High Lake Research Articles

Photointerpretation analysis of plant communities in Lake Ontario wetlands following 65 years of lake-level regulation

Abstract Regulation of Lake Ontario water levels since the St. Lawrence Seaway began operation in the early 1960s reduced the range of lake-level fluctuations and resulted in alteration of wetland plant communities, especially invasion of sedge/grass meadow marsh by cattails. A new regulation plan was implemented in January 2017 that seeks to restore some of the natural range in lake levels to benefit the environment. An adaptive management process accompanied the new Plan 2014, requiring before-after data for evaluation. Aerial photographs from 2014/2015 were obtained from existing sources for 16 wetlands previously assessed from 2001 photographs, and photointerpretation was used to re-map the vegetation types from the earlier study. The updated data set provides further information on wetland response to lake-level regulation. Overall, area of Meadow Marsh decreased from 2001 to 2014/2015 in most wetlands. In some cases, losses were due to increased Cattail abundance and in others to Mixed Emergent abundance. Although area of Cattail did increase at half the sites, expansion landward into Meadow Marsh was likely limited to an upper elevation with drier soils that had not been flooded for at least 15 years. Waterward expansion of Cattail was slow because it occurs by formation of vegetatively-expanding floating mats. The updated data set can now serve as a baseline for future adaptive management evaluations, including response to extreme high lake levels in 2017 and future low lake levels that Plan 2014 should allow during periods of low water supply.

Orbital-scale environmental and climatic changes recorded in a new ∼200,000-year-long multiproxy sedimentary record from Padul, southern Iberian Peninsula

Padul is one of the few wetland sites in southern Europe and the Mediterranean region that exhibits an unusually large temporal span (>100 kyr) and continuous Quaternary sedimentary record. Previous core-based studies from Padul yielded paleoecological datasets (i.e., pollen and organic geochemistry), but with a poor age control that resulted in rather arbitrary climate inferences. Therefore, precise age control and a multidisciplinary approach is necessary to understand long-term regional environmental and climate change and the associated local response of the Padul wetland environment. Here we present a new long sediment record (Padul-15-05) from this wetland in the southern Iberian Peninsula with the aim of improving the age control of the sedimentary sequence and carrying out up-to-date high-resolution multiproxy analyses. In this study the age control is based on 61 AMS radiocarbon dates for the last ca. 50 kyr BP and on the extent of amino acid racemization (AAR) in mollusc shells extending back ∼118 kyr BP. No numerical ages are available for the bottom part of the core but the sediment accumulation rates (SAR) and the cyclostratigraphic analysis of the multiproxy data suggest that the core preserves a continuous record of the last ∼197 kyr (from late MIS 7 to present) with millennial-scale time resolution. Sedimentological (lithology, magnetic susceptibility, XRD, color), geochemical (XRF, TOC, C/N, % carbonate content) and paleontological (pollen, charophytes, gastropods) data show co-varying cyclical paleoenvironmental changes linked to orbital-scale climatic variability. Silicon, magnetic susceptibility (MS) and total organic carbon (TOC) data show periodicities between ∼26.2–19.6 kyr linked to insolation, which is strongly dominated by precession cycles at this latitude. High values of Si and MS data have been related to high siliciclastic/detrital input from Sierra Nevada range during minima in insolation due to enhanced soil weathering/erosion during regional aridity and lower forest cover recorded by the arboreal pollen, which could also be favored by a minor biogenic productivity. In addition, warm climate conditions during maxima in insolation mostly resulted in negative precipitation/evapotranspiration balance and low lake levels, while cold glacial and stadial periods were mainly characterized by positive precipitation/evapotranspiration balance, and therefore, high lake levels. The improved chronology of the Padul sedimentary sequence along with a multiproxy study permitted us to better relate environmental and vegetation changes to climatic events and to demonstrate how both local (i.e., lake level, sedimentation) and regional (i.e., vegetation) environments responded to orbital-scale climate changes.

Effects of Aquaculture on Lakes in the Central Yangtze River Basin, China, II: Benthic Macroinvertebrates

AbstractThere is limited information available on the effects of extensive aquaculture or “fish ranching” operations on lake ecosystems. To study the effects of aquaculture on lake ecosystems, benthic macroinvertebrate communities were investigated from July to September 2015 in 23 lakes within the middle reach of the Yangtze River basin. The lakes represented four lake management strategies: fish ranching supported by low (LOW), medium (MEDIUM), or high (HIGH) stocking rates; or fallowing (FALLOW) in which previously ranched HIGH lakes had not been stocked for 2 years. Total macroinvertebrate densities did not vary significantly but were highest in the FALLOW lakes (2,352 individuals/m2), lowest in the LOW lakes (544 individuals/m2), and intermediate in the HIGH (1,734 individuals/m2) and MEDIUM lakes (1,208 individuals/m2). Chironomid densities were significantly lower in LOW lakes compared to all others, and mollusks were not observed in LOW lakes. Chironomid and total macroinvertebrate biomasses were also significantly lower in LOW lakes than in the other lakes. The FALLOW lakes had significantly greater biomasses of mollusks, oligochaetes, and total macroinvertebrates than all other lakes. Two pollution‐tolerant taxa, Tubificidae and Chironomidae, were dominant in all lakes regardless of management strategy, indicating that all study lakes were experiencing some degree of eutrophication. Results indicated that fish ranching does not affect macroinvertebrate communities in a predictable manner based on stocking density, but allowing for a fallowing period could potentially benefit lake macroinvertebrates. Canonical correspondence analysis indicated that chlorophyll a, chloride, conductivity, and total nitrogen were affecting macroinvertebrate density in these lakes, while total suspended solids, alkalinity, turbidity, total hardness, and water depth affected macroinvertebrate biomass.

The effect of environmental conditions on Atlantic salmon smolts’ (Salmo salar) bioenergetic requirements and migration through an inland sea

The timing of the juvenile Atlantic salmon ocean-entry is considered a critical stage in the species’ life-history. Entry into the ocean at suboptimal times can have negative survival impacts on entire smolt cohorts. Previous studies have identified smolt residency time in the Bras d’Or Lakes as highly variable and correlated with body condition. This study combines energetic modelling using Dynamic Energy Budget (DEB) theory with acoustic telemetry to mechanistically link smolt bioenergetics to their migration strategy within the Bras d’Or. This study examines two main questions: 1) what is the relationship between smolts’ bioenergetics and smolts’ migration strategy, and 2) what effect would warmer water temperature have on smolts’ energetic requirements? Simulation results indicate that smolts requiring more food are more likely to exit the Bras d’Or during the observation period. The results also suggest higher lake temperature would result in faster depletion of smolt energy reserves, which is predicted to favour smolts migrating to the ocean sooner.

Pedogenic evidence of Urmia Lake's maximum expansion in the late Quaternary

The Urmia Lake recession, and the resulting increase in vast barren area around it, has been rapid in recent decades and thus has attracted attention of environmentalists and geoscientists alike. However, evidence for its different strandlines and the largest extension of the lake during the late Quaternary has not been reported yet. The principal goals of the current research were to figure out pedological evidence of its maximum expansion during the late Quaternary and mapping out the different strandlines along the western shores of Urmia Lake over time. Thirty-two soil pedons at different landscape positions, geomorphic surfaces and distances from Urmia Lake were studied during autumn in 2013 and 2014. Micromorphological and mineralogical studies were performed for some diagnostic horizons. Results showed along the transect under study three different entities diagnostic of the lake's history (1) lithological discontinuities, (2) saline lacustrine sediments, (3) buried soils. However, almost 2 km from the closest pedon to the lake, no evidence of saline playa sediments were detected. Based on previous chronology results from Urmia Lake, which indicated high lake levels with very low salinity since about 180 ky BP, the sediments of this part of the study area were considered to have been deposited at the same period of time, indicating a maximum expansion of Urmia Lake during the late Quaternary. The current results demonstrate that soil pedons which were situated at various distances from Urmia Lake denote different stages of the lacustrine evolution. Along with the distance from the lake the development of soils increases. Due to a longer and more intensive impact of pedogenic processes on the topstratum the overall soil system becomes more “mature”. The study of buried soils and their comparison to upper non-buried soils revealed that in some cases, the buried soils were more evolved than their upper soils or vice versa. Through these observations, the periods of exposure to soil-forming processes after each sedimentation period was detected and schematic diagrams illustrating periods of highstands and lowstands (recessions) of Urmia Lake were reconstructed. This study demonstrates that even though multiple episodes of lake recession were apparent, the level of Urmia Lake increased during hydroclimatic events conducive to lake expansion, which affected the soil evolution due to several fluctuations during the late Quaternary.

Insight into the Last Glacial Maximum climate and environments of the Baikal region

This study presents a multi‐proxy record from Lake Kotokel in the Baikal region at decadal‐to‐multidecadal resolution and provides a reconstruction of terrestrial and aquatic environments in the area during a 2000‐year interval of globally harsh climate often referred to as the Last Glacial Maximum (LGM). The studied lake is situated near the eastern shoreline of Lake Baikal, in a climatically sensitive zone that hosts boreal taiga and cold deciduous forests, cold steppe associations typical for northern Mongolia, and mountain tundra vegetation. The results provide a detailed picture of the period in focus, indicating (i) a driest phase (c. 24.0–23.4 cal. ka BP) with low precipitation, high summer evaporation, and low lake levels, (ii) a transitional interval of unstable conditions (c. 23.4–22.6 cal. ka BP), and (iii) a phase (c. 22.6–22.0 cal. ka BP) of relatively high precipitation (and moisture availability) and relatively high lake levels. One hotly debated issue in late Quaternary research is regional summer thermal conditions during the LGM. Our chironomid‐based reconstruction suggests at least 3.5 °C higher than present summer temperatures between c. 22.6 and 22.0 cal. ka BP, which are well in line with warmer and wetter conditions in the North Atlantic region inferred from Greenland ice‐cores. Overall, it appears that environments in central Eurasia during the LGM were affected by much colder than present winter temperatures and higher than present summer temperatures, although the effects of temperature oscillations were strongly influenced by changes in humidity.

Integrated Paleoseismic Chronology of the Last Glacial Lake Lisan: From Lake Margin Seismites to Deep‐Lake Mass Transport Deposits

AbstractSeismically disturbed sedimentary sequences (seismites) in the last glacial (70–14 ka) Lisan Formation are exposed in the marginal terraces of the Dead Sea and recovered from sedimentary core drilled by the International Continental Scientific Drilling Programs at the depocenter of the lake at water depth of 300 m. The core reveals various types of centimeter‐ to meter‐scale disturbed lake sediments: turbidites, homogenites, slumps, and other deformations, interspersed with undisturbed lamination. The transported sediments comprise a main source of the thickness tripling of the Lisan Formation at the depocenter of the lake compared to the margins. Excluding (mass transport deposits MTDs) from chronology yields a normal, event‐free age‐depth model for core. Moreover, time intervals of units missing at the exposed sections of the lake margin are synchronous with intervals of mass transport deposits (MTDs) at the deepest lake floors. In the deep core, the recurrence interval range of MTD with thickness > 1 cm is ~ 100–300 years, while that of the thick MTD (>50 cm) is ~ 2,500 years, twice the recurrence interval of the seismites at the lake's margins. The ~1,000 year recurrence at the lake's margins lies within the ranges that have been calculated for ~M6.5–7 earthquakes. The significantly higher figure shown by depocenter core suggests activity on various faults and the response of the lake sediments in the entire Dead Sea basin. Overall, an unprecedented chronology of seismic activity was achieved for the late Pleistocene Lisan Formation providing a framework of earthquake activity in the vicinity of the Dead Sea basin during the period of the last high lake stand.

Mineralogy and carbonate geochemistry of the Dali Lake sediments: Implications for paleohydrological changes in the East Asian summer monsoon margin during the Holocene

Hydrological variations in individual plateau lakes respond from both local hydrological processes and regional climatic changes. This study presents high resolution, absolutely-dated records of minerals in bulk samples and elements and stable isotopes of endogenic calcites from a sediment core from Dali Lake in Inner Mongolian Plateau, aiming to investigate the patterns and mechanisms of Holocene hydrological and climatic changes in the modern northern margin of the East Asian summer monsoon (EASM). Increases in the percentages of allogenic minerals (quartz, microcline and albite) and decreases in the percentages of endogenic/authigenic minerals (calcite, Mg-calcite and gypsum), together with decreases in the values of Ca and Mg concentrations and δ18O and δ13C of endogenic calcites indicate an excess of water input to the lake over evaporative losses, and vice versa. These data suggest that the hydrological balance of Dali Lake was controlled by strong evaporation before 9800 cal yr BP, and then the lake was supplied by significantly increased inflowing water between 9800 and 5900 cal yr BP. From 5900 to 4850 cal yr BP, the water input to the lake significantly decreased. Since 4850 cal yr BP, the inflowing water maintained a low level. In addition, the distinct characteristics of mineralogy and carbonate geochemistry of the Dali Lake sediments during the periods of high lake level between 9800–7700 and 7700–5900 cal yr BP imply that the lake was mainly fed by snow/ice melt water in the former period and then by regional precipitation in the latter period, which was further supported by the pollen records from the same sediment core. These results suggest that Holocene hydrological variations in the EASM margin were closely related to changes in regional temperature and precipitation which were ultimately controlled by changes in the Northern Hemisphere summer insolation, northern high latitude ice sheets, global sea level and physicochemical conditions of the North Atlantic and western tropical Pacific on orbital and millennial timescales. The datasets in this study support that the maximum EASM intensity occurred during the middle Holocene in the northern EASM regions.

The characteristics of tight oil sand reservoir-source assemblage in lacustrine basins: A case study of the Cretaceous Qingshankou Formation, Songliao Basin, northeast China

The complicated source-reservoir-assemblage characteristics of lacustrine tight oil sand in China are the main controlling factors of tight reservoir oiliness (i.e., oil richness). Several studies have focused on qualitative description of source-reservoir-assemblage characteristics without quantitative assessment. In this study, reservoir-source-assemblage (RSA) has been evaluated quantitatively by fitting the RSA log in the evaluation of Qijia Depression in the Songliao Basin. Total organic carbon (TOC) and sand volume (Vs) logs are used to fit the RSA log in three steps: (1) TOC and Vs log fitting and normalization, (2) RSA log fitting, and (3) extraction of root-mean-square (rms) amplitude and frequency (Frq(0)) information from the RSA log. The rms represents the reservoir capability and hydrocarbon potential, and Frq(0) represents the interbedding frequency that changes with the lake level. Positive values (0–1] of the RSA log correspond to a high lake level, whereas negative values [[Formula: see text], 0) correspond to a low lake level. Based on RSA log values, we defined the parameter RSAsuf, a product of rms and Frq(0), to quantitatively evaluate the tight oil sweet spot. RSAsurf serves as tight oil sweet spot indicator and correlates positively to oil richness. As a result, four types of effective reservoirs (RI, RII, RIII, and RIV), two types of effective sources (SI and SII), and three types of RSAs (R-S-R, S-R-S, and S-S-R) are identified based on cores and RSA logs. High RSAsuf values on the isoline map indicate the sweet spot zones around the G933 and J392 well areas, which correlates very well with the oilfield test data. The approach is appropriate for lacustrine basins with complicated RSA, in which RSA logs serve as indicator for the sedimentary rhythm, reservoir capability, and hydrocarbon potential.

5. Determining Groundwater Inputs into High Arctic Lakes (Cape Bounty, Melville Island, NU)

The focus of this research project is to determine the presence of groundwater seepage within two High Arctic lakes located in continuous permafrost on Melville Island, NU. Small isolated depressions were located at the bottom of each lake using bathymetric data – 21 in East and West Lake (unofficial names) combined. It was hypothesized that these depressions could be the sites of groundwater seepage into the lakes, and these locations then served as sample sites for CTD cast and water sample collection during the 2016 field season. Water chemistry and physical property data were used as indicators of groundwater seepage, as ground water would have properties similar to the source of the ground water, generating a change in water chemistry at each of these sites.
 Ionic analysis has showed site specific change at the bottom of both lakes, related to the underlying bedrock structure. Ionic ratios for the northern sites differ from ratios of the rest of the sample sites, as well as the ambient water of each lake. This correlates with the meeting of two geologic units within both lake limits. Physical characteristic data showed no change within East Lake and a localized change within West Lake, represented as an increase in electrical conductivity and decrease in dissolved oxygen. These results suggest that highly localized groundwater seepage is likely occurring in these High Arctic lakes, and that water property influences to ground water may be even more highly localized.

Arctic moistening provides negative feedbacks to riparian plants.

Arctic moistening will affect the circumpolar forested riparian ecosystems. Upward trends observed for precipitation in high latitudes illustrate that the moistening may be underway to influence the woody biomass production near the inland waters, lakes and streams with effects on carbon pools and fluxes. Although the flooding and waterlogging tolerance of seedlings has been investigated, our understanding of responses in mature trees is still limited. Here we employ tree-ring δ13 C and width data from a subarctic riparian setting in Lapland, where artificially high lake level (HLL) has already altered the ecophysiological and growth responses of riparian Pinus sylvestris trees to external drivers under conditions simulating moister environment. Prior to the HLL event, the carbon assimilation rate was primarily limited by irradiance as reflected in the δ13 C data and the radial growth of south-facing riparian trees remained increased in comparison to shaded upland trees. By contrast, the riparian trees were not similarly benefited during the HLL period when reduced assimilation depleted the riparian in comparison to upland δ13 C despite of increased irradiance. As a result, the radial growth of riparian trees was markedly reduced over the HLL event while the upland trees benefited from increased irradiance and summer time warming. Although the production of biomass at high latitudes is commonly considered temperature-limited, our results highlight the increasing role of Arctic moistening to limit the growth when increased precipitation (cloudiness) reduces the incoming solar radiation in general and when the riparian habitat becomes increasingly waterlogged in particular. The effects of high-latitude warming to induce higher biomass productivity may be restricted by negative feedbacks.

A salt lake under stress: Relationships among birds, water levels, and invertebrates at a Great Basin saline lake

Saline lakes are threatened globally and provide critical habitat for a diverse array of migratory and breeding waterbirds. The ability of large numbers of waterbirds to profitably use saline lakes is primarily dependent upon concentrations of invertebrate fauna that are only present within a narrow range of salinities. Additionally, waterbirds themselves can incur steep physiological costs as their salt loads increase, meaning that they are especially sensitive to changes in salinity. Nonetheless, relatively little is known about ecosystem function within natural saline lakes or how birds will respond to fluctuations in salinity across time, hindering efforts to maintain ecologically functional saline ecosystems. To help address this gap, we coupled data from waterbird surveys undertaken across 25 years at Lake Abert, Oregon, USA with data on lake area (a proxy for salinity) and invertebrate abundance to document how waterbird numbers changed in response to variation in lake area and the presence of their invertebrate prey. We found that as the area of Lake Abert decreased and salinity increased, both invertebrate and waterbird numbers declined, with especially high salinities associated with the presence of few waterbirds and invertebrates. However, we also found that at high lake levels and low salinities the abundance of most waterbirds and invertebrates either plateaued or declined as well. Our study reinforces physiological studies showing that both invertebrates and waterbirds can only tolerate a narrow range of salinities, and is among the first to document the effects of this tolerance range at the ecosystem level. As anthropogenic water usage increases and snowfall decreases in the coming century, Great Basin saline lakes are projected to increasingly face water shortages and high salinities. Conserving saline lake ecosystems thus requires mitigating these losses and maintaining water levels and salinities within the normal range of inter-annual variation. When conditions outside of this range occur too frequently or persist too long, they can result in dysfunctional ecosystems with deleterious consequences for the species that rely on them.

Morphodynamics of the Kulsi River Basin in the northern front of Shillong Plateau: Exhibiting episodic inundation and channel migration

The present study is undertaken in the Kulsi River valley, a tributary of the Brahmaputra River that drains through the tectonically active Shillong Plateau in northeast India. Based on the fluvial geomorphic parameters and Landsat satellite images, it has been observed that the Kulsi River migrated 0.7–2 km westward in its middle course in the past 30 years. Geomorphic parameters such as longitudinal profile analysis, stream length gradient index (SL), ratio of valley floor width to valley height (Vf), steepness index ( $$k_{s})$$ indicate that the upstream segment of the Kulsi River is tectonically more active than the downstream segment which is ascribed to the tectonic activities along the Guwahati Fault. $$^{14}\hbox {C}$$ ages obtained from the submerged tree trunks of the Chandubi Lake, which is located in the central part of the Kulsi River catchment suggests inundation (high lake levels) during 160 ± 50 AD, 970 ± 50 AD, 1190 ± 80 AD and 1520 ± 30 AD, respectively. These periods broadly coincide with the late Holocene strengthened Indian Summer Monsoon (ISM), Medieval Warm Period (MWP) and the early part of the Little Ice Age (LIA). The debris which clogged the course of the river in the vicinity of the Chandubi Lake is attributed to tectonically induced increase in sediment supply during high magnitude flooding events.

Chronological evolution of some morphological, tectonic and volcanic features in Lake Van, based on correlation of seismic and core data

The Lake Van is the largest Lake in Turkey and the fourth largest soda lake in the World. High resolution (HR) seismic data acquired during 2012 reveals sub-lacustrine terraces, delta clinoforms, channel-networks, active faults and volcanic edifices. The seismic data were correlated with the cores recovered during the 2008 coring and 2010 ICDP PaleoVan drilling campaigns, using synthetic seismograms produced from the MSCL data of the age-modelled cores, thus allowing to date seismic reflector surfaces and to discuss the temporal evolution of the some of the morphological features and structures. Sub-lacustrine channel-network systems are well developed on the shelf areas connect with the river drainage systems on land and extend to water depths of more than 100 m. These drainage systems developed during the major low-stand periods of Lake Van, the last two of which occurred during 15 ka BP and the Younger Dryas with water levels at −200 m and −70 m, respectively. High lake levels similar to today during the early Holocene were followed by lake level oscillations with some low-stands during the Late Holocene. The low stands are characterized by terraces and berms located at 15 m below lake surface (mbls), 25 mbls, 35 mbls and 60 mbls, 70 mbls and 105 mbls. They were most likely related to the rapid climate change (RCC) events such as the 4.2 ka aridity event, Dark Age Cold Period, Medieval Warm Period and Little Ice. The volcanic features are located along the Southern Boundary Fault (SBF). A significant NW-SE trending active fault in the eastern shelf left-laterally offsets a channel by about 500 m and has a small reverse component in the HR seismic profiles. This fault is considered to be the source of Mw = 5.7 Edremit Earthquake of 9 November 2011. NW-SE trending normal faults with a right-lateral strike slip component north of the Northern Basin provides extension in the area. Normal faults are also dominant in the Erciş Strait. Using ages of reflector surfaces we estimate a vertical slip rate of 0.40 mm/yr to ∼0.5 mm/yr on the normal faults in the shelf areas over the last 2–3 ka.

Lake levels in a discontinuous permafrost landscape: Late Holocene variations inferred from sediment oxygen isotopes, Yukon Flats, Alaska

ABSTRACT During recent decades, lake levels in the Yukon Flats region of interior Alaska have fluctuated dramatically. However, prior to recorded observations, no data are available to indicate if similar or more extreme variations occurred during past centuries and millennia. This study explores the history of Yukon Flats lake origins and lake levels for the past approximately 5,500 years from sediment analyses guided by previous work on permafrost extent, thermokarst, and modern isotope hydrology. Sediments dated by 210Pb and AMS radiocarbon indicate stable chronologies following initial lake initiation. Subsequent lithology is autochthonous, and oxygen isotope ratios of endogenic carbonate reflect lake level change at multiple time scales. Sediment results indicate high lake levels between approximately 4000 and 1850 cal yr BP, which is interpreted to reflect wetter-than-modern conditions. Lower lake levels with short-lived high stands during the past approximately 800 years reflect generally arid conditions with brief wet intervals similar to the region’s moisture regime today. The millennial trend is one of increasing aridity and corresponds closely with fire reconstructions and regional paleoclimatic trends. We conclude that high-magnitude lake-level fluctuations and decadal scale trends occurred before the observational period and are persistent hydroclimatic features of the Yukon Flats region.

Late Pleistocene paleolake evolution in the Hetao Basin, Inner Mongolia, China

The paleolake that once existed in the Hetao Basin, China, represents an important stage of the Yellow River drainage system evolution in the region, but it has not been studied in detail to date. In particular, the formation and driving forces of the paleolake evolution since the late Pleistocene is still poorly understood. In this study, optically stimulated luminescence and radiocarbon dating were combined with multiproxy analysis of lacustrine sediments in the central Hetao Basin to reconstruct the paleolake evolution. Proxies included carbonate 18O and 13C isotopes, grain size, magnetic susceptibility, and color. In combination with stratigraphic records, the proxies indicated the existence of a lake environment in the Hetao Basin between ∼150 and ∼18 ka BP. The paleolake between 150 and 130 ka BP was an open system. Between 130 and 54 ka BP, the paleolake basin closed, with high lake levels at the beginning of the period and then a gradual decrease. After 54 ka BP, the paleolake began to outflow and gradually shrank in size, and after 18 ka BP an alluvial fan covered the region, and the paleolake disappeared. We propose a combination of tectonic uplift and climate changes as the main drivers of paleolake formation and evolution since the late Pleistocene.

Late Holocene stable isotopic (δ13C and δ15N) records of lacustrine organic matter in Guangdong Province, south China, and their palaeoenvironmental implications

This study presents the results of TOC/TN (C/N) ratio, δ13C and δ15N analyses of lake sedimentary organic matter (OM) from the Hedong section, western Guangdong Province in south China, with the objective to reveal the history of hydrological and ecological variations in the region influenced by both the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM). Variations in δ13C and δ15N of sedimentary OM may be closely related to past climatic conditions, which results in variations in surface runoff, lake level, allochthonous and autochthonous sources of OM, and lake productivity. Based on the interpretation of these proxies, four periods, i.e. 4370–4100, 3700–2900, 2400–2100 and 1900–900 cal. a BP, are characterized by low lake level, weakened surface runoff and deteriorated status of terrestrial and aquatic ecosystems, whereas the periods 4100–3700, 2900–2400, 2100–1900 and 900–600 cal. a BP are dominated by high lake level, strengthened surface runoff, and flourishing terrestrial and aquatic plants. A remarkable positive correlation between the δ13C values of the section and the ENSO number record obtained from the tropical Pacific implies that the impact of the ISM is greater than that of the EASM in the study area. The abnormal correspondence between the δ13C and solar activity reconstructed from 10Be and 14C records in GRIP ice‐core occurred from 1500–800 and particularly from 4200–4000 cal. a BP, suggesting that these two cool and dry intervals may be caused by stronger volcanic activities that are recorded in the GISP2 and Dome C ice‐cores. This study reveals that changes in solar insolation and solar activity, as well as changes in oceanic–atmospheric circulation (e.g. the ENSO intensity) and intensive volcano eruptions may have exerted influence on late Holocene climate variability in the study area.

Transformation of ecosystems glacial lakes in Ukrainian Carpathians

The sizes of glacial lakes of the Ukrainian Carpathians without surface water runoff (Brebeneskul, Nesamovyte – the last 130 years, Verhne Ozirne, Nyzhne Ozirne – the last 50 years) and surface water runoff lakes Dogyaska (the last 30 years) has not substantial changes. The lakes Maricheyka and Vorozheska considerably decreased in area (20–40 % of previous squares), obviously, due to the erosion of rocky moraines-damages. Comparison of photos lakes Nesamovyte (1935–2008) has not showed changes of the outlines of the water area, the sedge-sphagnum alloy and the coastal thickets of the debris. The small glacial lakes Breskul has reduced its bed, because the sedge-sphagnum alloy overgrown with ray herbs, but the open water area is stable during the last 67 years. There are some increase alkalinity water of Brebeneskul and Verhne Ozirne and acidification of the Nesamovyte during the last 60 years. Unidirectional changes in the acid-alkaline balance of glacial lakes waters are not noted. The shrub covered decreases its area in basins of the all glacial lakes of Ukrainian Carpathians every year as a result of the cuttings of tourists for the campfires. For example, the number of the hearths in the Nesamovyte basin has decreased from 7 in the 2001 to the 80 in the 2017 years. The most intense in this process is in the basins of Nesamovyte and Brebeneskul. The number of tourists stopping for a night in the basins of high mountain lakes increased by 7–10 times according to the calculation of foci traces during 2001–2017 years. The clogging of shores and water areas of the glacial lakes and the formation of random garbage increases in the last two decades. The number of the oligosaprobic crustaceans species decrease and mesosaprobic are growing, appear polisabrobic species. The saprobic status of water lakes with the greatest recreational influence (Nesamovyte, Brebeneskul, Dogyaska) has a tendency to increase during the last 17 years. The loss of stenobiontic crustaceans species from glacial lakes (Streblocerus serricaudatus (Fischer, 1849), Mixodiaptomus tatricus (Wierzejski, 1883) and some others), the penetration of non-typical hydro- and amphibiontic species into highlands waters (Pohlia nutans (Hedwig) Lindberg, 1879, Bufo bufo (Linnaeus, 1758), Simocephalus vetulus (O. F. Müller, 1776) and others), and the increase in the rate of mass, mezosaprobic and eurybionts species in the total number of water groups are noted. Verhne Ozirne was the last untouched glacial lake of the Ukrainian Carpathians, but after the introduction of its basin to the Ramsar Convention there was laid a path there and today we will observe intensification of tourist and pasture influence on its ecosystem. The most anthropogenic negative influence has recreation (clogging, cutting, trampling, automotourism and other factors). Mountain tourism is one of the most dangerous types of anthropopression in high-altitude areas, as it is in the lakes located on permanent tourist routes and water catchments which is the place for overnight tourists, the degradation of populations and groups of mountainous species of hydrobionts has been noted. Moderate pastoral influence (up to thirty heads of cattle per hectare per day) does not make significant changes from the hydrobionts communities of the glacial lakes. The most effective mechanism for preventing the negative processes of anthropogenic transformation of ecosystems of the glacial lakes of the Ukrainian Carpathians is to determine the buffer number of tourists visiting basins of unique aquatic glacial ecosystems of Ukraine and the strict control over compliance by visitors with the rules of conduct regulated by environmental organizations.

Holocene paleohydrological reconstruction of Lake Strzeszy\u0144skie (western Poland) and its implications for the central European climatic transition zone

Western Poland is located in the central European climatic transition zone, which separates the mild and humid Atlantic climate of Western Europe and the East European continental climate. This region is sensitive to lateral shifts of the European climate zones and is particularly suitable for reconstructing Holocene climate variability. This paper presents detailed analyses of the sedimentary record from Lake Strzeszyńskie since the Late Pleistocene. These include smear-slide and thin-section observations, X-ray fluorescence core scanning, magnetic susceptibility measurements, pollen analyses, and radiocarbon dating. The sediment record reveals three distinct sedimentary units consisting of: (1) an alternation of sand layers and laminated silt and clay deposits accumulated prior to 14,600 cal yr BP; (2) faintly laminated calcareous sediments intercalated with organic matter-rich layers deposited between 14,600 and 10,200 cal yr BP; and (3) massive calcareous mud deposited after 10,200 cal yr BP. The Holocene period is marked by nine phases of organic-rich sedimentation and enhanced Fe deposition, which occurred at ca. 10.1, 9.3, 6.4–6.1, 5.5–5.1, 4.7–4.5, 2.7–2.4, 1.3–1.2, 0.8–0.6, 0.4–0.2 kyr cal BP. These phases are associated with high lake levels and correspond with wet periods recognized in several other records from Poland and central Europe. These phases partly coincide with North Atlantic cold periods, which may suggest that high lake levels are triggered by an ocean-continent linking mechanism.

Arid and humid phases in central Italy during the Late Pleistocene revealed by the Lake Trasimeno ostracod record

A multiproxy approach in a sediment core from Lake Trasimeno has been used to reconstruct the climate history of central Italy during the Late Pleistocene to Early Holocene period (ca. 47,000–9,000calyr B.P.). Ostracod assemblages and sedimentological data (lithology and carbonate content) have been used to infer past hydrological changes in the area. Ostracods were analyzed throughout the core using diversity indexes and multivariate statistic analyses (Cluster and PCA). Three main associations linked to lake level and salinity variations were recognized: 1) the C. torosa association, indicating permanent lacustrine conditions with high lake levels and low salinities; 2) the S. aculeata association, linked to very shallow/temporary waters with higher salinity conditions; and 3) the S. aculeata-E. mareotica association pointing to temporary water conditions and the highest salinities. Furthermore, the presence of C. fuscata and L. blankenbergensis during wide parts of the Late Pleistocene indicates temperatures lower than present days. Alternations of these three ostracod associations compares well with the oxygen isotope curve from Greenland (NGRIP) and are thus interpreted as climatically driven. At the Holocene transition (Termination 1), the ostracod associations indicate a delay in the increasing warming and humidity with respect to the NGRIP temperature record.