Reconstruction Of Environmental Changes Research Articles

Palaeoecological and palaeoenvironmental responses to abrupt climate changes during the Late Glacial: The unique archive recorded at the Osinki site (NE Poland) and its regional importance

The reconstruction of environmental changes at the termination of the Last Glaciation range in NE Europe during the Late Glacial is hampered by the multiplicity of processes underway at that time and during the Holocene that dynamically modified the Young Glacial landscape. In lake sediments, these changes are recorded in a manner that is almost always incomplete or disturbed. For this reason, the succession that was successfully reconstructed in two profiles from the Osinki site in NE Poland is extremely valuable. Palynological, Cladocera and geochemical analyses, as well as fragmentary malacofauna and diatom analyses, made it possible to trace the changes in the environment that took place in two differently functioning parts of a single lake, in not interrupted periods from the Oldest Dryas to the Younger Dryas. Detailed research results show that despite the proximity of natural environment components, their developments in both cases were conducted in different ways, what they prove to the changes in pollen record, Cladocera, and geochemical composition of sediments. Climate changes affected the changes in the vegetation, the composition of malacofauna, Cladocera and diatoms. They also influenced the erosion processes within the catchment and the oxidation-reduction conditions. On the basis of the research results, changes in water trophy, from oligotrophic to eutrophic, were also observed. In this case, we also observe significant differences between the two analysed profiles. These changes first occurred in Allerød in the shallow part of the lake, and then in its deeper zone in Young Dryas.In addition, Late Weichselian profiles from the Poland–Belarus–Lithuania borderland area were analysed in detail, and the age of the bottom of sediments is usually estimated to the Allerød, and the Bølling. The results of analyses from Osinki and Osinki2 profiles (beginning of sedimentation in the Oldest Dryas) indicate that the reason for this discrepancy is to be found in, among other things, the methodological limitations of the palynological analysis for most of the sites. The above-standard amount of mineral sediment allows the age of the sediment to be established as being much older than if determined using only pollen analysis of organic sediments.

Region Stavropol, Russland/Region Kachetien, Georgien. Umweltarchive und Archäologie im ­Kaukasus: Neue Methoden in der archäo­logischen Klimaforschung. Die Arbeiten des Jahres 2020

In 2020, a pioneering step was taken towards the development of high-precision climate data in the Northern Caucasus. Groundwork was laid for a cooperation of various partners, which also methodologically contributes fundamentally new components to climate research in the region. Up to now, reconstructions of environmental changes in the Caucasus have been based primarily on geoarchives. However, the systematic dendroclimatological investigation of wood from Bronze Age burial chambers in cooperation with the GFZ Potsdam will open up new methodological territory, all the more so as the cooperation with the Beuth University of Applied Sciences provides a measuring instrument that allows new access to images resolved down to the cell level.

The foraminiferal record in the Holocene evolution of the Mecklenburg Bay (south-western Baltic Sea)

Abstract Foraminiferal assemblages were analyzed in a 620-cm long core retrieved from the central part of the Mecklenburg Bay (MB, south-western Baltic Sea) to aid in the reconstruction of environmental changes occurring in the area during the Holocene and to complement a set of previously investigated palaeoenvironmental proxies. A total of five foraminifera-based stratigraphic units were identified, including an initial 80-cm thick layer devoid of foraminifera. The next two units featured an increasing abundance of the foraminiferal assemblage dominated by the calcareous Ammonia group species. Nearly all the calcareous foraminifera found in the core were decalcified. Following the maximum abundance within the 470–410 cm layer, the foraminiferal abundance declined sharply and the assemblage’s dominance structure changed to domination of the agglutinated foraminiferal species, Eggerelloides scaber, which continued up to the top of the core and marked a pronounced shift in environmental conditions (shallower depth, lower salinity, more dynamic sedimentation conditions). The foraminifera-based stratigraphy of the core proved to be complementary to that emerging from previous analyses of diatoms and sediment geochemistry.

Limnological response to the Laacher See eruption (LSE) in an annually laminated Allerød sediment sequence from the Nahe palaeolake, northern Germany

This paper presents evidence for a limnological response to the Laacher See eruption (LSE) as detected in lake sediments from Nahe, northern Germany. The sediment section of the Allerød period dating to between 13 422 and 12 708 cal. a BP is preserved in annual laminations. Within this section, the LSE was identified as a cryptotephra layer (12 944±44 cal. a BP). Microfacies analysis, continuous high‐resolution geochemical measurements and pollen analyses enabled a high‐resolution reconstruction of environmental change. The older part of the Allerød (c. 13 422 to 12 943 cal. a BP) was characterized by relatively stable sedimentation conditions. Evidence for windier conditions dating to c. 13 160 to 13 080 cal. a BP probably reflects the Gerzensee oscillation. Pronounced changes of the lake sedimentation followed the LSE. Four unusually thick varves with increased amounts of allochthonous material indicate serious disturbance of the local environment immediately after the LSE, related to increased storminess and/or the occurrence of high intensity rainfall events. A pronounced reduction of biogenic silica accumulation for c. 60 years after the LSE could reflect a period of acidification. Indications of a simultaneous lake level increase until c. 60 years after the LSE are in line with the supposed reduced evapotranspiration associated with cooler conditions. About 120 years after the LSE, increased oxygen access at the lake bottom, allochthonous input and Cl fluxes point to an onset of increasingly stronger westerly winds, probably as a long‐term response to the LSE. This supports the idea of a southward shift of the mid‐latitude westerlies wind system within the interval between the LSE and the beginning of the Younger Dryas. The pace of the southwards shift of this wind system decreased from 10 km a−1 in the initial phase (40–120 years after LSE) to 6 km a−1 in the later phase (120–200 years after LSE).

210Pb-derived sediment accumulation rates across the Wider Caribbean Region

The Wider Caribbean Region is an important tourist destination where agricultural, industrial and shipping activities are also carried on. Coastal zones are heavily populated and receive a high human pressure; however, few monitoring programmes allow assessing long-term anthropogenic impact trends in these areas, which are especially useful for integrated management programs. Through the support of the International Atomic Energy Agency (project RLA/7/012), sediment core activities of 210Pb and 137Cs were used to evaluate changes in sedimentation rates in 11 relevant coastal areas of the region, where environmental information is scarce, but needed to support national environmental policies. Most 210Pb activity profiles were atypical, attributed to non-steady sedimentation conditions; whereas 137Cs activity profiles, showing very low values, were of little help for 210Pb-dating corroboration. Results evidenced conspicuous changes in mass accumulation rates (MAR), specially through the Anthropocene (i.e. since ~1950s) in most cases, attributed to deforestation and land erosion (one of the clearest indicators of global change), and the input of urban and industrial untreated wastes. The recent MAR decrease in Havana Bay (Cuba) was attributed to the implementation of environmental policies, which showed that 210Pb-derived reconstruction of environmental changes is also useful to verify the effectiveness of management programs to control land-derived erosion and siltation issues. Since siltation can be detrimental to valuable coastal resources around the world, retrospective evaluations of sedimentation rates, based on 210Pb-dated cores, are highly recommended to assist integrated coastal zone management programs in the region and elsewhere.

Modelling the decadal dynamics of reach‐scale river channel evolution and floodplain turnover in CAESAR‐Lisflood

AbstractSedimentary deposits provide records of environmental change quantifying erosion fluxes conditioned by natural and anthropogenic disturbances. These fluxes are lagged by internal storage, particularly within floodplains, complicating reconstruction of environmental changes. The time sediment remains in storage underpins the interpretation of sedimentary records and accurate monitoring of pollutant fluxes. Turnover time is a measure of the timeframe to erode every floodplain surface. CAESAR‐Lisflood is used to simulate fluvial evolution at reach scale, providing a basis for quantifying environmental changes on the timescales of sediment storage. We evaluate the accuracy of CAESAR‐Lisflood simulations of channel changes and turnover times for alluvial floodplains using historical channel changes reconstructed for 10 reaches in northern England to quantify model accuracy in replicating mean annual erosion, deposition and channel lateral migration rates, alongside planform morphology. Here, a split‐sample testing approach is adopted, whereby five of the reaches were calibrated and the resulting parameter values were applied to the other reaches to evaluate the transferability of parameter settings. The lowest overall integrated error identified the best‐fit simulations and showed that modelled process rates were within ~25–50% of rates from historical reconstructions, generally. Calibrated parameters for some reaches are widely transferable, producing accurate geomorphic changes for some uncalibrated sites. However, large errors along some reaches indicate that reach‐specific parameterization is recommended. Turnover times are underpinned by the assumption that areas of floodplain previously unvisited by the channel are reworked. This assumption has been challenged by studies that show floodplain (re)occupation rates vary spatially. However, this limitation is less important for the short‐duration simulations presented here. The simulations reconstruct floodplain turnover times estimated by mapped rates mostly successfully, demonstrating the potential applicability of calibrated parameters over much longer timescales. Errors in the form of under‐predicted erosion rates propagated, resulting in over‐predicted turnover times by even greater magnitudes. © 2020 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.

Environmental changes in the Late Glacial and Holocene in the southeast of Belarus

Communicated by Academician Aleksey V. Matveev The reconstruction of environmental changes in the southeast of Belarus during the last 14700 cal. BP is based on the results of palynological, radiocarbon, isotope and lithological studies of Lake Staroje deposits. Climatic fluctuations, fires and human activities played a significant role in the transformation of the vegetation cover. The beginning of the lacustrine sedimentation was dated circa 16000 cal. BP. The intensification of erosion processes on the water catchment area was marked by an increase in the mineral material flow into the lake. These events have a positive correlation with the climate cooling and humidity phases in the Late Glacial and Early Holocene, and in the Late Holocene with anthropogenic impact stages. The traces of the episodic human activity were dated to 5800 cal. BP, while the expansion of farming and pasturing areas began at 3000 cal. BP Currently the consequences of human activities (including drainage of bogs) are reflected in the treeless landscapes adjacent to the lake.

Reconstruction of Environmental Changes in Western Siberia: Evidence from the Diatom Complexes of Lake Sediments

The information content of lake sediments in Western Siberia for reconstruction of the latest environmental and climatic changes was evaluated. The possibility of reliable registration of negative changes in the physicochemical parameters of lake waters was studied on the basis of classical and innovative methods of diatom analysis.

Multiproxy palaeontological investigations of Holocene sediments in the harbour area of the Hanseatic town Stralsund, North-Eastern Germany, southern Baltic Sea coast

Two archaeological excavation sites, Fundplatz 225 „Mischwasserspeicher“ and Fundplatz 290 „Ozeaneum“, located close to the medieval town centre of Stralsund at the Strelasund were investigated. Using methods of sedimentology and (micro)palaeontology, the aim of this study was the reconstruction of environmental changes from Mesolithic to Modern Times.Foraminifers, ostracods, molluscs, plant remains, vertebrates and archaeological finds of all kind were used to establish a reliable model of coastal site development at the shore of the Strelasund from about 5300 BC to the 1860s AD, comprising naturally induced environmental changes and human impact and providing new insights into the coastal evolution and harbour transformations in Stralsund of the past seven millennia.The clam species Mya arenaria, introduced by human activities into the Baltic Sea, proved to appear not earlier than in the 17th century in this region.

Application of malacological analysis in local and regional palaeoenvironmental reconstructions – a study from the Holocene of Łapsze Niżne (Podhale, southern Poland)

This malacological analysis was conducted at a site with peat and calcareous tufas in Łapsze Nizne, Podhale (southern Poland). The study was carried out in 6 main and several complementary sections, in which 37 mollusc species were recognized represented by almost 11 000 specimens. The study enabled the reconstruction of environmental changes during the accumulation of the Holocene deposits (from the Boreal Phase till present). Conclusions drawn from these reconstructions were compared with results of malacological and palynological studies from other sites in Podhale. As a result, regional environmental reconstructions for the Holocene of the area were made. The specific composition, ecological structure and succession of molluscan assemblages from Łapsze Nizne indicate a significant role for local factors, thus demonstrating the variability of environmental conditions within a geographic region.

Towards a better understanding of long-term wood-chemistry variations in old-growth forests: A case study on ancient Pinus uncinata trees from the Pyrenees

Dendrochemical studies in old forests are still underdeveloped. Old trees growing in remote high-elevation areas far from direct human influence constitute a promising biological proxy for the long-term reconstructions of environmental changes using tree-rings. Furthermore, centennial-long chronologies of multi-elemental chemistry at inter- and intra-annual resolution are scarce. Here, we use a novel non-destructive method by applying Micro X-ray fluorescence (μXRF) to wood samples of old Pinus uncinata trees from two Pyrenean high-elevation forests growing on acidic and basic soils. To disentangle ontogenetic (changes in tree age and diameter) from environmental influences (e.g., climate warming) we compared element patterns in sapwood (SW) and heartwood (HW) during the pre-industrial (1700–1849) and industrial (1850–2008) periods. We quantified tree-ring growth, wood density and relative element concentrations at annual (TRW, tree-ring) to seasonal resolution (EW, earlywood; LW, latewood) and related them to climate variables (temperature and precipitation) and volcanic eruptions in the 18th and 19th centuries. We detected differences for most studied elements between SW and HW along the stem and also between EW and LW within rings. Long-term positive and negative trends were observed for Ca and K, respectively. Cl, P and S showed positive trends during the industrial period. However, differences between sites were also notable. Higher values of Mg, Al, Si and the Ca/Mn ratio were observed at the site with acidic soil. Growing-season temperatures were positively related to growth, maximum wood density and to the concentration of most elements. Peaks in S, Fe, Cl, Zn and Ca were linked to major volcanic eruptions (e.g., Tambora in 1815). Our results reveal the potential of long-term wood-chemistry studies based on the μXRF non-destructive technique to reconstruct environmental changes.

Sediment Composition and Facies of Coral Reef Islands in the Spermonde Archipelago, Indonesia

Sedimentological and geomorphological characteristics of coral reef islands are strongly related to past and recent boundary conditions such as the hydrodynamic regime, wind directions, sea-level fluctuations, and the ecological footprint of the surrounding reef complexes. Alterations in the physical, chemical and biological boundary controls may affect the stability of reef islands. Additionally, these factors are of importance in the context of future climate change. Such alterations through time may well be documented within the sedimentary record of reef islands and a better knowledge on its effects could help to improve our understanding of island responses to future changes of the status quo. However, detailed studies on the sedimentology and geomorphology of reef islands from southwest Sulawesi, Indonesia, are still rare. Here we report on the sedimentary composition and related facies zonation of four uninhabited coral reef islands in the Spermonde Archipelago. Sediment samples from onshore- and reef-flat environments were analyzed in regard to their grain size, component assemblages and facies distribution. Our results show that the analyzed island sediments are characterized by medium- to coarse-grained sand fractions and are well to poorly sorted. Across all islands examined, the surface sediment is predominately composed of materials identified as scleractinian coral and coralline red algae fragments, with minor additions from bivalves, gastropods and foraminifers. Importantly, statistical analyses of the variations in the percentage of these components allow for a clear sedimentary distinction of the four study sites into three outer shelf islands, situated closer to the open marine Makassar Strait, and one inner shelf island. On the inner shelf island, additional subsurface sedimentological analyses indicate a potential shift in major sediment contributors through time, preserved as coral-dominated accumulations within the subsurface samples, and coralline red algae-dominated deposits on top. These findings highlight the practical use of detailed sedimentological studies for the reconstruction of environmental changes in the Spermonde Archipelago.

Environmental changes during the late Pleistocene and the Holocene in the Gonghe Basin, north-eastern Tibetan Plateau

Different types of aeolian sediments are widespread in Gonghe Basin on the north-eastern Tibetan Plateau. Despite that individual sections are often discontinuous, the analysis of a large number of individual sections distributed in the entire basin provides a valuable archive for the reconstruction of environmental changes since the late Pleistocene. This study presents 43 new OSL (optical stimulated luminescence) ages and combines them with 39 previously published ages from the Gonghe Basin for the last 16ka. From around 15 to 14ka onwards an increase in moisture facilitated the formation of a vegetation cover and the fixation of loess sediments on the northern and southern side of the basin. After enhanced mobility of aeolian sediments during the dry Younger Dryas greater than before precipitation fixated also the sands in the lower parts of the basin. The increase in moisture can be attributed to the strengthening of the Asian summer monsoon. A comparison with the timing of aeolian sediment accumulation in the neighbouring basins probably indicates a time-transgressive strengthening of the monsoon on the north-eastern Tibetan Plateau. Aeolian sands were first permanently stored from around 17ka at the Qinghai Lake in the north-east of the area and at 10.5ka at the Donggi Cona in the south-west. The Gonghe Basin is located in an intermediate position. Highest moisture values occurred during the mid-Holocene from around 7.5 until probably 2.5ka in the Gonghe Basin. In most parts of the basin aeolian activity was low during this time. In the central part of the basin aeolian sand movement occurred sporadically. Since 2.5ka aeolian activity in most parts of the basin resumed due to the late Holocene weakening of the Asian summer monsoon. However, the parallel accumulation of aeolian sands and silts indicates an increased human influence.

Macrofossils analysis of the peat to reconstruct holocene paleoecological conditions about Kansk forest-stepp zone (Yenisey Siberia)

В статье на примере болотного массива «Кускун», расположенного в пойме р.Есауловка (Канская лесостепь) приведены результаты изучения генезиса и эволюции болот северной лесостепи. На основании изучения макрофоссилий торфа, определения зольности и степени разложения, при применении экологических шкал Раменского и Элленберга были реконструированы палеоэкологические условия времени развития болот: дана оценка условий увлажнения за весь период торфонакопления, выделены фазы в развитии болота, описана свойственная им растительность.

Towards an event stratigraphy for Baltic Sea sediments deposited since AD 1900: approaches and challenges

Reconstructions of environmental changes at sub‐decadal to decadal resolution based on central Baltic Sea sediments rely on accurate and precise high‐resolution sediment depth/age relationships. A model chronology for Baltic Sea sediments is presented here based on established historical records of anthropogenic radionuclides (137Cs/241Am/bomb14C), polychlorinated biphenyls (PCBs), lead (Pb) and stable lead isotope (206/207Pb ratios), and radionuclide 210Pb and 14C decay dating methods. Marker horizons consisting of chemical precipitates formed by documented Major Baltic Inflow (MBIs) events and an extended diatom bloom period were also integrated into the model. The main time markers in Baltic Sea sediments that formed during the last 120 years were the following: (i) the deepest observation of 210Pbunsupp. (marking the 210Pb dating horizon) and departure of Hg from natural background levels at c. AD 1900; (ii) first detectable presence of PCBs at AD 1935; (iii) radionuclide production (i.e. 241Am) due to nuclear weapons testing between AD 1954 and AD 1975, with a peak in AD 1963; (iv) maximum heavy metal and PCB concentrations in the AD 1960s/1970s; (v) the Chernobyl nuclear accident in AD 1986 as a sharp 137Cs increase; (vi) exceptionally strong diatom blooms with a massive diatom layer found in the Eastern Gotland Basin in AD 1988–1990; and (vii) characteristic manganese‐carbonate layers in the deeper central basins formed by MBIs in AD 1993 and AD 2003. A precise and accurate sediment depth/age relationship can only be achieved in restricted areas of the Baltic Sea where continuous sedimentation has prevailed and there has been limited postdepositional disturbance. We demonstrate that parallel Hg and 137Cs measurements can be used to assess the quality of sediment sequences for high‐resolution environmental reconstructions. We show examples of sediment profiles that conform to the historical record, and examples from Western Baltic Sea areas where it appears to be impossible to establish accurate geochronologies.

Late Holocene environmental changes as recorded in the sediments of high Andean Laguna Chepical, Central Chile (32°S; 3050 m a.s.l.)

We present a reconstruction of environmental changes from sediments of high-altitude Laguna Chepical in the subtropical Andes of Central Chile (32°16′S; 70°30′W, 3050ma.s.l.) for the past 3100years. Based on subfossil pollen, microscopic charcoal and diatoms, we inferred changes in moisture (related to precipitation) and ice-cover/ice-free season (related to summer temperature) at decadal to millennial scales. Sustained wetter and colder summer temperatures than today prevailed between 1100BC and ca. AD1. Afterward, decreasing pollen accumulation rates and increased fire activity suggest drier conditions and possibly enhanced seasonality and/or inter-annual climate variability. Frequent changes between cold and warm summers were observed, particularly for the last 1000years. About AD1250 (during the Medieval Climate Anomaly), wet years and early break up of ice-cover occurred in central Chile, which is today typical for El Niño-like mean conditions. Conversely, and with the exception of a few wet pulses, a generally dry period with extended ice-cover (cool summers) was observed between AD1400 and AD1850 (Little Ice Age). This can be interpreted as a trend toward more La Niña-like mean conditions. Recent climate change and human disturbances during the last 100years have prompted changes in diatom and plant communities that are unprecedented in the late Holocene. First, planktonic diatoms increased as a result of hydraulic interventions in the lake during the late 19th century, and secondly, the Andean vegetation shifted upward as result of recent warming, and the frequency of arboreal taxa was significantly reduced. At the same time peaks of fire activity were observed.

High-resolution multi-proxy reconstruction of environmental changes in coastal waters of the Java Sea, Indonesia, during the late Holocene

ABSTRACTTo obtain insight into the natural variability of the coastal ecosystems off southern Kalimantan, late Holocene environmental conditions between ca. 2850 and 990 cal yr BP in the Java Sea were investigated. A 134-cm-long sediment core collected ∼50 km off the Pembuang River mouth was analysed for organic-walled dinoflagellate cysts, pollen/spores and biogeochemical parameters, e.g. organic carbon (Corg), total nitrogen (N) and calcium carbonate (CaCO3) as well as carbon and nitrogen stable isotope composition (δ13C, δ15N). Sediments consist of mixed terrestrial as well as marine organic matter, are characterised by low nutrient uptake and suggest generally low river discharge that is supported by very low pollen and spore concentrations (256 pollen grains cm−3 and 20 spores cm−3 at maximum, respectively). Foraminifera and coccolithophores dominated the plankton over cyst-producing dinoflagellates and diatoms. Dinoflagellate cyst assemblages are composed mainly of oxidation-resistant species of the genera Operculodinium and Spiniferites with a minor contribution of Impagidinium (mainly I. strialatum). The percentages of round brown and peridinioid cysts are low and decrease from the bottom of the core to the top. Palynological and biogeochemical data appear well correlated and synchronously reflect changes in the marine environment. It is reconstructed that after ca. 2480 cal yr BP, bottom waters became increasingly ventilated. A typical open-water dinoflagellate cyst association is gradually replaced by a more coastal association between ca. 2480 and 1530 cal yr BP that is most likely attributed to El Niño-induced seasonal differences between dry and wet periods of the year. After 1530 cal yr BP, a more pronounced influence of the Pembuang River is indicated by an increase in δ15N and decreased δ13C which is supported by the occurrence of nutrient-sensitive Lingulodinium machaerophorum and Nematosphaeropsis labyrinthus. The overall results indicate short-scale local environment fluctuations attributed to abiotic factors.

Palynological reconstruction of environmental changes in coastal wetlands of the Florida Everglades since the mid-Holocene

Palynological, loss-on-ignition, and X-ray fluorescence data from a 5.25m sediment core from a mangrove forest at the mouth of the Shark River Estuary in the southwestern Everglades National Park, Florida were used to reconstruct changes occurring in coastal wetlands since the mid-Holocene. This multi-proxy record contains the longest paleoecological history to date in the southwestern Everglades. The Shark River Estuary basin was formed ~5700calyr BP in response to increasing precipitation. Initial wetlands were frequently-burned short-hydroperiod prairies, which transitioned into long-hydroperiod prairies with sloughs in which peat deposits began to accumulate continuously about 5250calyr BP. Our data suggest that mangrove communities started to appear after ~3800calyr BP; declines in the abundance of charcoal suggested gradual replacement of fire-dominated wetlands by mangrove forest over the following 2650yr. By~1150calyr BP, a dense Rhizophora mangle dominated mangrove forest had formed at the mouth of the Shark River. The mangrove-dominated coastal ecosystem here was established at least 2000yr later than has been previously estimated.

Reconstruction of environmental changes during the late glacial and Holocene reflected in a soil-sedimentary sequence from the lower Selenga River valley, Lake Baikal region, Siberia, assessed by lipid molecular proxies

Sediments of Lake Baikal and smaller lakes in its surroundings have been frequently used to trace paleoenvironmental changes. However, these sediments integrate environmental proxies over large areas and the processes leading to alteration of terrestrial signals are not fully understood. More specific information can be derived from terrestrial archives such as alternating soil-sediment sequences. Near the village of Burdukovo, southeast of Lake Baikal, such sequences are accessible along the ∼5 m high right terrace of the Selenga River. However, terrestrial archives can be associated with degradation of organic matter. Therefore, lipid molecular proxies were applied in the current study to trace environmental and vegetation shifts as well as incorporation and degradation of organic matter. Alkane and fatty acid molecular proxies as part of the lipid fraction are well known for their diagnostic character to trace sources of organic matter and its degradation. Several parameters including the carbon preference indices of alkanes and fatty acids indicated a well preservation of the organic matter in the investigated sequence. Furthermore, the organic matter in the C horizons of the terrestrial upper part of the sediments was most likely overprinted by rooting of the plants growing on respective overlaying soils as reflected by the average chain length of fatty acids and alkanes and the relative composition of long-chain n-alkanes (C25–33). The 3.5 m thick sequence enabled tracing of vegetation shifts. The alkane composition argued for changes in the grass dominated vegetation cover within the different phases of the Holocene until today, whereas a birch and willow dominated deciduous forest vegetation as traced in other archives of the larger Baikal area could not be determined in the Burdukovo sequence by lipid molecular proxies. The scatter in the alkane and fatty acid composition revealed only minor vegetation shifts throughout the Holocene. Nevertheless, some changes in the lipid composition indicated a change in the plant community. As coniferous trees have often similar alkane patterns to grass vegetation, it cannot be excluded that conifers also contributed to a certain degree to the molecular record in the Burdukovo sequence. The general decrease in the carbon preference index of alkanes since approximately 4 ka BP until recent times further argues for an increasing admixture of coniferous lipids to the record. Lipid molecular proxies of sediment that formed 2.8–2.6 ka BP revealed the incorporation of deciduous tree-derived organic matter most likely originating from birch that grew elsewhere in the catchment of the Selenga River. The proxies enabled an assessment of site-specific vegetation shifts and degradation of organic matter in the soil-sediment sequence of the Burdukovo area, and thus provide more specific information related to a certain area than lacustrine sediments integrating over larger catchments.

Environmental assessment of vegetation and hydrological conditions in Everglades freshwater marshes using multiple geochemical proxies

Paleoecological reconstructions of environmental changes provide important information for Everglades restoration targets. Traditionally this has been achieved using a combination of biological and physical indicators. However, as microfossils may be sporadically abundant in Everglades soils, organic geochemical methods can provide information at the molecular level. To reconstruct vegetation trends over the last century, soil cores from Shark to Taylor Sloughs, the primary flowpaths of the southern Everglades, were examined using several geochemical proxies. The n-alkane derived biomarker Paq effectively distinguished organic inputs from sawgrass and slough habitats. Other proxies examined include Kaurenes, cyclic diterpenoids unique to sawgrass roots; biomarkers of algae (highly branched isoprenoids (C20HBIs) and Botryococcenes); lignin phenols as vascular plant indicators; and macrofossils. At all sites, soil profiles from sawgrass marshes showed vegetation had shifted over the last 100 years, from sloughs to sawgrass-dominated marshes, reflecting decreased water levels (shorter hydroperiods) induced by water management. Paleo-assessments of modern sloughs, however, indicate these habitats remained deeper water habitats throughout the period of record, though shifts toward shorter hydroperiod vegetation were observed. In Taylor Slough, evidence of increasingly dry conditions in sloughs was confirmed by seed inputs from woody species. At 3 of the 5 sites, recent increases in C20HBIs and Botryococcene concentrations indicated greater periphyton abundance, coincidental with increased mineral concentrations observed in surface waters during the mid-20th Century. Bulk proxies such as organic content and carbon:nitrogen ratios also supported findings of changes in relative contributions of microbial and higher plants in this ecosystem.