A rapid response of testate amoebae and vegetation to inundation of a kettle hole mire

Our palaeoecological study covers 73 years of history (1929-2002) of a kettle hole peatland inundated by water from a nearby, dammed lake. Testate amoebae, pollen and non-pollen palynomorphs (NPPs) were used to track the shift to wetter conditions in the peatland. Lead-210 was used to try and construct the chronology. We investigated how peatland testate amoebae communities changed since the damming of a nearby river. Furthermore, we evaluated how rapidly local vegetation responded to the increase in wetness, and how vegetation changes correlated with shifts in testate amoebae and NPPs. The Mukrza kettle hole provided palaeoecological evidence of trophic state and hydrological changes since the lake filled with water in 1929. Three stages of development were revealed. The first two were associated with initial inundation, and the third was related to Sphagnum expansion and acidification. Quantitative reconstruction of groundwater level and pH, inferred using testate amoebae, confirmed our hypotheses about changes in hydrology and trophic state. Subfossil desmid remains lend qualitative support to the reconstruction. The ecology of several testate amoeba taxa is discussed in the context of succession and population establishment. There was complete species replacement since the time of inundation. Our investigation has two important applied aspects: (1) it enables prediction of the response of peatlands to a rise in water table on restored sites; and (2) it provides analogues for palaeoclimatological studies. The history of the Mukrza mire is an example of how palaeoecological studies can be used to assess the degree of change in peatlands transformed by human activities.

Last millennium palaeoenvironmental changes from a Baltic bog (Poland) inferred from stable isotopes, pollen, plant macrofossils and testate amoebae

Mariusz Lamentowicz, Edward Mitchell

The Baltic coast of Northern Poland is a region of considerable potential interest for paleoclimatic studies because this region is under the influence of both oceanic and continental climates and that these two influences have likely changed through time. Also unlike many more intensively studied regions of Europe human impact was more limited until the 19th century. We present a multiproxy high-resolution record from Stążki mire, an ombrotrophic mire located in northern Poland 35 km from the Baltic sea coast. We combined four proxies from the peat: testate amoebae, stable isotopes (δ13C) of Sphagnum stems, pollen, and plant macrofossils supported by dendroecological data to assess the palaeoenvironmental changes that took place during the last millennium. The general aim of this study was to test if a range of proxies (testate amoebae, pollen, plant macrofossils and tree rings) could allow inferring a climatic signal from a peat monolith despite the considerable anthropogenic impact on the Pomerania landscape since the Early Medieval period. Combining internal (e.g. macrofossils and testate amoebae) and external (pollen) signals is key to distinguishing human from climatic signals in palaeoenvironmental studies of peatlands. Our more specific aims were to: a) reconstruct the last millennium palaeoenvironment in a Baltic raised bog and its surroundings, b) identify the major wet-dry shifts and correlate those events with climate change and human impact, c) assess the resilience of the Baltic bog ecosystem following human impact. We noted two disturbance periods in the history of the mire. The two major disturbances in the history of the mire were dry periods [(I) 1100-1500 AD and (II) 1650-1900 (2005) AD]. These are reflected in all indicators and can be interpreted as the mixture of climate impact and human activities. However, the pollen record shows little evidence of human indicators during the first dry shift. The second disturbance can be related to local peat exploitation of the mire and then in the 20th century with limited artificial drainage. From 1500 AD all proxies show that the water table abruptly rose in the mire. The beginning of this shift occurred during the Little Ice Age and therefore it is likely a climatic signal. Alternatively, this wet shift could have been interpreted as a re-wetting mire surface after peat burning, but this interpretation is rejected because there is no evidence of major local fire in the macrofossil record. The macrofossil data shows that Sphagnum fuscum dominated the pristine mire vegetation but then declined and finally disappeared. This pattern is comparable with the timing of extinction of Sphagnum austinii in Western Europe. This study illustrated the value of palynological analysis of peat archives (especially for last millennium) to assess the magnitude of anthropogenic land-use changes. For example the comparison of Fagus (beech) and Carpinus (hornbeam) history with the palaeohydrological record allowed us to exclude climate change as the most important factor for the decline and expansion of these tree species. This study is the first direct comparison of testate amoeba and stable isotope data.

2008

Environmental and taxonomic controls of carbon and oxygen stable isotope composition in Sphagnum across broad climatic and geographic ranges

Luca Bragazza, Mariusz Lamentowicz, Bjorn Jozef Maria Robroek

Rain-fed peatlands are dominated by peat mosses (Sphagnum sp.), which for their growth depend on nutrients, water and CO2 uptake from the atmosphere. As the isotopic composition of carbon (C-12(,)13) and oxygen (O-16(,)18) of these Sphagnum mosses are affected by environmental conditions, Sphagnum tissue accumulated in peat constitutes a potential long-term archive that can be used for climate reconstruction. However, there is inadequate understanding of how isotope values are influenced by environmental conditions, which restricts their current use as environmental and palaeoenvironmental indicators. Here we tested (i) to what extent C and O isotopic variation in living tissue of Sphagnum is speciesspecific and associated with local hydrological gradients, climatic gradients (evapotranspiration, temperature, precipitation) and elevation; (ii) whether the C isotopic signature can be a proxy for net primary productivity (NPP) of Sphagnum; and (iii) to what extent Sphagnum tissue delta O-18 tracks the delta O-18 isotope signature of precipitation. In total, we analysed 337 samples from 93 sites across North America and Eurasia us ing two important peat-forming Sphagnum species (S. magellanicum, S. fuscum) common to the Holarctic realm. There were differences in delta C-13 values between species. For S. magellanicum delta C-13 decreased with increasing height above the water table (HWT, R-2 = 17 %) and was positively correlated to productivity (R-2 = 7 %). Together these two variables explained 46 % of the between-site variation in delta C-13 values. For S. fuscum, productivity was the only significant predictor of delta C-13 but had low explanatory power (total R-2 = 6 %). For delta O-18 values, approximately 90 % of the variation was found between sites. Globally modelled annual delta O-18 values in precipitation explained 69 % of the between-site variation in tissue delta O-18. S. magellanicum showed lower delta O-18 enrichment than S. fuscum (-0.83 %0 lower). Elevation and climatic variables were weak predictors of tissue delta O-18 values after controlling for delta O-18 values of the precipitation. To summarize, our study provides evidence for (a) good predictability of tissue delta O-18 values from modelled annual delta O-18 values in precipitation, and (b) the possibility of relating tissue delta C-13 values to HWT and NPP, but this appears to be species-dependent. These results suggest that isotope composition can be used on a large scale for climatic reconstructions but that such models should be species-specific.

COPERNICUS GESELLSCHAFT MBH2018

Environmental and taxonomic controls of carbon and oxygen stable isotope composition in Sphagnum across broad climatic and geographic ranges

Luca Bragazza, Mariusz Lamentowicz, Bjorn Jozef Maria Robroek

COPERNICUS GESELLSCHAFT MBH2018

Last millennium palaeoenvironmental changes from a Baltic bog (Poland) inferred from stable isotopes, pollen, plant macrofossils and testate amoebae

Mariusz Lamentowicz, Edward Mitchell

2008