Similar to fresh- and brackish water aquaculture ponds, commercial shrimp farming in degraded saline areas holds the potential to bury carbon (C) in the sediments. However, studies on the mechanisms of sediment C dynamics and C-flux in response to inland saline aquaculture management practices are still scarce. Therefore, the objectives of the present study are to quantify the C burial rate in inland saline aquaculture ponds and assess the impact of inland saline aquaculture on sensitive C fractions in the bottom sediment of the ponds.
Materials and methodsThe sediment samples (n?=?12 from each pond) were collected from six shrimp farming ponds (1000 m2 area of each pond) of different ages. The sediment depth, sediment accumulation rate and the levels of total carbon (TC), total organic carbon (TOC) and sediment oxidizable organic carbon (SOC) and its different fractions were determined using standard procedures. The data were analysed by one-way analysis of variance (ANOVA), followed by the Duncan's multiple range test for comparing the means, and the Pearson correlation test was used to assess the relationship between the different pond sediment parameters and SOC content.
Results and discussionThe results revealed that the annual C accumulation rates varied from 902 to 1346 kg C ha?1 year?1 in 7-year-old earthen ponds (EPs) and bottom cemented ponds (BCPs), respectively. The sediment C fractions, including TC, TOC, SOC and its fractions (very labile, VLc; labile, Lc; less labile, LLc), and non-labile carbon (NLc)) were progressively increased over the pond age. The inland saline aquaculture practices over the years increased both active (AC) and passive carbon (PC) pools in the pond sediments, helped in the restoration and improvement of sediment quality and enhanced C sequestration potential of the sediments. Furthermore, a significant increase in the level of particulate organic carbon (POC) in BCPs justified that the non-ploughing practices at BCPs facilitated the formation of macro- and micro-aggregates, thereby increasing the C retention and stability of the pond sediments.
ConclusionThis study suggested that the shrimp farming ponds in semi-arid saline soils represented considerable C burial hotspots, enhanced the stable passive C pools and improved the sediment quality.
相似文献Here, the roles of sediment components in perfluorooctane sulfonate (PFOS) adsorption onto aquatic sediments and relevant adsorption mechanisms were investigated in terms of adsorption isotherms and influences of TiO2 nanoparticles (NPs) contamination.
Materials and methodsDue to the complexity of the sediments, instead of randomly selecting different component sediments, the selective dissolution method was used to better explore the effects of sediment compositions, such as sediment organic matter (SOM) and ferric oxides (dithionite–citrate–bicarbonate [DCB] Fe), and TiO2 NPs pollution on PFOS adsorption. Mathematical equations (Freundlich, Langmuir, and Temkin) were used to describe the adsorption behavior of PFOS on different sediments and adsorption mechanisms of multiple pollutant interactions. Moreover, the characterization methods of zeta potential, nitrogen (N2) adsorption–desorption, and scanning electron microscopy (SEM) analysis, as well as Fourier transform infrared (FT-IR) spectroscopy, explained effects of the sediment components and TiO2 NPs on PFOS adsorption properties in view of physicochemical theories.
Results and discussionThe adsorption isotherms of PFOS on six tested sediments were all nonlinear (Freundlich model, R2 = 0.992~1.000). The Freundlich sorption affinities (KF) of PFOS on S (original sediments), S1 (sediment organic matter (SOM)-removed S), and S2 (ferric oxides (DCB Fe)-removed S1) were 0.232, 0.179, and 0.120, respectively. Both SOM and DCB Fe influenced the physicochemical properties of the sediments, e.g., zeta potential, specific surface area, and permanent negative charge. The addition of TiO2 NPs increased the KF of PFOS for S, S1, and S2 by approximately 9.9%, 14.5%, and 26.7%, respectively, by increasing the zeta potential and specific surface area (SBET, Sext, and Smicro) and by changing the water and oil properties of the three sediments. However, the addition of TiO2 NPs decreased the linearity of the sorption isotherm (1/n). FT-IR spectroscopy showed that hydrophobicity, ion exchange, surface complexation, and hydrogen bonding interactions (non-fingerprint region) could all play a role in PFOS sorption onto tested sediments. However, the hypothesis of hydrogen bonding to promote PFOS adsorption on sediment layer silicates (fingerprint region) should be studied further.
ConclusionsThe content of both SOM and DCB Fe affected the physicochemical properties of sediment. Both SOM and DCB Fe showed a positive relationship with sorption of PFOS on sediment. The addition of TiO2 NPs increased PFOS sorption by altering the sediment surface properties. Hydrophobic interactions certainly impelled and ligand and ion exchange and hydrogen bonding (non-fingerprint region) could promote PFOS sorption on the sediments.
相似文献Suspended matter (SM) in streams is usually considered of minor importance in Danish environmental management. However, SM has some ecological effects as it may (1) clog fish spawning grounds and (2) act as an important agent for transport and exposure of biota to chemical substances, such as phosphorus and toxic inorganic (e.g. heavy metals) and organic (e.g. pesticides) substances.
Materials and methodsA large national data set of >?100,000 water samples analysed for SM and loss on ignition was investigated for spatial concentration patterns, sediment yields and temporal trends. Moreover, the importance of SM as a transport agent for phosphorus and heavy metals in streams was investigated through a correlation analysis.
Results and discussionThe mean suspended matter concentration (SMC) (including organic matter) amounted to 12 mg l?1, with an organic content of 4.9 mg l?1 (41%). A clear difference in SMC temporal trends over the sampling period was found between geographical regions. Sediment yields were calculated for all major catchments revealing low sediment yields (1–15 t km?2 year?1) compared to neighbouring countries and showed clear geographical patterns. Statistically significant relationships were established between SMCs, suspended sediment concentrations (SSCs) (excluding organic matter) and organic matter concentrations (OMCs) and particulate phosphorus (PP) concentrations, and again spatial patterns appeared. However, it was clearly shown that SMC/SSC/OMC could not be used as a robust, nationwide, indicator for PP concentrations. Analyses of the relationship between SMC and particle-bound heavy metal concentrations generally revealed weak correlations except for Pb and Ni (median R2?>?0.3).
ConclusionsRelatively low SM concentrations and sediment yields were found. SM is, in some geographical regions, an important transport agent for PP. Clear geographical patterns occurred in the relationships between SMC/SSC/OMC and both river water discharge and PP, as well as for sediment yields and for temporal trends in SMC.
相似文献The pollution of marine sediments by heavy metals is still a major concern, especially in zones affected by industry or mariculture. Toxicity of sediment heavy metal contents may be assessed using sequential extraction (SE) procedures, minding inherent constraints of such approaches. In this study, we investigated heavy metal speciation and toxicity in anoxic marine sediments in Zhelin Bay, a mariculture bay in Southern China, using an SE and acid volatile sulfur-simultaneously extracted metals (AVS-SEM) approach.
Materials and methodsSpeciation of Cd, Cu, Ni, Pb, and Zn were studied by a modified SE of five fractions, adapted to separate organic and sulfidic metal fractions in anoxic sediments: F1 weak acid soluble (readily available), F2 reducible fraction, F3 organic matter-bound fraction, F4 sulfide-bound fraction, and F5 residually bound fraction. Toxicity predictions based on the sum of non-residual (NR) metal fractions from sequential extraction were compared to predictions based on AVS-SEM.
Results and discussionResults showed that Cd, Ni, and Pb predominantly occurred in the weak acid soluble fraction (F1), residual fraction (F5), and sulfide-bound fraction (F4), respectively; Cu and Zn were mainly obtained in F4 and F5. Based on the distribution of indicator elements for metal fractions, the SEM from AVS extraction included different yields of non-residual and residual fractions besides the sulfidic fraction. Estimates for potential heavy metal toxicity based on NR metals of the SE procedure were thus based on a better-defined speciation compared to the simplistic approach of the AVS-SEM method.
ConclusionsBased on the contents of NR metals and normalizing them by organic matter content, toxic effects are not expected for any of the sampling sites, irrespective of the presence or absence of mariculture. Using Pearson correlation analysis to identify predominant fractions influencing toxicity, we conclude that toxicity of heavy metals in anoxic sediments can be well predicted by their non-residual heavy metal contents.
相似文献Run-off from industrial and agricultural activities has continued to be a major source of organohalogenated contaminants (OHCs) in the environment. Swartkops (SWE) and Sundays Estuaries (SDE) located in the city of Port Elizabeth, South Africa, were selected for this study because of their proximity to industrial and agricultural activities.
Materials and methodsIn this study, we determined the levels, seasonal occurrence as well as the ecological risk monitoring of 18 organochlorine pesticides (OCPs), 17 polychlorinated biphenyls (PCBs) and six polybrominated diphenyl ethers (PBDEs) in the sediments of SWE and SDE using a gas chromatograph coupled with a micro electron capture detector.
Results and discussionHCHs, BDE-17, tri- and tetra-CBs dominated the OHC profiles in sediments of both estuaries. The respective concentration ranges of OCPs, PCBs and PBDEs in SDE sediment were 0.06–0.93 μg g?1 dw, 0.08–1.71 μg g?1 dw and 0.08–32.41 ng g?1 dw while that of SWE in that order were 0.10–4.70 μg g?1 dw, 0.07–3.80 μg g?1 dw and 0.11–130.21 ng g?1 dw. The high concentrations of OHCs in SWE may be due to the high usage of its surrounding area for industrial activities. The concentrations of all OHCs with exception of PCBs were higher in spring for both estuaries probably due to the heavy rain experienced during spring season. Cluster analysis and spatial distribution of OHCs indicated that samples around the Motherwell Canal in the SWE were more polluted. Total organic carbon (TOC) was strongly correlated with most OHCs in SWE revealing that TOC controls the sorption of OHCs in this estuary. Risk analysis showed that most sampling points had PCBs and HCHs concentration greater than their respective sediment quality guideline (SQGL) indicating a high risk to benthic species in SDE and SWE.
ConclusionsSamples collected from the SWE were more polluted than those collected from the SDE probably due to the extensive use of the catchment of SWE for industrial activities. In comparison with SQGL, most sampling points had PCBs and HCHs concentrations greater than their respective ERL and TEL values, indicating the potential risk to biota in SDE and SWE. Thus, an urgent need to manage and mitigate the OHCs concentrations in these estuaries is recommended.
相似文献Mercury (Hg) and methylmercury (MeHg) are easily released from sediments to overlying water and cause secondary contamination. In general, Hg concentrations are low in natural aquatic environments, but Hg toxicity is high. Therefore, it is important to assess the mobility and release risks of Hg and MeHg from surface sediment using in situ high-resolution sampling techniques.
MethodsThe profile distribution of Hg and MeHg was obtained for samples from Weishan sub-lake (WL) and Dushan sub-lake (DL) of Nansi Lake, China, by high-resolution dialysis (HR-Peeper probes) and the diffusive gradients in thin films (DGT) technique at mm-resolution. Furthermore, Hg mobility and release risks in sediments were evaluated by combining BCR (European Community Reference Bureau) extraction and DGT-measured data.
ResultsThe soluble concentrations of Hg in surface sediments in WL and DL were 21.70 and 19.38 ng L?1 and the DGT-labile concentration of Hg were 8.21 and 10.30 ng L?1, respectively. The soluble and labile Hg and MeHg concentrations were higher in the surface sediments (from??40 to 0 mm) than in deep sediments. The distribution of the labile-Hg was controlled by the ferrimanganic (hydr)oxide and total nitrogen rather than organic carbon content. The non-residual components accounted for a greater proportion of the interface, which further confirmed Hg was more active on the surface layer of the sediment. The resupply ability indicated that the release of Hg from sediment was insufficient to maintain the initial concentration in the porewater before consumption. The MeHg fluxes in WL (6.18 ng m?2 day?1) were twice those in DL (2.89 ng m?2 day?1), and the risk assessment code revealed a higher risk in the surface layer (25.21–61.88%) than in the deep layer (0–27.75%).
ConclusionsDissolved Hg and MeHg accumulated on the surface of the sediments and were more active than in the deeper sediments. The DGT-labile state can be used for a better understanding of the bioavailability and mobility of Hg. The diffusion direction of Hg and MeHg was from sediment to the overlying water. The release risks of Hg and MeHg from surface sediments (especially in WL) were found to be worthy of concern.
相似文献Fluvial sediments can act as archives for lipophilic pollutants. However, their distribution within the highly dynamic regime of the river corridor is scarcely investigated. Herein, a novel approach combining geochemical investigations of sediment bodies in the river corridor of the Wurm River (catchment < 400 km2) and aerial photograph evaluation provide information about the history of river course change and the distribution of pollution by selected persistent organic compounds (POPs) and selected heavy metals.
Materials and methodsThe study is based on nine sediment cores and a total number of 45 subsamples. The sediment samples were analyzed for trace element inventory (X-ray fluorescence), grain size composition (laser diffraction particle size analyzer), and organic compounds (chromatography-mass spectrometry). On the basis of quantitative data of persistent organic substances as well as three heavy metals (Cu, Pb, and Zn) and morphological changes from 1953 until 2016 of the area of investigation provided by eight aerial photographs, analyzed sediments were assigned to different decades, and lateral migration rates as well as deposition rates were calculated.
Results and discussionHigh morphodynamics within the river corridor limits the explanatory power of single approaches (for example, geochronology and radiometric dating). However, a combination enables further insight into floodplains such as the pollution history, spatial pollutant dispersal, hotspot localization, meander migration rates (0.2–0.5 m year?1), sedimentation rates (0.5–5.2 cm year?1) and estimation of hotspot remobilization. Quantitative data for the analyzed heavy metals (Cu, Pb, and Zn) show a decreasing trend for locations with younger sediment bodies, whereas quantitative data for the synthetic organic pollutants reflect the corresponding history of emissions with increasing concentrations until a climax followed by decreasing concentrations due to restrictions regarding their application.
ConclusionsResults reveal hotspot areas for POPs and their degree of remobilization. This study demonstrates that by knowing the history of emissions of a lipophilic substance, potential hotspots can be localized solely based on a sufficient number of aerial photographs documenting the river channel migration and sediment body formation in the corresponding period of time.
相似文献Purpose
Marine mangrove sediments in the Manche-à-Eau lagoon (Guadeloupe, Caribbean Sea) harbor locally extensive, white microbial mats. These mats cover the surface of reduced sediments near the roots of red mangrove trees, Rhizophora mangle, and are mainly composed of sulfur-oxidizing bacteria belonging to the Beggiatoaceae family, with some filamentous cyanobacteria. The goal of this study was to investigate the possible influence of sediment characteristics on the presence of these microbial mats.Materials and methods
Four push cores were collected in April 2013, two from zones with microbial mats and two from zones without mats. Sediment characteristics (grain-size distribution, mineralogy, total organic carbon (TOC) and total nitrogen (TN) contents, atomic TOC/TN ratios, and organic matter (OM) δ13C values) were compared for all four cores.Results and discussion
Significant differences were observed between sediments below microbial mats and those without mats. Sediments with microbial mats contained greater amounts of clay, and higher TOC, TN, and TOC/TN ratios, with lower total carbonate content and δ13C values. The higher clay content most likely results from lower fluid flow velocity near to mangrove roots, while higher TOC/TN ratios and lower δ13C values indicate higher inputs of OM from mangrove trees. These results are consistent with the fact that microbial mats were observed near the roots of mangrove trees, which trap OM from terrestrial vegetation and fine sediments.Conclusions
The grain-size distribution of sediment particles, the total carbonate content, and the δ13C values are the main parameters discriminating between zones with microbial mats and those without mats. Variations in total carbonate content, which is mainly of biogenic origin, result from conditions that are more favorable for benthic organisms in zones without microbial mats. Variations of the TOC/TN ratios are controlled by the presence of a non-negligible amount of inorganic nitrogen bound to surface clay mineral particles and/or by microbial processes.The microbial turnover of sediment organic matter (OM) in ports and waterways impacts water quality, sonic depth finding and presumably also rheological properties as well as greenhouse gas emissions, especially if organic carbon is released as methane. As a consequence, sediment management practices as a whole are affected. This study aimed to discern spatial OM degradability patterns in the Port of Hamburg and investigated correlations with standard analytical properties as a basis for future predictive modelling.
Materials and methodsSediments in the Port of Hamburg were repeatedly sampled at nine locations along an east-west transect using a 1-m corer. In a stratified sampling approach, layers of suspended particulate matter (SPM), fluid mud (FM), pre-consolidated sediment (PS) and consolidated sediment (CS) were identified and individually analysed for long-term aerobic and anaerobic degradation of organic matter, DNA concentration, stable carbon isotope signature, density fractions and standard solids and pore water properties.
Results and discussionThe investigation area was characterised by a distinct gradient with a 10-fold higher OM degradability in upstream areas and lower degradability in downstream areas. Concomitantly, upstream locations showed higher DNA concentrations and more negative δ13C values. The share of bulk sediment in the heavy density fraction as well as the proportion and absolute amount of organic carbon were significantly larger at downstream locations. A depth and hence age-related gradient was found at individual locations, showing higher degradability of the upper, younger material, concomitant with higher DNA concentration, and lower OM turnover in the deeper, older and more consolidated material. Deeper layers were also characterised by higher concentrations of pore water ammonium, indicative of anaerobic nitrogen mineralisation.
ConclusionsOrganic matter lability is inversely linked to its stabilisation in organo-mineral complexes. The observed degradability gradient is likely due to the different OM quality in relation to its origin. Downstream OM enters the system with the tidal flood current from the direction of the North Sea whereas upstream locations receive OM originating from the catchment, containing more autochthonous, plankton-derived and more easily degradable components. At individual sampling points, depth-related degradability gradients reflect an age gradient, with easily degradable material in top layers and increasing stabilisation of OM in organo-mineral compounds with depth.
相似文献The purpose of this work is to study the dynamics between the matrix of a contaminated marine sediment, its contaminants and various desorbing solutions by means of equilibrium tests, sedimentation trials and zeta potential, with the focus on assessing optimum enhancing solutions for decontamination purposes.
Materials and methodsThe sediment samples were analysed to determine their physico-chemical characteristics: particle size distribution, solids concentration, total organic carbon (TOC), content of heavy metals, organic contaminants, mineralogical phases, zeta potential and buffer capacity. Twelve extracting solutions of different nature were used for equilibrium tests, in which the dynamic behaviour of the sediment was evaluated. Elemental analysis was carried out for the sediment samples and the solutions before and after the tests.
Results and discussionThe sediment was mainly composed of clay and lime, with a high content of iron, which has a strong influence on sorption-desorption processes. The sediment had a considerable buffer capacity at low and high pH values. The desorption of the metals was not proportional to pH. The highest decrease in the concentration of metals from the sediment was obtained with 0.2 M ethylenediaminetetra-acetic acid (EDTA) and 1 M nitric acid, while the lowest degree of metal extraction occurred in pure water and potassium iodide (KI).
ConclusionsThe most important parameters for contaminant release were complexation ability of the solution for the sediment components and pH of the solution. A promising design for the remediation treatment for the investigated sediment includes complexation and strong acid agents.
相似文献In contaminated streams, understanding the role of streambank and streambed source contributions is essential to developing robust remedial solutions. However, identifying relationships can be difficult because of the lack of identifying signatures in source and receptor pools. East Fork Poplar Creek (EFPC) in Oak Ridge, TN, USA received historical industrial releases of mercury that contaminated streambank soils and sediments. Here, we determined relationships between the contaminated streambank soils and sand-sized streambed sediments.
Materials and methodsField surveys revealed the spatial trends of the concentrations of inorganic total mercury (Hg) and methyl mercury (MeHg), Hg lability as inferred by sequential extraction, particle size distribution, and total organic carbon. Statistical tests were applied to determine relationships between streambank soil and streambed sediment properties.
Results and discussionConcentrations of Hg in streambank soils in the upper reaches averaged 206 mg kg?1 (all as dry weight) (n?=?457), and 13 mg kg?1 in lower reaches (n?=?321), while sand-sized streambed sediments were approximately 16 mg kg?1 (n?=?57). Two areas of much higher Hg and MeHg concentrations in streambank soils were identified and related to localized higher Hg concentrations in the streambed sediments; however, most of the streambank soils have similar Hg concentrations to the streambed sediments. The molar ratio of Hg to organic carbon, correlation between MeHg and Hg, and particle size distributions suggested similarity between the streambank soils and the fine sand-sized fraction (125–250 μm) collected from the streambed sediments. Mercury in the fine sand-sized streambed sediments, however, was more labile than Hg in the streambank soils, suggesting an in-stream environment that altered the geochemistry of sediment-bound Hg.
ConclusionsThis study revealed major source areas of Hg in streambank soils, identified possible depositional locations in streambed sediments, and highlighted potential differences in the stability of Hg bound to streambank soils and sediments. This work will guide future remedial decision making in EFPC and will aid other researchers in identifying source–sink linkages in contaminated fluvial systems.
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