Aquatic Ecosystems Research Articles

Freshwater salinisation: unravelling causes, adaptive mechanisms, ecological impacts, and management strategies.

Freshwater salinisation is a growing problem worldwide, affecting surface and groundwater resources. Compared with other global environmental issues, freshwater salinisation has been studied extensively in North America, Australia, and Europe but less so in South America, Asia, and Africa. Both the natural and anthropogenic sources can contribute for freshwater salinisation, through the concentration of dissolved salts in water rising above its normal levels. This review provides a comprehensive assessment of the causes of freshwater salinisation, the impacts on freshwater communities and ecosystem functions, the adaptive mechanisms for survival in an increasingly saline environment, and the management strategies available to control freshwater salinisation. Many human activities contribute to freshwater salinisation, including road salt use, agricultural practices, resource extraction, reservoir construction, and climate change. Aquatic organisms have evolved mechanisms to survive in increasingly saline environments, but excessive salinity can lead to mortality and non-lethal effects. Such effects can have cascading impacts on the structure and function of aquatic communities and ecosystem services. Therefore, monitoring programmes and chemical fingerprinting are needed to identify highly salinised areas, determine how various human activities contribute to freshwater salinisation, and implement management strategies. Furthermore, current research on freshwater salinisation has been limited to a few regions of the world. It is essential to expand the research further into exploring the impacts of salinisation on freshwater resources in unexplored geographic areas of the world that are mainly impacted by climate change scenarios.

Ecological Flow as a Water Stress Control Strategy: San Rodrigo River, Coahuila, Mexico

Ecological flow refers to the minimum amount of water that must be maintained in a body of water to protect and preserve aquatic ecosystems. This article aims to analyze the function of ecological flow to address the reproduction of the natural hydrological regime of the San Rodrigo River, Coahuila, Mexico. A quantitative methodology was used where the ecological flow was determined based on the Mexican Standard NMX-AA-159-SCFI-2012 considering the period from 1962 to 2016. The maximum data allows us to identify runoffs of low magnitude of 6.65–15.60, those with an average trend close to 500 Mm3, and floods of extraordinary volume (namely, those 844–1260 and 1670 Mm3) with a frequency of every 35 years. Likewise, the river marks drastic changes in the flow in certain years, ranging from 0.64 to 1260 Mm3, so that the rate of variation would possibly exceed several orders of magnitude scaled in an annual phase. In conclusion, this calculation indicates that the body of water may have the function of environmental conservation covered throughout the year, with the data suggesting that in the short term the river will recover part of the water that passed through its course and thus avoid its deterioration.

Zooplankton metacommunity knowledge over 20 years: a systematic review

Abstract The metacommunity theory aims to understand the species dynamics at different scales by considering the influence of local and regional processes. We conducted a systematic review of zooplankton metacommunity studies in global aquatic ecosystems (freshwater, marine and estuarine) looking for the distribution, time scale, type of system, type of environment, zooplankton group tested, ecological approach and metacommunity approach analyzed in the studies. We also present an overview of the observed patterns of the zooplankton metacommunity in different environmental conditions. We searched for scientific studies published until December 2022 on Scopus and Web of Science using the words: “zooplankton” and “metacomunnit*.” Our results show that studies on the zooplankton metacommunity have become recurrent over time (167 studies), especially for pond systems and for the groups of rotifers, cladocerans and copepods; however, several gaps remain related to studies distribution and the low number of studies in streams, reservoirs, with functional and phylogenetic diversity, and the elements of metacommunity structure. Our data improve the knowledge of the zooplankton metacommunity over time, help to identify the gaps that need to be explored in future studies and bring a general overview of the observed patterns for the zooplankton metacommunity.

CHEMICAL AND MICROBIOLOGICAL DIVERSITY DETECTED IN WATER BODIES IN THE MUNICIPALITY OF BARCARENA/PA, AMAZONIA, BRAZIL

Population growth linked to greater exploitation of nature compromises the quality of water, which is considered a limited natural resource and is vitally important for the survival of living organisms and directly influences the economy, leisure, culture and the social environment. This study evaluated the physicochemical, toxicological and microbiological parameters of rivers and streams in the municipality of Barcarena, State of PA, Amazonia, Brazil. We collected 58 samples in the period from 2021 to 2022. The average values ​​verified were above the limits allowed by Brazilian legislation (CONAMA 357/2005) for true color (µ = 218.09 ± 223.843), BOD (µ = 31.30 ± 64.992) and Escherichia coli (µ = 1243.76 ± 2838.743) in stream samples when compared to those from the river, demonstrating that there are statistical differences in these parameters between these two environments. We also analyzed traces of 10 toxic metals (Al, B, Ba, Be, Cd, Co, Cr, Cu, Li, Pb). The average levels of these pollutants ranged from 0 (<LD) to 1,504 mg/L. The highest concentration was found for Aluminum, which ranged from 0.003 to 1.504 mg/L with an average of 0.275 ± 0.289 mg/L. The greatest concentration similarity (75.16%) of these soluble metals was observed between the Pará river and the Dendê stream. Therefore, the studied area presents contamination of aquatic ecosystems due to mining activity, which has caused serious impacts on the remaining communities on the banks of the municipality's rivers that cross the Municipality of Barcarena-Pa.

Eco-Friendly TiO2 Nanoparticles: Harnessing Aloe Vera for Superior Photocatalytic Degradation of Methylene Blue

In recent years, the contamination of aquatic environments by organic chemicals, including dyes such as methylene blue (MB), Congo red, and crystal violet, has become an increasing concern, as has their treatment. In this work, titanium dioxide nanoparticles (TiO2 NPs) were studied for their photocatalytic performance by measuring the degradation of MB under UV light. TiO2 NPs were synthesized using two synthetic processes optimized in this study: a green method, namely leveraging the natural properties of Aloe vera leaf extract; and a conventional approach. The resulting NPs were thoroughly characterized using X-rays Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), UV–Vis and ζ-potential analysis. The TiO2 NPs synthesized by the green method demonstrated a degradation efficiency of (50 ± 3)% after 180 minutes, which was significantly higher than the (16 ± 3)% achieved by NPs synthesized through the conventional route. Moreover, the reaction rate constant for the green-synthesized TiO2 NPs was found to be approximately five times greater than that of the conventionally synthesized NPs. These results open up a new scenario in the pollution removal strategy research, using resources accessible in nature to synthesize NPs with high photocatalytic activity, which could also be useful for other applications, such as hydrogen production.

Study the Dynamics of the Transformation Processes for Nitrogen and Phosphorus Compounds in the Ecosystem of the Vistula Lagoon of the Baltic Sea using the Methods of Mathematical Modeling

By using mathematical modeling methods, a systematic study of the interaction of hydrobiological, hydrochemical, hydrological and hydrophysical processes that occur in the ecosystem of the Vistula Lagoon (VL) of the Baltic Sea was carried out, taking into account the processes in the active layer of bottom sediments (BS). The features of the dynamics of nitrogen and phosphorus compounds, the turnover time and the components of the balance of compounds of biogenic elements in the VL ecosystem, as well as the degree of their temporal variability have been analyzed. It is shown that the variability of nitrogen and phosphorus compounds in the aquatic environment increases in spring and autumn periods. This is due to an increase in river flow into the lagoon and an increase in the level of external biogenic load on the water area of the VL. Model calculations of matter fluxes allow us to state that the inputs of dissolved organic and suspended matter into the lagoon from external sources and the removal to the Baltic Sea are important processes that significantly affect their content in the VL ecosystem. It has been established that under strong winds the process of sedimentation of suspensions can be largely blocked, and the intensity of BS resuspension can increase significantly. An analysis of the main qualitative and quantitative features of the nature of the temporal dynamics of the DON and DOP turnover times, as well as the mineral compounds of nitrogen and phosphorus, indicates a close conjugation of the processes of transformation of dissolved organic and inorganic substances in the water of the VL. A quantitative assessment of the processes of consumption and excretion of compounds of biogenic elements by different groups of aquatic organisms has been performed, and the important role of heterotrophic bacterioplankton and protozoa in the processes of transformation of compounds of nutrients in the VL ecosystem has been shown. The model can be used to perform scenario modeling and analysis of possible changes in the VL ecosystem under changing climatic and anthropogenic conditions.

Advancements and Challenges in Nanoscale Zero-Valent Iron-Activated Persulfate Technology for the Removal of Endocrine-Disrupting Chemicals

Endocrine-disrupting chemicals are a new class of pollutants that can affect hormonal metabolic processes in animals and humans. They can enter the aquatic environment through various pathways and gradually become enriched, thus posing a serious threat to the endocrine and physiological systems of both animals and humans. Nano zero-valent iron has promising applications in endocrine disruptor removal due to its excellent reducing properties and high specific surface area. However, given the dispersed focus and fragmented results of current studies, a comprehensive review is still lacking. In this paper, it was analyzed that the types of endocrine disruptors and their emission pathways reveal the sources of these compounds. Then, the main technologies currently used for endocrine disruptor treatment are introduced, covering physical, chemical, and biological treatment methods, with a special focus on persulfate oxidation among advanced oxidation technologies. Also, the paper summarizes the various activation methods of persulfate oxidation technology and proposes the nZVI-activated persulfate technology as the most promising means of treatment. In addition, this paper reviews the research progress of different modification methods of nZVI in activating persulfate for the removal of EDCs. Finally, the discussion includes recycling studies of nZVI/PS technology and emphasizes the urgency and importance of endocrine disruptor treatment. The review of this paper provides further scientific basis and technical support for nZVI/PS technology in the field of endocrine disruptor management.

Composition of the Low Molecular Weight Metabolome of Potamogeton perfoliatus (Potamogetonaceae) as an Indicator of the Transformation of the Ecological State of the Littoral Zone

The composition and nature of changes in the low-molecular-weight metabolome (NM) of Potamogeton perfoliatus L., growing in 6 biotopes of Lake Ladoga with different types of the anthropogenic load has been analyzed. According to the research results, it was found that the total number of low molecular weight organic compounds (LMWOCs) in the P. perfoliatus NM composition is directly dependent on anthropogenic load, which is well marked by the development of cyanobacteria. The greater the intensity of pollution or eutrophication of waters, or the higher the number of cyanobacteria, the lower the total number of LMWOCs and their concentration. A strongly pronounced dependence of the total concentrations of groups of NM compounds on the anthropogenic disturbance of the biotope and the concentration of cyanobacteria was revealed. A decrease in the number, relative amount, total concentration of carboxylic acids, number and content of unsaturated fatty acids, and, at the same time, an increase in the composition and content of phenols and the total content of aldehydes and ketones depends on an increase in anthropogenic pressure. The specific composition of NM of pierced pondweed depends on its response to biotic and abiotic factors of the aquatic environment, including anthropogenic ones. The revealed features of the change in the composition of P. perfoliatus NM make it possible to use it as an integral indicator of the anthropogenic impact on the littoral biotopes of water bodies and the deterioration of their ecological state.

The Complex of Steroid Hormones in Invertebrate Hydrobionts

The presence of a complex of biologically active steroid compounds (BASC) – hydrocortisone, corticosterone, progesterone, testosterone and estrogens (vertebrate hormones) in invertebrate hydrobionts of different phylogenetic levels was revealed in the experiments. The features of the quantitative content of BASC in different organs/tissues of hydrobionts and their changes at different stages of development are shown. The level of BASC in organisms or their organs is largely due to their own steroidogenesis, but at the same time, organisms can accumulate exogenous steroid compounds. The adaptive role of ALS in some invertebrates in changing conditions of the aquatic environment has been found. The similarity of the concentration of steroid compounds in different groups of bionts leads to the idea of a certain “physiological constant” of this complex of compounds in all organisms.

Progressing a river health assessment framework to tropical waters

Diverse anthropogenic activities have threatened the valuable tropical biodiversity and freshwater reserves. Despite that, there is little concern in the Brazilian legislation about the ecological integrity of aquatic ecosystems. We proposed a framework based on two joint indices, allowing the creation of a management tool. The first is the Tropical Water Healthy Index (TWHI), a river index that integrates pressures on aquatic ecosystems, their conditions, and societal/governmental response. The second is the Suitability of the Class of Use (SCU), which measures whether rivers’ conditions are in accordance with their classes of use proposed for the legal Brazilian water framework. Our results showed that most sites had good river health conditions, with the worst conditions occurring in areas with high urban occupations followed by agricultural areas. The second index indicated that few streams were poorly or incompatible with their classes of use, suggesting their classifications were based on current conditions but not future intentions. The force of these joint analyses was shown in the Melchior River stretch, which was classified as compatible with SCU, but the TWHI was critical. This is good to show that we simultaneously have a problem with the legislation and to indicate something that needs to be done quickly for managers. Therefore, we built a management model that can assess the real situation of aquatic ecosystems and define efficient management strategies, producing alerts for the decision-maker.

Impact of Improper Waste Disposal on Surface and Ground Water

Pollution in water occurs when harmful substance (often chemicals or biological) contaminate streams, river, lakes, oceans or other bodies of water, degrading water quality and rendering it unhealthy to humans, animal and the environment. The widespread problem of water pollution is jeopardizing our health. Water pathogens, in form of disease-causing bacteria and viruses from human and animal waste, are a major reason of illness from contaminated drinking water. Owing to the improper treatment facilities, waste is often discharged into the surface and ground water sources. Water bacteria can be limited by recycling used plastic, standard disposal of chemicals, oils or non-biodegradable items and proper collection and transportation of solid waste to a processed disposal site. In addition, waste water should be treated properly to prevent adverse health risk of the user of both surface water and ground water in the aquatic ecosystems.

Screening of municipal effluents with the peroxidase toxicity assay

AbstractThe peroxidase (Per) reaction is a quick and inexpensive biosensor for the screening of environmental contaminants and wastewaters. The purpose of this study was to screen various municipal wastewaters before and after 7 different types of treatment processes using this sensor to identify potential sites under stress by urban pollution. The following wastewater samples before (influent) and after the commonly applied treatments (effluent) were tested using the Per activity test: advanced biofiltration, biofiltration, aerated lagoons, secondary aeration sludge, trickling filter, secondary membrane filtration, and primary. The influents and effluents were collected for 3 days and concentrated to 500 X on a reverse-phase (C18) extraction cartridge. The ethanol extracts were examined for dissolved organic carbon, plastic-like materials, polyaromatic hydrocarbons and polystyrene nanoplastics. The samples were then tested using the Per reaction alone and in the presence of DNA to detect DNA binding agents. The results show that population size tended to increase Per activity and 60% of the effluents decreased Per activity leading to H2O2 persistence and toxicity. More advanced treatments (biofiltration, membrane biofiltration, secondary aeration) produced stronger changes from the corresponding untreated influents corroborating their performance in reducing toxicity. The addition of DNA during the Per reaction revealed that population size had no influence and that 60% of treated effluents restored Per activity suggesting release of genotoxic compounds in the aquatic environment from treated wastewaters. The toxic implications of the continuous release of wastewaters in aquatic ecosystems are discussed in the light of emerging contaminants such as nanoplastics.

A systematic workflow of data mining confirms widespread ecological risks of SDHIs fungicides contamination in aquatic environment.

Succinate dehydrogenase inhibitors (SDHIs) are widely utilized fungicides that have been detected in various environments, raising significant concerns regarding their toxicity to aquatic organisms. A comprehensive analysis of SDHIs contamination and associated ecological risks has been challenging due to scattered data and varying scale. This study consolidated residue data from 194 aquatic environments across six regions, up to June 2024, providing an overview of SDHIs distribution and conducting a global-scale aquatic ecological risk assessment. We analyzed 20 SDHIs, with boscalid, fluopyram, flutolanil, fluxapyroxad, mepronil, and thifluzamide being the most frequently detected across Asia, Europe, North America, South America, Africa, and Australia. The concentrations and types of SDHIs varied significantly among continents, with data sourced from water, sediment and aquatic organisms. Utilizing a web-based Interspecies Correlation Estimation-Species Sensitivity Distribution (ICE-SSD) model, we identified substantial sensitivity differences among species, with benzovindiflupyr showing the lowest LC50 of 3.5 μg/L, indicating a high risk when concentrations exceed 0.035 μg/L (Maximum Acceptable Concentration, MAC). Risk quotient (RQ) values revealed that flutolanil posed high risks to eight aquatic ecosystems and medium risks to five, while boscalid presented medium risk to one ecosystem. Our findings also demonstrated a significant correlation between the aquatic ecotoxicity of SDHIs and their characteristics (log Kow, solubility, and pKa). Collectively, we advocate for the restricted use of SDHIs and emphasize the necessity for further evaluation of their environmental behavior and integrated risks within the "One Health" framework.

Synthesis of a hydrological, water chemistry, and contaminants research program in the Peace-Athabasca Delta (Canada) to inform long-term monitoring of shallow lakes

In a multistressor world, evidence-based stewardship of aquatic ecosystems requires long-term monitoring data to understand the timing and magnitude of environmental change and potential causes. At the Peace-Athabasca Delta (PAD; northeastern Alberta, Canada), concern for aquatic ecosystem degradation has triggered renewed and urgent calls by Indigenous, national, and international governance bodies for implementation of a long-term lake monitoring program capable of tracking changes in hydrological conditions and contaminant deposition attributable to major energy projects located upstream, climate change, and other unnatural and natural processes. Challenges imposed by the delta's size, hydrological complexity, inaccessibility of lakes, and other factors, however, have long impeded implementation of a delta-wide lake monitoring program. To address this pressing need, here we review and synthesize results obtained during 7 years (2015–2021) of intensive, multifaceted research at 60 shallow lakes spanning the delta's broad hydroecological gradients to inform an integrated hydrology, water chemistry, and contaminants monitoring program. The research involved systematic, repeated measurements of water isotope composition, water depth variation, water chemistry and turbidity, and metal(loid) concentrations in lake surface sediment and periphytic biofilm. Results reveal marked spatial and temporal variation of hydrological processes and their affects on lake water balance and depth, strong association between hydrological processes and lake water chemistry, and that concentrations of nickel and vanadium (key oil sands indicators) remain within the range of natural variation. Correspondence of generalized additive model trendlines for isotope-derived lake evaporation-to-inflow ratios and water chemistry with climate indices (Pacific Decadal Oscillation, Oceanic Niño Index) demonstrates the sensitivity, and predictability, of lake ecosystem processes in the delta to large-scale climatic patterns. We provide recommendations for field sampling, sample analysis, data display, and integration of information for ongoing monitoring at the PAD. These approaches are readily transferable to other complex landscapes with abundant shallow waterbodies threatened by multiple stressors that may alter hydrological regimes and contaminant delivery.

Biodegradation of Polyethylene Using Bacillus tropicus Isolated from Sewage Wastewater Treatment Plant

One of the most pressing environmental problems contemporary civilizations confront is the ever-increasing amount of plastic waste. Because of their impact on every living thing, these wastes are seen as a major issue on a global scale. To counteract the harmful environmental effects caused by conventional disposal methods, it is critical to show that eco-friendly alternatives are viable. Biodegradation is one of the best eco-friendly methods for removing plastic waste. In this study, we aimed to identify bacteria from sewage wastewater treatment plants (SWWs) that could degrade low-density polyethylene (LDPE). Bacterial strains isolated from sewerage wastewater were incubated for 120 days in 50 mL of minimal salt media (MSM) containing 60 mg of low-density polyethylene (LDPE). After four months, our research revealed that Bacillus tropicus (SH4) demonstrated significant potential, degrading the LDPE up to 21.6%. We observed the changes after biodegradation using FTIR, GC-MS, and SEM analysis. In conclusion, microorganisms extracted from sewage wastewater possess the ability to mitigate plastic contamination in aquatic ecosystems. Future proteomics and genome investigations are necessary to elucidate the enzymes and metabolic processes implicated in plastic breakdown.

Metal heteroatoms significantly enhance efficacy of TiO2 nanomaterials in promoting hydrolysis of organophosphates: Implications for mitigating pollution of plastic additives.

Organophosphate esters (OPEs) are prevalent pollutants in the aquatic environment. OPEs are released from many sources, particularly, from the breakdown and weathering of plastic wastes, as OPEs are commonly used plastic additives. Metal oxide mineral nanoparticles play critical roles in the hydrolytic transformation of OPEs. While natural minerals often contain metal impurities, it is unclear how metal heteroatoms affect the efficiency of mineral nanoparticles in mediating hydrolysis reactions. Herein, we show that transition metal-doped anatase titanium dioxide (TiO2) nanomaterials are more effective in catalyzing the hydrolysis of 4-nitrophenyl phosphate (pNPP), a model OPE compound, with the relative effects of the heteroatoms following the order of Fe > Cr > Mn ≈ Ni > Co > Cu. With multiple lines of evidence based on spectroscopic analysis, kinetics modeling, and theoretical calculations, we show that metal doping increases the Lewis acidity of the TiO2 nanomaterials by increasing the oxidation state of surface Ti atoms, inducing oxygen vacancies, and creating additional Lewis acid sites with stronger acidities. Moreover, the increased amounts of surface hydroxyl groups due to metal-doping enhance inner-sphere complexation of pNPP through ligand exchange. The interesting observation that Fe-doped TiO2 exhibited the highest catalytic efficiency may have important implications for reducing the risks of organophosphate plastic additives, as iron is the most common heteroatom of naturally occurring TiO2 (nano)materials.

Information and Analytical System Monitoring and Assessment of the Water Bodies State in the Mineral Resources Complex

Currently, one of the most pressing global issues is ensuring that human activities have access to water resources that meet essential quality standards. This challenge is addressed by implementing a series of organizational and technical measures aimed at preserving the ecology of water basins and reducing the level of harmful industrial emissions and other pollutants in the aquatic environment. To guarantee the necessary quality of water resources, monitoring is conducted based on selected parameters using various methods and means of technical quality control. From these results, suitable measures are formulated and applied to maintain water quality. Various scientific works extensively discuss different approaches to water quality management and compliance with specified requirements. Modern strategies for developing water monitoring systems leverage the capabilities of information systems that collect, process, store, and transmit information, enabling the resolution of issues in geographically distributed water bodies in real time. This paper proposes an approach that employs mathematical methods to identify the most significant factors determining water quality and to assess their interrelations using methods of a priori ranking, multivariate correlation regression analysis, and integral quantitative assessment. A hardware and software solution for the development of a unified integrated information and analytical system is proposed. This system enables continuous monitoring and assessment of water bodies based on a set of key parameters, addressing a range of critical tasks. This paper provides a detailed description of the software product, presents a demonstration using real-world data, and discusses the anticipated benefits of implementing such an information and analytical system.

Fabrication of CaCO3 Microcubes and Mechanistic Study for Efficient Removal of Pb from Aqueous Solution

Pb(II) contamination in aquatic environments has adverse effects on humans even at a low concentration, so the efficient removal of Pb at a low cost is vital for achieving an environmentally friendly, sustainable, and healthy society. A variety of CaCO3-based functional adsorbents have been synthesized to remove Pb, but the adsorption capacity is still unsatisfactory. Herein, calcite CaCO3 microcubes/parallelepipeds are synthesized via simple precipitation and a hydrothermal approach and found to outperform previously reported nano-adsorbents considerably. The CaCO3 achieves a high removal efficiency for Pb(II) (>99%) at a very low dosage (0.04–0.1 g/L) and an initial Pb(II) concentration of 100 mg/L. The CaCO3 presents an excellent adsorption capacity of 4018 mg/g for Pb(II) removal and depicts good stability over a wide range of pH 6–11. The maximum adsorption kinetics are fitted well by the pseudo-second-order kinetic model, whereas the Freundlich isotherm delineates the adsorption data at equilibrium well, indicating a multilayer adsorption process. The ex situ study confirms that the Pb(II) adsorption mechanism by CaCO3 can be attributed to the rapid metal-ion-exchange reaction between Pb(II) and Ca2+. Furthermore, a red shift in the Fourier Transform Infrared (FTIR) spectroscopy peak from 1386 cm−1 to 1374 cm−1 of CaCO3 after Pb removal indicates the adsorption of Pb onto the surface. This adsorbent provides an opportunity to treat wastewater and can be extended to remove other toxic heavy metals.

Potential hazards of octinoxate (ethylhexyl methoxycinnamate) exposure in the seagrass Posidonia oceanica (L.) Delile: Experimental evidence

Interest has risen in recent years to assess the fate and impacts of organic ultraviolet (UV) filters in aquatic environments, after being recognized as contaminants of emerging concern. Octinoxate, also known as ethylhexyl methoxycinnamate (EHMC), is among the widely used UV filters in sunscreen formulations. Its potential toxicological effects in aquatic biota have led to precautionary actions in some jurisdictions, such as restricting and even banning its presence in commercial sunscreens. However, research data is lacking for effective regulation of sunscreen ingredients in Mediterranean countries. Our study evaluated the response of the seagrass Posidonia oceanica to EHMC under a short-term experimental setup, recreating summer conditions in aquaria subjected to different environmentally relevant concentrations for the Mediterranean Sea (minimum: 30.57 ng L−1, intermediate: 710 ng L−1 and maximum: 1420 ng L−1) and a control (no addition). Negative responses were evidenced in the physiology of P. oceanica due to EHMC exposure, with decreased gross primary production rates, loss of leaf chlorophyll content and inhibition of the overall nitrogen fixation associated with the seagrass tissues. Elevated oxidative stress biomarkers in P. oceanica under EHMC addition (i.e., catalase activity, polyphenols concentrations and alkaline phosphatase activity in leaves) reflect the activation of antioxidant defenses to counteract oxidative damages possibly induced in cellular components by the presence of the contaminant. Our results may conservatively imply the high ecological risk imposed to P. oceanica by maximum concentrations of EHMC in Mediterranean coastal waters. Moreover, they contribute as experimental evidence of the potentially detrimental effects of sunscreen pollution in a keystone species, such as P. oceanica, which is the main structural component of a priority habitat for conservation in the Mediterranean Sea, currently affected by multiple stress factors leading to its recession in recent years.

Mitochondrial AOX1a and an H2O2 feed-forward signalling loop regulate flooding tolerance in rice.

Flooding is a widespread natural disaster that causes tremendous yield losses of global food production. Rice is the only cereal capable of growing in aquatic environments. Direct seeding by which seedlings grow underwater is an important cultivation method for reducing rice production cost. Hypoxic germination tolerance and root growth in waterlogged soil are key traits for rice adaptability to flooded environments. Alternative oxidase (AOX) is a non-ATP-producing terminal oxidase in the plant mitochondrial electron transport chain, but its role in hypoxia tolerance had been unclear. We have discovered that AOX1a is necessary and sufficient to promote germination/coleoptile elongation and root development in rice under flooding/hypoxia. Hypoxia enhances endogenous H2O2 accumulation, and H2O2 in turn activates an ensemble of regulatory genes including AOX1a to facilitate the conversion of deleterious reactive oxygen species to H2O2 in rice under hypoxia. We show that AOX1a and H2O2 act interdependently to coordinate three key downstream events, that is, glycolysis/fermentation for minimal ATP production, root aerenchyma development and lateral root emergence under hypoxia. Moreover, we reveal that ectopic AOX1a expression promotes vigorous root and plant growth, and increases grain yield under regular irrigation conditions. Our discoveries provide new insights into a unique sensor-second messenger pair in which AOX1a acts as the sensor perceiving low oxygen tension, while H2O2 accumulation serves as the second messenger triggering downstream root development in rice against hypoxia stress. This work also reveals AOX1a genetic manipulation and H2O2 pretreatment as potential targets for improving flooding tolerance in rice and other crops.