ABSTRACT To evaluate whether photosynthesis-induced calcium‒phosphorus (Ca‒P) coprecipitation in Hydrilla verticillata can be harnessed for eutrophic freshwater phytoremediation, we conducted controlled light incubator experiments to determine how key environmental factors regulate this process. We manipulated four drivers—light intensity (66 vs. 110 μmol m⁻² s⁻¹), inorganic carbon (HCO₃−: 0 vs. 50 mg L⁻¹ = 0.82 mM), calcium (CaCl₂: 0 vs. 50 mg L⁻¹) and phosphorus (K₂HPO₄: 0 vs. 1 mg L⁻¹)—and quantified the responses in dry weight total phosphorus (DWTP), total ash phosphorus (TAP) and its fractions: water-soluble H₂O-P, organic NaOH-P and calcium-bound HCl-P. The key results revealed that a higher light intensity (110 vs. 66 μmol m⁻²​​​​​​ s⁻¹) exerted a stronger influence on H₂O-P and HCl-P fractions (by percentage) than on NaOH-P or DWTP in the light‒phosphorus interaction experiments. This suggests that enhanced photosynthesis under high light boosted P adsorption and promoted coprecipitation with supersaturated CaCO₃. For the inorganic carbon × phosphorus interactions, TAP and H₂O-P peaked under high inorganic carbon and high P conditions. Inorganic carbon contributed more to H₂O-P (45.13%) than did P (35.33%), indicating that inorganic carbon-enhanced photosynthesis primarily drove P adsorption. In the calcium‒phosphorus experiments, the maximum HCl-P and TAP occurred under high Ca (50 mg L⁻¹) and high P conditions. Calcium contributed more to HCl-P than did P, identifying Ca as the primary driver of Ca-P coprecipitation in H. verticillata. In summary, photosynthesis-induced Ca-P coprecipitation in H. verticillata is a synergistic, multifactor process—highlighting Ca as a key regulator of remediation efficiency. Ecologically, H. verticillata is particularly effective at reducing P bioavailability via Ca-P coprecipitation in calcium-replete waters, while in calcium-limited systems, P removal relies more on adsorptive/absorptive pathways. These findings highlight the need to integrate nutrient availability and plant physiological processes for optimizing phytoremediation of eutrophic freshwater.

ABSTRACT Quantifying how wetlands regulate the magnitude, variability, and responsiveness of water temperature is essential to understanding their ecological functions and informing climate-adaptive management. To investigate the mechanisms underlying wetlands’ thermal influence, we monitored groundwater, open water, channel, and outlet temperatures across seven palustrine wetlands in Oregon’s forested Cascades in summer 2024. We identified early- and late-summer thermal phases based on water temperature shifts and used principal component analysis to define site-level thermal gradients. Generalized least squares modeling and multivariate dispersion analysis further identified landscape drivers and unexplained within-site temperature variability, respectively. We compared this variability with the Oregon Rapid Wetland Assessment Protocol (ORWAP) indicators of thermoregulation. This analytical approach explores how spatial scales influence distinct aspects of thermal regimes, with broad-scale factors such as elevation and air temperature shaping overall temperature magnitude, while site-level features such as vegetation structure and hydrology regulate day-to-day variability and thermal stability. Large wetlands with ponded surface water generally stabilized outflow temperatures despite relative warming compared to smaller wetlands with relatively more permanently saturated vegetated zones, which exhibited cooler but more variable atmospherically-driven changes. Within-site sub-seasonal shifts between early and late summer were minor relative to differences across sites. While comparing rapid-assessment scores to water temperature variability resulted in low explanatory power, vegetation structure indicating shade most consistently associated with lower temperature variability. These findings highlight both merits and limitations of ORWAP, and restoration trade-offs between creating open-water habitat and sustaining cool-water conditions in headwater systems.

ABSTRACT Macrophyte dynamics in rivers are expressed through spatiotemporal gradients that reflect the functioning of freshwater ecosystems. In Mediterranean rivers, characterized by irregular low-flow periods and sudden floods, these gradients strongly influence the distribution and structure of aquatic vegetation. In Morocco, however, the ecology and distribution of aquatic macrophytes remain poorly documented, particularly in the Upper Oum Er-Rbia Basin. This study analyzes the spatiotemporal dynamics of macrophyte diversity along this basin using thirteen monthly surveys (June 2018–June 2019) conducted at fourteen sites in five rivers spanning spring-fed, perennial, and temporary streams. Macrophyte diversity and evenness were quantified using Shannon–Weaver (H′) and Pielou’s (J′) indices and evaluated with a multivariate framework: PERMANOVA and NMDS to test community differentiation between rivers and months, PCA to summarize hydrochemical and hydromorphological gradients, and CCA to relate species composition to environmental drivers. The results reveal marked spatial structuring, with upstream–downstream organization and strong river-specific assemblages. Geographic position within the basin emerges as a key determinant of macrophyte diversity, while hydrochemical status and hydromorphological conditions—including flow velocity, water depth, channel substrate, and disturbance pulses associated with floods and low-flow phases—shape within-river trajectories of composition and cover. This work provides the first basin-scale ecological assessment of macrophyte distribution in the Upper Oum Er-Rbia and highlights the importance of integrating spatial and temporal processes when diagnosing and managing Mediterranean river ecosystems.

Springs and other groundwater-dependent ecosystems have received much less attention than rivers, lakes, and wetlands. Among freshwater springs, those that flow directly into oceans have been studied even less than those that flow into freshwater systems, the former being less common. The goal of this study was to document the fish assemblages of several springs that flow into the Gulf of Mexico and to compare these assemblages with those of springs that flow into rivers prior to flowing into the Gulf. To describe the fish assemblages, I deployed GoPro cameras along the first 650 m of each of 24 springs, five with a terminus in the Gulf and 19 that had a terminus in a river. On the 12-min footage from each camera, I counted the maximum number of individuals of each species that occurred in a frame together. From these counts, I calculated the total number of fish, species richness, and diversity. Across the geographic range of the study, springs varied in conductivity by more than an order of magnitude, but for any given spring, the conductivity was related more to the proximity of the spring head to saltwater than to a marine or riverine terminus. The total number of fish, species richness, and diversity of the springs did not differ between the two categories of springs; instead, species richness and diversity were related more to the size of the spring, the temperature (which is influenced by latitude), and the percent substrate coverage by primary producers. However, the composition of fish assemblages differed, with the addition of euryhaline species and some loss of sunfish (Lepomis sp.) in springs with more saline water. In addition, the springs in the most urban area had relatively high abundances and species richness of nonnative fishes. Therefore, the physical, chemical, and biological characteristics of springs, and the potential for human-caused disturbance, may be more important than the springs' exact terminus in predicting the composition of the fish assemblage. In particular, connection to saltwater and high salinity is important for migration of euryhaline fish species into a spring, but this connection need not be direct.

ABSTRACT The present study investigated the monthly dynamics of algal diversity in relation to the physicochemical parameters of the Dor River, a key freshwater tributary of the Indus Basin in Khyber Pakhtunkhwa, Pakistan. Water and algal samples were collected monthly for one year from two hydrological distinct stretches of the river, extending from Barengali to Dhamtor (freshwater zone) and from Domail to Tarbela Dam. Standard limnological protocols and taxonomic microscopy were employed to identify Chlorophyta species, quantify their community structure, and evaluate the environmental influences on the algal distribution. A total of 23 algal species belonging to 3 classes, 8 orders and 14 families were recorded, with Chlorophyceae being the most dominant group. Diversity indices revealed the highest species richness and Shannon diversity during autumn and late winter, while monsoon months exhibited reduced diversity associated with increased turbidity, dilution, and ionic fluctuations. The physicochemical variables, such as pH (7.1–7.87), conductivity (254–444 μS/cm), turbidity, and nutrient levels, displayed clear seasonal patterns, significantly shaping the algal abundance, frequency, and importance value index (IVI). Chlorophycean taxa, including Scenedesmus bijuga, Ulothrix zonata and Oocystis borgei, showed strong ecological plasticity and served as indicators of stable water quality. Overall, the Dor River maintained a healthy ecological status with strong resilience to seasonal variations, although monsoon-driven disturbances temporarily altered the algal community structure. This study highlights the value of integrating algal bioassessment with water quality monitoring as an effective tool for evaluating freshwater ecosystem health and guiding conservation strategies for the Dor River.

Microplastics (<5 millimeters) are a prominent contaminant globally, negatively affecting terrestrial, freshwater, and saltwater systems. Virtually no research has investigated microplastic contamination in remote, forested headwater streams in Pennsylvania. At five streams in central Pennsylvania, we assessed microparticle/microplastic contamination across three trophic levels: tertiary consumers (Salvelinus fontinalis), secondary consumers (Rhinichthys atratulus), and primary consumers (Trichoptera, Plecoptera, Ephemeroptera, Odonata, and Megaloptera). From 100-meter unblocked reaches, fish (n = 46 total, n = 21 tertiary consumers, n = 25 secondary consumers) and benthic macroinvertebrates (n = 106 total, Trichoptera: n = 40, Plecoptera: n = 39, Ephemeroptera: n = 22, Odonata: n = 4, Megaloptera: n = 1) were collected using standard wadeable stream sampling procedures. Fish gastrointestinal (GI) tracts and macroinvertebrates were digested in 10% potassium hydroxide (KOH) solutions, and microparticles were identified after vacuum filtration and visualization with a dissecting microscope at 45× magnification. Microparticles were categorized as microplastics at two of our five sites using μFTIR spectroscopy on Salvelinus fontinalis, Rhinichthys atratulus, and Plecoptera. Our efforts resulted in the identification of 159 microparticles and 5 microplastics among all heterotrophs across all sites. Microparticle contamination was highest among secondary consumers with no heterotroph or site effect on microparticle count (p > 0.05). The distribution of microparticle morphology and color combinations varied significantly across the heterotroph groups, and there were negative correlations between brook trout morphological characteristics and microparticle count (e.g. total length: r = –0.62, p = 0.03; weight: r = –0.62, p = 0.03; gastrointestinal tract weight: r = –0.66, p = 0.02). Negative relationships between size characteristics among all fish and microparticle count were expressed by δ15N analysis (r = –0.37, p = 0.03). We believe that the disparity in microparticle contamination by fish size and between trophic levels is driven by divergences in feeding strategies, ontogenetic shifts in feeding behavior, and contrasts in life histories. Overall, our data highlight the presence of microplastic/microparticle contamination in remote, forested headwater streams in Pennsylvania without any known upstream point-source pollution.

Nansi Lake, located in the southwestern region of Shandong Province, China, consists of four interconnected lakes—Nanyang, Dushan, Zhaoyang, and Weishan—and functions as an essential water conveyance and storage reservoir for the East Route of the South-to-North Water Diversion Project. The construction of the Erji Dam hydraulic complex between 1958 and 1973 resulted in the division of the lake into two distinct sub-lakes: Shangji Lake (upper lake) and Xiaji Lake (lower lake). This development significantly altered the hydrological connectivity and ecological conditions of the area. This research examines the effects of hydraulic engineering on the aquatic environment and ecosystem of Nansi Lake by analyzing water quality parameters and sedimentary diatom communities, with an emphasis on spatial variations between the northern and southern regions. The results demonstrate that Nansi Lake exhibits mild pollution, characterized by mesotrophic to eutrophic conditions. Sediments primarily consist of clay and silt, with minimal sand content, while organic matter originates from both autochthonous and allochthonous sources. A total of 181 diatom species from 37 genera were identified, revealing distinct dominant taxa between Shangji Lake and Xiaji Lake. Redundancy analysis (RDA) indicated that total nitrogen (TN) and Ca2+ were the primary factors influencing diatom communities in Shangji Lake, whereas total organic carbon (TOC) and dissolved oxygen (DO) predominantly governed those in Xiaji Lake. The research indicates that the water quality, nutrient levels, sedimentation patterns, and diatom distributions of Nansi Lake demonstrate considerable spatial heterogeneity, primarily influenced by anthropogenic activities such as hydraulic engineering and aquaculture, leading to marked variations between the northern and southern regions.

Heavy metals and metalloids (HMLs) are toxic, non-biodegradable pollutants that can accumulate in sediments and aquatic organisms, posing significant risks to ecosystems. Their persistence in the environment leads to long-term contamination, harming aquatic life, disrupting ecosystems, and threatening water quality. HMLs have not been extensively studied in Dukan Lake, Kurdistan region, northern Iraq; thus, their environmental fate remains largely unknown. To address this, we conducted a field monitoring study to examine the presence of HMLs in the lake, collecting samples from common carp, sediment, and water. HMLs were regularly measured during the sampling period, with median concentrations detected in common carp (Cyprinus carpio) tissues (0.01–2.9 × 102 µg/g), sediment (0.5–7.8 × 102 µg/g), and water (0.01−6.9 µg/L). Fe, Mg, and Zn were the dominant metals across all samples. Seasonal variations of the HMLs were observed, with higher concentrations found in summer and autumn seasons compared to winter and spring, indicating the impact of temperature and precipitation. Despite high concentrations in sediment and water, HMLs accumulation remained below the threshold. These results underscore the significance of lake monitoring in evaluating ecosystem health and surface water quality. The environmental impact and ecotoxicological significance of HMLs from places that are not monitored and still need further evaluation.

This study examines the impact of a flood event on macrobenthic biodiversity indices in the lowest zone of the Gharesou River, which flows into the Gorgan Gulf, in the southeastern Caspian Sea. Samples were collected after short summer drought in six surveys, from October 2018 to December 2019, with three surveys before and three surveys after the flood event of March 2019. Regarding the spatial distribution, the samples were collected at four sites (stations), with two replicates at each site. Eight types of macrobenthic taxa at the levels phylum (Nematoda), class (Ostracoda), family (Discorbidae, Chironomidae, Lumbriculidae, Naididae, and Tubificidea) and genus (Streblospio sp.) and two types of zooplankton, i.e. Cyclops sp. and Daphnia sp., were identified. The abundance of macrobenthic taxa increased gradually in the post-draught period, while it reduced and reached the lowest point in the summer after the flood event (August 2019). It was also observed that the flood significantly increased the organic matter in the riverbed (p < 0.05). The study of Gharesou River over post-drought and post-flood situations indicated that flood reduced the abundance of macrobenthic taxa, while macrobenthic taxa over post-drought had a higher recovery rate than that over post-flood periods. A potential explanation for this observation is that benthic taxa were more tolerant to short summer drought than extreme floods. In general, a steady and continuous flow could prevent undesired fluctuations in diversity indices.

In the face of river basin environmental challenges and the urgent need for sustainable development strategies, understanding the complex interactions among ecological services, human activities, and vegetation cover is of paramount importance. Although previous studies have extensively documented the widespread impact of human activities on ecosystem service value (ESV), the mechanisms by which different human activities affect ESV with different functions are still unclear. To bridge these gaps, this study investigated the relationships among ESV, human footprint index (HFI), and fractional vegetation coverage (FVC) in the Yangtze River Basin (YRB). We used land cover change analysis and the equivalent factor method to study the spatiotemporal structure of ESV in YRB from 2000 to 2020, and selected different human footprint indicators to evaluate HFI and vegetation cover assessment FVC. The results revealed that construction land in YRB has increased the most significantly, reaching 25014 km2, and ESV has increased by 4.55% in general, approximately 22915 billion CNY. Among them, the regulating service value (RSV) has increased by 18696 billion CNY. The FVC shows a pattern of 'high in the middle, low in the east and west', of which 71.30% shows a significant increase, especially in the upstream areas. Curve estimation analysis revealed that an increasing HFI is associated with decreases in RSV, supporting service value (SSV), and cultural service value (CSV), whereas provisioning service value (PSV) increases. Conversely, an increase in vegetation coverage, was positively correlated with ESV. The strong positive correlation between FVC and ESV highlights the importance of vegetation cover in sustaining ecosystem services. This underscores the significant impact of the HFI and FVC on ESV and emphasizes the need to consider regional differentiation in ecosystem assessments. These insights are crucial for policymakers and conservation practitioners aiming to promote sustainable ecosystem development and conservation in the YRB.