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Evaluating the ecological risks of metals and identifying their sources is useful for preventing and controlling heavy metal pollution in water bodies. Four sediment cores (S1~-S4) were collected from the Changhu Reservoir of South China to determine lead (Pb) concentrations and geochemical fractions, as well as the isotopic compositions of core S1. The results show that Pb concentrations increased from the upstream site (S1:173.2 mg kg-1) to the downstream site (S4:313.5 mg kg-1), resulting in a moderate to significant enrichment in the sediments. Sediment Pb in the geochemical fractions followed a decreasing order of residual (F4:54.7%) > reducible (F2: 23.1%) > oxidizable (F3: 16.6%) > acid-soluble fraction (F1: 5.8%). The geoaccumulation index (Igeo) and risk assessment code (RAC) showed that sediments were moderately polluted by Pb in S1 and S2 core, while sediments were moderately to heavily polluted in S3 and S4 core. The ecological risk of Pb in all sediment samples is generally at a low risk level, except for the sediments at a depth of 30-40 cm in the S4 core. Significant correlation between Pb concentration and 206Pb/207Pb ratios suggested possible binary mixing of Pb. In the present study, mining activities, which was the major anthropogenic Pb source base on its isotopic composition, contributed significantly (means: 45.3-77.5%) to sediment Pb. The anthropogenic Pb in sediments is most likely to come from Sphalerite and Galena. [ABSTRACT FROM AUTHOR]

Estuarine‐coastal systems receive pollutants from various sources at an alarming rate. Some systems are extremely susceptible to terrestrial input, as a relatively small amount of pollutant loading induces lasting water quality degradation. The Jiangsu coastal waters (JCWs), located in the southwestern Yellow Sea, are such areas that lack large river discharge but suffer from recurrent eutrophication recently. We hypothesize that the low flushing efficiency in the JCWs largely accounted for the susceptibility to coastal pollution. To test it, transit time (TT) and pollutant flushing rates in the JCWs were estimated under various scenarios using a validated three‐dimensional hydrodynamic model. Results show that TT in many inshore waters of the JCWs and the northern radial sand ridges is >240 days, which are consistent with the observed frequently eutrophic areas. The JCWs are better flushed and thus less eutrophic in summer, as a consequence of the stronger tidal residual coastal circulation. The baroclinic pressure gradient, modulated by the formation and destruction of thermal stratification in offshore waters, poses a dominant control on the seasonal variations of the coastal circulation and flushing rates, while wind effects are secondary. River‐borne pollutants from the Yangtze and Jiangsu local rivers are shown to primarily affect regions south and north of 32.5°N, respectively. Our study interprets the vulnerability of the JCWs to pollutant enrichment from a physical perspective and finds the flushing efficiency to be a good indicator of eutrophication, providing references for environmental managers of local and global estuarine‐coastal systems with recurrent pollution. Plain Language Summary: Some estuarine‐coastal systems are vulnerable to pollution, as a relatively small amount of pollutant loading induces lasting water quality degradation. The Jiangsu coastal waters (JCWs), located in the southwestern Yellow Sea, lack large river discharge but suffer from poor water quality in recent years. In order to understand the reason, this study simulated the tracer dispersal processes in a hydrodynamic model. The model is verified with observational water elevation, tidal currents, temperature, and salinity. It is found that the distribution and duration of pollution can largely be attributed to how fast the pollutants are flushed. Regions with a low flushing rate tend to accumulate nutrients in the JCWs and are observed to be frequently eutrophic. The JCWs are better flushed and thus less eutrophic in summer, as a consequence of the stronger coastal circulation. The summer circulation is primarily controlled by the density‐driven processes. Seasonal warming and cooling of surface offshore waters change seawater density and coastal circulation. Model results also show that the river‐borne pollutants from the Yangtze and Jiangsu local rivers mainly affect regions south and north of 32.5°N, respectively. The study provides pollutant‐control references for environmental managers of local and global coastal systems suffering from recurrent pollution. Key Points: The low flushing efficiency largely accounts for recurrent water quality degradation in the Jiangsu coastal waters (JCWs)The JCWs are better flushed and thus less eutrophic in summer due to the stronger tidal residual coastal circulationThe baroclinic pressure gradient poses a dominant control on the seasonal variations of coastal circulation and pollutant flushing rates [ABSTRACT FROM AUTHOR]

Oceanic absorption of heat generated by greenhouse gas emissions has resulted in warming of the dark ocean (>200 m) that contains a large refractory DOM (RDOM) pool. However, changes in microbially mediated production and degradation dynamics for RDOM components in response to warming of dark marginal basins remain unclear. Herein, we integrated data from the dark South China, Mediterranean and Japan Seas (temperature range: 0.09–15.1°C) to demonstrate that in situ production efficiency of two ubiquitous humic‐like fluorophores increased at higher dark ocean temperature, whereas chromophores at a wavelength of 325 nm (aCDOM(325)) changed from production to degradation at higher temperature. Increased oxygen consumption and a reduction of labile substrates in future warmer dark ocean environments may initiate the final degradation of some semi‐refractory components, thereby increasing the recalcitrance of RDOM, but decreasing the DOM inventory in dark basins and creating a positive feedback to rising atmospheric CO2. Plain Language Summary: Marine refractory dissolved organic matter (RDOM) in the dark ocean is primarily formed during heterotrophic degradation of labile organic matter, which has a pronounced sensitivity to temperature variation. Since the 1960s, the global dark ocean has exhibited an accelerated warming with a discernable temperature increase. Thus, determining the importance of temperature on microbial regulation of the oceanic RDOM pool is of great significance. This study utilized the ocean interior of the marginal South China, Mediterranean and Japan Seas as natural basin‐scale enclosed incubators along with optical DOM characterization methods to reveal a production‐degradation reaction series for RDOM components. A decrease in the DOM inventory by enhanced microbial mineralization (producing CO2) in a warmer dark ocean may create a positive feedback in response to global climate change. Key Points: Faster turnover for optical components of dissolved organic matter (DOM) was observed in dark marginal basins than in the open oceanIn situ production efficiency of two ubiquitous humic‐like fluorophores increased at higher dark ocean temperaturesAn increase of DOM recalcitrance and decrease of the bulk dissolved organic carbon pool may occur due to a future warming of dark basins [ABSTRACT FROM AUTHOR]

The dynamics of total phosphorus (TP) in 18 strategic reservoirs of the high-density reservoir network of the Brazilian semiarid was evaluated during the wet and dry periods for the past 12 years. Seasonal overlying concentrations presented no significant differences for about 90% of the reservoirs (p>0.05). This was attributed to a trade-off between the hydrological/limnological processes occurring in the two seasons. Then, a transient complete-mix mass balance model was applied with particular adaptations for the tropical semiarid reservoirs to estimate the TP load for each season. Because of the relatively well-mixed conditions and high hypolimnetic dissolved oxygen concentrations during the wet season, the wet load was assumed to represent the external TP load. On the other hand, because of the absence of reservoir inflow during the dry season, phosphorus release under anoxic sediment conditions and wind-induced resuspension under shallow water depths, the dry load was assumed to reflect the internal TP load. The maximum external loads were related to peak inflows, notably after drought periods. Consistently, the largest internal loads were obtained during the drought periods, when the reservoirs were shallower and more prone to phosphorus release and resuspension. By comparing the impact of the two input load types, the wet period load was predominant in 72% of the reservoirs. The areal phosphorus loads ranged from 0.66 to 7.29 gP m 2 year -1 , which were consistent with the literature, despite the very high density of reservoirs. Finally, power-law curves including data for all studied reservoirs were adjusted between the dry period load and volume, dry and wet period loads, wet period load and inflow, and total load and catchment area, resulting in satisfactory R 2 (0.84-0.98)., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Residence times and connectivity are computed for 12 subregions in an urban man-made lake in China using a high-resolution tracer-transport model. The renewal timescales are explicitly defined and computed for two groups of four freshwater inflow scenarios related to water diversion projects. First, the timescale values are computed and compared using different computational criteria for the upper limit of integration in the residence time equation. The sensitivity analysis suggests that a calculation time of 300 days is necessary to satisfy the relative error (0.001) and 5 % cutoff value criteria. Secondly, the residence times can range from 1.5 to 102 and 1.0 to 66 days under low and high flow conditions, respectively. Water in the inner lake would reside in the lake for less than 66 days prior to exiting the region of interest. The timescale values can be applied to impact studies that investigate the extent of sudden water pollution events that initially affect a subdomain of a lake. Finally, the lacustrine residence times are decomposed into the different subregion residence times, resulting in a connectivity matrix. This matrix can illustrate preferential connections among the individual subregions and reveal hidden patterns relating to local hydrodynamics in the lake. [ABSTRACT FROM AUTHOR]

Most biochemical processes and associated water quality in lakes depends on their flushing abilities. The main objective of this study was to investigate the transport time scale in a large floodplain lake, Poyang Lake (China). A 2D hydrodynamic model (MIKE 21) was combined with dye tracer simulations to determine residence and travel times of the lake for various water level variation periods. The results indicate that Poyang Lake exhibits strong but spatially heterogeneous residence times that vary with its highly seasonal water level dynamics. Generally, the average residence times are less than 10 days along the lake's main flow channels due to the prevailing northward flow pattern; whereas approximately 30 days were estimated during high water level conditions in the summer. The local topographically controlled flow patterns substantially increase the residence time in some bays with high spatial values of six months to one year during all water level variation periods. Depending on changes in the water level regime, the travel times from the pollution sources to the lake outlet during the high and falling water level periods (up to 32 days) are four times greater than those under the rising and low water level periods (approximately seven days). [ABSTRACT FROM AUTHOR]

The rationale of waterfront planning is an important issue for construction and usage. However, little attention had been given to the prediction of implementation effects and planning optimization using computational fluid mechanics. This resulted in many inharmonious problems after implementation. In this paper, the Environmental Fluid Dynamics Computer Code (EFDC) was applied and, for the first time, demonstrated successful waterfront planning. The quantitative prediction of the implementation effects and an improvement in planning feasibility were achieved. Using the Tianjin Harbor Economic Zone as an example, the planning was evaluated with regard to function, geometry, landscape, vegetation growth and water exchange. Waterfront plan was optimized based on the simulated results. Numerical results showed that the optimal plan met the planning requirements and was feasible. The present study proposed a predictive method for planning selection and optimization. [ABSTRACT FROM AUTHOR]

Dam construction causes the accumulation of phosphorus in the sediments of reservoirs and increases the release rate of internal phosphorus (P) loading. This study investigated the longitudinal variability of phosphorus fractions in sediments and the relationship between the contents of phosphorus fractions and its influencing factors of the Manwan Reservoir, Lancang River, Yunnan Province, China. Five sedimentary phosphorus fractions were quantified separately: loosely bound P (ex-P); reductant soluble P (BD-P); metal oxide-bound P (NaOH-P); calcium-bound P (HCl-P), and residual-P. The results showed that the total phosphorus contents ranged from 623 to 899 µg/g and were correlated positively with iron content in the sediments of the reservoir. The rank order of P fractions in sediments of the mainstream was HCl-P>NaOH-P>residual-P>BD-P>ex-P, while it was residual-P>HCl-P>NaOH-P>BD-P>ex-P in those of the tributaries. The contents of bio-available phosphorus in the tributaries, including ex-P, BD-P and NaOH-P, were significantly lower than those in the mainstream. The contents of ex-P, BD-P, NaOH-P showed a similar increasing trend from the tail to the head of the Manwan Reservoir, which contributed to the relatively higher content of bio-available phosphorus, and represents a high bio-available phosphorus releasing risk within a distance of 10 km from Manwan Dam. Correlation and redundancy analyses showed that distance to Manwan Dam and the silt/clay fraction of sediments were related closely to the spatial variation of bio-available phosphorus. [ABSTRACT FROM AUTHOR]

This study investigated temporal heavy metal characteristics over the past 20 years and the spatial variation of heavy metal characteristics at the Manwan Reservoir tail, center, and head in the Lancang River, Yunnan Province, China. The following heavy metals were selected for analysis: Hg, Cd, Pb, Cu, Zn, As, Cr, Fe, and Mn. Multivariate statistical methods, including principal component analysis (PCA) and the Pearson correlation matrix were used to distinguish the main pollution factors and sources before and after dam construction. The results indicate that the average annual values of heavy metals were far lower than the recommended values of the surface water quality standards in China with the exception of Hg. The concentration of metals showed considerable variation by season, where higher levels of metals generally occurred in high flow periods. The results from PCA show that three significant components were extracted, explaining 76.25% of the total variance. The ANOVA results indicate that Pb, Fe, Mn, and Cr had significant spatial variation ( P < 0.05) at the reservoir tail, center and head. The enrichment factor (EF) used to compare the accumulation effect of heavy metals indicated that there was no enrichment (EF < 1) of heavy metals with the exception of Mn, which showed minor enrichment (1 < EF < 3) between the reservoir center and head. The spatiotemporal variation and the accumulation effects of water heavy metals were not distinct due to the construction of the Manwan Reservoir. [ABSTRACT FROM AUTHOR]

The semi-enclosed bays impacted by heavy anthropogenic activities have weak water exchange and purification capacities. Most of the sea bays have suffered severe eutrophication, water quality deterioration, ecosystem degradation and other problems. Although many countries and local governments have carried out corresponding environmental protection actions, the evaluation of their effectiveness still requires monitoring technology and data support for long-term water environment change. In this study, we take Yueqing Bay, the fourth largest bay in China, as a case to study the satellite-based water quality monitoring and variation analysis. We established a nutrient retrieval model for Yueqing Bay to produce a long-term series of nutrient concentration products in Yueqing Bay from 2013 to 2020, based on Landsat remote sensing images and long-term observation data, combined with support vector machine learning and water temperature and satellite spectra as input parameters, and then we analyzed its spatiotemporal variations and driving factors. In general, nutrient concentrations in the western part of the bay were higher than those in the eastern part. Levels of dissolved inorganic nitrogen (DIN) were lower in summer than in spring and winter, and reactive phosphate (PO4-P) levels were lower in summer and higher in autumn. In terms of natural factors, physical effects (e.g., seasonal variations in flow field) and biological effects (e.g., seasonal differences in the intensity of plankton photosynthesis) were the main causes of seasonal differences in nutrient concentration in Yueqing Bay. Nutrient concentration generally increased from 2013 to 2015 but decreased slightly after 2015. Over the past decade, the economy and industry of Yueqing Bay basin have developed rapidly. Wastewater resulting from anthropogenic production and consumption was transported via streams into Yueqing Bay, leading to the continuous increase in nutrient concentrations (the variation rates: a D I N > 0 ,   a P O 4 − P > 0 ), which directly or indirectly caused high nutrient concentrations in some areas of the bay (e.g., Southwest Shoal at the mouth of Yueqing Bay). After 2015, the various ecological remediation policies adopted by cities around Yueqing Bay have mitigated, to some extent, the increasing nutrient concentration trends (the variation rates: a D I N < 0 ,   a P O 4 − P < 0 ), but not significantly (P > 0.1). The environmental restoration of Yueqing Bay also requires continuous and long-term ecological protection and restoration work to be effective. This research can provide a reference for ecological environment monitoring and remote sensing data application for similar semi-enclosed bays, and support the sustainable development of the bay. [ABSTRACT FROM AUTHOR]

The Poyang water system in Jiangxi Province, China, is important for floodwater storage, diversity maintenance, and the economy of the Poyang Lake watershed. In recent years, pollution has destroyed the ecosystem and impacted human health and the related economy. The water quality of the Poyang Lake watershed and the impact of human interference must be assessed. Conventional analysis and high-throughput sequencing were used to evaluate the structure of both zooplankton and fungi in six sub-lakes of the Poyang Lake watershed under different anthropogenic influences. The sub-lakes included were Dahuchi Lake (in natural preserve, DHC), Shahu Lake (in natural reserve, SH), Nanhu Lake (out of natural preserve, NH), Zhelinhu Lake (artificial reservoir, ZLH), Sixiahu Lake (agricultural lake artificially isolated from Poyang Lake, SXH), and Qianhu Lake (urban lake, QH). The densities and biomass of the zooplankton in DHC, SH, NH were higher compared with those in SXH, ZLH and QH (p < 0.05). Zooplankton distribution of SXH was the most strongly associated with total nitrogen (TN), total phosphorus (TP) and chlorophyll a (Chl a), while QH was highly associated with pH, conductivity (Cond), and water temperature (WT). For fungal diversity, a large number of beneficial fungi, Basidiomycota (phylum level) and Massarina (genus level) were obtained from DHC (55.3% and 27.5%, respectively), SH (54.4% and 28.9%, respectively), and NH (48.6% and 1.4%, respectively), while a large number of pathogenic Chytridiomycota (at phylum level) were identified from SXH (21.0%), ZLH (5.5%), and QH (7.5%). Manmade pollutants have impacted the natural hydrology and water quality and promoted variation between the zooplankton and fungi in the six sub-lakes, reducing the relative abundance of beneficial fungi and increasing the number of pathogens in the environment, which threatens human health and economic production. Understanding the diversity among the zooplankton and fungi in the six sub-lakes of the Poyang Lake watershed may help guide future water management practices. [ABSTRACT FROM AUTHOR]

Pyrethroid insecticides are among urban parks' most widely used and harmful insecticides. The advanced prediction method is the key to studying the pollution and diffusion risk of plant conservation insecticides in parks. A two-dimensional advection-dispersion model was established for the North Lake of Cloud Mountain Park in the subhumid area of Hebei Province. The temporal and spatial distribution of lambda-cyhalothrin pollution required by plant growth in artificial lakes under different rainfall intensities and the time of water renewal after rainfall was simulated and predicted. According to the model efficiency (E: 0.98), mean absolute error (MAE: 0.016-0.064 cm), and root mean square error (RMSE: 0.014-0.041 cm), the prediction results showed that the model fits well. The results showed that the concentration of lambda-cyhalothrin in the artificial lake was positively correlated with the increase in rainfall intensity. Under the three scenarios of moderate rain, heavy rain, and rainstorm, the variation of total pollutants into the lake over time conformed to the first-order dynamic equation (R 2 ＞0.97), and the cumulative rates were 0.013 min -1 , 0.019 min -1 and 0.022 min -1 , respectively. Under light rain, the accumulation rate of lambda-cyhalothrin showed a double-linear relationship, which was in accordance with the second-order kinetic equation (R 2 ＞0.97). The rapid accumulation rate of early-stage rainfall was 0.0024 min -1 , and the slow accumulation rate of late-stage rainfall was 0.0019 min -1 . The human health risk assessment predicted by the simulation was lower than the hazard value (R tg n (a-1): 9.65 E -11 a-1). However, the potential risk value to aquatic species was higher (RQ: 0.33-23.05). In addition, the increase in rainfall intensity has no significant effect on the acceleration of water renewal time. The two-dimensional dispersion model of pollutants driven by water dynamics provided relevant examples for evaluating the impact of runoff on pesticide scour in parks and supplied scientific support for improving the management of artificial lakes in urban parks.-10 a-1). However, the potential risk value to aquatic species was higher (RQ: 0.33-23.05). In addition, the increase in rainfall intensity has no significant effect on the acceleration of water renewal time. The two-dimensional dispersion model of pollutants driven by water dynamics provided relevant examples for evaluating the impact of runoff on pesticide scour in parks and supplied scientific support for improving the management of artificial lakes in urban parks., 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 © 2023 Elsevier Ltd. All rights reserved.)