Discontinuity in equilibrium wave–current ripple size and shape caused by a winnowing threshold in cohesive sand–clay beds

Sediments composed of mixed cohesive clay and non-cohesive sand are widespread in a range of aquatic environments. The dynamics of ripples in mixed sand–clay substrates have been studied under pure current and pure wave conditions. However, the effect of cohesive clay on ripple development under combined currents and waves has not been examined, even though combined flows are common in estuaries, particularly during storms. Based on a series of large flume experiments on ripple development under combined flows, we identified a robust inverse relationship between initial bed clay content, C0, and ripple growth rate. The experimental results also revealed two distinct types of equilibrium combined-flow ripples on mixed sand–clay beds: (a) large asymmetrical ripples with dimensions and plan geometries comparable to clean-sand counterparts for C0 ≤ 10.6%; and (b) small, flat ripples for C0 > 11%. The increase in bed cohesion contributed to this discontinuity, expressed most clearly in a sharp reduction in equilibrium ripple height, and thus a significant reduction in bed roughness, which implies that the performance of existing ripple predictors can be improved by the incorporation of this physical cohesive effect. These improvements are particularly important for sediment transport and morphodynamic models in muddy estuarine environments. For C0 ≤ 10.6%, strong clay winnowing efficiency under combined flows resulted in the formation of equilibrium clean-sand ripples and clay loss at depths far below the ripple base. In natural environments, this ‘deep cleaning’ of bed clay may cause a concurrent sudden release of a large amount of pollutants during storms, and lead to a sudden reduction in post-storm resistance to erosion of mixed sand–clay substrates.

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A Brief Review of the Structure, Cytotoxicity, Synthesis, and Biodegradation of Microcystins

Water ◽

10.3390/w13162147 ◽

2021 ◽

Vol 13 (16) ◽

pp. 2147

Author(s):

Anjali Krishnan ◽

Xiaozhen Mou

Keyword(s):

Health Hazard ◽

Aquatic Organisms ◽

Water Soluble ◽

Cyanobacterial Blooms ◽

Aquatic Environments ◽

Natural Environments ◽

Exposure Pathway ◽

Environmental Transformation ◽

Cyclic Heptapeptide ◽

Harmful Cyanobacterial Blooms

Harmful cyanobacterial blooms pose an environmental health hazard due to the release of water-soluble cyanotoxins. One of the most prevalent cyanotoxins in nature is microcystins (MCs), a class of cyclic heptapeptide hepatotoxins, and they are produced by several common cyanobacteria in aquatic environments. Once released from cyanobacterial cells, MCs are subjected to physical chemical and biological transformations in natural environments. MCs can also be taken up and accumulated in aquatic organisms and their grazers/predators and induce toxic effects in several organisms, including humans. This brief review aimed to summarize our current understanding on the chemical structure, exposure pathway, cytotoxicity, biosynthesis, and environmental transformation of microcystins.

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Sorption of Anionic Pentachlorophenol (PCP) in Aquatic Environments: The Effect of pH

Water Science & Technology ◽

10.2166/wst.1992.0271 ◽

1992 ◽

Vol 25 (11) ◽

pp. 41-48 ◽

Cited By ~ 30

Author(s):

Y. Shimizu ◽

S. Yamazaki ◽

Y. Terashima

Keyword(s):

Organic Carbon ◽

Aqueous Phase ◽

Cation Exchange Capacity ◽

Clay Content ◽

Exchange Capacity ◽

Poor Correlation ◽

Aquatic Environments ◽

Organic Carbon Content ◽

Swelling Clay ◽

Ph Range

The sorption of pentachlorophenol (PCP, pKa’ = 4.75) onto natural solids from aqueous phase was investigated by batch sorption experiments. The experimental aqueous phase was prepared for set values of pH (2 to 12) and ionic strength (0.1 M). Experimental results indicated that the sorption decreased with increasing pH over the entire pH range tested. A simple mathematical model, based on the hypotheses that the sorption coefficients of non-ionized and ionized species are different and the pH has only negligible effect on the natural solid characteristics, was applied to the pH range between 6 and 8, and the sorption coefficients (Kd) of both species were estimated. The Kd of ionized species (phenolate anion) was smaller than that of non-ionized species. The Kd of both species had poor correlation to the organic carbon content of natural solids. The Kd, however, correlated well with the swelling clay content and cation exchange capacity of natural solids. These results indicated that the sorption of PCP was not controlled by the organic carbon referenced hydrophobic sorption. For broader pH range (i.e., below 6 or above 8), the dependence of the natural solid characteristics on pH must be additionally included in the model.

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Effects of Antibiotics on Impacted Aquatic Environment Microorganisms

10.5772/intechopen.93910 ◽

2020 ◽

Author(s):

Lívia Caroline Alexandre de Araújo ◽

Sivoneide Maria da Silva ◽

Rafael Artur de Queiroz Cavalcanti de Sá ◽

Ana Vitoria Araujo Lima ◽

Amanda Virginia Barbosa ◽

...

Keyword(s):

Bacterial Community ◽

Mass Production ◽

Aquatic Environment ◽

Human Medicine ◽

Aquatic Environments ◽

Natural Environments ◽

Natural Ecosystems ◽

Composition And Structure ◽

Hospital Effluents

Due to their mass production and intense consumption in human medicine, veterinary, and aquaculture, antibiotics have been widely detected in different ecosystems, leading to a growing worldwide concern. These and their byproducts are being continuously discarded in natural ecosystems via excretion of human and animal urine and feces, also domestic and hospital effluents. Residues of these drugs can persist in natural environments through bioaccumulation due to their difficult biodegradation. Also, they have a gradual deposition in sediments, aquatic surfaces, and groundwater. Studies have shown the presence of these drugs in aquatic environments, which can trigger severe changes in the composition and structure of the bacterial community, such as the ability to develop and propagate genes resistant to these pollutants. In this context, this review aims to address the effects of the antibiotics on microorganisms present in impacted aquatic environments.

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A Mini-Review of Strategies for Quantifying Anthropogenic Activities in Microplastic Studies in Aquatic Environments

Polymers ◽

10.3390/polym14010198 ◽

2022 ◽

Vol 14 (1) ◽

pp. 198

Author(s):

Chun-Ting Lin ◽

Ming-Chih Chiu ◽

Mei-Hwa Kuo

Keyword(s):

Anthropogenic Activities ◽

Primary Source ◽

Aquatic Environments ◽

Natural Environments ◽

Watershed Scale ◽

Effective Management ◽

Potential Harm ◽

Scale Measure ◽

Management Policies ◽

Gis Software

Microplastic pollution is no longer neglected worldwide, as recent studies have unveiled its potential harm to ecosystems and, even worse, to human health. Numerous studies have documented the ubiquity of microplastics, reflecting the necessity of formulating corresponding policies to mitigate the accumulation of microplastics in natural environments. Although anthropogenic activities are generally acknowledged as the primary source of microplastics, a robust approach to identify sources of microplastics is needed to provide scientific suggestions for practical policymaking. This review elucidates recent microplastic studies on various approaches for quantifying or reflecting the degree to which anthropogenic activities contribute to microplastic pollution. Population density (i.e., often used to quantify anthropogenic activities) was not always significantly correlated with microplastic abundance. Furthermore, this review argues that considering potential sources near sample sites as characteristics that may serve to predict the spatial distribution of microplastics in aquatic environments is equivocal. In this vein, a watershed-scale measure that uses land-cover datasets to calculate different percentages of land use in the watershed margins delineated by using Geographic Information System (GIS) software is discussed and suggested. Progress in strategies for quantifying anthropogenic activities is important for guiding future microplastic research and developing effective management policies to prevent microplastic contamination in aquatic ecosystems.

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Simulation of soil carbon dynamics in Australia with {\sc Roth C}

10.5194/ismc2021-91 ◽

2021 ◽

Author(s):

Raphael Viscarra Rossel ◽

Juhwan Lee ◽

Mingxi Zhang ◽

Zhongkui Luo ◽

YingPing Wang

Keyword(s):

C:N Ratio ◽

Clay Content ◽

Natural Environments ◽

Soil Organic C ◽

Total N ◽

Organic C ◽

Continental Scale ◽

C Stocks ◽

C Decomposition ◽

Soil Measurements

We simulated soil organic carbon (C) dynamics across Australia with the Rothamsted carbon model ({\sc Roth C}) by connecting new spatially-explicit soil measurements and data with the model. This helped us to bridge the disconnection that exists between datasets used to inform the model and the processes that it depicts. We compiled publicly available continental-scale datasets and pre-processed, standardised and configured them to the required spatial and temporal resolutions. We then calibrated {\sc Roth C} and run simulations to estimate the baseline soil organic C stocks and composition in the 0--0.3~m layer at 4,043 sites in cropping, modified grazing, native grazing, and natural environments across Australia. We used data on the C fractions, the particulate, mineral associated, and resistant organic C (POC, MAOC and ROC, respectively) to represent the three main C pools in the {\sc Roth C} model's structure.&#160; The model explained 97--98\% of the variation in measured total organic C in soils under cropping and grazing, and 65\% in soils under natural environments. We optimised the model at each site and experimented with different amounts of C inputs to simulate the potential for C accumulation under constant and chainging climate in a 100-year simulation. Soils under native grazing were the most potentially vulnerable to C decomposition and loss, while soils under natural environments were the least vulnerable. An empirical assessment of the controls on the C change showed that climate, pH, total N, the C:N ratio, and cropping were the most important controls on POC change. Clay content and climate were dominant controls on MAOC change. Consistent and explicit soil organic C simulations improve confidence in the model's estimations, contributing to the development of sustainable soil management under global change.&#160;

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Simulation of soil carbon dynamics in Australia under a framework that better connects spatially explicit data with Rᴏᴛʜ C

10.5194/bg-2020-150 ◽

2020 ◽

Author(s):

Juhwan Lee ◽

Raphael A. Viscarra Rossel ◽

Zhongkui Luo ◽

Ying Ping Wang

Keyword(s):

C:N Ratio ◽

Clay Content ◽

Spatially Explicit ◽

Natural Environments ◽

Soil Organic C ◽

Total N ◽

Organic C ◽

Soil C ◽

Continental Scale ◽

C Stocks

Abstract. We simulated soil organic carbon (C) dynamics across Australia with the Rothamsted carbon model (Rᴏᴛʜ C) under a framework that connects new spatially-explicit soil measurements and data with the model. Doing so helped to bridge the disconnection that exists between datasets used to inform the model and the processes that it depicts. Under this framework, we compiled continental-scale datasets and pre-processed, standardised and configured them to the required spatial and temporal resolutions. We then calibrated Rᴏᴛʜ C and run simulations to predict the baseline soil organic C stocks and composition in the 0–0.3 m layer at 4,043 sites in cropping, modified grazing, native grazing, and natural environments across Australia. The Rᴏᴛʜ C model uses measured C fractions, the particulate, humus, and resistant organic C (POC, HOC and ROC, respectively) to represent the three main C pools in its structure. The model explained 97–98 % of the variation in measured total organic C in soils under cropping and grazing, and 65 % in soils under natural environments. We optimised the model at each site and experimented with different amounts of C inputs to predict the potential for C accumulation in a 100-year simulation. With an annual increase of 1 Mg C ha−1 in C inputs, the model predicted a potential soil C increase of 13.58 (interquartile range 12.19–15.80), 14.21 (12.38–16.03), and 15.57 (12.07–17.82) Mg C ha−1 under cropping, modified grazing and native grazing, and 3.52 (3.15–4.09) Mg C ha−1 under natural environments. Soils under native grazing were the most potentially vulnerable to C decomposition and loss, while soils under natural environments were the least vulnerable. An empirical assessment of the controls on the C change showed that climate, pH, total N, the C:N ratio, and cropping were the most important controls on POC change. Clay content and climate were dominant controls on HOC change. Consistent and explicit soil organic C simulations improve confidence in the model's predictions, contributing to the development of sustainable soil management under global change.

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Novel insights into the taxonomic diversity and molecular mechanisms of bacterial Mn(III) reduction

10.1101/695007 ◽

2019 ◽

Cited By ~ 2

Author(s):

Nadia Szeinbaum ◽

Brook L. Nunn ◽

Amanda R. Cavazos ◽

Sean A. Crowe ◽

Frank J. Stewart ◽

...

Keyword(s):

Cytochrome C ◽

Molecular Mechanisms ◽

Enrichment Culture ◽

Taxonomic Diversity ◽

Extracellular Electron Transfer ◽

Aquatic Environments ◽

Natural Environments ◽

Biological Reduction ◽

Lake Matano ◽

C Complex

SummarySoluble ligand-bound Mn(III) can support anaerobic microbial respiration in diverse aquatic environments. Thus far, Mn(III) reduction has only been associated with certain Gammaproteobacteria. Here, we characterized microbial communities enriched from Mn-replete sediments of Lake Matano, Indonesia. Our results provide the first evidence for biological reduction of soluble Mn(III) outside the Gammaproteobacteria. Metagenome assembly and binning revealed a novel betaproteobacterium, which we designate “Candidatus Dechloromonas occultata.” This organism dominated the enrichment and expressed a porin-cytochrome c complex typically associated with iron-oxidizing Betaproteobacteria and a novel cytochrome c-rich protein cluster (Occ), including an undecaheme putatively involved in extracellular electron transfer. This occ gene cluster was also detected in diverse aquatic bacteria, including uncultivated Betaproteobacteria from the deep subsurface. These observations provide new insight into the taxonomic and functional diversity of microbially-driven Mn(III) reduction in natural environments.Originality-Significance StatementRecent observations suggest that Mn(III)-ligand complexes are geochemically important in diverse aquatic environments. Thus far, microbially-driven Mn(III) reduction has only been associated with Gammaproteobacteria encoding three-component outer-membrane porin-cytochrome c conduits. Here, we demonstrate that Betaproteobacteria dominate in abundance and with respect to protein expression during biologically-mediated Mn(III) reduction in an enrichment culture from an anoxic lacustrine system. Using metaproteomics, we detect for the first time that Betaproteobacteria express a two-component porin-cytochrome c conduit, and an uncharacterized extracellular undecaheme (11-heme) c-type cytochrome. Although this is the first definitive report of an undecaheme within the Betaproteobacteria, we find evidence that they are widespread in uncultivated strains. These results widen the phylogenetic diversity of Mn(III)-reducing bacteria, and provide new insights into potential molecular mechanisms for soluble Mn(III) reduction

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Clast imbrication in coarse-grained mountain streams and stratigraphic archives as indicator of deposition in upper flow regime conditions

Earth Surface Dynamics ◽

10.5194/esurf-6-743-2018 ◽

2018 ◽

Vol 6 (3) ◽

pp. 743-761 ◽

Cited By ~ 2

Author(s):

Fritz Schlunegger ◽

Philippos Garefalakis

Keyword(s):

Flow Regime ◽

Critical Shear Stress ◽

Inertial Force ◽

Swiss Alps ◽

Coarse Grained ◽

Flume Experiments ◽

Energy Gradient ◽

Alpine Streams ◽

Bed Roughness ◽

Supercritical Flows

Abstract. Clast imbrication is one of the most conspicuous sedimentary structures in coarse-grained clastic deposits of modern rivers but also in the stratigraphic record. In this paper, we test whether the formation of this fabric can be related to the occurrence of upper flow regime conditions in streams. To this end, we calculated the Froude number at the incipient motion of coarse-grained bedload for various values of relative bed roughness and stream gradient as these are the first-order variables that can practically be extracted from preserved deposits. We found that a steeper energy gradient, or slope, and a larger bed roughness tend to favor the occurrence of supercritical flows. We also found that, at the onset of grain motion, the ratio ϕ between the critical shear stress for the entrainment of a sediment particle and its inertial force critically controls whether flows tend to be super- or subcritical during entrainment. We then mapped the occurrence of clast imbrication in Swiss streams and compared these data with the hydrologic calculations. Results indicate that imbrication may record supercritical flows provided that (i) ϕ values are larger than ca. 0.05, which is appropriate for streams in the Swiss Alps; (ii) average stream gradients exceed ca. 0.5 ± 0.1°; and (iii) relative bed roughness values, i.e., the ratio between water depth d and bed sediment D84, are larger than ∼ 0.06 ± 0.01. We cannot rule out that imbrication may be formed during subcritical flows with ϕ values as low as 0.03, as demonstrated in a large number of flume experiments. However, our results from Alpine streams suggest that clast imbrication likely reflects upper flow regime conditions where clasts form well-sorted and densely packed clusters. We consider that these differences may be rooted in a misfit between the observational and experimental scales.

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Electron Spectroscopic Imaging of Magnetotactic Bacteria: Magnetosome Morphology and Diversity

Microscopy and Microanalysis ◽

10.1007/s100050010047 ◽

2000 ◽

Vol 6 (5) ◽

pp. 463-470 ◽

Cited By ~ 8

Author(s):

Ulysses Lins ◽

Flávia Freitas ◽

Carolina N. Keim ◽

Marcos Farina

Keyword(s):

Imaging Technique ◽

Spectroscopic Imaging ◽

Magnetotactic Bacteria ◽

Aquatic Environments ◽

Natural Environments ◽

Electron Spectroscopic Imaging ◽

Multicellular Aggregates ◽

Structural Relationships ◽

Size And Morphology ◽

Uncultured Microorganisms

AbstractMagnetotactic bacteria from aquatic environments were analyzed with the electron spectroscopic imaging technique. Rod-shaped bacteria and cocci were present in most of the samples observed. Magnetotactic multicellular aggregates were also observed at some of the sampling sites. The use of electron spectroscopic imaging allowed the observation of magnetosomes inside magnetotactic microorganisms with exceptional clarity. The number, size, and morphology of magnetosomes, as well as their ultrastructural spatial disposition inside the bacterial cell, could be directly observed and associated with the disposition of flagella of the respective cells.This allowed us to examine the structural relationships between magnetosomes and flagella, which are important components in the mechanisms of magnetotaxis. In disrupted magnetotactic multicellular aggregates, connections between cells were also visualized. We believe this technique will be useful in studying not only magnetotactic bacteria but also other uncultured microorganisms from natural environments.

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Review of the Persistence of Nonylphenol and Nonylphenol Ethoxylates in Aquatic Environments

Water Quality Research Journal ◽

10.2166/wqrj.1999.003 ◽

1999 ◽

Vol 34 (1) ◽

pp. 37-78 ◽

Cited By ~ 116

Author(s):

R. James Maguire

Keyword(s):

Degradation Products ◽

Sewage Treatment ◽

Operating Conditions ◽

Aquatic Environments ◽

Natural Environments ◽

Nonylphenol Ethoxylates ◽

Plant Design ◽

Anaerobic Conditions ◽

Sewage Treatment Plants ◽

Nonylphenol Ethoxylate

Abstract Alkylphenol ethoxylates, in particular nonylphenol ethoxylates, are widely used nonionic surfactants that are discharged in high quantities to sewage treatment plants and directly to the environment in areas where there is no sewage or industrial waste treatment. This article reviews the treatability of nonylphenol ethoxylates and nonylphenol in sewage treatment plants and their persistence in aquatic environments. Nonylphenol ethoxylates can be biologically degraded in sewage treatment plants and in natural environments. Some of the degradation products, including nonylphenol, are more persistent than the parent surfactants and they are found in receiving waters of sewage treatment plants. Nonylphenol in particular is found at high concentrations in some sewage sludges that may be spread on agricultural lands. While some sewage treatment plants discharge significant amounts of nonylphenol ethoxylate degradation products in their final effluents and digested sludges compared to what enters the plant, others degrade nonylphenol ethoxylates more or less completely. The differences in treatment efficiency of such compounds and their degradation products among different sewage treatment plants have been attributed to the load of the surfactants in influent streams, plant design and operating conditions, and other factors such as temperature of treatment. The highest nonylphenol ethoxylate elimination rates were achieved in plants characterized by low sludge-loading rates and nitrifying conditions. In natural waters, it appears that parent nonylphenol ethoxylates are not persistent, but some degradation products may have moderate persistence, especially under anaerobic conditions. Recent results from mesocosm experiments indicate moderate persistence of nonylphenol in sediments, with half-lives of 28 to 104 days. Microbial acclimation to the chemicals is an important determinant of persistence vis-à-vis biodegradation. Sunlight photodegradation of such products is also likely important. Further research on the persistence in natural environments of the lower ethoxylate and carboxylate degradation products, as well as nonylphenol, is necessary. Based on the limited data available, nonylphenol and the lower ethoxylates and carboxylates are persistent in groundwater. They are also persistent in landfills under anaerobic conditions, but they do not appear to be persistent in soil under aerobic conditions. Recommendations are made for further research in order to more fully characterize the treatability of nonylphenol ethoxylates and their degradation products in sewage treatment plants and their persistence in the natural environment.

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