Modelling analysis of source regions of long-range transported birch pollen that influences allergenic seasons in Lithuania

This study analyses the spatial and temporal distribution of regional and long-range transported birch (Betula L.) pollen in Lithuania and the neighbouring countries. The potential long-range transport cases of birch pollen in Lithuania were analysed for the whole period of available observations, 2004–2007. The birch pollen was recorded at three measurement stations in Lithuania by using Hirst-type volumetric spore traps. The phenological observations in Lithuania were also used for the detection of potential long-range transport-induced episodes. Two variants of the regional and continental scale atmospheric dispersion model SILAM (Lagrangian and Eulerian) in an adjoint mode (used for inverse dispersion modelling and data assimilation), and the trajectory model HYSPLIT were employed to evaluate the source origins of the observed pollen. During four seasons in 2004–2007, we found in total 24 cases, during which remarkable pollen concentrations were recorded before the local flowering season. According to modelling, most of these were originated from the sources outside Lithuania: Latvia, southern Sweden, Denmark, Belarus, Ukraine and Moldova, possibly, also coastal regions of Germany and Poland. Two episodes were attributed to local early-flowering birch trees. The spatial and temporal patterns of the long-range transport of early pollen to Lithuania were found out to be highly variable; the predicted source regions for the cases considered were similar only for some dates in 2004 and 2006. During the analysed period, we found both cases, in which the predictions of the SILAM model variants and those of the HYSPLIT model were similar, and cases, in which there were substantial differences. In general, for complicated atmospheric circulation patterns the model predictions can be drastically different, with a tendency of trajectory model to fail reproducing the key episode features.     

Towards numerical forecasting of long-range air transport of birch pollen: theoretical considerations and a feasibility study

This paper considers the feasibility of numerical simulation of large-scale atmospheric transport of allergenic pollen. It is shown that at least small grains, such as birch pollen, can stay in the air for a few days, which leads to a characteristic scale for their transport of ∼10³ km. The analytical consideration confirmed the applicability of existing dispersion models to the pollen transport task and provided some reference parameterizations of the key processes, including dry and wet deposition. The results were applied to the Finnish Emergency Dispersion Modelling System (SILAM), which was then used to analyze pollen transport to Finland during spring time in 2002–2004. Solutions of the inverse problems (source apportionment) showed that the main source areas, from which the birch flowering can affect Finnish territory, are the Baltic States, Russia, Germany, Poland, and Sweden—depending on the particular meteorological situation. Actual forecasting of pollen dispersion required a birch forest map of Europe and a unified European model for birch flowering, both of which were nonexistent before this study. A map was compiled from the national forest inventories of Western Europe and satellite images of broadleaf forests. The flowering model was based on the mean climatological dates for the onset of birch forests rather than conditions of any specific year. Utilization of probability forecasting somewhat alleviated the problem, but the development of a European-wide flowering model remains the main obstacle for real-time forecasting of large-scale pollen distribution.     

Long distance pollen transport cause problems for determining the timing of birch pollen season in Fennoscandia by using phenological observations

The male flowering and leaf bud burst of birch take place almost simultaneously, suggesting that the observations of leaf bud burst could be used to determine the timing of birch pollen release. However, long‐distance transport of birch pollen before the onset of local flowering may complicate the utilization of phenological observations in pollen forecasting.

We compared the timing of leaf bud burst of silver birch with the timing of the stages of birch pollen season during an eight year period (1997–2004) at five sites in Finland. The stages of the birch pollen season were defined using four different thresholds: 1) the first date of the earliest three‐day period with airborne birch pollen counts exceeding 10 grains m^?3 air; and the dates when the accumulated pollen sum reaches 2) 5%; 3) 50% and 4) 95% of the annual total. Atmospheric modelling was used to determine the source areas for the observed long‐distance transported pollen, and the exploitability of phenological observations in pollen forecasting was evaluated.

Pair‐wise comparisons of means indicate that the timing of leaf bud burst fell closest to the date when the accumulated pollen sum reached 5% of the annual total, and did not differ significantly from it at any site (p<0.05; Student‐Newman‐Keuls test). It was found that the timing of leaf bud burst of silver birch overlaps with the first half of the main birch pollen season. However, phenological observations alone do not suffice to determine the timing of the main birch pollen season because of long‐distance transport of birch pollen.     

Factors that determine the severity of <Emphasis Type="Italic">Betula</Emphasis> spp. pollen seasons in Poland (Poznań and Krakow) and the United Kingdom (Worcester and London)

The aim of this paper is to analyse variations in the severity of Betula pollen seasons, particularly in relation to meteorological parameters at four sites, Poznań and Krakow in Poland, and Worcester and London in the United Kingdom. Results show that there is a significant relationship between Betula pollen season severity and weather conditions both in the year before pollination and in the same year that pollen is released from the plant. Furthermore, it is likely that the magnitude of birch pollen seasons in Poznań, Worcester and London is linked in some way to different phases of the North Atlantic Oscillation (NAO). Significant positive relationships exist between birch pollen counts at Poznań and temperatures, rainfall and averages of the NAO in the year before pollination. An opposite relationship is evident at the two sites studied in the United Kingdom. There were significant positive correlations between the severity of birch pollen seasons recorded at Worcester and temperatures and averages of the NAO during the winter and spring in the year of pollination, and negative correlations at both Worcester and London with similar variables from the previous year. In addition, Betula pollen seasons in Krakow do not appear to be influenced by the NAO, which is probably the result of Krakow having a more continental climate.     

Birch pollen production,transport and deposition for the period 1984–1993 at Kevo,northernmost Finland

Summary Betula pollen production and flowering, pollen transport and pollen deposition are considered for the mountain birch region of northern Finland for the ten-year period 1984–1993. The most abundant flowering year was 1989 and, after that, 1985. In these years the highest values were also recorded for pollen in the air. There is a significant correlation between the amount of pollen released and the thermal sum of the previous year. In terms of pollen deposition the peak years were 1989 and 1986. The correlation between the amount of pollen in the air and that being deposited on the ground is also statisticaly significant. It is evident that some birch pollen is already present in the air before local flowering begins and that, in some years, this non-local pollen can account for more than 20% of the yearly total. This preflowering proportion was highest in 1985 and 1993, the latter being a prolific flowering year in the south of the country. There is a clear relationship between the proportion of the non-local pollen in the air and the proportion ofBetula pubescens/pendula type pollen deposited on the ground and, conversely, there is a significant correlation between the amount of local pollen in the air and the amount ofBetula tortuosa plusB. nana type pollen being deposited on the ground. The questions both of the viability of this long-distance pollen and of its ability to cause allergic reactions are considered. An assessment is also made of the degree to which fossil birch pollen assemblages can be realistically interpreted in terms of local vegetation if a varying proportion of the same pollen type is non-local.     

Variations and trends of <Emphasis Type="Italic">Betula</Emphasis> pollen seasons in Moscow (Russia) in relation to meteorological parameters

This study investigates possible links of meteorological data and the start date, end date, duration, date of peak, peak value and Seasonal Pollen Index (SPI) of birch pollen seasons recorded in Moscow, Russia, during 1993–2015. Pollen data were collected by a volumetric spore trap. Correlation analysis was used to study relationships between various parameters of pollen seasons. Simple linear regression analysis was conducted to investigate trends over time; multiple stepwise regression analysis was used to describe SPI fluctuations as a function of seasonal or monthly climatic parameters. Air temperatures increased significantly during the study period, but no effect on the timing of the birch pollen season was found. Only the severity of the season showed significant changes that can be considered as a consequence of global warming. Rainfall in May and June of the year preceding flowering, total rainfall in the 40-day pre-season period and average temperature during the pollination were shown to be the most important parameters affecting birch pollen concentrations.     

The start of the birch pollen season in Finnish Lapland: separating non‐local from local birch pollen and the implication for allergy sufferers

Determining the start of the birch pollen season requires the reliable separation of non‐local from locally produced birch pollen. The research was undertaken close to the latitudinal birch tree line at the Kevo Subarctic Research Institute (69°45′N 27°01′E) in northern Finland. By comparing phenological and aerobiological observations, the proportion of birch pollen present in the air before local anthesis commences can be delimited. We coupled this with data of pollen deposition monitored by means of a modified Tauber trap. The dominant birch species at Kevo is the mountain birch Betula pubescens ssp. czerepanovii, whereas B. pubescens ssp. pubescens is very rare, hence we consider the proportion of the southerly B. pubescens‐type pollen deposited in the pollen trap to be non‐local in origin.

We did not observe any trend towards an earlier start of the phenologically observed mountain birch anthesis at Kevo as predicted from work elsewhere. Moreover, the fixed 2.5% threshold method for determining the birch pollen season proved not to be applicable since in many years this threshold was reached before the end of continuous snow cover. The results indicate that in some years non‐local birch pollen contributes considerably to the allergen load in Lapland with up to 57% of the total birch pollen sum being recorded before the day on which local anthesis commenced, and up to 70% of the annual birch pollen deposited being of the southerly birch type.     

Variations and trends of birch pollen seasons during 15 years (1996–2010) in relation to weather conditions in Poznań (western Poland)

Birch (Betula) pollen seasons were examined in relation to meteorological conditions in Poznań (1996–2010). Birch pollen grains were collected using a volumetric spore trap. An alternate biennial cycle of birch pollen season intensity was noticed in Poznań. The main factors influencing birch pollen season intensity were average daily minimum temperatures during the second fortnight of May and the month of June one year before pollination as well as the intensity of the pollen season of the previous year. Most of the pollen grains are recorded during the first week of the season; the number of pollen grains recorded at this time is positively correlated with mean maximum temperature and negatively correlated with daily rainfall. The significant effect of rainfall in reducing the season pollen index was noticed only during weak pollen seasons (season pollen index <?mean). In addition, mean daily maximum temperature during the first two weeks of the birch pollen season markedly influences its duration. No significant trends in duration and intensity of the pollen season were recorded, however, a slight tendency towards early pollination was observed (?0.4 days/year, p?=?0.310).     

Copenhagen – a significant source of birch (Betula) pollen?

Current aerobiological research applies the hypothesis that the main source of atmospheric birch (Betula) pollen is forest trees. Our results indicate that the measured levels in Copenhagen are not only due to birch trees in Danish forests but that the urban areas also seem to be a significant source of birch pollen. A number of episodes in 2003 with enhanced pollen levels in Copenhagen seem to be associated with parks and gardens inside and just outside the city. Our results also indicate one long-range transport episode from remote sources in Poland and Germany. Finally, our results show that the pollen levels vary considerably over the day and geographically between Copenhagen and the city of Roskilde, 40 km away. We suggest, that these differences in time and space in the pollen levels are mapped using an integrated monitoring strategy.     

Long-distance transport ofBetula pollen grains and allergic symptoms

Summary An example of the potential importance of air masses as carriers of aero-allergens from distant source areas is provided. Considerable amount ofBetula pollen is relatively often transported to Fennoscandia before the local birch flowering period, mainly by southeastern air masses from eastern part of central Europe. Although the distance and the transport time in some cases can be extensive, the pollen grains seem to cause allergic reactions among sensitive persons.A comparison between the clinical results andBetula pollen counts from the time before the local flowering season in Stockholm in 1989 is presented.     

Live pine pollen in rainwater: reconstructing its long-range transport

Raindrops brim with pollen even when there is no ambient local pollen. How does this nonlocal pollen get inside rain? The likely answer is long-range transport beneath or inside clouds. To test this hypothesis, we captured rain-delivered pollen on Ocracoke Island, NC, USA over a 12-day interval before local pine pollen release then reconstructed its trajectory and its atmospheric exposure conditions. Findings were as follows: four rain episodes yielded a total of 632 pollen grains of which 6.7% germinated. To find pollen sources, we first identified pollen-releasing forested areas using a predictive heat sum equation for each rain episode. Next, we constructed the backward trajectory for air parcels carrying rain-delivered pollen from those forests using the MLDP atmospheric transport and dispersion model. Nonlocal sources were located at distances up to 300 km from Ocracoke Island and distances lessened with each successive episode. Below-cloud transport time was 8 and 17 h for Episodes A and B, respectively. Pollen grains were exposed to harsh atmospheric conditions during below-cloud transport, yet some grains still germinated. Atmospheric turbulence patterns changed for each episode, so distance from pollen source was poorly correlated with pollen transport time. Pollen germination was not closely correlated with either distances or transport time. In-cloud transport was more likely for pollen sampled during Episodes C and D. Pine pollen, although rarely allergenic, brings fresh insights into how atmospheric events can trigger human respiratory distress.

     

A long-term study of winter and early spring tree pollen in the Tulsa, Oklahoma atmosphere

Since 1986 the atmosphere in Tulsa, Oklahoma has been monitored for airborne pollen and spores with a Burkard 7-day spore trap situated on the roof of a building at The University of Tulsa. The present study specifically examined the early spring tree pollen season for several local taxa and the occurrence of pre-season pollen during December and January. Knowledge of the local pollen season will help identify the presence of out-of-season pollen and possible long distance transport (LDT) events. Average daily concentrations of airborne pollen for species ofBetula, Quercus, Ulmus, and Cupressaceae were determined for each year from 1987 to 1996. The data showed that during the early spring the precise pollination periods for these allergenic tree species are highly variable. There were considerable variations in start date, season length, peak concentration, date of peak, and cumulative season total. The start dates forUlmus, Betula, andQuercus varied by 30 days or more, while the early spring Cupressaceae pollen showed the least variation in start date (only 23 days). More research is needed to understand the mechanisms which govern the onset and magnitude of pollen release. Although several reports have documented episodes of long distance transport (LDT) of pollen, the actual contribution of out-of-season or out-of-region pollen to local air spora is poorly known. The current study also re-examined the LDT ofJuniperus ashei pollen in Oklahoma.Juniperus pollen appeared in the Tulsa atmosphere on 40% of the days in December and January with concentrations as high as 2400 pollen grains/m³ of air; however, no local populations ofJuniperus pollinate at this time of the year. High concentrations occurred on days with southerly winds suggesting thatJuniperus ashei populations in southern Oklahoma and Texas were the pollen source. Since no local pollen is present in the Tulsa atmosphere in December and January, this example of LDT has been easy to document.     

Contribution of upwind pollen sources to the characterization of Juniperus ashei phenology

Local and long-range components of Juniperus ashei pollen deposition were isolated to provide a more accurate record of local pollination activity in the Arbuckle Mountains of south central Oklahoma. An aerobiological sampler recorded airborne pollen concentrations and deposition at the sample site from mid-December 1998 to the end of January 1999. Grid-based weather data was used to model the movement, position, and elevation (air mass trajectories) across the region. While a normal concentration distribution is expected for a pollination event at a single site, "very high" concentrations (>1500 pollen grains per cubic meter) creating "peaks" in the deposition record were identified using bi-hourly sample analysis of the pollen registrations in the sampler. These occurrences happened over a 2 1/2 week period beginning January 11 and are coincident with the occurrence of southerly winds throughout the region. Modeled trajectories indicate that the air masses associated with those occurrences traveled at ground level through the J. ashei population on the Edwards Plateau, some 200 kilometers to the south in Texas, then gained altitude prior to crossing the sample site, thus introducing a long-range pollen component at the sample site. Peaks with "high" concentrations (90 to 1500 pollen grains per cubic meter) were evaluated using the same methodology. Those peaks associated with trajectories having the potential of introducing a long-range component to the pollen deposition record were removed from the aerobiological record. The resulting adjusted aerobiological record shows a more normal pollen concentration distribution, reduced hourly variability, and a marked shift in the pollination initiation date. Based on the comparison of non-adjusted and adjusted aerobiological records, contributions from upwind pollen sources account for 55% of the total pollen record.     

Allergic symptoms caused by long-distance transported birch pollen

Birch pollen allergy is very common in northern Sweden, and the local flowering season never starts before the middle part of May. In the last week of April 1989 patients with birch pollen allergy developed typical symptoms requiring treatment. This pattern was confirmed in a group of patients who registered their symptoms in diaries, while contemporaneous pollen measurements demonstrated high amounts of birch pollen in the air. At that time in the northern part of Sweden, however, no birches were flowering. Meteorological data indicated that strong winds from the south-east during the period transported birch pollen from the Baltic states. Similar weather conditions in 1982, 1984 and in 1990 have also resulted in high amounts of birch pollen in the air long before the local flowering season. It is concluded that long distance transport of pollen may result in clinically significant allergy problems before, and even after the normal local season.     

The contribution of long-distance transport to the presence of <Emphasis Type="Italic">Ambrosia</Emphasis> pollen in central northern Italy

Ragweed is an allergenic weed of public health concern in several European countries. In Italy ragweed occurs prevalently in north-north-eastern regions, where sensitization is increasing. Because of the small diameter of pollen grains, ragweed pollen is often involved in episodes of long-range transport, as already shown in central Italy. The objective of this study was to evaluate the extent of such transport by comparing pollen and meteorological data for two northern Italian cities (Parma and Mantova) with data from Pistoia and Florence in central Italy. In 2002 and 2004 peaks in ragweed pollen levels were detected in these four cities on the same day, and concentrations of the grains were above clinical thresholds. Weather-map analysis and computation of back-trajectories showed that air masses from eastern Europe might carry ragweed pollen to a wide area of central and northern Italy. These findings suggest that episodes of long-range transport of ragweed pollen could be clinically relevant, resulting in sensitization of a large number of people. The results might provide a basis for monitoring and forecasting periods of long-distance transport with the objective of reducing their effects on allergic patients.     

Integration of flowering dates in phenology and pollen counts in aerobiology: analysis of their spatial and temporal coherence in Germany (1992–1999)

We studied the possibility of integrating flowering dates in phenology and pollen counts in aerobiology in Germany. Data were analyzed for three pollen types (Betula, Poaceae, Artemisia) at 51 stations with pollen traps, and corresponding phenological flowering dates for 400 adjacent stations (< 25 km) for the years 1992–1993 and 1997–1999. The spatial and temporal coherence of these data sets was investigated by comparing start and peak of the pollen season with local minima and means of plant flowering. Our study revealed that start of birch pollen season occurred on average 5.7 days earlier than local birch flowering. For mugwort and grass, the pollen season started on average after local flowering was observed; mugwort pollen was found 4.8 days later and grass pollen season started almost on the same day (0.6 days later) as local flowering. Whereas the peak of the birch pollen season coincided with the mean flowering dates (0.4 days later), the pollen peaks of the other two species took place much later. On average, the peak of mugwort pollen occurred 15.4 days later than mean local flowering, the peak of grass pollen catches followed 22.6 days after local flowering. The study revealed a great temporal divergence between pollen and flowering dates with an irregular spatial pattern across Germany. Not all pollen catches could be explained by local vegetation flowering. Possible reasons include long-distance transport, pollen contributions of other than phenologically observed species and methodological constraints. The results suggest that further research is needed before using flowering dates in phenology to extrapolate pollen counts.     

Are the birch trees in Southern England a source of <Emphasis Type="Italic">Betula</Emphasis> pollen for North London?

Birch pollen is highly allergenic. Knowledge of daily variations, atmospheric transport and source areas of birch pollen is important for exposure studies and for warnings to the public, especially for large cities such as London. Our results show that broad-leaved forests with high birch tree densities are located to the south and west of London. Bi-hourly Betula pollen concentrations for all the days included in the study, and for all available days with high birch pollen counts (daily average birch pollen counts >80 grains/m³), show that, on average, there is a peak between 1400 hours and 1600 hours. Back-trajectory analysis showed that, on days with high birch pollen counts (n = 60), 80% of air masses arriving at the time of peak diurnal birch pollen count approached North London from the south in a 180 degree arc from due east to due west. Detailed investigations of three Betula pollen episodes, with distinctly different diurnal patterns compared to the mean daily cycle, were used to illustrate how night-time maxima (2200–0400 hours) in Betula pollen counts could be the result of transport from distant sources or long transport times caused by slow moving air masses. We conclude that the Betula pollen recorded in North London could originate from sources found to the west and south of the city and not just trees within London itself. Possible sources outside the city include Continental Europe and the Betula trees within the broad-leaved forests of Southern England.     

Construction,validation, and application of nocturnal pollen transport networks in an agro‐ecosystem: a comparison using light microscopy and DNA metabarcoding

1. Moths are globally relevant as pollinators but nocturnal pollination remains poorly understood. Plant–pollinator interaction networks are traditionally constructed using either flower‐visitor observations or pollen‐transport detection using microscopy. Recent studies have shown the potential of DNA metabarcoding for detecting and identifying pollen‐transport interactions. However, no study has directly compared the realised observations of pollen‐transport networks between DNA metabarcoding and conventional light microscopy. 2. Using matched samples of nocturnal moths, we constructed pollen‐transport networks using two methods: light microscopy and DNA metabarcoding. Focussing on the feeding mouthparts of moths, we developed and provide reproducible methods for merging DNA metabarcoding and ecological network analysis to better understand species interactions. 3. DNA metabarcoding detected pollen on more individual moths, and detected multiple pollen types on more individuals than microscopy, although the average number of pollen types per individual was unchanged. However, after aggregating individuals of each species, metabarcoding detected more interactions per moth species. Pollen‐transport network metrics differed between methods because of variation in the ability of each to detect multiple pollen types per moth and to separate morphologically similar or related pollen. We detected unexpected but plausible moth–plant interactions with metabarcoding, revealing new detail about nocturnal pollination systems. 4. The nocturnal pollination networks observed using metabarcoding and microscopy were similar yet distinct, with implications for network ecologists. Comparisons between networks constructed using metabarcoding and traditional methods should therefore be treated with caution. Nevertheless, the potential applications of metabarcoding for studying plant–pollinator interaction networks are encouraging, especially when investigating understudied pollinators such as moths.     

Elevated birch pollen episodes in Denmark: contributions from remote sources

The purpose of this study was to investigate the relationship between possible long-distance transport of birch pollen and episodes of elevated concentration in Denmark. By analysis of a twenty-six year (1980–2006) time-series of bi-hourly birch pollen counts from two sites (Copenhagen and Viborg) episodes of elevated counts (more than 100 grains) were identified in fewer than 2% of cases. Trajectory analysis showed that such episodes are primarily associated with long-distance transport from Eastern Europe and Scandinavia (43 and 33% of events, respectively); the lowest contribution originated from the British Isles. Long-term episodes (as in 1993 and 2006) occurred when atmospheric conditions favored long-distance transport from several source regions in succession.     

Source areas and long-range transport of pollen from continental land to Tenerife (Canary Islands)

The Canary Islands, due to their geographical position, constitute an adequate site for the study of long-range pollen transport from the surrounding land masses. In this study, we analyzed airborne pollen counts at two sites: Santa Cruz de Tenerife (SCO), at sea level corresponding to the marine boundary layer (MBL), and Izaña at 2,367 m.a.s.l. corresponding to the free troposphere (FT), for the years 2006 and 2007. We used three approaches to describe pollen transport: (1) a classification of provenances with an ANOVA test to describe pollen count differences between sectors; (2) a study of special events of high pollen concentrations, taking into consideration the corresponding meteorological synoptic pattern responsible for transport and back trajectories; and (3) a source–receptor model applied to a selection of the pollen taxa to show pollen source areas. Our results indicate several extra-regional pollen transport episodes to Tenerife. The main provenances were: (1) the Mediterranean region, especially the southern Iberian Peninsula and Morocco, through the trade winds in the MBL. These episodes were characterized by the presence of pollen from trees (Casuarina, Olea, Quercus perennial and deciduous types) mixed with pollen from herbs (Artemisia, Chenopodiaceae/Amaranthaceae and Poaceae wild type). (2) The Saharan sector, through transport at the MBL level carrying pollen principally from herbs (Chenopodiaceae-Amaranthaceae, Cyperaceae and Poaceae wild type) and, in one case, Casuarina pollen, uplifted to the free troposphere. And (3) the Sahel, characterized by low pollen concentrations of Arecaceae, Chenopodiaceae-Amaranthaceae, Cyperaceae and Poaceae wild type in sporadic episodes. This research shows that sporadic events of long-range pollen transport need to be taken into consideration in Tenerife as possible responsible agents in respiratory allergy episodes. In particular, it is estimated that 89–97% of annual counts of the highly allergenous Olea originates from extra-regional sources in southern Iberia and northern Africa.