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Lake Taihu is an important drinking water source for cities in the Yangtze River Delta region, while the dramatic fluctuation in turbidity has caused severe problems for local waterwork management. The effects of sediment resuspension and migration on turbidity of water intake in a waterworks located in the south of Lake Taihu are studied. Because the sediment behavior induced by wind disturbance was believed to be the main factor for the matter, the effect of wind field on the hydrodynamics and sediment distribution of Lake Taihu was conducted based on a wind-driven numerical model. The obtained results indicate that wind direction was more influential on the structure of flow and wave fields, while wind speed contributed more to the field intensity. The suspended sediment concentration (SSC) of water intake area was most sensitive to onshore winds, which led to significant increase in suspended sediment concentration at 3 m/s, while for alongshore winds, the incipient speed was 4 m/s, and offshore winds were less influential. In addition, the suspended sediment of the water intake area was primarily migrated from other erosion regions rather than local suspended particles. A 7-h lag was found between SSC and the measured turbidity confirmed the lag effect of wind disturbance on turbidity change. The high consistency between the 2 series demonstrated the potential of this method to turbidity prediction when combined with the weather forecast technique., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Resuspended sediment is an important carrier of underwater material circulation, and bed shear stress is usually considered to be closely related to sediment resuspension. To analyze the resuspension dynamics in severely eutrophic Lake Chaohu, China, three fixed stations were set up to collect wave, current, and suspended sediment concentrate (SSC) data under windy weather, and two significant sediment resuspension events were recorded. Based on the Gaussian-shaped spectrum characteristics of waves in Lake Chaohu, the wave orbital velocity was estimated by using the wave parameter method. The selection of the general wave spectrum is important for the accurate estimation of wave orbital velocity. The results of the simple linear wave method were very similar to those of the wave parameter method with a Gaussian-shaped spectrum in Lake Chaohu. The total bed shear stress combining waves and currents during the observation period was calculated, and most of it was contributed by wind-driven waves. The bed material of Lake Chaohu has silt-enriched and weak cohesive features, and an examination of critical shear stress showed that the modified Shields curve method was still applicable to Lake Chaohu. When a sediment resuspension event occurred, the vertical gradient of SSC increased significantly, and the peak SSC value depended on the peak value of bed shear stress. As a predictor, bed shear stress only showed a good linear relationship during sediment resuspension events. At other times, the prediction of SSC using bed shear stress may be biased, especially at the time after a significant sediment resuspension event., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Capturing precipitation-based episodes is a longstanding issue for estimating tributary loads; however, wind-driven resuspension in Lake Huron creates similar uncertainties in its estimated load to Lake Erie. Recent suggestions that the phosphorus load from Lake Huron is underestimated because sampling frequencies miss contributions from resuspension events are speculative because they did not include direct load measurements, address all resuspension regions, or assess the potential bioavailability of the load. We address these shortcomings by evaluating Lake Huron's nearshore regions, characterizing the biological availability of the load, and providing direct comparisons of load estimates with and without the resuspended load. We show that total phosphorus concentrations in Lake Huron and the St. Clair River are higher during resuspension events and that bioavailability of that material is comparable to that reported elsewhere. New load estimates, based on continuous turbidity measurements converted to phosphorus through P-turbidity relationships, were almost 90% higher than traditional load estimates, providing empirical evidence for the significantly underestimated previous load. This confirmation is important because if the Lake Huron load is not decreased, reductions from other sources would be needed to meet the overall reduction targets set by the binational Great Lakes Water Quality Agreement.

Wind-induced sediment resuspension in shallow lakes may enhance nutrient availability while reducing light availability for phytoplankton growth, thereby affecting the entire food-web. Lake restoration projects that reduce wind-induced resuspension are expected to enhance trophic transfer efficiencies, thereby improving food-web structure and functioning. Yet, reduced resuspension may also lead to lower nutrient concentrations in the water column, promote benthic algae development, reduce phytoplankton biomass production and thereby reduce secondary production by zooplankton. Lake Markermeer is a shallow delta lake in The Netherlands subject to wind-induced sediment resuspension. Restoration project Marker Wadden consists of newly built islands aiming to reduce sediment resuspension and promote higher trophic levels. Here, we tested the effects of reduced sediment resuspension on phytoplankton biomass build-up, benthic algae development, and zooplankton abundances at different temperatures in a 14-day indoor microcosm experiment. We used Marker Wadden sediment with three resuspension intensities combined with three temperatures, to also test effects of higher temperatures in shallow sheltered waters. Reduced sediment resuspension decreased nutrient concentrations and phytoplankton biomass build-up, while increasing light availability and enhancing benthic algae biomass development. Reduced sediment resuspension furthermore increased zooplankton biomass. Enhanced sediment resuspension and higher temperatures synergistically interacted, maintaining a high level of inorganic suspended solids. Our experimental results are in line with long-term seasonal observations from Lake Markermeer. Our findings demonstrate that for shallow lakes suffering from wind effects, measures such as Marker Wadden aimed at reducing sediment resuspension can be effective in restoring secondary production and supporting higher trophic levels., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2021. Published by Elsevier B.V.)

Environmental sediment dredging is one of the most common methods for the remediation of contaminated sediments in lakes; however, debate continues as to whether the effectiveness of dredging methods contributes to this phenomenon. To determine sediment resuspension and nutrient release following dredging with a variety of dredging methods, four dredging treatments at wind speeds of 0-5.2 m/s were simulated in this study, namely suction dredging (SD), grab dredging (GD), ideal dredging with no residual sediments (ID), and non-dredging (ND). Field sediments from suction and grab dredging areas (including post-dredged and non-dredged sediments) of Lake Taihu were used to assess the release abilities of soluble reactive phosphorus (SRP) and ammonia nitrogen (NH 4 -N) from the sediment-water interface. The effects of residual sediments on nutrient concentrations in water were also evaluated. The results reveal that inhibition of resuspension of particulate matter and nutrients released through sediment dredging decreases with increasing levels of residual sediment. Total suspended particulate matter content in the mean water columns of ID, SD, and GD under wind-induced disturbance (1.7-5.2 m/s) decreased by 67.5%, 56.8%, and 44.3%, respectively; total nitrogen and total phosphorus in ID (SD) treatments were 19.8% (12.9%) and 24.5% (11.2%) lower than that in ND treatment. However, there were ~ 1.6 and 1.5 times higher SRP and NH + -N in the GD treatment compared with the ND treatment at the end of the resuspension experiment (0 m/s). A significant increase in the SRP and NH 4 -N release rates at the sediment-water interface was also observed in field sediments from a grab dredging area, indicating that GD may pose a short-term risk of nutrient release to the water body. Hence, dredging methods with less residual sediments both during and after dredging improves the dredging quality.+ -N in the GD treatment compared with the ND treatment at the end of the resuspension experiment (0 m/s). A significant increase in the SRP and NH 4 + -N release rates at the sediment-water interface was also observed in field sediments from a grab dredging area, indicating that GD may pose a short-term risk of nutrient release to the water body. Hence, dredging methods with less residual sediments both during and after dredging improves the dredging quality.

Sediment resuspension induces endogenous nutrient release in shallow lakes, which has been demonstrated to be associated with eutrophication. In addition to natural wind-driven resuspension, navigable shallow lakes (such as Lake Taihu, China) also experience resuspension from human activities, such as ship waves. Both processes determine the intensity, frequency, and duration of sediment resuspension, and may consequently affect the pattern of cyanobacteria blooms in the lake. In this study, acoustic Doppler Velocimeter (ADV), Optical Backscatter Sensor (OBS), and temperature wave tide gauge (instrument model :RBR duo TD|wave) were placed in an observation platform in the lake to obtain high-frequency flow velocities, suspended sediment concentration (SSC), and wave parameters before, during, and after a cargo ship passed by. We found that the ship wave disturbance intensity is greatly influenced by the draft depth. The movement generated by ship disturbance is primarily horizontal rather than vertical. Compared with the wind-induced wave, the disturbance caused by the ship waves has a high intensity, short duration, and narrow range of influence. The maximum total shear stress under ship disturbance can reach 9~90 times the critical shear stress under a natural state. Therefore, the effect of ship waves on sediment resuspension near the channel of Lake Taihu is much greater than that of wind-induced waves. These findings represent an important step towards understanding the quantitative relationship between ship wave disturbance and sediment resuspension, and lay the foundation for future research in order to understand and control the eutrophication of shallow lakes.

Sediment resuspension is one of the main factors impacting the ecological restoration of shallow eutrophic lakes, but the mechanisms connecting suspended particles and algal growth have not been clarified. Our research presents an innovative approach based on P reallocation among particles with various sizes, considering the changes in redox and pH conditions from the sediments to the overlying water during resuspension. A lab-scale experiment was conducted to simulate P reallocation in particles during sediment resuspension by periodically dosing the system with P and/or organic carbon. The sediments were sampled and sieved into five particle size groups, namely, 50-150 μm, 30-50 μm, 10-30 μm, 5-10 μm and <5 μm, and their P fractions during the operation were analyzed. The bioavailable P associated with aluminum (Al) and iron (Fe) (hydr)oxides showed exponential enrichment as the median grain size of particles decreased, with 54% of the added P adsorbed by fine particles of <10 μm (5-10 μm and <5 μm). Furthermore, a bioassay of algae growth potential (Microcystis aeruginosa sp.), along with P adsorption isotherms, was conducted to test the ability of the different size-resolved particles to supply P for algae growth. The fine particles of <10 μm supplied more P to algae under elevated pH values than did the coarse particles (>10 μm). The restoration of shallow eutrophic lakes faces great challenges due to the connection mechanisms between sediments and algae, as revealed by this research., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Dissolved phosphate (P i ) can be released during resuspended sediments exposed to sunlight. However, the significance of this phenomenon in the process of eutrophication is not clear. In this study, the behavior of photo-induced P i release during sediment resuspension in shallow lakes with the different trophic states was investigated. The amount of photo-induced P i release in the sediment resuspension from Lake Liangzi, Lake Dong, Lake Tangxun and Lake Longyang in China was 0.013, 0.019, 0.032, and 0.048 mg/L, respectively, and increased as the trophic states of the lakes increased. The results of phosphorus speciation analysis showed that the phosphate monoester in the particulate phosphorus is the organic phosphorus species participated in the photochemical reaction. The steady-state concentration of hydroxyl radical (OH) in the sediment resuspension also increased along with the trophic states of lakes increased and dissolved organic matter (DOM), nitrate, and Fe 3+ presented in sediment resuspension were the main photosensitizers for OH production. All these results indicate that the increase of trophic states of lakes leads to the accumulation of organic phosphorus and OH, resulting in more dissolved phosphate photo-released, which accelerate the eutrophication process in a form of positive feedback., Competing Interests: Declaration of competing interest The authors declared that they have no conflicts of interest to this work., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Intermittent turbulent bursts have great impacts on sediment resuspension in coastal regions, tidal estuaries, and lakes. In this study, the role of turbulence structure on sediment resuspension was examined at Meiliang Bay of Lake Taihu, the third largest freshwater lake in China. The instantaneous three-dimensional velocity and suspended sediment concentrations were synchronously recorded by Acoustic Doppler Velocimetry (ADV) and Optical Backscatter Sensor (OBS) placed close to the lakebed. Statistical and quadrant analyses results revealed that the coherent structure contributed significantly to sediment particle entrainment. The intermittent burst events (dominant ejection and sweep) were the main energy source for sediment resuspension processes. 99.2% of turbulent sediment fluxes were triggered by ejection and sweep events, whereas the contributions coming from the outward interactions and inward interactions were relatively small. The large-amplitude burst events in the coherent structure dominated the influence on the sediment diffusion. Additionally, it was found that instantaneous sediment particle entrainment occurred earlier than the mean critical shear stress, which was induced by the stochastic nature of turbulence. The amount of sediment flux considering the turbulence characteristics was one or two larger magnitudes than the flux amount assessed by the time-averaged flow field, which indicated the critical shear stress approach might underestimate the sediment resuspension. Therefore, the influence of turbulence performance on sediment entrainment shall be seriously considered when evaluating sediment flux and internal nutrient loads in Lake Taihu.

In this work, the distribution of organic phosphorus (P o ) species in sediment profiles of five shallow lakes was analyzed and its effect on the photo-release of dissolved phosphate (P i ) was investigated during sediment resuspension under simulated sunlight irradiation. The results show that P o was highly enriched in the surface sediment and gradually decreased as sediment depths increased: 33.10 ± 2.55-96.71 ± 7.60 mg/kg, 33.55 ± 2.34-142.86 ± 5.73 mg/kg, 57.50 ± 3.46-149.68 ± 7.67 mg/kg, 55.18 ± 4.67-168.73 ± 8.31 mg/kg, 98.75 ± 7.56-275.74 ± 10.70 mg/kg for Lake Hou, Lake Tuan, Lake Tangling, Lake Guozheng and Lake Miao, respectively. The photo-release amount of dissolved P i in the resuspension composed of surface sediments was also higher than that of deep sediment during sediment resuspension under the simulated sunlight irradiation for 9 h. The potential reasons for these results are: (1) difference in morphology and composition of sediments at different depths: the mean particle size of sediment decreased first and then increased as sediment depths increased; (2) difference in composition of P o species with depths in the sediment profiles: more photolytic P o species existed in surface sediments confirmed by sequential extraction and 31 P NMR analysis; and (3) more OH production in the resuspension composed of surface sediment under simulated sunlight irradiation, which directly influence the photo-release of dissolved P i from photodegradation of organic phosphorus. All of these results indicate that the distribution of organic phosphorus species in the sediment profiles plays an important role in P cycle and its photodegradation during sediment resuspension may be one of the potential pathways for phosphate supplement in shallow lakes., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Wind-induced hydrodynamics are important forcing mechanisms of sediment resuspension in lakes. However, the relative contributions of wind-induced waves and currents on sediment resuspension during a wind event remain unclear. This study used high-frequency sensors to investigate the effects of wind waves, lake currents, and shear stress on sediment resuspension under different wind conditions (10 September to 17 October 2017) in Lake Taihu (China). Measurements showed that wind speed varied from 0.3 to 11.5 m/s, wave height varied from 0.035 to 0.46 m, lake current speed ranged from 0.001 to 0.39 m/s, and turbidity changed from 36.5 to 158.7 NTU. Sediment resuspension resulted primarily from wave- and current-induced shear stresses. Calculation showed these quantities varied in the range 0.045-0.338 and 0.002-0.127 N/m 2 , respectively. Total shear stress showed positive correlation with turbidity. Wave-induced shear stress contributed more than 60% of the total. Waves and currents have different responses to wind. During periods of increasing turbidity, the percentage of wave-induced shear stress was initially high (> 85%) before decreasing with the development of the current. During periods of decreasing turbidity, the percentage of wave-derived shear stress declined initially before increasing with the decrease of current speed. The results showed a clear process regarding the contributions of shear stress from waves and currents during different stages of hydrodynamic development, which could be used to describe sediment resuspension in large shallow lakes that would help in the development of high-efficiency sediment resuspension models.

The disturbance of the water-sediment interface by wind-driven currents and waves plays a critical role in sediment resuspension and internal nutrient release in large, shallow lakes. This study analyzed the effects of the interactions between wind-induced currents an1d waves on the driving mechanism of sediment resuspension in Lake Taihu, the third largest freshwater lake in China, using acoustic and optic techniques to collect long-term, high-frequency, synchronous in situ measurements of wind, currents, waves, and suspended solid concentrations (SSCs). The results suggested that water turbidity started to increase at wind speeds of approximately 4 m/s and significantly increased when wind speeds exceeded 6 m/s. In most cases, wind-induced waves were the main energy source for changes in turbidity. Wave-generated shear stress contributed more than 95% to sediment resuspension and that only in weak wind conditions (<4 m/s) did the lake bottom shear stresses generated by currents and waves contributed equally. The relationship between SSC and bottom shear stress generated by wave was established by fitting the observed results. The processes of sediment dynamics were divided into four stages (A through D) according to three shear-stress thresholds. In stage A, SSC remained stable (about 45 mg/L) and τ w was less than 0.02 N/m 2 . In stage B, the sediment bed was starting to be activated (SSC 45∼60 mg/L) and τ w was in the range of 0.02∼0.07 N/m 2 . In stage C, a medium amount of sediment was suspended (SSC 60∼150 mg/L) and τ w ranged from 0.07 to 0.3 N/m 2 . In stage D, large amount of sediment was suspended (SSC 150∼300 mg/L) and τ w was larger than 0.3 N/m 2 . The findings of this paper reveal the driving mechanism of sediment resuspension, which may further help to evaluate internal nutrient release in large shallow Lake Taihu.

The objective of this study was to investigate the impact of sediment resuspension and phosphorus (P) release on phytoplankton growth under different kinds of wind-wave disturbance conditions in the large and shallow eutrophic Lake Taihu in China. Short-term strong wind (STSW) conditions, long-term moderate wind (LTMW) conditions, and static/calm conditions were investigated. To address this objective, we (1) monitored changes in surface water P composition during field-based sediment resuspension caused by STSW conditions in Lake Taihu, and also conducted (2) a series of laboratory-based sediment resuspension experiments to simulate LTMW and calm conditions. The results showed that under both strong and moderate wind-wave conditions, suspended solids (SS) and total phosphorus (TP) in the water column increased significantly, but total dissolved phosphorus (TDP) and soluble reactive phosphorus (SRP) remained low throughout the experiments, indicating that the P released from sediments mainly existed in particulate forms. In STSW conditions, alkaline phosphatase activity (APA) and enzymatically hydrolysable phosphorus (EHP) increased rapidly, with the peak value occurring following the peak value of wind speed for 1-2 days, and then rapidly decreased after the wind stopped. Under LTMW conditions, APA and EHP increased steadily, and by the end of the laboratory experiments, APA increased by 11 times and EHP increased by 5 times. Chlorophyll a (Chl-a) in LTMW conditions increased significantly, but remained low under STSW conditions, demonstrating that the former type of sediment P release promoted phytoplankton growth more effectively, and the latter type did not. Despite the fact that STSW conditions resulted in the release of more TP, TP settled to the bottom rapidly with SS after the wind stopped, and did not promote algal growth. Under LTMW conditions, suspended particulate P was hydrolyzed to SRP by phosphatase and promoted algae growth. Algal growth in turn secreted more phosphatase and accelerated particulate P regeneration, which may be the main mechanism of sediment bio-available P release that promotes phytoplankton growth in shallow lakes.

In lakes with a large surface area to watershed ratio 137 Cs delivery is primarily by direct atmospheric fallout to the lake surface, where its activity in the sediments has been used to estimate the exposure to organisms and sediment mass deposition rates. Comparison of 137 Cs in the historical atmospheric fallout record with 137 Cs activity profiles in sediment cores reveals that although the general features of a maxima in the fallout deposition can be matched to activity peaks in the core, the general shape of the 137 Cs profile is not an exact replica of the fallout history. Instead, the sediment reflects post-depositional processes such as resuspension, bioturbation, partitioning of 137 Cs between the sediment solids and the pore fluids, and molecular diffusion of 137 Cs through the pore fluids. Presented here is a model that couples these processes to a system time averaging (STA) model that accounts for the time history of 137 Cs fallout and the particle residence time in the water column or in the 'active' surface sediment subject to resuspension. Sediment profiles are examined by comparing reasonable ranges of each of the coefficients of each of these major processes and by applying the model to cores collected from two large, shallow lakes, Lake Erie (USA/Canada) and Lake Winnipeg (Canada). The results indicate that the STA model with molecular diffusion and sediment resuspension best describes the data from these large, shallow lakes., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Endogenous phosphorus release from sediments is a major cause of eutrophication in water bodies. To investigate the endogenous phosphorus morphological features and migration patterns in lakes under the influence of agricultural irrigation areas, we analyzed the changes of polymorphic phosphorus content in lake sediments under irrigation withdrawal conditions based on field sampling tests and sediment phosphorus release dynamics simulation experiments and used the diffusive flux method to determine the flux of phosphorus release from the sediment-water interface (SWI). The results showed that: (1) Data from encrypted sampling during the receding period revealed total phosphorus (TP) of lake water decreased from 0.11 mg/L to 0.05 mg/L, and TP of sediment increased from 723.53 mg/kg to 955.89 mg/kg. (2) The order of polymorphic phosphorus content of sediments at the lake inlet before the irrigation period was Fe-Al bound phosphorus (NaOH-nrP) > insoluble phosphorus > Fe-Al oxide bound phosphorus (NaOH-rP) > Calcium bound phosphorus (Ca-P) > Fe-Mn chelated phosphorus (BD-P) > active phosphorus. Interconversion between sedimentary polymorphic phosphorus is more drastic after the irrigation period. (3) The phosphorus forms extracted from sediments were ranked as insoluble phosphorus > NaOH-nrP > NaOH-rP > active phosphorus > Ca-P > BD-P. Insoluble phosphorus is the predominant form of phosphorus in sediments. (4) The TP exchange fluxes between the SWI by the diffusive flux method were 0.30 mg/(m2·h) and -0.33 mg/(m2·h) respectively. Receding water conditions promote sediment adsorption of TP from overlying water. The research findings establish a theoretical foundation for endogenous phosphorus from lake sediments in agricultural irrigation areas., Competing Interests: Declarations. Conflict of 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., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Modified clay-based solid-phase phosphorous (P) sorbents are increasingly used as lake geoengineering materials for lake eutrophication control. However, some still dispute the feasibility of using these materials to control internal P loading from shallow eutrophic lakes. The lack of information about P behavior while undergoing frequent sediment resuspension greatly inhibits the modified minerals' use. In this study, a sediment resuspension generating system was used to simulate the effect of both moderate winds (5.1 m/s) and strong winds (8.7 m/s) on the stability of sediment treated by two geoengineering materials, Phoslock ® (a lanthanum modified bentonite) and thermally-treated calcium-rich attapulgite. This study also presents an analysis of the P dynamics across the sediment-water interface of two shallow eutrophic lakes. In addition, the effect of wind velocity on P forms and P supply from the treated sediment were studied using chemical extraction and diffusive gradients in thin films (DGT) technique, respectively. Results showed that adding geoengineering materials can enhance the stability of surface sediment and reduce the erosion depth caused by wind accordingly. All treatments can effectively reduce soluble reactive phosphorus (SRP) concentration in overlying water when sediment is capped with thermally-treated calcium-rich attapulgite, which performs better than sediment mixed with modified attapulgite but not as well as sediment treated with Phoslock ® . However, their efficiency decreased with the increase in occurrences of sediment resuspension. The addition of the selected geoengineering materials effectively reduced the P fluxes across sediment-water interface and lowered P supply ability from the treated sediment during sediment resuspension. The reduction of mobile P and enhancement of calcium bound P and residual P fraction in the treated sediment was beneficial to the long-term lake internal P loading management. All of the results indicated that the studied geoengineering materials are suitable for application in shallow eutrophic lakes with frequent sediment resuspension activity., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A yearlong campaign to examine sediment resuspension was conducted in large, shallow and eutrophic Lake Taihu, China, to investigate the influence of vegetation on sediment resuspension and its nutrient effects. The study was conducted at 6 sites located in both phytoplankton-dominated zone and macrophyte-dominated zone of the lake, lasting for a total of 13 months, with collections made at two-week intervals. Sediment resuspension in Taihu, with a two-week high average rate of 1771 g·m(-2)·d(-1) and a yearly average rate of 377 g·m(-2)·d(-1), is much stronger than in many other lakes worldwide, as Taihu is quite shallow and contains a long fetch. The occurrence of macrophytes, however, provided quite strong abatement of sediment resuspension, which may reduce the sediment resuspension rate up to 29-fold. The contribution of nitrogen and phosphorus to the water column from sediment resuspension was estimated as 0.34 mg·L(-1) and 0.051 mg·L(-1) in the phytoplankton-dominated zone. Sediment resuspension also largely reduced transparency and then stimulated phytoplankton growth. Therefore, sediment resuspension may be one of the most important factors delaying the recovery of eutrophic Lake Taihu, and the influence of sediment resuspension on water quality must also be taken into account by the lake managers when they determine the restoration target.

Contaminants released by wind-induced sediment resuspension could influence the water quality in shallow lakes. This study aims to reveal the quantitative relationship between wind speed (v) and sediment resuspension rate (r) in Meiliang Bay of Lake Taihu. The study was conducted in three steps. First, the in situ wind speed and current velocity were measured over a period of 2 days in Meiliang Bay to establish the relationship between wind and hydrodynamic conditions; second, an indoor experiment was conducted in a cylindrical simulator with sediment from the study area to determine sediment resuspension rates under different hydrodynamic conditions; and third, linkages between sediment resuspension and wind were determined. The average sediment resuspension rate was highly correlated with the wind speed (R(2) = 0.99), and was expressed by r = 20.72v(2.034) at wind speeds in the range of 0-14 m/s. The critical wind speed for sediment resuspension is about 7 m/s. Under these conditions, the average resuspension rate could reach 1,000 g/(m(2)d), with a total phosphorus release rate of 1.1 g/(m(2)d) and a total nitrogen release rate of 18.1 g/(m(2)d).

Drinking water treatment residuals (WTRs), nonhazardous by-products generated in a drinking water treatment plant, can be reused to immobilize phosphorus (P) to control the internal P loading from lake sediments for eutrophication control. Reasonably, before practical application, it is essential to determine the P immobilization capability of WTRs in lake sediments under various conditions. In this work, laboratory scale experiments were conducted to investigate the effects of light, microbial activity, and sediment resuspension on the P immobilization capability of WTRs. The results suggested that absence of light, low microbial activity, and sediment resuspension can increase the internal P loading from lake sediments. WTRs can, however, reduce the internal P loading significantly. Further analysis demonstrated that WTRs can stabilize P, decreasing the P bioavailability in the sediments under varied conditions. WTRs also presented little undesirable effects on the dissolved oxygen levels and pH of overlying water. Therefore, light, microbial activity, and sediment resuspension have little effect on the P immobilization capability of WTRs in lake sediments.

As an essential drinking water source and one of the largest eutrophic shallow lakes in China, the management of Lake Taihu requires an adequate understanding of its hydrodynamic characteristics. Studying the hydrodynamic characteristics of Lake Taihu based on field observations is limited owing to its large area and the lack of flow field stability. Previous studies using hydrodynamic models experienced challenges, such as dimensionality and lack of dynamic response analysis between flow field and realistic wind; therefore, the results were still inconclusive. In this study, a 3D model of Lake Taihu, calibrated and validated based on field observations, was used to simulate and compare three scenarios: windless, steady wind, and realistic wind. The hydrodynamic characteristics of Lake Taihu were analyzed as close to the actual conditions as possible. The results showed that wind-driven currents dominated the flow field in Lake Taihu, and the horizontal velocity driven by wind was more than 6 times that without wind. Observing a stable flow field in Lake Taihu was difficult because of the variability of realistic wind. The hydrodynamic characteristics of Lake Taihu were defined as "strongly affected by wind," "higher on the surface and smaller at the bottom," and "difference between the surface and the bottom." Vertical turbulent kinetic energy can be used to characterize the variable flow field of a wind-driven lake and has a positive correlation with wind speed. Therefore, it could be used as a key component to predict water blooms with practical implications., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

A simulated experiment was conducted to investigate the impacts of sediment dredging on sediment resuspension and phosphorus transfer in the summer and winter seasons under the common wind-wave disturbance, and the contaminated sediment used in this study was from Meiliang Bay, Taihu lake. The result showed that 20 cm dredging could effectively inhibit the sediment resuspension in study area, dredging in winter has a better effect than that in summer, and the higher values of the total suspended solid (TSS) in undredged and dredged water column during the process of wind wave disturbance were 7.0 and 2.2, 24.3 and 6.4 times higher than the initial value in summer and winter simulation respectively. The paired-samples t-test result demonstrated that total phosphorus (TP) and phosphate (PO4(3-)-P) loading positively correlated to TSS content in dredged (P<0.01) and undredged water column (P<0.05), which proved that internal phosphorus fulminating release induced by wind-wave disturbance would significantly increase the TP and PO4(3-)-P loading in the water column. The effect of dredging conducted in summer on the TP and PO4(3)-P loading in the water column was negative, but not for winter dredging (P<0.01). The pore water dissolved reactive phosphorus (DRP) profile at water-sediment interface in summer simulation was also investigated by diffusive gradients in thin films (DGT) technique. Diffusion layer of the DRP profile in undredged sediment was wider than that in dredged sediment. However, the DRP diffusion potential in dredged sediment was greater than that in undredged sediment, showing that dredging can effectively reduce the risk of the DRP potential release in dredged pore water, but also would induce the DRP fulminating release in the short time under hydrodynamic action. Generally, dredging was usually deployed during the summer and the autumn. Considering Taihu Lake is a large, shallow, eutrophic lake and the contaminant distribution is spatially heterogeneous, it is vital to determine the optimal time, depth and scope of dredging.

To inhibit eutrophication caused by endogenous pollutants release, the experiment explored the efficiency and mechanism of the synchronous control of nitrogen (N) and phosphorus (P) release from sediments in shallow lakes under wind disturbance by modified Ca/Al-based sludge (MS) and modified zeolite (MZ). High-temperature calcination and NaCl impregnation increased the pore volume of MS and Na + content of MZ, and the adsorption capacity of MS for PO 4 3- -P and MZ for NH 4 . The results of a 90-day incubation experiment showed that the addition of MS and MZ increased the abundance of Thauera, Nitrospira, Denitratisoma, and Clostridium, while decreasing the proportion of Proteus Hauser and Saccharimonadales, thereby reducing the active N and P contents in sediments through microbial transformation. At the same time, the efficient adsorption performance of the MS and MZ resulted in a significant decrease in pollutants in the interstitial water and sediments. In addition, sediment resuspension caused by wind disturbance increased the contact between sediments and remediation agents, resulting in the action depth of covering materials exceeding 100 mm. Compared to adding MS or MZ alone, the combination of the two (MSZG) could synchronously, efficiently, and stably inhibit N and P release. Under the coupling effects of physical interception, physicochemical adsorption, and biotransformation, the average TN, NH + -N was as high as 42.01 and 20.28 mg g -1 -P in the overlying water of the MSZG decreased by 72.13%, 88.92%, 69.28%, and 81.26%, respectively, compared to Control, which satisfying the Class III standard for surface water. Therefore, this study could provide reference for controlling endogenous release, improving eutrophication in shallow lakes under wind disturbance, and recycling residual sludge from sewage plants.4 + -N, TP, and PO 4 3- -P in the overlying water of the MSZG decreased by 72.13%, 88.92%, 69.28%, and 81.26%, respectively, compared to Control, which satisfying the Class III standard for surface water. Therefore, this study could provide reference for controlling endogenous release, improving eutrophication in shallow lakes under wind disturbance, and recycling residual sludge from sewage plants., 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 Inc. All rights reserved.)

In this study, we sampled the original sediment columns from three points located in the eastern, central, and western areas of Chaohu Lake, and then investigated sediment resuspension under hydraulic disturbances in the laboratory. The results showed that when the hydraulic disturbance is weak and sediment surface shear stress is small (<0.02 N/m²‌), sediment surface layer moves alone. When the hydraulic disturbance is moderate and sediment surface shear stress is within a threshold (3.7 N/m²‌), only a small proportion of the surface sediments begins to move. However, when the hydraulic disturbance is further strengthened and sediment surface shear stress is larger than the threshold value, surface sediments move smoothly. By the experimental results, we found that the plankton layer is about 1 mm (1.56% of the maximum content of suspended matter (SSCmax)), which is the major contribution of individual sediment initiation. The new sediment layer is about 19–22 mm (20.9% of the SSCmax), which considerably affects sediment resuspension in shallow lakes. The consolidated layer is about 22 mm below the bed surface, which requires high shear stress and is hard to be transferred to the water column. The quantified experimental observation results are further verified with the theoretical results. [ABSTRACT FROM AUTHOR]

The comparative study of the transformation among sediment phosphorus (P) fractions in different lake types is a global issue in lake ecosystems. However, interactions between sediment P fractions, environmental factors, and microorganisms vary with the nutrient status of lakes. In this study, we combine sequential extraction and metagenomics sequencing to assess the characteristics of P fractions and transformation in sediments from different lake types in the Inner Mongolian section of the Yellow River Basin. We then further explore the response of relevant microbial and environmental drivers to P fraction transformation and bioavailability in sediments. The sediments of all three lakes exhibited strong exogenous pollution input characteristics, and higher nutritional conditions led to enhanced sediment P fraction transformation ability. The transformation capacity of the sediment P fractions also differed among the different lake types at the same latitudes, which is affected by many factors such as lake environmental factors and microorganisms. Different drivers reflected the mutual control of weakly adsorbed phosphorus (WA-P), potential active phosphorus (PA-P), Fe/Al-bound phosphorus (NaOH-P), and Ca-bound phosphorus (HCl-P) with the bio-directly available phosphorus (Bio-P). The transformation of NaOH-P in reducing environments can improve P bioavailability, while HCl-P is not easily bioavailable in weakly alkaline environments. There were significant differences in the bacterial community diversity and composition between the different lake types at the same latitude (p < 0.05), and the role of P fractions was stronger in the sediments of lakes with rich biodiversity than in poor biodiversity. Lake eutrophication recovery was somewhat hindered by the microbial interactions of P cycling and P fractions within the sediment. This study provides data and theoretical support for exploring the commonalities and differences among different lake types in the Inner Mongolian section of the Yellow River Basin. Besides, it is representative and typical for promoting the optimization of ecological security patterns in ecologically fragile watersheds., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The depth of contaminated sediments constrains the water environment of large shallow lakes and can affect shallow lake water quality through sediment resuspension and nutrient release. Although such effects can be avoided by sediment dredging methods, we still cannot precisely quantify the depth of sediment dredging. Therefore, we used organic index method, pollution index method and potential ecological risk evaluation to evaluate the contamination status of split samples of in situ sediments layer by layer, and established a comprehensive contamination index evaluation method for layer-by-layer sediments, then combined with the contamination release characteristics of split samples to assess the contamination degree of the sediments obtained. The results show that the content of nitrogen and phosphorus in the surface layer of Lake Townsend sediments is generally higher than that in the middle and bottom sediments, and the heavy metals also satisfy this pattern, which is consistent in the sediments of both east and west regions. We also simulated the release process of nitrogen and phosphorus nutrients in the in situ sediment of Tangxun Lake in 2019, and the experimental results showed that the risk of nitrogen and phosphorus nutrient release in the sediment was mainly concentrated in the surface and middle layers, and the risk of elemental nitrogen release was significantly greater than that of phosphorus release. Finally, a comprehensive evaluation was carried out to obtain the desilting depth of the sediments in Lake Townsend, and it can be determined that the recommended desilting depth is about 20 cm for West Lake and 30 cm for East Lake. The results show that the recommended dredging depth can be determined based on this method, which provides an important scientific basis for sediment dredging in Tangxun Lake and even provides a new paradigm for sediment dredging depth estimation in similar large shallow lakes., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

Eutrophication in inland lakes is occurring frequently with the rapid urbanization, the increases in human population, and the intensive agricultural activities. Traditional management programs focusing on external nutrient reduction failed in recovery of certain aquatic environments where internal nutrient releases are substantial. In this study, we evaluated the effects of aquatic vegetation in altering the phosphorus concentrations in a shallow, eutrophic lake through laboratory flume experiments. Our measurements demonstrated that aquatic vegetation could effectively lower the phosphorus levels in the water column, and the average reduction reached 90% for submerged vegetation and 80% for emergent vegetation. The experimental results showed that the submerged vegetation was effective to reduce phosphorus concentrations in the top and mid layers of pore waters and sediments. Differently, the emergent vegetation would assimilate more phosphorus in the bottom layer due to its deep root distributions. The flowing-water environment favored phosphorus removal for emergent vegetation, while the submerged vegetation was more functional in static waters according to our observations. The flux results showed that phosphorus transports from water columns to leaves, roots to leaves, and sediments to roots were all inhibited in flowing-water environments for submerged vegetation. Oppositely, the fluxes of emergent vegetation groups were all enhanced in flowing waters. Our experiments could inform ecosystem management concerning the potentials of aquatic vegetation in nutrient removal at regional and lake-wide scales., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Cyanobacterial bloom accumulation and dissipation frequently occur in Lake Taihu, a typically shallow, eutrophic lake due to wind wave disturbance. However, knowledge of the driving mechanisms of cyanobacterial blooms on underwater light attenuation is still limited. In this study, we collected a high-frequency in situ monitoring of the wind field, underwater light environment, and surface water quality to elucidate how cyanobacterial bloom accumulation and dissipation affect the variations in underwater light attenuation in the littoral zone of Lake Taihu. Results showed that cyanobacterial blooms significantly increased the diffuse attenuation coefficient of ultraviolet-B (K d (313)), ultraviolet-A (K d (340)), and photosynthetically active radiation (K d (PAR)); the scattering of total suspended matter (b bp (λ)); and the absorption of phytoplankton (a ph (λ)) and chromophoric dissolved organic matter (CDOM, a g (λ)) (p < 0.01). The K d (PAR) decreased quickly during the processes of bloom dissipation, but the decrease of K d (313) and K d (340) lagged 0.5 day. Our results suggested that cyanobacterial blooms could increase particle matters and elevated the production of autochthonous CDOM, resulting in underwater light attenuation increase. Ultraviolet radiation (UVR) and PAR attenuation both have significant responses to cyanobacterial blooms, but the response processes were distinct due to the different changes of particle and dissolved organic matters. Our study unravels the driving mechanisms of cyanobacterial blooms on underwater light attenuation, improving lake ecosystem management and protection., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

In recent years, the total nitrogen concentration in Taihu Lake has decreased significantly. Denitrification, as the main nitrogen removal process, is the key reason for the decrease. Here, the denitrification parameter values in the Environmental Fluid Dynamic Code (EFDC) model were calculated based on isotope-labeled denitrification experiment instead of selecting the recommended values directly. This study further focused on EFDC denitrification parameter derivation with an experimental denitrification rate (D tot ) to reduce simulation errors. According to the EFDC nitrate deposition flux mechanism, the conversion equation between the denitrification rate of the first sediment layer ([Formula: see text]) in EFDC and D tot was successfully derived. The results revealed a linear correlation between [Formula: see text] and (D tot ) 1/2 . The [Formula: see text] values of sampling points ranged from 0.25 to 0.27 m·day -1 , within the range of model parameters. After substituting [Formula: see text] into the Taihu Lake EFDC model, the average percentage bias and determination coefficient of total nitrogen were 16.25% and 0.87, respectively. The average total nitrogen concentration reduction caused by denitrification at water quality calibration points ranged from 0.027 to 0.305 mg·L -1 ., (© 2024. 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.)

Ecologists collectively predict that climate change will enhance phytoplankton biomass in northern lakes. Yet there are unique variations in the structures and regulating functions of lakes to make this prediction challengeable and, perhaps, inaccurate. We used archived Landsat TM/ETM+ satellite products to estimate epilimnetic chlorophyll-a (Chl-a) concentration as a proxy for phytoplankton biomass in 281 northern temperate lakes over 28 years. We explored the influence of climate (air temperature, precipitation) and landscape proxies for nutrient sources (proportion of wetlands in a contributing catchment, size of the littoral zone, potential for wind-driven sediment resuspension as estimated by the dynamic ratio) or nutrient sinks (lake volume) in a random forest model to explain heterogeneity in peak Chl-a. Lakes with higher Chl-a (median Chl-a = 2.4 μg L -1 , n = 40) had smaller volumes (<44 × 10 4  m 3 ) and were more sensitive to increases in temperature. In contrast, lakes with lower Chl-a (median Chl-a = 0.6 μg L -1 , n = 241) had larger volumes (≥44 × 10 4  m 3 ), contributing catchments with smaller proportions of wetlands (<4.5% of catchment area, n = 70), smaller littoral zones (<16.4 ha, n = 137), minimal wind-driven sediment resuspension (as defined by the dynamic ratio; <0.45, n = 232), and were more sensitive to increases in precipitation. Lakes with larger volumes were generally less responsive to climate factors; however, larger volume lakes with a significant proportion of wetlands and larger littoral zones behaved similarly to lakes with smaller volumes. Our finding that lakes with different landscape properties respond differently to climate factors may help predict the susceptibility of lakes to eutrophication under changing climatic conditions., (© 2022 John Wiley & Sons Ltd.)

Lake water eutrophication has become one of the leading obstacles to sustainable economic development in China. Research on the effects of mainstream currents on reservoirs has been relatively underdeveloped compared with research on tributaries, though changes in the water-sediment transport regime in a downstream river may affect nutrient transport behavior in a lake connected to that river. This is particularly problematic because certain wastewater sources, including runoff from agricultural wastes and industrial discharges, adversely affect lake water. Our study focused on Sanshiliujiao Lake, a significant drinking water source in Fujian, Southeast China, that has suffered considerably from eutrophication over the past few decades. This study aimed to estimate the phosphorus and nitrogen loads to the lake, exploring their sources and their ecologic effects using in situ observation and the export coefficient model. Our results showed that the pollution loads of total phosphorus (TP) and total nitrogen (TN) were 2.390 and 46.040 t/year, respectively, most of which were derived from the water diversion (TP 45.7%, TN 29.2%) and non-point source (TP 30.2%, TN 41.6%). The TN input was the highest in East river (3.557 kg/d), followed by Red river (2.524 kg/d). During the wet season, the input of TP and TN increased by 14.6 and 18.7 times, respectively, but produced only slight variations in concentration. Water diversion enriched the nutrients inputs and altered the structure and abundance of phytoplankton communities. In addition, when water flows from the main river directly to Sanshiliujiao Lake, algal blooms in river-connected lakes are significantly exacerbated, so our study may also serve as a theoretical basis to regulate eutrophication in Sanshiliujiao Lake., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

Lake Villarrica, one of Chile's main freshwater water bodies, was recently declared a nutrient-saturated lake due to increased phosphorus (P) and nitrogen (N) levels. Although a decontamination plan based on environmental parameters is being established, it does not consider microbial parameters. Here, we conducted high-throughput DNA sequencing and quantitative polymerase chain reaction (qPCR) analyses to reveal the structure and functional properties of bacterial communities in surface sediments collected from sites with contrasting anthropogenic pressures in Lake Villarrica. Alpha diversity revealed an elevated bacterial richness and diversity in the more anthropogenized sediments. The phylum Proteobacteria, Bacteroidetes, Acidobacteria, and Actinobacteria dominated the community. The principal coordinate analysis (PCoA) and redundancy analysis (RDA) showed significant differences in bacterial communities of sampling sites. Predicted functional analysis showed that N cycling functions (e.g., nitrification and denitrification) were significant. The microbial co-occurrence networks analysis suggested Chitinophagaceae, Caldilineaceae, Planctomycetaceae, and Phycisphaerae families as keystone taxa. Bacterial functional genes related to P (phoC, phoD, and phoX) and N (nifH and nosZ) cycling were detected in all samples by qPCR. In addition, an RDA related to N and P cycling revealed that physicochemical properties and functional genes were positively correlated with several nitrite-oxidizing, ammonia-oxidizing, and N-fixing bacterial genera. Finally, denitrifying gene (nosZ) was the most significant factor influencing the topological characteristics of co-occurrence networks and bacterial interactions. Our results represent one of a few approaches to elucidate the structure and role of bacterial communities in Chilean lake sediments, which might be helpful in conservation and decontamination plans., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The pathway of dense river inflows into lakes, which affects the lake water quality, is not accurately predicted by existing models. The pathway of a dense riverine inflow in a lake with a submerged canyon is analyzed based on measurements during a 4‐month period of weakening lake stratification and weakening density excess between river and epilimnion. In line with models, the dense riverine inflow plunges upon entering the lake, continues as an underflow on the sloping lake bottom, and finally intrudes at its level of neutral buoyancy. Underflow and interflow velocities are O(0.1 m s−1). The river inflow is finally trapped in the pycnocline most of the time, even when the river's density excess and the lake's stratification are marginal. This trapping in the pycnocline is explained by the reduction of the inflow density excess due to the intense plunging mixing, which is an order of magnitude larger than that obtained in confined laboratory flumes. The pathway of the dense riverine inflow is affected by interactions of the underflow with the lake bottom and sedimentary processes. A canyon carved by the underflows confines and accelerates the underflow, which enhances its capacity to entrain and carry sediment. The entrainment of sediment that was previously deposited on the canyon bottom accelerates the underflow. Due to both effects, the underflow can temporarily break through the pycnocline and reach the hypolimnion. Existing models explain these observations qualitatively, but a quantitative prediction would require better parameterizations of the plunging mixing and the sedimentary processes. Plain Language Summary: The pathway of river inflows into lakes is not accurately predicted by existing models. We investigate the physical processes affecting the pathway of dense riverine inflow (i.e., inflow with a density higher than lake water) into a stratified lake. We investigate the conditions under which a dense riverine inflow get trapped in the pycnocline (the layer that separates warmer surface waters from cold deep waters) or break through it. Unprecedented long records of the temporal evolution of the pathway of the riverine flow into the lake during a period of weakening riverine density excess and lake stratification are conceptualized in a model, which extends existing concepts for dense riverine inflows. The entrainment of lake waters into the riverine inflow in the plunging region is larger than predicted by laboratory studies. This explains why the riverine inflow is trapped in the pycnocline most of the time. Flow confinement by a canyon carved by the riverine inflow into the lake bottom accelerates the riverine inflow and enhance sediment entrainment capacity causing short‐lived self‐accelerating turbidity currents along the lake bottom that break through the pycnocline and reach deep waters. Our results allow improved estimates of oxygen replenishment or sediment deposition from riverine water. Key Points: Plunging mixing into an unconfined ambient is an order of magnitude larger than in a confined ambientPronounced plunging mixing reduces the initial density excess explaining why the inflow is mostly trapped in the pycnoclineResuspension of lake bottom sediment can cause short‐lived self‐accelerating turbidity currents that break through the pycnocline [ABSTRACT FROM AUTHOR]

The river-lake transitional zone provides a unique environment for the biological community and can reduce pollution inputs in lake ecosystems from their catchments. To explore environmental conditions with high purification potential in Lake Taihu and indicator species, we examined the river-to-lake changes in water and sediment quality and benthic invertebrate communities in the transitional zone of four regions. The spatial variations in the environment and invertebrate community observed in this study followed the previously reported patterns in Taihu; the northern and western regions were characterized by higher nutrient concentrations in water, higher heavy metal concentrations in sediment, and higher total invertebrate density and biomass dominated by pollution-tolerant oligochaetes and chironomids. Although nutrient concentrations were low and transparency was high in the eastern region, the taxon richness was the lowest there, which disagreed with the previous findings and might be due to a poor cover of macrophytes in this study. The river-to-lake change was large in the southern region for water quality and the invertebrate community. Water circulation induced by strong wind-wave actions in the lake sites of the southern region is assumed to have promoted photosynthetic and nutrient uptake activities and favored invertebrates that require well-aerated conditions such as polychaetes and burrowing crustaceans. Invertebrates usually adapted to brackish and saline environments are suggested to be indicators of a well-circulated environment with active biogeochemical processes and a less eutrophic state in Taihu, and wind-wave actions are key to maintaining such a community and natural purifying processes., (© 2023. The Author(s).)

Sediment resuspension is critical to the internal nutrient loading in aquatic systems. Turbidity is commonly used as an indicator for sediment resuspension and is proved to be highly correlated to wind speed in large shallow lakes. A field observation of wind speed and turbidity was conducted using a portable weather station and a YSI 6600V2-2, and an observation lasting for 39 days was evaluated in this study (the data points with wind speed > 4 m/s account for 75%). The daily average values (DA dataset) as well as daily maximum (MX dataset) and minimum values (MI dataset) were calculated from the instantaneous observations (IN dataset). Correlations in IN dataset were deduced based on machine learning methods and were compared to those obtained from DA, MI, and MX datasets. Furthermore, the correlation in IN dataset was analyzed by using two statistical methods, and from the view of statistical the turbidity is regarded as a variable. Results indicate that the correlations in IN datasets follow the exponential function or power function pattern with a critical wind speed of 6 m/s, Regression on IN dataset revealed that linear regression model had the best performance on predicting the turbidity in test dataset and no significant differences are observed between exponential function and power function pattern. Correlations in DA and MX datasets exhibit higher maximal information coefficient (MIC) than IN dataset and error of turbidity prediction introduced by using these correlations in IN dataset is within the tolerance level. Statistical analysis on the IN dataset shows that a strong relationship exists among the wind speed and expectation of turbidity with a MIC over 0.99, and follows the exponential function or the power function as well with a different critical wind speed of 4 m/s. Over 95% data points fall in the predicted intervals of turbidity for both methods, suggesting a high predicting accuracy.

Organic aggregates (OA) are the important circulation hub of matter and energy in aquatic ecosystems. However, the comparison studies on OA in lakes with different nutrient levels are limited. In this study, spatio-temporal abundances of OA and OA-attached bacteria (OAB) in oligotrophic Lake Fuxian, mesotrophic Lake Tianmu, middle-eutrophic Lake Taihu, and hyper-eutrophic Lake Xingyun were investigated in different seasons during 2019-2021 using a scanning electron microscope, epi-fluorescence microscope, and flow cytometry. The results showed that:① the annual average abundances of OA in Lake Fuxian, Lake Tianmu, Lake Taihu, and Lake Xingyun were 1.4×10 4 , 7.0×10 4 , 27.7×10 4 , and 16.0×10 4 ind·mL -1 , whereas the annual average abundances of OAB in the four lakes were 0.3×10 6 , 1.9×10 6 , 4.9×10 6 , and 6.2×10 6 cells·mL -1 . The ratios of OAB:total bacteria (TB) in the four lakes were 30%, 31%, 50%, and 38%, respectively. ② OA abundance in summer was significantly higher than that in autumn and winter; however, the ratio of OAB:TB in summer was approximately 26%, which was significantly lower than that in the other three seasons. ③ Lake nutrient status was the most important environmental factor that affected the abundance variations of OA and OAB, accounting for 50% and 68% of the spatio-temporal variations in OA and OAB abundances. ④ Nutrient and organic matters were enriched in OA, especially in Lake Xingyun; the proportions of particle phosphorous, particle nitrogen, and organic matters in this lake were as high as 69%, 59%, and 79%, respectively. Under the circumstance of future climate change and the expansion of lake algal blooms, the effects of algal-originated OA in the degradation of organic matters and nutrient recycling would be increased.

To regulate the water level and minimize the occurrence of water eutrophication in shallow lakes, dams and gates are often constructed in rivers. However, this practice may result in a deterioration of water quality in some estuaries. In the present study, using the correction of Nemerow pollution index (CNPI) and a redundancy analysis (RDA), water samples from different dammed rivers around Taihu Lake were compared to assess the pollution risk and identify the factors responsible for water eutrophication. The average total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC) concentrations, and chemical oxygen demand (COD Mn ) were 2.45 ± 2.28, 0.08 ± 0.06, 43.01 ± 18.75, and 10.78 ± 4.86 mg L -1 , respectively. The CNPI values indicated that approximately 76.47% of the estuarine water was moderately polluted (1 < CNPI < 7.28). A positive correlation was observed between dam construction and nutrient concentrations (e.g., r TN = 0.38, p < 0.05; r TP = 0.89, p < 0.01). Under the effects of dam construction, land use change, estuary shape, and meteorological conditions, there was a clear spatial variation of the TN concentrations. Dams that were closed all year round accelerated the TN accumulation in the water around them. The pollution risk in a trumpet-shaped estuary was higher than that in other regions (t = 2.92, p = 0.02). Endogenous release of pollutants was an important factor that may have a priming effect on algal blooms and should be given more attention. In Wuli Lake, exogenous pollution was the dominant pollutant source. A total of 74.49% of the nitrogen losses with the runoff into the estuarine water in 2018 were derived from urban domestic sewage and constructed land, with the load being 4.40 times higher than in 2000. The RDA results revealed that dam construction was the main factor (43.70%) affecting water quality, while meteorological conditions, land use types, estuary shape, and other factors contributed 56.30%. Scientific regulation and control of dam operation is important to protect the water environment of Taihu Lake.

This article discusses the effects of shorter ice cover on shallow lakes as a consequence of predicted climatic changes in Finland. According to the authors, total phosphorus loading will increase due to wind-induced sediment resuspension. They measured resuspension rates under ice cover and after ice break. A strong increase in phosphorus loading was due to phosphorus–rich resuspended particles. They estimated that if atmospheric carbon dioxide doubles it would would result in a shorter ice cover period and a significant increase in particulate phosphorus.