Spatial and temporal distribution of polycyclic aromatic hydrocarbons (PAHs) in sediments of the Nansi Lake, China

Polycyclic aromatic hydrocarbons (PAHs) were measured in surface sediments and dated core sediments from the Nansi Lake of China to investigate the spatial and temporal distribution characteristics. The concentrations of 16 kinds priority PAH compounds were determined by GC-MS method. And ²¹⁰Pb isotope dating method was used to determine the chronological age of the sediment as well as the deposition rate. The results indicated that the total PAHs concentration ranges in surface and core sediment samples were 160 ~32,600 and 137 ~ 693 ng/g (dry wt.), respectively. The sediment rate and the average mass sedimentation were calculated to be 0.330 cm·year^???1 and 0.237 g·cm^???2·yr^???1 and the sediment time of the collected core sample ranged from 1899 to 2000. The peak of PAH concentrations came at recent years. The source analysis showed PAHs mainly came from the contamination of low temperature pyrogenic processes, such as coal combustion. The PAHs concentrations were lower than ERL and LEL values for most collected samples. However, in several surface sediment samples especially in estuary sites, the PAHs concentrations were not only higher than ERL and LEL values, but also higher than ERM values.     

Discriminant analysis for the prediction of sand mass distribution in an urban stormwater holding pond using simulated depth average flow velocity data

The approach of this paper is to predict the sand mass distribution in an urban stormwater holding pond at the Stormwater Management And Road Tunnel (SMART) Control Centre, Malaysia, using simulated depth average floodwater velocity diverted into the holding during storm events. Discriminant analysis (DA) was applied to derive the classification function to spatially distinguish areas of relatively high and low sand mass compositions based on the simulated water velocity variations at corresponding locations of gravimetrically measured sand mass composition of surface sediment samples. Three inflow parameter values, 16, 40 and 80 m³ s^?1, representing diverted floodwater discharge for three storm event conditions were fixed as input parameters of the hydrodynamic model. The sand (grain size?>?0.063 mm) mass composition of the surface sediment measured at 29 sampling locations ranges from 3.7 to 45.5 %. The sampling locations of the surface sediment were spatially clustered into two groups based on the sand mass composition. The sand mass composition of group 1 is relatively lower (3.69 to 12.20 %) compared to group 2 (16.90 to 45.55 %). Two Fisher’s linear discriminant functions, F ₁ and F ₂, were generated to predict areas; both consist of relatively higher and lower sand mass compositions based on the relationship between the simulated flow velocity and the measured surface sand composition at corresponding sampling locations. F ₁?=??9.405?+?4232.119?×?A???1795.805?×?B?+?281.224?×?C, and F ₂?=??2.842?+?2725.137?×?A???1307.688?×?B?+?231.353?×?C. A, B and C represent the simulated flow velocity generated by inflow parameter values of 16, 40 and 80 m³ s^?1, respectively. The model correctly predicts 88.9 and 100.0 % of sampling locations consisting of relatively high and low sand mass percentages, respectively, with the cross-validated classification showing that, overall, 82.8 % are correctly classified. The model predicts that 31.4 % of the model domain areas consist of high-sand mass composition areas and the remaining 68.6 % comprise low-sand mass composition areas.     

Impacts of climate-induced changes on the distribution of pesticides residues in water and sediment of Lake Naivasha, Kenya

This study reports evidence of increased chlorpyrifos contamination in sediment and water in Lake Naivasha following its intensive application in the horticultural farms in the catchment area. Analytical results show that levels of chlorpyrifos residues were influenced by climate-induced rainfall pattern with higher levels reported during period of heavy precipitation with significant decrease during low rainfall. On average, the levels ranged between 14.8 and 32.8 ng g^?1 in sediment during rainy season compared to a range of 8.5–16.6 ng g^?1 in the dry season. Additionally, the mean concentration of chlorpyrifos in water ranged between 8.61 and 22.4 μg L^?1 during rainy season and below detection limit (bdl) ?13.6 μg L^?1 in dry season as quantified by enzyme-linked immunosorbent assay. Meanwhile, independent t test analysis indicated that there was significant difference in concentration at p?≤?0.05 between the seasons with respect to sediment and water samples. This demonstrated that climate-induced variations had considerable influence on contamination. While diazinon and carbofuran were equally applied intensively, their levels were below the detection limit in the all the samples analyzed. ELISA results were validated by the capillary-HPLC photodiode-array detector instrument analysis, and statistical comparison showed no significant difference between them. It was evident that chlorpyrifos residues determination in water and sediment by ELISA can be a useful strategy in environmental management and monitoring program, and a complimentary analytical tool to high performance liquid chromatography. Levels of chlorpyrifos detected in sediment and water were found to exceed recommended criteria for protection of aquatic life and preservation of water quality and may be hazardous if not regularly monitored.     

Integration of multi-disciplinary geospatial data for delineating agroecosystem uniform management zones

The aim of this study was the development of analytical methods for the simultaneous determination of 25 selected pharmaceuticals, metabolites, and pesticides, belonging to the various chemical classes, in river sediments and their corresponding surface and ground water with the purpose of monitoring the contamination levels. The methods were based on the solid-phase extraction as the sample preparation method for water samples, and the ultrasonic solvent extraction for the sediment samples, followed by the liquid chromatography–tandem mass spectrometry. High recoveries were achieved for extraction from both water and sediment samples for the majority of analytes. Low limits of detection were achieved for all investigated compounds in the water sample (1–5 ng L^?1) as well as in the sediment (1–3 ng g^?1). Applicability of the developed methods was demonstrated by determination of pharmaceutical and pesticide residues in 30 surface water, 44 groundwater, and 5 sediment samples from the Danube River Basin in Serbia. Sixty percent of target compounds were detected in environmental samples. The most frequently detected analytes in river sediments were the pesticides dimethoate and atrazine, while carbamazepine and metamizole metabolites 4-AAA and 4-FAA were the most frequently found in water samples.     

Phosphorus sorption–desorption behaviour of river bed sediments in the Abshineh river, Hamedan, Iran, related to their composition

Phosphorus (P) sorption by sediments may play a vital role in buffering P concentration in the overlying water column. To characterize P sorption–desorption in the river bed sediments, 17 bed sediment samples collected from Abshineh river, in a semi arid region, Hamedan, western Iran were studied through a batch experiment and related to sediment composition. The sorbed fraction ranged from 4.4% to 5.4% and from 38.5% to 86.0% of sorption maxima when 20 and 1,500 mg P kg^?1, respectively, was added to the sediment samples. Phosphorus sorption curves were well fitted to the Langmuir model. Zero equilibrium P concentration ranged from 0.10 to 0.51 mg P l^?1 and varied with sediment characteristics. Phosphorus desorption differed strongly among the studied bed sediments and ranged from 10.8% to 80.2% when 1,500 mg P kg^?1 was added. The results of the geochemical modelling indicated that even under low P addition (2 mg l^?1), the solutions are mainly saturated with respect to hydroxyapatite and ß-tricalcium phosphate minerals and undersaturated with respect to other Ca and Mg minerals, whereas under higher P addition (150 mg l^?1), most Ca–P solid phases, except the most soluble mineral (brushite), will likely precipitate. A Langmuir sorption maximum was positively correlated with carbonate calcium. Estimated P retention capacity of the bed sediments are generally lower and zero equilibrium P concentration values higher in upstream sites than at the downstream sites, suggesting that sediments in upstream and downstream may act as source and sink of P, respectively.     

Effect of heavy metals (Cu, Pb, and As) on the ultrastructure of Sargassum pallidum in Daya Bay, China

Concentrations of Cu, Pb, and As were determined in seawater, surface sediment, Sargassum pallidum collected from the Daya Bay, China. The influence of metal contamination on the marine alga was investigated at chemical and ultrastructural level. Mean concentrations of Cu (19.44 mg kg^?1) and Pb (33.99 mg kg^?1) were found to be high in sediment, whereas concentration of As (122.29 mg kg^?1) in S. pallidum was higher than that in water and sediment. The ultrastructure of S. pallidum cells was anomalous and aberrant. Energy-dispersive x-ray spectroscopic analysis revealed that the nanometal particles in the form of comparatively high-electron density substance diffused in the cell structures constituted by Cu, Pb, As, etc. There is a remarkable similarity or correspondence in the anomalous elements between the geochemistry and the botanic cell, and the heavy metals have potential hazardous effect on the ocean ecology system in Daya Bay.     

Water quality and bacteriology in an aquaculture facility equipped with a new aeration system

The HOBAS aeration system was tested to compare changes in environmental and bacteriological parameters in ponds growing Penaeus monodon during a single production cycle. The stocking density in the aerated pond was doubled to 12 post-larvae (PL) m^???2 in contrast to the non-aerated pond with 6 (PL) m^???2. Microbial abundance in the ponds ranged between 10^5???6 cells ml^???1. Among the physiological groups of bacteria enumerated, the heterotrophs dominated with an abundance of 10⁴ CFU ml^???1. Of the nitrogen and sulfur cycle bacteria, the nitrifiers flourished in the aerated pond and could maintain ammonia-N concentration within permissible levels. Bacterial activity also maintained sulfide concentrations at <?0.03 mg l^???1. Non-aerated conditions promoted denitrification maintaining nitrate concentration between 0.32 and 0.98 μM NO₃ ^???-N l^???1. However, a marked increase in ammonium content was observed in the non-aerated pond at the end of the culture period. Thus in high-density ponds, the aerators served to stimulate bacterial growth and activity which consequently maintained the quality of the water to match that of low-density ponds. Accordingly, these aerators could be effectively used to sustain higher yields. The effluent from the aerated pond is less likely to alter the redox balance of the receiving waters.     

Monitoring of arsenic in aquatic plants, water, and sediment of wastewater treatment ponds at the Mae Moh Lignite power plant, Thailand

Mae Moh is a risky area for arsenic contamination caused by the effluent from biowetland ponds in Mae Moh lignite-fuelled power plant. The objective of this study was to investigate the arsenic concentrations of Mae Moh biowetland ponds and determine the main factors which are important for arsenic phytoremediation in the treatment system. The result revealed that arsenic concentrations in the supernant were in the range of less than 1.0 μg As L^???1 to 2.0 μg As L^???1 while those in the sediment were in the range of 25–200 μg As kg soil^???1. Both values were below the Thailand national standard of 0.25 mg As L^???1 for water and 27 mg As kg soil^???1 for the soil. Arsenic accumulation in the biomass of 5 aquatic plants at the biowetland ponds ranged from 123.83 to 280.53 mg As kgPlant^???1. Regarding the result of regression analysis (R ²?= 0.474 to 0.954), high concentrations of organic matter and other soluble ions as well as high pH value in the sediment could significantly enhance the removal of soluble arsenic in the wetland ponds. From the regression equation of accumulated arsenic concentration in each aquatic plant, Eichhornia crassipes (Mart.) Solms. (R ²?= 0.954), Ipomoea aquatica Forsk. (R ²?= 0.850), and Typha angustifolia (L.) (R ²?= 0.841) were found to be preferable arsenic removers for wastewater treatment pond in the condition of low Eh value and high content of solid phase EC and phosphorus. On the other hand, Canna glauca (L.) (R ²?= 0.749) appeared to be favorable arsenic accumulator for the treatment pond in the condition of high Eh value and high concentration of soluble EC.     

Dissipation kinetics and assessment of processing factor for chlorpyrifos and lambda-cyhalothrin in cardamom

The dissipation kinetics and method for estimation of residues of chlorpyrifos and lambda-cyhalothrin in cardamom were studied and developed. The limit of detection and limit of quantitation arrived for the compounds were 0.01 and 0.025 μg?g^?1, respectively. Gas chromatographic response of chlorpyrifos and lambda-cyhalothrin residues was linear in the range of 0.01–0.50 μg?g^?1 and the mean recovery obtained was 97.3 % for chlorpyrifos and 98.9 % for lambda-cyhalothrin with satisfactory relative standard deviation values. The mean initial residues of chlorpyrifos applied at a concentration of 0.05 % in cardamom was 2.5 μg?g^?1 and the residue was 8.1 μg?g^?1 after processing, with a processing factor of 3.24, while lambda-cyhalothrin when applied at 0.0025 % resulted in initial residues of 1.63 μg?g^?1 that magnified to 4.86 μg?g^?1 on curing, with a processing factor of 2.98. The half-life of chlorpyrifos was in the range of 5.1–5.24 days while that of lambda-cyhalothrin was in the range of 4.40–4.55 days. The processing factor arrived at in the above experiment lead to the conclusion that the residues of chlorpyrifos got magnified to 3.24–3.68 times and that of lambda-cyhalothrin got magnified to 2.98–3.46 times of initial residues, consequent to loss of weight due to dehydration during curing.     

Distribution and bioaccumulation of organochlorine pesticides (OCPs) in food web of Nansi Lake,China

The concentration of 12 organochlorine pesticides (OCPs) were measured in water, sediment, aquatic plant, and animal (shrimp and fish) of Nansi Lake by gas chromatography equipped with an electron capture detector. The total OCPs concentrations were 65.31–100.31 ng L^?1 in water, 2.9–6.91 ng g^?1 dry weight (dw) in sediments, 1.29–6.42 ng g^?1 dw in aquatic plants and 7.57–17.22 ng g^?1 dw in animals. The OCPs composition profiles showed that heptachlor compounds was also the predominant OCPs contaminants in addition to hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in Nansi Lake. According to the source of HCHs and DDTs in sediment samples, there was no new input and the HCHs pollution mainly came from the use of Lindane in Nansi Lake. Bioaccumulation of OCPs in aquatic biota indicated that DDTs and heptachlor compounds had a strong accumulation, followed by HCHs and drins. The accumulation abilities of fish for OCPs were higher than those of plants and shrimps. The OCPs biota-sediment accumulation factor values of Channa argus was the highest in fish samples, followed by Carassius auratus, and Cyprinus caspio. Risk assessment of sediment showed that heptachlor epoxide had a higher occurrence possibility of adverse ecological effects to benthic species. Based on the calculation of acceptable daily intake and hazard ratio, HCHs in fish and shrimps from Nansi Lake had a lifetime cancer risk of greater than one per million. The risk assessment of water, sediment, and fish indicated the water environment of Nansi Lake is at a safe level at present.     

Distribution of gamma-ray emitting radionuclides in the marine environment of the Burullus Lake: II. Bottom sediments

The sediment compartment has the ability to trap large amounts of radionuclides and to indicate the radiological impact of pollution. The present work shows the results obtained related to the concentrations of ¹³⁷Cs and natural radionuclides in sediment in the Burullus Lake, Egypt. The average values of ²²⁶Ra, ²³²Th, and ⁴⁰K in the bottom sediments collected from the east of the Burullus Lake ranged from 10.3 to 21.8 Bq/kg, from 11.9 to 34.4 Bq/kg, and from 268 to 401 Bq/kg, respectively. The study has shown that ⁴⁰K concentration is nearly uniform throughout the studied area while ²²⁶Ra and ²³²Th are more concentrated in the northeastern shore. Lake sediments showed contamination with ¹³⁷Cs (2.7–15.9 Bq/kg). The ¹³⁷Cs sediment activities indicated higher concentrations in the off-shore sites. Concentrations of all γ -ray emitting radionuclides except ⁴⁰K in water samples were below the detection limits. The ⁴⁰K sediment–water distribution coefficients of the near-shore samples were higher than the off-shore samples.     

Spatial distribution and concentration assessment of total petroleum hydrocarbons in the intertidal zone surface sediment of Todos os Santos Bay, Brazil

The primary objective of this study was to investigate the concentrations and spatial distribution of the total petroleum hydrocarbons (TPHs) in the intertidal zone surface sediment of Todos os Santos Bay, Brazil, to assess the distribution and degree of contamination by TPHs, measure the level of TPH degradation in the surface sediment, and identify the organic matter sources. The surface sediment used in this study was collected in 50 stations, and TPHs, isoprenoid alkanes (pristane and phytane), and unresolved complex mixture (UCM) were analyzed by gas chromatography with a flame ionization detector. The total concentrations ranged from 0.22 to 40,101 μg g^?1 dry weight and showed a strong correlation with the total organic carbon (TOC) content. The highest TPH concentrations were observed in samples from the mangrove sediments of a river located near a petroleum refinery. Compared with other studies in the world, the TPH concentrations in the intertidal surface sediment of Todos os Santos Bay were below average in certain stations and above average in others. An analysis of the magnitude of UCM (0.11 to 17,323 μg g^?1 dry weight) and the ratios nC17/Pr and nC18/Ph suggest that an advanced state of oil weathering, which indicates previous contamination. The molar C/N ratios varied between 5 and 43, which indicate organic matter with a mixed origin comprising marine and continental contributions.     

Joint ecotoxicology of cadmium and metsulfuron-methyl in wheat (Triticum aestivum)

Herbicide is indispensable for crop production. However, substantial usage of herbicide has led to its increasing accumulation in soils and crops. In addition, cadmium has become one of the widely occurring contaminants in soils due to its significant release into environment via anthropogenic activities. In this study, ecotoxicological investigations were made by exposing the food crop wheat to joint contaminations of Cd and metsulfuron-methyl, a sulfonylurea herbicide. We analyzed growth and physiological and molecular responses in wheat exposed to 0.5 mg kg^?1 Cd and 0.02 mg kg^?1 metsulfuron-methyl (MSM). Soils contaminated with Cd and MSM complex caused significantly detrimental effect on wheat growth and physiological process. Combinative treatments with Cd and MSM damage more severely the plant cells as compared with Cd or MSM treatment alone. Compared with the growth parameter, the biochemical and molecular responses of wheat appeared more pronounced to Cd and MSM complex. Furthermore, compared with control, wheat plants exposed to Cd?+?MSM generated more O^2?.and H₂O₂, both of which were shown to be the cause of enhanced activity of several antioxidant enzymes. Native polyacrylamide gel eletrophoresis and molecular response analyses were performed to validate the results indicated above. Our results indicated that joint contamination with Cd and MSM was more toxic to wheat than a single contamination. These sensitive biological parameters can be used as biomarkers monitoring the ecotoxicological process in plants.     

Metabolic degradation of imidacloprid in paddy field soil

The metabolic degradation and persistence of imidacloprid in paddy field soil were investigated following two applications of imidacloprid at 20 and 80 g a.i. ha^?1 at an interval of 10 days. The soil samples were collected at various time intervals. The limit of quantification for the analysis of imidacloprid and its metabolites was obtained at the concentration of 0.01 mg kg^?1. The initial deposits of total imidacloprid were found to be 0.44 and 1.61 mg kg^?1 following second applications. These residues could not be detected after 60 and 90 days following second applications of imidacloprid at lower and higher dosages, respectively. In soil, urea metabolite was found to be the maximum, followed by olefine, nitrosimine, 6-chloronicotinic acid, 5-hydroxy and nitroguanidine. The half-life values (t _1/2) of imidacloprid were worked out to be 12.04 and 11.14 days, respectively, when applied at lower and higher doses, respectively.     

Persistence behaviour of imidacloprid and its metabolites in soil under sugarcane

The persistence and metabolism of imidacloprid in soil under sugarcane were studied following application of imidacloprid at 20 and 80 g active ingredient (a.i.) ha^?1. Soil samples were collected at different time intervals (7, 15, 30, 45, 60 and 90 days after application), and the residues of imidacloprid and its metabolites (6-chloronicotinic acid, nitrosimine, imidacloprid-NTG, olefin, urea and 5-hydroxy) were quantified by high-performance liquid chromatography. In soil, the total imidacloprid residues were mainly constituted by the parent compound followed by 6-chloronicotinic acid, nitrosimine and imidacloprid-NTG metabolites. Maximum residues of imidacloprid and its metabolites were 4.29 and 7.81 mg kg^?1 in soil samples collected 7 days after the application of imidacloprid at 20 and 80 g a.i. ha^?1, respectively. At both doses, these residues declined to below the detectable limit in soil after 90 days of application. Olefin, urea and 5-hydroxy metabolites were not detected in soil. Dissipation of total imidacloprid residues did not follow the first-order kinetics with a coefficient of determination value of 0.883 and 0.838 for the recommended dose and four times the recommended dose, respectively. The half-life (T _1/2) value of total imidacloprid was observed to be 10.64 and 10.10 days for the recommended dose and four times the recommended dose, respectively.     

Distribution patterns of nitroaromatic compounds in the water, suspended particle and sediment of the river in a long-term industrial zone (China)

Nitroaromatic compounds are known to be hazardous to ecological and human health. To assess the status of nitroaromatic compounds contamination in the main rivers in the important industrial bases of the northeastern China, we collected water, suspended particulate matter (SPM) and sediment samples from 28 sites in the Daliao River watershed and analysed them for eight nitroaromatic compounds by gas chromatography. The total concentrations of eight nitrobenzenes in the water column including aqueous and SPM phases ranged from 740 to 15,828 ng L^???1, with a mean concentration of 3,460 ng L^???1. The total concentrations of eight nitrobenzenes in the sediment were 7.47 to 8,185.76 ng g^???1, with a mean concentration of 921.98 ng g^???1, and several times higher than those found from the Yellow River in China. 4-Nitrotoluene was the predominant contaminant in the water and sediment of the three rivers of the Daliao River watershed. 2,6-Dichloro-4-nitroaniline was generally dominant in the SPM. The levels of nitroaromatic compounds were different among different sites in the Daliao River watershed, mainly caused by the distribution of pollution sources. No obvious correlation was found between the total concentrations of eight nitrobenzenes concentrations and TOC or the slit-clay content of the sediments.     

Assessment of nitrogen and phosphate balance and the roles of bacteria and viruses at the water-sediment interface in the Allal El Fassi reservoir (Morocco)

Balances of nitrogen and phosphate were studied in the Allal El Fassi reservoir (Morocco); the results showing that nitrogen input (296 mg m^?2 d^?1) was 161 % higher than output (183 mg m^?2 d^?1). Phosphate input (35.65 mg m^?2 d^?1) was 865 % higher than output (4.12 mg m^?2 d^?1), causing a progressive increase in the internal phosphate stock. Sedimentation flux was equally high (53.80 and 18 mg m^?2 d^?1) for both nitrogen and phosphate input, mainly from the Sebou River and in particulate form which immediately settles upon arrival in the reservoir. The release of nitrogen and phosphate from the sediment (5.40 and 1.15 mg m^?2 d^?1, respectively) depended on physicochemical and biological (bacteria and viruses) variability and the calcareous nature of the catchment basin. Calcium-bound phosphate prevailed in the reservoir. Drastic control of phosphate input is suggested to avoid accumulation of calcium-bound phosphate which may dissociate and thereby contribute to eutrophication.     

Contamination by perfluorinated compounds in water near waste recycling and disposal sites in Vietnam

There are very few reports on the contamination by perfluorinated chemicals (PFCs) in the environment of developing countries, especially regarding their emission from waste recycling and disposal sites. This is the first study on the occurrence of a wide range of PFCs (17 compounds) in ambient water in Vietnam, including samples collected from a municipal dumping site (MD), an e-waste recycling site (ER), a battery recycling site (BR) and a rural control site. The highest PFC concentration was found in a leachate sample from MD (360 ng/L). The PFC concentrations in ER and BR (mean, 57 and 16 ng/L, respectively) were also significantly higher than those detected in the rural control site (mean, 9.4 ng/L), suggesting that municipal solid waste and waste electrical and electronic equipment are potential contamination sources of PFCs in Vietnam. In general, the most abundant PFCs were perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluoroundecanoic acid (PFUDA; <1.4–100, <1.2–100, and <0.5–20 ng/L, respectively). Interestingly, there were specific PFC profiles: perfluoroheptanoic acid and perfluorohexanoic acid (88 and 77 ng/L, respectively) were almost as abundant as PFOA in MD leachate (100 ng/L), whereas PFNA was prevalent in ER and BR (mean, 17 and 6.2 ng/L, respectively) and PFUDA was the most abundant in municipal wastewater (mean, 5.6 ng/L), indicating differences in PFC contents in different waste materials.     

Comparative study based on sediment characteristics and macrobenthic communities in two Italian lagoons

The aims of this study were to analyse sediment characteristics and macrobenthic assemblages in two very close Italian coastal lagoons (Lesina and Varano) and to assess the different behaviour between the two basins and the relationship between sediment matrix and benthic organisms within and between the two lagoons. The comparative study was performed in July 2007 at 13 sampling sites in Lesina lagoon and 15 sites in Varano basin for sediment grain size, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP) and macrobenthic structure analyses. Both lagoons were generally dominated by fine-grained sediments (clay and silt components). The average contents of TOC and TN measured in Lesina was higher than in Varano (3.31% vs 2.52% for TOC and 5,200 μg·g^???1 vs 3,713 μg·g^???1 for TN); in contrast, the TP was lower (540 μg·g^???1 vs 620 μg·g^???1). Based on macrobenthic community patterns, the central zone in Varano lagoon and the eastern area in Lesina lagoon were characterised by the lowest abundance (168.7 ind·m^???2 and 503.2 ind·m^???2, respectively) and by the lowest number of species, as highlighted by the diversity indices (Shannon–Wiener, H ^′ range was 0.47–1.45 for Lesina and 0.00–1.68 for Varano; Margalef species richness, d range was 0.00–1.67 for Lesina lagoon and 0.00–2.38 for Varano basin). Ordination diagrams suggested an influence of marine and freshwater inputs on the sediment distribution in Varano lagoon and on macrobenthic assemblages in Lesina lagoon.     

Optimizing the weight loss-on-ignition methodology to quantify organic and carbonate carbon of sediments from diverse sources

The sequential weight loss-on-ignition (WLOI) method for determination of organic and carbonate or inorganic carbon (C) content was evaluated on sediments from diverse sources with a great range of C contents. The sediments were collected from canal, wetland, river, estuary, lake, and marine sites. The organic and inorganic C contents of these samples ranged from 1 to 430 g kg^???1 and from 4 to 97 g kg^???1, respectively. Combinations of the combustion time and temperature and optimal weight ranges of representative samples were tested, and comparisons of the WLOI method with other methods, including dry combustion and wet combustion, were made. These methods were (1) use of the carbon?Cnitrogen?Csulfur (CNS) autoanalyzer with normal and reduced temperatures for total and organic C, (2) thermogravimetry for both organic and inorganic C, (3) use of the CNS autoanalyzer after removal of inorganic (carbonate) C by fumigating samples with concentrated HCl for organic C, (4) Walkley?CBlack wet combustion method for organic C, and (5) pressure-calcimeter associated with subtraction method (total C minus inorganic C) for organic C determinations. The results of analyzing samples of sediments of diverse origins showed that the optimal combination of temperature and time of WLOI depended mostly on the sources of the analyzed sediment. The WLOI analysis of sediment samples for organic C from wetlands, canal, estuary, or river sites needed a relatively low temperature but that of sediment samples from lake and marine sites required a relatively high temperature. Overall, to obtain reliable analysis results of samples from widely varied sediment sources except marine sediments, 500°C for 12 h was optimal for organic C content determination, and 800°C for yet another 12 h was optimal for inorganic C content determination. The temperature could even be reduced to 475°C if only wetland and stream sediments were included, but for marine sediments, 550°C for 12 h was necessary. Precise C content determinations for most sediment sources could be obtained by WLOI when sample quantities ranged from 2.0 to 4.0 g. The WLOI method, when conducted properly, resulted in precise measurements of C contents in ??standard samples?? used for calibration, and these values were closely comparable to results obtained with other dry combustion methods (R ²????0.96). We conclude that WLOI, which has advantages of simplicity, cost-effectiveness, and no waste disposal over other methods, can provide precise measurements of organic and inorganic C contents in sediments from a wide range of sources, but the selection of heating temperature and exposure time should be carefully considered based on sediment sources.