► We developed a new protocol to determine conservation status of freshwater fishes. ► 83% of California’s inland fishes are extinct or declining, a 21% increase since 1989. ► Only 51% of 33 species ...rated as endangered were listed under state and federal endangered species acts. ► The rapid decline of California’s fishes is consistent with declines in other regions that are less well documented.
A quantitative protocol was developed to determine conservation status of all 129 freshwater fishes native to California. Seven (5%) were extinct; 33 (26%) were found to be in danger of extinction in the near future (endangered); 33 (26%) were rated as sufficiently threatened to be on a trajectory towards extinction if present trends continue (vulnerable); 34 (26%) were rated as declining species but not in immediate danger of extinction. Only 22 (17%) species were found to be of least concern. Of 31 species officially listed under federal and state endangered species acts (ESAs), 17 (55%) were rated as endangered by our criteria, while 12 (39%) were rated vulnerable. Conversely, of the 33 species that received our endangered rating, only 17 (51%) were officially listed under the ESAs. Among the seven metrics used to assess extinction threat, climate change, area occupied and anthropogenic threats had the largest negative impacts on status. Of 15 categories of causes of decline, those most likely to diminish status were alien species, agriculture, and dams. Overall, 83% of California’s freshwater fishes are extinct or at risk of becoming so, a 16% increase since 1995 and a 21% increase since 1989. The rapid decline of California’s inland fishes is probably typical of declines in other regions that are less well documented, indicating a strong need for improved conservation of freshwater ecosystems
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Cyanobacterial harmful algal blooms (cyanoHABs) in freshwater bodies are mainly attributed to excess loading of nutrients nitrogen (N) and phosphorus (P). This study provides a comprehensive review ...of how the existing nutrient (i.e., N and P) conditions and microbial ecological factors affect cyanobacterial community succession and cyanotoxin production in freshwaters. Different eutrophic scenarios (i.e., hypereutrophic vs. eutrophic conditions) in the presence of (i) high levels of N and P, (ii) a relatively high level of P but a low level of N, and (iii) a relatively high level of N but a low level of P, are discussed in association with cyanobacterial community succession and cyanotoxin production. The seasonal cyanobacterial community succession is mostly regulated by temperature in hypereutrophic freshwaters, where both temperature and nitrogen fixation play a critical role in eutrophic freshwaters. While the early cyanoHAB mitigation strategies focus on reducing P from water bodies, many more studies show that both N and P have a profound contribution to cyanobacterial blooms and toxin production. The availability of N often shapes the structure of the cyanobacterial community (e.g., the relative abundance of N2-fixing and non-N2-fixing cyanobacterial genera) and is positively linked to the levels of microcystin. Ecological aspects of cyanotoxin production and release, related functional genes, and corresponding nutrient and environmental conditions are also elucidated. Research perspectives on cyanoHABs and cyanobacterial community succession are discussed and presented with respect to the following: (i) role of internal nutrients and their species, (ii) P- and N-based control vs. solely P-based control of cyanoHABs, and (iii) molecular investigations and prediction of cyanotoxin production.
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•CyanoHABs in hypereutrophic freshwaters are mostly dominated by Microcystis.•Cyanobacterial succession in eutrophic freshwaters is regulated by nutrient and temperature.•Nitrogen shapes the composition of N2-fixing/non-N2-fixing cyanobacteria and cyanotoxin.•Ecological factors (e.g., presence of grazers) trigger cyanotoxin production and release.•Combined P- and N-based control over solely P-based control of cyanoHABs is preferred.
The concepts of ecosystem regime shifts, thresholds and alternative or multiple stable states are used extensively in the ecological and environmental management literature. When applied to aquatic ...ecosystems, these terms are used inconsistently reflecting differing levels of supporting evidence among ecosystem types. Although many aquatic ecosystems around the world have become degraded, the magnitude and causes of changes, relative to the range of historical variability, are poorly known. A working group supported by the Australian Centre for Ecological Analysis and Synthesis (ACEAS) reviewed 135 papers on freshwater ecosystems to assess the evidence for pressure-induced non-linear changes in freshwater ecosystems; these papers used terms indicating sudden and non-linear change in their titles and key words, and so was a positively biased sample. We scrutinized papers for study context and methods, ecosystem characteristics and focus, types of pressures and ecological responses considered, and the type of change reported (i.e., gradual, non-linear, hysteretic or irreversible change). There was little empirical evidence for regime shifts and changes between multiple or alternative stable states in these studies although some shifts between turbid phytoplankton-dominated states and clear-water, macrophyte-dominated states were reported in shallow lakes in temperate climates. We found limited understanding of the subtleties of the relevant theoretical concepts and encountered few mechanistic studies that investigated or identified cause-and-effect relationships between ecological responses and nominal pressures. Our results mirror those of reviews for estuarine, nearshore and marine aquatic ecosystems, demonstrating that although the concepts of regime shifts and alternative stable states have become prominent in the scientific and management literature, their empirical underpinning is weak outside of a specific environmental setting. The application of these concepts in future research and management applications should include evidence on the mechanistic links between pressures and consequent ecological change. Explicit consideration should also be given to whether observed temporal dynamics represent variation along a continuum rather than categorically different states.
•We assessed evidence for multiple stables states in freshwater ecosystems.•Evidence was mainly limited to studies of shallow temperate lakes.•Most studies using such terms lacked convincing evidence or appropriate data.•There were few reports of freshwater ecosystem recovery from alleviated pressures.•Inconsistent terminology and vague links with theory lead to its inappropriate use.
•Water-soluble polymers represent an overlooked global issue.•The effects of polyvinyl alcohol were investigated on freshwater organisms.•Chronic toxicity was evaluated through behavioural and ...neurotoxicity biomarkers.•Polyvinyl alcohol did not induce significant effects on exposed organisms.
Despite the pollution induced by plastics become a well-known and documented problem, bringing many countries to adopt restrictions about their production, commercialization and use, the impact of another emerging category of synthetic polymers, represented by the Water-Soluble Polymers (WSPs), also known as “liquid plastics”, is overlooked by scientific community. WSPs are produced in large quantities and used in a wide plethora of applications such as food packaging, pharmaceuticals and personal care products, cosmetics and detergents, with a consequent continuous release in the environment. The aim of this study was the investigation of the possible toxicity induced by polyvinyl alcohol (PVA), one of the main produced and used WSPs, on two freshwater model organisms, the crustacean Daphnia magna and the teleost Danio rerio (zebrafish). We evaluated the effects of solubilized standard PVA powder and PVA-based commercial bags for carp-fishing, at 3 different concentrations (1 µg/L, 0.5 mg/L and 1 mg/L), through the exposures for 14 days of D. magna (daphnids; age < 24 h) and for 5 days of zebrafish embryos (up to 120 h post fertilization - hpf). As acute effects we evaluated the immobilization/mortality of specimens, while for chronic toxicity we selected several endpoints with a high ecological relevance, as the behavioural alteration on swimming performance, in real-time readout, and the activity of monoamine oxidase (MAO), a neuro-enzyme with a potential implication in the organism movement. The results showed the lack of significant effects induced by the selected substances, at all tested concentrations and in both model organisms. However, considering the wide plethora of available WSPs, other investigations are needed to provide the initial knowledge of risk assessment of these compounds contained in some consumer products.
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Freshwater wetlands provide a range of ecosystem services, one of which is climate regulation. They are known to contain large pools of carbon (C) that can be affected by land-use change. In New ...Zealand, only 10 % of the original freshwater wetlands remain due to conversion into agriculture. This study presents the first national estimation of C stocks in freshwater wetlands based on the compilation of soil carbon data from 126 sites across the country. We estimated C stocks for two soil sample types (mineral and organic) in different classes of wetlands (fen, bog, swamp, marsh, pakihi and ephemeral), and extrapolated C stocks to national level using GIS. Bogs had high C content and low bulk densities, while ephemeral wetlands were the reverse. A regression between bulk density and C content showed a high influence of the soil type. Average C densities (average ± standard error) were 1,348 ± 184 t C ha⁻¹ at full peat depth (average of 3.9 m) and 102 ± 5 t C ha⁻¹ (0.3 m depth) for organic soils, and 121 ± 24 t C ha⁻¹ (0.3 m depth) for mineral soils. At national level, C stocks were estimated at 11 ± 1 Mt (0.3 m depth) and 144 ± 17 Mt (full peat depth) in organic soils, and 23 ± 1 Mt (0.3 m depth) in mineral soils. Since European settlement, 146,000 ha of organic soils have been converted to agriculture, which could release between 0.5 and 2 Mt CO₂ year⁻¹, equivalent to 1–6 % of New Zealand’s total agricultural greenhouse gas emissions.
The continuous increase in synthetic plastic production and poor management in plastic waste have led to a tremendous increase in the dumping into our aqueous environment. Consequently, microplastics ...commonly defined as sizes less than 5 mm are produced and stay in both seawater and freshwater environment. The presence of microplastics as a new type of emerging contaminant has become a great issue of concerns from public and government authorities. The sources of microplastics to freshwater systems are many with the largest portion from wastewater treatment plants. The abundance of microplastics varies with the location, from above 1 million pieces per cubic meter to less than 1 piece in 100 cubic meters.
Microplastics can cause several harmful physical effects on humans and living organisms through such mechanisms as entanglement and ingestion. The microplastics can act as carriers of various toxins such as additives from industrial production processes and persistent contaminants by the sorption in waters. Those toxins may cause great health problems to humans. A few studies on the fishes demonstrated that the microplastics and the associated toxins are bio-accumulated and cause such problems as intestinal damage and change in metabolic profiles.
In studies of microplastics, fresh water is first sampled by the nets with typical mesh size of 330 μm for collection of microplastics. After the volume reducing process, the samples will then go through the purification process including density separation by such inorganic salts as sodium chloride and digestion process by oxidizing agents or enzymes. The sequence of these two processes (namely purification and digestion) is dependent on the sample type. The purified samples can be studied by several analytical methods. The commonly used methods for the qualification studies are FTIR spectroscopy, Raman spectroscopy, pyrolysis-GC/MS, and liquid chromatography. A tagging method can be used in the quantification study. Our literature study finds that there is still no universal accepted quantification and qualification tools of microplastics in fresh waters. More work is anticipated so as to obtain accurate information on microplastics in freshwater, which can then be used for the better assessment of the environmental risk.
•Microplastics exhibit high abundance in freshwater systems.•The knowledge about health impacts of freshwater microplastics is limited.•A summary of current microplastics research methodology is included.•Combination of appropriate analytical approaches should be adopted to assess microplastics in freshwaters.
Freshwater fluxes from the Greenland ice sheet have increased over the last two decades due to increases in liquid (i.e., surface and submarine meltwater) and solid ice (i.e., iceberg) fluxes. To ...predict potential ice sheet‐ocean‐climate feedbacks, we must know the partitioning of freshwater fluxes from Greenland, including the conversion of icebergs to liquid (i.e., meltwater) fluxes within glacial fjords. Here we use repeat ~0.5 m‐resolution satellite images from two major fjords to provide the first observation‐based estimates of the meltwater flux from the dense matrix of floating ice called mélange. We find that because of its expansive submerged area (>100 km2) and rapid melt rate (~0.1–0.8 m d−1), the ice mélange meltwater flux can exceed that from glacier surface and submarine melting. Our findings suggest that iceberg melt within the fjords must be taken into account in studies of glacial fjord circulation and the impact of Greenland melt on the ocean.
Plain Language Summary
Over the last two decades, the volume of icebergs breaking‐off (i.e., calving) from the Greenland ice sheet has increased substantially. This increase has raised sea level and has potentially influenced the thermohaline ocean circulation that helps regulate the Earth's climate. Although ocean models can be used to estimate the impacts of increased iceberg calving on ocean circulation, the accuracy of these models depends on knowledge of the spatial distribution of the meltwater produced by Greenland's icebergs. In this paper we use iceberg size information from repeat satellite images to estimate the rates of iceberg melting and cumulative iceberg melt volumes in glacial fjords that connect two of Greenland's largest glaciers to the open ocean. We find that despite being previously overlooked by most scientific investigations of glacier‐ocean interactions, iceberg meltwater dominates these fjords' freshwater budgets throughout the majority of the year. We also find that up to 50% of iceberg volume is melted‐out by the time icebergs reach the open ocean. These results suggest that ocean models must take iceberg melting into account in order to accurately simulate changes in ocean circulation in response to increased iceberg production both now and in the future.
Key Points
Freshwater fluxes from melting ice melange vary with submerged ice area and area‐averaged melt rate and can exceed 1000 m3/s
Ice melange meltwater fluxes can dominate the freshwater budget of glacial fjords throughout the majority of the year
Solid freshwater fluxes to the open ocean cannot be estimated from glacier discharge because up to 50% of iceberg mass is melted in fjords
Using strontium (Sr) and barium (Ba) in otoliths to determine natal origins and understand patterns of fish movements is based on the fundamental assumption that otoliths record water chemistry ...signals without any major alterations. Although prior studies highlighted that fish physiology can modify the water signal in otoliths, studies for freshwater fish are scarce. We exposed different groups of Atlantic salmon parr Salmo salar to different scenarios of ambient-level variations in Sr/Ca and Ba/Ca ratios and then combined otolith chemical profiles with environmental data (water chemistry and temperature), Fulton's index, and otolith growth rates to assess what factors explain/influence the elemental ratios of Sr and Ba in otoliths. Generalized additive mixed models (GAMMs) using water-based otolith composition, temperature, Fulton's index, and “individual” as explanatory variables allow to demonstrate that water chemistry alone cannot fully explain measured ratios in otoliths, except in scenarios involving significant changes in water chemistry. Other factors (physiological effects) should be accounted for reproducing short and minimal seasonal variations in water composition, considering that inter-individual variability contributes quite significantly in most scenarios.
The introduction of non-native species is recognized as a major threat to biodiversity, particularly in freshwater ecosystems. Pikeperch Sander lucioperca, is a recent invader to Portugal, primarily ...providing commercial and angling interest. The aim of this work was to study the diet of this top predator across Portuguese basins and to evaluate its potential impact on recipient ecosystems. In total, 256 pikeperch stomachs from seven basins were examined, of which 88 (n = 34%) were empty. Pikeperch diet was dominated by R. rutilus, M. salmoides and Diptera in northern populations, while A. alburnus, P. clarkii and Atyidae were important prey in more humid highlands. Variation in diet was most strongly linked to latitude and ontogeny, with both size classes showing signs of cannibalism. The population niche breadth remained low and was accompanied by higher individual diet specialization, particularly in northern populations. Pikeperch dietary patterns denoted an opportunistic ability to use locally abundant prey in each ecosystem, and was size dependent, with larger individuals becoming more piscivores, causing a higher impact in the lotic systems. This first perspective about the pikeperch diet presents a very broad view of the feeding traits of this non-native predator across Portugal, being very important to deepen our knowledge about the impact of these introduced piscivores.
This paper investigated the hydrodynamics, spatio-temporal variability of temperature/salinity and the residence time of tracer concentrations in a largest brackish water coastal lagoon in Asia, ...namely the Chilika lagoon, India. An integrated approach combined the measurement and 2D hydrodynamic-advection/dispersion model is used to simulate circulation and temperature/salinity, and estimated the water residence time in lagoon under different forcing mechanisms, such as tide, wind and freshwater discharge during the dry and wet periods. Water circulation inside the lagoon is simulated when wind is included with the tide only forcing during dry period, and freshwater influx is included with the tide and wind forcing during wet period. Under the realistic forcing conditions, the computed temporal variability of water temperature and salinity are well correlated with the measurements in both the periods. The spatial variations of water temperature within the lagoon is influenced by the meteorological conditions, tide and freshwater influx as well as the shallowness of the lagoon, whereas the salinity is spatially controlled by the freshwater influx from the riverine system and seawater intrusion through the tidal inlets. The numerical model results show that in the Chilika lagoon tidal and river influx affect significantly the residence time spatially, and is site specific. The residence time varies from values of 4–5 days in the outer channel (OC) and 132 days at the northern sector (NS) in the main body of lagoon. The current study represents a first attempt to use a combined model approach, which is therefore, a useful tool to support the ecological implication of the lagoon ecosystem.
•Hydrodynamics and residence time is investigated under different scenarios.•A 2D hydrodynamic-AD model is used for model simulations with observations.•Temperature/salinity distribution mainly controlled by tidal and river inflows.•Spatially heterogeneous residence time, and is site specific that varies seasonally.
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