Effects of Nitrogen Emissions on Fish Species Richness across the World's Freshwater Ecoregions

Non-synergistic effects of microplastics and submerged macrophytes on sediment microorganisms involved in carbon and nitrogen cycling

Submerged macrophyte communities play a crucial role in regulating sediment carbon and nitrogen cycling in lake ecosystems. However, their interactions with emerging pollutants such as polystyrene microplastics (PS-MPs) remain poorly understood. In this study, we employed metagenomic analysis to examine the combined effects of submerged macrophyte communities and PS-MPs on sediment microbial communities, focusing on microbial populations, functional genes, and metabolic pathways involved in carbon and nitrogen cycling. Our results revealed a non-synergistic interaction between macrophyte communities and PS-MPs in shaping sediment biogeochemical processes. While increasing PS-MPs concentrations (from 0.5 to 2.5 % w/w) significantly enhanced microbial diversity (species richness increased from 533 to 1301), the presence of macrophytes moderated this response. Notably, we observed differential selective pressures on functional genes involved in key carbon and nitrogen cycling steps, particularly amoAB and amoC, nirS, and nirK, indicating distinct shifts in microbial functional groups. Furthermore, we identified complex substrate-pathway interactions: nitrate and ammonium differentially influenced fermentation and methanogenesis, while inorganic carbon positively regulated nitrate dissimilatory reduction. These findings provide novel insights into the regulatory mechanisms of submerged macrophytes in sediment biogeochemical cycling under microplastic stress, highlighting their potential role in maintaining ecosystem functions in contaminated aquatic environments.

Global spatiotemporal characterization factors for freshwater eutrophication under climate change scenarios

Nutrient enrichment of water bodies can lead to eutrophication, which poses a global threat to freshwater ecosystems, affecting biodiversity and water quality. While human activities have accelerated eutrophication, climate change further complicates the dynamics of nutrient cycling and ecosystem responses. Here, we provide global, spatially explicit freshwater eutrophication characterization factors, at an annual resolution from 2021 up to 2099 based on eight different climate change scenarios. A substantial spatial and temporal variability is identified, with higher characterization factors observed in tropical and arid regions, as well as densely populated areas, revealing a location-specific influence of climate change on eutrophication impacts. A comparison between different Representative Concentration Pathway scenarios suggests that climate change intensifies the eutrophication impact of phosphorus and its fluctuations, with hotspots identified in central and south America, Australia, southeastern Asia, central Africa and eastern Europe. Results highlight the importance of spatially- and temporally-explicit characterization factors, especially in prospective life cycle assessments. Finally, novel insights are provided into the complex interactions between nutrient fate, hydrological dynamics, and climate change, crucial for the development of phosphorus emission control strategies and the protection of freshwater ecosystems.

Chemical contaminants and environmental stressors induced teratogenic effect in aquatic ecosystem - A comprehensive review

Aquatic environments, including marine and freshwater ecosystems, are vital for ecological balance and biodiversity. The rising global demand for aquaculture products necessitates increased production, with intensified aquaculture practices posing significant environmental risks. This review explores the pathways through which chemical pollutants, heavy metals, pharmaceuticals, and environmental stressors induce teratogenic effects in aquatic species. The review highlights the impact of pesticide include triazine herbicides, organophosphate and organochlorine insecticides, and carbamates on aquatic life, emphasizing their interference with endocrine systems and developmental processes. Heavy metals like mercury, lead, cadmium, arsenic, and chromium are noted for their persistence and bioaccumulative properties, disrupting cellular and hormonal functions. Pharmaceuticals, including NSAIDs, antibiotics, and chemotherapeutic agents, exert teratogenic effects by disrupting physiological and developmental pathways. Environmental stressors includes temperature fluctuations, salinity variations, pH changes, and oxygen level imbalances exacerbate the teratogenic impact of pollutants. This review highlights the importance of comprehensive environmental management and understanding these complex interactions is essential for formulating efficient strategies to safeguard the effective measures to protect aquatic ecosystems and the biodiversity.

Multidirectional Fate Path Model to Connect Phosphorus Emissions with Freshwater Eutrophication Potential

Excessive anthropogenic phosphorus (P) emissions put constant pressure on aquatic ecosystems. This pressure can be quantified as the freshwater eutrophication potential (FEP) by linking P emissions, P fate in environmental compartments, and the potentially disappeared fraction of species due to increase of P concentrations in freshwater. However, previous fate modeling on global and regional scales is mainly based on the eight-direction algorithm without distinguishing pollution sources. The algorithm fails to characterize the fate paths of point-source emissions via subsurface pipelines and wastewater treatment infrastructure, and exhibits suboptimal performance in accounting for multidirectional paths caused by river bifurcations, especially in flat terrains. Here we aim to improve the fate modeling by incorporating various fate paths and addressing multidirectional scenarios. We also update the P estimates by complementing potential untreated point-source emissions (PSu). The improved method is examined in a rapidly urbanizing area in Taihu Lake Basin, China in 2017 at a spatial resolution of 100 m × 100 m. Results show that the contribution of PSu on FEP (62.6%) is greater than that on P emissions (58.5%). The FEP is more spatially widely distributed with the improved fate modeling, facilitating targeted regulatory strategies tailored to local conditions.

Global regionalized characterization factors for phosphorus and nitrogen impacts on freshwater fish biodiversity

Inefficient global nutrient (i.e., phosphorus (P) and nitrogen (N)) management leads to an increase in nutrient delivery to freshwater and coastal ecosystems and induces eutrophication in these aquatic environments. This process threatens the various species inhabiting these ecosystems. In this study, we developed regionalized characterization factors (CFs) for freshwater eutrophication at 0.5 × 0.5-degree resolution, considering different fates for direct emissions to freshwater, diffuse emissions, and increased erosion due to agricultural land use. The CFs were provided for global and regional species loss of freshwater fish. CFs for global species loss were quantified by integrating global extinction probabilities. Results showed that the CFs for P and N impacts on freshwater fish are higher in densely populated regions that encompass either large lakes or the headwaters of large rivers. Focusing on nutrient-limited areas increases country-level CFs in 51.9 % of the countries for P and 49.5 % of the countries for N compared to not considering nutrient limitation. This study highlights the relevance of considering freshwater eutrophication impacts via both P and N emissions and identifying the limiting nutrient when performing life cycle impact assessments.