Search Results (8,841)

Lake Vrana on Cres Island (northern Adriatic Sea) is a rare hydrogeological system consisting of a large freshwater body located within a karst cryptodepression with its bottom below sea level and surface above it. This study investigates long-term hydroclimatological changes using daily records of lake water level (1978–2024), water temperature (1979–2024), precipitation, and air temperature (1981–2024). Linear regression, the Mann–Kendall trend test, Sen’s slope estimator, and day-to-day variability metrics were applied to quantify long-term trends and system responses. A multi-index approach was used to enable a robust assessment of drought dynamics in this unique karst system: the Standardized Precipitation Index (SPI), representing meteorological conditions based on precipitation; the Standardized Hydrological Index (SHI), reflecting hydrological response derived from lake levels; and the New Drought Index (NDI), integrating precipitation and temperature to account for evapotranspiration effects. Results indicate a statistically significant decline in lake water levels (−4.5 to −5.2 cm yr⁻¹), while precipitation shows no significant trend. In contrast, both air and water temperatures exhibit a significant increase (~0.5 °C per decade) and are strongly correlated (R² = 0.767). The lake demonstrates pronounced thermal inertia and delayed response to atmospheric forcing. Day-to-day analysis reveals increasing variability in water temperature and decreasing variability in air temperature, suggesting changes in system energy dynamics. Drought indices (SHI and NDI) show significant negative trends, whereas SPI does not, indicating that drought intensification is primarily driven by rising temperatures and enhanced evapotranspiration rather than precipitation deficits. These findings demonstrate that Lake Vrana acts as a sensitive integrator of climatic forcing. Full article

Winter wheat (Triticum aestivum L.) production in the Yellow River Delta is limited by saline–alkali soils and freshwater scarcity, while the responses of different straw-returning modes under contrasting irrigation regimes remain unclear. A field experiment was conducted with two irrigation regimes, normal irrigation (W1) and deficit irrigation (W2), and four straw-returning modes, direct straw return (RS), straw-derived cattle manure return (RM), straw biochar return (RB), and straw pellet return (RG). The experiment followed a split-plot randomized block design with three replicates. Soil properties, leaf physiology, photosynthetic performance, grain yield, and irrigation water use efficiency (IWUE) were evaluated. Compared with W2, W1 increased mean grain yield by 9.4%, whereas W2 increased mean IWUE by 36.7%. Among the straw-returning modes, RS showed the most consistent performance. Under W1, W1RS produced the highest grain yield (3509.72 kg ha⁻¹). The stable performance of RS was characterized by relatively favorable soil moisture status, lower MDA content, higher antioxidant enzyme activity, and better maintenance of Pn. Pearson correlation analysis showed that grain yield was positively correlated with Pn and CAT activity, whereas MDA was negatively correlated with Pn. These results suggest that RS may be a feasible straw-returning mode for winter wheat production in saline–alkali soil. Full article

Access to freshwater is one of the major global challenges, driven by population growth, industrial development, climate change, and increasing water stress, particularly in economically constrained regions. In this context, this study designs, builds, and experimentally and numerically evaluates an indirect solar concentration desalination system (ICST) composed of a humidification–dehumidification (HDH) subsystem thermally powered by a Linear Fresnel Concentrator (LFC) under the appropriate technology paradigm. The methodology integrates an experimental campaign conducted under real climatic conditions in Bucaramanga, Colombia, mathematical modeling based on mass and energy balances, and the implementation of a TRNSYS simulation model validated through qualitative and quantitative analyses using absolute and relative errors. Results showed close agreement between experimental and simulated data, with daily freshwater production deviations of 0.53 and 0.65 L/day in tests 04 and 05, respectively, while mean relative errors remained below 5% for the main thermal and productivity variables. Experimentally, an average freshwater production of 1.13 L/h was achieved, with a production gain ratio (GOR) of 0.32 and a recovery ratio (RR) of 0.021, while maintaining total dissolved solids below 500 mg/L. Economic assessment estimated a production cost of $0.065/L, demonstrating the technical and economic feasibility of the system for decentralized small-scale applications in regions with high solar irradiance throughout the year. Full article

Cyanobacterial toxins (cyanotoxins) threaten aquatic ecosystems and human health, yet the factors influencing their production and distribution in freshwater remain unclear. In north-central Tennessee, nutrient-rich runoff from agricultural and urban areas, combined with a karst landscape that supports drinking and recreational water use, heightens the need to understand cyanotoxin behavior. To examine cyanotoxin patterns, the U.S. Geological Survey and the Tennessee Department of Environment and Conservation monitored 18 sites, including two wells under the influence of surface water, every two weeks from September 2022 to November 2024. At least one cyanotoxin was detected at all sites, with the highest concentrations in deep reservoirs and lower levels in shallow systems. Most detections occurred during summer and fall, aligning with high temperatures and rapid-onset drought. Statistical analysis indicated that increased specific conductivity and pH raised the likelihood of detecting total microcystin, likely resulting from drought conditions and nutrient-laden runoff. Additionally, dissolved microcystin showed an inverse relationship with Cumberland River water levels, and principal component analysis showed that Secchi depth, chlorophyll a, pH, temperature, and conductivity explained most water quality variability. These results help increase understanding of cyanotoxin distribution and associated water quality conditions during detections to guide future freshwater cyanotoxin monitoring studies. Full article

The goal of this Special Issue was to collect the latest research results on the topics of (1) the physiological response of fish to various stressful situations and nutritional changes, (2) the replacement of fish meal and fish oil with sustainable, alternative protein and lipid sources in fish feeds, and (3) supplementing fish feeds with various additives in order to enhance the immune response and increase the stress and disease resistance of fish reared in intensive systems. These topics are very important for the development of a more effective and sustainable intensive aquaculture, as fish farming systems are becoming more intensive and industrialized, which results in a more stressful environment for farmed fish. Another important challenge is providing enough high-quality fish feed to fulfill the increasing demand of intensive aquaculture. There are 14 original research articles published in this Special Issue. The authors come from a wide array of countries, and they worked with a wide variety of freshwater and marine fish species, which are important for intensive aquaculture. These articles represent only a modest contribution to the overall literature of stress and nutritional physiology of farmed fish. However, each of these papers contain interesting new information regarding the solution of the two major problems of intensifying aquaculture: environmental stresses and nutrition management. Full article

Rhizosphere microorganisms play central roles in nutrient cycling and contaminant transformation in sediment-associated freshwater systems, yet their responses to newer pesticides remain insufficiently characterized. In this study, a 28-day Vallisneria natans–rhizosphere sediment microcosm was used to compare the effects of trifluenfuronate and fluopyram at nominal concentrations of 0.01, 0.1, and 1 mg L⁻¹. Bacterial community composition was assessed using 16S rRNA gene sequencing, and shotgun metagenomic data were used to evaluate relative functional annotation patterns. Plant physiological traits and rhizosphere sediment enzyme activities were measured as ecological context for interpreting microorganism-associated responses. Fluopyram, particularly at 1 mg L⁻¹, produced clearer ordination-level shifts in rhizosphere bacterial community composition than trifluenfuronate, although pairwise treatment separation was not statistically resolved after multiple-testing correction. Annotation-based metagenomic profiles also differed between the two pesticides: stronger exposure was associated with reduced relative signals for several xenobiotic-, transport-, and regulation-related annotations, while high-dose fluopyram showed a methane-metabolism-related annotation signal and high-dose trifluenfuronate showed relative enrichment of secondary-metabolism-related annotations. These microbial and annotation-profile responses coincided with stronger inhibition of V. natans growth and greater suppression of rhizosphere sediment enzyme activities under fluopyram exposure. Overall, fluopyram induced more consistent microorganism-associated response patterns than trifluenfuronate in the tested rooted macrophyte–sediment microcosm. The results highlight the sensitivity of rhizosphere microbial communities and metagenomic annotation profiles to pesticide exposure in sediment-associated freshwater systems. Full article

Nutrient enrichment poses a major threat to freshwater ecosystems, yet integrated assessments of its effects on multiple dimensions of biodiversity remain limited. In this study, we investigated the responses of taxonomic, functional, and phylogenetic diversity (alpha and beta) of macroinvertebrate communities along a nutrient gradient in the Taizi River, a boreal river in northern China. The results revealed that macroinvertebrate abundance was 4.51 ind./m², belonging to three phyla and 68 species. Total phosphorus (TP) was the primary environmental driver, reducing functional evenness and dispersion at the alpha level, thereby promoting functional homogenization. At the beta level, TP increased nestedness and decreased turnover, leading to the loss of endemic species and a community dominated by species with broad ecological tolerance. Structural equation modeling showed that TP exerted stronger effects on functional and phylogenetic diversity than on taxonomic diversity. These findings provide multidimensional insights into nutrient-driven biodiversity loss and suggest that TP should be prioritized in water quality management to prevent functional homogenization and maintain beta diversity turnover. Collectively, these findings inform targeted conservation strategies for nutrient-enriched river ecosystems. Full article

Water hyacinth (Eichhornia crassipes) is a widespread invasive plant in tropical and subtropical regions, creating serious ecological and hydrological problems. Beyond disrupting aquatic ecosystems, it increases unaccounted water loss and alters key physicochemical properties. This study evaluated the evapotranspiration of water hyacinth and its influence on water quality in Lake Tana, Ethiopia’s largest freshwater lake. Two artificial ponds (one control and one covered with water hyacinth), each measuring 1 m × 1 m × 0.94 m, were monitored over three months to quantify water loss. In parallel, water samples were collected from the lake at 0.5 m depth along 2 km intervals, comparing hyacinth infested and open-water sites. The results showed clear differences between conditions. Dissolved oxygen was significantly lower in hyacinth-covered areas (6.65 ± 0.44 mg/L) than in open water (7.93 ± 0.42 mg/L). Similarly, pH decreased under hyacinth cover (5.53 ± 0.53) compared to non-infested sites (6.53 ± 0.40). In contrast, water temperature increased in infested areas (23.70 ± 0.42 °C) relative to open water (22.08 ± 0.33 °C). Total dissolved solids were slightly but significantly lower in hyacinth-covered water. Evapotranspiration from water hyacinth was about 1.6 times higher than evaporation from open water, with an estimated monthly loss of 0.28 m³ per square meter. When scaled to lake conditions, this corresponds to approximately 0.78 to 7.01 million m³ of water loss per month, though actual values may vary due to environmental factors. Overall, water hyacinth substantially affects both water quantity and quality, highlighting its importance for lake management and sustainable water use. Full article

Biological invasions are among the main threats to freshwater biodiversity, yet ecological patterns associated with assemblage structure and high relative abundances of non-native fishes in spring ecosystems remain insufficiently documented. We evaluated seasonal variation in community composition, reproductive traits, and trophic interactions in La Zarcita springs, part of the Natural Protected Area Laguna de Zacapu, central Mexico. Bimonthly sampling was conducted, including stomach content analysis and reproductive trait assessment. A total of 14 fish taxa were recorded (seven native and seven non-native), with the assemblage numerically dominated by Oreochromis niloticus (30%), Pseudoxiphophorus bimaculatus (24%), and Xiphophorus hellerii (14%). Overall diet composition did not differ significantly between taxa classified as native and non-native (PERMANOVA, p > 0.05), consistent with overlap in resource use within the assemblage. Exploratory assemblage-level analyses detected differences in omnivory index values among taxa grouped according to species origin (LMM, p < 0.05). Reproductive analyses detected variation in fertility values (GLMM, p < 0.05), reproductive activity (Wilcoxon test, p < 0.05), gonadosomatic index values, and Fulton’s condition factor values (LMM, p < 0.01) among taxa within the assemblage. Physicochemical variables varied seasonally but were not significantly associated with trophic composition, condition factor values, or reproductive traits in the statistical analyses performed. Overall, the results document variation in reproductive characteristics and trophic patterns among taxa within this urbanized spring system and highlight the value of assemblage-level ecological studies for understanding fish community structure in small freshwater habitats. Full article

Extreme summer droughts increasingly threaten freshwater biodiversity in monsoonal regions, yet community responses within heterogeneous small water bodies (SWBs) remain poorly understood. This study evaluated how drying events influence macroinvertebrate taxonomic and functional composition across different SWB types and explored the mechanisms driving post-drought recovery. We sampled isolated ponds (IPs), stream-fed ponds (SFPs), pond-linked streams (PLSs), and non-pond-linked streams (NPLSs) in Eastern China during an extreme summer drought (2022) and a subsequent recovery year (2023). Ponds exhibited high resistance, maintaining stable taxonomic and functional richness. PLSs suffered substantial summer biodiversity declines but showed rapid post-drought recovery, possibly facilitated by spatial dispersal from nearby pond refuges. In contrast, NPLSs experienced severe, lasting biodiversity loss. Drought conditions drove overall community homogenization, with spatial dispersal playing a more important role in structuring assemblages than environmental filtering. Furthermore, functional trait analysis indicated that post-drought recovery was more closely associated with resilience-linked traits rather than resistance traits. These findings demonstrate that lateral connectivity within SWB networks buffers drought impacts by providing refugial support and enabling rapid recolonization. Preserving diverse, interconnected SWBs is a critical management strategy for maintaining metacommunity resilience under growing climatic volatility. Full article

This study comprehensively explores the environmental implications of two feeding strategies in pig farming, focusing on three scenarios: Brazilian tables (BT-2017), NRC (NRC-2012), and AGPIC (AGPIC-2021). The comparison involves conventional phase-feeding (CON) and the daily fit model (DFM). The five-phase system provided the same diet to all pigs within a group during each proposed phase. In contrast, the DFM adjusted the diet based on the nutritional requirements of pigs, anticipating subsequent diets through daily adjustments. We employed a cradle-to-gate approach, with the functional unit defined as one barrow with an initial body weight of 20.61 ± 0.85 kg, raised to 138.94 ± 0.90 kg over a 120-day growing-finishing period. Input data were sourced from observed commercial records from pig farms in Brazil, including over 1,000,000 data points from pigs raised under standard industry conditions. We evaluated the impact of the life cycle by considering factors such as acidification, climate change, ecotoxicity, eutrophication, land use, resource use, and water use. The OpenLCA software (version 1.11.0) and the Environmental Footprint 3.0 impact assessment method were used. Our results indicate that the DFM consistently outperforms the CON strategy in terms of reducing environmental impacts. Among the three scenarios, BT-2017 results in higher environmental impact reductions compared with NRC-2012 and AGPIC-2021. This is due to the higher concentration of corn and soybean meal in diets. Notable reductions include in relation to land use-related climate change impacts (12.55%), freshwater eutrophication (6.21%), mineral and metal resource depletion (6.11%), and fossil resource use (4.88%). These findings highlight that even modest adjustments to feeding strategies can effectively reduce the environmental footprint of pig farming. Full article

In Morocco, snow constitutes a crucial freshwater resource, particularly in the Atlas Mountains, where seasonal snowpack significantly contributes to surface water availability, groundwater recharge, and down-stream water supply. However, snow monitoring in these regions remains challenging due to the scarcity and uneven distribution of ground-based snow depth measurements, especially at high altitudes. This lack of observations limits the accurate assessment of snowpack dynamics and hampers hydrological modeling and water resource management. In this study, we assessed the performance of an empirical approach to estimate snow depth from satellite-derived fractional snow cover (FSC) obtained from MODIS observations. Five empirical FSC snow depth models, including linear and nonlinear exponential formulations, are developed and applied across multiple regions of the Moroccan Atlas Mountains. Model coefficients are calibrated independently for each region using three complementary optimization techniques, nonlinear least squares regression, genetic algorithms, and simulated annealing. Model skill was evaluated during calibration and validation using the Kling–Gupta Efficiency (KGE), Pearson correlation coefficient (R), and absolute error metrics (RMSE and MAE). Results show substantial performance differences across formulations and regions. The most flexible exponential model achieved highest efficiency (KGE up to 0.87; R > 0.85) and 0.26 cm (MAE) under moderate snow conditions. Linear formulations exhibited limited robustness, whereas exponential models better captured snow depth dynamics, particularly in high-altitude areas with deep and persistent snowpacks. These results highlight the potential of FSC-based empirical modeling as a practical and operational solution for snow depth estimation in data-scarce mountainous regions of Morocco. Full article

The increasing demand for safer and environmentally sustainable products has intensified the search for natural alternatives to synthetic dyes. Filamentous fungi are promising sources of natural pigments due to their metabolic diversity and the feasibility of large-scale production. In this study, filamentous fungi isolated from Amazonian freshwater environments were evaluated for their potential to produce natural pigment-associated metabolites under different nutritional conditions. Forty-five fungal isolates were screened in solid media and subsequently cultivated in submerged fermentation using three media: potato dextrose broth supplemented with yeast extract (BD + YE); malt extract broth (ME); and yeast extract–sucrose broth supplemented with magnesium sulfate (YES). Among the 39 pigment-producing isolates, seven were selected for further investigation. Sucrose favored the highest absorbance values of pigment extracts, particularly for isolates identified as Talaromyces amestolkiae. In addition, the extract of T. amestolkiae TA10P5-3 exhibited the highest absorbance value (6.83 abs. units at 400 nm) when cultivated in YES medium, indicating stronger chromophore-associated spectral signals. This extract also showed antimicrobial activity against Pseudomonas aeruginosa (625 μg/mL), Staphylococcus epidermidis (312 μg/mL), and Candida tropicalis (625 μg/mL). Finally, the TA10P5-3 extract presented high total phenolic content (246.30 mg GAE/g) and antioxidant activity (EC₅₀ = 5470 μg/mL). These findings highlight Amazonian freshwater fungi as promising sources of natural pigments with potential industrial applications. Full article

Caffeine (CAF) is a widely consumed psychostimulant known to modulate adenosine receptors and neurotransmitter systems, although its effects in invertebrates remain poorly understood. Environmentally relevant concentrations (5, 30, and 50 µg/L) are associated with altered behavior, including locomotion, exploration, and feeding, in the freshwater gastropod Physella acuta. This study examined molecular responses underlying these effects. Adult snails were exposed to CAF for 24 h and 7 days. Gene expression related to the nervous system and stress pathways was analyzed by RT-PCR, including A1AR, ADORA2B, AChE, GLRA2, DRD2, RYR, HSD11β, HSP70, SLC6A2, and SLC6A1. After 24 h, exposure to 50 µg/L CAF altered A1AR expression and caused downregulation of AChE, GLRA2, and DRD2, associated with observed behavioral changes. A1AR upregulation may indicate compensatory adjustment in adenosine signaling. After 7 days, A1AR remained upregulated, while genes linked to inhibitory neurotransmission showed partial recovery. Increased expression of genes involved in dopamine regulation and steroid metabolism suggested physiological adaptation. Overall, CAF induced dose- and time-dependent molecular responses in P. acuta, linking neurochemical disruption with behavioral changes and highlighting its ecological risk as an emerging freshwater contaminant. Full article

Galaxolide (HHCB), a synthetic polycyclic musk widely used as a fragrance ingredient in numerous personal care and household products, has raised increasing environmental concern due to its persistence, bioaccumulation potential, and widespread occurrence in aquatic environments. In this context, the need to establish a concrete ecotoxicological risk profile, defining both the toxicity levels and the mechanisms of action, is fundamental. For this reason, in the current study, we selected the freshwater leech Hirudo verbana as a suitable in vivo model to assess the HHCB ability in inducing inflammatory response and oxidative stress. By means of morphological, immunofluorescence, and molecular analyses, HHCB was shown not only to affect the leech innate immune response by modulating angiogenesis and macrophage-like cells recruitment, but also to promote the expression of enzymes involved in the antioxidant response, such as superoxide dismutase (SOD), glutathione S-transferase (GST) and catalase (CAT). Overall, these findings indicate that HHCB could induce significant physiological alterations, with sub-lethal concentrations able to affect immune homeostasis. Furthermore, this study supports the use of alternative invertebrate models to better understand the possible harmful effects of emerging contaminants. Full article