Testing theories of mire development using multiple successions at Crymlyn Bog, West Glamorgan, South Wales, UK

1 Direct observations of long-term plant succession can be made using quantified plant macrofossil records from peat bogs, providing a means to re-evaluate theories of succession previously based on time-space substitution studies or field stratigraphic surveys. 2 Multiple successions from fen towards raised mire recorded at Crymlyn Bog demonstrate that divergent pathways exist, even when initial conditions are similar within a single bog. 3 Over time-scales relevant to the later stages of mire succession, allogenic forcing factors are significant and may be responsible for driving the direction and rate of species turnover in both forward and reversed hydroseral successions. 4 Differences in the local climatic regime may be responsible for the contrasting character of the mid- and late-Holocene transitional mire communities represented in Core CRB93 at Crymlyn Bog. 5 Plant macrofossil analyses show that Sphagnum is not always a dominant part of the mire community before the establishment of raised peats. Other species including Eriophorum vaginatum, may be equally important 'ecosystem engineers' at the fen–bog transition

Mire development across the fen-bog transition on the Teifi floodplain at Tregaron Bog, Ceredigion, Wales, and a comparison with 13 other raised bogs

1 A literature comparison of 14 radiocarbon-dated macrofossil records of raised peat bog initiation indicates that there is a relationship between the prevailing climate and the character of the first ombrotrophic vegetation communities at peatland sites in Britain and Ireland.2 All that is required for ombrotrophy is the separation of the mire growing surface from the influence of surface and subsurface waters. This could occur via vertical accumulation of the peat mass or a lowering of the water table. The establishment of bog species can be rapid once isolation occurs.3 Peatlands may become ombrotrophic in a variety of water table conditions and climatic regimes. There are at least two distinctive routes to ombrotrophy, via a 'dry-pioneer oligotrophic community' or via a 'wet-pioneer oligotrophic community'.4 Tregaron South-east Bog does not fit the pattern suggested by the literature comparison. The Fen-Bog Transition (FBT) occurred in a period of increased effective precipitation but the first ombrotrophic community was indicative of relatively dry, 'hummocky' bog and a deep or unstable water table.5 The transitional poor fen communities at Tregaron South-east Bog were short-lived. Sphagnum palustre mire lasted for 90 years compared to 300 years at Bolton Fell Moss in Cumbria, and the FBT was synchronous across much of the bog.6 The Tregaron peatland complex has a long history of water table fluctuations as shown by the stratigraphy of the marginal peats.7 Channel incision in the River Teifi could have contributed to the development of 'dry hummock' pioneer bog in the humid climatic conditions at 7300 cal. BP, by reducing the level of lagg streams

Bioaerosols on the atmospheric super highway: An example of long distance transport of Alternaria spores from the Pannonian Plain to Poland

Alternaria spores are pathogenic to agricultural crops, and the longest and the most severe sporulation seasons are predominantly recorded in rural areas, e.g. the Pannonian Plain (PP) in South-Central Europe. In Poland (Central Europe), airborne Alternaria spore concentrations peak between July and August. In this study, we test the hypothesis that the PP is the source of Alternaria spores recorded in Poland after the main sporulation season (September–October). Airborne Alternaria spores (2005–2019) were collected using volumetric Hirst spore traps located in 38 locations along the potential pathways of air masses, i.e. from Serbia, Romania and Hungary, through the Czech Republic, Slovakia and Ukraine, to Northern Poland. Three potential episodes of Long Distance Transport (LDT) were selected and characterized in detail, including the analysis of Alternaria spore data, back trajectory analysis, dispersal modelling, and description of local weather and mesoscale synoptic conditions. During selected episodes, increases in Alternaria spore concentrations in Poznań were recorded at unusual times that deviated from the typical diurnal pattern, i.e. at night or during morning hours. Alternaria spore concentrations on the PP were very high (>1000 spores/m3) at that time. The presence of non-local Ambrosia pollen, common to the PP, were also observed in the air. Air mass trajectory analysis and dispersal modelling showed that the northwest part of the PP, north of the Transdanubian Mountains, was the potential source area of Alternaria spores. Our results show that Alternaria spores are transported over long distances from the PP to Poland. These spores may markedly increase local exposure to Alternaria spores in the receptor area and pose a risk to both human and plant health. Alternaria spores followed the same atmospheric route as previously described LDT ragweed pollen, revealing the existence of an atmospheric super highway that transports bioaerosols from the south to the north of Europe

Contrasting pathways to ombrotrophy in three raised bogs from Ireland and Cumbria, England

The plant macrofossil records from three raised bogs from western and central Ireland and from Cumbria were compared to investigate variations in the character and timing of the fen-bog transition (FBT). Two modes of raised or ombrotrophic peat formation were recognized. In the first mode the transition develops through a sedge-fen stage directly to raised-bog lawn, maintaining a near surface water table throughout the FBT (Abbeyknockmoy Bog). The second mode is characterized by a switch from fen or reedswamp to a dry Eriophorum-dominated mire type, suggestive of low or unstable water tables (Mongan Bog and Bolton Fell Moss). Comparisons with the Holocene effective precipitation record suggest that the type of transition and its timing may be affected by the prevailing climate regime. All that is required for ombrotrophy is a separation of the growing peat surface from the influence of ground and surface waters. This separation may be achieved by rapid peat accumulation in a moist climate, the accumulation of decay-resistant Eriophorum vaginatum hummocks or by a lowering of the water table, leading to a 'perched peat bed'. In the latter two cases, a 'pseudo-raised bog' community often persists, laying down highly humified peat, until increased oceanicity enables Sphagnum to dominate