but biostratigraphical analyses show that during peat initiation the vegetation was mesotrophic. Results show that plant macrofossils provide the most accurate age in the mineral-to-peat transition and are therefore recommendable to use for ¹⁴C dating basal peat. If these are unattainable, the humic fraction provides the best alternative and is interpreted as a terminus-ante-quem for peat initiation. The potential large age difference between dates of plant macrofossils and humic or humin dates (up to ∼1700 years between macrofossil and humic ages, and with even larger differences for humins) suggests that studies reusing existing bulk dates of basal peat should take great care in data interpretation. The potentially long timespan of the peat initiation process (with medians of ∼1000, ∼1300 and ∼1500 years within our case study peatland) demonstrates that choices regarding sampling size and resolution need to be well substantiated. We summarise our findings as a set of recommendations for dating basal peats, and advocate the widespread use of OM determination to obtain a low-cost, quantitative and reproducible definition of basal peat that eases intercomparison of studies.     

Products and Kinetics of the OH‐radical‐induced Dealkylation of Atrazine

Hydroxyl radicals, generated radiolytically in N₂O/O₂‐saturated solutions, yield in their reaction with atrazine equal amounts of deethylatrazine and acetaldehyde (40% of OH radical yield) and deisopropylatrazine and acetone (16%), respectively. The precursors of deethylatrazine and acetaldehyde is their Schiff base which hydrolyzes slowly (OH^–‐catalyzed: k = 5.2 dm³ mol^–1 s^–1). The hydrolysis of the Schiff base of deisopropylatrazine and acetone is too fast to be detected. In a pulse radiolysis experiment, the intermediate formed upon OH‐radical attack (k = 3·10⁹ dm³ mol^–1 s^–1) has a strong absorption at 440 nm. It decays in the presence of oxygen (k = 1.3·10⁹ dm³ mol^–1 s^–1), and upon deprotonation [pK_a(peroxyl radicals) ≈ 10.5] the peroxyl radicals thus‐formed eliminate superoxide radicals (k = 2.9·10⁵ s^–1). s‐Triazine itself reacts much more slowly with OH radicals (k = 9.7·10⁷ dm³ mol^–1 s^–1). This can explain, why in the case of atrazine in comparison to other aromatic compounds, e.g. toluene, the addition of the OH radical to the ring (estimated at ca. 40%) is of relatively little importance as compared to an H‐abstraction from (activated) positions of the side groups.     

Towards a conceptual model of hydrological change on an abandoned cutover bog,Quebec

Cutover bogs do not return to functional peatland ecosystems after abandonment because re‐establishment of peat‐forming mosses is poor. This paper presents a conceptual model of bog disturbance caused by peat harvesting (1942–1972), and the hydrological evolution that occurred after abandonment (1973–1998). Two adjacent bogs of similar size and origin, one harvested and the other essentially undisturbed, provide the basis for understanding what changes occurred. The model is based on historical trends evident from previous surveys of land‐use, bog ecology and resource mapping; and from recent hydrological and ecological data that characterize the current condition. Water balance data and historical information suggest that runoff increased and evapotranspiration decreased following drainage, but tended towards pre‐disturbance levels following abandonment, as vegetation recolonized the surface and drainage became less efficient over time. Dewatering of soil pores after drainage caused shrinkage and oxidation of the peat and surface subsidence of approximately 80 cm over 57 years. Comparisons with a nearby natural bog suggest that bulk density in the upper 50 cm of cutover peat increased from 0·07 to 0·13 g cm^?3, specific yield declined from 0·14 to 0·07, water table fluctuations were 67% greater, and mean saturated hydraulic conductivity declined from 4·1 × 10^?5 to 1·3 × 10^?5 cm s^?1. More than 25 years after abandonment, Sphagnum mosses were distributed over broad areas but covered less than 15% of the surface. Areas with ‘good’ Sphagnum regeneration (>10% cover) were strongly correlated with high water tables (mean ?22 cm), especially in zones of seasonal groundwater discharge, artefacts of the extraction history. Forest cover expanded from 5 to 20% of the study area following abandonment. The effect of forest growth (transpiration and interception) and drainage on lowering water levels eventually will be countered by slower water movement through the increasingly dense soil, and by natural ditch deterioration. However, without management intervention, full re‐establishment of natural hydrological functions will take a very long time. Copyright © 2002 John Wiley & Sons, Ltd.     

Solar forcing on the 7Be-air concentration variability at ground level

This paper analyzes the correlation between the temporal and spatial variability of ⁷Be-air concentration at ground level to precipitation. Data, obtained from 26 stations distributed throughout North and South America, Australia and Antarctica, were analyzed. Variations in the data were extracted by the empirical orthogonal function (EOF) and principal component (PC) analysis. The results presented here show that the variability of ⁷Be-air concentration at ground level is influenced simultaneously both by solar cycle and atmospheric processes, such as precipitation, turbulent transport and advection. Solar forcing dominates ⁷Be annual variability worldwide. On the other hand, atmospheric processes influence ⁷Be air–concentration at ground level regionally and seasonally.     

Transport and dispersal of organic debris (peat blocks) in upland fluvial systems

This paper assesses the mechanisms and pathways by which peat blocks are eroded and transported in upland fluvial systems. Observations and experiments from the north Pennines (UK) have been carried out on two contrasting river systems. Mapping of peat block distributions and appraisal of reach‐based sediment budgets clearly demonstrates that macro‐size peat is an important stream load component. In small streams block sizes can approximate the channel width and much of the peat is transported overbank. Local ‘peat jams’ and associated mineral deposition may provide an important component of channel storage. In larger systems peat blocks rapidly move down‐channel and undergo frequent exchanges between bed and bank storage. Results of peat block tracing using painted blocks indicate that once submerged, blocks of all sizes are easily transported and blocks break down rapidly by abrasion. Vegetation and bars play an important role in trapping mobile peat. In smaller streams large block transport is limited by channel jams. Smaller blocks are transported overbank but exhibit little evidence of downstream fining. In larger rivers peat blocks are more actively sorted and show downstream reduction in size from source. A simple model relating peat block diameter (D_p) to average flow depth (d) suggests three limiting transport conditions: flotation (D_p < d), rolling (d < D_p > d/2) and deposition (D_p > d/2). Experiments demonstrate that peat block transport occurs largely by rolling and floating and the transport mechanism is probably controlled by relative flow depth (d/D_p ratio). Transport velocity varies with transport mechanism (rolling is the slowest mode) and transport lengths increase as flow depth increases. Abrasion rates vary with the transport mechanism. Rolling produces greater abrasion rates and more rounded blocks. Abrasion rates vary from 0 to 10 g m^?1 for blocks ranging in mass from 10 to 6000 g. Copyright © 2001 John Wiley & Sons, Ltd.     

Differences between Humic Substances from Riverine,Estuarine, and Marine Environments Observed by Fluorescence Spectroscopy

Sixteen samples of fulvic acids and XAD‐4 fractions of riverine, estuarine, coastal, and open ocean origin have been studied by emission and synchronous molecular fluorescence spectroscopy. Certain features of the molecular fluorescence are related to the nature, the content, and the origin of those aquatic humic substances (HS). Riverine HS appear several times richer in fluorophores than marine HS, which can be well observed by emission fluorescence spectroscopy. Synchronous‐scan spectra of fulvic acids and of XAD‐4 fractions from the aquatic environments studied, emphasized the quality differences of their fluorophores. These features are useful as tracers of humic substances related with their natural environment source or even with their anthropogenic origin.     

Sediment and fluvial particulate carbon flux from an eroding peatland catchment

Erosion and the associated loss of carbon is a major environmental concern in many peatlands and remains difficult to accurately quantify beyond the plot scale. Erosion was measured in an upland blanket peatland catchment (0.017 km²) in northern England using structure-from-motion (SfM) photogrammetry, sediment traps and stream sediment sampling at different spatial scales. A net median topographic change of –27 mm yr^–1 was recorded by SfM over the 12-month monitoring period for the entire surveyed area (598 m²). Within the entire surveyed area there were six nested catchments where both SfM and sediment traps were used to measure erosion. Substantial amounts of peat were captured in sediment traps during summer storm events after two months of dry weather where desiccation of the peat surface occurred. The magnitude of topographic change for the six nested catchments determined by SfM (mean value: 5.3 mm, standard deviation: 5.2 mm) was very different to the areal average derived from sediment traps (mean value: –0.3 mm, standard deviation: 0.1 mm). Thus, direct interpolation of peat erosion from local net topographic change into sediment yield at the catchment outlet appears problematic. Peat loss measured at the hillslope scale was not representative of that at the catchment scale. Stream sediment sampling at the outlet of the research catchment (0.017 km²) suggested that the yields of suspended sediment and particulate organic carbon were 926.3 t km^–2 yr^–1 and 340.9 t km^–2 yr^–1, respectively, with highest losses occurring during the autumn. Both freeze–thaw during winter and desiccation during long periods of dry weather in spring and summer were identified as important peat weathering processes during the study. Such weathering was a key enabler of subsequent fluvial peat loss from the catchment. © 2019 John Wiley & Sons, Ltd.     

Adsorbed and Bound Residues in Fulvic Acid Fractions of a Contaminated Groundwater – Isolation:, Chromatographic and Spectroscopic Characterization

Humic substances (HS) were isolated from two contaminated groundwater samples (B22 and B53) from a site of a former gas facility. The isolation yielded almost only the fulvic acid fractions (FA). For characterization spectroscopic (UV, fluorescence) and chromatographic techniques (hydrophobic interaction chromatography – HIC as well as size-exclusion chromatography – SEC) were applied. The sample designated B22 FA was collected from the contamination plume whereas the sample B53 FA was collected downstream. Distinct differences were exhibited by these samples. The UV and fluorescence spectra as well as the HIC and SEC chromatograms of the B53 FA sample resemble those of the FA fraction obtained from natural water (groundwater, bog). The HIC and SEC chromatograms reveal the presence of organic compounds in B22 FA which can be derived from coal tar contaminants or their metabolites. Some of the compounds can be extracted from the FA fraction with non-polar organic solvents indicating adsorptive forces between the contaminants and the FA fraction.     

Spatio‐temporal changes in bog pool bottom topography – temperature effect and its influence on pool development: an example from a raised bog in Estonia

Increases in pool water and peat temperature in summer accelerate peat decomposition and production of biogenic gases, which can be trapped in peat pores and cause oscillation of peatland surfaces and the rise of peat from the bottom of bog pools. Associated changes in peat water conductivity, holding capacity and transpiration also affect bog hydrology. Our multi‐year study is the first to show in detail the extent and dynamics of changes in bog pool depth and bottom topography associated with changes in temperature, peat type and other factors. The true seasonal rise of peat from the pool bottom begins once the water temperature at the pool bottom exceeds 13–14 °C, although the speed and extent of the rise depends on peat properties, making the rise more erratic than its subsequent descent. The more rapid descent occurs after the first large drop in the temperature of the pool's surface water at the end of summer, resulting from the combination of reduced methane production and increased gas solubility with less influence by peat properties. Much higher dissolved organic carbon concentrations (216 ± 26 mg l^?1) in the pore water of peat risen from the bottom to the pool surface compared with that in the same type of peat at the pool bottom (62 ± 20 mg l^?1) indicate an acceleration of peat decomposition at the warmer pool surface. We show the extent and character of changes in pool depth and bottom topography and how annual differences relate to temperature. Only a few degrees' increase in pool water temperature could induce the pool bottom to rise faster and more extensively for a longer period and enhance decomposition in the peat at the pool surface. This should be evaluated in greater detail to assess the effects of temperature increase on the carbon budget and hydrology of peatlands. Copyright © 2012 John Wiley & Sons, Ltd.