History Of Lake Research Articles

Reconstruct hydrological history of terrestrial saline lakes using Mg isotopes in halite: A case study of the Quaternary Dalangtan playa in Qaidam Basin, NW China

Saline lakes are sensitive to climatic changes, however, it is challenging to reconstruct paleoclimate based on terrestrial evaporite records using conventional elemental and isotopic proxies. Magnesium is a major element in saline lakes, and the Mg isotope composition of brine is responsive to climate-driven processes such as carbonate precipitation and freshwater input. However, little has been explored on the application of Mg isotopes to studies of saline lakes. In this study, the Middle Pleistocene halite deposit from the Xiaoliangshan (XLS) evaporite section in the Qaidam Basin, Northwest China, was selected as a case to evaluate the response of Mg isotopes in the saline lake to environmental events. The Mg isotope data of the halite are complemented by geochemical analyses major elements and Sr-Cl isotopes of the halite component, and C-O isotopes of the associated carbonates. The 87Sr/86Sr ratios of the halite remained homogeneous (0.7111 to 0.7112) throughout the section, suggesting that the material source did not change significantly during the precipitation of the halite beds. By contrast, element ratios (Mg/Na and K/Na) and stable isotope ratios of C, O, Cl, and Mg show remarkable fluctuations along with the sediment profile. Based on the C-O-Cl isotope data, we identified events of freshwater recharging and desalination in an overall dry climatic background that were recorded in the halite. Notably, halite δ26Mg values vary by up to 2‰ in the section (from −1.63‰ to 0.46‰), and the low δ26Mg signature of halite was interpreted to reflect the input of light Mg isotopes into the saline lake in a freshwater recharging event, while the high δ26Mg values were produced by the precipitation of carbonate minerals under arid climatic conditions. Collectively, we suggest that Mg isotopes in terrestrial halite could be a sensitive tracer of basin hydrology. This study for the first time demonstrates the potential of Mg isotopes in terrestrial evaporites to unravel paleoclimatic events.

The lake-level changes of Lop Nur over the past 2000 years and its linkage to the decline of the ancient Loulan Kingdom

Study regionLop Nur, Xinjiang Province, China Study focusLop Nur has been a vast playa which was a historic lake in eastern Tarim Basin, northwest China. The lake's catchment played a significant role in the development of oasis states in the early Common Era, such as the ancient Loulan Kingdom. However, the history of lake dynamics remains unclear, and its potential linkage to the decline of Loulan Kingdom has been not well-examined. This paper aims to reconstruct the lake-level changes in Lop Nur over the last 2000 years using synthetic aperture radar (SAR) data, optically stimulated luminescence (OSL) dating of lacustrine and aeolian sediments, and radiocarbon (14C) dating of ancient bio-remains. Furthermore, the relationships between Lop Nur' fluctuation and the decline of ancient Loulan Kingdom were discussed New hydrological insights for the regionThe results suggest that Lop Nur once covered an area more than 11, 602 km2 and that lake-level reduced gradually during 360–470 C.E. Subsequently, the lake experienced a few stages of lake-level fluctuation which never reached the upper-most shorelines. Also, the historical changes in the lake level were temporal coincided with the ancient Loulan Kingdom's collapse, showing that the dynamics of hydrological conditions in catchment may have a direct influence on the fall of human settlement in drylands.

Theoretical basis and Chinese practice for environmental protection of lakes with better water quality

目前，我国湖泊富营养化及蓝藻水华问题十分突出，国家高度重视湖泊的生态环境保护.自“九五”以来，国家就投入太湖、巢湖、滇池“老三湖”等重污染湖泊的治理，但成本巨大，且历经近30年才初见成效.按照湖泊污染程度，湖泊治理与保护可分为“污染治理型”“防治结合型”“生态保育型”3大类.“老三湖”的治理是典型的“先污染、后治理”的模式，水质较好湖泊主要属于生态保育型湖泊，因此，“老三湖”治理模式不适用于水质较好湖泊的保护.本文系统总结了我国水质较好湖泊优先保护理念的形成和水质较好湖泊专项实施的历程.根据水质较好湖泊的特点，及其生态系统退化与修复的一般过程，提出了水质较好湖泊保护的基本思路.从热力学角度，阐明了氮磷营养盐输入湖泊生态系统中是熵增过程，也是湖泊生态系统退化的根本原因，湖泊氮磷污染负荷源头控制是关键.湖泊流域生态安全格局是确保湖泊生态系统健康的基础，从景观生态学角度，阐明了优化湖泊流域水土资源利用、优化发展模式是减轻湖泊环境压力的重要途径.在浅水湖泊生态系统，以沉水植物占优势的“清水态”和以浮游植物占优势的“浊水态”转换过程不是沿着同一条途径，存在上临界阈值和下临界阈值，水生态修复过程表现出一种迟滞的现象.从湖泊水生态系统稳态转换理论角度，阐明了湖泊生态修复工程应在湖泊生态系统发生退化转变之前实施，才能获得较高的环境效益.通过国家财政专项对81个水质较好湖泊的支持，既能促进湖泊流域经济社会发展，又能确保湖泊水环境质量变好，湖泊水生态系统逐步改善.建议加强不同类型湖泊保护模式的总结，深入对水质较好湖泊生态系统演替理论和保护技术研究，支撑国家系统开展水质较好湖泊保护.;At present, the problems of lake eutrophication and cyanobacterial blooms in China are still very prominent and the state attaches great importance to the ecological environment protection of lakes. Since the Ninth Five-Year Plan, the government has started to control the old three lakes of Lake Taihu, Lake Chaohu and Lake Dianchi, but it has spent huge treatment costs. After nearly 30 years of governance, the trend of further deterioration of water quality in the old three lakes was initially curbed. According to the degree of lake pollution, lake control and protection can be divided into three types:pollution control type, combined prevention and control type and ecological conservation type. The governance of the old three lakes was a typical pollution first, treatment later model, and the lakes with better water quality mainly belong to ecological conservation type, so the treatment model for old three lakes is not suitable for the protection of lakes with better water quality. This paper systematically summarizes the formation of the concept of priority protection of lakes with better water quality in China and the implementation history of special lakes with better water quality. According to the characteristics of the lake with better water quality and the general process of ecosystem degradation and restoration, the basic idea for the protection of the lakes with better water quality was put forward. From a thermodynamic perspective, the entropy increase process of nitrogen and phosphorus nutrient input into the lake ecosystem was analyzed, revealing the root cause of the degradation of the lake ecosystem and the importance of source control of nitrogen and phosphorus pollution load into lakes. The ecological security pattern of lake basin is the basis for ensuring the health of lake basin ecosystem. From the perspective of landscape ecology, this paper clarifies that optimizing the use of soil and water resources in lake basin and optimizing the development pattern are important ways to reduce the environmental pressure on the lake. The transition process of the clear water state dominated by submerged plants and the turbid water state dominated by phytoplankton in shallow lake ecosystems is not along the same pathway. There are upper and lower critical thresholds, and the aquatic ecological restoration process shows a hysteresis phenomenon. From the theory of steady-state transformation of lake water ecosystem, we clarified that the lake ecological restoration project should be implemented before the degradation transformation of lake ecosystem to obtain higher protection benefits. The support of 81 lakes with better water quality through the special national finance can not only promote the economic and social development of the lake basin, but also ensure the improvement of the quality of the lake water environment and improvement of lake water ecosystem. We recommended to strengthen the summary of different types of lake protection models, conduct in-depth research on the theory of ecosystem succession and protection technology of lakes with better water quality, and support the state to carry out the protection of lakes with better water quality systematically.

Mid-Late Holocene Sub-Millennial Scale Inverse Trends of South Asian Summer and Winter Monsoons in Sri Lanka

The South Asian Monsoon (SAM) brings precipitation crucial for agriculture across the densely populated region of South Asia. Identifying the key long-term drivers of the SAM is essential to improve the predictability of future monsoonal trends in the context of current global climate scenarios and increasingly frequent drought and flooding events in this part of the world. Here, we reconstruct ∼6000 years of climatic and environmental history of the South Asian summer monsoon-fed Bolgoda South Lake and the Horton Plains, and the winter monsoon-fed Panama lagoon, in Sri Lanka to better understand monsoonal operation over this island and its connection to broader climate systems. Multiple proxies (diagnostic biomarkers, hydrogen and carbon isotopes of individual n-alkane, grain size, and Zr/Rb elemental ratio) indicate a sub-millennial scale decreasing trend of summer monsoon rainfall in the wet zone of Sri Lanka alongside an increasing trend of winter monsoon rainfall in the dry zone during the last ∼6000 years. We also observed multi-centennial scale arid events in the Bolgoda South Lake and Horton Plains records at ∼3,500 and ∼1,000 cal years BP. Inverse monsoonal behavior during the mid- and late Holocene seems to be led by the southward migration of the mean latitudinal position of ITCZ, induced by varying solar energy distribution between the Northern and Southern hemispheres due to Earth’s processional cycle. Our observations are broadly supported by existing paleoclimatic records from the Indian sub-continent, but abrupt arid phases are asynchronous in the regional records. In addition, these short-term arid conditions do not show systematic correlations with the different modes of climate variables known to have teleconnections with the Indian Ocean monsoon.

Identifying the influence of terrestrial–aquatic connectivity on palaeoecological inferences of past climate in Arctic lakes

Increased hydrological connectivity due to permafrost degradation is likely to have substantial implications for shallow aquatic systems common to sub‐arctic landscapes due to changes to overland and subsurface flow of water and transport of sediments and dissolved nutrients. Here, we explore the influence of increased connectivity on aquatic productivity based on multi‐parameter palaeolimnological analysis of two lakes located near Inuvik (Northwest Territories, Canada). We contrast a lake with little evidence of permafrost degradation in the surrounding area (Lake PG03) to one that has multiple connections to the terrestrial landscape through a network of thaw polygons in the lake catchment (Lake PG09). Comparisons of biological indicators (chironomids) and organic carbon and nitrogen elemental and isotope composition reveal recent divergent lake histories. The chironomid assemblage of Lake PG03 followed an expected temperature gradient, with a warming signal evident since ˜1970 CE, whereas the chironomid assemblage of Lake PG09 was found to primarily respond to nutrient availability and changes in habitat, likely as a result of increasing hydrological connectivity to the landscape. Rapid assemblage and habitat change along with a prominent increase in chironomid abundance were observed at Lake PG09 after ˜1960 CE, following a shift to greater inputs from the terrestrial environment as indicated by high C:N ratios (>15) and low δ13Corg (−30‰). Increased aquatic productivity following high allochthonous additions (˜1960–2014 CE) is supported by decreased C:N and rapidly increasing organic matter (Corg, N). These results demonstrate that increased connectivity along the terrestrial–aquatic interface for lakes is likely to foster elevated productivity in the future. Likewise, increased production poses a challenge to chironomid‐inferred July air temperature reconstructions in lakes that are less resilient to secondary gradients, where analogue mismatches can occur due to shifts in dominance of indicators that are orthogonal to the temperature gradient.

When Environmental History Goes Public in China

This article starts out from looking at what is missing from environmental history in China today, and then goes on to ask a particular set of questions: How does one interpret environmental history with the public? How does one present environmental history in public space? How does one engage with an environmentally conscious public? And ultimately, is it possible to establish public environmental history as a new mode of knowledge? In answer to these questions, it focuses on relationships, including the relationships between nature and culture, the environment and people, and history and memory. Using the dredging history of West Lake in Hangzhou as an illustrative case, it explores nature as material culture, calls attention to the rhetorical power of nature, and argues that environmental history should be interpreted and presented as public memory.

Review: Perilous Bounty: The Looming Collapse of American Farming and How We Can Prevent It, by Tom Philpott

Book Review| November 01 2021 Review: Perilous Bounty: The Looming Collapse of American Farming and How We Can Prevent It, by Tom Philpott Tom Philpott. Perilous Bounty: The Looming Collapse of American Farming and How We Can Prevent It. New York: Bloomsbury, 2020. 246 pp. Paperback $17.00. Philip Garone Philip Garone Philip Garone is professor and chair of the Department of History at California State University Stanislaus. He earned a PhD in history and an MS in ecology from the University of California Davis, and his research has focused on the environmental history of the Central Valley and the Sacramento–San Joaquin Delta. He is the author of The Fall and Rise of the Wetlands of California's Great Central Valley (2011; paperback released in 2020) and is currently working on an environmental history of the terminal lakes of the western Great Basin. Search for other works by this author on: This Site PubMed Google Scholar California History (2021) 98 (4): 117–120. https://doi.org/10.1525/ch.2021.98.4.117 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Philip Garone; Review: Perilous Bounty: The Looming Collapse of American Farming and How We Can Prevent It, by Tom Philpott. California History 1 November 2021; 98 (4): 117–120. doi: https://doi.org/10.1525/ch.2021.98.4.117 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentCalifornia History Search This content is only available via PDF. © 2021 by The Regents of the University of California2021 Article PDF first page preview Close Modal You do not currently have access to this content.

Developing a System Dynamics Model for the Nizhniy Kaban and Sredniy Kaban Lakes, Kazan, Russia, Assessing the Impacts of Phosphorus and Nitrogen Inputs on Lake Ecology

The Kaban Lakes Integrated Assessment Model (KLIAM) was developed for the lake hydrology, chemistry, and plankton dynamics of the Nizhniy Kaban and Sredniy Kaban lakes, Kazan, Russia. KLIAM is able to describe the variations seen in the Kaban lakes chemical and biological states as far seen through measurements available at the moment. KLIAM is able to reconstruct the lake history as it is approximately known from the data and written narratives. KLIAM was used to assess the measures to return the lakes to their original pre-urban status as alkaline and semi-oligotrophic lakes. The Kaban Lakes periodically goes through plankton blooms, as seen in the lake in the last decades since before World War II, which are caused by plankton growth promoted by phosphorus and nitrogen coming to the lakes as pollution from the human environment. In the new plans for development of the area surrounding the Nizhniy Kaban and Sredniy Kaban lakes, we suggest that attention is paid to reducing phosphorus and nitrogen flows to the lakes, as the best way to improve their ecological status. This is based on simulations with KLIAM. We recommend that the monitoring of lake chemistry and lake ecology is improved with reoccurring analysis of samples from the Kaban Lakes.

Ecology and climate sensitivity of a groundwater-fed lake on subtropical North Stradbroke Island (Minjerribah), Queensland, Australia over the last 7500 years

Lake sediments are important archives of past climate variability and lake responses to climate. In order to accurately infer past climates, it is necessary to understand, and account for, the ecological processes that affect the record of indicators preserved in lake sediment. This is particularly the case with respect to the concentration of carbon and nitrogen (TOC, TN, and calculated C:N), and the stable isotope composition of organic matter preserved in lake sediments. These are common, yet ambiguous, tracers of environmental change. Ideally, palaeoenvironmental reconstructions using the concentration and isotope composition of organic matter should be grounded in a detailed understanding of the sources of the organic material. This study documents the history and evolution of Blue Lake, an environmentally and culturally important oligotrophic, groundwater window lake on North Stradbroke Island, Queensland, Australia. We utilise organic matter δ13C, TOC, TN, and C:N from a 2.4 m sediment core with a basal age of 7.5 cal kyr BP, to investigate changing organic matter sources as a measure of the climate sensitivity of Blue Lake. This interpretation is supported by data from contemporary algae, aquatic and terrestrial plants, and catchment soils. We show that lake nutrient dynamics drove an increase in algal biomass at 4.2 cal kyr BP. This change coincides with a widely documented intensification of the El Niño-Southern Oscillation, which we infer to have influenced lake nutrient concentrations by reducing groundwater throughflow. Climatic changes resulted in marked changes in lake primary productivity, despite relatively little turnover of the lake diatom flora and catchment vegetation. This suggests that south-east Queensland dune lakes are sensitive to climate changes and helps to refine past and future palaeoclimate research using sediments from these lakes. It also indicates that increased nutrient concentrations in Blue Lake may result from projected changes in 21st Century climate.

Holocene mountain landscape development and monsoon variation in the southernmost Russian Far East

A c. 9720‐year history of a mountain lake–mire complex on the Shufan Plateau (southern Primorye, Russian Far East) is based on a multi‐proxy study of peat deposits. The chronology is based on eight radiocarbon dates in addition to two dated tephra horizons. The sediment contains eight cryptotephra layers attributable to Baitoushan, a volcano on the Korea/China border. Pollen, diatom and botanical macrofossil analyses indicate climate fluctuations during the Holocene and a compositional response of biodiverse mountain forests to changes in temperature and humidity. Widespread, diverse broadleaf‐dominated forest marked a warm Early Holocene (~9500–9280 cal. a BP). Korean pine (Pinus koraiensis) rose to dominance in the Middle Holocene (after c. 7630 cal. a BP). Evergreen conifers, fir (Abies) in particular, became widespread after 2.9 ka BP and show a positive response to the Little Ice Age cooling. Over the c. 10 000‐year record, moisture appears largely controlled by gradually declining intensity of the summer monsoon, trending from moist conditions in the Early Holocene to cooler and drier conditions in the Late Holocene with shorter‐term hydrological changes superimposed. Peat composition indicates significant changes in mire vegetation, and diatom assemblages indicate four stages of inundation and three dry stages in the basin, probably controlled by precipitation changes. The initial importance of atmospheric precipitation shifted over time to a greater input from groundwater. During a long episode in the Late Holocene the basin may have dried out. Forest fires occurred during much of the Middle and Late Holocene, and their prominence, as marked by macro‐charcoal, is related to changes in humidity. Human activities mark the past few centuries. Medieval fires were probably anthropogenic, and there is evidence of agricultural impact on the landscape during the Jin Empire settlement period 900–700 years ago and of more recent forest exploitation, particularly a reduction in conifer taxa.

Orbital control of Pleistocene euxinia in Lake Magadi, Kenya

Abstract Lake Magadi is an internally drained, saline and alkaline terminal sump in the southern Kenya Rift. Geochemistry of samples from an ~200 m core representing the past ~1 m.y. of the lake's history shows some of the highest concentrations of transition metals and metalloids ever reported from lacustrine sediment, including redox-sensitive elements molybdenum, arsenic, and vanadium. Elevated concentrations of these elements represent times when the lake's hypolimnion was euxinic—that is, anoxic, saline, and sulfide-rich. Euxinia was common after ca. 700 ka, and after that tended to occur during intervals of high orbital eccentricity. These were likely times when high-frequency hydrologic changes favored repeated episodes of euxinia and sulfide precipitation. High-amplitude environmental fluctuations at peak eccentricity likely impacted water balance in terrestrial habitats and resource availability for early hominins. These are associated with important events in human evolution, including the first appearance of Middle Stone Age technology between ca. 500 and 320 ka in the southern Kenya Rift.

Population age structure of ostracods in lake sediment and its implication for within-lake transport of microfossils

In palaeolimnology, microfossils play an important role as ecological indicators of lake history. A reliable interpretation of microfossil data requires a comprehensive understanding of transport processes as well as determining whether microfossil assemblages are representative of their living communities. The occurrence of transport in ostracod taphocoenoses can be identified from the population age structure of valves. In this study, 23 surface sediment samples from Dalongchi Lake, northwestern China, were analysed for species composition, and 16 were also analysed for the population age structure of Fabaeformiscandona gyirongensis. Ostracod valves are dominated by F. gyirongensis, with frequently occurring Ilyocypris sp. in the surface sediments. The distribution and abundance of ostracods are significantly correlated with the sampling depth and grain size, implying that hydrological conditions are the major controlling factor. The dominant species F. gyirongensis seems to prefer relatively deep and stable lacustrine conditions, while Ilyocypris sp. seems to prefer shallow conditions with rich submerged macrophytes and relatively coarse substrate in Dalongchi Lake. The spatial changes in the population age structure of F. gyirongensis match the different hydrodynamic regimes within the lake, with abundant early and middle instars in deeper waters and abundant middle and late instars in shallower waters, denoting that downslope transport of valves may be responsible for the spatial changes in the population structure. Our findings, together with previous works, indicate that downslope transport of instars and subsequent depth differentiation of the population structure of ostracods can occur for different species in both marine and lacustrine settings, which potentially leads to some biases based on the “in situ” inference of microfossils in palaeoenvironmental reconstruction. Hence, careful transport process assessment of fossil assemblages based on population age structure and other characteristics, such as the ratios of adults to juveniles and carapaces to valves, is a valuable prerequisite for palaeoenvironmental analysis.

Channel-amphitheatre landforms resulting from liquefaction flowslides during rapid drawdown of glacial Lake Fraser, British Columbia, Canada

Unusual channel-amphitheatre landforms are present in Late Pleistocene–early Holocene, subaqueous fan and delta deposits in the glacial Lake Fraser basin, central British Columbia. The lake formed during the decay of the last Cordilleran Ice Sheet and drained ~11,500 years ago during a large outburst flood. The fronts of a delta and two subaqueous fans consisting of silt to fine sand are marked by branching networks of wide, nearly flat channels that terminate upstream in digitate, steep-walled amphitheatres. We propose that these channel-amphitheatre landforms formed by liquefaction flowslides that were induced by the rapid drawdown of glacial Lake Fraser during the outburst flood. Similar geomorphic forms, which we believe also to be associated with rapid drawdowns of large Late Pleistocene–early Holocene lakes, occur elsewhere in North America. A recent tailings dam failure and an intentional breaching of a 100-year-old hydroelectric dam provide insights into the processes responsible for the landforms. By using geomechanical analysis, we show how rapid lake drawdown can trigger liquefaction flowslides in deposits of silt to fine sand. The novelty of our approach lies in combining geomechanical reasoning with geomorphic analogues to understand histories of ancient glacier-dammed lakes and of the glacial lake outburst floods that are sourced from them.

Life-history responses of a freshwater rotifer to copper pollution.

In organisms with dormant stages, life‐history responses to past pollution can be studied retrospectively. Here, we study such responses in a rotifer (Brachionus calyciflorus) from the once heavily copper‐polluted Lake Orta (Italy). We extracted resting eggs from sediments, established clonal lineages from hatchlings, and exposed newborns of these lineages to one of three copper concentrations that each mimicked a specific period in the lake's pollution history. For each rotifer, we daily collected life‐table data. We then estimated treatment‐specific vital rates and used a stage‐structured population model to project population growth rate λ. We also estimated elasticities of λ to vital rates and contributions of vital rates to observed Δλ between copper treatments. As expected, λ decreased with increasing copper concentration. This decrease resulted mostly from a decline in juvenile survival rate (SJ ) and partly from a decline in the survival rate of asexually reproducing females (SA ). Maturation rate, and with one exception fecundity, also declined but did not contribute consistently to Δλ. λ was most elastic to SJ and SA , indicating that survival rates were under stronger selection than maturation rate and fecundity. Together, our results indicate that variation in juvenile survival is a key component in the rotifers’ copper response. The consistent decrease in SJ with increasing copper stress and the sensitivity of λ to that decrease also suggest that juvenile survival is a useful indicator of population performance under environmental pollution.

Unravelling climate change impacts from other anthropogenic influences in a subalpine lake: a multi-proxy sediment study from Oberer Soiernsee (Northern Alps, Germany)

Mountain lakes are increasingly impacted by a series of both local and global disturbances. The present study reveals the eutrophication history of a remote subalpine lake (Oberer Soiernsee, Northern Alps, Germany), triggered by deforestation, alpine pasturing, hut construction, tourism and atmospheric deposition, and identifies the intertwined consequences of on-going global warming on the lake’s ecosystem. The primary objective was to disentangle the various direct and indirect impacts of these multiple stressors via down-core analyses. Our multi-proxy approach included subfossil diatom assemblages, carbon and nitrogen stable isotope ratios and subfossil pigments from dated sediments. Shifts within the diatom assemblages were related to variations in trophic state, lake transparency, water temperature and thermal stratification. The organic carbon isotope (δ13Corg) records, the diatom valve density and the pigment concentrations documented the development of primary production and composition. Total nitrogen isotope values (δ15N) are more likely to reflect the history of atmospheric nitrogen pollution than lake-internal processes, also mirrored by the decoupling of δ15N and δ13Corg trends. The composition of sedimentary pigments allowed a differentiation between planktonic and benthic primary production. Concordant trends of all indicators suggested that the lake ecosystem passed a climatic threshold promoted by local and long-distance atmospheric nutrient loadings.

Genomic and immunogenic changes of Piscine novirhabdovirus (Viral Hemorrhagic Septicemia Virus) over its evolutionary history in the Laurentian Great Lakes.

A unique and highly virulent subgenogroup (-IVb) of Piscine novirhabdovirus, also known as Viral Hemorrhagic Septicemia Virus (VHSV), suddenly appeared in the Laurentian Great Lakes, causing large mortality outbreaks in 2005 and 2006, and affecting >32 freshwater fish species. Periods of apparent dormancy have punctuated smaller and more geographically-restricted outbreaks in 2007, 2008, and 2017. In this study, we conduct the largest whole genome sequencing analysis of VHSV-IVb to date, evaluating its evolutionary changes from 48 isolates in relation to immunogenicity in cell culture. Our investigation compares genomic and genetic variation, selection, and rates of sequence changes in VHSV-IVb, in relation to other VHSV genogroups (VHSV-I, VHSV-II, VHSV-III, and VHSV-IVa) and with other Novirhabdoviruses. Results show that the VHSV-IVb isolates we sequenced contain 253 SNPs (2.3% of the total 11,158 nucleotides) across their entire genomes, with 85 (33.6%) of them being non-synonymous. The most substitutions occurred in the non-coding region (NCDS; 4.3%), followed by the Nv- (3.8%), and M- (2.8%) genes. Proportionally more M-gene substitutions encoded amino acid changes (52.9%), followed by the Nv- (50.0%), G- (48.6%), N- (35.7%) and L- (23.1%) genes. Among VHSV genogroups and subgenogroups, VHSV-IVa from the northeastern Pacific Ocean has shown the fastest substitution rate (2.01x10-3), followed by VHSV-IVb (6.64x10-5) and by the VHSV-I, -II and-III genogroups from Europe (4.09x10-5). A 2016 gizzard shad (Dorosoma cepedianum) from Lake Erie possessed the most divergent VHSV-IVb sequence. The in vitro immunogenicity analysis of that sample displayed reduced virulence (as did the other samples from 2016), in comparison to the original VHSV-IVb isolate (which had been traced back to 2003, as an origin date). The 2016 isolates that we tested induced milder impacts on fish host cell innate antiviral responses, suggesting altered phenotypic effects. In conclusion, our overall findings indicate that VHSV-IVb has undergone continued sequence change and a trend to lower virulence over its evolutionary history (2003 through present-day), which may facilitate its long-term persistence in fish host populations.

The Hydrogeomorphic History of Garu Crater: Implications and Constraints on the Timing of Large Late‐Stage Lakes in the Gale Crater Region

AbstractPaleolake deposits offer a valuable record for constraining ancient Martian environments and climate. Gale crater provides extensive evidence for a long and complex history of lakes; however, the exact timing, source of water, and climate under which these large lakes persisted are still unclear. We examined the geomorphology and mineralogy of Garu crater, an ∼30 km diameter crater ∼150 km to the east of Gale crater with an age of ∼3.5 Ga (Hesperian). Garu hosts a large NE‐prograding sedimentary deposit that emanates from an incised bedrock canyon. Based on detailed geomorphic analysis, we infer it to be a Gilbert‐type delta that records steadily rising water levels over 104–105 years. This aggradational stage is followed by a period of rapid desiccation, which is evidenced by a lack of post‐depositional incision into the delta. Coupled surficial and groundwater modeling and paleo‐flow analysis suggest that the highest mapped lake stand in Garu would have been coeval with one of the largest late‐stage lakes in Gale. Both lake stands would have been supported by groundwater and surface runoff, under a semiarid climate. Unlike Gale, there is no spectral evidence for salts in Garu, which suggests that lacustrine sedimentation in Garu occurred after the deposition of the sulfate layers within Gale's central sedimentary mound. The hydrogeomorphologic record of Garu crater suggests that the climatic conditions that allowed for late Hesperian lakes in Gale crater were not isolated, and other nearby craters and basins may have responded to similar forcings from a regionally integrated hydrologic system.

Magnetic Fly Ash as a Chronological Marker in Post-Settlement Alluvial and Lacustrine Sediment: Examples from North Carolina and Illinois

Fly ash consists of mainly silt-size spherules that form during high-temperature coal combustion, such as in steam locomotives and coal-burning power plants. In the eastern USA, fly ash was distributed across the landscape atmospherically beginning in the late 19th century, peaking in the mid-20th century, and decreasing sharply with implementation of late 20th century particulate pollution controls. Although atmospheric deposition is limited today, fly ash particles continue to be resedimented into alluvial and lacustrine deposits from upland soil erosion and failure of fly ash storage ponds. Magnetic fly ash is easily extracted and identified microscopically, allowing for a simple and reproducible method for identifying post-1850 CE (Common Era) alluvium and lacustrine sediment. In the North Carolina Piedmont, magnetic fly ash was identified within the upper 50 cm at each of eight alluvial sites and one former milldam site. Extracted fly ash spherules have a magnetite or maghemite composition, with substitutions of Al, Si, Ca, and Ti, and range from 3–125 µm in diameter (mainly 10–45 µm). Based on the presence of fly ash, post-1850 alluvial deposits are 15–45 cm thick in central North Carolina river valleys (<0.5 km wide), ~60% thinner than in central Illinois valleys of similar width. Slower sedimentation rates in North Carolina watersheds are likely a result of a less agricultural land and less erodible (more clayey) soils. Artificial reservoirs (Lake Decatur, IL) and milldams (Betty’s Mill, NC), provide chronological tests for the fly ash method and high-resolution records of anthropogenic change. In cores of Lake Decatur sediments, changes in fly ash content appear related to decadal-scale variations in annual rainfall (and runoff), calcite precipitation, land-use changes, and/or lake history, superimposed on longer-term trends in particulate pollution.

Structure and dynamics of a Pampa plain, (Argentina) shallow lake over the last 600 years

A multi-proxy analysis, including pollen, non-pollen palynomorphs and plant macrofossil remains was performed to reconstruct the paleoenvironmental history of the Cabeza de Buey shallow lake (36°17′S, 61°10′W) over the last 600 years. We identified the main forcing factors behind changes in the structure and dynamics of the lake communities. Given the relatively low intensity of human activity during the early period of the lake history (prior to 1880 AD), changes in dominant communities were mainly controlled by climate. Afterwards, changes probably resulted from a combination of climate and human impacts that generated an accelerated eutrophication. Four periods in the lake’s evolution were recognized based on changes in macrophyte and algae communities’ structure. Between ca. 1320 and ca. 1630 AD a shift was evidenced from an oligotrophic brackish with low nutrient content (dominated by Botryococcus braunii) to a mesotrophic fresh water body (dominated by Pediastrum and Scenedesmus), due to an increase in the water level associated with an increase in precipitation. At ca. 1840 AD a transition towards a phase dominated by Myriophyllum spicatum was noted, induced by a low water level as a consequence of low precipitation. Later, at ca. 1880 AD, the current lake conditions were established, and the increase in nutrient and organic matter supply influenced plant community structure towards organic tolerant species of submerged macrophytes (Potamogeton pectinatus). Towards the beginning of the twenty-first century, the lake turned to a more eutrophic state, which is evidenced by the dominance of the phytoplankton community. The last hundred years of the lake history were characterized by the eutrophication process related to the impact of agriculture and cattle breeding implemented in the landscape as well as to the urban settlement. This study made it possible to infer changes in the structure and dynamics of Cabeza de Buey lake and to elucidate the forcing factors that induced these changes on a high-resolution scale.

Fecal Contamination and High Nutrient Levels Pollute the Watersheds of Wujiang, China

Freshwaters in China are affected by point and non-point sources of pollution. The Wujiang District (Suzhou City, China) has a long history of canals, rivers, and lakes that are currently facing various water quality issues. In this study, the water quality of four rivers and a lake in Wujiang was assessed to quantify pollution and explore its causes. Seventy-five monthly samples were collected from these water bodies (five locations/samples per area) from August to October 2020 and were compared with nine control samples collected from a water protection area. Fifteen physicochemical, microbiological, and molecular–microbiological parameters were analyzed, including nutrients, total and fecal coliforms, and fecal markers. Significant monthly variation was observed for most parameters at all areas. Total phosphorus, phosphates, total nitrogen, ammonium–nitrogen, and fecal coliforms mostly exceeded the acceptable limits set by the Chinese Ministry of Environmental Protection. The LiPuDang Lake and the WuFangGang River were the most degraded areas. The studied parameters were correlated with urban, agricultural, industrial, and other major land use patterns. The results suggest that fecal contamination and nutrients, associated with certain land use practices, are the primary pollution factors in the Wujiang District. Detailed water quality monitoring and targeted management strategies are necessary to control pollution in Wujiang’s watersheds.