In peat sampled at the Tunguska Cosmic Body (TCB) explosion area, the sharp increase of the N concentration (about three-fold) and the positive N isotopic anomaly (δ15N = +3.5‰, see eqn) have for the first time been revealed. In contrast with the C and H effects observed earlier which were clearly limited to the epicentre area, the same N effect has also been shown in peat sampled near the Vanavara settlement, 65 km south of the explosion epicentre. A clear connection of the observed anomalies in peat to the 1908 permafrost boundary, synchronism of the changes of δ15N and the N concentration and also good agreement with data on the K/T boundary deposits allow us to connect the observed effects to acid rain fall-out after passage and an explosion of the TCB.

Boreal wetlands are thought to be a large source of atmospheric methane, but this idea is based on very few measurements. Thus, a regional survey in the low boreal forest region of central Ontario, Canada, consisting of 24 sites over 12 wetlands and three beaver ponds was conducted to determine the temporal and spatial trends in emissions and the net annual methane (CH4) flux. Conifer swamps represented nearly 50 percent of the wetland coverage, but emit a small amount of CH4 (seasonal means less than 8 mg/sq m per d). The significant emitters of CH4, in order from highest to lowest seasonal means, were beaver ponds (30-90 mg/sq m per d), thicket swamps (0.1-88 mg/sq m per d), and bogs (6-21 mg/sq m per d). Mixed swamps, marshes, and fens emitted very little CH4 (less than 3 mg/sq m per d). Moisture saturation was the key determinant of high emissions, and, when satisfied, differences in emissions could be explained by peat and sediment temperatures. On the basis of the areal extent of wetlands from peatland inventories, it is calculated that the low boreal region of Canada contributes approximately 0.15 Tg CH4/yr to the atmosphere. This is an order of magnitude lower than the flux would be using the estimate of Aselmann and Crutzen (1989) for the same boreal region.

Measured rates of soil respiration from terrestrial and wetland ecosystems are reviewed to define the annual global CO2 flux from soils, identify uncertainties in the global flux estimates, and to investigate the influences of temperature, precipitation, and vegetation on soil respiration rates. The annual global CO2 flux from soils is estimated to average 68 +/- 4 PgC/yr, based on extrapolations from biome land areas. On a global scale, soil-respiration rates are positively correlated with mean annual air temperatures and mean annual precipitation. There is a chosen correlation between mean annual net primary productivity of different vegetation biomes and their mean annual soil respiration rates. Estimates of soil C turnover rates range from 500 years in tundra and peaty wetlands to 10 years in tropical savannas. The impacts of human activities on soil-respiration rates are poorly documented, and vary among sites. Of particular importance are potential changes in temperatures and precipitation. Based on a review of in situ measurements, the Q10 value for total soil respiration has a median value of 2.4. Increased soil respiration with global warming is likely to provide a positive feedback to the greenhouse effect.

Not less than 2% of the Earth's land surface is peat-covered, so it is important to try to understand the dynamics of peat accumulation. Peat-forming systems (mires) accumulate peat because conditions within them impede the decay of the plant material produced by their surface vegetation. This paper concerns the rate of peat production and some unexpected consequences of the processes of decay. These consequences are likely to be of interest to those concerned with mire ecology and with the history of vegetation during Flandrian times. Most peat-forming systems consist of two layers: an upper 10-50 cm deep aerobic layer of high hydraulic conductivity, the acrotelm, in which the rate of decay is relatively high; and a thicker, usually anaerobic, lower layer, the catotelm, of low conductivity and with a much lower rate of decay. Plant structure at the base of the acrotelm collapses as a consequence of aerobic decay, and the hydraulic conductivity consequently decreases. As long as precipitation continues the water table therefore rises to this level, thus engulfing material at the base of the acrotelm. The rate, p_c, of this input to the catotelm is exactly analogous to the rate, p_a, of input to the acrotelm i.e. of primary productivity of the vegetation. During passage through the acrotelm the peat becomes richer in the more slowly decaying components. The depth of, and the time for transit through, the acrotelm thus control p_c. The catotelm, however, usually forms much the largest part of the peat mass. Selective decay may continue in the catotelm. The specific composition of the peat thus becomes a progressively poorer indicator of the surface vegetation that formed it, and to a degree that is not generally realized: reconstructions of the past surface vegetation may become very inaccurate. If p_c were constant and there were no decay in the catotelm then for the centre of a peat bog the profile of age against depth (measured as cumulative mass below the surface) would be a straight line. But if either or both these conditions is untrue then the profile would probably be concave. Most of the cases for which data exist are consistent with a concave profile and a value (constant over several thousand years) of p_c of about 50 g m-2 a-1 and a decay rate coefficient, α_c, proportional to the amount of mass remaining, of about 10-4 a-1. This rate of input to the catotelm is about 10% of the primary productivity i.e. about 90% of the matter is lost during passage through the acrotelm. The relation seems to hold in spite of short-term fluctuations such as those represented by recurrence surfaces. Although 10-4 a-1 seems a very slow rate, it has important consequences. (i) The peat mass tends towards a steady state in which the rate of addition of matter at the surface, p_a, is balanced by losses at all depths: the rate of accumulation is zero. This depth is, for the cases examined, about 5-10 m. (ii) The very concept of `peat accumulation rate' thus needs careful consideration. To calculate it as the difference between two 14C dates divided by the depth between the samples from which they were measured, as is commonly done, may be seriously misleading. The error is likely to increase with age, depth and time span. (iii) Progress in such studies can be made only if the easily measured profile of bulk density is known. The position of the profile in the peat bog must also be known. There is some evidence that peat contains, or comes to contain, about 1% or less of the original mass in a highly refractory state, so that the concept of a steady state is unlikely to be correct if times much greater than about 50 000 years are involved. Three more consequences of the continued very slow decay in the catotelm may be of interest to mire ecologists. (iv) Most of the mass that leaves the catotelm probably does so as methane gas. The concentration of methane increases with depth and may be as high as 5 μ mol cm-3 at 5 m depth (about 10% by volume). Diffusion alone is able to remove mass at the necessary rate and would create concentration profiles similar to those observed. The solubility of methane in water is exceeded, however, and much of the methane may in practice be lost by mass flow of bubbles to the surface. (v) The amplitude of temperature fluctuations, as well as the mean temperature, may have a significant effect on the rate of peat decay, particularly in a cold climate. (vi) If this analysis is correct then the maximum depth of peat which can accumulate in 50 000 years is determined largely by the value of the quotient p_c/α_c. The usual view that the maximum depth is determined directly by climate operating through hydrology may be incorrect, though hydrology may have an indirect effect on the value of p_c, the rate of input to the catotelm at the bog centre. Away from the centre p_c is probably variable p_c and determined by hydrology. Its dependence on distance from the centre and on time is complicated: p_c/p_c may be more than, equal to, or less than 1.0. The age against depth profile away from the bog centre may be directly affected by hydrology, though the effect is not large except near the edge of the bog or near the base of the peat. There may, of course, be catastrophic failure - a bog-burst or `flow' - before the p_c/α_c limit is reached in the centre, or slower but equally destructive development of gullies and erosion.

The status of a four-phase development program to confirm that biogasification is a technical and economical process for the conversion of peat into pipeline quality methane is presented. The biogasification of peat is based on a two-stage process. In the first processing stage (assumed to follow hydro-mining) an oxidative pretreatment of peat breaks down the lignocellulosic structure to water soluble, lower molecular weight organics, i.e., simple aromatics, wood sugars, and carboxylic acids. The exothermic reaction provides the necessary heat to maintain moderate pretreatment temperatures of less than 180 C. Unreacted peat solids are separated (to be processed as boiler fuel), while the recovered liquid, containing the soluble organics, is converted to methane and carbon dioxide by conventional anaerobic fermentation is the second stage of the process. A significant advantage of the biogasification process is that technical difficulties of peat dewatering (to greater than 50% solids) necessary for conventional gasification are eliminated. Biogasification can be readily integrated into an environmentally acceptable and economically viable peat utilization concept involving hydro-mining, slurry transport, and wet processing.