Lake Stage Research Articles

Environmental Changes on Kunashir Island (Kuril Archipelago) during the Middle and Late Holocene

Sea level rise during the Pleistocene-Holocene transition period caused the formation of lagoon lakes along the western and eastern coasts of the Kuril Islands. These lakes include Lake Serebryanoye, located in the northern part of the South Kuril Isthmus near the Pacific coast of Kunashir Island (44°03'21" N; 145°49'46" E). The total thickness of sediments in the lake was 367 cm. They are characterized by diatom flora (334 species), representing various ecological groups: freshwater, brackish water, marine, marsh, lacustrine, rheophilic, planktonic, benthic. The analysis of diatoms made it possible to distinguish two complexes. As shown by radiocarbon dating, in the Middle Holocene (100.5-367 cm interval) the sediments corresponded to the lagoon stage, which changed in the Late Holocene (100.5-0 cm interval) to the freshwater lake stage. Palynological analysis showed a successive change of biocenoses, reflecting the development in the Middle Holocene of birch-broadleaved forests with the participation of Pinus koraiensis, Picea sp. The most abrupt change in biocenoses is observed at the boundary of the Middle and Late Holocene. This change of biocenoses is expressed by the dominance of conifers in the vegetation cover, represented by various species of Picea, Pinus, Abies, Larix. It also shows the relative cooling of the climate in the Late Holocene.

OSL Dating of the Sukor Earthquake-induced Rockslide in Gorny Altai: Paleoseismological and Paleogeographic Implications

Abstract —Lacustrine sediments, related subaerial aeolian sands, as well as fluvioglacial sands enclosed in ablation moraines in the Chuya River valley between the Chuya and Kurai basins in Gorny Altai, have been dated by optically stimulated (OSL) and infrared stimulated (IRSL) luminescence. The OSL and IRSL ages indicate that the formation of the lake, which spread into the Chuya Basin, was caused by the Sukor rockslide that dammed the Chuya Valley. The rockslide was triggered by a large earthquake (shaking intensity at least IX-X) generated by an active fault in the Kurai Fault Zone about 16 ka, which is the oldest known date for its activity. Thus, large landslides or rockslides can remain geomorphically expressed for at least 16 ka in the climate and landscape conditions as in the Chuya and Kurai basins. The lake existed till ~10 ka BP and then was gradually drained. The Kuyuktanar glacier reached its greatest extent in the early marine isotope stage (MIS) 2, and its ablation moraines formed about 25 ka. Judging by the age and good preservation of moraines left by the glacier, the hilly terrain in the area of the Sukor rockslide, and the presence of lacustrine sands in the vicinity of the lake dam, no catastrophic flooding events in the Chuya and Katun valleys have occurred since the Last Glacial Maximum (LGM; ~20 kyr BP). The water table of the glacier-dammed lake that occupied the Kurai Basin around the LGM could not have exceeded 1750 m above sea level (a.s.l.). Higher lake terraces traceable till elevations of 2100–2200 m a.s.l. should be attributed to more ancient lake stages. Archaeological sites in the area of the junction between the Chuya and Kurai basins were formed in the post-lake period, the oldest dating back to the latest Late Paleolithic time.

Variation of lacustrine carbonate deposition in the Eocene Dongying Depression and its comparison with Holocene environments

AbstractThe sedimentary characteristics and preservation potential of lacustrine carbonates provide fundamental information on climate change. The lacustrine carbonate deposition in the Eocene Dongying Depression was investigated using a combination of mineralogical, petrological and geochemical analyses. Micritic calcite/dolomite, granular calcite, columnar calcite, calcareous shell fragments and reworked detrital calcite were identified. Varying patterns of carbonates (VPC) including lithofacies, geochemical indicators and carbonate distribution were revealed in the Dongying Depression: (i) carbonates hardly precipitate in the nearshore area (average 12 wt %); (ii) carbonate content is high (average 53 wt %) in the shallow lake and (iii) gradually decreases to reach a minimum (average 24 wt %) in the deeper part of the lake. Comparison of VPC in four Holocene lakes (the Qinghai Lake and Barkol Lake in China, Oro Lake in Canada and Montcortès Lake in Spain) with the Dongying Depression suggests that four distinct lake stages were developed, namely the terrigenous clastic/gypsum-rich, carbonate-rich, carbonate-decreasing and carbonate-poor stages. A depositional model of lacustrine carbonates influenced by detrital influx, climate, palaeoproductivity and salinity is developed. This study contributes to the understanding of the genetic mechanisms of lacustrine carbonate deposition to reconstruct environmental changes.

Paleoclimate reconstruction of the last 36 kyr based on branched glycerol dialkyl glycerol tetraethers in the Padul palaeolake record (Sierra Nevada, southern Iberian Peninsula)

Quantitative continental climate reconstructions covering the last glacial cycle from the Iberian Peninsula are scarce. In order to fill this gap, we obtained for the first time a high-resolution mean annual air temperature (MAAT) record based on the distribution of specific bacterial membrane lipids (i.e., branched glycerol dialkyl glycerol tetraethers; brGDGTs) from the last 36.0–4.7 kyr palaeolake record recovered by the Padul-15-05 sedimentary core (Padul, Sierra Nevada, southern Iberia). The fractional abundance of the three major groups of GDGTs present in the Padul sediments, GDGT-0, crenarchaeol and the summed brGDGTs, is comparable with that of other shallow and small (<10 km2) European lakes. Despite variations in the lithology in the studied section, the GDGT composition remains relatively stable, except for the uppermost 116 cm of the record, representing the ephemeral/emerged lake stage, which is characterized by higher crenarchaeol fractional abundances. The identification of a specific brGDGT that has only been detected in anoxic lakes provides evidence for in-situ brGDGT production in the water column and/or sediments in the Padul palaeolake. Its presence/absence probably denotes a succession of periods with a variable oxygen content in the bottom waters of the palaeolake. MAAT was reconstructed based on the distribution of brGDGTs using an African lake calibration and ranged between 12 and 20 °C. A new Bayesian calibration to mean temperature of Months Above Freezing (MAF) depicts similar temperature variations with a mean absolute difference of 0.7 °C. The MAAT reconstruction in the Padul palaeolake for the 36.0–4.7 kyr period reveals similarities with climate variability described at high-latitudes and in the westernmost Mediterranean area during this interval, showing cold conditions during the last three Heinrich Stadials and the Younger Dryas and warm conditions during the Dansgaard–Oeschger interstadials (7–1) and the Bölling-Alleröd period. Despite the more stable and warm general climate conditions during the Early and Mid-Holocene, rapid centennial-scale temperature changes are registered in the Padul palaeolake in good agreement with variations observed in the Mediterranean forest record.

Predicting effects of water management on breeding abundance of three wading bird species

AbstractWetland conservation often involves creating hydrological regimes that maximize habitat and resources for wildlife. In the greater Everglades ecosystem in Florida, USA, where wading birds are food‐limited in some years, models predicting the influence of hydropatterns on foraging habitat availability are used to guide the management of water levels for wading bird nesting populations. These models are useful but do not consider that nesting wading birds are central place foragers, and thus resource availability is a colony‐level measure. We examined long‐term nest abundance patterns of the great egret (Ardea alba), snowy egret (Egretta thula), and white ibis (Eudocimus albus) to determine effects of hydropatterns on wading bird nest abundance in a 400‐km2 littoral marsh in Lake Okeechobee, Florida. We developed 2 sets of statistical models for each species: 1 examining variation in nest abundance (1977–1992, 2006–2019) and 1 predicting colony‐level nest abundance (2006–2019). Models of nest abundance predicted that great egret nesting will peak when March–April lake stage is 4.3–4.5 m, coinciding with the peak in area of available foraging habitat. Neither recession rate nor stage explained total snowy egret or white ibis nest abundance, though snowy egret nest abundance has increased since the 1990s, when the water management schedule favored higher lake stages for longer duration. For all species, colony‐level models predicted that nesting increased with increased habitat availability, faster water‐level recession rates, and greater number of days dry in the previous 2 years at nest sites. When applied to simulated hydrological data representing changes to water‐level regulations in Lake Okeechobee, our models predicted that management regimes allowing extreme flooding (stage &gt; 5.18 m) in &lt;220 days per 5.0 years and Carolina willow (Salix caroliniana) recruitment (stage &lt; 3.9 m) &gt;3.0 years per 5.0 years resulted in the highest nest abundance for snowy egret and white ibis. Snowy egret and white ibis nesting decreased by 575 nests/year and 465 nests/year, respectively, when regulation schedules increased the management envelope by 0.46 m, whereas great egret nest abundance increased modestly (149 nests/year). Operational rules that allow intermediate drought disturbance in dry years and prioritize increased habitat availability at short‐hydroperiod colonies in wet years should result in overall benefits to the wading bird community at Lake Okeechobee.

Detailed results of diatom analysis of bottom sediments from lake Big Miassovo (Chelyabinsk region, Russia)

Diatoms are good indicators of a variety of lake water conditions including salinity, pH, light availability, temperature and nutrient levels, but diatoms as palaeoindicators are relatively poorly studied in the Chelyabinsk region. The diatom results of analysis a 498 cm long continuous sediments core from the Lake Big Miassovo (Southern Urals, Russia) are presented. The core was collected in July 2018 from central part of the lake from a depth of 24 m. Diatom analysis of 51 samples revealed 124 taxa, belonging to 47 genera. Diatom diagram has been divided into two diatom zones and five subzones on the basis on changing diatom abundances and taxa composition. The predominance of cosmopolitan, alkaliphilic benthic, oligogalobic species with the growth under the moderate temperatures is noted. The prevalence of Handmannia comta diatom in sediments have been established. The first period reflected the stage of an oligotrophic-mesotrophic lake with a low water level. The second period is characterized by an increase in the number of planktonic species and diversity of diatoms communities, the formation of a deep water body in a warm climate.

Climate signals in the Holocene bottom sediments of shallow saline lakes of the Southwestern Siberia

Abstract. We present the results of the study of the Holocene sediments from two shal low lakes of different salinity located in the East Baraba lowland (Southwestern Siberia). The research methods: X-ray diffractometry (XRD), IR spectroscopy, laser particle size analysis, AMS dating, etc. By the mathematical modeling of complex XRD patterns Mg-calcites with different Mg contents, excess-Ca dolomite and aragonite have been established in the assemblages of carbonate minerals. Based on studies of mineralogical-crystallochemical features and quantitative ratios of Ca-Mg carbonates the evolution stages of lakes corresponding to the regional cycles of aridization/humidization were identified and the correlations with global climatic events were carried out. The obtained results is an important source of new information about the Holocene climate in the Southwestern Siberia.

Influence of lake stage on the recruitment of Florida bass in Lake Okeechobee

Influence of lake stage on the recruitment of Florida bass in Lake Okeechobee

Monitoring the water balance of seepage lakes to track regional responses to an evolving climate

Understanding the causes of large fluctuations in lake water levels is important for adaptive resource management. The relatively simple water budgets of small seepage lakes make them potentially useful model systems, provided that key water balance components can be well constrained. Here, spatial variability in measured rates of evaporation (E) and precipitation (P) at the whole lake scale was investigated, and the effect on daily and seasonal water balance estimates was quantified. To estimate spatial variability, triplicate sensor platforms were deployed on and near an 18 ha seepage lake. Lake stage (S) was monitored at a single node in the lake. The water balance was closed by estimating net groundwater seepage (Gnet) analytically as Gnet = ΔS – (P – E). Instrumentation on a second seepage lake was maintained by citizen scientists to assess the potential for more widespread sensor deployments. Data were collected at 30-minute time steps for six months. The results indicate that low-cost sensor networks with single nodes to measure E, P, and ΔS provide well-constrained water budgets at daily and seasonal time scales.

Insects and molluscs of the Late Pleistocene at the Gornovo site (Southern Ural foreland, Russia): New data on palaeoenvironment reconstructions

The paper presents new data on the subfossil insects and molluscs, as well a new radiocarbon date for the Gornovo site in the Southern Fore-Urals. As a result, the stratigraphic interpretation of the sediments of the lower part of the first above floodplain terrace of the Belaya River is corrected and they are assigned to the Tabulda Horizon (MIS 3) of the Upper Pleistocene in the regional scheme of the Fore-Urals Quaternary. The malacofauna of the locality is represented by 27 species of terrestrial and freshwater molluscs. The composition of molluscs in the deposits of MIS 3 indicates the succession of deposit accumulation in the river valley from the stage of reservoirs that periodically connecting with the river to the stage of the overgrown oxbow lake. Single occurrence of mollusc shells in the loams of MIS 2 is a result of sharp climate change. New insect material includes 136 species of Coleoptera from 17 families, as well as Heteroptera and Hymenoptera representatives. 29 species of beetles (Carabidae, Histeridae, Scarabaeidae, Elateridae, Tenebrionidae, Chrysomelidae, Brentidae and Curculionidae) are recorded for the Pleistocene for the first time. The insect assemblages from Gornovo site are assigned to periglacial and humid boreal faunal types. The entomofauna of the periglacial type has no analogues in the recent fauna; it corresponds to the deposits assigned to the middle of MIS 3. This entomofauna is characteristic to the MIS 2 and MIS 3 insect assemblages from the south of West Siberian Plain. Based on entomological data, the climate of the middle of MIS 3 of the Southern Fore-Urals is reconstructed as dry and cold, extracontinental, with mean July temperature not exceeding +15 °C. Steppe landscapes likely prevailed in open areas and coniferous forests were restricted to river valleys. Beetles from deposits dated to end of MIS 3 are assigned to the fauna of the boreal humid type. These insect assemblages are significantly poorer in diversity than periglacial type assemblages and are represented mainly by near water and forest Coleoptera. Based on these species, meadow and forest landscapes were reconstructed. The reconstructed mean air temperature of July ranged from +16 to +19 °C. This suggests a trend towards more mild conditions in the region connected to the climate warming at the end of MIS 3. It is likely that humidification during this period was regional, determined by the proximity of the site to the Southern Urals Mountains.

Sedimentation history of Lake Taymyr, Central Russian Arctic, since the Last Glacial Maximum

ABSTRACTHydro‐acoustic and seismic data and 2‐ to 16‐m‐long sediment cores from the central area of Lake Taymyr (Taymyr Peninsula, central Russian Arctic) were investigated to reconstruct its sedimentation history. Granulometric, chronological, geochemical and biological data from the sediment cores reveal two lowstands and two highstands of the lake level, which is today located ca. 5 m above sea level during summer. Our study confirms the presence of an ice sheet blocking the drainage of Lake Taymyr during the latest Weichselian. Although chronological control of the sediment cores does not allow us to unambiguously constrain the time frame for each of the lake stages, the proposed timing of events is in good agreement with regional terrestrial archives as well as marine signals on the Kara Sea Shelf. Overall, the data show that the evolution of Lake Taymyr involved a complex interplay of regional climatic, glacial and sea‐level changes.

From a large basin to a small lake: Siliceous microfossils stratigraphy of the isolation basins on Big Solovetskiy Island (the White Sea, NW Russia) and its implication for paleoreconstructions

This paper discusses the results of siliceous microfossils studies performed in a “staircase” of four isolation basins (33.7 m–2.9 m a.s.l.) on Big Solovetskiy Island (Solovki Archipelago, the White Sea). Diatoms were used as a primary group for paleoinferences, while chrysophyte cysts and sponge spicules also demonstrated high indicative potential. In all study lakes, the siliceous microfossils stratigraphy revealed three main stages of their evolution, i.e. large-basin, transitional and small-lake stages, each characterized by certain composition of the diatom assemblages and floristic diversity, relative abundances of chrysophyte cysts and sponge spicules, and siliceous microfossils concentrations. In the uppermost lake, glaciolacustrine environments unfavorable for aquatic biota existed during the large-basin stage. The proglacial lake stage terminated prior to ca. 10.4 cal ka BP, followed by a (semi)terrestrial episode before the transition to small-lake environments. In the other three lakes, marine environments were inferred at the earlier stage, characterized by the predominance of marine and brackish-marine diatoms, increased proportions of sponge spicules and low “cysts to diatoms” ratio. At the transitional marine-freshwater stage, mass growth of small fragilarioid diatoms and decreased abundances of spicules indicated unstable environments, while increased proportions of cysts pointed to progressive freshening of the basins. The duration of the marine-freshwater transition expectedly prolonged from ca. 200 yr in the upper basin (16.6 m a.s.l) to ca. 500 yr in the lowermost lake (2.9 m a.s.l.). The isolation from the sea took place between ca. 6.3 and 1.4 cal ka BP. At the small-lake stage, siliceous microfossils stratigraphies reflected local specifics of the basins and their catchments. We argue that besides traditionally used diatom data, relative and absolute abundances of siliceous microfossils also possess high indicative value for isolation basin studies. Our study demonstrated that marine waters on Big Solovetskiy Island never reached ca. 34 m a.s.l. during the Holocene, unlike the western coast of the Onega Bay where the Preboreal marine intrusion was recorded even at higher elevated localities. Different rates and amplitudes of shoreline displacement are thus suggested for the inner and outer parts of the Onega Bay. During the mid-Holocene Tapes transgression, before ca. 6.3 cal ka BP, the relative sea level on Big Solovetskiy Island exceeded 17 m a.s.l. The average estimated rates of the shoreline retreat during the second half of the Holocene gradually decreased from 0.28 cm year−1 to 0.2 cm year−1, indicating slowed isostatic uplift.

When were the straits between the Baltic Sea and the Kattegat inundated by the sea during the Holocene?

The timing of the flooding of the Danish/German/Swedish straits and the first marine influence in the Baltic Basin after the Ancylus Lake stage has been much debated. Here we present 47 new radiocarbon ages from sediment cores retrieved from Danish waters, ages that record the marine transgression of the area. Most of the ages are based on shells of marine molluscs, hence the ages are uncertain because we do not know the precise reservoir age in the past. We use a reservoir age of 400 years, which is based on dating of museum specimens collected live before testing of nuclear bombs. It appears from the ages that the Great Belt (Storebælt) was inundated before The Sound (Øresund). The oldest ages on marine shells from the northern part of the Great Belt region are about 8.9 cal. ka BP. From the central part of the Great Belt, the oldest ages are about 8.2 cal. ka BP, in Mecklenburg Bay 8.1 cal. ka BP and in the Arkona Basin 7.1 cal. ka BP. Sediments deposited prior to the occurrence of marine molluscs contain brackish‐water ostracods (Cyprideis torosa and Cytheromorpha fuscata); the sediments are usually laminated and non‐bioturbated mud. The brackish‐water phase may have lasted 500–1000 years. The youngest lake deposits without signs of marine influence are dated to c. 8.8 cal. ka BP (central Great Belt), 8.7 cal. ka BP (Little Belt) and 8.5 cal. ka BP (Arkona Basin). We see no evidence for marine influence at c. 10 cal. ka BP as recorded by some studies from the Baltic Basin.

Morphology and origin of the palaeo cliff area in the Sambia Peninsula nearshore (SE Baltic Sea)

The article scrutinizes stratigraphy, morphology, and origin of the terraced underwater slope of the Sambia Peninsula next to the Taran Cape, the SE Baltic Sea, using a combination of multi-beam and single-beam bathymetry, side-scan sonar survey, CHIRP, single-channel seismoacoustic data, and sediment grain-size results. The underwater slope and its minor landforms were formed by changes of a relative sea-level during the Late Pleistocene and Holocene. Landforms, such as terraces and palaeo cliffs, sinks, remnants, stacks, karst sinkholes, ravines, cuestas, and drowned valleys, are associated with positions of older shorelines, sea-level changes and outcropped Pre-Quaternary formations. Six main stages of the underwater slope development have been recognized. The most important topographic feature is a high palaeo cliff (10 m high) with its toe at a water depth of 26–34 m. The cliff was cut in Cretaceous deposits and has different age and origin in different locations. Its northern sector with a toe at a depth of 34–35 m is polygenetic, formed by tectonic faulting and subsequent abrasion at the Baltic Ice Lake stage. The southern sector, with a toe at a depth of 26–27 m, was cut by wave erosion at the Ancylus Lake stage. Terraces on the underwater slope at depths of 29 m, 34 m, 40 m, 43 m, 48 m and 52 m b.s.l. were formed probably by the Baltic Ice Lake and Yoldia Sea transgressions and survived owing to relatively rapid and short changes of the sea-level. At a depth of 0–26 m, at a sea-level slowstand, selective erosion formed a transgressive wave ravinement surface with karst and cuesta-like landforms on monoclinal Paleogene beds. The depths and the locations of described terraces and palaeo cliffs in the SE Baltic Sea allow us to rectify the relative sea-level curve for the Late Pleistocene-Holocene.

Profiling interactions between the Westerlies and Asian summer monsoons since 45 ka: Insights from biomarker, isotope, and numerical modeling studies in the Qaidam Basin

AbstractThe Qaidam Basin marks a crucial boundary between the Westerlies and the Asian summer monsoons. Previous studies in the Qaidam Basin have advanced our knowledge of the paleoclimate over glacial to interglacial cycles. However, our understanding of the paleoclimatic sensitivity of the Qaidam Basin to the relative strength of these two climatic driving forces remains limited due to the lack of regional paleoclimatic reconstructions. The Qaidam Basin is proposed as a regional and global eolian dust source during the glacial periods, during which a cold, dry climate is associated with the equatorward shift of the jet stream. On the contrary, paleoshoreline records suggest that a highstand lake stage prevailed in late Marine Isotope Stage 3 (MIS 3) and lasted until 15 ka. To address this conundrum, we have applied an integrated approach to reconstructing the regional paleoclimatic history by combining compound-specific isotope analysis, lake temperature reconstruction, and numerical modeling. Our results show varying paleoclimate associated with the dynamic climate boundary since 45 ka: (1) a wet climate during late MIS 3, when the Asian summer monsoons are strengthened under high summer insolation and penetrate further into Central Asia; (2) a general cold, dry but wetter than at present climate in the Last Glacial Maximum (LGM), when the Asian summer monsoons retreat and the Westerlies become dominant; and (3) three short periods of extreme aridity corresponding to the Younger Dryas and Heinrich 2 and 4 events, when the normal moisture transport via the Westerlies and Asian summer monsoons is interrupted. The numerical modeling supports an increase in the effective precipitation during the LGM due to reduced evaporation under low summer insolation. These results suggest that the Westerlies and Asian summer monsoons alternately controlled the climate in the Qaidam Basin in response to precessional forcing during the late Pleistocene.

Peatland Development, Vegetation History, Climate Change and Human Activity in the Valdai Uplands (Central European Russia) during the Holocene: A Multi-Proxy Palaeoecological Study

Peatlands are remarkable for their specific biodiversity, crucial role in carbon cycling and climate change. Their deposits preserve organism remains that can be used to reconstruct long-term ecosystem and environmental changes as well as human impact in the prehistorical and historical past. This study presents a new multi-proxy reconstruction of the peatland and vegetation development investigating climate dynamics and human impact at the border between mixed and boreal forests in the Valdai Uplands (the East European Plain, Russia) during most of the Holocene. We performed plant macrofossil, pollen, testate amoeba, Cladocera, diatom, peat humification, loss on ignition, carbon and nitrogen content, δ13C and δ15N analyses supported by radiocarbon dating of the peat deposits from the Krivetskiy Mokh mire. The results of the study indicate that the wetland ecosystem underwent a classic hydroserial succession from a lake (8300 BC–900 BC) terrestrialized through a fen (900 BC–630 AD) to an ombrotrophic bog (630 AD–until present) and responded to climate changes documented over the Holocene. Each stage was associated with clear changes in local diversity of organisms responding mostly to autogenic successional changes during the lake stage and to allogenic factors at the fen-bog stage. The latter can be related to increased human impact and greater sensitivity of peatland ecosystems to external, especially climatic, drivers as compared to lakes.

Characteristics and origin of the Fengcheng Formation water in Mahu depression and its significance to hydrocarbon migration and accumulation

Formation water is the power and carrier of oil and gas generation, migration and accumulation, which has important significance for oil and gas migration, accumulation and preservation. The groundwater characteristics and genetic mechanism of the Permian Fengcheng Formation in Mahu sag are mainly studied through the chemical composition, isotope test, inclusion temperature measurement and salinity analysis. The study shows that the formation water of Fengcheng Formation in Mahu sag has special hydrochemical characteristics of high salinity, high HCO3 − concentration, low Ca2+, Mg2+ concentration and high pH value NaHCO3 water type. The characteristics of inclusion temperature measurement, carbon and oxygen isotope, strontium isotope and boron isotope show that the Fengcheng Formation fluid has deep hydrothermal source, and volcanism contributes significantly to its CO2 source. The source of deep hydrothermal solution, volcanism and a large amount of hydrocarbon generation and expulsion from source rocks may be the main reasons for high HCO3 − content in formation water. The Fengcheng Formation in Mahu sag is an alkalized lake deposit. The highest alkalization degree of water in the study area may be distributed in the southwest slope of Mahu lake. From the evolution stage of the alkali lake, the first member of the wind is the initial stage of the formation of the alkali lake, corresponding to the late stage of the high water level of the lake, and the water salinity is low; the second member of the wind is the strong alkali forming stage, corresponding to the Lake recession period, the water surface drops, the water body is strongly concentrated, and the salinity is high; the third member of the wind is the fading period of the alkali lake, corresponding to the early stage of the lake advance, the water salinity gradually decreases. On the whole, the groundwater mineralization degree of Fengcheng Formation in Mahu depression is high, and the formation sealing property is relatively good. The side near the edge of the basin is affected by the infiltration of atmospheric water, which results in the decrease of mineralization degree and the appearance of Na2SO4 type water. The water head decreases gradually from Mahu sag to northwest margin, and the gradient of water head near Wuerhe in the north section is relatively strong, which is not conducive to hydrocarbon accumulation and preservation. Baikouquan and Karamay areas are low potential areas, and the water head gradient becomes gentle, which is conducive to oil and gas accumulation.

Summer temperatures and lake development during the MIS 5a interstadial: New data from the Unterangerberg palaeolake in the Eastern Alps, Austria

Investigations of interstadials during early stages of glacial periods are of special interest, because they featured large-scale transformations of the climate system and the build-up of land-based ice sheets. Lacustrine sediment sequences are considered to be important natural archives that register past climate and environmental signals. Here, we present new multi-proxy data obtained from a palaeolake succession preserved in the inner-alpine terrace of Unterangerberg, Eastern Alps. These sediments formed during the second Early Würmian Interstadial, equivalent to Marine Isotope Stage (MIS) 5a, and were used to reconstruct changes in lake conditions and to infer past air temperatures. The sediment geochemical data and subfossil aquatic biota provide evidence of a cyclic lake–fen–lake development during this interstadial. The proxy records reveal stable lacustrine conditions with dense charophyte meadows and abundant aquatic fauna during the early part of the interstadial, a progressive shallowing of the lake resulting in the spreading out of fen vegetation in the middle part, and a transition from wetland to a renewed shallow lake stage towards the end of the interstadial. Chironomids were used to reconstruct mean July air temperatures, employing a combined Norwegian-Swiss chironomid temperature inference model. The reconstruction indicates a temperature close to present-day values of ca. 18 °C in the middle part of the record, while temperatures of ca. 13–14 °C are recorded for the lower and upper parts. The proxy data from this palaeolake provide evidence of heat and drought in the middle part of MIS 5a, supported by the chironomid-based temperature reconstruction. Our reconstruction shows a climate pattern broadly similar to that found in pollen-based estimates of mean July air temperatures from sites in the northern Alpine foreland and compares well to other European palaeoclimatic reconstructions of MIS 5a climate.

Deriving optimal operational policies for off-stream man-made reservoir considering conjunctive use of surface- and groundwater at the Bar dam reservoir (Iran)

Study regionThe off-stream artificial Bar lake, built in 2015 to store the flood flows of the Bar river for domestic and industrial needs and with the objective to intentionally recharge the aquifer, is situated in the Razavi Khorasan province (Iran). Study focusWe present a methodology, based on the combination of a MODFLOW groundwater flow model for estimating seepage rates, and an optimization model, for the management and operation of an artificial reservoir considering surface/groundwater interactions for satisfying 12 Mm3/year of water demand. We simulated the reliable amount of water that can be supplied from the reservoir, considering reservoir seepage, maximizing water supply yields subject to the water supply reliability requirements, and the additional intentional volume of groundwater recharge. New hydrological insights for the regionOur results demonstrate the reliability of conjunctive use of surface-and ground-water in water scarce areas by exploiting reservoir infrastructures with relevant leakage losses, also for creating additional aquifer storage. In such systems, man-induced changes of lake stages can significantly affect the volume of water that seeps through the lakebed. The aquifer, under managed aquifer recharge operations, may then provide the resource not satisfied by the reservoir release, fulfilling 100 % reliability of water supply. The conjunctive use of surface- and ground-water, by improving water security, may open new sustainability views for leaking reservoirs, even if they were not initially designed for increasing aquifer recharge, in many areas worldwide.

Climate and hydrologic controls on late Holocene sediment supply to an Amazon floodplain lake

Organic and inorganic geochemical analyses on sediments from Preto Lake, a central Amazon basin floodplain water body, were used to document hydrological changes of the Solimoes River during the late Holocene. Between 3600 and 400 cal yr BP, Preto Lake received smectite-rich sediment from the Solimoes River, with high concentrations of Al (~ 53 × 103 ppm) and Si (~ 210 × 103 ppm). The high detrital input suggests there was a direct connection between Preto Lake and the main river channel. High river inflow maintained lake stage and was responsible for the contribution to sediments of phytoplankton-derived organic matter. Low sediment organic carbon concentrations characterized this period (mean ~ 3.8 wt%), probably because of dilution by river-borne lithogenic matter. Although the river inputs remained high, abrupt increases in TOC content around 1800 and 1200 cal yr BP suggest brief increases in fluvial nutrient supply to Preto Lake. During the last 400 cal yr, substantial declines in smectite (mean 40%), Al (~ 29 × 103 ppm) and Si (138 × 103 ppm) suggest the establishment of a semi-isolated lake, with reduced river inflow. A large proportion of C3-plant-derived organic matter, supplied by runoff from the kaolinite-rich watershed, was observed during this period, and was accompanied by high autochthonous primary production, driven by development of an aquatic macrophyte community. This change in sediment organic matter source accounted for the greater TOC content (~ 20%) of sediments deposited during this period. Although Holocene climate change was an important control on fluvial sediment supply to upper and lower Amazon Basin floodplain lakes, sedimentation processes in Preto Lake can also be linked to changes in the river’s course. The transition to a semi-isolated lake could have been a consequence of lateral and vertical sediment accretion, which formed a natural levee that blocked fluvial input to Preto Lake.