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The occurrence of microplastics in aquatic environments has attracted increasing interest from both the public and scientists, especially their migration behaviors. Although several environmental behaviors of microplastics have been studied, the issue of microplastic suspension and deposition in lake sediment–water systems remains to be elucidated. In this study, we built an indoor sediment–water system with input and output rivers that simulated the actual situations in lakes, and aimed to explore the suspension and deposition behavior of microplastics using eight group experiments. The abundance of microplastics in overlying water and sediments in different periods was analyzed, and the characteristics of hydrodynamic disturbance on microplastic suspension and deposition were identified. Importantly, the exchange of microplastics in sediments and water under dynamic flow conditions was assessed. The results showed that the middle-scale experiment designed in this study effectively simulated the dynamic transport process of microplastics in lakes, and the hydrodynamic force had a significant impact on the suspension and deposition behaviors of microplastics. The average abundance of polystyrene, polyethylene terephthalate and polyamide microplastics was 1.07, 0.60 and 0.83 particles/L in overlying water during the suspension experiments, respectively. This showed a pattern of first rising and then falling with the extension of suspension time. Even in the environment with the maximum input water volume (8000 ml/min) in this study, only microplastics at a depth of 0 to 2 cm from the sediment were suspended. The average abundance of microplastics was 313.02 particles/kg during the deposition experiments, which gradually increased with the extension of deposition time in sediments. Finally, microplastic sizes in water of the suspension experiments and in sediments of the deposition experiments were concentrated in the range of 500 to 1500 μm and 300 to 1000 μm, respectively. [ABSTRACT FROM AUTHOR]

Abstract The effect of hydrodynamic mixing on controlling Microcystis blooms or changing the algal community to diatom dominance has been widely studied; however, the effects of colonial Microcystis biomass on the development of the algal community are poorly known. Here, in order to study the changes in Microcystis blooms under continuous aeration mixing, an experiment was carried out in a greenhouse with factors of varying biomass of Microcystis and inorganic nitrogen and phosphorus enrichment in summer. There were three chlorophyll a (Chl-a) levels in six treatments: low Chl-a level of 68.4 μg L-1 (treatments L, L-E), medium Chl-a level of 468.7 μg L-1 (treatments M, M-E), and high Chl-a level of 924.1 μg L-1 (treatments H, H-E). Treatments L-E, M-E and H-E were enriched with the same inorganic nitrogen and phosphorus nutrients. During the experiment of 30 days, the concentration of Microcystis and Chl-a decreased, and diatom Nitzschia palea cells appeared in all the treatments, which became dominant in treatments M, M-E, H and H-E, with the highest biomass of 9.41 ± 1.96 mg L-1 Nitzschia in treatment H-E on day 30. The rank order of the biomass of Nitzschia from low to high was (L = L-E)

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In this study, the effect of the addition of natural (AT) and purified attapulgite (PAT) on the migration and transformation of phosphorus (P) in mariculture ponds sediments under static and hydrodynamic disturbance conditions was studied using sediment core incubation experiments. Whether under static or disturbance condition, the AT/PAT amendment suppressed the release of dissoluble reactive phosphorus (SRP) from sediments into the overlying seawater. The results showed that the addition of AT/PAT decreased the concentration of SRP in overlying seawater (maximum reduction rate: Rmax = 76.82%), the concentration of SRP in pore seawater (Rmax = 62.62%) and the diffusion flux of SRP at the sediment-water interface (SWI) (Rmax = 34.22%). Furthermore, adding AT/PAT to the top sediments (0–1 cm) not only reduces the content of Mobile-P in the added layer, but also reduces Mobile-P in the sediments (1–2 cm) below the added layer. In addition, under the condition of disturbance, the reduction rate of Mobile-P in the PAT added layer (42.16%) was higher than that of AT (21.12%). The reduction of Mobile-P in the top sediment, SRP in the pore seawater as well as the diffusion flux of SRP from the pore seawater to the overlying seawater across the SWI played a key role in the control of SRP release from sediments to the overlying seawater by the AT/PAT amendment. Results of this work indicate that the AT and PAT are very promising amendment for the control of SRP release from mariculture ponds sediments under static and hydrodynamic disturbance conditions. [ABSTRACT FROM AUTHOR]

Shallow water has low depth, and hydrodynamic conditions may change with the effect of wind and waves, resulting in sediment suspension and pollutant release. To investigate the influence of sediment incipient motion on ammonia nitrogen (NH3-N) release in shallow lakes under hydrodynamic disturbance, we monitored ammonia nitrogen concentration in the overlying water of sediments in Chaohu Lake under static, weak, and strong disturbance conditions and analyzed the ammonia nitrogen release rate based on the these concentrations. In static condition, the sediment particles on the surface moved individually (individual movement), and the ammonia nitrogen release rate was 9.59 mg/m2/day. When the disturbance was weak and a small proportion of sediment particles started to move (small movement), the ammonia nitrogen release rate increased to 34.21 mg/m2/day. When the disturbance was further strengthened, and most of the sediment particles moved (general movement), the ammonia nitrogen release rate was 77.04 mg/m2/day. Distribution showed that the release rate varied the most in the western area followed by the eastern area, and the central area had the lowest release rate. The daily release of ammonia nitrogen in Chaohu Lake ranged from 8742.3 kg to 61,008.59 kg. In this experiment, we combined sediment movement and pollutant release, which provides a new reference for the study of pollutant release in shallow lakes and for ammonia nitrogen management in other shallow lakes. [ABSTRACT FROM AUTHOR]

The occurrence of black blooms, a kind of black water phenomenon, mostly formed by the decomposition of cyanobacterial blooms poses a threat to both drinking water supplies and the survival of aquatic organisms. Meteorological and hydrological conditions play a crucial role in their formation, while the specific impact of hydrodynamic disturbances on the black blooms remains unclear. The aim of this study is to investigate in depth the impact of hydrodynamic disturbances on the formation and development of black blooms, as well as their effects on the microbiota in surface sediments during the process. During the occurrence of black blooms in Lake Taihu, in-situ water and surface sediment samples were collected. By combining studies of the changes in water quality and microbial communities, the potential driving mechanisms of hydrodynamic disturbances were analyzed. The results indicate that during the outbreak stage (MS), hydrodynamic disturbances drove the release of anaerobic byproducts in sediments (NH 4 +-N ≥ 0.5 mg/L, TN ≥ 2.03 mg/L, TP ≥ 0.15 mg/L), and varying levels of hydrodynamic disturbance led to significant differences in microbial communities (ANOSIM, R = 0.477, p < 0.05). This influenced the abundance of microorganisms with carbon and sulfur cycling functions in sediments, where stronger hydrodynamics promoted the coupling of carbon mineralization and fermentation processes, while weaker hydrodynamic disturbances facilitated the coupling of carbon mineralization and sulfate reduction processes. Additionally, hydrodynamic disturbances influenced the potential functions of sulfate-reducing bacteria (SRB) in sediments, altering the interactions between SRB and other microorganisms. This study, for the first time, investigated the impact of hydrodynamics on the formation of black blooms from the perspective of their interaction with microorganisms. These findings broaden our understanding of the significance of hydrodynamic disturbances during black bloom occurrences and contribute to our ability to predict the formation of black blooms through modeling. [ABSTRACT FROM AUTHOR]

The estuary is an energetic area connecting the inland, river, and ocean. The migration of microplastics (MPs) in this highly complex area is tied to the entire ecosystem. In this study, the effects of cohesive SPM (clay) and noncohesive SPM (sand) on the vertical migration of positively buoyant MPs, polyethylene (PE), and negatively buoyant MPs, polytetrafluoroethylene (PTFE), in the estuarine environment under hydrodynamic disturbances were investigated. The settling of positively buoyant MPs was more reliant on the cohesive SPM compared to the settling of negatively buoyant MPs. Moreover, MPs interacting with the SPM mixture at a clay-to-sand ratio of 1:9 settled more efficiently than those interacting with clay alone. A significant positive correlation was observed between MP settling percentage and the salinity level. MP settling percentage was significantly negatively correlated with fluid shear stress for both types of MPs, meanwhile, negatively buoyant MPs were able to resist greater hydraulic disturbances. In the low-energy mixing state, for both types of MPs, the settling percentage reached about 50% in only 10 min. The resuspension process of MPs under hydrodynamic disturbances was also uncovered. Additionally, the migration and potential sites of MPs were described in the context of prevalent environmental phenomena in estuaries.

In order to provide effective measures for reclamation management and alleviate damages on ecosystems under multiple anthropologic interferences, quantification of coastal reclamation hydrodynamic disturbance (CRHD) and determination of the related threshold value of ecosystem are presented in this research. Eleven monitoring areas (approximately 1 km 2 each) in Dongying Port of China are considered. Each monitoring areas were further divided into the affected and non-affected areas based on impact of coastal reclamation engineering by comparing the distribution of hydrodynamic disturbance. According to c the CRHD, which enhance quantification method in terms of (a) quantifying the CRHD for coastal environment under different types of coastal habitants, (b) developing the definition of hydrodynamic disturbance based on ecological threshold, and (c) prognosticating the distribution of IHD with the case study of Dongying port. As the results, IHD for most of affected area was 23.58% higher than that non-affected area in average. Also, CRHD was insensitive to sessile organisms’ growth, relatively sensitive to suspended organisms, and extremely sensitive to swimming organisms. The maximum ecological threshold value for sessile organisms was approximately 3.5, exceeding 45.32% and 38.83% actual intensity for the affected and non-affected areas, respectively. Also, the threshold value for suspended organisms was approximately 2.56, which was 3.55% less than that of the affected area. Comparatively, the threshold value for swimming organisms was approximately 2.05, which was 10.75% less than that of affected area. Therefore, it is not suitable to invest constructional project of coastal reclamation engineering at the northeast and northwest of Dongying port administrative regions. Overall, the quantitative modeling of CRHD is advantageous for policy maker to manage coastal reclamation engineering and protect aquatic biodiversity. [ABSTRACT FROM AUTHOR]

Since tetrabromobisphenol A (TBBPA) has been increasingly used and found widely in the aquatic environment, it has attracted much attention due to its high toxicity to aquatic organisms. However, less work has been carried out for the TBBPA environmental fate in water-sediment systems. In this paper, the distribution, release and removal of TBBPA in different forms of the water-sediment system were investigated under three typical hydrodynamic conditions using a specialized racetrack-style flume. Three water-sediment systems which are water, suspended particulate matter (SPM) and sediment were taken into account in this study. The results of 34 days experiments showed that the equilibrium of physicochemical parameters was reached under different disturbance conditions within a relatively short period. The distribution ratio of TBBPA in three water-sediment systems will also reach a relatively equilibrium state over time under different disturbance conditions. The fluctuation range in each form was <1.26%. The TBBPA released to the water and SPM, increased remarkably with hydrodynamic enhancement due to adsorption and resuspension processes. Removal efficiency of TBBPA in each form was found to be observably accelerated with hydrodynamic disturbances. The half-lives ( T 1 / 2 ) in water, SPM and sediment ranged from 10.1 to 12.6 days in strong hydrodynamic condition, comparing to the static control, it ranges from 34.7 to 37.1 days. This phenomenon may result from the increase of dissolved oxygen (DO) and nutrient concentrations in overlying water affected by hydrodynamic force. The results of the experiment demonstrate that hydrodynamic disturbance may be an important driving factor which will influence the TBBPA environmental fate in aquatic environment. [ABSTRACT FROM AUTHOR]

• Propeller jet-induced migration and distribution of PFAAs were investigated. • PFAAs in overlying water exhibited transient characteristics and hysteresis with time. • Variations in jet strength influenced the adsorption rates of PFAAs onto SPM. • V x and R yy promoted PFAA release from sediments. • Vorticity , DOC, and pH influenced PFAA distribution between SPM and overlying water. Perfluoroalkyl acids (PFAAs) are continuously accumulated in surface sediments due to extensive and long-term application. However, the mechanisms through which disturbances induced by ship propeller jets at the riverbed cause secondary release of PFAAs from sediments remain unclear. In this study, the effects of different propeller rotational speeds on PFAA migration, release, and distribution in multiphase media were investigated by performing indoor flume experiments combined with particle tracking velocimetry. Moreover, key factors influencing PFAA migration and distribution were identified, and partial least squares regression (PLS) method was applied to develop quantitative prediction models of relationships among hydrodynamics, physicochemical parameters, and PFAA distribution coefficients. The total PFAA concentrations (ΣPFAAs) in overlying water under propeller jet action exhibited transient characteristics and hysteresis with time after the disturbance. In contrast, the ΣPFAAs in suspended particulate matter (SPM) exhibited an upward trend throughout the process with consistent characteristics. The spatial distribution trends of PFAAs in overlying water and SPM at different propeller rotational speeds featured vertical variability and axial consistency. Furthermore, PFAA release from sediments was driven by axial flow velocity (V x) and Reynolds normal stress R yy , while PFAA release from porewater was inextricably linked to Reynolds stresses R xx , R xy , and R zz (p < 0.05). PLS regression models showed that variations in Vorticity , dissolved organic carbon, and pH influenced the decreases in PFAA distribution coefficients between SPM and overlying water (K D-SW) as propeller rotational speed increased, except for very long-chain PFAAs (C > 10). The increases in PFAA distribution coefficients between sediment and porewater (K D-SP) were mainly determined by physicochemical parameters of sediments, and the direct effect of hydrodynamics was relatively weak. Our study provides valuable information regarding the migration and distribution of PFAAs in multiphase media under propeller jet disturbance (both during and after disturbance). [Display omitted] [ABSTRACT FROM AUTHOR]

Glauconite sands (GS) are abundantly available iron (Fe)-rich minerals that are efficient in lowering the release of phosphorus (P) from sediments to the overlying water. Many river sediments are, however, net sinks for P rather than sources and it is unclear if these GS minerals also enhance the P uptake from water. This is because the concentration of Fe(III) minerals at the sediment-water interface (SWI) depends on the redox potential that is affected by physicochemical processes. This study was set-up to investigate if a sediment amendment with GS can both lower P release from the sediment and enhance P uptake from the overlying water. The P fluxes across the SWI were compared between GS-amended (added at 10% weight fraction) and non-amended river sediment in static (incubation) and dynamic (flume) systems. The net P uptake was measured in response to a pulse external P loading (0.5–5 mg P L−1). Sodium glutamate was added to all treatments to simulate water with a high oxygen demand. Before the P pulse, the GS-amended sediments released significantly less P to the overlying water than the non-amended sediments in both static as dynamic systems. Spiking the water reverted the net P flux over the SWI only in the dynamic system, and the net P uptake in the sediment was factor two larger in GS-amended sediment compared to the non-amended sediment. This study showed that GS addition not only reduced internal P release, but also enhanced P uptake from the overlying water. However, the long-term efficiency in streams likely decreases over time due to saturation processes. [Display omitted] • The iron-rich GS addition on external and internal P immobilization was investigated. • The P immobilization of GS was evaluated under different hydrological regimes. • The internal P immobilization by GS (75%–80%) was not affected by flow conditions. • The external P removal by GS depends on flow conditions and added P concentration. [ABSTRACT FROM AUTHOR]

Tetrabromobisphenol A (TBBPA) exists widely in river and lake sediments; it has raised growing attention in recent years as emerging contaminant due to its possible threats to the aquatic environment and human health. Using a specialized simulator, the relationships between hydrodynamic disturbances and resuspension characteristics were simulated, with an emphasis on microscopic characteristics. Furthermore, TBBPA release from sediment was studied in relation to hydrodynamic disturbances and resuspension characteristics. The results show that stronger water disturbances caused an increase in suspended solids concentration (SSC) and produced different behaviors of particle size distribution (PSD) and media diameter (D 50 ) in the slight and large-scale resuspension situations. As for microscopic resuspension characteristics, the specific surface area (SSA) of suspended particulate matter (SPM) was very different from that of smooth particles. This difference may result from the fractal nature of the SPM. The fractal dimension (FD) of SPM was found to have a significant correlation with turbulent kinetic energy. TBBPA release into overlying water and adsorption onto SPM both increased with hydrodynamic disturbances; but the release into overlying water is more dominant. The TBBPA concentrations in SPM under different hydrodynamic conditions were significant related to SSA, indicating that SSA is a key factor affecting the TBBPA adsorption capacity of SPM. TBBPA concentrations in sediment decreased slightly with the increased hydrodynamic dispersion. Findings from this research show the importance of considering the hydrodynamic disturbance and resuspension characteristics in understanding TBBPA release behavior in aquatic environment. [ABSTRACT FROM AUTHOR]

Detailed swimming kinematics of the yellowtail kingfish Seriola lalandi were investigated after unilateral ablation of superficial neuromasts ( SNs). Most kinematic variables, such as tail-beat frequency, stride length, caudal fin-beat amplitude and propulsive wavelength, were unaffected but lateral amplitude at the tip of the snout ( A0) was significantly increased in SN-disrupted fish compared with sham-operated controls. In addition, the orientation of caudal fin-tip relative to the overall swimming direction of SN-disrupted fish was significantly deflected (two-fold) in comparison with sham-operated control fish. In some fish, SN disruption also led to a phase distortion of the propulsive body-wave. These changes would be expected to increase both hydrodynamic drag and thrust production which is consistent with the finding that SN-disrupted fish had to generate significantly greater thrust power when swimming at ≥1·3 fork lengths ( LF) s−1. In particular, hydrodynamic drag would increase as a result of any increase in rotational (yaw) perturbation and sideways slip resulting from the sensory disturbance. In conclusion, unilateral SN ablation produced directional instability of steady swimming and altered propulsive movements, suggesting a role for sensory feedback in correcting yaw and slip disturbances to maintain efficient locomotion. [ABSTRACT FROM AUTHOR]

Contaminants resuspension in sediments induced by wind-wave could influence the water quality in shallow lakes. Resuspension of surface sediments from the Zhushan Bay, Taihu Lake was simulated under different wind forcing by using a pneumatic annular flume in this study. Acoustic Doppler Velocimeter (ADV) was used to measure flow velocity at each wind speed, and the characteristics of sediment resuspension were studied with the layered sampling technology. The experimental results show that the flow velocity increases with wind speed obviously and 6m/s is a critical wind speed which affected hydrodynamic conditions significantly. The distribution of flow velocity and water depth is different from that in ordinary open channel. With the enhanced hydrodynamic factors, the Suspended Solids Concentration (SSC) in water increases accordingly, and the incipient velocity of sediment resuspension is about 0.21 m/s. Based on the analysis of wind speed and average SSC in water column, the quantitative relationship is obtained. The SSC of the bottom layer is higher than the content of surface layer under different hydrodynamic conditions, and there are similar distributions between SSC and flow velocity in different water layers. [ABSTRACT FROM AUTHOR]

In fresh waters, non-native invertebrate species preferentially spread via navigation waterways, where they often dominate assemblages. Littoral habitats in navigation waterways are regularly exposed to ship-induced waves. We conducted experiments to test the effects of artificial wave exposure on the relative performance of wide-spread native and non-native species. We compared physiological and behavioural response variables (i.e. growth rate, glycogen content, feeding and swimming activity) of two amphipods (native Gammarus roeselii and non-native Dikerogammarus villosus) and two gastropods (native Bithynia tentaculata and non-native Physella acuta) subject to wave and control (i.e. no wave) treatment flumes across a 6-week period. Growth, and in part glycogen content (as a measure of energy storage), were significantly reduced after exposure to waves in native invertebrates, but not in non-native invertebrates. The reduction in growth may be associated with the disturbance effects of waves, such as the higher swimming activity of G. roeselii and lower food uptake of B. tentaculata. In comparison, the effective hiding behaviour observed for D. villosus and good swimming ability of P. acuta, were identified as important traits facilitating the successful colonisation of the harsh habitat conditions of littoral waterways. Our study demonstrates that artificial wave regimes may contribute significant selective pressure, thus explaining the observed dominance of non-native species in navigational waterways. The success of non-native species under the harsh hydraulic habitat conditions of these socio-economically driven ecosystems may consequently be traced directly to behavioural and/or physiological traits. [ABSTRACT FROM AUTHOR]

Little is known about the effects of waves on predator-prey interactions in the littoral zones of freshwaters. We conducted a set of mesocosm experiments to study the differential effects of ship- and wind-induced waves on the foraging success of littoral fish on benthic invertebrates. Experiments were conducted in a wave tank with amphipods ( Gammarus roeseli) as prey, and age-0 bream ( Abramis brama, B0), age-0 and age-1 dace ( Leuciscus leuciscus, D0 and D1) as predators. The number of gammarids suspended in the water column was higher in the wave treatments compared to a no-wave control treatment, especially during pulse waves mimicking ship-induced waves in comparison to continuous waves mimicking wind-induced waves. The resulting higher prey accessibility in the water column was differently exploited by the three types of predatory fish. D0 and D1 showed significantly higher foraging success in the pulse wave treatment than in the continuous and control treatments. The foraging success of D0 appears to be achieved more easily, since significantly higher swimming activity and more foraging attempts were recorded only for D1 under the wave treatments. In contrast, B0 consumed significantly fewer gammarids in both wave treatments than in the control. Hence, waves influenced predator-prey interactions differently depending on wave type and fish type. It is expected that regular exposure to ship-induced waves can alter littoral invertebrate and fish assemblages by increasing the predation risk for benthic invertebrates that are suspended in the water column, and by shifting fish community compositions towards species that benefit from waves. [ABSTRACT FROM AUTHOR]

Abstract: Environmental conditions such as illumination, hydrodynamics, and densities of organisms affect behavior of both, fish fry and their prey with impacts on trophic interactions in ecosystems and aquaculture management alike. The present study demonstrated that the copepod Pseudodiaptomus annandalei perceived juvenile fry of the grouper Epinephelus coioides as predators and exhibited escape reactions mediated mainly by physical and/or chemical signals. Under illumination, prey capture rates were significantly greater (p <0.01, Mann–Whitney U test) at moderate turbulence (747±104 individuals/h, n =3) than in calm water (597±76 individuals/h, n =3). The maximum darting speed of copepods in response to sensing fish fry in calm water was significantly greater (one-way ANOVA, p <0.05) than that in either turbulent or enhanced flow conditions, indicating that the ability of copepods to escape from predators was greater in calm water than in turbulent water or enhanced flow conditions. The maximum number of copepods eaten by the fish larvae increased in slow and medium hydrodynamic turbulence compared to either calm water or strong turbulence, suggesting that intermediate levels of turbulence favor predatory larvae. [ABSTRACT FROM AUTHOR]

• Simple and chemical-free approach for scaling inhibition in MD. • Air NBs have neutral buoyancy, small size (128.81 nm), high concentration (7.8 × 107 bubbles mL−1), and negative surface charge. • A one-time addition of air NBs in high-salinity feed reduced scaling and prolonged the effective MD operating time. • The use of NBs resulted in significantly less salts deposition and prevented the occurrence of pore wetting. • Scaling inhibition mechanisms include NB-induced surface shear forces, and NBs-counterions electrostatic attractions. In this study, we report the use of nanobubbles (NBs) as a simple and facile approach to effectively delay scaling in membrane distillation (MD) during the treatment of highly saline feed (100 g L−1). Unlike conventional gas bubbling in MD for improving the hydrodynamic flow conditions in the feed channel, here we generated air NBs with an average size of 128.81 nm in the feed stream and examined their impact on membrane scaling inhibition during MD operation. Due to their small size, neutral buoyancy, and negative surface charge, NBs remain in suspension for a longer time (14 days), providing homogenous mixing throughout the entire feed water. The MD performance results revealed that severe membrane scaling happened during the DCMD treatment of high salinity brine in the absence of nanobubbles, which dramatically reduced the distillate flux to zero after 13 h. A one-time addition of air NBs in the saline feed significantly reduced salt precipitation and crystal deposition on the PVDF membrane surface, delayed the occurrence of flux decline, prevented membrane wetting, thereby prolonging the effective MD operating time. With similar feed concentration and operating conditions, only 63% flux decline after 98 h operation was recorded in nanobubble-assisted MD. Two key explanations were suggested for the delayed membrane scaling upon addition of air NBs in the MD feed: (1) NB-induced turbulent flow in the feed channel that increases the surface shear forces at the membrane surface, alleviating both temperature and concentration polarization effect, (2) electrostatic attractions of the counterions to the negatively charged NBs, which reduces the availability of these ions in the bulk feed for scale formation. [Display omitted] [ABSTRACT FROM AUTHOR]

This study showed that metal transport and partitioning are primarily controlled by suspended solids with seasonal flow regimes in plain river networks with sedimentary resuspension. Eight metal species containing iron (Fe), manganese (Mn), cadmium (Cd), chrome (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn), in multiple phases of sediments, suspended solids (>0.7 μm), colloids (1 nm-0.7 μm) and dissolved phase (<1 nm) were analysed to characterize their temporal-spatial patterns, partitioning and transport on a watershed scale. Metal concentrations were associated with suspended solids in the water column and decreased from low flow to high flow. However, metal partitioning between particulate phase (suspended solids) and dissolvable phases (colloids and dissolved phase) was reversed and increased from low flow to high flow with decreased concentration of total suspended solids and median particle size. Partition coefficients (k p) showed differences among metal species, with higher values for Pb (354.3–649.0 L/g) and Cr (54.2–223.7 L/g) and lower values for Zn (2.5–25.2 L/g) and Cd (17.3–21.0 L/g). Metal concentrations in sediments increased by factors of 1.2–3.0 from upstream to downstream in watersheds impacted by urbanization. The behaviours of metals in rivers provide deeper insight into the ecological risks they pose for downstream lakes, where increased redox potential and organic matter may increase metal mobility due to algal blooms. Areas with heavy pollution of metals and the transport routines of metals in the river networks were also revealed in our research. [Display omitted] • Particles are sorted during sediment resuspension and transported with flow regime. • Suspended solids controlled metal partitioning in turbid water of river networks. • Partition coefficients of Pb and Cr were higher than that of Cd and Zn. • Metal mobility in downstream lakes was linked to their behaviour in upstream rivers. [ABSTRACT FROM AUTHOR]

Shell colour polymorphism was examined in a population of the polyplacophoran Ischnochiton striolatus (Gray, 1828) living on intertidal rocks in Búzios, Rio de Janeiro State, Brazil. Nine shell colours were identified: green (most common), grey, pink, cream, brown, orange, white, black and purple. The species habitat was also examined using three rock characteristics: volume; turnover frequency, caused by hydrodynamic disturbance; and chromatic composition. Chitons were most frequently encountered on the undersides of rocks of intermediate volume which experienced medium-intensity hydrodynamic disturbance, and which harboured a chromatically rich biotic community. These findings were in agreement with the Intermediate Disturbance Hypothesis. As chitons depend on the biotic community on rocks for food and shelter, a greater variety of colours could increase the chances of camouflage of the morphs against the background, favouring crypsis. It is likely that the frequency at which intermediate-volume rocks are overturned − thus exposing the chitons on them to light − would be sufficient for visual predators to act as selective agents. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85, 543–548. [ABSTRACT FROM AUTHOR]

Despite increasing concerns about the global threat of cordgrass (S. alterniflora) expansion and the interest in its invasion mechanisms, there is not yet a general understanding of the mechanistic processes underlying the interaction between cordgrass invasion and geomorphic structures such as tidal channels. This study elucidated the effects of the hydrodynamic disturbance of tidal channels on initial seedling establishment of cordgrass in the margins of two different types of tidal channels (i.e., main tidal channels and secondary tributaries). We performed field experiments that transplanted cordgrass seedlings to above-mentioned tidal channel margins with on-site controlled hydrodynamic conditions. The results showed that high hydrodynamic disturbance intensity (i.e., HDI) on the margin of main tidal channels (i.e., MMC) was not beneficial to cordgrass invasion, whereas low HDI created windows of opportunity for cordgrass invasion to the margin of secondary tributaries (i.e., MST) by facilitating the survival, growth, and stability of cordgrass seedlings. The presence of high HDI predominantly reduced the seedling survival and total biomass of cordgrass, whereas root biomass allocation of cordgrass increased significantly to resist dislodgment and toppling. Moreover, field investigations showed that soil salinity and moisture in the margin of tidal channels were not the limiting factors affecting the establishment of cordgrass seedlings. However, higher propagule pressure combined with suitable soil salinity-moisture conditions (i.e., low salinity and high moisture) laid a firm foundation favoring seedling establishment. Our results highlight the importance of hydrodynamic disturbance as a dominating driver regulating seedling establishment of cordgrass in tidal channel margins and the potential implications for controlling cordgrass landward invasions. Image 1 • Low hydrodynamic disturbance creates cordgrass invasion window to channel margin. • High hydrodynamic disturbance reduces survival and total biomass of seedlings. • High hydrodynamic disturbance increases root biomass allocation of seedlings. • Soil salinity-moisture are not key factors for seedlings to invade at channel margin. • Propagule pressure is higher in margins of secondary tributaries than main channels. [ABSTRACT FROM AUTHOR]

In this study, the effect of the addition of zirconium-modified zeolite (ZrMZ) on the migration and transformation of phosphorus (P) in river sediments under static and hydrodynamic disturbance conditions was studied using sediment core incubation experiments. Results showed that, whether under static or hydrodynamic disturbance condition, the ZrMZ amendment suppressed the release of SRP from sediments into the overlying water. Furthermore, the addition of ZrMZ to the upper sediment (0-10 mm) not only resulted in the decrease of the dissoluble reactive P (SRP) concentration in the overlying water at a depth of 0-30 mm, but also led to the decrease of the diffusion flux of SRP from the pore water to the overlying water across the sediment-water interface (SWI). In addition, the ZrMZ amendment induced the transformation of the redox-sensitive P (BD-P) and HCl extractable P (HCl-P) into the metal oxide-bound P (NaOH-rP) and residual P (Res-P), thus resulting in the reduction of mobile P (sum of NH 4 Cl extractable P and BD-P) in the top 10 mm of sediment. In addition, the addition of ZrMZ into the top 10 mm of sediment resulted in reduction of the content of mobile P in 10-20 mm of sediment. Furthermore, the effect of ZrMZ addition on the migration and transformation of P in sediments under hydrodynamic disturbance condition had a certain difference from that under static condition. The presence of hydrodynamic disturbance enhanced the immobilization efficiency of SRP in the pore water at a depth of 0-20 mm by the ZrMZ amendment, and also increased the reduction efficiency of the SRP diffusion flux from the pore water to the overlying water across the SWI by the ZrMZ amendment. However, the efficiency of the control of SRP release from sediments to the overlying water by the ZrMZ amendment was slightly reduced by the hydrodynamic disturbance. The reductions of mobile P in the top sediment, SRP in the pore water as well as the diffusion flux of SRP from the pore water to the overlying water across the SWI played a key role in the control of SRP release from sediments to the overlying water by the ZrMZ amendment. Results of this work indicate that ZrMZ is a very promising amendment for the control of SRP release from river sediments under static and hydrodynamic disturbance conditions.