Peat Volume Research Articles

Determination of the amount of carbon stored in Indonesian peatlands

Extensive peatlands in Indonesia are a major store of carbon. Deforestation, conversion to other land uses, especially plantations of oil palm and pulpwood trees, and recurrent fires have recently caused the release of large amounts of this carbon to the atmosphere. If these large emissions from degrading peatlands are taken into account Indonesia is one of the largest emitters of CO 2 worldwide. To improve estimates of the amount of carbon stored in Indonesian peatlands we applied 3D modelling based on the combined analysis of satellite imagery (Landsat ETM+, SRTM) and 750 in situ peat thickness measurements. We demonstrate that SRTM radar data can be used to determine the extent and topography of the dome shaped surface of a selection of peatlands in Central Kalimantan, South Sumatra and West Papua. A strong correlation was obtained between the convex peat dome surface and the underlying mineral ground, which was used to calculate the peat volume and carbon store. Conservatively, we estimate that at least 55 ± 10 Gt of carbon are stored in Indonesia's peatlands. This amount is higher than previous results published because it takes into account the biconvex nature of the tropical peatlands. With this huge carbon storage and the current rate of degradation the tropical peatlands of Indonesia have the power to negatively influence the global climate.

Tensile strength of peat: laboratory measurement and role in Irish blanket bog failures

The morphological characteristics of bogflows, bog bursts and other types of peat failures suggest that the tensile strength of peat may have had a significant influence on their occurrence and development. This paper describes a method for the determination of peat tensile strength utilising small block samples (100 mm × 100 mm, up to 60 mm thick) in a newly developed laboratory apparatus. The results, demonstrating good reproducibility and being consistent with published data, were applied to a case example. The stability of a recent 35,000-m3 bogflow on Maghera Mountain, Co. Clare, Ireland, was analysed using a standard limit equilibrium technique. The breaking stress (i.e. maximum tensile strength) of the acrotelm peat at the Maghera bogflow was 5.35 kPa (range 2.9–7.6 kPa). Using this value to represent the overall strength of the acrotelm in the model, analyses showed that even above the crest of an escarpment, the acrotelm was strong enough to contain a large volume of low or zero-strength lower catotelm peat within the blanket bog upslope from the escarpment. Furthermore, simple analysis of single blocks of peat at the upslope edge of a retrogressively developing failure established the size of blocks that should develop, i.e. 3–4 m. The floating acrotelm rafts observed in the Maghera bogflow, typically up to around 3 m, were broadly consistent with this analysis. This paper therefore presents for the first time quantitative evidence of the importance of the acrotelm tensile strength in bogflows and a new method for routinely obtaining tensile strength data.

Spatiotemporal variability in peatland subsurface methane dynamics

Peatlands are large natural sources of atmospheric methane (CH4). While many studies have measured CH4 emissions to the atmosphere, less is known about the stock and residence time of subsurface CH4. In this study we examined dissolved CH4 concentration in near‐surface peatland pore waters of a poor fen near Québec City, Canada, in order to (1) investigate the variability in and potential controls on these concentrations and (2) combine measured dissolved CH4 concentration with estimated bubble CH4 stock and measured CH4 fluxes to estimate the mean residence time of subsurface CH4. Concentrations ranged from 1 to 450 μM during both study seasons. Depth profiles were generally consistent at one location within the peatland throughout the sampling period but varied between locations. Patterns with depth were not well correlated to pore water pH or EC; however, changes in CH4 concentration through time in the upper 30 cm were related to temperature and water table at some locations. Depth profiles taken at 2‐ to 5‐cm intervals revealed discrete concentration “spikes” which were often maintained throughout the season and are likely related to bubble CH4 dynamics. Estimated subsurface CH4 stocks indicate that even when relatively low bubble volume (5% of peat volume) is assumed, bubble CH4 accounted for greater than half of total stocks. Calculated mean residence times were 28–120 days. This implies that CH4 flux may lag changes in water table and temperature which happen on shorter timescales (hours or days). To improve our description of subsurface CH4 stocks, links between dissolved and bubble CH4 stocks and peatland CH4 residence time, coincident measurement of pore water CH4 concentrations, entrapped gas content and composition, diffusive CH4 flux, and ebullition are required.

Behavior of Stabilized Peat Soils in Unconfined Compression Tests

Problem statement: Deep stabilized peat columns were known to be economical at forming foundations to support highway embankments constructed on deep peat land. However, failure in the formation of the columns with adequate strength was often attributed to unsuitable type and insufficient dosage of binder added to the soil. Organic matter in peat was known to impede the cementing process in the soil, thus retarding the early strength gain of stabilized peat. Approach: To evaluate the strength characteristics of stabilized peat, laboratory investigation on early strength gain of the stabilized soil was conducted to formulate a suitable and economical mix design that could be effectively used for the soil stabilization. To achieve such purpose, the study examined the effect of binder, sodium chloride as cement accelerator and siliceous sand as filler on the unconfined compressive strength of stabilized peat soils after 7 days of curing. Binders used to stabilize the peat were Ordinary Portland cement, ground granulated blast furnace slag, sodium bentonite, kaolinite, lime and bentonite. All the stabilized peat specimens were tested using unconfined compression apparatus. Results: The test results revealed that the stabilized peat specimen (80% OPC: 10% GGBS: 10% SB) with addition of 4% sodium chloride by weight of binder and 50% well graded siliceous sand by volume of wet peat at 300 kg m-3 binder dosage yielded the highest unconfined compressive strength of 196 kPa. Such finding implied that the higher the dosage of siliceous sand in stabilized peat, the more solid particles were available for the binder to unite and form a load sustainable stabilized peat. Conclusions/Recommendations: It could be summarized that as the rate of hydration process of stabilized peat was accelerated by inclusion of sodium chloride, the solid particles contributed to the hardening of stabilized peat by providing the cementation bonds to form between contact points of the particles.

Characteristics of the Shetland Islands (UK) peat slides of 19 September 2003

An extreme rainfall event over the southern Shetland Islands in northern Scotland, UK, on 19 September 2003, triggered at least 20 significant peat slides and at least 15 smaller landslides of varying types. The peat slides were examined and surveyed to characterise and explain the distinctive morphological features that were produced. The failures varied in size from 0.4 to 7.3 ha (2,300 to 59,000 m3 displaced volumes of peat) and involved blanket peat up to 3 m deep and slope gradients as low as 4°. Almost all of the failure surfaces were located at the peat–mineral interface. The morphological features included large areas (up to 0.5 ha) of intact peat that moved without breaking up, linear compression and thrust features and unusual occurrences of mineral debris. These features suggest peat of high tensile strength throughout its depth and the generation of high and sometimes artesian water pressures at the base of the peat during the event. However, the variations between peat slides highlight some of the difficulties of trying to assess the susceptibility of blanket peat to failure without full knowledge of the local peat geotechnical properties and structural features within the peat mass.

Field methods for measuring hydraulic properties of peat deposits

AbstractNew field techniques were developed and tested to evaluate peat storativity and hydraulic conductivity in a Boreal fen. Enclosed drainage tests and pumping tests were successfully completed in the thawed peat above an impermeable frozen layer and then repeated when the peat was fully thawed. A loading test experiment constrained values of vertical hydraulic conductivity within an order of magnitude for the peat below a depth of 2 m. An inherent advantage of these tests is that volumes of undisturbed peat on the scale of cubic metres may be characterized. Storativity of the fen peat as determined by enclosed drainage tests ranged from about 1·0 at the peat surface to 0·35 at a water table depth of 0·15 m. Laboratory drainage tests of peat cores gave similar, but widely scattered results. Hydraulic conductivity near the surface was as high as 9·0 × 10−3 ms−1 determined with pumping tests and in the range of 10−6 to 10−5 ms−1 below a depth of 2 m, estimated with the loading test. Slug tests gave similar results. Pumping tests, enclosed storativity tests and loading tests are practical large‐scale field tests for determining peat properties. Copyright © 2006 Crown in the right of Canada, and John Wiley & Sons, Ltd.

The hydrology of northern peatlands as affected by biogenic gas: current developments and research needs

AbstractRecent research indicates that accumulation and release of biogenic gas from northern peatlands may substantially affect future climate. Sudden release of free‐phase gas bubbles into the atmosphere may preclude the conversion of methane to carbon dioxide in the uppermost oxic layer of the peat, resulting in greater contribution of methane to the atmosphere than is currently estimated. The hydrology of these peatlands also affects and is affected by this process, especially when gas is released suddenly and episodically. Indirect hydrological evidence indicates that ebullitive gas releases are relatively frequent in some peatlands and time‐averaged rates may be significantly greater than diffusive releases. Estimates of free‐phase gas contained in peat have ranged from 0 to nearly 20% of the peat volume. Abrupt changes in the volume of gas may alter hydraulic gradients and movement of water and solutes in peat, which in turn could alter composition and fluxes of the gas. Peat surfaces also move vertically and horizontally in response to accumulation and release of free‐phase gas. Future research should address the distribution, temporal variability, and relative significance of ebullition in peatlands and the consequent hydrological responses to these gas‐emission events. Copyright © 2006 John Wiley & Sons, Ltd.

First Report of Rhizoctonia solani AG 4 on Lamb's Lettuce in Italy.

Lamb's lettuce or corn salad (Valerianella olitoria) is increasingly grown in Italy and used primarily in the preparation of mixed processed salad. In the fall of 2005, plants of lamb's lettuce, cv Trophy, exhibiting a basal rot were observed in some commercial greenhouses near Bergamo in northern Italy. The crown of diseased plants showed extensive necrosis, progressing to the basal leaves, with plants eventually dying. The first symptoms, consisting of water-soaked zonate lesions on basal leaves, were observed on 30-day-old plants during the month of October when temperatures ranged between 15 and 22°C. Disease was uniformly distributed in the greenhouses, progressed rapidly in circles, and 50% of the plants were affected. Diseased tissue was disinfested for 1 min in 1% NaOCl and plated on potato dextrose agar amended with 100 μg/liter of streptomycin sulfate. A fungus with the morphological characteristics of Rhizoctonia solani was consistently and readily isolated and maintained in pure culture after single-hyphal tipping (3). The five isolates of R. solani, obtained from affected plants successfully anastomosed with tester isolate AG 4, no. RT 31, received from R. Nicoletti of the Istituto Sperimentale per il Tabacco, Scafati, Italy (2). The hyphal diameter at the point of anastomosis was reduced, and cell death of adjacent cells occurred (1). Pairings were also made with AG 1, 2, 3, 5, 7, and 11 with no anastomoses observed between the five isolates and testers. For pathogenicity tests, the inoculum of R. solani (no. Rh. Vale 1) was grown on autoclaved wheat kernels at 25°C for 10 days. Plants of cv. Trophy were grown in 10-liter containers (20 × 50 cm, 15 plants per container) on a steam disinfested substrate (equal volume of peat and sand). Inoculations were made on 20-day-old plants by placing 2 g of infected wheat kernels at each corner of the container with 3 cm as the distance to the nearest plant. Plants inoculated with clean wheat kernels served as controls. Three replicates (containers) were used. Plants were maintained at 25°C in a growth chamber programmed for 12 h of irradiation at a relative humidity of 80%. The first symptoms, consisting of water-soaked lesions on the basal leaves, developed 5 days after inoculation with crown rot and plant kill in 2 weeks. Control plants remained healthy. R. solani was consistently reisolated from infected plants. The pathogenicity test was carried out twice with similar results. This is, to our knowledge, the first report of R. solani on lamb's lettuce in Italy as well as worldwide. The isolates were deposited at the AGROINNOVA fungal collection. The disease continues to spread in other greenhouses in northern Italy.

The liquid limit of peat and its application to the understanding of Irish blanket bog failures

Catastrophic failures of blanket bogs, involving the escape and outflow of large volumes of semi-liquid basal peat, are well-known phenomena in Ireland but have only very rarely been reported from elsewhere in the world. Their precise causes and mechanisms are as yet unclear. The liquid limit (wL) was identified as a potentially useful indicator of the susceptibility of peat to such failure because peat has extremely high natural water contents and, as an index property, wL takes no account of the properties or structures of highly heterogeneous intact peat. However, the usual procedure for determining the wL of peat is not fully standardised. Prepared samples will normally include potentially highly reactive particles of disrupted fibres and wood fragments that would not be present in such freshly disintegrated form in the field. This paper presents results from wL determinations of peat obtained from the scar margins of three bog failures in northwest Ireland, using four different test procedures including a method involving wet-sieving of the peat to separate the humified <425-μm fraction for testing without incorporating artificially fragmented particles of fibres. The sampled peat was classified as H8–H10 according to the von Post humification scale. The fibre contents varied between the sites, but the ash contents were <3% in all but one test sample, and bulk densities (dry and field-wet) of the peat from all three sites were almost identical. wL results from the wet-sieving method were 708–785%, compared with 633–980% from the standard method. The highest measured field water contents exceeded the wet-sieved wL for all three of the field sites. Tests of cone penetration into intact peat cores demonstrated the influence of the reinforcing effect of in situ fibres. The results strongly suggest the need to adopt a fully standardised procedure for determining the wL of peat. Additional shear vane measurements of intact and remoulded peat from a bog failure in Northern Ireland indicated a very high ‘strength sensitivity’. This leads to the suggestion that a slight disturbance of basal peat can lead to a loss of strength that rapidly propagates as local stresses change and cause further remoulding as water contents exceed wL.

A conceptual model of volume-change controls on the hydrology of cutover peats

Modeling hydrological processes in certain peats requires a detailed understanding of short-term changes in soil volume and it's influence on the system's hydraulic properties. A study of cutover sites abandoned for 7-years (H92) and 2-years (H97), and an undisturbed section of the Lac Saint-Jean (LSJ) cutover bog was conducted to characterize peat volume changes and its associated hydrological behaviour. Shrinkage and compression accounted for 96–97% of seasonal volume change. Saturated hydraulic conductivity ( K S) varied linearly with peat compression; a 1 cm decrease in peat thickness causing a 5.2 cm d −1 decrease in K S at H92, and a 1.4 cm d −1 decrease in K S at H97. A 2–6% seasonal decrease in saturated volumetric moisture content ( θ S) at the cutover sites was partly due to soil compression, although the development of CH 4 bubbles possibly affected moisture content. In the unsaturated zone moisture retentivity ( θ– Ψ) was seasonally transient due to the shifting soil structure. The greater volumetric response to a change in water storage of the more porous and less decomposed peat at H97 indicates a long-term decreasing trend in peat compressibility due to irreversible losses in pore volume. Deterioration of high water storage and low water retention properties at H92 suggests that cutover sites abandoned for longer periods will become increasingly hostile to Sphagnum recolonization despite the blockage of drainage ditches.

Pressure variations in peat as a result of gas bubble dynamics

AbstractTransient high pore‐water pressures, up to 50 cm higher than ambient pressure, developed over the summer season at various depths in a shallow (1 m) fen peat. The excess pressures had a pattern of gradual increases and sharp drops, and their initiation and release typically corresponded to abrupt changes in atmospheric pressure. We conclude that these phenomena depend on gas bubbles (probably methane) generated by biological activity, both by clogging pores and by building up pressure as they grow. These transient and spatially discontinuous high‐pressure zones were found using pressure transducers in sealed (backfilled) pits, but not in piezometers open to the atmosphere. Piezometers may provide a conduit for the release of gas and pressure, thus rendering them unsuitable for measuring this phenomenon.Although the development of localized zones of high pressure causes erratic and unpredictable hydraulic gradients, we suggest that their effect on the flow of water or solutes is offset by the reduced permeability caused by the bubbles, which allows them to be sustained. These zones, however, probably deflect flows driven by the dominant hydraulic gradients. Furthermore, they may cause the peat volume to adjust (swell). The use and interpretation of traditional methods for estimating hydraulic head and conductivity in peat soils thus require great caution. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Six chemicals with animal repellent or insecticide properties are screened for phytotoxic effects on the germination and viability of ash, birch, Corsican pine and sycamore seeds

Summary As a prelude to direct sowing experiments, a laboratory study was carried out to determine whether six chemicals with insect and/or rodent repellent properties (Aaprotect, Capsaicin, Guardsman, Hallmark, Scuttle, Treeguard) affected the germination capacities and/or viability percentages of European ash (Fraxinus excelsior L.), silver birch (Betula pendula L.), Corsican pine (Pinus nigra ssp. laricio L.) and sycamore (Acer pseudoplatanus L.) seeds. None of the chemical repellents had a significant effect on either the germination capacity or viability of ash or birch seeds. One repellent (Guardsman) significantly reduced the germination capacity of sycamore from 49 to 32 per cent (P ≤ 0.01). Two repellents (Aaprotect and Scuttle) significantly reduced the germination capacity of Corsican pine from 74 to 62 per cent (P ≤ 0.05) and 11 per cent (P ≤ 0.001), respectively. Corsican pine was therefore the most sensitive of the species investigated to phytotoxic effects. Viability percentages (at the end of germination tests on repellent-treated seeds) showed that virtually all ungerminated seeds were dead. Greater phytotoxicity was observed for small-seeded species when they were incubated on a substrate of moist filter paper than when they were sown in moist peat + sand. One explanation is that the larger volume of peat + sand in the seed-tray allowed the chemicals to leach away from the seeds more quickly. Alternatively, perhaps the peat inactivated the chemicals through adsorption. The results are used to exclude certain chemical and tree seed combinations from future seed predation studies associated with direct sowing.

IN VITRO ROOTING OF STRAWBERRY TREE (ARBUTUS UNEDO L.) IN MEDIUM SOLIDIFIED BY PEAT - PERLITE MIXTURE IN COMBINATION WITH AGAR

Microcuttings of strawberry tree (Arbutus unedo L.) were produced in WPM supplemented with MS vitamins, sucrose 20 g l -1 , agar 5 g l -1 and 22 μM BA. Experimentation related to in vitro rooting was carried out in glass jars containing 70 ml of WPM supplemented with either IBA (0, 2.5, 5, 10 μM) or IAA (0, 10, 20 μM). Highest percentages of rooting were achieved in 10 μM IBA (92%) and 10 μM IAA (82%), although the respective survival rates during acclimatization were only 28 and 55%. Equal volume (70 ml) of peat - perlite (1:4, v/v) mixture was added to the above medium during in vitro rooting. This novel medium resulted in higher survival rates and well-branched roots, in all auxin concentrations, reaching up to 90% of acclimatization rate in the case of 10 μM IAA. Ex vitro rooting was performed in peat - perlite (1:1, v/v) mixture. Microcuttings were dipped in dilutions of either 0.5 g l -1 IBA for 24h or 2 g l -1 IBA for 5 sec. The respective average percentages of rooted plantlets were 62% and 59%, 50 days later.

Holocene sea-level rise and its effect on the mass balance of coastal deposits

A mass balance study of the Holocene accumulation wedge has been carried out in the lowland area between the Ems and Weser rivers on the German North Sea coast. This region, which comprises various sedimentary environments, such as barrier islands, sheltered and open tidal flats, bay flats, and estuaries, is highly suitable for such quantitative studies and can serve as a model for general mass transport and accumulation processes connected with transgressions over coastal lowlands. Data for the study was taken from borehole records, hydrographic soundings and topographic surveying to prepare structure contour maps and sequence maps at a scale of 1:25,000 showing the outlines and the internal make-up of the Holocene accumulation wedge. The irregularly distributed data was interpolated into a regular grid and the volumes of allochthonous clastic sediments and autochthonous peat, which make up 90% and 10%, respectively, of the coastal Holocene, were calculated. A comparison of the amount of clastic material supplied by the Ems, Weser, and Elbe rivers during the last 7500 years with the total volume of the accumulation wedge shows that about 90% is from marine and only 10% from riverine sources. By comparing the results of the quantitative analysis of the Holocene sedimentation with the present-day morphological and hydrodynamic observations, predictions of the future development of the coastal lowland area can be made.

Planning for Shoreline Response to Spills in Arctic Environments

ABSTRACT The Arctic coasts present three unique shoreline types that are common in North America and Eurasia, but that are not found in lower latitudes or in the southern hemisphere: tundra cliffs, peat shorelines, and inundated low-land tundra. Tundra cliffs range in character from ice-rich exposures that are dominated by rapid thermo-erosional processes to high (10–15 meters) sediment-rich cliffs that may be eroded by slumping or basal sapping. One product of this rapid erosion of the tundra is to produce large volumes of peat and in many sections these form the dominant shore-zone material. In low-lying areas the flooding of the tundra has produced extremely complex shoreline configurations characterized by the elevated rims of patterned ground. These unique arctic shore types present different sets of challenges for shoreline cleanup and treatment and have been included in the U.S. marine oil spill response guide published in 2001 by API, NOAA, USCG, and USEPA and several specialized Arctic response manuals published recently by Environment Canada. A low-altitude aerial videotape survey in 2001 produced continuous images of the mainland and barrier island coasts of the Alaskan Beaufort and Chukchi Sea coasts from the Canadian border to Point Hope, used to map the shore types as part of a mapping project for the Minerals Management Service. The mapping revealed that the three arctic shoreline types are present on more than half (54 per cent) of the coast between the Canadian border and Point Hope.

Rooting Foliage Plant Cuttings in Compost-formulated Substrates

Three composts, derived from municipal solid waste with biosolids, yard trimmings, and yard trimmings with biosolids, were mixed by volume with sphagnum peat and pine bark to formulate 12 substrates. After characterizing physical and chemical properties, the substrates, along with a control, were used for rooting single eye cuttings of pothos (Epipremnum aureum) and terminal cuttings of maranta (Maranta leuconeura) and schefflera (Schefflera arboricola) in enclosed polyethylene tents. All cuttings initiated roots with no significant difference in root numbers per cutting 14 days after sticking, but root lengths 21 days and root-ball coverage ratings 45 days after sticking were significantly affected by substrates. Five of 12 compost-formulated substrates resulted in root lengths of cuttings equal to or longer than the control. In addition to desirable physical properties such as bulk density, total porosity, and air space, common chemical characteristics of the five substrates included low concentration of mineral elements, initial electrical conductivity ≤3.0 dS·m-1 based on the pour through extraction method, and pH between 3.8 to 5.0. The five substrates were formulated by combining composted municipal solid waste with biosolids or yard trimmings with biosolids volumetrically at 20% or less or composted yard trimmings at 50% or less with equal volumes of sphagnum peat and pine bark.

Soil organic matter distribution and below‐ground competition between Calluna vulgaris and Nardus stricta

Summary We conducted an experiment to investigate the effect of organic matter distribution on below‐ground competition between the dwarf shrub Calluna vulgaris (L.) Hull and the coarse upland grass Nardus stricta (L.). The two species were grown alone, or in competition in pots where the substrate was either a sand layer overlain by a peat layer (layered), or the same volume of peat evenly mixed with sand throughout the pot (mixed). Root length and allocation in the top, middle and bottom of each pot was measured, along with plant biomass. Calluna allocated the greatest proportion of root length to the top of the pot, irrespective of the peat distribution. Nardus allocated a large proportion of root length to the bottom of the pot. Root allocation by Nardus to the top and middle of the pot was positively related to the distribution of peat. Nardus grown alone attained greater shoot mass in the layered than in the mixed substrate, but this was not the case when Calluna was present. Calluna was the superior competitor in both layered and mixed‐substrate pots, but more so in the latter. This was attributed to (i) the ability of Calluna to exclude Nardus roots from the upper organic material in the layered substrate, and (ii) the greater plasticity of root allocation of Nardus, enabling it to avoid competition with Calluna.

The Regeneration of a Highly Disturbed Ecosystem: A Mined Peatland in Southern Québec

We studied the natural regeneration of an ombro- trophic peatland (Cacouna bog) located in southern Quebec that was disturbed by peat mining and other anthropogenic activities over a 200-year pe- riod. Using an extensive collection of historical doc- uments, as well as dendrochronological data, we reconstructed the history of the peatland. We also sampled vegetation and environmental variables, and integrated the data in a geographic information system. More than 60% of the total area of the bog was mined between 1942 and 1975, and 98 km of ditches were dug to drain the site. The peatland lost 34% of its initial peat volume between 1946 and 1998. Although the bog was severely disturbed, the spontaneous revegetation of the site by vascular plants was successful (90%-100% cover). How- ever, only 10% of the total mined area has been recolonized by Sphagnum species, mainly because drainage ditches are still operational and contribute to drying out the bog. Water table level, peat de- posit thickness, and pH are abiotic factors strongly influencing the vegetation composition in the bog. Spatial and historical factors are also important components in this study since they explain, either alone or in interaction with abiotic factors, 44% of the variation of the species data. The intensity of mining activities and the pattern of abandonment of mined sectors strongly influenced abiotic factors, which in turn affected the revegetation process. Even if the Sphagnum cover of the bog is low, the rapid "recovery" of the vegetation cover in the peatland indicates that after the reestablishment of an appro- priate hydrological regime, a highly disturbed peat- land has a considerable potential for regeneration.

Importance of shrinkage and compression in determining water storage changes in peat: the case of a mined peatland

This study examines changes in peat volume in a mined peatland near Lac St Jean, Quebec, during the spring and summer of 1995 and 1996, and the implication for water storage changes. Lowering of the water table caused drainage above the water table, but the specific yield (S y ) of the peat was relatively small (0.48), and did not adequately describe the water storage change. Lowering of the water table also caused surface subsidence, which was shown to be partly due to shrinkage above the water table (<3.6 cm), and partly due to compression of the saturated peat (about 6 cm). Measured total surface subsidence ranged from 6.5 to 10 cm. The change in peat volume occurred over the entire depth of the peat deposit (h), and so the storativity due to peat compression (bS s ), estimated to be 0.13, was more important than specific yield in determining water storage changes. Total storativity (S tot ) was best estimated as the sum S y + bS s . Changes in peat volume in the 0-3 cm layer were evident in the temporally variable bulk density (83-101 kg m -3 ). Its relationship with volumetric moisture content was highly hysteretic, reflecting the complexity of the process in the unsaturated zone. However, there was a linear relationship with water tension, suggesting a more direct causal relationship. Changes in peat volume were also recorded below the water table, as the volumetric water content of the saturated peat decreased by 3.5% over the season. Since this applied to a relatively thick layer of peat, its total effect was greater than shrinkage in the zone above the water table. It was concluded that most peatland water balances should make account of storage changes associated with peat volume changes, and that peat volume changes may increase the water limitations to plants when the water table drops below the surface.

The potential of crushed rocks and mine tailings as slow-releasing K fertilizers assessed by intensive cropping with Italian ryegrass in different soil types

In search for a source for a slow-releasing K fertilizer, the plant availability of mineral K in selected crushed rocks and mine tailings was investigated by growing Italian ryegrass for six months in small volumes of peat, loamy sand or silt loam mixed with different K-sources. The K supplied as K-feldspar was nearly unavailable to the plants, whereas nearly 60% of the K supplied as biotite and nepheline in a carbonatite, was nearly unavailable to the plants, parts. The carbonate content of the rocks and tailings seemed to be more important for the availability of the K than the specific surface of the mineral particles. It is concluded that a rock-based fertilizer containing biotite as its main K-bearing mineral and between 5 and 20% carbonate, will release K at a slower rate than soluble K fertilizers do and still supply considerably more K to the plants than is supplied from the fraction of non-exchangeable K in the soil.