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The mobilization of internal phosphorus (P) plays a crucial role in transitioning nutrient limitations within lake ecosystems. While previous research has extensively examined P release in littoral zones influenced by fluctuating water levels, there is a paucity of studies addressing the implications of sustained water level rise in this context, particularly as it pertains to nutrient limitations in benthic algae. To address this gap, we conducted an integrated study in Qinghai Lake. In the field sampling and microcosm experiment, we found that P concentrations are elevated in areas subjected to short-term inundation compared to those enduring prolonged inundation, primarily due to the dissolution of sedimentary P fractions. The results of nutrient diffusing substrata (NDS) bioassays indicated that benthic algae in Qinghai Lake displayed either P limitation or NP co-limitation. The transition from P limitation to NP co-limitation suggested that internal P release may serve to ameliorate nutrient limitations in benthic algae. This phenomenon could potentially contribute to the proliferation of Cladophora in the littoral zones of Qinghai Lake, thereby posing long-term implications for the lake's aquatic ecosystem, particularly under conditions of sustained water level rise., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Urban rainstorm and waterlogging occurred more frequently in recent years, causing huge economic losses and serious social harms. Accurate rainstorm and waterlogging simulation is of significant value for disaster prevention and mitigation. This paper proposed a numerical model for urban rainstorm and waterlogging based on the Storm Water Management Model (SWMM) and Geographic Information System (GIS), and the model was applied in Lianhu district of Xi'an city of China. Furthermore, the effects of rainfall characteristics, pipe network implementation level and urbanization level on waterlogging were explored from the perspectives of spatial distribution of waterlogging points, drainage capacity of pipe network and surface runoff generation and confluence. The results show that: (1) with the increase of rainfall recurrence period, the peak of total water accumulating volume, the average decline rate of water accumulating volume and the number of waterlogging nodes increase; (2) optimizing the pipe diameter can shorten the average overload time of the pipe network from the entire pipe network, but for a single pipe, optimizing the pipe diameter may lead to overloading of unoptimized downstream pipeline; (3) the lower the imperviousness, the less the number of waterlogging nodes and average time of water accumulating, and (4) the west, northwest and southwest areas are relatively affected by the imperviousness, only improving the underlying surface conditions has limited influence on waterlogging in the study area. This study can provide reference for urban waterlogging prevention and reduction and pipe network reconstruction., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Lake sediments can provide valuable insights into anthropogenic disturbances such as intensive aquaculture and land use changes. These disturbances often manifest as elevated levels of nutrients and elements within the sediments. This paper uses several analytical techniques, i.e., FTIR (Fourier-transform infrared spectroscopy), XRD (X-ray diffraction), EDS (energy-dispersive X-ray spectroscopy), and SEM (scanning electron microscopy), to examine the elemental constituents of lake sediments, along with their relative mineral abundances and surface morphology. The selected freshwater lakes are from the Central Gangetic Plain. The analysis provides a "fingerprint" of geogenic and biogenic mineral constituents of the sediments. Physicochemical, mineralogical, and elemental analysis shows that intensive aquaculture activities in lake alter the sediment chemistry as evidenced by the increase in pH, organic carbon, organic matter, and total phosphorus which is not observed in the lake where aquaculture is prohibited. Freshwater lake sediment is characterized by a high content of biogenic silica and carbonate minerals. The variations in sediment nutrients and mineral fluxes of the selected lakes are mainly attributed to diverse anthropogenic pressures, differences in lake productivity, and the overall ecological condition of the lakes. In the selected three lakes, major variation was reported in the autochthonous sediments in comparison to the allochthonous sediments. The study concludes that catchment and biotic deposit variations in the lakes cannot be evened out by in-lake mixing mechanisms due to variations in the terrigenous and pelagic deposits of the lake. The results highlight the importance of studying annual fluctuations and spatial variations in geogenic and biogenic mineral particle fluxes in lakes. Such investigations provide valuable insights into the annual dynamics of minerals within lakes, contributing to a more comprehensive understanding of their behavior and distribution., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Nitrogen transport from terrestrial to aquatic environments could cause water quality deterioration and eutrophication. By sampling in the high- and low-flow periods in a highly disturbed coastal basin of Southeast China, hydrochemical characteristics, nitrate stable isotope composition, estimation of potential nitrogen source input fluxes, and the Bayesian mixing model were combined to determine the sources and transformation of nitrogen. Nitrate was the main form of nitrogen. Nitrification, nitrate assimilation, and NH 4 + volatilization were the main nitrogen transformation processes, whereas denitrification was limited due to the high flow rate and unsuitable physicochemical properties. For both sampling periods, non-point source pollution from the upper to the middle reaches was the main source of nitrogen, especially in the high-flow period. In addition to synthetic fertilizer, atmospheric deposition and sewage and manure input were also major nitrate sources in the low-flow period. Hydrological condition was the main factor determining nitrate transformation in this coastal basin, despite the high degree of urbanization and the high volume of sewage discharge in the middle to the lower reaches. The findings of this study highlight that the control of agricultural non-point contamination sources is essential to pollution and eutrophication alleviation, especially for watersheds that receive high amounts of annual precipitation., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Soil erosion and sediment yield in watersheds are comprehensively affected by land use/cover changes and climatic factors. The current sediment yield index (SYI) model incorporates parameters of area (A), delivery ratio (DR), and curve number (CN), which reflect the character of underlying surface conditions, while the impact of rainfall intensity on sediment yield could not be properly considered. This study aims to improve the current SYI model by introducing rainfall-related factors such as rainfall erosivity (R) and applying it to estimate the sediment yield of river basin. Taking the Dongjiang River basin, South China, as a case study, the performances of the improved simplified SYI model (SYI-CN + R) were compared and demonstrated at multi-spatiotemporal scales. The results showed that (1) compared with the SYI model which only has the parameter CN (SYI-CN), the model SYI-CN + R achieves better simulation performances at yearly (the efficiency coefficient (CE) is 81% in the whole basin and 62% in the sub-basin) and half-month (CE is 69% in the whole basin and 57% in the sub-basin) time scales. (2) On the basin scale, the simulation performance in the whole basin is better overall compared to that in the sub-basin, and the model SYI-CN + R at the half-month time scale is more suitable for the sediment yield simulation in the Dongjiang River basin, with higher value of correlation coefficient (CC) of 87% and 83% for the whole basin and the sub-basin, respectively. And (3) the values of CN and R have an obvious spatial gradient in the whole basin, showing an increasing trend from northeast to southwest as a whole, with larger values concentrated in the lower reaches and smaller values in the middle and upper reaches. This study extends the application and improves the performance of the SYI model, and provides a basis for soil and water conservation in a river basin with fewer observation data., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Concern over the influences of constant addition of emerging anthropogenic chemicals to the environment has become a public issue during the rapid urbanization. Here, we investigated the occurrence of organophosphate esters (OPEs) in soil and corresponding tree bark in a megacity, Western China. Our results showed levels of OPEs in tree bark (1250 ± 573 ng/g dry weight (dw)) were 1-2 orders of magnitude higher than those in soil (40.4 ± 30.8 ng/g dw). Rooster Mountain is a background mountain area, exhibiting significantly lower concentrations of OPEs in soil and tree bark than those in other sites with relatively high population density. This result highlights the effect of human activities on the distribution of OPEs in environmental matrices. Alkyl-OPEs were predominant compounds in soil, whereas halogenated- (Cl-) OPEs were characterized in tree bark. Furthermore, tris(2-chloroethyl) phosphate (TCEP) positively correlated with tris(2-chloroisopropyl) phosphate (TCIPP) in soil (r 2  = 0.43, P < 0.05) while negatively correlated with TCIPP in tree bark (r 2  = 0.31, P < 0.05). The ratios of logarithm concentrations of OPEs in tree bark to those in soil correlated well with logK OA values of OPEs from 6 to 10, indicating the equilibrium status was achieved between OPE partitioning in soil and in tree bark. Nevertheless, tris (2-butoxyethyl) phosphate (TBEP) and tris(2-ethylhexyl) phosphate (TEHP) with high values of logK OA deviated from this linear tendency, which was possibly due to the fact that they were subjected to the particle-bound deposition process, leading to partition into the soil., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Environmental regulations are considered a prerequisite for environmental performance. However, very limited studies have explored the asymmetric relationship between clean energy consumption, environmental regulation, and CO 2 emissions. This study scrutinizes the asymmetry phenomenon in environmental regulation-clean energy consumption and environmental quality nexus in China by using the time series nonlinear ARDL approach by covering the period 1993-2019. The result reveals that the impact of environmental regulation on clean energy consumption and CO 2 emissions is asymmetric. A positive change in environmental regulation has a positive effect on clean energy consumption but a negative impact on CO 2 emissions in the long run. While a negative change in environmental regulation has insignificant effects on clean energy consumption and CO 2 emissions in the long run. The study suggests that China should need to revisit environmental regulation policies that could help in improving environmental quality., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Quantifying the effect of hydraulic disturbances on sediment phosphate release is a key issue in the water quality assessment of lakes, especially for the shallow lakes which are susceptible to winds and waves. Here, we sampled the original sediment columns from 12 positions in the eastern, central, and western areas of the Chaohu Lake, a representative shallow lake in China, and observed phosphate release under three levels of hydraulic disturbances in the laboratory. When the disturbance was weak and sediment on the surface of bottom mud moved individually (the Individual Motion Mode), sediment phosphate release rate was insignificant (0.24 mg/m 2 /day). When the disturbance was medium and only a small percentage (< 16%) of surface sediment started to move (the Small Motion Mode), the phosphate release rate sharply increased to 4.81 mg/m 2 /day. When the disturbance was further strengthened and most (≥ 16%) of the surface sediment moved (the General Motion Mode), the phosphate release rate was more than doubled (10.23 mg/m 2 /day). With the increase in hydraulic disturbance intensity, the variation range of phosphate release also became wider. Spatial distribution showed that the release rate varies the most in the western area, followed by the eastern and the central areas. By extrapolating the experimental results to the real scale, it was found that the phosphate release fluxes would probably fall within a wide range between 203.43 to 7311.01 kg/day under different levels of hydrodynamic disturbances which considerably affects phosphate release from shallow lakes. This study also has implications for the pollutant management in other shallow lakes., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Urban road traffic network (URTN) plays an important role in city operation, while it is also suffered a lot from the urban flood disasters which caused negative impacts frequently, like traffic congestion, and road collapse. The function loss of URTN not only destroy normal urban life and work order, but also pose a serious threat to people's lives and properties. Therefore, it is urgent to quantitatively explore the flood resilience of URTN. The concept of resilience puts forward new ideas to help solve the problem of urban flooding disasters from a holistic view. Exploring the flood resilience of urban traffic network may help to mitigate urban flooding and improve the urban resilience. This paper developed a flood resilience evaluation model of URTN, which contains 26 indicators based on the 4R theory. A case study was conducted in southern China to validate the model with real data. It evaluated the urban flood resilience of road traffic network with a comparison of before and after reconstruction of the pipeline. The results demonstrated that the flood resilience of URTN is at a relatively low level in the study area, and the limitation of single traditional engineering measure to the flood resilience of URTN. Suggestions such as strengthening the citizen participation and enhancing the complementary capability of multiple engineering measures are proposed to further promote the flood resilience of the URTN., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In this study, spatiotemporal investigations were conducted along five cascade dams in the main channel of the North River of China during 2019 to explore bacterioplankton community indicators of water environments in a fragmented, highly regulated river. Bacterioplankton communities were good bioindicators of temporal variation in river environments, especially when considering the bacterial class level. Specifically, the most dominant bacterial classes (Gammaproteobacteria, Oxyphotobacteria, and Actinobacteria) and sub-dominant bacterial classes (Bacteroidia, Betaproteobacteria, and Acidimicrobiia) exhibited obvious temporal variation. Rainfall, water temperature (WT), water transparency (SD), and pH were all highly associated with temporal variation. In contrast, bacterioplankton indicators of spatial variation were limited to individual dominant bacterial classes for individual study periods, while rainfall, total phosphorus (TP), and pH were also associated with spatial variation. Clustering of bacterioplankton community compositions revealed that temporal differences were much stronger than spatial differences, which is consistent with most environmental parameters exhibiting obvious temporal differences, but minimal spatial differences. A possible reason for these observations could be that river fragmentation caused by cascade dams weakened spatial differences in communities, with WT, rainfall, and river runoff playing key roles in these patterns. In conclusion, bacterioplankton communities were good bioindicators of water environments in the fragmented river ecosystem of this study and their temporal variation was more apparent than their spatial variation., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

In this study, the sedimentary records, sources, and ecological risks of polycyclic aromatic hydrocarbons (PAHs) in Dianchi Lake were analyzed. The concentrations of ΣPAH 16 in the sediments of Dianchi Lake ranged from 368 to 990 ng/g, with an average value of 572 ng/g, peaking in 1988. Economic development, rapid population growth, and rapid growth of coal consumption have a greater impact on the HMW (high molecular weight) PAHs than on the LMW (low molecular weight) PAHs in the sedimentary environment. The results of the diagnostic ratios and PCA (principal component analysis) model show that the main sources of PAHs were coal and biomass combustion, as well as the fossil fuel combustion in individual years. The risk assessment results showed that the PAH concentrations in the sediment were within a safe range. In the past 100 years of sediment pore water, other 2-3 ring LMW PAHs were within a safe range (except for Phe, which reached chronic toxic pollution levels in some years). With an increase in industrialization and urbanization, the burning of fossil fuels such as coal and petroleum has increased, and some of the 4-6 ring HMW PAHs have reached chronic toxicity or even acute toxicity in the sediment pore water., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Both bacterioplankton and eukaryoplankton communities play important roles in the geochemical cycles and energy flows of river ecosystems. However, whether a seasonal change in bacterioplankton and eukaryoplankton communities is synchronous remains unclear. To test the synchronicity and analyze how physical and chemical environmental factors affect these communities, we compared bacterioplankton and eukaryoplankton communities in surface water samples between March (dry season) and June (rainfall season) considering water environmental factors. Our results showed that there was no significant difference in operational taxonomic unit number, Shannon index, and Chao1 index in bacterioplankton and eukaryoplankton communities between March and June. However, principal component analysis showed that the communities were significantly different between the sampling times and sampling sites. Water temperature (WT), oxidation-reduction potential (ORP), water transparency (SD), NO 3 -N, and NH 3 significantly influenced bacterioplankton communities, and WT, SD, ORP, and NH 4 -N significantly influenced eukaryoplankton communities in the river. These results implied that compared with the sampling sites, sampling times more significantly affected the bacterioplankton and eukaryoplankton river communities by influencing WT, ORP, SD, and nitrogen forms., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Excessive use of agricultural chemicals and unreasonable utilization of agricultural wastes have led to severe agricultural non-point source pollution (ANPSP) problems in China. Based on the agricultural pollution loads and pollution control strength, the ecological risk index (ERI) was constructed and was used to explore the spatial-temporal pattern of agricultural ecological risks in China during 1978-2017. The findings indicated that Chinese agricultural ERI was gradually increased from 0.031 to 0.348 in 1978-2017, which has the same phased change characteristics as the succession of agricultural policies. At present, the ecological risk grade of ANPSP was present in the stair-step distribution characteristics of "high in the east and south and low in the west and north" as a whole. Southern China, as the main producing area of aquatic products, had the higher ecological risks. Northeastern China, the Huang-Huai-Hai Area, and the middle and lower reaches of the Yangtze River, as the grain-producing bases, had moderate ecological risks, but Southwestern China and Northwestern China with the poor agricultural production conditions had the lower ecological risks. It evidently showed that the ecological risk problems faced by the high-quality development of Chinese agricultural industrialization are increasingly severe., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Coastal ecosystem is vulnerable to heavy metal contamination. The northern Hangzhou Bay is under intensifying impact of anthropogenic activities. To reveal the heavy metal pollution status in the coastal environment of the Hangzhou Bay, a long-term investigation into the heavy metal contamination during 2011 to 2016 was initiated. Seawater and sediment samples of 25 locations depending on the sewage outlet locations in the northern Hangzhou Bay were collected to analyze the concentrations and temporal and spatial distribution of Cu, Pb, Zn, Cd, Hg, and As. Pollution condition, ecological risk, and potential sources were additionally analyzed. Results show that the annual mean concentrations of Cu, Pb, Zn, Cd, Hg, and As were 2.13-4.59, 0.212-1.480, 7.81-20.34, 0.054-0.279, 0.026-0.090, and 1.08-2.57 μg/L in the seawater, and were 16.34-28.35, 16.25-26.33, 67.32-97.61, 0.084-0.185, 0.029-0.061, and 6.09-14.08 μg/L in the sediments. A decreasing trend in Cu, Pb, Zn, Cd, and Hg concentrations and an increasing trend in As of the seawater were observed. However, in the sediment, the heavy metals demonstrated a rising trend, except for Hg. The single-factor pollution index showed an increasing trend in Cd and As in the seawater, depicting an enhanced pollution of Cd and As, while in the sediments, Cu, Pb, and As were in pollution-free level (average Geo-accumulation index (I geo ) values below 0) in general, and only occasional slight pollution occurred in individual years, e.g., As with 0.403 in 2016. The mean I geo values of Cd ranged from - 0.865 to 0.274 during 2011 to 2016, indicating that the pollution level of Cd was slight, but is likely to increase in the forthcoming years. The level of heavy metal contamination in sediments was low in 2011 (5.853) and 2012 (5.172), and moderate during 2013 to 2016 (in the range of 6.107 to 7.598), while the degree of potential ecological risk was low in the study period, except moderate in 2013 (125.107). The highest contamination degree and potential ecological risk appeared in 2013 (Cd = 7.598; RI = 125.107), while Cd and Hg contributed over 75% of the ecological risk. Overall, the results show low pollution level and low potential ecological risk in the northern Hangzhou Bay; however, more attention should be paid to the potential ecological risk due to Hg and Cd. Graphical abstract Spatial distribution of the heavy metal levels in the sediment of the coastal environment of the northern Hangzhou Bay on a long-term basis.

Sedimentary archives preserved in geomorphic sinks provide records of historical sediment dynamics and its related natural and anthropogenic controls. This study reinterpreted sedimentary processes in Changshou Lake of the Three Gorges Reservoir Area in China by combining a rainfall erosivity index with multiple tracing proxies, and the impacts of natural and anthropogenic drivers on sediment production were also explored. Erosive rainfalls with low frequency and large magnitude in the rainy season contribute to a substantial proportion of annual total rainfall, which thus can be used to infer erosion and sediment yield events. The sedimentary chronology was determined by comparing rainfall erosivity index with depth distribution of 137 Cs and absolute particle size, which revealed annual sedimentation rates ranging from 1.1 to 2.3 cm a -1 . The multi-proxy dating index and variation of sedimentation rate divided the sediment profile into three major periods. The reference period (1956-1982) displays low variability of TOC, TN, trace metal concentrations, and mean sedimentation rate. In the stressed period (1982-1998), industrial and sewerage discharge led to input and deposition of TOC, TN, and trace metals (e.g., Cd, Co, Cu, Cr, and Ni). The highest annual sediment accumulation rate of 2.3 cm a -1 may be ascribed to the 1982 big flood event. In the present period (1998-2013), increased TOC, TN and decreased trace metals in the top layers of the sediment core indicated changes in lake ecology. Fish farming promoted algal growth and primary productivity which caused eutrophication until 2004-2005. The reduced mean sedimentation rate of 1.7 cm a -1 between 1998 and 2004, and thereafter, may be attributed to soil and water conservation and reforestation policies implemented in the Longxi catchment. Human activities such as deforestation, cultural and industrial revolution, and lake eutrophication associated with fish farming since 1989, therefore led to appreciable limnological variations. Overall, the dated sedimentary profile from Changshou Lake displays high consistency with archived historical events and reflects the impact of both natural and anthropogenic controls on sediment production.