Peat Erosion Research Articles

Use of magnetic and radiometric measurements to investigate erosion and sedimentation in a British upland catchment

AbstractIn response to the potential shortcomings of single‐technique strategies in the investigation of erosion and sedimentation, a combined magnetic and radiometric (13Cs and 210Pb) approach has been undertaken in the upland, watershed‐lake system of Howden Reservoir, Derbyshire. By combining these techniques, some assessment of sediment sources and the erosion status of the catchment has been achieved. Alone, each approach would have been unable to determine unequivocally sediment provenance. Furthermore, the parallel use of these measurements has highlighted limitations and/or uncertainties in both the magnetic and 137Cs techniques. These problems reflect the particular soil characteristics and drainage conditions of this upland catchment. Despite the documented severity of peat erosion in the region, Howden Reservoir has a mixture of sediment sources and a relatively moderate rate of sedimentation. Sediment yields (total 127·7 t km−2 yr−1 including organic fraction 31·3 t km−2 yr−1) are, however, higher than in other British upland areas.

Nature, extent and severity of soil erosion in upland Scotland

AbstractThis paper examines the nature, extent and severity of soil erosion in upland Scotland, an area subject to land management pressures typical of temperate maritime uplands. Erosion features were classified and their area measured from aerial photographs. Some 12 per cent of the upland area sampled was subject to some form of erosion, which is very similar to the percentage for Europe as a whole. The most significant erosion category was peat erosion, with 6 per cent of the area being affected; a figure which increased to 20 per cent in one sub‐region. Peat erosion varied in severity, with the most severe erosion being in areas of eastern Scotland with the greatest land management pressures. Gully erosion of slopes on mineral soils was found in almost 5 per cent of the area sampled, particularly in sub‐regions with large amplitude of relief. Debris flow/cone features and screes were less extensive and largely found at higher altitudes. Footpath erosion was mapped in popular mountain areas, but overall the mean length of eroded footpaths was less than that of large gullies. There was little evidence of spatial linkages between erosion of mineral soils and land management at the scale of the survey. Separating the roles of upland management and extreme rainfall events in the inception of erosion remains a key issue in the study of accelerated erosion in temperate maritime upland areas. Some guidance for management is presented.

L’érosion côtière en Guyane

Coastal erosion in french Guiana Modem shoreline changes in French Guiana are very active, linked to the Amazon Dispersal System : approximately 250 million m3 of fine grained sediments are transported annually by the currents and the waves along the Guianas coastline. As the result, a specific sedimentation pattern with alternating sectors of deposition (mudbanks and mudflats, with coastal progradation) and erosion (interbank zones, with erosion of the mangrove forest and of the siliclastic shorelines) characterizes the foreshore/shoreface area. Mudbanks and mudflats migrate slowly to the NW. On account of this dynamic, shoreline is continually changing. Our paper focused on modem coastal erosion within some interbank areas representing seasonal, interannual and decade time scales, owing to field studies and Remote Sensing data (SPOT-1 and LANDSAT MSS and TM) ; the results reveal that these areas (in Kourou-Sinnamary and Mana) are being extensively eroded despite the considerable amazonian supply. Such conclusion is important, furthermore coastal erosion in French Guiana was (and still is) considered as a minor event, coastal silting and correlated mangrove development being uphold as consistent barriers against shoreline retreat... To minimize coastal erosion is however a mistake : most significant has been the retreat of mangroves, of the cheniers' coasts, of the coastal swamps and even the mechanical erosion of peat. One of the most striking exemples is presently the zone of Mana (near the Maroni River mouth) where a sharply indented shoreline indicates a maximum of coastal erosion.

Geochemistry and fluxes of hydrocarbons to the Beaufort Sea shelf: A multivariate comparison of fluvial inputs and coastal erosion of peat using principal components analysis

The allochthonous inputs of hydrocarbon to the Canadian Beaufort Shelf were studied by applying principal components analysis (PCA) to well-validated and rigorously blank-corrected samples. Incorporation of a wide range of perdeuterated n-alkanes and PAH into the analysis scheme ensured that only reliably quantified variables were used to interpret the hydrocarbon geochemistry. Application of PCA to Mackenzie River samples demonstrated a homogeneous system, from which we infer coupling or equilibrium between the river particulate hydrocarbons and the dissolved fraction. Particulate (particle size > 0.7 μm) hydrocarbon flux from the Mackenzie River is by far the most important terrestrially derived source of hydrocarbons to the Beaufort Sea. The Mackenzie River particulates have a distinct n-alkane signature which can be used to identify the riverine influence on the hydrocarbon geochemistry of the Beaufort Sea shelf. Based on one year's data, the flux of total alkanes is 440 ± 94 tonne/ a, and PAH is 49 ± 8 tonne/ a (uncertainties are one standard deviation of the sampling and analytical variation). The particulate flux exceeds the accompanying dissolved hydrocarbon flux by two orders of magnitude and has a strong seasonal cycle: winter contributes less than an estimated 0.6% of total annual flux. Deltaic silt from the western Mackenzie delta and the smaller amounts of detritus from coastal erosion of peat are minor hydrocarbon sources and contribute, in total, less than 10% to the budget for most alkanes. An important exception, with regard to shelf geochemistry, is the significant quantity of peat-derived higher plant n-alkanes.

Blanket peat erosion in a Mid-Wales catchment during two drought years : Francis, I S Earth Surf Process LandV15, N5, Aug 1990, P445–456

Blanket peat erosion in a Mid-Wales catchment during two drought years : Francis, I S Earth Surf Process LandV15, N5, Aug 1990, P445–456

Blanket peat erosion in a mid‐wales catchment during two drought years

AbstractThe rate of blanket peat erosion was measured at an upland site in central Wales during the 1983‐1984 drought years. Erosion pins, a peat surface sediment trap, and sediment sampling in the effluent stream, were used to estimate the rate of peat surface recession and the rate of organic sediment loss from the catchment. An overall rate of surface recession of 16 mm y−1 on exposed peat faces was recorded; this differed between faces of different aspects, with the greatest recession on southwest faces. Eroding peat surfaces exhibited maximum recession during the summer, but the peat surface sediment trap indicated that the highest rates of sediment loss from peat faces due to rain wash occurred during the autumn and early winter. Stream sediment sampling showed that the yield of organic sediment from the catchment was 34·4 t km−2 yr−1, with greatest losses also during the autumn and early winter. The evidence suggested that the surface recession, as measured on erosion pins, included a ‘wastage’ or shrinkage component, which possibly accounted for as much as 80 per cent of the apparent loss. Direct and circumstantial evidence suggested that peat wastage during the summer months was the most important agent of surface recession in the study period, which encompassed the two dry summers. Desiccation provided available sediment during the autumn, but organic sediment supply became limited as the winter progressed, despite the occurrence of frost heave.

The cause of peat erosion: a palaeolimnological approach

SUMMARYPalaeoecological analyses of two lake sediment cores from the Round Loch of Glenhead, Galloway, S.W. Scotland and Loch Laidon, Ratinoch Moor, Central Scotland have been conducted to elucidate the cause of the observed blanket peat erosion in their catchments. Both simple physical measurements such as percentage loss on ignition and the pollen and diatom record reveal clearly the onset of peat erosion in these catchments. Accurate dating of erosion is still problematical. Nevertheless, some of the competing hypotheses that have been advanced to explain blanket peat erosion are evaluated. Acid deposition cannot be responsible for the peat erosion in these two catchments since the combined use of 211Pb and 14C dating suggests that erosion was initiated between c. AD 1500 and AD 1700, an age well before the effects of atmospheric deposition are documented by the core. However, it remains to he resolved what the effects have been of land‐management changes such as grazing, burning and climatic effects, such as the Little Ice Age.

Destruction of Wetland Habitats by Lesser Snow Geese: A Keystone Species on the West Coast of Hudson Bay

SUMMARY (1) Large numbers of lesser snow geese breed in colonies in coastal brackish and freshwater marshes in the lowlands along the west coast of Hudson Bay. Where colonies are present, the geese determine the structure and species composition of the coastal plant communities. (2) During recent decades, substantial increases in the number of birds have occurred, resulting in the outward spread of the colonies into new areas which are used for nesting, feeding and moulting. (3) Patterns of foraging vary in space and time. In spring at the nesting sites, before the onset of above-ground growth of vegetation, adult geese grub for roots and rhizomes of graminoid plants in relatively dry areas, and in wet habitats they eat the swollen bases of shoots of sedges, particularly Carex aquatilis. In summer, adults and goslings graze intensively on leaves of grasses and sedges over wide areas. Swards dominated by Carex subspathacea are produced in brackish marshes, but the leaves of graminoids of the freshwater sedge meadows are also clipped extensively. (4) Grubbing of vegetation by geese each spring creates bare areas (1-5 mi2) of peat and sediment. The increased numbers of birds have increased the scale of disturbance, with large areas now stripped of vegetation, particularly by the McConnell River. At some sites, erosion of peat has exposed the underlying glacial gravels. There is little likelihood that the vegetation which re-establishes will closely resemble the original. Further expansion of goose colonies in this region may be limited by available food resources.

Estimates of CO 2 production from eroding peat surfaces

The rates of carbon mineralization for the different strata in the exposed peat faces of a hill peat erosion channel were estimated to range from 782 to 21331. fresh peat ha −1 year −1 for specified moisture and temperature regimes. The rates of carbon loss were calculated by measuring rates of carbon dioxide evolution using gas chromatography. Changes in selected physical and chemical characteristics of the eroding peat were measured prior to sampling for basal CO 2 evolution.

Controls on peat accumulation in the Permian Vryheid Formation in a part of northern Natal, South Africa

The early Permian Vryheid Formation is a fluviodeltaic tongue of sediment deposited on the passive northern margin of an asymmetric, intracontinental linear trough (Karoo basin). In the study area these strata attain a maximum thickness of about 270 m, comprising three informal lithostratigraphic members (Lower zone, Coal zone and Upper zone). The Coal zone is characterized by arkosic, coarse to very coarse, pebbly sandstones and subordinate fines arranged in upward-fining sequences, many of which are coal-capped. These units are interpreted as distal outwash fan deposits. Sedimentation patterns in the Upper and Lower zones are dominated by superimposed upward-coarsening sequences representing repeated wave/fluvially-dominated fan delta progradation. Peat accumulation in the cool, seasonal climate which prevailed during Vryheid Formation sedimentation was slow. Significant peat thicknesses were deposited only in areas of low basin/compaction subsidence in the Coal zone during a period of general stability. Extensive upper delta plain and alluvial plain peats formed on broad platforms created by abandonment of braided channel systems. The thickest peats accumulated in raised swamps where vegetation-stabilized contemporaneous channels promoted a high water table. Peat erosion by later channel activity was slight since channel widening rather than stream-bed erosion prevailed. Coals thin, split and contain more ash near loci of contemporaneous channel activity. Upper delta plain coals were not marine-influenced. Some lower delta plain coals also formed on broad abandoned deltas and are likewise extensive. Rapid compaction subsidence rates attracted channel activity or marine incursions and the seams are thin. Peats also accumulated in restricted emergent interdistributory bays during delta construction. These coals are thin, discontinuous, marine-influenced and contain numerous clastic partings.

Lipid geochemistry of late Pleistocene lacustrine sediments from Burland, Cheshire, U.K.

Extractable lipids isolated from a lacustrine sediment sequence ∼ 50 ka old were analysed by GC and C-GC-MS to determine the persistence of certain biological markers and to characterize the depositional environment. The central peat deposit gave unimodal distributions of homologous n-alkanes, n-alkanoic acids, alkan-1-ols and alkyl esters typical of higher plants. Triterpenoids of similar origin, including partial aromatic and de- A-ring hydrocarbon derivatives, were detected throughout the profile, as were prokaryote-derived hopanoids. Two sections overlying the peat also contained more-labile lipids, including C 14-C 18 fatty acids, mainly unsaturated C 30-C 38 alkyl esters and triacylglycerols, preservation of which is attributed to rapid burial; a geolipid input to the older section was recognized by the presence of αβ-hopanes. Algal biomarkers in these sediments include C 37 alkenones, 4α-methyl-steroids and 2,6,10-trimethyl-7-(3-methylbutyl)-dodecane; the last two biomarkers also occurred in sediment below the peat. The profile reflects slow deposition of sediment within a mesotrophic lake, succeeded by more rapid input arising initially from erosion of marginal peat, and later from erosion of mineral soils, as a result of climatic deterioration.

The extent and time-course of mountain blanket peat erosion in Ireland.

Erosion of upland blanket pent is widespread in Britain and Ireland and suggestions for its initial causes have included recent human disturbance and changes in the mechanical stability of the peat masses through time. A survey of blanket peat in five mountain areas in Ireland revealed extensive erosion in all areas, and two cores of mountain lake sediment contained inwashed peat in their upper sections. Detailed analysis of the core from the Wicklow Mountains revealed pollen evidence for initial peatland development, tree clearance and eventual peat erosion. The inwashed peat contained abundant Sphagnum leaves. Peat inwash began 1500 years ago in Donegal, N.W. Ireland and 3000 years ago in Wicklow near the east coast. The occurrence of erosion over these time periods does not suggest that recent human activity and changes in land-use are the original causes of erosion. Recent human activity has merely intensified erosion that probably originated from peat flows or the development of natural drains in mature peat masses developing on sloping ground.

Fire and Flood at Holme Moss: Erosion Processes in an Upland Blanket Mire

(1) Holme Moss is an upland blanket mire in the southern Pennines that is unusual for the variety and severity of its peat erosion. (2) The results of microfossil and macrofossil analyses of peat formed in the last 1200 years at eleven sites on Holme Moss are presented. Quantitative estimates of the frequency of leaves of Sphagnum and Racomitrium lanuginosum in the various peat cores are compared, with the aid of a dating template based on the pollen diagrams, and used to infer conditions on the mire surface at different times in the past. (3) The pollen-stratigraphic data indicate that peat erosion has been active on Holme Moss for four to five centuries, and has involved several distinct episodes. The current mire vegetation has developed subsequent to these episodes of erosion, and represents the effects of air pollution and intense sheep grazing superimposed on an already eroded ecosystem. (4) The main peat gullies on Holme Moss probably originated following clearance of forest from the surrounding hillslopes in the eleventh century. Well-defined soakways or flowlines formed on the mire surface, and subsequently developed into open drainage channels. However, certain of the peat gullies were probably not incised until the eighteenth or nineteenth century; and considerable areas of Holme Moss were still unaffected by gullying when renewed Sphagnum growth in the sixteenth century led to the formation of a Sphagnum-dominated mire surface over much of the western half of the moss. (5) Concentrations of burnt plant material at certain levels in the peat cores indicate that the drier eastern half of Holme Moss was severely burnt at least once in the eighteenth century; much peat may have been lost as a result of the fire and subsequent erosion. (6) A freak cloudburst is recorded for the Holme Moss area in July 1777. This cloudburst may have caused extensive damage to the margins of the peat blanket, and accentuated existing erosion features. (7) It is concluded that much of the peat erosion currently visible on Holme Moss has been produced by exceptional events, either natural or man-made; and that analysis of current environmental stresses at Holme Moss offers few clues to the causes of peat erosion.

RECENT ACCUMULATION AND EROSION OF BLANKET PEAT IN THE WICKLOW MOUNTAINS, IRELAND.

Active peat erosion is widespread in the Wicklow mountains, and it has been suggested that peat accumulation has slowed or ceased in the area associated with the erosive processes. Analysis of the recent deposition of pollen and magnetic minerals at three sites shows that significant quantities of peat (6.5 to 16.5 cm) have accumulated within the last 150 years. The fallout of magnetic pollutants is far below that found in the Pennine peats, ruling out certain hypotheses about the causes of montane blanket peat erosion.

Observations on the Erosion of Blanket Peat in Yell, Shetland

This paper reports observations on peat erosion made during a heavy rain storm on the island of Yell, Shetland. Storm water stripped a surface crust from unvegetated peat. The effect of this was to remove large quantities of peat and to expose the underlying peat to other erosion forces.

Mass Movement and Erosion of a Southern Pennine Blanket Peat

(1) Pollen and macrofossil analyses were carried out at nineteen sites within a 1-km2 area of Featherbed Moss, Derbyshire. The sites covered a range of uneroded and eroded blanket peat types. (2) Pollen diagrams were compared using five dated horizons between 1580 A.D. and 3600 B.C. (calibrated dates). These pollen horizons formed a template for comparing the macrofossil stratigraphy at the nineteen sites, and for calculating the rates of peat accumulation at six sites. (3) Peat accumulation rates varied considerably, both within and between sites, from about 6 to 96 g m-2 year-' (measured as dry mass). The most striking differences occurred in the time interval 400-1000 A.D., when some sites showed an increased rate of peat accumulation and others a decreased rate. Pollen and macrofossil types indicative of better drained peat (Empetrum and Vaccinium pollen, leaves of Racomitrium lanuginosum) occurred at several sites towards the end of this interval. These changes are interpreted as resulting from the onset of erosion 1000-1200 years ago. (4) Two features of the growth of the peat blanket on Featherbed Moss are suggested to have been of major importance in ultimately bringing about its degradation and erosion: a very early spread of peat over flatter ground to the limits imposed by topography (so that no further lateral extension was possible); and a rapid build-up of largely unhumified Sphagnum peat over more consolidated peat after 400 A.D. In conjunction, these features resulted in an unstable peat mass developing on parts of Featherbed Moss by 700800 A.D. (5) The onset of peat erosion on Featherbed Moss 1000-1200 years ago is interpreted as a natural phenomenon, instituted by a series of bog slides and bursts around the margin of the peat blanket. These led to the formation of drainage gullies extending back into the peat, slumping of the marginal peat downslope, and drawing-off of water from the pools of the hummock-hollow complex on the watershed. (6) Over much of the Moss a wet Sphagnum-dominated bog surface developed after c. 1100 A.D., and partial recolonization of some of the earlier erosion features may have occurred. The death of Sphagnum from air pollution some 200-300 years ago led to renewed peat erosion, which is still in progress.

Aerial biomass distribution in an undisturbed and disturbed subarctic bog

During powerline construction, a portion of a wooded (Picea mariana) peat plateau in northern Manitoba was stripped of surface vegetation. Seven years later, aerial biomass of plants recolonizing the surface of the disturbed area was estimated to be 2098 kg ha−1, only 26.4% of the undisturbed portion's aerial biomass of 7939 kg ha−1.Tree biomass represented 28.7% of the aboveground biomass of the wooded plateau. The relative proportions of photosynthetic phytomass increased from 17% in the wooded to 53% in the disturbed area. Major ericaceous species (Ledum groenlandicum, Chamaedaphne calyculata, and Kalmia polifolia) responded after disturbance by increasing reproductive effort and the ratio of photosynthetic to woody tissue.Permafrost subsidence in the disturbed portion was not evident in the period since vegetation removal, although surface erosion of peat was visible and could be expected to increase in the next several years.

THE EROSION OF PEAT IN THE UPLANDS OF NORTHERN IRELAND

Whereas in Britain the erosion of peat in upland areas has been mapped and discussed widely, in Ireland there has been only brief mention of peat erosion and few attempts to map its distribution. In this paper the erosion of the peat in the uplands of Northern Ireland is mapped and classified; water erosion is of two types, anastomosing channels and parallel or sub-parallel gullies. The relationships of these two types to relief, to vegetational patterns, to the distribution of rock basins and to piping in the peat are discussed. Studies of townland boundaries cut in the peat surface have also shown that the activity of man in the recent past has contributed to the development of erosion. Finally, changes in climate towards wetter conditions are considered in relation to the other factors.

Blanket peat erosion: Theoretical considerations and observations from selected conservation sites in slieveanorra forest national nature reserve, county Antrim

Geomorphological investigation of blanket peat at three conservation plots in Slieveanorra Forest National Nature Reserve, County Antrim, suggests that various stages of peat erosion are concurrent. The proximity of undisturbed peat, gullies and haggs, peat flats, redistributed peat and regenerated peat is described. Morphological evidence may be interpreted in terms of a natural cycle or system of peat erosion but pollen analysis suggests a linkage between agricultural activity and the commencement of erosion. A C14 date of 2108 BP implies a much earlier date for peat erosion than generally considered. Erosion processes and origins are discussed and related to theories of upland blanket peat erosion.

The peatland vegetation of Lewis

SynopsisThe vegetation of the peatland of Lewis is described. Several different types of mire are distinguished according to their morphological features. The gradual transition from minerotrophic conditions within valley mires to fully ombrotrophic conditions in the blanket mires of watersheds is demonstrated. Whilst most of the blanket mire of Lewis is affected by severe peat erosion, examples were chosen to demonstrate the nature of the flora and vegetation within those mire systems at present unaffected by erosion, as well as the more characteristic eroded peatland.