Continental Freshwater Research Articles

Continental freshwater discharge influences sea surface salinity variability near world’s megadeltas

Sea surface salinity ([Formula: see text]) is a key parameter in the thermohaline circulation of global oceans. Near the megadeltas, inland streamflow through large catchments plays a crucial role in mediating salinity. While some regional studies have investigated how [Formula: see text] is impacted through water cycle and climate components, a global scale quantification of inland streamflow contribution on [Formula: see text] variability is lacking. Here, we utilized remote sensing and observation-driven datasets to quantify the statistical associations between [Formula: see text] and streamflow ([Formula: see text]) at 48 megadeltas worldwide. This study uncovers a robust negative association between [Formula: see text] and [Formula: see text], with correlation coefficients [Formula: see text] less than [Formula: see text] for seasonal data found in 26 of the 48 megadeltas, and less than [Formula: see text] for deseasoned data in 21 megadeltas. The anticorrelation relationship is more pronounced in large deltas, particularly near tropical climates and in river-influenced deltas. The study also underscores the significant roles of climate, morphological, and anthropogenic stratification in impacting the natural influence of freshwater discharge on SSS. By highlighting the interconnected impacts of alterations in terrestrial water cycle upstream and [Formula: see text], this work contributes to enhancing our understanding of global ocean and climate circulation patterns and in tackling environmental issues pertaining to marine ecosystems.

What Drives the Mean Along‐Shelf Flow in the Northwest Atlantic Coastal Ocean?

AbstractA long‐standing hypothesis is that the steady along‐shelf circulation in the Northwest Atlantic (NWA) coastal ocean is driven by buoyancy input from continental freshwater runoff. However, the forcing from the freshwater runoff has not been adequately evaluated and compared with other potential driving mechanisms. This study investigates the roles of both wind stress and freshwater runoff in driving the mean along‐shelf flow in the NWA coastal ocean and examines other potential drivers using a newly developed high‐resolution regional model with realistic forcing conditions. The results reveal that wind stress has a larger impact than freshwater runoff on the overall mean circulation and along‐shelf sea‐level gradient on the NWA shelf. While the continental freshwater input consistently contributes to the equatorward along‐shelf flow and higher sea level along the coast, wind stress is more effective for the setup of the broad‐scale circulation pattern by driving the along‐shelf flow on the Labrador Shelf and opposing the flow in the Mid‐Atlantic Bight and on the Scotian Shelf. In addition to the local wind and continental runoff, the sub‐Arctic inflow from higher latitude is an essential part of the NWA shelf circulation system. This remote driver directly contributes to the along‐shelf flow and insulates the shelf flow from the Gulf Stream on the southern shelves.

In-situ conversion of low-to medium-mature organic-rich shales by nuclear irradiation

Organic-rich shale is an important potential energy resource in the world. In situ organic-rich shale conversion has been discovery highly efficient to convert kerogen to oil through electric heating. However, the heating method is highly energy-consuming and less economically feasible. Finding other replaceable technique becomes an urgent task. Low-to medium-mature shale samples from continental freshwater and saline lake were irradiated by a cobalt-60-source with energy doses of 0.5 kGy, 1 kGy, 10 kGy, 100 kGy, and 1000 kGy. The changes of minerals and organic matters in shale were thoroughly monitored using various analysis including rock thin section, X-ray diffraction, scanning electron microscope, TOC, pyrolysis test, gas chromatography, and infrared spectrum. The results show that the TOCs of shale samples decrease gradually as irradiation doses increase and their organic matter functional group compositions change greatly. Irradiation reduces the content of long-chain hydrocarbons (especially C30+) in shale and generates short-chain hydrocarbons and gaseous substances. M-1 (Santanghu shale) and ZK-1 (Ordos shale) shows largest yields after irradiation, amount to 62 kg and 130 kg per ton shale respectively. Those two samples are S-rich shale which may have low activation energy for petroleum transformation from kerogen and thus benefit for hydrocarbon generation after irradiation. Therefore, we infer that the irradiation method can provide a new idea for the effective development of medium-to low-mature shale oil in the future, especially for those shales depositing at S-rich, saline, deep to semi-deep lacustrine environments.

Surface water oxygenation and low bioproductivity during deposition of iron formation of the Jacadigo Group (Brazil): Insights from combined cadmium – Chromium isotopes

The Banda Alta Formation (Urucum district, Mato Grosso do Sul, Brazil) comprises ∼600 Ma Fe and Mn deposits, which are among the world's youngest and largest Neoproterozoic sedimentary Fe and Mn formations (IF; MnF). These have been deposited in a redox-stratified, marine sub-basin (Jacadigo Basin), which was strongly influenced by glacial advance/retraction cycles with temporary influx of continental freshwater and upwelling of metal-enriched deep anoxic seawater. Cr and Cd isotopes measured on meticulously separated hematite mesobands from drill core samples are relatively homogenous throughout the ca. 325 m thick sequence sampled in the Banda Alta Fm., with average authigenic δ53Cr values of +0.93 ± 0.24 ‰ (2σ; n = 23) and δ114Cd values of −0.14 ± 0.14 ‰ (2σ; n = 15). The significant enrichment of Cr, in parallel with the strong enrichments of other redox sensitive elements (U, Mo), attests for effective and efficient reduction removal processes in the surface waters during cycles where upwelling Fe2+-rich waters reached the oxygenated surface layer exposed to the atmosphere during episodic glacier retreat stages. Assuming a similar quantitative and efficient removal pathway of dissolved Cd by iron oxyhydroxides, the so-inferred average δ114Cd signature of −0.14 ± 0.14 ‰ in the Jacadigo Basin surface water is significantly lower than signatures of modern ocean surface waters with a range of δ114Cd of ca. ∼0.4 to ∼1 ‰ and even lower than the signature of modern ocean deep waters with δ114Cd of ∼0.3 ‰. It possibly attests to reduced primary production levels and lower nutrient utilization rates during deposition of the Late Neoproterozoic Jacadigo Group, compared to today. This despite the inferred oxidized surface water layer that must have prevailed during this time, as implied by the strongly positively fractionated Cr isotope signatures and pronouncedly negative Ce-anomalies recorded in the seawater-like, shale-normalized Rare Earth Element and Yttrium (REY) patterns exhibited by the hematite mesobands. Data presented herein speak for: (1) a stable, isotopically heavy Cr input to the Jacadigo Basin at the time of deposition, implying high atmospheric O2 levels in the Late Neoproterozoic (2) likely quantitative, reductive incorporation / adsorption processes of dissolved Cr and Cd, respectively, into/onto precipitating iron oxyhydroxides, and (3) the prevalence of low nutrient concentrations and utilization rates in the Jacadigo Basin during glacier retreat cycles. Banded iron formations are considered suitable archives for reconstructing redox and bioproductivity levels in past marine depositional basin, including those prevalent in Neoproterozoic glacial conditions, via employing the CrCd isotope double tracer to iron-rich mesobands.

A comprehensive review of the biodiversity of freshwater fish species in Valleys worldwide and in the Kingdom of Saudi Arabia.

An overview of freshwater fish variety worldwide and the variables influencing trends in variation between and within river basins are given in this review. Continental freshwater ecosystems are highly diverse and species-rich, housing nearly 18,000 species of fish (=50% of all fish species) in <0.5% of the total land area and providing a negligible (<0.01%) share of the planet's water supply. Large lowland tropical river basins such as the Amazon, Congo, and Mekong basins are home to the greatest freshwater fish diversity. Freshwater species of fish depth variation at the global magnitude is correlated with the total amount and variation of aquatic habitats and the environment's equilibrium overtime during the evolution of scales. The river continuum concept states that there is a predictable shift in fish species depth, diversity of species, and functional characteristics along gradients of environment from headwater to estuary. The ongoing trade of minerals and organic matter related to nearby floodplains is a strong factor in the number and variety of riverine fishes in most parts of the world (the flood pulse concept). Without coordinated conservation efforts, freshwater fishes will suffer significant losses in abundance and diversity due to the numerous threats they currently face worldwide. However, further development, adaptation, training, and guidance are needed. New technologies based on water conservation, suitable species, and local traditions are needed. Waste materials and local feed additives can also be used. Farmers should be provided with the necessary training and information.

Extraction of eutrophic and green ponds from segmentation of high-resolution imagery based on the EAF-Unet algorithm

Inland ponds exhibit remarkable ubiquity across the globe, playing a vital role in the sustainability of global continental freshwater resources and contributing significantly to their biodiversity. Numerous ponds are eutrophic and experience recurrent seasonal or year-round algal blooms or persistent duckweed cover, conferring a characteristic green hue. Here, we denote these eutrophic and green ponds as EGPs. The excessive proliferation of algal blooms and duckweed within these EGPs poses a significant threat to the ecological functioning of these aquatic systems, which can lead to hypoxia or the release of microcystins. To identify these EGPs automatically, we constructed an Efficient Attention Fusion Unet (EAF-Unet) algorithm using Gaofen-2 (GF2) panchromatic and multispectral imagery. The attention mechanism was incorporated in Unet to help better detect EGPs. Using the first EGP labeled dataset, we determined the best input feature combination (RGB, NIR, NDVI, and Bright) and the most effective encoding (Rasnet50) for EAF-Unet for distinguishing EGPs from other ground cover types. The evaluation indices – Precision (0.81), Recall (0.79), F1-Score (0.80), and Intersection over Union (IoU, 0.67) – indicate that EAF-Unet can accurately and robustly extract EGPs from GF2 images without relying on pond water masks. Remote-sensing EGP products can assist in identifying ponds with severe eutrophication. Moreover, these products can serve as references for identifying high-risk areas prone to improper sewage discharge or inadequate sewer construction.

Genomic Basis of Freshwater Adaptation in the Palaemonid Prawn GenusMacrobrachium: Convergent Evolution Following Multiple Independent Colonization Events.

Adaptation to different salinity environments can enhance morphological and genomic divergence between related aquatic taxa. Species of prawns in the genus Macrobrachium naturally inhabit different osmotic niches and possess distinctive lifecycle traits associated with salinity tolerance. This study was conducted to investigate the patterns of adaptive genomic divergence during freshwater colonization in 34 Macrobrachium species collected from four continents; Australia, Asia, North and South America. Genotyping-by-sequencing (GBS) technique identified 5018 loci containing 82,636 single nucleotide polymorphisms (SNPs) that were used to reconstruct a phylogenomic tree. An additional phylogeny was reconstructed based on 43 candidate genes, previously identified as being potentially associated with freshwater adaptation. Comparison of the two phylogenetic trees revealed contrasting topologies. The GBS tree indicated multiple independent continent-specific invasions into freshwater by Macrobrachium lineages following common marine ancestry, as species with abbreviated larval development (ALD), i.e., species having a full freshwater life history, appeared reciprocally monophyletic within each continent. In contrast, the candidate gene tree showed convergent evolution for all ALD species worldwide, forming a single, well-supported clade. This latter pattern is likely the result of common evolutionary pressures selecting key mutations favored in continental freshwater habitats Results suggest that following multiple independent invasions into continental freshwaters at different evolutionary timescales, Macrobrachium taxa experienced adaptive genomic divergence, and in particular, convergence in the same genomic regions with parallel shifts in specific conserved phenotypic traits, such as evolution of larger eggs with abbreviated larval developmental.

Global Nitrogen Mass Flux From the Active Freshwater Aquifer Element Pool

AbstractThe estimated current global mean nitrogen concentration (geogenic + anthropogenic) in the active continental freshwater aquifer element pool is 1.1 mg/L as N, or between four and five times greater than the assumed geogenic mean. This concentration, combined with groundwater flux, generates a continental mass flux of 17 Tg N/y (teragrams of nitrogen, as N, per year) as a result of direct ocean discharge (0.67 Tg N/y), endorheic basins (1.2 Tg N/y), and cold‐wet (0.82 Tg N/y); cold‐dry (1.4 Tg N/y); warm‐dry (1.6 Tg N/y); and warm‐wet (11 Tg N/y) exorheic basins. These values are derived from a geospatial machine learning algorithm and combined groundwater‐modeled recharge in an ArcGIS environment. This active continental freshwater aquifer mass flux is between 35% and 40% of the continental integrated riverine system discharge, thus a significant component of the Earth's active continental freshwater nitrogen budget. We estimate the active continental freshwater aquifer volume to be between 1.4 and 2.8 million km3 suggesting a legacy of between 1.5 and 3.1 Pg as N (petagrams nitrogen as N) with mean residences of 90–180 years.

A carbonate palustrine system with marshes and shallow ephemeral lakes (Campanian, northeastern Iberian Basin)

The sedimentary and stratigraphic features of the low-gradient slope carbonate palustrine system of the Fortanete Formation (northeast Spain) during the early Campanian have been studied. The succession of the Fortanete Fm provides depositional record of a progressive transition to continental settings in an area that was predominantly marine for most of the Late Cretaceous. Palustrine systems can be developed in a wide variety of environments, however, modern analogues are scarce. The Fortanete Fm thus presents a great opportunity to study the stratigraphy, the sedimentary features and isotopic composition of a palustrine–marine influenced system. A total of 10 stratigraphic sections distributed along a 40 km wide and 80 km long area have been carried out in order to decipher the facies distribution in the system. This study led to the differentiation of three palaeoenvironments based on predominant lithofacies and sedimentary structures: (1) marshes and shallow low-gradient slope lakes; (2) ephemeral lakes, lake margins and prairies with variable water level and marine influence; and (3) mudflats with evaporites and fine siliciclastic input. The Fortanete Fm serves as an excellent case study for palustrine environments with the presence of typical palustrine features such as pseudomicrokarst, brecciation, black pebbles, desiccation cracks, nodules, Microcodium, and fenestral fabric. Most palustrine systems are associated with continental freshwater settings, whereas the Fortanete Fm displays evidence of intermittent marine influence in the distal studied sections. Carbon and oxygen isotope composition is within the range of typical freshwater lake carbonates and also corresponds to isotope composition of palustrine carbonates with marine influence. The Fortanete Fm shares a number of characteristics with freshwater continental and freshwater modern analogues. Comparison with these systems provides new insights on how modern analogues can be used to decipher the complexity of the processes developing these systems in the past.

The formation and evolutionary characteristics of organic matter and pyrites in the continental shales of the 3rd submember of Chang 7 Member, Yanchang formation, Ordos Basin, China

Through microscopic analyses (e.g., organic macerals, thin section observation, scanning electron microscope (SEM) imaging of fresh bedding planes via argon ion milling, and energy spectrum tests) combined with Rock-Eval analyses, this study systematically investigated the organic matter and pyrites in the continental shales in the 3rd submember of the Chang 7 Member (Chang 73 submember) in the Yanchang Formation, Ordos Basin and determined their types and the formation and evolutionary characteristics. The results are as follows. The organic matter of the continental shales in the Chang 73 submember is dominated by amorphous bituminites and migrabitumens, which have come into being since the early diagenetic stage and middle diagenetic stage A, respectively. The formation and transformation of organic matter is a prerequisite for the formation of pyrites. The Ordos Basin was a continental freshwater lacustrine basin and lacked sulphates in waters during the deposition of the Chang 7 Member. Therefore, the syndiagenetic stage did not witness the formation of large quantities of pyrites. Since the basin entered early diagenetic stage A, large quantities of sulfur ions were released as the primary organic matter got converted into bituminites and, accordingly, pyrites started to form. However, this stage featured poorer fluid and spatial conditions compared with the syndepositional stage due to withdraw of water, the partial formation of bituminites, and a certain degree of compaction. As a result, large quantities of pyrrhotite failed to transition into typical spherical framboidal pyrites but grew into euhedral monocrystal aggregates. In addition, pyrites are still visible in the migrabitumens in both microfractures and inorganic pores of mudstones and shales, indicating that the pyrite formation period can extend until the middle diagenetic stage A.

Integrative study of Permian coal-bearing horizons: biostratigraphy, palaeovegetation, and palaeoclimate in the South Karanpura Basin.

The article deals with the integrated and comprehensive study of the coal-bearing horizons from the South Karanpura Basin to delineate the biostratigraphy, palaeovegetation, palaeodepositional settings, and palaeoclimate in and around the investigated area during the deposition of Permian sediments. Highly diversified megafloral assemblages consist 13 genera and 72 species of order Glossopteridales, Cordaitales and Equisetales are documented among which 37 taxa are newly reported from Barakar and Raniganj formations of the area. Palynoassemblages-I and -II are recovered, which demonstrate the biostratigraphic age as Kungurian and Wordian-Capitanian, respectively. Overall the vegetation represents a luxuriant forest subjugated by arborescent deciduous trees bearing Glossopteris foliage with some conifers, cordaites, filicales, and peltaspermales. The biomarker study of the basin illustrates the unimodal distribution of n-alkanes in the sample set ranges from C14 to C29 which suggests major input from a single source of organic matter. The involvement of microbial activity and algal input is suggested for the basin. A relatively moderate-to-high water level condition can be inferred from elevated n-C25. The high CIA, PIA values and A-CN-K plot suggest intense weathering conditions in the source area. The source rocks are characterized by mature clayey type with abundant clay mineral, i.e., kaolinite. The current study portrays that the Permian climate was cooler in initial phase, which later on became warm temperate with high humidity. The palaeofloral entities and geochemical parameters suggest absolute diversification of Permian flora, the existence of continental freshwater setting in the vicinity and oxic to anoxic environment with fluctuating ground water conditions during the deposition of sediments.

Characteristics and Paleoenvironment of High-Quality Shale in the Triassic Yanchang Formation, Southern Margin of the Ordos Basin

A set of high-quality lacustrine shales at the bottom of the Chang 7 member of the Yanchang Formation in the Ordos Basin is one of the main source rocks of tight oil and gas and shale oil in the Yanchang Formation. Based on outcrop, core, drilling and seismic data, by the quantitative characterization of outcrops, fine characterization of logging facies and seismic facies, and geochemical tests, the lithofacies types, geophysical response characteristics and organic geochemical characteristics of this high-quality shale are clarified, and the formation paleoenvironment, including redox conditions, paleoclimate, paleosalinity and paleowater depth, is analyzed. The high-quality shale at the bottom of the Chang 7 member is divided into three lithofacies types: black shale, dark massive mudstone and silty mudstone. The organic matter in black shale is mainly interbedded or stratified, the organic matter in dark massive mudstone is dispersed and the organic matter content in silty mudstone is lower. The shale shows high gamma (more than 260 API), a high acoustic time difference (more than 280 μs/m), a high resistivity (more than 330 Ω m) well-logging phase and strong-amplitude parallel–subparallel seismic phase characteristics. Based on the logging and seismic facies characteristics, the plane distribution range of this set of shales is defined. The sedimentary thickness gradually increases from the edge (5–10 m) to the center of the basin, among which the Jiyuan–Huachi–Yijun black shale has the largest thickness (more than 30 m). This set of high-quality shales was mainly formed under a warm and humid paleoclimate, in water depths of 60–120 m, and in an anaerobic reducing and continental freshwater paleoenvironment. The fine identification, distribution range and formation conditions of black shale lithofacies are of practical significance for predicting the distribution of favorable lithofacies of shale oil and gas and the deployment of horizontal wells.

Seasonal variability in water‒air CO2 exchanges and carbon origin in a subtropical estuary

The seasonal and interannual variabilities in the water‒air net carbon dioxide (CO2) flux were investigated in the lower zone of the Patos Lagoon Estuary (PLE), the largest choked lagoon worldwide. The studied region experienced periods of CO2 ingassing (outgassing) during ocean-dominated (riverine-dominated) conditions. During ocean-dominated conditions (summer/autumn), CO2 uptake was an average of −15 mmol m–2 d–1, whereas under riverine-dominated conditions (winter/spring), CO2 emissions prevailed, reaching an average of 22 mmol m–2 d–1. The magnitude of CO2 uptake in summer/autumn was comparable to the CO2 released to the atmosphere in winter/spring in the mesomixohaline zone. However, the CO2 uptake in summer/autumn was 4-fold higher than the CO2 released in winter/spring in the euhaline zone of the PLE. Unlike most estuarine systems, the PLE acted as a net CO2 sink, with a net CO2 uptake of −2 mmol m–2 d–1 during the period investigated (May 2017 to June 2021). The water‒air CO2 exchanges are modulated mainly by the balance between continental freshwater discharge and the inflow/outflow of seawater. However, the combined effect of wind speed, biological activity, and water residence time adds complexity to understanding the carbon exchanges in this region. The higher concentration of organic matter entails the highest estuarine CO2 concentration during autochthonous production, which indicates heterotrophy in estuarine waters. Part of this carbon produced in the estuary is likely exported to the coast, as suggested by the high CO2 concentration in the estuary mouth. The CO2 export from the PLE to the coastal zone appears to make the lagoon resilient to regional anthropogenic CO2 build-up. Owing to the water‒air net CO2 flux range associated with complex PLE biogeochemistry dynamics, further investigations as a long-term time-series program will improve knowledge of regional CO2 exchanges in the context of climate and elucidate the role of large estuaries and coastal bays in the global carbon budget.

Space and Time Use of European Eel Restocked in Upland Continental Freshwaters, a Long-Term Telemetry Study

There is a lack of information on many biological and ecological aspects of the critically endangered European eel during its growth phase in inland waters, such as when the sedentary life stage begins, mobility according to age and response to habitat alteration. We used mobile radio frequency identification (RFID) telemetry technology to track tagged eels over 6 years after their restocking as glass eels in six typologically different rivers. We also cross-referenced telemetry data with those of several electrofishing monitoring sessions to better understand the mobility and behaviour of eels. The relative abundance (maximum 52 individuals km−1) and detection rate (maximum 28%) of eels were not significantly correlated with the time/age after restocking. Eels were present in all restocked rivers, but their abundance was low and mobility was high in a slightly acidified, oligotrophic river that had experienced a great loss of fish habitat heterogeneity. This loss of habitat heterogeneity was due to flooding events and machinery works in riverbeds to restore the altered riverbanks. Four years after glass eel release, restocked eels became sedentary and moved from shallow to deep microhabitats with riverbeds dominated by blocks as the bottom substrate. After this age, they exhibited high fidelity to the residence site. This study provides new insights concerning the biology and ecology of eels restocked as glass eels in freshwaters, which should lead to improved management plans for the species through the implementation of more effective conservation measures and strategies.

New geochemical data for defining origin and distribution of mercury in groundwater of a coastal area in southern Tuscany (Italy)

A geochemical study was conducted in a coastal plain in the Orbetello Lagoon area in southern Tuscany (Italy), acquiring new data on groundwater, lagoon water, and stream sediment for insights into the origin, distribution, and behaviour of mercury in a Hg-enriched carbonate aquifer. The main hydrochemical features of the groundwater are ruled by the mixing of Ca–SO4 and Ca–Cl continental fresh waters of the carbonate aquifer and Na–Cl saline waters of the Tyrrhenian Sea and Lagoon of Orbetello. Groundwater had highly variable Hg concentrations (< 0.1–11 μg/L) that were not correlated with the percentage of saline water, depth in the aquifer, or distance from the lagoon. This excluded the possibility that saline water could be the direct source of Hg in groundwater and responsible for release of the element through interaction with the carbonate lithologies of the aquifer. The origin of Hg in groundwater could be ascribed to the Quaternary continental sediments overlying the carbonate aquifer because i) high Hg concentrations were found in the continental sediments of the coastal plain and in the contiguous lagoon sediments; ii) waters from the upper part of aquifer had the highest Hg concentrations; iii) Hg levels in groundwater increased with increasing thickness of the continental deposits. The high Hg content in the continental and lagoon sediments is geogenic due to regional and local Hg anomalies and to sedimentary and pedogenetic processes. It can be assumed that i) water circulating in these sediments dissolves the solid Hg-bearing constituents and mobilises this element mainly as chloride complexes; ii) Hg-enriched water moves from the upper part of the carbonate aquifer due to the cone of depression generated by intense pumping of groundwater by fish farms in the study area.

ЦИАНОБАКТЕРИАЛЬНЫЕ ЦВЕТЕНИЯ ВОДЫ В ПРЕСНОВОДНЫХ КОНТИНЕНТАЛЬНЫХ ВОДОЕМАХ: ОБЗОР

Cyanobacterial blooms of continental freshwater reservoirs are currently one of the global challenges facing humanity. The main factors increasing the scale and frequency of cyanobacterial blooms are increasing human population, intensification of agriculture, growth in industrial production, increased consumption of ores and other minerals, and global climate change. Mass development of cyanobacteria causes the breakage of trophic links between primary producers and consumers, leading to the excessive accumulation of cyanobacterial biomass and soluble products of their metabolism and autolysis, including biologically active secondary metabolites and cyanotoxins, and contributes to the formation of hypoxic conditions in the water column. Cyanobacterial blooms significantly reduce the consumer qualities of aquatic ecosystems, including their recreational attractiveness, water quality and its suitability for drinking and household purposes. The main reason for the excessive development of phytoplankton in continental freshwater reservoirs is the influx of an excessive amount of nutrients, primarily phosphorus, as well as a decrease in water circulation, causing stagnation, and high air temperatures, leading to excessive heating of water for a long period. The requirement of specialized monitoring is emphasized in order to assess and control the factors leading to the mass development of certain species of cyanobacteria. The review discusses the main bloom-forming species of cyanobacteria in freshwater reservoirs, the features of their development and environmental requirements, the consequences of cyanobacterial blooms for aquatic ecosystems and the population. The necessity of reducing the external biogenic load on reservoirs as the most important condition for the long-term prevention of cyanobacterial blooms is emphasized. An overview of various intra-reservoir methods of restoration and rehabilitation of reservoirs is given. Since their effectiveness strongly depends on the limnological and hydrobiological characteristics of the reservoir, the choice of certain methods should be based on a complete and comprehensive description of the ecosystem of the rehabilitated reservoir.

Reconstruction of Paleoenvironment and Paleoclimate of the Neogene Guantao Formation in the Liaodong Sub-Uplift of Bohai Bay Basin in China by Sedimentary Geochemistry Methods

The paleosedimentary environment and paleoclimate of the Neogene Guantao Formation in the Liaodong sub-uplift of Bohai Bay Basin in China, which is an important oil and gas exploration horizon, are not clear owing to the lack of quantitative analysis. The paleosedimentary environment and paleoclimate can be qualitatively or semi-quantitatively reconstructed by sedimentary geochemical indicators sensitive to the environment and climate. Based on the evaluation of whether the elements and isotopes can effectively record paleosedimentary environment and paleoclimate information or not, the paleoclimate (temperature and humidity), paleoenvironment (salinity, water depth, redox conditions), and evolution of the paleoenvironment and paleoclimate are studied by analyzing the trace elements, carbon and oxygen isotopes, strontium isotopes, whole-rock mineral compositions, and clay minerals of mudstones of the Guantao Formation in the Liaodong sub-uplift, Bohai Bay Basin. The study results show that (1) according to the trace element distribution patterns, high concentrations of continental elements (Ti, Zr, Th), clay minerals, and detrital content, the Guantao Formation is a product of proximal deposits, and the provenance mainly originates from the intermediate–acidic magmatic rocks near surrounding uplifts. (2) The paleoclimate during the sedimentation of the Guantao Formation was mainly semi-arid and semi-humid, as revealed by the Sr/Cu ratio. However, the high Rb/Sr and 87Sr/86Sr ratios demonstrate that the paleoclimate is relatively warm and humid. (3) The paleosedimentary temperature calculated by the Sr content and δ18O is roughly 30 °C, indicating that the Guantao Formation was deposited in a subtropical to tropical climate. (4) The Guantao Formation was deposited in continental freshwater according to the Li, Ni, and Sr content, Sr/Ba ratios, 87Sr/86Sr ratios, and salinity index Z. (5) The water depth of the paleoenvironment of the Guantao Formation is mainly in nearshore shallow water, reflected by the Mn/Ti ratio and calculated by the Co content, and the oxidizing condition of the paleoenvironment of the Guantao Formation, reflected by the U/Th, V/Cr, and Ni/Co ratios, is in a good coupling relationship with this environment. (6) As revealed by the variations in the geochemical data in the section, the temperature, humidity, and water depth of the Guantao Formation gradually increased from the early to late period, while the salinity gradually decreased, and the chemical weathering effect gradually increased.

Multiproxy investigation of the last 2,000 years BP marine paleoenvironmental record along the western Spitsbergen margin

ABSTRACT A reconstruction of the last 2,000 years BP of environmental and oceanographic changes on the western margin of Spitsbergen was performed using a multidisciplinary approach including the fossil assemblages of diatoms, planktic and benthic foraminifera and calcareous nannofossils and the use of geochemistry (X-ray fluorescence spectroscopy, X-ray diffraction). We identified two warm periods (2,000–1,600 years BP and 1,300–700 years BP) that were associated with the Roman Warm Period and the Medieval Warm Period that alternate with colder oceanic conditions and sea ice coverage occurred during the Dark Ages (1,600–1,300 years BP) and the beginning of the Little Ice Age. During the Medieval Warm Period the occurrence of ice-rafted debris and Aulocoseira spp., a specific diatom genus commonly associated with continental freshwater, suggests significant runoff of meltwaters from local glaciers.

Planktonic microbial communities from microbialite-bearing lakes sampled along a salinity-alkalinity gradient.

Continental freshwater systems are particularly vulnerable to environmental variation. Climate change-induced desertification and the anthropogenic exploitation of hydric resources result in the progressive evaporation and salinization of inland water bodies in many areas of the globe. However, how this process impacts microbial communities and their activities in biogeochemical cycles is poorly known. Here, we take a space-for-time substitution approach and characterize the prokaryotic and eukaryotic microbial communities of two planktonic cell-size fractions (0.2-5μm and 5-30 μm) from lakes of diverse trophic levels sampled along a salinity-alkalinity gradient located in the Trans-Mexican Volcanic Belt (TMVB). We applied a 16S/18S rRNA gene metabarcoding strategy to determine the microbial community composition of 54 samples from 12 different lakes, from the low-salinity lake Zirahuén to the hypersaline residual ponds of Rincón de Parangueo. Except for systems at both extremes of the salinity gradient, most lakes along the evaporation trend bear actively forming microbialites, which harbor microbial communities clearly distinct from those of plankton. Several lakes were sampled in winter and late spring and the crater lakes Alchichica and Atexcac were sampled across the water column. Physicochemical parameters related to salinity-alkalinity were the most influential drivers of microbial community structure whereas trophic status, depth, or season were less important. Our results suggest that climate change and anthropogenic-induced hydric deficit could significantly affect microbial communities, potentially altering ecosystem functioning.

Short-term paleogeographic reorganizations and climate events shaped diversification of North American freshwater gastropods over deep time

What controls species diversity and diversification is one of the major questions in evolutionary biology and paleontology. Previous studies have addressed this issue based on various plant and animal groups, geographic regions, and time intervals. However, as most previous research focused on terrestrial or marine ecosystems, our understanding of the controls on diversification of biota (and particularly invertebrates) in freshwater environments in deep time is still limited. Here, we infer diversification rates of North American freshwater gastropods from the Late Triassic to the Pleistocene and explore potential links between shifts in speciation and extinction and major changes in paleogeography, climate, and biotic interactions. We found that variation in the speciation rate is best explained by changes in continental fragmentation, with rate shifts coinciding with major paleogeographic reorganizations in the Mesozoic, in particular the retreat of the Sundance Sea and subsequent development of the Bighorn wetland and the advance of the Western Interior Seaway. Climatic events in the Cenozoic (Middle Eocene Climate Optimum, Miocene Climate Optimum) variably coincide with shifts in speciation and extinction as well, but no significant long-term association could be detected. Similarly, no influence of diversity dependence was found across the entire time frame of ~ 214 Myr. Our results indicate that short-term climatic events and paleogeographic changes are relevant to the diversification of continental freshwater biota, while long-term trends have limited effect.