Water Sediment Research Articles

Fingerprinting of emerging contaminants in L'Albufera natural park (Valencia, Spain): Implications for wetland ecosystem health

Wetlands are crucial ecosystems that are increasingly threatened by anthropogenic activities. L'Albufera Natural Park, the second-largest coastal wetland in Spain, faces significant pressures from surrounding agricultural lands, industrial activities, human settlements, and associated infrastructures, including treated wastewater inputs. This study aimed at (i) establishing pathways of emerging pollutants entering the natural wetland using both target and non-target screening (NTS) for management purposes, (ii) distinguishing specific contamination hotspots through Geographic Information System (GIS) and (iii) performing basic ecological risk assessment to evaluate ecosystem health. Two sampling campaigns were conducted in the spring and summer of 2019, coinciding with the start and end of the rice cultivation season, the region's primary agricultural activity. Each campaign involved the collection of 51 samples. High-resolution mass spectrometry (HRMS) was employed, using a simultaneous NTS approach with optimized gradients for pesticides and moderately polar compounds, along with complementary NTS methods for polar compounds, to identify additional contaminants of emerging concern (CECs). Quantitative analysis revealed that fungicides comprised a substantial portion of detected CECs, constituting approximately 50% of the total quantified pesticides. Tebuconazole emerged as the predominant fungicide, with the highest mean concentration (>16.9 μg L−1), followed by azoxystrobin and tricyclazole. NTS tentatively identified 16 pesticides, 43 pharmaceuticals and personal care products (PPCPs), 24 industrial compounds, and 12 other CECs with high confidence levels. Spatial distribution analysis demonstrated significant contamination predominantly in the southwestern region of the park, gradually diminishing towards the north-eastern outlet. The composition of contaminants varied between water and sediment samples, with pharmaceuticals predominating in water and industrial compounds in sediments. Risk assessment, evaluated through risk quotient calculations based on parent compound concentrations, revealed a decreasing trend towards the outlet, suggesting wetland degradation capacity. However, significant risk levels persist throughout much of the Natural Park, highlighting the urgent need for mitigation measures to safeguard the integrity of this vital ecosystem.

Desertic siliciclastic stromatolites in the Upper Jurassic Guará Formation from southwestern Gondwana: Trapping and binding in a non-marine setting

Siliciclastic stromatolites are rare in the geologic record, and their occurrence recorded in the literature is restricted to marine and coastal environments. The Upper Jurassic Guará Formation, from the Paraná Basin in southern Brazil, hosts unique non-marine siliciclastic stromatolites, providing a rare opportunity to study trapping and binding mechanisms by microbial mats in a continental setting. These microbialites occur interbedded with eolian and fluvial facies. The structural layering of the stromatolite domes is formed by the intercalation of sandy layers, resulting from trapping and binding of siliciclastic grains by microbial mats and in situ precipitation of amorphous to cryptocrystalline silica, which directly replaced the microbial colonies. The silica layers contain partially preserved spherical to ovoid bodies interpreted as colonies of coccoid microorganisms. These siliciclastic stromatolites were formed due to a specific balance of environmental factors, namely water chemistry and sediment supply, which enhanced the processes of trapping and binding and in situ precipitation. They record the presence of microbial life in a non-marine, silica-rich, fluvial-eolian environment in which there were no previous published occurrences of agglutinated stromatolites. These specimens record macroscopically identifiable evidence of microbial life in a continental environment that must be accounted for in the search for ancient life on Earth and Mars.

The Correlation between Water–Sediment Index and Floodplain Transverse Slope Based on Wavelet Analysis

The floodplain transverse slope is a significant parameter reflecting the degree of development of a secondary suspended river, as well as a crucial index of the flood risk in the river channel. Clarifying the factors that influence the evolution of the floodplain transverse slope has always been a hot and difficult topic for researchers working on the Yellow River management. We took the severe section of the secondary suspended river from Dongbatou to Gaocun in the lower Yellow River as the research object, selecting the annual runoff, annual sediment load, annual sediment coefficient, and the intensity of flood-season flow scouring at the Huayuankou station in the downstream as the water–sediment indexes. The correlation between different water–sediment indexes and the floodplain transverse slope under three modes: interannual, flood season, and flood-season overbank was studied through methods such as cross-wavelet transform and wavelet coherence analysis. The results showed that under the three modes, the annual sediment load and annual sediment coefficient had a high correlation with the evolution cycle of the transverse slope, followed by the intensity of flood-season flow scouring, and the annual runoff had the lowest correlation. Meanwhile, the change in the transverse slope had a good correlation with the flood-season overbank mode, indicating there was a high similarity between the water–sediment characteristics of floodplain flooding and the evolution cycle of the transverse slope; that is, the change in the transverse slope is greatly influenced by floodplain flooding events.

Simulating the near-field dynamic plume behavior of disposed fine sediments

Projections of the effects of fine sediment disposals, relevant for managed estuaries and tidally influenced coastal areas, are typically based on numerical far-field models. For an accurate consideration of the disposal itself, near-field models are often needed. The open source near-field model, PROVER-M, simulates the relevant processes of the physics based, dynamic behavior of disposed fine sediments in coastal waters and is applied in this study. First, new small scale laboratory experiments of instantaneous disposals are presented, documenting the dynamic behavior of fine material disposed in shallow waters. Second, results of the PROVER-M model are shown for disposals in three different settings: (1) a field-scaled study complementary to the laboratory set-up, (2) a parametric study of sequentially varied model input and (3) a far-field model coupling for estimation of the PROVER-M impact. By comparing results of the laboratory experiments to the PROVER-M model, the physical behavior of PROVER-M is successfully validated. The impact of the ambient setting and dredged material parameters is evaluated by the PROVER-M simulations, where the results show non-linear, complex interdependencies of the input parameters on disposal properties in dependence of ambient site conditions and material composition. In this context, limits of the model application are assessed and critically discussed. Finally, an exemplary coupling to a far-field model based on a real set of disposals in the tidally influenced Weser estuary (Germany) illustrates the potential impact of PROVER-M for assessing far-field suspended sediment concentration (SSC), with increased maximum SSC values of up to 10%.

Quantifying the functional genes of C, N, P, and S cycling in a deep lake: Depth patterns and drivers

Microbial functional composition is important for biogeochemical cycles, and is usually constrained by taxonomic species pool and natural environmental gradients. However, the distribution of functional genes in deep lakes and the driving factors remains elusive. Here, we quantified the abundance of 71 functional genes relevant to carbon degradation, carbon fixation, methane metabolism, nitrogen cycling, phosphorus cycling, and sulfur cycling in 38 sediments along the water depth ranging from 0 to 90 m in Lugu Lake, China, using Quantitative Microbial Ecology Chip (QMEC) and then explored their water-depth diversity pattern and abiotic and biotic drivers. Functional gene diversity showed a hump-shaped pattern along the depth and peaked at around 50 m which is the low boundary of thermocline layer. There were specific environmental preferences among functional gene subgroups such as nitrogen and sulfur cycling genes preferring to deeper and shallow waters, respectively. The dissimilarity of total functional genes increased with water depth distance indicating a distance-decay relationship. There was a congruence between functional and taxonomic composition by showing the positive correlations between the compositions of functional genes and bacteria or archaea. This phenomenon is consistently observed for the six functional gene subgroups, and the congruence strength was highest for nitrogen cycling while lowest for sulfur cycling. Compared to abiotic factors, biotic factors were more relevant to the functional gene diversity and composition. Biotic factors explained 28.5 % of the variance of functional gene diversity, while water depth and other environmental factors such as water total phosphorus and sediment carbon explained 4.2 % and 3.8 %, respectively. For functional gene composition, biotic factors accounted for 25.2 % of the variance, whereas water depth and other environmental factors contributed to 0.7 % and 4.4 %, respectively. Among all explanatory variables for function genes, bacterial composition had the highest contribution, which was further supported by showing its direct effects of 1.45 and 0.86 on functional diversity and composition, respectively. This study for the first time quantified the microbial functional genes along water depth in deep lakes and provided a more comprehensive understanding of the functional dynamics in microbial communities within aquatic ecosystems.

Sediment water content drives movement of intertidal crab Helice tientsinensis more strongly than salinity variations

Intertidal wetlands undergo dynamic water and salinity variations, creating both promising and challenging habitats for diverse organisms. Crabs respond strongly to these variations by means such as altering their movements, thereby restructuring their spatial distribution and influencing coastal ecosystem resilience. However, the movements of crabs under varying environmental conditions require further elucidation. We conducted a systematic mesocosm experiment using the ubiquitous intertidal crab species Helice tientsinensis with four amount levels and six salinity levels of sprayed water applied through a custom apparatus, with a primary focus on crab movement. Crab movement from the experimental side of the apparatus (with altered conditions) to the control side (resembling field conditions of the intertidal wetlands of China's Yellow River Delta) and vice versa was recorded. The results revealed significant differences in moving out of the experimental side and moving in among the different water and salinity conditions, both separately for the two factors and simultaneously. Decreases in water content had a more pronounced effect on crab movement, leading to an increased number of crabs moving out of the experimental side of the apparatus. Conversely, as the experimental side became wetter, crabs tended to move towards it, and this movement was intensified by increases or decreases in water salinity. A structural equation model revealed that the moving-out and moving-in played fundamental roles in determining the number of resident crabs at the end of each experiment. While crabs preferred moist sediment with lower salinity, changes in salinity alone had minimal direct effect compared to sediment water contents. Our results clarify crab movements under varying water and salinity conditions, offering valuable insights to support adaptive interventions for crab populations and inform adaptive conservation and management strategies in intertidal wetlands.

Wastewater-effluent discharge and incomplete denitrification drive riverine CO2, CH4 and N2O emissions

Rivers are well-known sources of the greenhouse gasses (GHG) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). These emissions from rivers can increase because of anthropogenic activities, such as agricultural fertilizer input or the discharge of treated wastewater, as these often contain elevated nutrient concentrations. Yet, the specific effects of wastewater effluent discharge on river GHG emissions remain poorly understood. Here, we studied two lowland rivers which both receive municipal wastewater effluent: river Linge and river Kromme Rijn. Dissolved concentrations and fluxes of CH4, N2O and CO2 were measured upstream, downstream and at discharge locations, alongside water column properties and sediment composition. Microbial communities in the sediment and water column were analysed using 16S rRNA gene sequencing. In general, observed GHG emissions from Linge and Kromme Rijn were comparable to eutrophic rivers in urban and agricultural environments. CO2 emissions peaked at most discharge locations, likely resulting from dissolved CO2 present in the effluent. CH4 emission was highest 2 km downstream, suggesting biological production by methanogenic activity stimulated by the effluents' carbon and nutrient supply. Dissolved N2O concentrations were strongly related to NO3− content of the water column which points towards incomplete riverine denitrification. Notably, methanogenic archaea were more abundant downstream of effluent discharge locations. However, overall microbial community composition remained relatively unaffected in both rivers. In conclusion, we demonstrate a clear link between wastewater effluent discharge and enhanced downstream GHG emission of two rivers. Mitigating the impact of wastewater effluent on receiving rivers will be crucial to reduce riverine GHG contributions.

Analysis of Bathymetry Accuracy Using Sentinel 2 Satellite on Different Characteristics Waters in Bali Island

Bathymetry surveys today are often carried out using the echo-sounding method, but this method has disadvantages, such as requiring a lot of time and being quite expensive. Along with the development of technology, some alternative methods can be used to visualize bathymetry, such as remote sensing. Remote Sensing uses satellite imagery in the operation, while the technique to acquire bathymetry is called Satellite-Derived Bathymetry (SDB). This method uses an optical satellite with several color bands or multispectral images. In this research, a satellite used to map ocean depth is Sentinel-2. The SDB technique used in this research is the Lyzenga Algorithm. The Lyzenga algorithm uses multilinear logarithms in its operation and can be used using three optical image channels (blue, green, and red channels). Supported by the SDB algorithm, an analysis of research locations was carried out at several points in the waters of Bali Island due to the diversity of water characteristics such as sea depth and wave height. From several analysis results of different characteristic waters in Bali Island, We can see that many parameters impact the result of the Satellite to visualize bathymetry. The Satellite's optimal result for reading the bathymetry depth is approximately 30 meters. But in reality, some cases can interfere with the accuracy of Satellite visualizing bathymetry within this depth. Breaking waves, high water sedimentation, and some objects that could guide the Satellite to misread them as elevation.

Comprehensive evaluation of the distribution, transport and ecological risk of heavy metals in intra-urban river sediments using high-resolution techniques

Determining the distribution trends, transport mechanisms, and ecological risks of heavy metals (HMs) in urban river sediments is essential for the government to conduct appropriate remediation work. In this study, we collected sediment cores from the Yayao Waterway in Foshan City, China. The vertical distribution profiles of dissolved and labile Fe, Mn, Cd, Zn, Cu, Cr, Ni, Pb, As, and Co in the sediments were obtained using the thin-film diffusive gradient (DGT) and high-resolution peeper (HR-Peeper) techniques. In addition, the transport rates, contamination levels, and ecological concerns of the HMs were evaluated using the European Community Bureau of Reference (BCR) sequential extraction technique, the DGT-induced sediment fluxes (DIFS) model, and multiple contamination evaluation metrics. The results showed that most of the DGT-labile HMs were associated with Fe/Mn (hydrogen) oxides, and in particular, Zn, Ni, and Cr showed a significant negative correlation with Fe/Mn (p < 0.001). Additionally, Cd had the highest bioavailability (89.17%), and its net diffusive flux at the sediment–water interface (SWI) was positive, which indicated a high release risk from the sediment. However, the R-value of Cd based on the DGT-induced sediment fluxes (DIFS) operation was extremely low, suggesting that although Cd had the biggest supply pool of releases, its release rate was slow. The majority of sampling sites had significantly higher total HM contents in the surface sediments than the background values. The HM contamination in the sediments originated from human activities, primarily from industrial enterprises and with a large contribution from both agricultural and domestic sources. The most polluted HM with the highest ecological danger was Cd, followed by Cu, Zn, Ni, and As when the results of the four pollution evaluation indicators were combined. Consequently, the risk of contamination by HMs in inner-city river sediments should receive more attention.

Aquacultural source of nitrous oxide revealed by nitrogen isotopes

The rapid expansion of coastal aquaculture has led to an increase in the coverage of aquaculture ponds, where intense feed-derived nitrogen is causing significant emissions of nitrous oxide (N2O). Multiple N2O production pathways and the relative importance of water column vs. sedimentary production in aquaculture ponds remain uncertain. Clarifying these pathways is vital for sustainable aquaculture development. Using 15N-labeled dissolved inorganic nitrogen, the pathways and rates of N2O production in subtropical aquaculture ponds located in south China, cultivating whiteleg shrimp, Japanese seabass, and giant river prawn, were successfully characterized. Total N2O production rates ranged from 6 to 70 µmol-N m−2 d−1, with the shrimp pond exhibiting the highest total N2O production rates, followed by ponds for seabass and prawn. These differences are primarily due to varying feed amounts causing differences in dissolved nutrients in water column and sediment. Particularly, nutrient and organic matter accumulation at the surface sediment stimulated N2O production. The oxygenated sediment on a centimeter scale could produce substantially more N2O compared to the water column above on a meter scale. Partial denitrification, i.e., nitrate and nitrite reduction to N2O, was more important (> 60 %) for N2O production in aquaculture ponds. The availability of nitrite is likely a major factor driving partial denitrification for both sedimentary and water column N2O production.

Decomposition of waterside plants greatly affects the transformation and mobility of sedimentary antimony in water–sediment systems after emergency treatment: A microcosm study

Polyferric sulfate (PFS) coagulation has proven to be effective in addressing antimony (Sb) water pollution accidents; however, the impact of waterside plant decomposition on its effectiveness has not been adequately elucidated. This study investigated the effects of Alternanthera philoxeroides (AP) and Digitaria sanguinalis (DS) decomposition on Sb cycling after PFS treatment. Without plant decomposition, the Fe(OH)3 hydrolysate-associated Sb remained stable, and the sediment continued to exhibit Sb sink properties. Plant residue decomposition facilitated sedimentary Sb release, and DS decomposition had a greater impact than AP decomposition. The strong decomposition phases triggered abiotic/biotic reduction processes, leading to Fe(OH)3 dissolution and subsequent Sb(V) release. Concurrently, sulfate reduction and dissolved organic matter (DOM) release regulated Sb mobility. In addition, Sb(V) reduction occurred, and Sb(III) was elevated in the overlying water. The Sb(III) levels gradually decreased during the later aerobic stages, however, did not completely disappear within a short timeframe. Furthermore, the role of the sediment as an Sb sink was significantly hindered, maintaining relatively high levels of dissolved Sb. Sedimentary Sb speciation analysis revealed that plant decomposition induced a shift in Fe-oxyhydroxide-bound Sb to more bioavailable and stable fractions. Our results indicate that plant residue decomposition easily deteriorates PFS efficiency and increases the risk of secondary Sb pollution in water–sediment systems.

Phosphorus inactivation mitigates the effect of warm winters in a temperate shallow lake (Mielenko Lake, Poland)

Direct and indirect anthropopressure on water ecosystems is the serious problem throughout the world.. In the Northern Hemisphere, an increase in average air temperatures is observed, which implies the occurrence of a shorter period of snow and ice cover during the winter season. The winter 2019/2020 was unusual, because that was the first time in the record, that a complete lack of permanent ice cover was observed on numerous lakes in Poland. Such unusual conditions could influence lake functioning. Hence we analyzed the chemistry of the water–sediment interface (near-bottom and interstitial water and sediment) in the shallow, eutrophic Mielenko Lake (area 7.9 ha, max depth 1.9 m) in 2013 and 2019–2022 period to assess the influence of prolonged water circulation on the bottom zone. Mielenko Lake was subjected to a phosphorus inactivation procedure using Al and Fe salts (PAX 18, PIX 111) in 2020 and 2021. Our research revealed that unusually prolonged winter circulation caused a significant decrease in organic matter content in bottom sediment in 2020, as well as a decrease in NaOH-nrP fraction and TP amounts. That effect was short-term and it did not significantly influence the NaOH-rP fraction amounts. The released P was probably built in macrophytes biomass during vegetation season, because P inactivation has been limiting phytoplankton proliferation, and it favored shifting to a clearwater state with macrophytes domination. This was confirmed by decreasing in phytoplankton biomass, and a massive expansion of the macrophytes range noted in the second year of restoration. Our study shows, that P inactivation could mitigate the negative effects of warm winters in shallow lakes.

Characteristics and Mechanisms of Spring Tidal Mixing and Sediment Transport in a Microtidal Funnel-Shaped Estuary

Information about estuarine mixing and its control of sediment transport is crucial to elucidating the dynamics and evolution of estuaries. Here, the microtidal and funnel-shaped Zhenhai Estuary, located in the southwestern Pearl River Delta of China, is used to investigate the characteristics and mechanisms of water mixing and sediment transport based on observations from three spring tides. The results reveal that the studied estuary remains well mixed during spring tides from 2013–2022 despite its microtidal regime. Tidal stirring, which is enhanced by tidal energy convergence and benefits from the funnel-shaped geometry and shallow bathymetry, favors vertical mixing, contributing to the formation of strong mixing in the estuary. Due to the well-mixed regime, sediment transport in the estuary is dominated by the advective term, followed by a moderate tidal pumping term and minor estuarine circulation term. Accordingly, sediments within the estuary tend to be transported landward owing to the regulation of the funnel-shaped geometry, and a gradual but slow infilling trend is predictable. This paper deepens our understanding of hydrodynamics and sediment transport in microtidal estuaries.

Influence of seawater loading on the thermal history of underlying strata in an oceanic basin—an example from the eastern Gulf of Papua

The eastern Gulf of Papua, at the easternmost end of the Papuan Basin, has been subjected to extended seawater loading during the Cenozoic, allowing an investigation into the influence of seawater loading on the thermal development of the underlying rock layers in the oceanic basin. Utilising paleontological, lithologic and paleobathymetric data, along with present-day temperature fields, this study reconstructed the burial history, thermal history and maturity of the eastern Papuan Basin using PetroMod2012.2 1D software. Burial history curves for the virtual wells were employed to trace the evolutionary stages in different regions, revealing a positive relationship between predicted vitrinite reflectance (R o) and modelled thermal history. R o values displayed a gradual decrease from northeast to southwest, with higher R o values observed in areas unaffected by seawater loading. The presence of seawater loading had a notable impact on thermal history, particularly influencing the upper boundary condition and the sediment–water interface temperature of the temperature field. This research enhances our understanding of the Meso-Cenozoic thermal history of the eastern Papuan Basin and reveals the factors influencing stratigraphic thermal evolution.

The Effect of Land Cover Change on Soil Erosion in Awach Kibuon Sub-basin, Kenya

Land cover change is a significant driver of soil erosion. While soil erosion is a natural process, human activities can significantly alter the landscape, making soil more vulnerable to erosion. This erosion reduces a watershed&amp;apos;s capacity to sustain vital natural resources and ecosystem services. This study investigated the impact of these changes on soil erosion within four hydrological units (Awach Kibuon, Awach Owade, Awach Kasipul, and Awach Kabondo) of the Awach Kibuon sub-basin between 2018 and 2023. The specific objective of the study was to quantify the effect of land cover change on soil erosion rate and determine how specific land cover types affect soil erosion in the study area. This study employed a quasi-longitudinal design to assess the influence of land cover changes on soil erosion. Sentinel-2 NDVI satellite imagery provided land cover data. The land cover maps, soil data, rainfall data and the Digital Elevation Model were used in the Revised Universal Soil Loss Equation Model within a GIS environment to estimate soil erosion rates. The study revealed a consistent decline in vegetation cover across all hydrological units, as indicated by a decrease in NDVI. The mean NDVI decreased by 12.88%, 10.92%, 4.78%, and 11.92% in Awach Kibuon, Awach Owade, Awach Kasipul and Awach Kabondo respectively. Conversely, the mean soil erosion rate increased by 23.9% in Awach Kibuon, 17.85% in Awach Owade, 24.43% in Awach Kasipul, and 20.54% in Awach Kabondo. Sediment yield increased by 33% in Awach Kibuon, 18% in Awach Owade, 17% in Awach Kasipul, and 23% in Awach Kabondo. These findings suggest a direct relationship between reduced vegetation and elevated soil erosion. The relationship between land cover and erosion varies depending on the density of vegetation. Areas with dense vegetation cover have an inverse relationship, highlighting the protective role of vegetation cover. However, the study also observed that very dense vegetation areas which were also found in high-sloped areas experienced high soil erosion rates. The erosion rate increases even in areas that have experienced an increase in vegetation cover. This is because these areas are also found in high-sloped areas. The slope factor superseded the ability of vegetation cover to protect against soil loss. In conclusion, the change in land cover has significantly increased soil erosion in the Awach Kibuon Sub-basin, however, the slope factor also accelerated soil loss in the basin. Therefore, a holistic approach that combines promoting vegetation cover with land management techniques like terracing and drainage channels is crucial for mitigating soil degradation and water sedimentation in sub-basin.

What to monitor? Microplastics in a freshwater lake – From seasonal surface water to bottom sediments

Marine microplastics have received considerable attention, and efforts are underway to develop standardised methods for sampling, sample treatment, and analysis, while the observation of freshwater ecosystems remains relatively overlooked. To address this understudied environment, we present a comprehensive case study on microplastics in an urban lake from Baltic region of Northern Europe covering the seasonal dynamics of microplastics in surface water, deposition rate throughout one year in sediment traps and distribution of microplastics in dated sediment archive to determine the most representative environmental compartment for microplastic pollution monitoring. The following well-established microplastic research methods have been used: Manta trawling for surface water, trapping for assessing microplastics sedimentation rate and coring for sediments. Attenuated total reflection and micro-Fourier transform infrared spectroscopy methods were used to investigate the synthetic nature of identified particles. The sediment core chronology was based on 210Pb and Bayesian Plum model revealing sediment layers to represent even the time before the beginning of plastic mass production (approximately 1950). The surface water microplastic concentrations were higher in summer (5.71 particles/m3) and gradually decreased towards winter (0.75 particles/m3); they were almost 25 times higher in more recent (2018) sediments than in the deeper layers referring to years prior to 1890. Surprisingly, microplastic particles were found in sediments before the year 1950. The microplastic deposition rate was 9.47 particles/cm2/year or 4.31 µg/cm2/year. The most abundant polymers were polyethylene, polystyrene and polypropylene, and the prominent particle shapes were fibres in surface water and fragments in sediments. Our results provide a baseline for evaluating future contamination level changes in highly urbanized area. We recommend the combination of surface water filtering with net and sediment trapping methods for monitoring microplastics in lakes since this method requires little time and financial resources for sampling and processing and produces information on temporal microplastic occurrence and deposition.

Boat effects on lake water clarity and the efficacy of a no-wake zone policy

Boating activity in shallow waters of lakes can lead to sediment resuspension and potential nutrient release, affecting water quality parameters. No-wake zones, to minimize boating-induced effects, are often defined based on distance from shore. This study assessed the effects of boating on shallow waters and the efficacy of an existing no-wake zone policy in a midsize lake. Two experiments were conducted: (1) Turbidity and pressure data were collected along a broad shallow shelf on the southern shore of Lake Tahoe in the summer of 2019 and (2) turbidity and pressure observations were conducted while boats traveled at speeds between 8 kmh−1 (5 mph) and 40 kmh−1 over a water depth of ≈ 2.5 m. Results showed that boat-induced sediment resuspension occurred at speeds exceeding 8 kmh−1, with turbidity increases of up to ∼7 NTU. Boat-induced filtered pressure signal was a maximum of 40% of the total daily wave activity, with peaks observed between 10:00 and 12:00. Nevertheless, during the summer and fall of 2019, winds were the dominant driver of sediment resuspension, contributing around 80% of the total wavefield. An evaluation of the current no-wake zone policy at Lake Tahoe suggested that an 8 kmh−1 (5 mph) speed limit is suitable for preventing wake effects. However, the policy falls short in preventing sediment resuspension in the northwestern and southern shores of Lake Tahoe. This calls for the consideration of multiple variables, such as lakebed sediment type and water depth, when defining no-wake zone policies to effectively mitigate boating-induced effects.

Nitrate and silicate fluxes at the sediment–water interface of the deep North Pacific Ocean illuminated by 226Ra/230Th disequilibria

By taking advantage of recent analytical advances, we herein develop the 226Ra/230Th isotope systematics as a novel tool for quantifying nitrate and dissolved silicate fluxes across the sediment–water interface of the deep-ocean floor. Sediment cores were retrieved from the seabed between 4927 m and 5951 m in the North Pacific Ocean. Downcore profiles of 230Th and both dissolved and total 226Ra were measured using a high-sensitivity inductively coupled plasma mass spectrometer. At all study sites, a marked deficit of total 226Ra with respect to 230Th was observed between 0 and 20 cm, indicating active migration of soluble 226Ra from the sediment into the overlying seawater. By constructing the mass balance of 226Ra in the sediment column, the flux of dissolved 226Ra across the sediment–water interface was estimated to range from 461 to 1320 dpm m−2 yr−1. When coupled to a diffusive transport model as developed by early investigators, these flux values of 226Ra enabled us to calculate the flux of any dissolved constituent of interest by measuring their bottom water concentrations and pore water “saturation” concentrations. Based on the 226Ra/230Th disequilibrium approach, the derived fluxes vary between 4.1 and 10.5 mmol m−2 yr−1 for nitrate and between 11 and 49 mmol m−2 yr−1 for dissolved silicate. A compilation of nitrate and silicate fluxes from the seabed in the deep Pacific Ocean shows that these values are consistent with historical flux measurements based on the conventional core incubation method in the same study region. In addition, both nitrate and silicate fluxes exhibit a clear depth-dependent trend. Overall, our results suggest that sedimentary diagenetic alterations at the North Pacific Ocean floor below ∼ 5000 m are efficient so that only < 2 % of the particulate organic carbon and < 12 % of the biogenic opal raining to the seafloor are ultimately preserved in the sediment.

Impacts of hydrodynamic disturbance on black blooms: An in-situ study in Lake Taihu

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 (NH4+-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.

Spatiotemporal evolution of runoff and sediment and their dominant driving factors in the Lower Jinsha River basin

The Jinsha River Basin (JRB) contributes a significant amount of sediment to the Yangtze River; however, an imbalance exists between runoff and sediment. The underlying mechanisms and primary factors driving this imbalance remain unclear. In this study, the Shapley Additive Explanation (SHAP) and Geographical Detector Model (GDM) were employed to quantify the importance of the driving factors for water yield (WYLD) and sediment yield (SYLD) using the Soil and Water Assessment Tool (SWAT) model in the JRB. The results indicated that the SWAT model performed well in simulating runoff and sediment, with R2 > 0.61 and NSE > 0.5. Based on the simulated data, SYLD exhibited strong spatiotemporal linkages with WYLD. Temporally, both sediment and runoff showed decreasing trends, with the sediment decrease being more pronounced. Spatially, WYLD and SYLD displayed similar distribution patterns, with low values in the southwest and high values in the northeast. By quantifying the driving factors, we found that climatic factors, including precipitation and potential evapotranspiration, were the main influencing factors for WYLD and SYLD across the entire region, though their contributions to the two variables differed. For WYLD, climatic factors accounted for 70 % of the total influencing factors, whereas their contribution to SYLD was 50 %. Furthermore, soil type and land-use type played significant roles in the SYLD, with importance values of 16 % and 12 %, respectively. Under the influence of surface conditions, the proportion of SYLD in the JRB to the total SYLD in the Yangtze River Basin was greater than that of WYLD. The findings of this study provide scientific evidence and technical support for local environmental impact assessments and the formulation of soil and water conservation plans.