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Eutrophication is an ecological process showing the state shift of a lake. This shift could be triggered when the external nitrogen (N) loads exceed N thresholds. Meanwhile, external water inputs and the resulting changes in lake water depth could affect N thresholds. Thus, the shift towards eutrophication may occur more quickly when the N thresholds decrease. Lake Baiyangdian is located in the North China Plain and plays an essential role in ecosystem service provision. However, this lake may have seen a decrease in the N threshold decrease due to frequent water replenishment since 2015. In this study, we compared the external N loads to Lake Baiyangdian with the N thresholds from 2012 to 2017. For this, we considered the effects of water replenishment by linking the MARINA-Lakes and the PCLake + models. Then, we assessed how N thresholds could be met by external N loads from sub-basins of Lake Baiyangdian under 2017 and different N management cases, including improved crop yield and efficiency (S1), improved sewage treatment (S2), improved manure management (S3), and combined options (S4). Results indicate that a 45% reduction in river export of N to Lake Baiyangdian was found from 2012 to 2017. Agricultural sources (fertilizer and manure) accounted for 59% of river exports of N in 2017. River N exports to the lake are projected to be reduced by 13-67% under the four cases. In 2017, the N-load response curve exhibited hysteresis with a 56-87% decrease in N thresholds compared to 2012. Measures in S4 can help to reduce external N exports to Lake Baiyangdian below the N thresholds. Our study emphasizes the importance of combined N management strategies to mitigate the eutrophication risk of the lake. These results offer valuable insights for N management in lake basins experiencing increasing water depth resulting from water replenishment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Novel 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) and legacy PFASs, such as perfluorohexane sulfonate (PFHxS), have been used to replace perfluorooctane sulfonate (PFOS), a known persistent organic pollutant. Thus, it is critical to understand these PFOS alternatives regarding their sources and concentrations in the natural environment. In this study, 41 surface water samples as well as edible aquatic organisms were collected from Baiyangdian Lake, the largest freshwater lake in Hebei Province, China. Perfluorooctanoate acid (PFOA) and PFHxS were the predominant PFASs detected in the surface water, reaching concentrations of 8 397.23 ng/L and 1 478.03 ng/L, respectively, with PFHxS accounting for the greatest proportion (∼80.00%) in most water samples. PFHxS (mean: 87.53 ng/g) and PFOS (mean: 35.94 ng/g) were also the most prevalent compounds detected in aquatic organisms. Estimated daily intake (EDI) values of PFOS (16.56 ng/kg bw/d) and PFHxS (16.11 ng/kg bw/d) via aquatic food and drinking water were the highest among PFASs, indicating potential exposure risks to residents. In addition, fish product consumption was the important exposure pathway for residents to PFOA, PFHxS, PFOS, and 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA). This study reports on the highest PFHxS levels ever recorded in surface water, suggesting that further quantification of PFHxS in human serum and assessment of its health risks to local residents are warranted and critical., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Background: The drastic change in an ecosystem as a threshold phenomenon caused by abrupt changes in environmental conditions is a focus of current ecological research. However, the study of ecological thresholds has generally been limited to estimating the threshold values of single factors. Using eDNA metabarcoding technology, we collected zooplankton data from Baiyangdian Lake, the largest freshwater lake in the North China Plain, to explore the zooplankton community distribution characteristics and the relevant environmental factors. We used Threshold Indicator Taxa Analysis (TITAN) to determine the thresholds of key environmental factors and to identify the factors influencing biological diversity. Results: By comparing previous studies, we found that the zooplankton community composition based on eDNA metabarcoding was similar to that based on morphological methods, and that the data could be used to estimate ecological thresholds and assess risk conditions. Temperature (T), electrical conductivity (EC), and turbidity were the major environmental factors affecting the zooplankton community structure. The composition and structure of zooplankton communities in rivers and lakes were significantly different due to the influence of specific environmental factors. The results of TITAN analysis showed that there were different indicator species for T and EC in rivers and lakes. The protection thresholds of zooplankton in rivers were T = 19.0 °C and EC = 795 μS/cm, whereas the protection thresholds of zooplankton in lakes were T = 14.3 °C and EC = 1920 μS/cm. The overall values for the Baiyangdian watershed were T = 15.5 °C and EC = 1073 μS/cm. Compared with the field monitoring results, approximately 50% of the water quality index values at the sampling points in the Baiyangdian watershed exceeded the negative response threshold, indicating that Baiyangdian Lake was disturbed. Conclusions: The validity of eDNA technology in biodiversity analysis was confirmed by the zooplankton community data from Baiyangdian Lake. The ecological thresholds derived by combining eDNA technology with Threshold Indicator Taxa Analysis (TITAN) are beneficial to the biological conservation of the region. [ABSTRACT FROM AUTHOR]

Introduction: As the largest shallow freshwater lake in the North China Plain, Baiyangdian lake is essential for maintaining ecosystem functioning in this highly populated region. Sediments are considered to record the impacts of human activities. Methods: The abundance, diversity and metabolic pathways of microbial communities in sediments were studied by metagenomic approach to reveal patterns and mechanism of C, N, P and S cycling under the threat of lake eutrophication. Results: Many genera, with plural genes encoding key enzymes involved in genes, belonging to Proteobacteria and Actinobacteria which were the most main phylum in bacterial community of Baiyangdian sediment were involved in C, N, S, P cycling processes, such as Nocardioides (Actinobacteria), Thiobacillus, Nitrosomonas, Rhodoplanes and Sulfuricaulis (Proteobacteria). For instance, the abundance of Nocardioides were positively correlated to TN, EC, SOC and N/P ratio in pathways of phytase, regulation of phosphate starvation, dissimilatory sulfate reduction and oxidation, assimilatory sulfate reduction, assimilatory nitrate reduction and reductive tricarboxylic acid (rTCA) cycle. Many key genes in C, N, P, S cycling were closely related to the reductive citrate cycle. A complete while weaker sulfur cycle between SO42- and HS- might occur in Baiyangdian lake sediments compared to C fixation and N cycling. In addition, dissimilatory nitrate reduction to ammonia was determined to co-occur with denitrification. Methanogenesis was the main pathway of methane metabolism and the reductive citrate cycle was accounted for the highest proportion of C fixation processes. The abundance of pathways of assimilatory nitrate reduction, denitrification and dissimilatory nitrate reduction of nitrogen cycling in sediments with higher TN content was higher than those with lower TN content. Besides, Nocardioides with plural genes encoding key enzymes involved in nasAB and nirBD gene were involved in these pathways. Discussion: Nocardioides involved in the processes of assimilatory nitrate reduction, denitrification and dissimilatory nitrate reduction of nitrogen cycling may have important effects on nitrogen transformation. [ABSTRACT FROM AUTHOR]

Abstract: In order to study the seasonal variations in the structure and dynamics of phytoplankton community of the Lake Baiyangdian in China, quantitative samples were collected in each season during 2005. A total of 152 taxa were identified by microscope, phytoplankton had an abundance ranging from 131.25×104 ind. L-1 to 745.88×104 ind. L-1. The highest phytoplankton abundance were observed in spring and the lowest in autumn. Cyanophyta, Euglenophyta and Cryptophyta were the most important groups in terms of abundance and biomass. The preponderant and sub-preponderant species changed in accordance with the seasons. Canonical Correspondence Analysis (CCA) was used to investigate the relationship between environmental factors and phytoplankton community. The results indicated that nutrient gradient had a positive correlation with axis 1 in spring, summer and autumn. But in winter, the nutrient gradient had a positive correlation with axis 2. The varieties of environmental factors affected the structure of phytoplankton community in each season. CCA shows a slight, but significant method to understand the spatial distribution of phytoplankton community in lake systems. [ABSTRACT FROM AUTHOR]