This paper evaluates the impact of the crusades on the landscape and environment of northern Latvia between the 13th-16th centuries (medieval Livonia). The crusades replaced tribal societies in the eastern Baltic with a religious state (Ordenstaat) run by the military orders and their allies, accompanied by significant social, cultural and economic developments. These changes have previously received little consideration in palaeoenvironmental studies of past land use in the eastern Baltic region, but are fundamental to understanding the development and expansion of a European Christian identity. Sediment cores from Lake Trikāta, located adjacent to a medieval castle and settlement, were studied using pollen, macrofossils, loss-on-ignition and magnetic susceptibility. Our results show that despite continuous agricultural land use from 500 BC, the local landscape was still densely wooded until the start of the crusades in AD 1198 when a diversified pattern of pasture, meadow and arable land use was established. Colonisation followed the crusades, although in Livonia this occurred on a much smaller scale than in the rest of the Ordenstaat; Trikāta is atypical showing significant impact following the crusades with many other palaeoenvironmental studies only revealing more limited impact from the 14th century and later. Subsequent wars and changes in political control in the post-medieval period had little apparent effect on agricultural land use.

Most studies that utilize ancient DNA have focused on specific groups of organisms or even single species. Instead, the whole biodiversity of eukaryotes can be described using universal phylogenetic marker genes found within well-preserved sediment cores that cover the post-glacial period. Sedimentary ancient DNA samples from Lake Lielais Svētiņu, eastern Latvia, at a core depth of 1,050 cm in ~150 year intervals were used to determine phylotaxonomy in domain Eukaryota. Phylotaxonomic affiliation of >1,200 eukaryotic phylotypes revealed high richness in all major eukaryotic groups-Alveolata, Stramenopiles, Cercozoa, Chlorophyta, Charophyta, Nucletmycea, and Holozoa. The share of organisms that originate from terrestrial ecosystems was about one third, of which the most abundant molecular operational taxonomic units were Fungi and tracheal/vascular plants, which demonstrates the usefulness of using lake sediments to reconstruct the terrestrial paleoecosystems that surround them. Phylotypes that originate from the lake ecosystem belonged to various planktonic organisms; phyto-, proto,- and macrozooplankton, and vascular aquatic plants. We observed greater richness of several planktonic organisms that can be associated with higher trophic status during the warm climate period between 4,000 and 8,000 years ago and an increase in eukaryotic richness possibly associated with moderate human impact over the last 2,000 years.

It is commonly assumed that the majority of buried ice-blocks in Europe melted at the end of Late Glacial period and during the first part of the early-Holocene. We show, however, that scattered dead-ice-blocks may have been preserved in the ground until 8500 cal. yr BP. We analysed thermokarst features in Lake Ķikuru, western Latvia, by means of a multi-proxy approach (pollen, non-pollen palynomorphs, plant macrofossils, diatoms, loss-on-ignition, magnetic susceptibility, C:N ratio, carbon accumulation rate and radiocarbon dating). Abiotic and biotic processes following the ice-block meltdown suggests abrupt development of a thermokarst from 8500 to 7400 cal. yr BP. Important changes in local vegetation occurred with the deepening of a kettle-hole during the transition from a fen to a lake that nearly coincided with the appearance of the first fish at 7800 cal. yr BP, thus forming a clear indication of a lacustrine environment. Our study shows that a thin peat layer formed at first and, due to the meltdown of the ice-block, it gradually lowered to the bottom of the kettle-hole, and gyttja begun to accumulate afterwards. Given that thermokarst arise when the mean summer air temperature gradually increases to a value above the present-day temperature, we must assume that the local conditions must have been exceptional to secure ice-block from the meltdown for so long. Therefore, the legacy of the last ice age was still evident even ca. 5500 years after the Weichselian ice retreat from the eastern Baltic.

The hemispheric-scale climatic fluctuations during the Holocene have probably influenced the large Siberian rivers. However, detailed studies of the West Siberian Plain postglacial environmental change are scarce and the records of millennial-scale palaeohydrology are nearly absent. This paper presents the Holocene palaeoecological reconstruction based on the sedimentary record of Lake Svetlenkoye, located near the confluence of major Siberian rivers Ob and Irtysh. Postglacial history of flooding, dynamics of regional and local vegetation, sedimentation regime, geochemical changes and lake water pH were reconstructed based on multi-proxy studies. We used palaeobotanical (plant macrofossils, pollen, diatoms), geochemical (organic matter, total organic carbon and nitrogen content, carbon/nitrogen ratio) and chronological (14C dates, spheroidal fly-ash particle counts) methods. The studied sediment section started to accumulate ~11,400 cal. yr BP. The initial shallow water body was flooded by Ob River waters ~8100–8000 cal. yr BP as confirmed by a remarkable increase in the sedimentation rate and the accumulation rate of the aquatic vegetation proxies. The period of flooding coincides with the high humidity periods reconstructed from regional palaeobotanical records. About 6800–6700 cal. yr BP, the study site became isolated from the Ob River floodplain and remained a small lake until present. The diatom-based lake water pH estimates suggest fluctuations in the pH values during the Holocene, the recent decrease since 1960s being the most notable. The vegetation record revealed constant postglacial presence of tree taxa – Betula, Pinus and Picea – although in different pollen ratios and accumulation rates through time. The paludification of the surroundings occurred since ca. 8500 cal. yr BP.

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