History Of Lake Research Articles

Springwater provenance and flowpath evaluation in Blue Lake, Bonneville basin, Utah

Water in Utah and Nevada is important for agriculture, municipal use, solute transport, and ecosystem preservation. Large spring wetland systems occur on the playa margin of the Bonneville basin, including Blue Lake, 15 km south of the Bonneville Salt Flats on the Utah-Nevada state border. Large spring systems have historically been studied as water budgets don't apparently balance from direct mountain front recharge (Nelson and Mayo, 2014; Gardner and Heilweil, 2014; and others). Blue Lake is no exception; prior studies here have suggested discharge rates 0.04 - 0.05 km3/yr (Louderback and Rhode, 2009), greater than expected for modelled recharge in the surrounding mountain range (0.03 km3/yr). Three hypothesized recharge mechanisms for Blue Lake are tested: mountain-front recharge, interbasinal groundwater flow, and infiltration from historic Lake Bonneville. Remote sensing suggests that a conservative estimate of Blue Lake discharge constitutes 50-64% of modelled mountain-front recharge (Flint et al., 2011). Major ions, δ18O, δ2H, dissolved gases (14C, 3He, 4He, Ne, Ar, Kr, Xe) and trace elements (Sr and 87Sr/86Sr isotopes) comprehensively constrain recharge conditions, water-rock interactions, flowpaths, and groundwater provenance of this large spring system. 14C signatures suggest that Blue Lake discharge has a transit time between 5,600 and 12,200 years, older than that of Fish Springs. Noble gas concentrations in Blue Lake water suggest an elevated recharge temperature greater than 19°C and low salinity, indicating a deep water table and high geothermal gradient in the recharge area. 87Sr/86Sr ratios of playa-margin springs are elevated from that of mid-playa groundwaters, springwaters from the adjacent mountain range, and alluvial fill groundwater from the valley directly south of Blue Lake. Playa-margin spring Sr isotope values (0.713-0.714) are most similar to direct runoff from the Deep Creek Range granodiorite outcrop (>0.713). Interbasinal groundwater flow in combination with mountain-front recharge is best supported by chemical data rather than mountain-front recharge alone or the slow discharge of regional aquifers recharged by lacustrine infiltration from Lake Bonneville.

Eutrophication forcings on a peri-urban lake ecosystem: Context for integrated watershed to airshed management.

Peri-urban lakes increasingly experience intensified anthropogenic impacts as watershed uses and developments increase. Cultus Lake is an oligo-mesotrophic, peri-urban lake near Vancouver, British Columbia, Canada that experiences significant seasonal tourism, anthropogenic nutrient loadings, and associated cultural eutrophication. Left unabated, these cumulative stresses threaten the critical habitat and persistence of two endemic species at risk (Coastrange Sculpin, Cultus population; Cultus Lake sockeye salmon) and diverse lake-derived ecosystem services. We constructed water and nutrient budgets for the Cultus Lake watershed to identify and quantify major sources and loadings of nitrogen (N) and phosphorus (P). A steady-state water quality model, calibrated against current loadings and limnological data, was used to reconstruct the historic lake trophic status and explore limnological changes in response to realistic development and mitigation scenarios. Significant local P loadings to Cultus Lake arise from septic leaching (19%) and migratory gull guano deposition (22%). Watershed runoff contributes the majority of total P (53%) and N (73%) loads to Cultus Lake, with substantial local N contributions arising from the agricultural Columbia Valley (41% of total N load). However, we estimate that up to 66% of N and 70% of P in watershed runoff is ultimately sourced via deposition from the nutrient-contaminated regional airshed, with direct atmospheric deposition on the lake surface contributing an additional 17% of N and 5% of P. Thus, atmospheric deposition is the largest single source of nutrient loading to Cultus Lake, cumulatively responsible for 63% and 42% of total N and P loadings, respectively. Modeled future loading scenarios suggest Cultus Lake could become mesotrophic within the next 25 years, highlighting a heightened need for near-term abatement of P loads. Although mitigating P loads from local watershed sources will slow the rate of eutrophication, management efforts targeting reductions in atmospheric-P within the regional airshed are necessary to halt or reverse lake eutrophication, and conserve both critical habitat for imperiled species at risk and lake-derived ecosystem services.

The history of the Atlantic Salmon in Lake Ontario

The history of the Atlantic Salmon (Salmo salar), also referred to as Salmon below, in Lake Ontario is an accumulation of authentic published accounts, which were almost completed by J. R. Dymond before his death. H. H. MacKay completed the work on Dymond’s behalf (Dymond and MacKay, unpublished, 1966), but it remained largely unknown. The present authors (MEB, EH, PWB) have sought to present an updated subset of Dymond and MacKay’s work as the history of Lake Ontario Salmon is a crucial story in the history of the Great Lakes and its fisheries. The information provided should add materially to the knowledge of the causes that led to the decline and ultimate extirpation of a fascinating and valuable fish, notwithstanding all the efforts that were made to restore it by artificial means.

Development of Improved Characteristic Equations for Lake Rukwa in Tanzania

Often Lake Rukwa characteristics have been misreported in literature giving different volumes and surface areas at similar water surface elevations. This study aimed at establishing reliable lake characteristics elevation-area-storage equations for Lake Rukwa by utilising all available data and information to define the bathymetry and derive characteristic equations. A procedure was developed that combines historical lake extents, spot heights from topographical maps and surveyed lake bathymetry to define refined bathymetry to levels it has never reached. It combined spot heights around the lake and selected 13,934 surveyed points (from 107,938 available) within the lake confined by the 820 m land contour boundary and define topographical raster image, which was used to extract lake volumes and surface areas between the lowest point (778 m) and 820 m boundary. Change-point analysis was used to detect segmentation of the elevation-area and elevation-volume relationships, which were fitted to a shifted power model. Contours generated from a refined bathymetry raster indicated Lake Rukwa to comprise two north and south lake basins, which are separated by a ridge lying at an altitude of 794.3 m. The north and south lakes consist respectively of five (5) and three (3) deeper depressions (pools) paralleling the northwest- southeast Konongo Scarp, which are disconnected below altitudes 792 m (north) and 789.4 m (south). Characteristic elevation-area and elevation-volume equations are segmented for lake below ridge altitude (794.3 m) whereas single relationships prevail for a single Lake Rukwa. Comparison of lake volumes estimated by refined and old equations indicated underestimation of lake stored volumes between 782.2 m and 805.65 m altitudes and overestimation thereafter by the old equations although the under/over-estimation remained within 10% between 801 m and 812 m. Old elevation-area equations underestimate lake surface area of up to 796.8 m, thereafter overestimate the lake area up to an altitude of 804.85 m and above this altitude underestimation re-appear. The old equations under/over-estimation, however, remains within 11% for altitudes between 794.3 m and 810 m. The refined equations indicate surface areas of north and south lakes at ridge altitude to be 2,554.4 and 837.1 km2 , respectively forming a 3,391.5 km2 lake while at its highest recorded historical elevation of 804.69 m, Lake Rukwa is 183 km long and 17-51 km wide occupying an area of 5,614.7 km2 (north: 4,409.8 km2; south: 1,204.9 km2) and containing 58.243 km3 of water (north: 44.318 km3; south: 13.925 km3). The developed characteristic equations can be used for water management studies of Lake Rukwa.

Phosphorus fractions in sediments and their relevance for historical lake eutrophication in the Ponte Tresa basin (Lake Lugano, Switzerland) since 1959

Lake Lugano is one of several deep lakes in Switzerland that have not yet recovered from eutrophication after large reductions of external phosphorus (P) loadings. Persistent eutrophication has been attributed mainly to internal P loadings from sediments. To achieve the restoration goals, it is critically important to evaluate the sediment P availability and release risk in this lake. In this study, we combined sequential P extraction (four fractions) with enzyme hydrolysis to assess distribution characteristics of P forms and potential bioavailability of organic P in an anoxic sediment profile from the Ponte Tresa basin of Lake Lugano, southern Switzerland. Labile P forms, i.e. mostly redox-sensitive iron bound P and metal oxides bound P (Al/Fe-P), comprised ~70% of total P in the sediment profile (1959–2017 CE), suggesting a high potential for P release from the anoxic sediment. Potentially bioavailable organic P forms (determined by addition of substrate specific enzymes) were considerably higher in the surface sediments (top 5 cm), which is very likely to release P in the near future with early diagenesis. The net burial rates (NBR) of redox sensitive Fe-P fraction and total P in sediments both showed significant decreasing trends from 1959 to 2017 CE, when trophic levels of the lake increased from mesotrophic to hypertrophic status. We suggest that, in the Ponte Tresa basin, higher eutrophication conditions led to enhanced sediment P release (mainly from redox sensitive Fe-P fraction), thus reducing P-NBR in sediments. This study highlights the concern that in deep monomictic lakes, eutrophication restoration might be hindered by extensive internal P cycling and reduced capacity of sediment P-trapping.

Distribution of mineral phases in the Eocene Green River Formation, Piceance Basin, Colorado—Implications for the evolution of Lake Uinta

The mineralogy of the Eocene Green River Formation in the Piceance Basin, Colorado, has been the subject of numerous studies since the 1920s. Most previous work has focused on the resource potential of these lacustrine mudrocks, which in addition to substantial oil shale potential (in-place resources of 353 billion barrels of synthetic crude oil for rocks yielding at least 25 gallons per ton, GPT), includes nahcolite, a currently utilized soda ash resource, and dawsonite, a potential alternative source of aluminum. Another reason to study the mineralogy in this system is that the geographic and stratigraphic distribution of various authigenic minerals may provide insights into the geochemistry and depositional environment of the long-lived Eocene Lake Uinta. In this study, legacy non-quantitative (presence/absence) X-ray diffraction (XRD) data recently published by the U.S. Geological Survey (USGS) for more than 9,000 samples collected from 30 coreholes in the Green River Formation, Piceance Basin were examined. These data were used to better define the stratigraphic and paleogeographic extent of a set of indicator minerals (illite, analcime, albite, dawsonite, and nahcolite) within the Piceance Basin lacustrine strata. This set of minerals was selected based on observations from previous work and variability in their occurrence and co-occurrence within the Piceance Basin. The USGS database has been used to (1) construct maps showing geographic variations in mineral occurrences for 14 stratigraphically defined rich and lean oil shale zones; (2) assess co-occurrences of indicator minerals; and (3) compare occurrence results with quantitative XRD datasets collected on Piceance Basin oil shales. Occurrences of many authigenic minerals (analcime, dawsonite, and nahcolite) varied in the lacustrine strata near and around the depocenter, but others, like quartz, dolomite, and feldspar (potassium + undifferentiated), were widely and consistently present (>90% of samples) across the basin. Shifts in the distribution of indicator mineral occurrences generally coincide with changes identified in previous lake history descriptions and indicate that the water chemistry of Lake Uinta varied significantly going from near-shore to the depocenter and through time.

Eruption history and petrogenesis of rocks from Nyos volcano (NW Cameroon): Evidence from lithostratigraphy and geochemistry

Even though ca 1746 people and over 3000 cattle were killed in 1986 by sudden release of about 800 million m3 of CO2 from Lake Nyos volcano in northwest Cameroon, the lake's formation history is not known. Here we report results of a lithostratigraphic and petrogenetic study of Nyos volcano that allows us to confirm its phreatomagmatic (maar) origin. Eruptive products are divided into 2 units, the phases of each of which are closely related in time. Unit A comprises 4 phases, the last (A-4) represents the cataclysmic phreatomagmatic formation of Nyos maar and may have been triggered by collapse of the vent system of the previous (A-1 to A-3) phases, and/or reactivation of basement faults. After a repose period, activity shifted NE of the maar to form Unit B products. The B-1 phase of this unit deposited the scoria now covering most of the Lake Nyos area. Unit B-2 constructed the Fon's cone. A small lava flow (Unit B-3) represents the latest phase of volcanic activity of Nyos volcano. Based on area-thickness estimation methods, a total of ca 0.8 km3 of eruptive material was produced from the volcano. Geochemical data suggest that magma of the 2 units probably formed by melting of the same garnet-bearing OIB-like asthenospheric mantle source, and evolved mainly by crustal contamination and fractional crystallization in independent magma batches that erupted without mixing. Our results provide a basis for advice on general hazard mitigation in the Lake Nyos area.

Holocene Thermokarst Lake Dynamics in Northern Interior Alaska: The Interplay of Climate, Fire, and Subsurface Hydrology

The current state of permafrost in Alaska, and meaningful expectations for its future evolution are better informed by long-term perspectives of previous permafrost degradation. Thermokarst processes in permafrost landscapes often leads to widespread lake formation. The spatial and temporal evolution of thermokarst lake landscapes reflects the combined effects of climate, ground conditions, vegetation, and fire. To further explore the Holocene history of Yukon Flats thermokarst lakes, we conducted a detailed study of Greenpepper lake, located on the southern loess uplands, including bathymetry and sediment core analyses across a water depth transect. The sediment results, dated by radiocarbon and 210Pb, indicate that Greenpepper basin development initiated ~8000 cal yr BP through inferred thermokarst processes. Thermokarst expansion to the modern lake’s near-shore shallow water depths continued to ~5000 and 4000 cal yr BP. Subsequently stable sediment chronologies and properties indicate the lake established levels ~4 m higher than present. At that time, water overflowed into an over-deepened gully system no longer occupied by perennial streams and connected to nearby partially drained lakes. By ~1000 cal yr BP, Greenpepper lake levels had lowered below the outflow elevation, which is interpreted to reflect a response to drier conditions and possibly to downgradient catastrophic lake drainage that increased subsurface water loss, although this mechanism is untested. Timing of Greenpepper thermokarst initiation and lake expansion was later than previously documented elsewhere in the southern loess upland and post-dates the establishment of spruce forest. After the lake stabilized by ~4 ka, the late Holocene millennial trend of increased aridity corresponds with Yukon Flats regional fire and paleoclimate reconstructions and suggest linkages with large scale Holocene patterns of North Pacific atmospheric circulation.

Coalescent models characterize sources and demographic history of recent round goby colonization of Great Lakes and inland waters.

The establishment and spread of aquatic invasive species are ecologically and economically harmful and a source of conservation concern internationally. Processes of species invasion have traditionally been inferred from observational data of species presence/absence and relative abundance. However, genetic‐based approaches can provide valuable sources of inference. Restriction site‐associated DNA sequencing was used to identify and genotype single nucleotide polymorphism (SNP) loci for Round Gobies (Neogobius melanostomus) (N = 440) from 18 sampling locations in the Great Lakes and in three Michigan, USA, drainages (Flint, Au Sable, and Cheboygan River basins). Sampled rivers differed in size, accessibility, and physical characteristics including man‐made dispersal barriers. Population levels of genetic diversity and interpopulation variance in SNP allele frequency were used in coalescence‐based approximate Bayesian computation (ABC) to statistically compare models representing competing hypotheses regarding source population, postcolonization dispersal, and demographic history in the Great Lakes and inland waters. Results indicate different patterns of colonization across the three drainages. In the Flint River, models indicate a strong population bottleneck (<3% of contemporary effective population size) and a single founding event from Saginaw Bay led to the colonization of inland river segments. In the Au Sable River, analyses could not distinguish potential source populations, but supported models indicated multiple introductions from one source population. In the Cheboygan River, supported models indicated that colonization likely proceeded from east (Lake Huron source) to west among inland locales sampled in the system. Despite the recent occupancy of Great Lakes and inland habitats, large numbers of loci analyzed in an ABC framework enable statistically supported identification of source populations and reconstruction of the direction of inland spread and demographic history following establishment. Information from analyses can direct management actions to limit the spread of invasive species from identified sources and most probable vectors into additional inland aquatic habitats.

Late Holocene development of Lake Rangkul (Eastern Pamir, Tajikistan) and its response to regional climatic changes

This study was aimed at collecting and examining a sediment core from Lake Rangkul (Eastern Pamir, Tajikistan) to better understand the lake's development and to assess past variations in climatic conditions in this particular area in comparison with data available from other lakes from the neighboring locations. For the purposes of this study, we performed detailed geochemical and palynological analyses on the sediment core taken from Lake Rangkul in 2014. Moreover, we obtained historical satellite and meteorological data and performed field tests for ground ice presence to identify trends in recent lake development. We distinguished 5 distinct stages over the past 2000 years of the lake's history that differ in geochemical and palynological characteristics. Despite the fact that Lake Rangkul is shallow and sensitive to various disturbances in sedimentation, the recorded stages are in accordance with general climatic trends observed for the Northern Hemisphere in the Late Holocene. Satellite data from the past 45 years shows a noticeable increase in the lake's area, which coincides with rising air temperatures. As the lake is located in the permafrost region with ground ice present immediately below the soil surface, its functioning is influenced by permafrost thawing, which will lead to future changes in the lake area and the distribution of surrounding wet meadows, used as pastures by local inhabitants.

Dioxins in Great Lakes fish: Past, present and implications for future monitoring

Dioxins/furans are considered among the most toxic anthropogenic chemicals, and are ubiquitous in the environment including in the North American Great Lakes, which contain one fifth of the world's surface freshwater. Our exposure to dioxins/furans is mainly through contaminated diet. Elevated levels of dioxins/furans in Great Lakes fish have resulted in issuance of fish consumption advisories. Here we examine spatial/temporal trends of dioxins/furans in the edible portion (fillet) of fish from the Canadian waters of the Great Lakes using the data collected by the Province of Ontario, Canada. Our analyses show that the Toxic Equivalent (TEQ) dioxin/furan concentrations declined between 1989 and 2013 in Lake Trout from Lakes Ontario, Huron and Superior by 91%, 78% and 73%, respectively, but increased in Lake Whitefish from Lake Erie by 138%. An expanded dataset created by combining our data with historical Lake Ontario Lake Trout measurements from the literature showed a greater decline of >96% (from 64 to 2.3 pg/g) between 1977 and 2013. Measurements collected for 30 types of fish show overall low levels but local/regional concerns at some locations in Lakes Huron, Erie and Ontario. Dioxins/furans are globally present in foodstuff and “zero concentration” target is considered impractical. Based on the observations for the Great Lakes in the context of risk to human health from eating fish, it is concluded that comprehensive monitoring of dioxins/furans can be replaced with targeted locations and/or indicator species, and the saved resources can be more efficiently utilized for monitoring of other priority or emerging contaminants.

The sedimentary and environmental history of Tortonian-Messinian lakes at the east Mediterranean margins (northern Israel)

During the late Neogene, the east Mediterranean margins of the Levant went through major morphological changes due to tectonic activity associated with the Dead Sea Transform Fault. The regional fluvial systems inverted their flow direction from westward towards the Mediterranean to eastward towards the Jordan Valley. Tectonic basins that developed at that time in northern Israel were filled by lakes with intermittent connections to the sea. The tectonic processes were accompanied by volcanism of alkali basalts. This study focuses on the evolution of sedimentary-volcanic sequences, mainly included in the Bira and Gesher Formations that were deposited in lacustrine and palustrine environments in northern Israel. The study presents a comprehensive dataset and interpretation integrating new and old lithological and paleontological records from outcrops and drill holes, together with new petrographic and mineralogical data. The Bira Formation of Tortonian age, which overlies the Lower Basalt unit, consists mainly of lacustrine littoral limestone and dolostone and basinal marl. Sporadic occurrences of marine macrofauna indicate pulses of marine ingressions that reached the Jordan Valley depocenter, where thick sequences of gypsum and salt were deposited. The overlying Gesher Formation of Messinian-early Zanclean age, which has a similar lithology to that of the Bira Formation, represents an environmental evolution from restricted shallow lakes into a larger lake, or lakes, and finally to shallow isolated water bodies. The latter stage coincides with the Messinian Salinity Crisis, when climate became more arid in the Levant. Pyroclasts and some lava flows recorded an ongoing volcanic activity during this period that intensified toward the eruption of the Cover Basalt unit, that overlies the Gesher Formation. Overall, the Bira and Gesher formations provide a detailed sedimentological, tectonic and volcanic history of the continental margins of the east Mediterranean and its connection to the tectonic evolution of basin associated with the Dead Sea Transform Fault.

The Calcium Isotope Systematics of the Late Quaternary Dead Sea Basin Lakes

AbstractWe report the calcium isotopic composition (δ44Ca) of primary aragonite laminae, primary gypsum, and secondary gypsum in sediments deposited from Lake Lisan, the last glacial cycle of the Dead Sea (70–14.5 ka). The δ44Ca of primary gypsum varies between 0.17‰ and 0.71‰ versus bulk silicate earth, with an average of 0.29‰, whereas the aragonite δ44Ca varies between −0.68‰ and −0.16‰ with an average of −0.4‰. The secondary gypsum δ44Ca is close to the calcium isotope composition of the aragonite, averaging at −0.3‰. The aragonite δ44Ca shows small variations temporally in sync with lake level fluctuations, suggesting the aragonite δ44Ca reflects changes in the lake calcium balance, which in turn reflects changes in the local hydrological cycle. The secondary gypsum calcium isotope composition (−0.3‰) overlaps with that of coeval aragonite, suggesting the calcium for secondary gypsum was derived from the aragonite through quantitative, or near‐isotopic equilibrium, recrystallization of the aragonite to gypsum after the lake desiccation and exposure of sediments during the Holocene. A numerical box model is used to explore the effect of changing lake water levels on the calcium isotope composition of the aragonite and gypsum in the lake. The relatively low variability in the δ44Ca over the lake's history suggests that a high‐concentration calcium‐rich brine buffers the calcium cycle.

A 14 ka high-resolution δ18O lake record reveals a paradigm shift for the process-based reconstruction of hydroclimate on the northern Tibetan Plateau

The influence of the mid-latitude westerlies (MLW) competing with the Asian summer monsoons (ASM) over the Tibetan Plateau (TP) remains a matter of discussion on how and to which extent both atmospheric systems have been controlling hydro-climate during the Holocene. Depleted oxygen isotopes in lake deposits were commonly interpreted in terms of enhanced summer monsoon moisture supply, implying a migration of the ASM deep into the interior of the plateau during Holocene periods. In order to test this relationship we used a high resolution oxygen isotope record (mean 20 yr resolution) in combination with carbonates and mineral phases, titanium flux, grain size and ostracod abundances derived from a 6.84 m long sediment core in the endorheic Kuhai Lake basin, north-eastern TP. The results confirm 1) continuous positive co-variance between enriched δ18Ocarb and total carbonates during the last 14 ka, indicative of dominant seasonal influence on multi-decadal to centennial scale isotopic signatures in lake water and respective carbonate precipitation, 2) negative co-variance between allochthonous sediment flux and δ18Ocarb (and carbonates) attributed to relative increase of flux rates during non-summer seasons, 3) correspondence of lake level variations with carbonate mineral phases and the occurrence/disappearance of ostracod assemblages, and 4) inverse relationships between isotopic signatures in ASM-dominated and MLW-controlled lake records across the TP. Enriched δ18Ocarb in Kuhai Lake sediments was primarily a result of high evaporation during the summer seasons, while ASM-related rainfall amount did not play an important role, likely counterbalanced by isotopic signatures from different water sources. Conversely, depleted δ18Ocarb was mainly attributed to water supply during non-summer seasons of colder temperatures and generally light isotopic signatures from MLW-derived sources. This finding may lead to a paradigm shift in such way that depleted δ18O in carbonates is primarily not the result from ASM-related rainfall as previously assumed. The reconstructed hydro-climatic history of Kuhai Lake indicates the dominance of westerly-derived climate during the Younger Dryas interval (12.8–11.5 ka) under very shallow pond-like conditions. Despite climate amelioration during the early Holocene (11.5–7.5 ka) hydrological conditions remained unstable with frequent alternations between dominance of summer and winter seasons. During the middle Holocene (7.5–5.5 ka) the lake experienced highest lake levels dominated by summer monsoon-related water supply, assigned to the Holocene hydro-climatic optimum. Frequent high-amplitude fluctuations afterwards (5.1–2.9 ka) refer to cooling/drying events under enhanced MLW influence accompanied by a strong lake level decline. The late Holocene (2.9 ka- Present) period experienced moderate isotopic variations and fluctuating lake levels in response to variable influence of summer- or winter-related hydro-climatic conditions.This seesaw-like pattern with amplitudes of >10‰ in δ18Ocarb resembles fluctuations in cave records and variations between air and seawater (Dole effect). High correspondence with cooling events derived from North Atlantic drift ice and meltwater discharge indicate close ties to northern hemispheric climate transmitted by the MLW across the TP.

Vegetation and climate history of Anggertu Lake in the Tengger Desert over the last millennium

Reconstructing climate change of the last millennium is important to understand the current relationship between human-social activities and natural environmental changes. Pollen assemblages, losson-ignition (LOIorg at 550°C), and grain size data collected from sediment core AGE15A from the center of Anggertu lake (eastern Tengger Desert, Inner Mongolia) were used to reconstruct the regional vegetation and climate history of the last millennium. Desert or steppe desert, dominated by Artemisia and Amaranthaceae, expanded around this region during the period of 988–1437 AD indicating a generally dry climate condition with two short humid periods (1003–1082 AD and 1388–1437 AD). These two wet periods were characterized by relatively high vegetation cover and bioproductivity, as reflected by high pollen concentrations and LOIorg values. Increases in steppe and meadow vegetation communities (Poaceae, Cyperaceae) and vegetation cover during 1437–2015 AD suggest a wetting trend, which was also deduced from a gradual trend towards fine grains and higher lake biological productivity as reflected by LOIorg values. An unstable lacustrine environment was identified via frequent fluctuations in pollen concentration and grain size after 1842 AD. This study also recorded a relatively dry Medieval Warm Period (MWP, 1082–1388 AD) and a wet Little Ice Age (LIA, 1437–1842 AD). Increased Amaranthaceae and high abundance of Poaceae may be related to overgrazing and agricultural activities that took place during those time periods. The evolution of vegetation in the lake region was influenced by climate change and human activities. These results could provide more fundamental support for studies of the environmental evolution of the Tengger Desert.

Heavy metal concentrations in sediments from Xingyun lake, southwestern China: implications for environmental changes and human activities

Environmental changes influenced by human activities were recorded in the sediment cores from Xingyun lake. Based on the 137Cs and 210Pb dating, multi-proxy records, enrichment factor (EF), and geoaccumulation index (Igeo) methods, the history of human–environment interactions in Xingyun lake catchment during the past 140 years was studied. The results showed that the total heavy metal pollution in Xingyun lake followed the decreasing order: the northwestern > the middle > the southwestern > the southern > the north easterly. These distributions were controlled by regional geochemical background values, pollution load, and the lake current driven by prevailing southwesterly winds. The total EF value of heavy metals followed the decreasing order: EF (Zn) > EF (Cr) > EF (Pb) > EF (Cd) > EF (Cu). The total Igeo value of heavy metals also followed the decreasing order: Igeo (Zn) > Igeo (Cr) > Igeo (Pb) > Igeo (Cd) > Igeo (Cu). Consequently, the total pollution level of heavy metals followed the decreasing order: Zn > Cr > Pb > Cd > Cu. Before 1910 AD, the natural erosion caused by climate changes was the key factor for the heavy metals accumulated. After 1910 AD, the heavy metal concentrations were mainly controlled by anthropogenic impacts, the dominant sources were from industrial pollution, agricultural pollution, mining, and organic degradation. Finally, the sedimentary evolution history of Xingyun lake can be divided into four stages, i.e., (1) natural evolution stage during 1862–1910 AD, (2) anthropogenic disturbance stage during 1910–1953 AD, (3) anthropogenic reconstruction stage during 1953–1984 AD, and (4) eutrophication stage after 1984 AD.

Comparative post-IR IRSL (pIRIR290) K-feldspar age estimates for Qinghai Lake highstands: A comment

Using a post-IR IRSL (pIRIR290) K-feldspar luminescence dating method, Long et al. (2018) suggest the highest exposed shoreline features of Qinghai Lake date to early MIS 3. This age estimate is in conflict with a host of quartz and post-IR IRSL (pIRIR290) K-feldspar luminescence age estimates suggesting lake highstands in other basins, which, like Qinghai Lake, are also fed by Qilian Mountains precipitation, date to MIS 5. We think the apparent conflict may be due to the use of different average water content estimates. Depending on whether estimates of 10–20% are used, many samples can date to anywhere from late MIS 5 to early MIS 3. It thus becomes critical that better ways to estimate water content must be developed before OSL chronologies can be used for understanding lake histories, and by extension, climatic change.

The lacustrine microbial carbonate factory of the successive Lake Bonneville and Great Salt Lake, Utah, USA

AbstractThe Bonneville Basin is a continental lacustrine system accommodating extensive microbial carbonate deposits corresponding to two distinct phases: the deep Lake Bonneville (30 000 to 11 500 14C bp) and the shallow Great Salt Lake (since 11 500 14C bp). A characterization of these microbial deposits and their associated sediments provides insights into their spatio‐temporal distribution patterns. The Bonneville phase preferentially displays vertical distribution of the microbial deposits resulting from high‐amplitude lake level variations. Due to the basin physiography, the microbial deposits were restricted to a narrow shoreline belt following Bonneville lake level variations. Carbonate production was more efficient during intervals of relative lake level stability as recorded by the formation of successive terraces. In contrast, the Great Salt Lake microbial deposits showed a great lateral distribution, linked to the modern flat bottom configuration. A low vertical distribution of the microbial deposits was the result of the shallow water depth combined with a low amplitude of lake level fluctuations. These younger microbial deposits display a higher diversity of fabrics and sizes. They are distributed along an extensive ‘shore to lake’ transect on a flat platform in relation to local and progressive accommodation space changes. Microbial deposits are temporally discontinuous throughout the lake history showing longer hiatuses during the Bonneville phase. The main parameters controlling the rate of carbonate production are related to the interaction between physical (kinetics of the mineral precipitation, lake water temperature and runoff), chemical (Ca2+, Mg2+ and HCO3− concentrations, Mg/Ca ratio, dilution and depletion) and/or biological (trophic) factors. The contrast in evolution of Lake Bonneville and Great Salt Lake microbial deposits during their lacustrine history leads to discussions on major chemical and climatic changes during this interval as well as the role of physiography. Furthermore, it provides novel insights into the composition, structure and formation of microbialite‐rich carbonate deposits under freshwater and hypersaline conditions.

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.

Resisting annihilation: relationships between functional trait dissimilarity, assemblage competitive power and allelopathy

Allelopathic species can alter biodiversity. Using simulated assemblages that are characterised by neutrality, lumpy coexistence and intransitivity, we explore relationships between within-assemblage competitive dissimilarities and resistance to allelopathic species. An emergent behaviour from our models is that assemblages are more resistant to allelopathy when members strongly compete exploitatively (high competitive power). We found that neutral assemblages were the most vulnerable to allelopathic species, followed by lumpy and then by intransitive assemblages. We find support for our modeling in real-world time-series data from eight lakes of varied morphometry and trophic state. Our analysis of this data shows that a lake's history of allelopathic phytoplankton species biovolume density and dominance is related to the number of species clusters occurring in the plankton assemblages of those lakes, an emergent trend similar to that of our modeling. We suggest that an assemblage's competitive power determines its allelopathy resistance.