Journal of Freshwater Ecology

Despite tropical and subtropical aquatic systems suffering from increasing invasion of floating plants, the effects of floating plants invasion on aquatic greenhouse gas (GHG) emissions remain poorly understood. In this study, CO2 and CH4 fluxes were measured in water lettuce (Pistia stratiotes) and open water areas in Huixian wetland in Guangxi, Southwest China, from November 2020 to November 2021. Our results indicated that CO2/CH4 emissions showed obvious seasonal variations, CO2 fluxes for the water lettuce and open water zones showed a significant CO2 sink in winter, and CH4 fluxes for the water lettuce showed a maximum emission in September 2021. The annual cumulative CO2 fluxes for the water lettuce zone were 5,578.63 ± 957.99 g m−2 yr⁻¹, which were significantly higher than that from the open water area (2,551.77 ± 482.49 g m−2 yr⁻¹). Likewise, the annual cumulative CH4 emissions from the water lettuce area (693.39 ± 142.88 g m−2 yr⁻¹) were significantly higher than those from the open water zone (119.17 ± 4.45 g m−2 yr⁻¹). CO2 fluxes were significantly positively correlated with air and water temperature, and significantly negatively correlated with TN and DO. CH4 fluxes were significantly negatively correlated with HCO3⁻. This study indicated that the increased invasion of water lettuce may enhance GHG emissions from a subtropical lake, thus contributing to global warming. More attention should be paid to the invasion of floating plants into subtropical karst lakes because geological conditions and aquatic plants might significantly influence greenhouse gas emissions.

We examined the relationship between larval fish numbers and discharge during a high flow event in Bear Creek, Arkansas, a small Ozark stream. Additionally, we examined the relationship between fish numbers and time of day, and the spatial distribution of families and size classes. A total of 3,083 fish from five families were collected. Leuciscidae was the dominant family collected, followed by Percidae, and Catostomidae. Larval fish in Bear Creek were not susceptible to increased discharge from the flood event, as all three families exhibited strong significant negative relationships to discharge at night when discharge began to decline. Larval fish in Bear Creek drifted significantly more at night than during the day, with the exception of large percids, which exhibited no diel pattern. Leuciscidae and small Percidae showed a spatial pattern of distribution across the stream at night, with higher drift densities in near shore nets. The results from our study indicate that fish drift in Bear Creek was an active process, with most larval fish drifting in response to decreased light intensity. We suggest future studies consider the effects of flood intensity on larval fish drift relative to diel periodicity.

Many large lakes in northern Scandinavia have become oligotrophicated due to hydroelectric water regulation in the twentieth century, causing a loss of littoral habitat and negative consequences for ecosystem productivity, fish populations, and fisheries. Compensatory nutrient enrichment is a potential remediation method that has successfully been carried out in Canada and the US. Here we assessed the response of Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) to nutrient addition in a whole lake experiment in Stor-Mjölkvattnet, Sweden, with nearby Burvattnet as a reference. Nitrate and phosphate were added for eight consecutive years. The study also included sampling the seventh year after discontinuation of nutrient addition, which allowed us to investigate how long nutrient enrichment would be effective on fish growth. Populations of Arctic charr and brown trout responded quickly and vigorously to the treatment, with approximately a doubling of the catch per unit effort. Nutrient addition had a consistent positive effect on charr length, weight, and condition at a given age, with a median response to nutrient addition (as measured by Shapley values) of 32 mm, 45 g, and 0.087 g cm⁻³ × 100. The response in length and weight was strongest in the age classes 4+ and 5+. The corresponding responses of trout were 13 mm, 32 g, and 0.044 g cm⁻³ × 100, respectively. Seven years after the enrichment had ended, charr at ages ≤6+ years were back to their previous state before treatment, i.e. slow growing and in bad condition. The older age-classes of charr (≥7+), however, were in good condition, suggesting that those fish, as young had experienced the excellent conditions prevailing in the last years of nutrient enrichment and largely kept this advantage. We conclude that compensatory nutrient addition is a useful method for restoring charr populations and reversible.

Urban wetlands are often polluted by heavy and trace metals being discharged from industries, urbanisation and agriculture, which tend to alter the sediment quality. Sediments are important as they act as a sink for nutrients in aquatic environments. Wetlands play an important role in maintaining ecological balance, preventing floods and droughts, providing shelter for various animals and plants and supporting human well-being through essential services such as carbon sequestration and water purification. The present study aimed to assess the spatiotemporal distribution and sediment pollution indices of trace and heavy metals in surface sediments and identify potential sources of contamination in urbanised Austral wetlands. Sediment samples were collected within the Riverside’s Wetlands, City of Nelspruit, South Africa, across three seasons (i.e. hot–dry, hot–wet and cool–dry seasons). A multivariate principal component analysis was used to determine the metal relationship. The metal pollution indices, such as contamination factor, enrichment factor, geo-accumulation factor and pollution load index were used to determine the pollution of metals in the sediments across different sites among seasons. The study found that only the lower Na concentration was observed during the cool-dry season, which was lower compared to the concentrations of other metals. The pollution indices indicated that wetland sediments were highly contaminated, mainly with Mn, Co, Cu, Pb, Zn, Al and Fe, especially during the cool–dry season. The current study highlights an urgent need to come up with immediate measures to control severe heavy metal pollution from the industrial emission into the wetlands. Those immediate measures should be carried out to minimise the rate of contamination and extent of future metal contamination.

Water quality of Lake Tana has been deteriorating due to nutrient enrichment associated with various anthropogenic stressors including domestic and industrial effluents, and agricultural runoff. Changes in the ecological health of a lake are better understood by studying the community structure of phytoplankton as they react quickly to environmental changes. Human-induced stressors can lead to changes in the taxonomic composition and Reynolds functional groups (RFGs) of phytoplankton resulting in biodiversity impoverishment. RFGs are more effective in detecting stressor-induced alterations in phytoplankton compared to taxonomy-based assemblages as the former reflect common adaptive or functional traits. Information on RFGs of phytoplankton in the northern gulf of Lake Tana, Ethiopia, is however non-existent. Therefore, this study aimed to assess the spatio-temporal changes in phytoplankton community structure and identify the variables influencing the dynamics of RFGs in the lake. Samples were collected from five sampling sites between May 2023 and April 2024. A total of 113 phytoplankton species belonging to six taxonomic groups and 11 RFGs were identified. The predominant RFGs which collectively accounted for 97% of the total phytoplankton abundance were M, B, N, D, Lo, P and S2. Other RFGs, such as J and X1–X3, constituted 2.4% and 0.8% of the total abundance, respectively. Redundancy analysis indicated significant association of RFGs with electrical conductivity, pH, turbidity and some algal growth limiting nutrients. This suggests that both biotic and anthropogenic stressors have a substantial impact on RFGs. Therefore, continuous monitoring is essential to prevent future ecological imbalances in the lake.

Freshwater mussels (Order: Unionida) and fishes are two imperiled taxa that make up an important part of global freshwater biodiversity. Mussels exhibit a complex life cycle that can contribute to their imperilment. Most mussels parasitize a host fish during their larval stage to reach maturity, making host fishes and the mussels that they support coevolved taxa thus mussel diversity and distribution can correspond to that of fishes. The Host-Habitat Continuum Concept (HHCC) seeks to explain mussel distribution by combining life history theory, host fish distributions, and stream ecological gradients. The HHCC predicts increases in fish and mussel species richness, shifts in mussel life history strategy and fish family composition as habitat area, complexity, and stability increase with stream size. Here, we combined observational data on fish and mussel assemblages from seven mussel bed reaches with published mussel and host fish relationships and mussel life history traits to evaluate if HHCC explains mussel and fish distribution. We found weak support for HHCC as fish and mussel species richness, increased with watershed area, but only mussel densities were positively related to watershed. The relationship between fish densities and watershed area was seasonally dependent, showing no relationship in summer when stream discharge was greater and a negative relationship in autumn when stream discharge was lower. Centrarchids (sunfish) and leuciscids (minnows) were the most abundant fishes among sites, equilibrium life history strategies and luring host infestation strategies dominated mussels assemblages, but there was no longitudinal change in proportional abundances of fish families, mussel life history or infestation strategies as expected. There was a high degree of host partitioning among coexisting mussels, but we found no relationship between known host fish occurrences and mussel occurrences. The complex nature of freshwater systems and biological interactions between species likely influenced our ability to detect strong associations. Strong host fish partitioning among mussels at sites distributed along a stream size gradient indicates that management aimed at protecting interactions between fishes and mussels may be valuable for conserving these codependent taxa.

Zooplankton play pivotal roles in aquatic ecosystems, yet the mechanisms by which species interactions shape their community structure remain poorly understood, particularly in urbanized river networks. Here, we investigated the assembly processes of zooplankton communities across 44 sites in Shanghai’s megacity river network during winter. Using canonical correspondence analysis (CCA) and variance partitioning analysis (VPA), we identified water temperature (WT), Secchi depth (SD), and pH as significant environmental drivers, albeit with limited explanatory power (11.10%). Neutral community model (NCM) analysis revealed that deterministic niche processes dominated community assembly, emphasizing the critical role of biotic interactions. Co-occurrence network analysis further identified 29 keystone species, predominantly generalist rotifers (58.62%), which exhibited broad niche breadth and strong competitive traits (e.g. pollution resistance and omnivory). High modularity (0.55) and interspecific competition (18.67% niche overlap > 0.5) indicated structural instability within the community. These findings highlight the interplay of environmental filtering and species interactions in shaping urban zooplankton communities, offering insights for biodiversity conservation and ecological monitoring in anthropogenically impacted aquatic systems.

Bosten Lake is a typical inland lake in the arid and semiarid region of northwestern China. However, the influence of the dissolved organic matter (DOM) source composition on the bacterial community structure and diversity across various functional zones, as well as the role of the bacterial community structure in regulating DOM composition, remains unclear. In this study, we combined excitation-emission matrix (EEM) fluorescence spectroscopy with the parallel factor analysis (PARAFAC) method to investigate the characteristics and source distribution of the DOM fluorescence components in the water of Bosten Lake. The bacterial community characteristics in both water and sediment samples were analysed through high-throughput sequencing. The relationships among bacterial communities, DOM fluorescence components, and environmental factors were elucidated through principal component analysis and redundancy analysis. The results revealed that (1) the DOM of Bosten Lake contained three humus-like fractions and one protein-like fraction, with endogenous proteins being the primary source of DOM, complemented by exogenous humus inputs. (2) The richness and diversity of bacterial communities in sediments are significantly higher than those in water bodies, among which Proteobacteria dominate the composition of bacterial communities. (3) Ammonia nitrogen (NH4⁺–N) significantly influenced the bacterial community composition, with microorganisms associated with the nitrogen cycle dominating the bacterial community in both water and sediment. Total dissolved solids (TDS) is a key factor influencing the composition of bacterial communities in water bodies. Across all sampling sites in Bosten Lake, the mean TDS concentration was 900 mg/L, with high levels causing structural damage to microbial enzymes (4) The DOM fluorescence component explained 64.9% of the variation in the bacterial community composition, indicating a strong response relationship between bacterial communities and DOM components. Overall, these results provide a scientific basis for the protection of the ecological environment of Bosten Lake.

This study collected 24 samples from 6 sampling points in Inner Mongolia in different seasons in 2023 to study and analyze the spatiotemporal variation of nitrous oxide (N2O) flux at the water air interface and its influencing factors. The research results show that the average N2O emission flux is 6.63 ± 11.86 mg·m⁻²·d⁻¹, which is the overall source of N2O emissions. The main influencing factors are total phosphorus (TP) and water temperature (Tw). From a seasonal perspective, summer (July) is mainly affected by potential and temperature, autumn (September) is mainly affected by total suspended solids (TSS), and winter (November) is mainly affected by TP, which are the ‘sources’ of N2O emissions; Spring (April) is the ‘sink’ of N2O emissions. From a spatial distribution perspective, the N2O flux in Lao Niu Bay (LNW) is the highest, influenced by dissolved organic carbon (DOC); Next is Linhe (LH), which is affected by total nitrogen (TN); Next are Wuhai (WH) and Urad Front Banner (QQ); Tuo County (TX) has the lowest; Baotou (BT) takes second place and is affected by ammonia nitrogen (NH4⁺- N). The N2O flux of WH, QQ, and TX is not significantly correlated with environmental factors.

Surface sediment analysis offers a cost-effective way to document the spread of exotic micro-organisms, potentially presaging the spread of other exotic and invasive species. An analysis of surface sediment samples from 11 inland lakes in Ohio revealed the presence of an exotic diatom species, Discostella asterocostata, in seven lakes. While the presence of D. asterocostata has been documented in the waterways of surrounding states, this is the first documentation of the species in the lakes of Ohio. Previous research suggests the exotic diatom may have crossed the Pacific in the digestive tracts of the invasive bighead (Hypophthalmichthys nobilis) and silver carp (Hypophthalmichthys molitrix), planktivorous fish that were originally imported from Asia to North America for aquaculture. However, these carp species have not been reported in the Ohio lakes in which the exotic diatom was found, making it likely that D. asterocostata has spread throughout the state’s inland waterways via a different vector, potentially stocked fish. All seven lakes containing D. asterocostata are in the Ohio River Watershed, while the remaining four without D. asterocostata are in the Lake Erie Watershed. Ordination of the diatom assemblage data from each lake revealed that the diatom communities form two distinct groups, separated by watershed, which were significantly different from each other. Exotic and invasive diatoms can outcompete native diatoms and can potentially affect the environmental availability of nutrients and silica in a lake, leading to the restructuring of algal communities; however, it is currently unclear whether the presence of D. asterocostata is causing a restructuring of the assemblages in this case. Future work should focus on retrieval and analysis of sediment cores to shed light on the timing and ecological consequences of D. asterocostata’s introduction into Ohio’s inland lakes.

Freshwater ecosystems are vulnerable to various land use impacts, resulting in concern for aquatic biota and humans. Understanding the occurrence of pesticide contamination is necessary to safeguard aquatic biodiversity and human health. We hypothesize that sub-catchments with a higher proportion of agricultural activities have a higher concentration of pesticides in the water sample. Our study assessed the nexus between land uses and pesticide contamination in three zones of the Chanchaga River, namely, a control site, an agricultural area (S1), and an urban area (S2). Various classes of land use around the catchment were determined using ArcGIS 10.8 GIS software. At the same time, analysis of pesticide residues was carried out using the liquid–liquid extraction method, followed by gas chromatography–mass spectrometry. A total of 10 herbicides and 12 insecticides were recorded in each sampled sub-catchments, with a statistically significant difference across the sampled sub-catchments. Sampled sites in agricultural and urban areas had higher concentrations of pesticide residues than the control zone, with less anthropogenic influence. Redundancy analysis revealed farming and urbanized land use were the main sources of pesticide contamination in the waterbody. Pesticides may have chronic or acute impacts on aquatic biodiversity and a higher trophic effect on human health. It was evident that all sampled sub-catchments had pesticide concentrations exceeding the WHO permissible limit for human consumption. Prioritizing alternative methods to pesticides for managing pests and weeds is crucial for sustainable agriculture and environmental sustainability.

Wetlands play a crucial role in maintaining hydrological balance, conserving biodiversity, and storing carbon. However, they are increasingly threatened by climate change, agricultural expansion, urbanization, and excessive water use. Lake Karataş, a critical wetland in Türkiye that supports diverse avian and aquatic species, has experienced significant hydrological changes in recent decades. This study examines the spatiotemporal changes in the lake’s surface area and its interaction with land use between 1985 and 2024 using remote sensing techniques. Landsat 5 TM and Landsat 8 OLI/TIRS summer imagery were analyzed to assess water surface changes using the MNDWI, NDVI, and NDMI indices. The results indicate that Lake Karataş, which covered 11.45 km² in 1985, had completely dried up by 2024, leading to biodiversity loss and the disappearance of aquatic habitats. According to CORINE land use data, between 1990 and 2018, permanently irrigated areas expanded by 21.78%, while dry farming areas decreased by 14.39%. These land use changes coincide with a significant decline in lake water levels, confirming that agricultural expansion has been a major driver of ecosystem degradation. Temporal analysis shows that between 1985 and 2005, lake surface fluctuations were primarily influenced by climatic factors, as indicated by proportional trends in the NDMI, MNDWI, and NDVI indices. However, after 2005, anthropogenic activities, particularly the expansion of irrigated agriculture, became the dominant cause of lake desiccation. To protect the Lake Karataş ecosystem and ensure sustainable water management, it is essential to regulate irrigated agriculture and prioritize regionally adapted crop production models. Key strategies include promoting drought-resistant crops, implementing high-efficiency irrigation systems, and adopting sustainable water management policies. This study highlights the effectiveness of remote sensing in monitoring long-term wetland transformations and identifying their primary drivers.

When large river ecosystems exhibit shifting habitat mosaics and fish community composition, understanding spatial-temporal dietary patterns may inform season-specific dietary overlap between species. Backwater areas of the Mississippi River exhibited an ecological shift to a macrophyte-dominated clear water state with an associated increase in yellow perch (Perca flavescens) abundance from 2005 to 2010. This exploratory study assessed diet patterns and overlap between the more newly abundant yellow perch and previously established bluegill (Lepomis macrochirus). We examined the gut content of both species in three backwater contiguous lakes of Mississippi River Lower Pool 4. We removed stomach content of bluegill (n = 61) and yellow perch (n = 189) from May 2018 through January 2019 and categorized stomach content remains to the lowest identifiable taxonomic level. Bluegill and yellow perch exhibited overlapping generalized feeding strategies during spring, summer, and fall and non-overlapping specialized feeding strategies during winter. Yellow perch diets in the winter were significantly different from all other seasons (all pairwise ANOSIM p < 0.05, R statistic > 0.36). In winter, 99.7% of prey fish volume in yellow perch occurred in large-size-class fish. During the winter, age-0 bluegill made up 97% (by volume) of the prey fish found in large-size-class yellow perch. Yellow perch and bluegill diets overlapped the least in winter (ANOSIM p < 0.05; Schoener’s Index = 0.10) and the most in spring and fall (ANOSIM p > 0.05; Schoener’s index = 0.41 and 0.50), respectively. Overall, dietary overlap between yellow perch and bluegill varies seasonally. Due to the limited sample size of this study, follow-up research is needed to further assess seasonal and size-dependent patterns and to assess if competition and or predation from the newly abundant yellow perch population is affecting bluegill abundance, recruitment and growth.

Shifting precipitation patterns associated with global climate change are significantly impacting lotic ecosystems worldwide. To understand how these changes influence stream fish community assembly, we conducted a space-for-time study under a steep natural rainfall gradient in the coastal plain region of Texas (USA). Leveraging multi-year intra-annual fish surveys and environmental data from nine streams, we assessed the effects of precipitation regime on functional diversity and trait distributions, focusing on the relative importance of environmental filtering, interspecific interaction, and individual environmental drivers. Fish communities transitioned from functionally underdispersed to overdispersed with increasing precipitation rate, suggesting that filtering was a key assembly mechanism in more arid communities, while species interaction played a more important role under wetter climates. Deviations in functional dispersion across the rainfall gradient were best explained by changes in relative distributions of traits (functional evenness) as opposed to losses or additions of traits (functional richness) between sites, and the best predictors of these deviations were mean annual rainfall, low-flow frequency, and prevalence of hypoxic conditions. Proportional abundances of hypoxia-tolerant, herbivorous taxa within communities were associated mainly with the same predictors, illustrating the importance of these fishes’ increasing prevalence with increased aridity. Relationships between their abundances and benthic primary producer densities may also point to changes in grazing pressure, possibly stemming from top-down trophic processes. The shift from communities with low functional diversity dominated by hypoxia-tolerant, herbivorous taxa to more diverse assemblages as rainfall rates increased was non-linear, which may represent an important precipitation-driven threshold in community assembly. Our observations across this spatial rainfall gradient may translate to similar community-level changes in lotic ecosystems experiencing temporally shifting precipitation patterns, ultimately leading to increased understanding of relationships between functional trait distributions and climate, as well as providing valuable knowledge for predicting the impacts of changing precipitation regimes in freshwater ecosystems worldwide.

Human activities have degraded riverbed substrate structure via reduced heterogeneity of substrate particle sizes and increased fine sediment loadings. Despite increasing recognition of the importance of substrate quality in river ecosystems, our ability to assess substrate condition effects on biodiversity and functioning of river ecosystems is at present inadequate resulting in discrepancies between the needs of conservation, restoration, and mitigation of running waters, and water management practice. Several macroinvertebrate-based metrics are currently used to assess the impacts of degraded riverbed substrate structure. However, few metrics confer a direct relationship to the functions that substrates provide independent of interacting and potentially confounding factors (e.g. current velocity, excess nutrients and pesticides) or, based solely on presence-absence of taxa so that they may be implemented regardless of the identification method. Data on riverbed substrates and benthic macroinvertebrates was extracted from several databases. Using stream data on riverbed substrates and macroinvertebrates, we developed a macroinvertebrate-based multimetric index (MMI) for riverbed substrate condition (LISSA) to assess impacts of and recovery from substrate degradation using information on measures of traits. The dataset was explored for correlation between measures of traits to riverbed substrate condition. A substrate quality gradient (SQG) was constructed by combining four components of substrate quality in an index where decreasing substrate quality is defined as an increasing percentage of fine sediment and sand and decreasing substrate diversity and evenness. Significantly correlated candidate metrics were chosen using forward stepwise linear regression models against SQG. Five metrics were included in LISSA: one trait state of aquatic stages (egg), two trait states of reproduction (isolated eggs, cemented + clutches, cemented or fixed and clutches, free + asexual reproduction), one trait state of locomotion and substrate relation (crawler + temporarily attached) and the locomotion trait state (% burrowing/boring). LISSA is a promising metric for stream macroinvertebrate assessments of riverbed substrate condition and monitoring impacts and recovery across Sweden and potentially elsewhere.

Medium- and long-term runoff time series are characterized by strong nonlinearity and non-stationarity, which makes it difficult to predict accurately in the model. Taking the runoff data from three hydrological stations in the lower reaches of the Yellow River as an example, an improved complementary ensemble empirical mode decomposition (ICEEMD) is proposed. The runoff prediction model is established by combining the success-history adaptive differential evolution algorithm for linear population size reduction (L-SHADE) and simple recurrent unit (SRU). ICEEMD reconstructs the components of CEEMD with similar frequency and amplitude to obtain the frequency terms, which is used as the training data for the SRU. L-SHADE is employed to complete the parameter optimization of the SRU. The results showed that ICEEMD-L-SHADE-SRU achieved the best performance in runoff prediction, showing distinct improvements when compared to tested models in terms of both NSE (0.91–0.93) and QR (72%–74%). Considering the influence of extreme weather, the atmospheric circulation factors that have a greater impact on runoff are screened out and fused into the frequency term for prediction, and the model performs well. The innovation of this study lies in the distinct functionality of each component: ICEEMD effectively decomposes complex runoff data, L-SHADE optimizes model parameters, and SRU provides accurate predictions, collectively enhancing the reliability of runoff prediction. It can be used for medium- and long-term monthly runoff prediction.

Non-native Yellow Bass Morone mississippiensis have recently expanded their range in Iowa’s glacial natural lakes since their initial introductions in Clear Lake, Iowa circa 1930. Little is known regarding Yellow Bass population dynamics inhabiting natural lakes of varying complexity, thus limiting management options for the species. This study aimed to assess and compare age and size structure, condition, growth, and mortality of Yellow Bass collected from ten natural lakes in Iowa between 2017 and 2022. We also evaluated the effect of Yellow Bass relative abundance and lake size on Yellow Bass size structure, growth, and condition. Our results indicate substantial variation in Yellow Bass population parameters among and within natural lakes of different sizes and infestation periods; however, some general trends were observed. Lakes that were recently infested typically had higher Yellow Bass growth, size structure, and mortality than those with established populations. Likewise, lowest mortality rates were observed in lakes with the poorest growth, poorest condition, and poorest size structure, yet densities in these lakes differed considerably. Natural lakes ≥394 ha had better growth, condition, and size distribution than smaller lakes, regardless of the year they were infested. This study provides insight into the population dynamics of non-native Yellow Bass in natural lakes and identified several population responses they may display post-infestation. Our findings reiterate the importance for fisheries managers to perform routine fisheries surveys in lakes to document the expansion and monitor the population dynamics of Yellow Bass.

With the growing understanding of the importance of microplastic (MP) pollution, which has significantly impacted several aquatic ecosystems of the world. The diverse range of aquatic ecosystems, including seas, oceans, freshwater bodies and wetlands, coupled with the rich variety of species inhabiting them, continually provides new insights into the daily impacts of MP pollution. In this study, it was planned to determine the presence and identification of MP in the tissues (muscle, gastro-intestinal tissue [GIT]) and gill) of crayfish (Astacus leptodactylus), which is an important economic species in the world and in Türkiye and known as the ‘ecosystem engineer’. For this purpose, 20 specimens of A. leptodactylus were sampled from Keban Dam Lake (Elazığ, Türkiye), then MP digestion was performed on the determined tissues and µ-Raman spectroscopy was used to determine the polymer type in the particles obtained. In the findings obtained, MP was not found in muscle tissue, while 1.95 particles/individual, and 1.30 particles/individual MP were detected in GIT and gill tissues, respectively. The dominant MP color in the GIT (51.3%) and gill (57.7%) tissues of crayfish is black. The dominant MP shapes in crayfish tissues were determined to be fiber at the highest rate (GIT: 64.1%, gill: 57.7%). When the sizes of MPs were evaluated, it was seen that they were more distributed in the range of 100–500 µm. The most common polymer type was polyethylene (30%), while the least common polymer type was polydienes (5%). The findings of this study, the first of its kind in the field, showed that MP accumulation in crayfish was lower compared to studies conducted in fish in the same region.

Lake Tana, which contains nearly 50% of Ethiopia’s freshwater, is experiencing growing industrialization, urbanization, and agricultural expansion. These activities, especially in the northern part, threaten the lake’s ecosystem due to increasing human impact, such as resort development. To evaluate the effects of buffer zone degradation on water quality, data were collected from four sites twice a month between December 2020 and May 2021, with three replications. Key water quality parameters were analyzed across sites with varying degrees of anthropogenic disturbance. Most parameters exhibited significant spatial variability (p < 0.01), influenced by buffer zone integrity and human activities. Water temperatures (23.30–26.04 °C) remained within optimal ranges for aquatic life, though degraded littoral sites showed marginally higher temperatures linked to reduced vegetation and increased sediment heat absorption. DO levels (6.71–7.99 mg L⁻¹) were consistent across sites, reflecting similar atmospheric interactions. pH varied spatially (6.89–8.30), with lower values at disturbed sites attributed to organic decomposition and agrochemical runoff. Secchi depth and turbidity differed significantly (p < 0.05), with clearer waters in vegetated littoral (Debresina: 39.6 cm) and pelagic zones (105.54 cm), contrasting sharply with degraded sites (Seraba: 13.33 cm) due to erosion and sediment resuspension. Conductivity and TDS peaked at disturbed sites (Seraba: 192 µS cm⁻¹, 142 mg L⁻¹), reflecting nutrient and pollutant influx. Nutrient loads (TN, TP) were elevated in littoral zones, driven by agricultural runoff and wastewater, signaling eutrophication risks. Strong correlations emerged between habitat degradation (HDA score) and reduced water clarity (r = −0.97) or increased turbidity (r = 0.86). The study highlights the importance of buffer zones in protecting Lake Tana’s water quality and ecosystem. It urges policymakers to implement integrated management strategies and establish a well-defined buffer zone along the lakeshore to mitigate human-induced impacts.

Larval fish and aquatic macroinvertebrates are believed to be at greater predation risk by visual riverine predators during periods of higher lunar illumination. Predation rates may also be affected by the taxonomic composition and relative abundance of alternative co-distributed prey. We experimentally tested whether differences in larval lake sturgeon (Acipenser fulvescens) predation levels were attributed to changes in prey selectivity, or to an overall decrease in consumption of co-distributed and dispersing prey consumed by predatory riverine species under different light conditions. Larvae from three common riverine prey taxa observed nocturnally dispersing together (lake sturgeon, white suckers (Catostomus commersonii), and Hetptageniid mayflies) were released concurrently into raceway mesocosms. Raceways contained one of two abundant predacious riverine fishes [either rock bass (Ambloplites rupestris) or hornyhead chub (Nocomis biguttatus)]. Trials were conducted in light conditions simulating a full or new moon. Both predators consumed fewer prey under new moon relative to full moon light conditions. In full moon conditions, rock bass selected for mayflies and against white suckers, but in new moon conditions rock bass selectivity was similar for all prey. Hornyhead chub selected for mayflies under both light conditions. Results indicate rock bass and hornyhead chub rely on visual cues to detect prey. Rock bass also appeared to visually differentiate between prey taxa, whereas hornyhead chub may use alternative senses to select prey. Variation in larval lake sturgeon mortality during the downstream drifting period was a function of the taxonomic composition and size distribution of predators, and composition and relative abundance of alternative co-distributed prey. Nocturnal light levels likely also influence predation rates in natural populations of nocturnally dispersing aquatic larvae. Light levels during larval dispersal should be considered when interpreting intra- and inter-annual variation in recruitment in species of regional conservation concern.

The carbon stock in tidal freshwater wetlands in the upper estuaries has often been overlooked and not typically included in either the teal or blue carbon accounting. It was in this context that we measured the carbon stock at three selected representative sites (one is distal and the other two are proximal to a water tributary) in a wetland sanctuary of the Chesapeake Bay, United States. The measured average organic carbon stock of 243 ± 31 MgC ha⁻¹ (n = 5) in the top 68 cm soil is consistent with the recently reported high carbon stocks in the tidal freshwater wetlands. More intriguing and potentially more important, however, are that the latitude comparison between the data garnered from the sites distal and proximal, respectively, to a water source and the longitude comparison between the data of this and a 1993 study reveal the remarkable importance of soil moisture in keeping organic carbon. Particularly, the distal site that suffered from soil drying (i.e. had less soil moisture content) revealed a loss of ca. 57% carbon stock over a 28-year span. The measured lower soil pH at the distal site is possibly caused by the lower-moisture-enabled higher activity of oxidizing organic matters, particularly in warm seasons. Accordingly, we proposed that a 59% soil moisture content could be used as the minimum soil-moisture-level criterion for ensuring an effective preservation of carbon stocks and a soil pH decrease in warm seasons as an indicator of potential degradation in its carbon stocking capacity.

Fish are diverse aquatic organisms, economically significant as a primary source of food and nutrients. Accurate species identification is crucial for conservation, taxonomy and management. This study combined morphological and COI gene-based approaches to identify and characterize fish diversity from three locations in Malakand Division, Khyber Pakhtunkhwa Pakistan. All species were identified morphologically. DNA was extracted using phenol-chloroform method followed by PCR and sequencing. The consensus sequences were then utilized as search queries in BLASTn. BioEdit was used for trimming and MEGA X for phylogenetic study. Fourteen specimens representing eight species (Tariqilabeo latius, Mastacembelus armatus, Tor putitora, Carassius auratus, Cyprinus carpio, Garra gotyla, Channa punctata and Channa gachua) from three orders were analyzed. Results showed AT (54.23%) and GC (45.77%) contents, and a high Simpson’s diversity index (0.925), indicating rich species presence and evenness. Density, relative density, frequency, relative frequency and morphometric measurements were also calculated. This study validates the effectiveness of integrating morphological and molecular identification using COI gene for fish species in the region, highlighting its potential for broader application. Biodiversity metrics provide insights into its distribution in the area. Our findings contribute to the understanding of fish diversity in Pakistan and inform conservation and management efforts.

This study aims to determine the fatty acid composition of Pontastacus leptodactylus Eschscholtz, 1823 crayfish living in Cernek Lake in Bafra Fish Lakes in four seasons. The study was carried out over a period of one year. The crayfish used in the study were randomly sampled from their natural habitat at legal catch sizes. It was found that there was no difference in saturated fatty acid (SFA) concentrations among autumn/summer and spring/winter seasons, but there was a difference (p < 0.05) among autumn/winter and spring/summer seasons. It was found that there was a difference (p < 0.05) between the concentrations of monounsaturated fatty acids (⅀MUFA) in the spring and summer seasons. While the concentrations of polyunsaturated fatty acids (⅀PUFA) showed similar characteristics in the summer and autumn seasons, it was found that the concentrations were different in the other seasons (p < 0.05). It was also found that eicosapentaenoic acid (EPA) concentrations were lowest in spring and highest in summer, and the annual mean was 13.16 ± 1.10. Docosahexaenoic acid (DHA) concentrations were highest in winter and the annual mean was 6.79 ± 0.33. EPA+DHA concentrations were highest in the summer season and the annual mean was 19.96 ± 1.26. Omega-3 (ω-3) concentrations were highest in spring and lowest in autumn. In addition, the average annual ⅀Omega 3 (ω-3) concentration was 25.05 ± 4.62. ⅀Omega 6 (ω-6) concentrations were highest in winter and lowest in summer, and the annual general average was 18.60 ± 2.12. The annual average of ⅀ω-3/⅀ω-6 ratios was 1.36 ± 0.33. Based on the results of this study, these crayfish are an important source of (ω-3) fatty acids. This investigation will have a beneficial impact on the local market and potential aquaculture activities.

ABSTRACTS It is widely recognized that rivers serve as significant sources of greenhouse gas emissions. However, the monitoring and analysis of factors influencing methane (CH4) emissions from the Yellow River remain inadequate, particularly regarding high-frequency and detailed temporal differentiation studies. This study selected six sampling points in the Inner Mongolia section of the Yellow River (IMYR) to investigate the spatio-temporal variations in CH4 flux (FCH4) and CH4 concentration (CCH4) at the water-gas interface, along with their influencing factors. The results indicate that the range of FCH4 at the gas-water interface in IMYR is −30.41 to 84.75 mg·m⁻²·d⁻¹. The CCH4 in water varies from 0.07 to 0.22 μmol·L⁻¹, indicating an overall ‘source’ effect on atmospheric CH4. Both FCH4 and CCH4 exhibit higher values in summer and lower in spring, primarily driven by temperature fluctuations. Significant spatial differentiation of FCH4 and CCH4 is observed in the Inner Mongolia section of the Yellow River, with the highest CCH4 and FCH4 values recorded in Baotou (BT) and Wuhai (WH), respectively. On a seasonal scale, dissolved oxygen (DO) and water temperature (Tw) are the primary determinants affecting CH4 emissions. Given its importance within freshwater ecosystems, greater attention should be paid to CH4 emissions from river ecosystems.

The prospect of using fallowing as an ecosystem management measure to restore ecosystem functions in disturbed aquatic environments under cage culture was evaluated in this study. The cage aquaculture site in the Southeast arm of Lake Malawi was studied following the abandonment of cage aquaculture activities in 2022 after 18 years of operation. A Hydrolab CTD MS5 series probe was cast at each station to a maximum depth to collect electronic data and provide in situ depth profiles of temperature, dissolved oxygen, oxygen saturation, pH and salinity. Chlorophyl-extraction was done using a mixture of acetone and methanol and analyzed on a turner series 10 fluorometer. The study found that physical-chemical parameters such as temperature, pH, ammonia, turbidity and dissolved oxygen were not significantly different (p > 0.05) across the cage and non-cage sites and between seasons. However, ammonia levels recorded in this study were lower than the values reported during the cage culture operations period, an indication that some recovery processes are happening at the site. Chlorophyl a level was found to be insignificantly higher in cage and non-cage sites (p > 0.0.5) and significantly different between season (p < 0.05). High levels of Chl-a observed in this study are independent of cage aquaculture but might be linked to external inputs associated with tributaries as they collectively drain into the lake. Chl-a was found to be significantly and directly correlated to temperature, followed by total suspended solids and pH. Overall, the site is undergoing recovery with respect to the abandonment, but the effect is masked by external inputs of nutrients into the Lake. Although the study confirmed the oligotrophic status of the lake, the increasing levels of Chl-a are alarming and calls for inclusion of watershed management in agriculture and environmental management programming to sustainably safeguard the health of the Lake.