Floating Peat Mat Research Articles

Lake Tagimaucia Montane Lake as a Potential Late Holocene Environmental Archive in Fiji's Volcanic Highlands

Lake Tagimaucia, a montane volcanic lake on Taveuni Island, is Fiji's only high-elevation lake. This study examined a lacustrine sediment core to explore the lake's potential as a palaeoenvironmental archive through the Late Holocene. Dating reveals no simple age–depth relationship due to sediment age-reversals. However, phases of fire activity are evidenced by two distinct charcoal bands. Catchment burns were probably related to significant ENSO-driven drought, although fire ignition by volcanic eruptions on Taveuni cannot be ruled out. Above the dominant charcoal band, the sediment profile exhibits notable positive shifts in organic matter, bulk density, δ13C, and C:N ratio. These peaks suggest a phase of accelerated catchment erosion, possibly triggered by post-burn instability. We introduce a conceptual model to explain the influence of sedge peat swamps on lake sedimentation processes. Surrounding sedge-dominated peatlands have extensively encroached Lake Tagimaucia. Floating peat mats, gradually accumulating through time, act as a repository of organic material that is stored directly on the lake surface. Episodes of drought and fire release old organics directly into the lake itself, probably contributing to the complex chronological sequence in the Late Holocene stratigraphy.

Overcoming establishment thresholds for peat mosses in human-made bog pools.

Globally, peatlands have been affected by drainage and peat extraction, with adverse effects on their functioning and services. To restore peat‐forming vegetation, drained bogs are being rewetted on a large scale. Although this practice results in higher groundwater levels, unfortunately it often creates deep lakes in parts where peat was extracted to greater depths than the surroundings. Revegetation of these deeper waters by peat mosses appears to be challenging due to strong abiotic feedbacks that keep these systems in an undesired bare state. In this study, we theoretically explore if a floating peat mat and an open human‐made bog lake can be considered two alternative stable states using a simple model, and experimentally test in the field whether stable states are present, and whether a state shift can be accomplished using floating biodegradable structures that mimic buoyant peat. We transplanted two peat moss species into these structures (pioneer sp. Sphagnum cuspidatum and later‐successional sp. S. palustre) with and without additional organic substrate. Our model suggests that these open human‐made bog lakes and floating peat mats can indeed be regarded as alternative stable states. Natural recovery by spontaneous peat moss growth, i.e., a state shift from open water to floating mats, is only possible when the water table is sufficiently shallow to avoid light limitation (<0.29 m at our site). Our experiment revealed that alternative stable states are present and that the floating structures facilitated the growth of pioneer S. cuspidatum and vascular plants. Organic substrate addition particularly facilitated vascular plant growth, which correlated to higher moss height. The structures remained too wet for the late‐successional species S. palustre. We conclude that open water and floating peat mats in human‐made bog lakes can be considered two alternative stable states, and that temporary floating establishment structures can induce a state shift from the open water state to peat‐forming vegetation state. These findings imply that for successful restoration, there is a clear water depth threshold to enable peat moss growth and there is no need for addition of large amounts of donor‐peat substrate. Correct species selection for restoration is crucial for success.

Formation and Development of Floating Peat Mats in a European Eutrophic Lake: A Case Study

In a case study, we analyzed the development of a spatially extended eutrophic floating marsh in a mid-European river floodplain lake. Such buoyant fringe marshes occur occasionally in lakes or river floodplain waters which have accumulated considerable amounts of very soft organic sediments. There are two hypotheses about their formation: 1) diverse helophytes, among them Cicuta virosa and Carex pseudocyperus, colonize floating-leaf plant communities or floating plant residues washed ashore, and 2) normal reed stands detach from the soft lake bottom which then float up caused by their rhizome aerenchyma and by marsh gas accumulation. The following questions were pursued: 1) How did these floating peat mats develop and do they grow horizontally on the water surface? and 2) How will they develop in future? Our study is mainly based on the analysis of historical maps, aerial photographs, and the zonation of the riparian vegetation. In the first half of the 20th century, the formation of floating swamps began on the waterside edge of large reeds that had developed on huge mud banks. The succession proceeded at this edge to alder carr without substantial expansion toward the open water. This and other findings led us to the conclusion that the floating mat formation proceeds according to the second hypothesis. Since there is no significant horizontal growth of these floating marshes, the riparian vegetation belt of the lake will only spread by repeating the entire process.

Paleoecological and paleoenvironmental interpretation of three successive macrofloras and palynofloras from the Kola Switch locality, lower Permian (Archer City Formation, Bowie Group) of Clay County, Texas, USA

Fossil floras have been recovered from a unique deposit of early Permian age in North-Central Texas. The site, Kola Switch, preserves three distinct floras in different lithofacies, in a succession from a single outcrop. The sedimentary environment appears to be a floodplain channel fill of primarily siltstones and claystones. The lowermost flora, preserved in a kaolinitic siltstone, indicates active water flow. It is dominated by plants typical of well-drained substrates, dominated by Sphenopteris germanica, and contains no wetland elements. The middle flora is from a finely laminated carbonaceous claystone and is dominated by marattialean tree ferns, with no elements from habitats typical of seasonal moisture availability. It contains no roots and appears to have formed as a floating peat mat. The upper flora is a mixed assemblage of wetland taxa and those typical of well-drained soil environments or a seasonal rainfall regime. Unlike the two lower floras, it has a relatively even distribution of dominance and is the most diverse of the three assemblages. Palynofloras also were recovered from each of these beds. The palynofloras, although varying between and even within the beds, indicate a common background species pool during the time interval sampled, suggesting that these distinct floras reflect local changes in microhabitat conditions under a constant climatic background. The palynoflora from each bed has characteristics in common with the macroflora of that bed, but also distinct differences. Together, the macroflora and microflora provide an unusually broad picture of this site through time. Kola Switch compares favorably with the recently described flora from the nearby Sanzenbacher Ranch site of approximately the same age and also with floras of Rotliegend age from Central Europe.

Autogenic and allogenic factors affecting development of a floating Sphagnum-dominated peat mat in a karst pond basin

Lateral expansion of floating vegetation mats over the surface of aquatic ecosystems (terrestrialization) is one of the ways of peatland development. This process was commonly studied in kettle-hole lakes, whereas karst ponds have received less attention. We used a suite of palaeoecological analyses at Karstovoe mire (Mordovia, Russia) to reconstruct the formation of a floating Sphagnum-dominated peat mat over the karst pond. The results show that the floating peat mat had covered the central part of the pond by ca. AD 1600. Remains of Scirpus sp. and Calamagrostis sp. in the basal layers indicate that these plants might form a framework on which Sphagnum mosses and sedges were established. The terrestrialization could be triggered by the ‘Medieval Warm Period’ (AD 950–1250) as droughts reduce water levels and allow the pioneering plants to colonize exposed bottom sediments on the margins of lakes. Later, the development of the mire was mainly driven by autogenic factors that could be explained by the relatively stable hydrological regime in freely floating or poorly attached vegetation mats. In the mid 19th century, the surface wetness of the mire started to decline that can be related to both increased human activity associated with fires and to a greater thickness of the mat so that autogenic and allogenic effects were difficult to disentangle. In less than a century after that, the fen transformed to a pioneer raised mire. Our results show complex and context-dependent effect of autogenic and allogenic factors on the development of floating peat mats.

VEGETATION AND ENVIRONMENTAL FACTORS OF KARST MIRES IN BROAD-LEAVED FOREST ZONE: METHODICAL APPROACHES, "БОТАНИЧЕСКИЙ ЖУРНАЛ"

Vegetation cover and environmental factors were studied in the system of karts mires in the broad- leaved forest zone in Tula Region, Central European Russia. Mires are formed in the sinkholes and characterized by rather low anthropogenic disturbances. These mires are characterised by floating peat mats and variety of vegetation communities which are differ by ecological conditions (water levels, acidity and nutrition). Development and growth of floating mats change water and mineral feeding that leads to succession of vegetation communities.

Post‐dispersal probability of germination and establishment on the shorelines of slow‐flowing or stagnant water bodies

AbstractQuestionIn Dutch fens, species that colonize open water and induce the formation of floating peat mats have become rare. Many such riparian pioneer species occur predominantly on shorelines sheltered from the wind, whereas the majority of seeds tend to be deposited on exposed shorelines, as seeds are dispersed via wind‐driven waves and currents. Do differences in germination and seedling survival between sheltered and exposed shorelines explain this difference?LocationThe fen reserve ‘De Westbroekse zodden’ (52 °10′ N; 5 °07′ E)MethodsWith a sowing experiment, the germination, seedling survival and overall recruitment of Berula erecta, Calla palustris, Comarum palustre, Glyceria maxima and Mentha aquatica were studied on sheltered and wind‐exposed banks in eight fen ponds. Temperature, light availability, water level, wave impact, litter and seed deposition and vegetation height were recorded over 16 wk. The probability of washing away was quantified with small seed mimics. With a greenhouse experiment, we separately examined the effects of environmental differences between sheltered and exposed banks.ResultsIn the field, compared to sheltered shorelines, exposed shorelines had a higher wave impact, higher light availability in spring and more litter and seeds deposited on them. In the greenhouse experiment, only litter addition decreased germination. This effect was overridden in the field, where the higher light availability on exposed banks increased germination. In the field, the number of seedlings decreased strongly over time, and eventual recruitment was determined by the degree to which seeds and seedlings were washed away by wave action. The probability of being washed away was highest on exposed shorelines (where waves were larger), which resulted in higher recruitment on sheltered shorelines.ConclusionsThe recruitment of colonizing species to fen pond shorelines is limited by the probability that seeds and seedlings may be washed into the open water. This process can eventually cause more successful recruitment on upwind or lee‐side shorelines despite lower seed inputs there.

Multiple effects of land-use changes impede the colonization of open water in fen ponds

Question: Dutch fen areas have become embedded in intensively used landscapes, resulting in biodiversity loss. Hence, plant species that colonize open water inducing the formation of species-rich floating peat mats have disappeared. Despite many restoration efforts, they have not returned. Is natural succession towards floating mats impeded by site conditions, dispersal limitations or changed biotic interactions? Location: Six Dutch fen reserves: De Deelen, De Weerribben, De Wieden, Westbroek, Molenpolder and Terra Nova. Methods: In 62 fen ponds we determined plant species richness and expansion into open water. We related these to habitat quality (chemical composition of soil and surface water, pond morphology), dispersal potential (distance to remnant populations, likelihood of dispersal) and biotic interactions (presence of muskrats [Ondatra zibethicus L.] and the keystone species Stratiotes aloides). Results: Factor analysis showed that plants expanded further into open water and bank vegetation had higher species richness in areas with older ponds and lower muskrat densities. Locally, high turbidity hampered colonization. Whenever the water was clear, colonization was higher in shallow ponds, and in deep ponds only if Stratiotes was present. Species richness was negatively correlated to nutrient availability in soil and positively correlated to hydrological isolation (decreased sulphate concentrations). We also found that species richness was higher in sheltered banks. Conclusions: Multiple habitat characteristics (turbidity, water depth, nutrient and sulphate concentrations) and the influence of muskrats and Stratiotes all play a role in the lack of restoration success in Dutch fen ponds. Dispersal limitations seem to be overruled by habitat limitations, as colonization often fails even when sufficient propagule sources are present, or when connectivity is high.

Hydroclimatic variability drives episodic expansion of a floating peat mat in a North American kettlehole basin

The coming century is predicted to feature enhanced climatic variability, including increased frequency, intensity, and duration of extreme climatic events. Ecologists are faced with the critical challenge of anticipating potentially nonlinear ecosystem responses to these changes. High-resolution paleoecological data sets that capture past ecosystem responses to climate variability provide valuable long-term perspectives on the sensitivity of ecosystems to climate-forced state shifts. We used a suite of paleoecological analyses at Titus Bog in northwestern Pennsylvania, USA, to test the hypothesis that the development and expansion of floating peatlands in kettlehole basins represents a threshold response to hydroclimate variability. In contrast with expectations of gradual autogenic peat mat expansion, our results indicate that peat mat expansion at Titus Bog was highly episodic and occurred in three distinct pulses centered on 800, 650, and 400 cal yr BP. Each of these expansion events coincided with or immediately followed decadal-to-mutlidecadal droughts recorded in regional paleoclimate reconstructions. These patterns indicate that peatland development in kettlehole basins can follow nonlinear trajectories, with episodes of rapid advancement triggered by climatic forcing. Future climate changes may increase the likelihood of peatland expansion in kettlehole basins, potentially leading to abrupt changes in adjacent lake ecosystems.

Testing the climate sensitivity of peat-based paleoclimate reconstructions in mid-continental North America

The sensitivity of peatland water-table depth reconstructions to past hydroclimate variability was assessed by comparing 210Pb-dated, testate amoeba-based reconstructions of water-table depth with instrumental records of temperature, precipitation, and Palmer Drought Severity Index (PDSI). Comparisons were made for the past century at five sites in the western Great Lakes region of North America. The primary objectives were (1) to assess the relative influence of temperature and precipitation on proxy records from these systems, (2) compare an integrated index of past moisture variability, PDSI, to records of peatland surface-moisture, and (3) compare the relative climate sensitivity of paleohydrological records from a raised bog and two types of kettle peatland, including those with and without floating peat mats. Results indicated that the raised bog surface-moisture reconstructions were most strongly correlated with PDSI, with precipitation variability more important than temperature variability. Proxy records from two non-floating kettle peatlands were also correlated with PDSI, although the importance of precipitation and temperature varied between the two sites. Records from floating mats were not correlated with instrumental climate records, although patterns suggest that additional research is needed to assess the sensitivity of these systems to high-magnitude or prolonged drought events. Although the relative importance of precipitation and temperature in controlling peatland surface-moisture conditions may vary in space and time, consistent correlations with PDSI indicate that peatland archives are well suited for studies of past drought variability and should be particularly valuable in humid regions at mid-to-high latitudes where moisture-sensitive records are scarce.

The Romeriksporten railway tunnel — Drainage effects on peatlands in the lake Northern Puttjern area

This study presents the results of an investigation of drainage effects of the Romeriksporten railway tunnel on peatlands in the Lake Northern Puttjern area. Drainage impacts on peatlands occurred in marked depressions reflecting faults or weakness zones in bedrocks. The impacts were most evident near the tunnel trace, but dry peatlands and streams were observed as far as 600 m from the tunnel trace. Several types of drainage effects were observed on peatland surfaces after tunnelling; surface subsidence and formation of local depressions, peat slides, peat cracking, dry peat holes, and death of vegetation. The effects depended clearly on peatland properties. The greatest and most damaging effects were associated with thick peat layers around open water surface. Here lowering of the water table caused peat slides. Such areas will generally be extremely vulnerable to lowering of the water level. The magnitude of subsidence of peatlands depends on peat thickness, peat decomposition and groundwater lowering. Even after seven years with artificial infiltration in bedrock wells in dry periods to counteract water table lowering, peat subsidence and peat slides were evident, demonstrating that temporary draw down of water can result in irreversible impacts on peatlands. To better be able to avoid damaging effects of tunnel drainage on environment, investigations of properties of peatlands above possible tunnel traces should be integrated in the planning procedure for tunnel constructions. In mires above such traces, the occurrence of floating peat mats, degree of peat decomposition, peat thickness, deliveries of water from surrounding catchments in dry periods and possible pathways of leakage through subsoils and bedrocks should be examined as basis for assessment of vulnerability of peatlands to tunnel drainage and selection of tunnel traces that evade the most vulnerable peatlands. When such areas can not be avoided, requirements should be set to the tightening of the tunnel to prevent damaging water draw downs in dry periods. Observations of drainage effects on peatland surfaces can complement hydrological information from measurements of tunnel leakages and groundwater levels and thus contribute to provide a broader picture of hydrological impacts and bedrock hydrogeology.

Water-holding capacity of a floating peat mat determines the survival and growth ofMenyanthes trifoliata L (bog bean) in an oligotrophic lake

Menyanthes trifoliata is a threatened and endangered species in Korea and USA. To assess the important ecological characteristics for its conservation and restoration, we measured the level of soluble reactive phosphorus (SRP) in the water, total N and C contents in the plants, and the water-holding capacity of the surrounding floating peat mat. These factors, which limit the success of aquatic macrophytes, were examined for their effects on the growth of this species. Leaflet areas and petiole lengths ranged from 6.1 cm2 and 12.4 cm, respectively, at a water depth of 5 cm, to 22.7 cm2 and 33.0 cm, respectively, at 40 cm. The peat mat was able to retain water at a depth of 5 to 45 cm. SRPs ranged from 10 to 46 ppb, while total C and N contents were between 0.62% (petiole) and 2.76% (leaf), and between 39.7% (petiole) and 43.8% (stem), respectively. The water-holding level was not correlated with SRP, and neither phosphorus nor nitrogen content affected plant growth. However, the capacity of the floating mat to hold water as the depth subsided was positively related to growth. This suggests that such mats are good tools for restoring populations ofM. trifoliata when materials with high water-holding capacities are used.

Effects of shallow flooding on vegetation and carbon pools in boreal peatlands

AbstractQuestion:What are the effects of shallow flooding on boreal peatlands on vegetation composition and size of carbon pools in the living and dead vegetation?Location:Lake 979, Experimental Lakes Area, northwestern Ontario, Canada.Methods:A boreal basin peatland complex with treed bog, open bog, and open water was experimentally flooded by raising water level ca. 1.3 m. Vegetation and above‐ground biomass were compared between pre‐flood conditions and those nine years after flooding. Peat accumulation since flooding was also quantified.Results:Flooding caused almost all trees to die, leading to a net loss of 86% of the above‐ground living plant biomass after nine years of the flooding. Floating up of peat was rapid in the central part of the basin, and the floating peat mats were characterized by newly established open bog community. Wetland types were diversified from bog into open bog, fen, and marsh, accompanied with great species turnover. Floating open bog community accumulated the greatest amount of peat since flooding.Conclusions:This study shows that shallow flooding of bog vegetation can lead to quick re‐establishment of open bog vegetation upon the floating up of peat mats as well as changes to more diverse vegetation over decadal time spans. We estimate that the carbon pools in 2002 in living and dead plant biomass since 1992 are comparable to what they were in the above‐ground biomass in 1992. Flooding caused an initial net decrease in carbon stores, but carbon in the pre‐flood living plant biomass was replaced by both carbon in dead biomass of the pre‐flood vegetation and newly sequestered carbon in new peat growth and post‐flood living plant biomass. Possible vegetation change toward bog‐dominated system could lead to increasing rate of new peat growth, which could affect future carbon sink/source strength of the system.

Seasonal changes in redox properties of peat, nutrition and phenology of Menyanthes trifoliata L. in a floating peat mat in Mizorogaike Pond, central Japan

Seasonal changes in leaf population per area, nutrient absorption rate and elemental concentration of Menyanthes trifoliata L. were studied in a floating peat mat in Mizorogaike Pond, central Japan, with reference to the peat redox potential. Leaf population of M. trifoliata showed a rapid increase in May, reached the maximum in June, and then decreased to 12% of the maximum density in July. The foliage density of M. trifoliata again increased and reached its second maximum in September, and then it decreased to zero in December. The decrease of the foliage density from June to July corresponded to the minimum of redox potential (Eh) of the surface peat. Low Eh in the rhizosphere of M. trifoliata relates to the temporary disappearance of the foliage of the plant from June to July. Nutrient concentration (K, Mg, Ca, Fe) in M. trifoliata roots showed minimum in June to August. The nutrient absorption rate of M. trifoliata evaluated from the rubidium absorption rate of excised root of M. trifoliata showed a minimum value in June and July. Peat redox properties would affect the nutrient absorption activity of the roots and the consequent foliage phenology of M. trifoliata in Mizorogaike Pond.

Testate Amoebae as Paleoclimatic Proxies in Rocky Mountain Peatlands: A Case Study in the Greater Yellowstone Ecosystem

We investigated the potential of testate amoebae (Protozoa: Rhizopoda) for reconstructing past climate changes in the Rocky Mountain region. Our specific objectives were to determine environmental controls on modem testate amoeba distribution in Sphagnum-dominated peatlands of the region, reconstruct past temporal changes in testate amoebae from a Sphagnum-dominated peatland in southwestern Yellowstone National Park, and assess relationships between climate variability and testate amoebae for the past century. Our results indicate that substrate moisture is the dominant control on modem testate amoeba distribution in the region, consistent with studies from other regions. Temporal changes in testate amoebae reconstructed from a floating peat mat in the Greater Yellowstone Ecosystem show considerable variability during the past several hundred years, and variability during the past century was correlated with the instrumental record of drought at decadal timescales. The patterns suggest that sensitive paleoclimatic reconstructions are possible from floating mats in the region, and perhaps elsewhere. Testate amoebae from peatlands in the Rocky Mountains show great potential for reconstructing past climate variability, corroborating and extending records inferred from other proxies.

Pollinator limitaton in a deceptive orchid, Pogonia japonica, on a floating peat mat

Deceptive orchid species that offer no floral rewards to pollinators often experience pollinator limitation because they. The breeding system and fruit set were investigated in order to examine pollinator limitation for a population of a deceptive orchid, Pogonia japonica, on a floating peat mat in Mizorogaike Pond, western Japan. Fruit sets for outcross-pollinated, self-pollinated and pollinator-excluded flowers were 75%, 80%, and 0%, respectively. Thus, this species was self-compatible but neither autogamous nor apogamous. The fruit set for open-pollinated flowers was 22.9% and 17.4% in 1994 and 1995, suggesting that pollinator limitation did occur in the field. Larger flowers were more likely to develop into fruit than smaller ones in open pollination (36%vs 8%). Thus, flower size seems to affect fruiting of this species. No effective visits by major pollinators such as bees, which could carry pollinia, were observed during 16.5 h of observation during daytime. Instead, thrips were often found moving on gynostemium or pollinia and circumstantial evidence that suggests thrips may partly transfer pollen in pieces out of a granular pollinium of P. japonica was obtained. Pogonia japonica should come to use thrips as a pollinator to supplement low fruit set under limited flower visitation by major pollinators.

Key variables controlling the vegetation of a cool‐temperate mire in northern Japan

Abstract. In the cool‐temperate Bibi Mire, Hokkaido, Japan, valley fens and flood‐plain fens have quite different vegetation. The main variables controlling the vegetation were all hydrological: mean water level, water level fluctuation and surface water flow. Chemical factors such as electrical conductivity, dissolved oxygen and related peat decomposition were less important. The pH was about neutral and has little effect. The flood‐plain fen developed under fluctuating water table conditions. The dominant species are Calamagrostis langsdotffii and Carex pseudocuraica. When temporal inundation occurs in the rainy or typhoon seasons, the submergence stimulates bud germination of the stoloniferous C. pseudocuraica, which can rapidly elongate its stolons upward. Some large floating peat mats occurred in the flood‐plain fen zone. On these mats some Alnus japonica saplings establish and patches of alder forest can arise. Here the water level was higher than in the peripheral alder forest zone.The valley fen is dominated by Carex lasiocarpa var. occultans and/or C. limosa. It is formed under stable water table conditions in the inundated parts of the mire ‐where the non‐inundated wet areas are dominated by alder trees. In the area where the surface water is flowing, these two fen sedges grow in deeper water since the high oxygen content is considered to compensate the flooding stress.

Rhizome growth of Menyanthes trifoliata L. in a population on a floating peat mat in Mizorogaike Pond, central Japan

The growth of rhizomes of Menyanthes trifoliata L. was investigated in a floating mat in central Japan in order to examine the phenotypic properties of the rhizomes and hence to clarify the role of these organs. The part of the rhizome which elongated in autumn had high specific dry weight during autumn and winter, and the specific dry weight decreased in early spring when generative buds and leaves started to develop. This part of the rhizome has a function for dry matter storage. The part of the rhizome which elongated in summer had a low specific dry weight. Rhizomes with low specific dry weight are thin and long and are useful for occupation of the peat surface, hence playing a role in vegetative expansion. The percentage of generative buds and lateral buds formed was related to the size of rhizomes formed in the preceding year. The percentage of generative bud formation increased with increasing rhizome size. In contrast to generative buds, lateral bud formation was restricted to rhizomes 2–32 cm in length: rhizomes longer than 32 cm never formed lateral buds.

Phenotypic and phenological plasticity of an aquatic macrophyteMenyanthes trifoliata L.

Phenotypic and phenological properties ofMenyanthes trifoliata L. were investigated within and outside of aPhragmites australis (Cav.) Trin. ex. Steud. canopy in a floating peat mat in Mizorogaike Pond, Central Japan. Under theP. australis canopy,M. trifoliata adjusted its phenotypic properties to the conditions of decreased light by increasing leaf blade area, decreasing leaf blade thickness and elongating petioles. The earlier expansion of leaves ofM. trifoliata within theP. australis community than outside the community was advantageous in terms of allowing the plant in the mixed community to produce as much dry matter as possible before the foliage ofP. australis could overgrow it. Despite the harmful effect ofP. australis onM. trifoliata's vegetative growth and reproduction, the latter species can persist in aP. australis community by changing its phenotypic and phenological properties.

13C natural abundance variations in carbonates and organic carbon from boreal forest wetlands

13C natural abundance variations were measured in peat soil and vegetation from two contrasting boreal forest wetlands: an upland watershed basin and a permanently saturated lowland mire. Evidence of methane oxidation was shown in the permanently saturated wetland with δ13C values as low as -97 ‰ in carbonate minerals found in floating peat mats. It is postulated that13C depleted CH4 is oxidized in the mat and reacts with calcium ions to form calcite (identified through x-ray diffraction). Methane flux measurements during the summer of 1992 showed much lower fluxes in areas with floating peat mats relative to open water. Secondary carbonates in the basin peat have isotope compositions close to the δ13C values of the peat organic carbon (-25 ‰), indicating their origin from fermentation and possibly from sulfate-reduction. In the upland basin peat deposits, the δ13CPDB values of organic C were constant with depth, while the permanently saturated mire had localities of13C enrichment in deeper layers of the peat. The13C enrichment may reflect areas of intense CH4 production in which13C enriched residual substrate is left behind during the production of highly13C depleted CH4.