Peaty Sediments Research Articles

Arsenite Binding to Natural Organic Matter: Spectroscopic Evidence for Ligand Exchange and Ternary Complex Formation

The speciation of As in wetlands is often controlled by natural organic matter (NOM), which can form strong complexes with Fe(III). Here, we elucidated the molecular-scale interaction of arsenite (As(III)) with Fe(III)-NOM complexes under reducing conditions. We reacted peat (40-250 μm size fraction, 1.0 g Fe/kg) with 0-15 g Fe/kg at pH <2, removed nonreacted Fe, and subsequently equilibrated the Fe(III) complexes formed with 900 mg As/kg peat at pH 7.0, 8.4, and 8.8. The solid-phase speciation of Fe and As was studied by electron paramagnetic resonance (Fe) and X-ray absorption spectroscopy (As, Fe). Our results show that the majority of Fe in the peat was present as mononuclear Fe(III) species (RFe-C = 2.82-2.88 Å), probably accompanied by small Fe(III) clusters of low nuclearity (RFe-Fe = 3.25-3.46 Å) at high pH and elevated Fe contents. The amount of As(III) retained by the original peat was 161 mg As/kg, which increased by up to 250% at pH 8.8 and an Fe loading of 7.3 g/kg. With increasing Fe content of peat, As(III) increasingly formed bidentate mononuclear (RAs-Fe = 2.88-2.94 Å) and monodentate binuclear (RAs-Fe = 3.35-3.41 Å) complexes with Fe, thus yielding direct evidence of ternary complex formation. The ternary complex formation went along with a ligand exchange reaction between As(III) and hydroxylic/phenolic groups of the peat (RAs-C = 2.70-2.77 Å). Our findings thus provide spectroscopic evidence for two yet unconfirmed As(III)-NOM interaction mechanisms, which may play a vital role in the cycling of As in sub- and anoxic NOM-rich environments such as peatlands, peaty sediments, swamps, or rice paddies.

Aproximación a la correlación marino-continental del Plioceno inferior en el Sur de España. El yacimiento de micromamíferos de Alhaurín el Grande-1 (Cuenca de Málaga, Cordillera Bética, España)

Un nuevo yacimiento de micromamíferos en Alhaurín el Grande (Málaga, Sur de España) situado sobre depósitos marinos del Plioceno inferior permite una aproximación a la correlación marino-continental para esa época. El relleno sedimentario marino del Plioceno inferior en el conjunto de la cuenca de Málaga comprende tres secuencias transgresivas-regresivas (unidades Pl-1, Pl-2 y Pl-3) limitadas por discordancias. A techo de la secuencia intermedia Pl-2, sedimentos turbosos han liberado restos de Rodentia, Lagomorpha, Insectivora y Crocodylia. La presencia de Cricetus barrieri Mein &amp; Michaux, 1970 en asociación con dos múridos, uno con morfología primitiva (Apodemus gudrunae Van de Weerd, 1976) y otros más evolucionados próximo a Occitanomys brailloni Michaux, 1969 y Stephanomys donnezani cordii Ruiz Bustos, 1986, permiten inferir una edad Rusciniense inferior (biozona MN14). En función de los foraminíferos planctónicos, los datos bioestratigráficos indican que los sedimentos marinos justo por debajo del nivel de micromamíferos pertenecen a la biozona MPL-2 del Zancliense inferior. Los datos paleomagnéticos disponibles muestran que el nivel de micromamíferos se localiza entre el subcron geomagnético normal C3n3n (4.89-4.80 Ma) y el subcron C3n2n (4.63-4.49 Ma), limitando la edad del yacimiento a la parte superior del Zancliense inferior.

Contribution of the subsurface drainage system in changing the nitrogen speciation of an agricultural soil located in a complex marsh environment (Ferrara, Italy)

This study focuses on the distribution of major anions and inorganic N species after the installation of a subsurface drainage system in loamy clay soils overlaying paleo-marsh peats and paleo-channel sediments. An agricultural field of 6ha was chosen as the experimental site. Its stratigraphy was reconstructed thanks to a high resolution core sampling in 13 boreholes. In the lower undisturbed portion of the soil profile a large vertical and horizontal heterogeneity for nitrate and ammonium content was noticed, mainly due to the type of sediment underling the cultivated layer. On the contrary, the upper portion of the soil profile (0.5–0.6m) displayed a homogeneous texture, organic matter content and permeability, most likely induced by tillage. The presence of the subsurface drainage system, reduces soil salinity and avoids soil waterlogged conditions guaranteeing an oxic/suboxic environment, where nitrate is the dominant N species. Underneath the subsurface drainage system, the elevated ammonium, chloride and bromide concentrations are directly related to the presence of non-drained peaty sediments, suggesting a natural origin of these species. Shallow groundwater samples displayed very similar content of anions with respect to the soils extractions, proving chemical equilibrium conditions between matrix/solution and confirming that advection is not dominant and that, the chemical fluxes are driven by diffusion.This paper shows that subsurface drainage systems are effective in ameliorating soil properties even in agricultural field consisting of low permeability materials with naturally high content of organic matter and salinity and that they can induce changes in redox conditions responsible for the large differences in N speciation found in soil profiles.

Ammonium occurrence in a salinized lowland coastal aquifer (Ferrara, Italy)

AbstractTo understand the spatial distribution and the possible sources of high ammonium concentration in the unconfined coastal aquifer of the Po River Delta lowland (Italy), a detailed characterization of inorganic nitrogen species was completed. A total of 59 boreholes were drilled to collect core samples and groundwater samples of the aquifer. Among them, four piezometers, located along a representative flow line, were chosen to monitor the inorganic nitrogen concentrations with depth. Ammonium is the prevalent nitrogen inorganic species in groundwater, and its concentration increases with depth and salinity. Very high ammonium concentrations are found in coincidence with peaty sediments in the salinized anoxic aquifer and in the low‐lying aquitard. In particular, the elevated ammonium concentration derives from mineralization of organic matter present in fine sediments deposited in paleo‐marsh environments. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Spatio-temporal evolution of the Choisille River (southern Parisian Basin, France) during the Weichselian and the Holocene as a record of climate trend and human activity in north-western Europe

The morpho-sedimentary evolution of the Choisille floodplain (lowland river, catchment: 288 km 2), a tributary of the River Loire in the south-western Parisian Basin, was studied through 61 core drillings along eight transects and a geophysical survey located in four stretches of the river: stretches A and B correspond to two sub-catchments, and stretches C and D are in the main valley. Sixty 14C and four OSL datings were obtained, and sediments were analysed on seven reference cores. Eight phases of evolution differing markedly from the evolution of more northern areas in the Parisian Basin and north-western Europe were identified from spatio-temporal distribution of nine lithological facies. The deepest incision phase (1) occurred during the first part of the Weichselian, followed by the deposition of a gravelly-sandy unit (phase 2) during the Middle Pleniglacial, which was deeply incised (phase 3), probably during the Bölling. From the Allerød up to the last third of the Boreal (phase 4), sedimentation was continuously dominated by peaty deposits, with no evidence of either increased hydraulic energy during the Younger Dryas, or of incision during the LateGlacial–Holocene transition. This trend seems to reflect the specificity of the south-western Parisian Basin climate from the Late Weichselian up to the end of the Boreal, due to the influence of the Atlantic Ocean, compared to more northern areas where the climate was more continental. The downstream incision trend during the last third of the Boreal up to the Subatlantic (phases 5 and 6) indicates a sharp increase in precipitation and vegetation cover; the lack of peaty sediments, widespread in north-western Europe, and also of precipitated carbonates frequent in the Parisian Basin, seems to be due to local physiographic characteristics. The main part of the sediment filling, which is principally silty and retrograde, began during the Subatlantic (phase 7 and 8) as a result of deforestation of the plateaux for crop farming. High human-induced sediment yield and storage concealed the possible impacts of climate change on fluvial dynamics: lithological facies change from phase 7 to 8 can only indicate the autogenic morphological evolution of the floodplain in accretion. The non-univocal upstream–downstream variation in the start of phase 7 shows that sediment yield varied in space and time in the catchment, particularly in relation to the agricultural potential of the different areas; this observation could be used to testify human-induced sedimentation in other catchments.

Significance of the correlation between the electrical conductivity dataset and lithology in Pleni-Lateglacial and Holocene alluvial archives.A case study: the Choisille catchment (SW Paris Basin, France)

Introduction Alluvial floodplains constitute rapidly evolving sedimentary environments, registering both climate changes and human impact. In the Paris Basin, the floodplain filling is generally composed of two major units (Pastre et al., 2003; Macaire et al., 2006): coarse deposits (sands and gravels) from the Pleniglacial or Late Glacial in the lower part and fine deposits (clayey-silty to carbonated or peaty sediments) from the Late Glacial and Holocene in the upper part. Because of its hi...

Geochemical study of arsenic and other trace elements in groundwater and sediments of the Old Brahmaputra River Plain, Bangladesh

The geochemical study of groundwaters and core sediments from the Old Brahmaputra plain of Bangladesh was conducted to investigate the distribution of arsenic and related trace elements. Groundwaters from tube wells are characterized by pH of 6.4–7.4, dissolved oxygen (DO) of 0.8–1.8 mg/l, Ca contents of 5–50 mg/l, and Fe contents of 0.2–12.9 mg/l. Arsenic concentrations ranged from 8 to 251 μg/l, with an average value of 63 μg/l. A strong positive correlation exists between As and Fe (r2 = 0.802; p = 0.001) concentrations in groundwater. The stratigraphic sequences in the cores consist of yellowish silty clays at top, passing downward into grayish to yellowish clays and sands. The uppermost 3 m and lower parts (from 13 to 31 m) of the core sediments are oxidized (average oxidation reduction potential (ORP) +170 and +220 mV, respectively), and the ORP values gradually become negative from 3 to 13 m depths (−35 to −180 mV), indicating that anoxic conditions prevail in the shallow aquifers of the Brahmaputra plain. Age determinations suggest that clay horizons at ~10 m depth were deposited at around 2,000 and 5,000 years BP (14C ages) during the transgressive phase of sea-level change. Elevated concentrations of As, Pb, Zn, Cu, Ni, Cr, and V are present in the silts and clays, probably due to adsorption onto clay particles. Significant concentrations of As occur in black peat and peaty sediments at depths between 9 and 13 m. A strong positive correlation between As and Fe was found in the sediments, indicating As may be adsorbed onto Fe oxides in aquifer sediments.

Thermodynamic indices of active invertase from the buried soil horizons of Late Pleistocene age in northern Yakutia

New data on the enzymatic activity of the tundra peaty gleyey soil and permafrost sediments of Late Pleistocene age (11–25 thousand years) are analyzed. It is shown that invertase, protease, phosphatase, catalase, and peroxidase are well conserved in yedoma and in buried soil horizons; urease is conserved to a smaller extent. On the basis of the investigation of thermodynamic characteristics of active invertase, such as temperature coefficient and activation energy, it was established that this enzyme is present in soil in the free and bound forms (immobilized on the surface of organomineral colloids). The degree of immobilization of active invertase in the buried soil horizons is high, which plays an important part in the long-term conservation of its molecules at subzero temperatures.

Sponge spicules in peaty sediments as paleoenvironmental indicators of the Holocene in the upper Paraná River, Brazil

The presence of freshwater sponge spicules was analyzed in samples of peaty sediments obtained in two vibro-cores from the Taquarussu region (22o30'S, 52o20'W, Mato Grosso do Sul State, Brazil) . Four samples were dated by 14C method as 11,570±80 years BP (depth 240 cm), 9,710 ± 80 years BP (depth 220 cm), 4,610 ± 70 years BP (depth 130 cm) and 4,010 ± 80 years BP (depth 29-35 cm). The freshwater sponges detected were Heterorotula fistula Volkmer-Ribeiro & Motta, 1995, Radiospongilla amazonensis Volkmer-Ribeiro & Maciel, 1983, Corvospongilla seckti Bonetto & Ezcurra de Drago, 1966 and Trochospongilla repens Hinde, 1888. The first two species are typical of lentic environments and the other two of lotic habitats. These two pairs of species are found in alternating throughout the length of core 2, indicating flooding pulses, which may be responsible for the peat formation and accumulation along the river Esperanca marginal embayments during the Holocene. There is also evidence of a wetter period between 4,610 and 4,010 years BP. The results corroborate the palynological studies previously produced for the region. This is the first dated fossil record of Heterorotula fistula and Trochospongilla repens.

Quantification and regulation of organic and mineral sedimentation in a late-Holocene floodplain as a result of climatic and human impacts (Taligny marsh, Parisian Basin, France)

Quantification in grams per metres squared per year of the sediment accumulation in a flood plain (‘marsh’) located in the southwestern Parisian basin showed that there is no close relationship between the accumulation of organic matter (OM) and mineral matter (MM) during the late Holocene, and provided an accurate view of the distinct yield and storage conditions of both sediment components. Endogenic OM accumulation in peaty sediments is not related to the climate but to felling of the alder forest and its substitution by Cyperaceae and paludal taxa in the marsh (Iron Age and Middle Ages). MM accumulation expresses mainly the sediment yield on the slopes, determined by landuse. During an initial phase (from the late Neolithic to the early Middle Ages), land-use change from crop cultivation to pastureland, possibly related to climate deterioration, led to a decrease in the sediment yield. During a second phase, since the early Middle Ages, the considerable development of crop cultivation over pasturing, even during periods of climate deterioration (such as the ‘Little Ice Age’), led to a sharp increase in sediment yield. However, although sediment yield was high, the hydrodynamics in the fen did not favour particle retention. Thus, since the Neolithic, yield and storage of OM and MM sediment have been marked by human activities, initially with high climatic stress, but since the Middle Ages without significant climatic stress.

Inferred history of a boreal pond from sediment and vegetation characteristics

Shallow ponds associated with peatlands in boreal Alberta contain large quantities of stored carbon in their peaty sediments, and exhibit spatial changes in response to dry or wet conditions. Peatland ponds around Utikuma Lake experienced a partial to nearly complete drawdown in 2002, in response to drought. A fourfold investigation was begun to assess the natural drought and flood cycles, assess the current C stocks along the shore, determine what species were colonizing the newly exposed shorelines, and to place the magnitude of the current drought into historical perspective. Ten vegetation communities were found to have colonized the exposed sediments. Paleostratigraphy shows that the surface communities differ markedly from paleocommunities. Stratigraphy of the wetland sediments demonstrates that only two changes occurred, one a successional switch from a sedge-dominated marsh to a forested bog, the other a much more recent disturbance that caused water levels near the pond to rise. No evidence of constantly changing paleocommunities was found, suggesting that previous droughts have not left a visible paleorecord. The more recent disturbance has likely redistributed peat into the pond basins and subsequently it has broken down to detritial peat, altering its physical structure, and perhaps its rate of decomposition. Continued exposure of the peat is likely to enhance decomposition. In this study both flooding and drought may have impacted the wetland in ways likely to result in higher rates of decomposition and enhanced CO2 emissions under global warming. Key words: Peat stratigraphy, Holocene climate, thermokarst melting, detrital peat, carbon stocks

北海道北部，豊富に分布する泥炭層の 花粉分析による後期更新世テフラ，利尻アチャル（Rs-Ac）の 降下時期推定と古環境復原

北海道北部，豊富に分布する泥炭層の 花粉分析による後期更新世テフラ，利尻アチャル（Rs-Ac）の 降下時期推定と古環境復原

Vertical distribution of arsenic in ganges delta sediments in Deuli Village, Bangladesh

Major and trace elements, including total arsenic (T-As), 1 M HCl-extractable arsenic (Ex-As), total organic carbon (TOC), total nitrogen (TN), and total sulfur (TS), in sediment columns collected in 2000 through 5 boring operations to a depth of 15 m in Deuli Village, Bangladesh were analyzed to reveal the source of arsenic contamination in groundwater. This area mainly consists of sandy, clayey, and peaty layers, and the chemical composition changes considerably with the sediment properties. The concentrations of T-As (20 to 111 mg kg−1) in the samples of peat and peaty clay sediments from a depth of 7 to 10 m were significantly higher than the concentrations in the samples of clayey sediments (4 to 18 mg kg−1) or sandy sediments (3 to 7 mg kg−1), and the concentrations of the other elements were also high in the samples of peaty sediments. T-As concentration shows a significant correlation with the contents of both TS and TOC (p < 0.05). These results suggest that arsenic is retained in the sediments in the form of sulfide or is combined with organic matter. On the other hand, the extraction rate (Ex-As / T-As) changed depending on the Toe content in the sediments, in spite of the high correlation between the concentrations of T-As and Ex-As. This indicates that arsenic speciation was different in the samples of peaty sediments from the sandy and clayey sediments with a relatively low TOC content. The peat layer, in which arsenic is concentrated as a pool, may be the key layer to elucidate the mechanism of solubilization of arsenic in the sediments by groundwater.

Subbottom acoustic and sedimentary records of past surface water?groundwater exchange through sinkhole lakes in south Georgia, U.S.A

Lake Balboa is a deep sinkhole lake in south Georgia. Subbottom acoustic profiling and long sediment cores reveal four stratigraphic units within >20 m of lacustrine fill above acoustically stratified and faulted Miocene/Pliocene overburden and basement Eocene limestone which hosts the Floridan Aquifer system (FAS). Fill consists of thin, rhythmically bedded, peaty sediments (Unit I), indicative of slow sedimentation in a shallow swamp until 13,110–12,680 cal BP, a mix of desiccated and over-consolidated clay and silty sand (Unit II) implying periodic subaerial exposure of the lake bed until 9470–9025 cal BP, and gyttja associated with a rapid 8 m rise in water level by 9120–9020 cal BP (Unit III), as well as an additional rise of 10 m to modern lake levels (Unit IV). Accumulation of nearly 4.5 m of low permeability gyttja, and higher lake levels have fundamentally changed exchange between surface water and groundwater, reducing by 40% or more the rate of vertical leakage to the FAS and increasing shallow aquifer discharge to the lake.

Palaeoenvironmental reconstruction of the Port Moody Interstade, a nonglacial interval in southwestern British Columbia at about 18 000 14C years BP

New palynological data from peaty sediments deposited during the Port Moody Interstade, at about 18 000 14C years, indicate that the environment in the western Fraser Lowland of British Columbia consisted of subalpine forest and parkland with abundant fir and spruce that grew under a temperate and moist climate, similar to the wetter subzones of the present-day Engelmann Spruce – Subalpine Fir biogeoclimatic zone. The moist conditions interpreted for the Port Moody Interstade are consistent with recent computer modelling and earlier palynological data from unglaciated western Washington State, but appear to contradict regional Cooperative Holocene Mapping Project (COHMAP) reconstructions and some earlier palaeoenvironmental studies that support dry conditions. Strong seasonality is suggested as part of the explanation, with Pacific storms in summer following the southern margin of the last Cordilleran ice sheet, bringing abundant moisture to the study area during the growing season, but probably not in winter, when storm tracks were displaced to the south. The cold and dry anticyclonic winds postulated by COHMAP were probably also relatively weak in summer, resulting in stronger expression of moist Pacific air masses than previously thought. The timing of the Port Moody Interstade coincides with that of a short climatic fluctuation reported from several other sites in both the northern and southern hemispheres. These events, if causally related, suggest a rapidly propagated atmospheric–oceanic signal.

Survival of Micromycetes and Actinobacteria under Conditions of Long-Term Natural Cryopreservation

Almost all of the investigated samples of the Arctic and Antarctic permafrost sediments of different genesis with ages from 5–10 thousand to 2–3 million years were found to contain viable micromycete and bacterial cells. The maximum amounts of viable cells of fungi (up to 104CFU/g air-dried sample) and bacteria (up to 107–109CFU/g air-dried sample) were present in fine peaty sediment samples taken from different depths. The identified micromycetes belonged to more than 20 genera of the divisions Basidiomycota, Ascomycota, and Zygomycota, and some represented mitosporic fungi. Thawing the samples at 35 and 52°C allowed the number of detected fungal genera to be increased by more than 30%. Aerobic heterotrophic prokaryotes were dominated by coryneform, nocardioform, and spore-forming microorganisms of the order Actinomycetales.Analysis of the isolated fungi and actinomycetes showed that most of them originated from the microbial communities of ancient terrestrial biocenoses.

Pollen and diatom stratigraphy of a dendritic fluviaI/lacustrine mire system at Tasik Bera, Malaysia: Preliminary results

The Tasik Bera mire system represents deposition of peat and peaty sediments within a dendritic fluvial drainage basin in the humid tropics. Peaty sediments have been accumulating for at least 4,500 years in the lowest part of the basin, but accumulation rates and hence the thickness and lateral extent of the mire underwent a rapid increase and expansion beginning at about 660 years BP. In this preliminary study, pollen and diatom stratigraphy of two cores is related to some physical and chemical characteristics of the organic rich sediments. The sediments are highly variable, both vertically and laterally, the variations principally controlled by the type of vegetation dominant. Vegetation in turn is related to the degree of wetness of the site. Three environments of deposition contribute peat with distinctive palynological and physical characteristics. The limnetic environment, dominated by algae and easily degraded aquatic macrophytes, contributes very fine hemic peaty sediment with high fine silt content and a large algal component. The littoral environment is dominated by sedges and the woody shrub Pandanus, both of which have a large sub-aqueous biomass, and are quite resistant to degradation. Sediment from this environment is woody, hemic to coarse hemic, with a moderate to high very fine silt content and a much smaller algal element. Forest swamps, which occupy most of the mire area, contribute woody, fibric to hemic peaty sediments with low to moderate mineral matter content in the form of clays and very fine silt. Succession from both limnetic to forest swamp, and the reverse, is recorded in cores from different sites. No part of the mire yet studied is approaching oligotrophic conditions.

Accumulation of organic rich sediments in a dendritic fluvial/lacustrine mire system at Tasik Bera, Malaysia: implications for coal formation

The Tasik Bera mire system represents deposition of peat and peaty sediments within a dendritic fluvial drainage basin in the humid tropics. As such, it serves as an analogue for the earliest stages of coal deposition in low-relief topogenous coal swamps. Peaty sediments have been accumulating for at least 4500 years in the lowest part of the basin, but accumulation rates and hence the thickness and lateral extent of the mire underwent a rapid increase and expansion beginning at about 660 years B.P. The sediments are highly variable, both vertically and laterally, the variations principally controlled by the type of vegetation dominant. Vegetation in turn is related to the degree of wetness of the site. Three distinct environments of deposition contribute peat with physical characteristics which can be related to coals. The limnetic environment, dominated by algae and easily degraded aquatic macrophytes, contributes very fine hemic peaty sediment with high fine silt content and a large algal component. The littoral environment is dominated by sedges and the woody shrub Pandanus, both of which have a large subaqueous biomass, and are quite resistant to degradation. Sediment from this environment is woody, hemic to coarse hemic, with a moderate to high very fine silt content and a much smaller algal element. Forest swamps, which occupy most of the mire area, contribute woody, fibric to hemic peaty sediments with low to moderate mineral matter content in the form of clays and very fine silt. Succession from both limnetic to forest swamp, and the reverse, is recorded in cores from different sites. In coals these transitions would be manifest as both brightening-upward (algaedominated peat to woody peat) and dulling-upward (the reverse sequence) trends, the first in the topographically lower part of the basin, the second in the middle reaches. No part of the mire yet studied is approaching oligotrophic conditions. Allowing for a compression ratio of 5:1, thin, stony coals from the Tasik Bera mire would be laterally discontinuous and would vary from about 1 m in thickness at channel margins, tapering out to nothing as they onlap the interfluves.

A new method for the preparation of peat samples for petrographic study by transmitted and reflected light microscopy

A new method to allow water removal and impregnation of peat and peaty sediment samples prior to microscopic study avoids deformation of the original texture. This method resolves a variety of problems that other techniques encountered in the preparation of these materials, including incomplete impregnation of sediments with organic matter or an unreasonably lengthy process. The new method is based on fixation of the organic matter with formaldehyde, and chemical dehydration with ethanol. The specimens are then impregnated with conventional epoxy or polyester waxes, and the addition of acetone for reduction of the viscosity. The method is quick and easy, and it produces reliable results.

Manganese behavior in the sediments of diverse Scottish freshwater lochs

Mn concentrations were determined in sediments and pore waters of five freshwater lochs in Scotland. The aim was to establish whether the geochemical behavior of Mn differed in a range of limnological conditions: oligotrophic/mesotrophic Loch Lomond; eutrophic unstratified Loch Leven; seasonally stratified eutrophic Balgavies Loch; oligotrophic, acidified Round Loch of Glenhead; and oligotrophic, acid‐sensitive Loch Coire nan Arr.Although redox‐driven diagenesis of Mn was evident in all lochs, the diversity of conditions in the lochs resulted in some cases in modifications to behavior predicted by conceptual models for transport of Mn at a redox boundary. These differences were reflected in the chemical associations and trends in concentration of Mn. A classic example of Mn redox cycling in the sediments of Loch Lomond provided a basis for comparison with other systems. Higher inventories of Mn in sediment collected from eutrophic Loch Leven during the summer, compared with sediment from autunm and winter sampling, were explained by the effects of enhanced primary productivity (high pH and dissolved oxygen concentrations) during a summer algal bloom. In Balgavies Loch, where the bottom water was hypoxic, at the time of sampling, previous diagenetic enrichment of Mn in the surface sediment was subject to modification by dissolution and release from the solid phase to pore water, which was elevated in Mn. The increase in solid‐phase Mn concentration with depth and lack of significant surface enhancement of Mn in Round Loch contrasted markedly with results from other lochs. This was attributed mainly to acidification, producing a pH‐related decrease in Mn sedimentation. Mn partitioning and porewater data for Loch Coire nan Arr were in some respects similar to those at Round Loch, with both lochs having peaty sediment. However, Mn concentration patterns attributed to acidification effects at Round Loch were not found in Loch Coire nan Arr.