Testate Amoebae Analysis Research Articles

Response of arboreal pollen abundance to late-Holocene drought events in the Upper Midwest, USA

The impact of short-term climate anomalies and disturbances on past plant communities can be understood using high temporal or contiguous sedimentary pollen analysis. The response of pollen assemblages to decadal- to multidecadal-scale moisture variability was analyzed for the time intervals 3000–2200 and 1400–500 cal. yr BP. The hydroclimate and vegetation history for Minden Bog in southeastern Michigan were reconstructed using analyses of sedimentary testate amoebae and pollen. Results indicated that moisture anomalies accounted for 3% to 24% of the variation in arboreal pollen abundance for Fagus, Pinus, Quercus, and Tsuga. Betula pollen percentages did not appear to be affected by moisture variability. Given the longevity of these taxa, rapid arboreal pollen assemblage responses to moisture variability at decadal to multidecadal timescales were likely due to climate-induced changes in pollen productivity. Our data suggest that pollen–climate relationships may be counterintuitive at these fine temporal scales. For example, Tsuga pollen percentages generally increased during short-term dry events, in contrast to expected decreases in abundance with drying at millennial timescales based on empirical pollen–climate relationships. Results suggest caution should be used when inferring subdecadal to multidecadal climate variation from highly resolved pollen records. Rather, high-resolution pollen data may more accurately represent superimposed plant responses that are the composite of reproductive output nested within long-term plant community compositional changes in response to climatic variation.

How a Sphagnum fuscum‐dominated bog changed into a calcareous fen: the unique Holocene history of a Slovak spring‐fed mire

AbstractIn general, mires develop by autogenic succession from more groundwater‐fed to more rainwater‐fed. This study from a calcareous mire in the West Carpathians (Slovakia) describes a similar development in the Early Holocene, followed by a reverse development in the Middle and Late Holocene. Pollen, macrofossil and testate amoeba analyses show that the site started as a minerotrophic open fen woodland. After 10 700 cal a BP autogenic succession led to the accumulation of at least 1 m of Sphagnum fuscum peat. Around 9000 cal a BP, as climate could no longer sustain a stable water regime, the bog desiccated and a fire broke out. The fire removed part of the peat layer and as a consequence relative water levels rose, leading to the establishment of a wet minerotrophic swamp carr with Thelypteris palustris, Equisetum sp. and Alnus sp. with extremely slow peat accumulation. After 600 cal a BP, rapid peat accumulation with calcareous tufa formation resumed as a result of anthropogenic deforestation and hydrological changes in the catchment and resulting increased groundwater discharge. At present the mire still hosts a wealth of relict and endangered plant and animal species typical of calcareous fens and fen meadows. Copyright © 2011 John Wiley & Sons, Ltd.

Holocene carbon accumulation rates from three ombrotrophic peatlands in boreal Quebec, Canada: Impact of climate-driven ecohydrological change

Understanding the processes controlling peatland carbon (C) sequestration is critical to anticipate potential changes in the global C cycle in response to climate change. Although identification of these factors may be relatively straightforward on seasonal timescales, at centennial to millennial timescales complexities arise because of interactions between climate, vegetation, hydrology and long-term ecological processes. To better understand the factors controlling long-term C accumulation, Holocene rates of C sequestration were quantified from three pristine ombrotrophic peatlands in boreal Quebec, northeastern Canada (52°N, 75–76°W). Bulk density and loss-on-ignition analyses, combined with radiocarbon dating and age–depth modelling, were used to estimate long-term apparent rates of carbon accumulation. Past changes in vegetation and water-table depth were obtained from plant macrofossil and testate amoeba analysis. Earliest regional peat accumulation started ~7520 cal. BP, with long-term rates of C sequestration varying between 14.9 and 22.6 g/m2 per yr. High C sequestration rates occurred during the mid Holocene when relatively stable Sphagnum section Acutifolia communities were present, while low rates were found during the cooler late Holocene when Cyperaceae and ligneous vegetation were more dominant. However, C sequestration was highly variable among cores, implying that local topography, geomorphology and hydrology, or disturbance factors such as fire, mediate the influence of climate on C accumulation. Reconstructed water-table depths reveal several dry shifts since 3000 cal. BP, suggesting that episodic cold and dry conditions during the late Holocene may have contributed to lower C sequestration rates. Given the intensity of the water-table shifts at these times, we hypothesize that recurrent episodes of frozen subsurface peat might have intensified surface drying. As projected by climate scenarios, anticipated warmer and wetter conditions may lead to greater stability of hummock Sphagna cover and increased C sequestration potential in boreal peatlands.

The relationship of fine-resolution, multi-proxy palaeoclimate records to meteorological data at Fågelmossen, Värmland, Sweden and the implications for the debate on climate drivers of the peat-based record

Fluctuations in bog surface wetness (BSW) over an 86-year period were reconstructed using fine-resolution analyses of testate amoebae, plant macrofossils and peat humification from Fågelmossen, an ombrotrophic bog in western Sweden. Results were compared with local instrumental temperature and precipitation data and reconstructed values of total seasonal water table deficit using an age–depth model based on spheroidal carbonaceous particle analysis and a historically dated, geochemically typed tephra layer. Statistically significant correlations between decadal means of the fine-resolution data and climate parameters lend support to the notion that a climate signal may be present in those data, enhancing confidence in the peat-based record to address pressing research questions on abrupt climate change. All three proxies were correlated most significantly with annual precipitation, plant macrofossils only when correlations were time-lagged by 10 years, suggesting that precipitation, rather than temperature, is the primary driver of the BSW record at Fågelmossen. However, plant macrofossils also correlated significantly with annual temperature when time-lagged by 10 years. The correlation of individual physical and biological proxies with climate parameters on different time-scales, coupled with the significant correlation of plant macrofossil results with annual temperature in addition to annual precipitation, may bring into question the use of composite curves of BSW that combine results from multi-proxy studies. The correlations reported here partly support those from other similar studies, but highlight that regional variability may be greater than previously hypothesised and that it may not be possible to apply a single explanation of climatic forcing where bog surface wetness reconstructions are concerned.

Analysis of fossil testate amoebae in Selisoo Bog, Estonia: local variability and implications for palaeoecological reconstructions in peatlands

Niinemets, E., Pensa, M. & Charman, D. J. 2010: Analysis of fossil testate amoebae in Selisoo Bog, Estonia: local variability and implications for palaeoecological reconstructions in peatlands. Boreas, 10.1111/j.1502-3885.2010.00188.x. ISSN 0300-9483. Local variability in decadal water-table changes on an ombrotrophic peatland was explored using testate amoebae analysis of near-surface peats in an Estonian raised bog. The distribution of testate amoebae assemblages was studied along the gradient from hummock to hollow in the upper 30-cm layer of peat. As expected, testate amoebae assemblages in different micro-ecotypes from hummock to hollow, even as close as 10 m apart, are distinctly different. Past water-table change was reconstructed by applying a transfer function based on modern samples from throughout Europe. Results show a decline in water level from the mid-late 20th century on Selisoo bog in all profiles from the different micro-ecotypes. However, the absolute water-table depths and amplitudes of fluctuations vary between reconstructions from different sampling micro-ecotypes. Cores were correlated using changes in non-mire pollen concentrations down-core, but it was not possible to correlate minor changes in water-table owing to non-contiguous sampling and variable accumulation rates. We conclude that different microtopes show the same decadal trends in relative water-table change but that the absolute magnitude of change may be more variable locally. It is important that reconstructed palaeohydrological changes in bogs consider changes in bog micro-ecotypes, and their variation over time, as this may alter the sensitivity of an individual record to drivers such as climate change. Comparison and compilation of data from parallel cores from different micro-ecotypes and/or different sites are likely to provide more robust reconstructions.

Can testate amoeba‐based palaeohydrology be extended to fens?

AbstractNumerous palaeoecological studies have used testate amoeba analysis to reconstruct Holocene hydrological change in peatlands, and thereby past climatic change. Current studies have been almost exclusively restricted to ombrotrophic bogs and the period since the fen–bog transition. Although the critical link between peatland surface wetness and climate is less direct in minerotrophic peatlands, such records may still be of value where there are few others, particularly if multiple records can be derived and inter‐compared. Expanding the temporal and spatial scope of testate amoeba‐based palaeohydrology to minerotrophic peatlands requires studies to establish the primacy of hydrology and the efficacy of transfer functions across a range of sites. This study analyses testate amoeba data from wetlands spanning the trophic gradient in the eastern Mediterranean region. Results demonstrate that different types of wetlands have distinctly different amoeba communities, but hydrology remains the most important environmental control (despite water table depth being measured at different times for different sites). Interestingly, Zn and Fe emerge as significant environmental variables in a subset of sites with geochemical data. Testate amoeba–hydrology transfer functions perform well in cross‐validation but frequently perform poorly when applied to other sites, particularly with sites of a different nutrient status. It may be valid to use testate amoebae to reconstruct hydrological change from minerotrophic peatlands with an applicable transfer function; however, it may not be appropriate to use testate amoebae to reconstruct hydrological change through periods of ecosystem evolution, particularly the fen–bog transition. In practice, the preservation of amoeba shells is likely to be a key problem for palaeoecological reconstruction from fens. Copyright © 2010 John Wiley & Sons, Ltd.

The methodological basis for fine-resolution, multi-proxy reconstructions of ombrotrophic peat bog surface wetness

The need for Holocene peat-based palaeoclimatic records of increased temporal resolution has been widely identified in recent research. The often rapid growth rates of ombrotrophic bogs, when combined with fine-resolution (i.e. millimetre-scale) sampling, provide an as yet largely unexploited potential to derive sub-decadal palaeoclimatic data from this proxy-archive. However, multi-proxy, fine-resolution analyses require changes to standard methodologies, and the application of sampling techniques that are new to peat-based palaeoclimate research. A peat sampler was custom-built to allow precise and replicable millimetre-scale subsampling. Subsequent methodological testing revealed that, irrespective of sample thickness (i.e. resolution), halving the standard sample volume used for plant macrofossil (from 4 cm3 to 2 cm3) and testate amoebae (from 2 cm3 to 1 cm3) analyses and the sample weight used for peat humification analysis (from 0.2 g to 0.1 g dried peat) did not affect the interpretation of the results. A contiguous 1-mm sampling resolution for plant macrofossil analysis was also tested, but it was found that contiguous 5-mm samples provided a more reliable background record to fine-resolution testate amoebae and peat humification analyses. Based on these findings, a standardized and systematic methodological approach was developed, using the custom-built peat slicer to take millimetre-scale samples that provide enough sample material for both testate amoebae and peat humification analyses to be performed at 1-mm resolution. This approach will facilitate the testing of the palaeoclimatic reliability of multi-proxy, fine-resolution peat-based records.

Late Holocene paleoecohydrology and carbon accumulation estimates from two boreal peat bogs in eastern Canada: Potential and limits of multi-proxy archives

The stratigraphy of four peat sequences collected in two peat bogs located in the Eastmain River watershed (52° N, 76° W), James Bay lowlands, Québec, Canada, was investigated to reconstruct past hydroclimatic conditions of peat accumulation and associated carbon dynamics during the late Holocene. Analyses of macrofossils, testate amoebae, peat humification, C/N ratio and bulk density were performed at high-resolution along each peat core, allowing the potential of each proxy indicator under varying nutrient status and hydroclimatic conditions to be evaluated. Some synchronous changes were recorded both within and between peatlands, suggesting the influence of allogenic factors in the development of these peatlands. Other reconstructed changes have highlighted autogenic succession processes related to the local geomorphic and hydrologic context. Highest peat carbon accumulation rates (LORCA) were correlated with either wet conditions or high woody debris percentages, suggesting that residence time of the biomass in the acrotelm and the nature of plant material can both influence carbon accumulation rates in peat bogs. This study provides the first high-resolution paleoecohydrological reconstructions from the mid-boreal ecoregion of eastern Canada, a region in which peatlands occupy 30 to 60% of the land surface.

Reconstruction of recent sea-level change using testate amoebae

Proxy-based sea-level reconstructions place the instrumentally observed rates of recent sea-level rise in a longer term context by providing data that extend the instrumental sea-level record into past centuries. This paper presents the first sea-level reconstructions based on analyses of testate amoebae, to test their ability to produce high-precision reconstructions of past sea level. We present two reconstructions for the past 100 yr from sites in Maine (USA) and Nova Scotia (Canada) based on short cores from salt marshes, and modern training data from North America and the United Kingdom. These are compared with tide-gauge records and reconstructions based on foraminifera from the same cores. The reconstructions show good agreement with both the tide-gauge data and the foraminifera-based reconstructions. The UK data perform well in predicting known elevations of North American surface samples and produce sea-level reconstructions very similar to those based on the North American data, suggesting the methodology is robust across large geographical areas. We conclude that testate amoebae have the potential to provide robust, higher precision sea-level reconstructions for the past few centuries if modern transfer functions are improved and core sites are located within the main zone of testate amoebae occurrence on the salt marsh.

Effects of climatic change and bog development on Holocene tufa formation in the Lorze Valley (central Switzerland)

A massive tufa complex in the lower Lorze Valley (550 m a.s.l., north-central Switzerland) formed between 9000 and 5000 cal. yr BP. In the plain 4 km southeast of the complex lies Neugrundmoor (830 m a.s.l.), a mire in the hydrologic recharge area of the springs responsible for the tufa formation. Here we address an earlier, untested hypothesis that the transition of Neugrundmoor from fen to raised bog caused the end of the tufa formation, by means of pollen and testate amoebae analyses on a peat section. The chronology of the section is based on ten AMS 14C-dates of terrestrial plant macrofossils. Our results suggest that until 7100 cal. yr BP the plain had shallow ponds, which gradually developed into fens. Starting 5350 cal. yr BP, large raised bogs developed in the fens in a few centuries. This agrees with the hypothesis that the end of tufa formation coincided with the transition from fen to raised bog. It also coincided with the end of the mid-Holocene temperature optimum, when climate became cooler and wetter. We suggest that the main factor causing the end of tufa formation at 5500—5000 cal. yr BP was declining air temperatures, which on the one hand led to diminished calcium precipitation, on the other to enhanced bog formation. Peat has a low hydraulic conductivity, so we suggest that less water became available for tufa formation because of increased thickness of peat layers, exacerbating the direct effect of cooling on calcium precipitation. Noticeable human influence in the surroundings did presumably not start before c. 3500 cal. yr BP and was then very weak, so this was not responsible for the end of the tufa formation. Extrapolation of our results suggests that climatic cooling alone is sufficient to explain the widespread termination of tufa formation after the mid Holocene.

Is There a Size Limit for Cosmopolitan Distribution in Free-Living Microorganisms? A Biogeographical Analysis of Testate Amoebae from Polar Areas

A long-standing debate in microbial ecology is the extent to which free-living microorganisms exhibit cosmopolitan distributions. We use a comparison of testate amoebae communities in cold "polar" locations (Arctic, Antarctic, and Tibet) to investigate how a microorganism's size affects its probability of having a cosmopolitan distribution. We show that the probability a given taxa being reported in all three locations increases as testate size decreases. Likewise, excluding those testates found only in Tibet, very small testates (<20 microm) are more likely to occur in both the Arctic and Antarctic than in either of these poles alone. Attempting to correct for phylogeny reduces the number of statistically significant relationships--both because of decreased sample size and potentially real phylogenetic patterns, although some size-dependent effects were still apparent. In particular, taxa found in both the Arctic and Antarctic poles were significantly smaller than congeneric taxa found only in Tibet. This pattern may in part be due to habitat effects, with the Tibetan samples being more likely to have come from aquatic sites which may be more suitable for larger taxa. Overall, our analysis suggests that, at least within testate amoebae, a cosmopolitan distribution becomes increasingly common as median taxon size decreases.

Testate amoeba analysis of lake sediments: impact of filter size and total count on estimates of density, species richness and assemblage structure

Testate amoebae are informative about palaeoecological conditions, but the methods generally used for their analyses in lake sediments differ from those used for their analyses in peats, making comparisons difficult. This study examines how filter mesh size and total number of individuals counted affect species richness, Shannon diversity, equitability, density and assemblage structure. We analysed the complete testate amoeba contents of six sediment samples from Lake Lautrey, France. The abundance of testate amoebae was high (1,403–10,870 shells cm−3), and species smaller than 63 μm in both length and width represented up to 89% of total abundance and 43% of species richness. A simulation showed that using 47- or 63-μm mesh-size filters reduced inter-sample differences and changed the patterns of abundance, species richness and assemblage structure, causing loss of information and leading to potential erroneous palaeoecological interpretation. Rarefaction analyses suggest that although 170 shells are sufficient to assess the general structure of assemblages, such small sample sizes can underestimate species richness by overlooking taxa with relative abundances <4%. Total counts of 400 shells yield better estimates of assemblage structure and recover at least 50% of total species richness, although species with absolute frequencies below 2% may still be missed. Higher counts are required to obtain reliable estimates of species richness and assemblage structure in samples that have high testate amoeba densities but are dominated by a few small taxa. Further studies should determine the bioindicator value and functional roles of small and/or rare species in lakes and thus to what extent overlooking them affects palaeoecological interpretations.

A preliminary investigation into the use of testate amoebae for the discrimination of forensic soil samples

We present the results of an initial investigation into the efficacy of using testate amoebae for the discrimination of soils from wet ground and puddles, as little attention has been given to these organisms in forensic science. The preservation of testate amoebae in these sediments is generally good, although test concentrations are low. Statistical analysis suggests that testate amoebae assemblages are somewhat spatially distinct and have potential to be used for soil discrimination. A case study is presented where mineralogical (X-ray diffraction) and testate amoebae analyses are used in conjunction to clarify the scene of crime in a 'cold case' murder enquiry. Testate amoebae were recovered from dried sediment residues on clothing 10 years after the murder. Despite these promising results, further experimental work is crucial to examine the spatial and temporal variation of amoebae assemblages in water films, wet ground and puddles before they can be added to the armoury of methods available to the forensic biologist.

Distal volcanic impacts on peatlands: palaeoecological evidence from Alaska

Despite the fact that volcanic ash (tephra) layers are found preserved in peat deposits around the world, comparatively little research has investigated the impacts of distal volcanic emissions on peatlands. This study investigates the impacts of several late-Holocene volcanic eruptions on five peatlands in southern Alaska using a palaeoecological approach. Testate amoebae analysis, peat humification analysis and a basic analysis of plant macrofossil components were applied across 11 tephra layers. Changes in macrofossil and testate amoebae assemblages occur across several of the tephra layers. The humification results were considered unreliable because of a methodological problem, a finding which may have implications for other studies using this technique. Redundancy analyses on testate amoebae data show statistically significant changes associated with two tephras. The most likely causes of the impacts are volcanic gases, acidic precipitation or tephra-derived leachates. The finding that some tephras are associated with impacts whereas others are not may relate to the season of the eruption or meteorological conditions at the time of ash fall. These results suggest the sensitivity of peatlands and peatland microbial communities to distal volcanic products and imply that changes in key palaeoclimatic proxies may be caused by a mechanism independent of climate change. Implications of the results for peat-based palaeoclimatic studies are discussed, as are possible directions for future research.

The disappearance of Sphagnum imbricatum from Butterburn Flow, UK

The disappearance of the previously abundant moss species Sphagnum imbricatum has been investigated at Butterburn Flow, northern England, using organic geochemical, elemental, macrofossil, pollen and testate amoebae analyses. Variations in the assemblage of peat-forming plants were tracked using the macrofossil distributions as well as the relative chain lengths of n-alkanes and concentrations of 5- n-alkylresorcinols and triterpenols. No significant changes to the vegetation assemblage could be detected prior to the loss of S. imbricatum. Variations in water depth were reconstructed using a testate amoebae transfer function and inferred qualitatively using bulk elemental composition and biomarkers for changing redox conditions in the bog subsurface: the degree of isomerization in the C31 hopanes, and the concentrations of bishomohopanol and archaeol. Pollen analysis reconstructed the landscape surrounding the mire and revealed evidence for human disturbance. The results suggest that bog surface wetness increased with the transition from Sphagnum imbricatum to Sphagnum magellanicum, but the increase was not large and S. imbricatum had previously survived similar periods of wetness. However, the loss of S. imbricatum coincides with increasing human disturbance surrounding the bog, which may have altered nutrient inputs to the bog surface from agriculturally derived dust, to the detriment of S. imbricatum but to the benefit of S. magellanicum and Eriophorum vaginatum. It is proposed here that the stresses imposed by the combination of changing nutrient inputs and a rapidly rising water-table drove the disappearance of S. imbricatum from Butterburn Flow at c. cal. AD 1300.

Two decadally resolved records from north‐west European peat bogs show rapid climate changes associated with solar variability during the mid–late Holocene

AbstractTwo 14C accelerator mass spectrometry (AMS) wiggle‐match dated peat sequences from Denmark and northern England record changes in mire surface wetness reconstructed using plant macrofossil and testate amoebae analyses. A number of significant mid–late Holocene climatic deteriorations (wet shifts) associated with declines in solar activity were recorded (at ca. 2150 cal. yr BC, 740 cal. yr BC, cal. yr AD 930, cal. yr AD 1020, cal. yr AD 1280–1300, cal. yr AD 1640 and cal. yr AD 1790–1830). The wet shifts identified from ca. cal. yr AD 930 are concurrent with or lag decreases in solar activity by 10–50 years. These changes are replicated by previous records from these and other sites in the region and the new records provide improved precision for the ages of these changes. The rapidly accumulating (up to 2–3 yr cm−1, ∼1310 yr old, 34 14C dates) Danish profile offers an unprecedented high‐resolution record of climate change from a peat bog, and has effectively recorded a number of significant but short‐lived climate change events since ca. cal. yr AD 690. The longer time intervals between samples and the greater length of time resolved by each sample in the British site due to slower peat accumulation rates (up to 11 yr cm−1, ∼5250 yr old, 42 14C dates) acted as a natural smoothing filter preventing the clear registration of some of the rapid climate change events. Not all the significant rises in water table registered in the peat bog archives of the British and Danish sites have been caused by solar forcing, and may be the result of other processes such as changes in other external forcing factors, the internal variability of the climate system or raised bog ecosystem. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Palaeoecological evidence for anthropogenic acidification of a kettle-hole peatland in northern Poland

The Holocene developmental history of a small kettle-hole peatland in northern Poland was studied using radiocarbon dating and analyses of pollen, plant macrofossils and testate amoebae with the aim of sorting out the influences of climate change, autogenic succession and human impact. The mire followed the classical succession from lake to a Sphagnum-dominated peatland, but peat accumulation only started about 3000 cal. BP. A rapid shift to wetter conditions, lower pH and higher peat accumulation rate took place about 110—150 years before present, when the vegetation shifted to a Sphagnum-dominated poor fen with some bog plants. While the first shift to a peat-accumulating system was most likely driven by climate, the second one was probably caused by forest clearance around the mire. This shift towards a Sphagnum-dominated vegetation mirrors both in pattern and timing the changes observed in similar situations in North America and New Zealand. While human activities have overall caused the loss of vast expanses of peatlands worldwide in recent centuries, locally they may have also allowed the development of communities that are now ironically considered to have a high conservation value. However, in the case of the site studied the likely anthropogenic shift to bog vegetation was at the expense of a species-rich poor fen, which today has even higher conservation value than ombrotrophic bogs. Thus this study also illustrates the value of palaeoecology for peatland management and biodiversity conservation.

Testate amoebae analysis in ecological and paleoecological studies of wetlands: past, present and future

Testate amoebae are an abundant and diverse polyphyletic group of shelled protozoa living in aquatic to moist habitats ranging from estuaries to lakes, rivers, wetlands, soils, litter, and moss habitats. Owing to the preservation of shells in sediments, testate amoebae are useful proxy indicators complementary to long-established indicators such as pollen and spores or macrofossils. Their primary use to date has been for inferring past moisture conditions and climate in ombrotrophic peatlands and, to a lesser extent, to infer pH in peatlands and the trophic or nutrient status of lakes. Recent research on these organisms suggests other possible uses in paleoecology and ecology such as sea-level reconstruction in estuarine environments, as indicators of soil or air pollution, and monitoring recovery of peatland. We review the past and present use of testate amoebae, the challenges in current research, and provide some ideas on future research directions.

Increased aeolian activity during humidity shifts as recorded in a raised bog in south-west Sweden during the past 1700 years

Abstract. Analyses of testate amoebae and aeolian sediment influx (ASI) were used to reconstruct effective humidity changes and aeolian activity in the coastal zone of south-west Sweden. Cores were taken from an ombrotrophic peat sequence from the Undarsmosse bog. Since both types of analysis were carried out on the same core, a direct comparison between humidity fluctuations in the bog and aeolian activity was possible, potentially providing detailed information on atmospheric circulation changes in this region. Relatively wet bog surface conditions occurred from around 1500 to 1230 and 770 to 380 cal. yrs BP, whereas dry conditions dominated from ca. 1630 to 1530, 1160 to 830 and 300 to 50 cal. yrs BP. The transitions between these phases occurred within 60–100 years and are characterised by a major change in the testate amoebae assemblages. A watertable reconstruction was used to study the hydrological changes at the bog surface in more detail. ASI peak events were reconstructed around 1450, 1150, 850 and after 370 cal. yrs BP. Most interestingly, these aeolian activity peaks started during the recorded hydrological transitions, regardless of the direction of these shifts. Our results therefore suggest that humidity shifts in this region were associated with temporary intensifications of atmospheric circulation during the past 1700 years. Several ASI peaks apparently coincide with reduced solar activity, possibly suggesting a solar related cause for some of the observed events.

Seasonal Influences on the Ecology of Testate Amoebae (Protozoa) in a Small Sphagnum peatland in Southern Ontario, Canada

Testate amoebae (Protozoa) were studied in spring, summer, and fall from the same microhabitats in a small Sphagnum-dominated peatland in southern Ontario, Canada. A total of 32 sampling stations were established in two wetland plant communities, 19 in an open Ericaceae low-shrub community and 13 in a closed Picea mariana and Larix laricina swamp community. Sphagnum was collected in each station for analysis of testate amoebae and measurement of soil water content parameters and water table depth in May, August, and October 2001. pH and dissolved oxygen of the groundwater under the Sphagnum were measured also. A total of 52 taxa including the rotifer, Habrotrocha angusticollis, were identified. Soil water content and water table variables emerged as the primary factors separating testate amoebae between the open bog/fen community and swamp community. Testate amoebae in the open bog/fen community showed a clear separation between the May sampling period and the August and October sampling periods. Sampling stations in May had much higher water table and were wetter than those in August and October. Conversely, testate amoebae in the swamp community did not show a clear difference between sampling periods. Soil moisture and water tables appear to be more constant in the swamp communities. Biological factors or other microscale environmental factors may need to be considered to explain seasonal changes in testate amoebae. A greater understanding of relationships between testate amoebae and microenvironmental factors is necessary to track seasonality in testate amoebae distributions.