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A 12-year field experiment was conducted to assess straw mulch effects on soil organic carbon fractions, the carbon pool management index (CPMI) at different depths, and crop yield under a no-till rice-wheat rotation system on the Chengdu Plain, southwestern China.
Materials and methodsThere were two treatments in the experiment: no-till without straw mulch (CK) and no-till with straw mulch (SM). The soil was sampled at 0–5, 5–10, 10–20, and 20–30-cm depths. Soil total organic carbon (TOC), the labile organic carbon fractions, including particulate organic carbon (POC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and permanganate-oxidizable carbon (KMnO4-C), and the CPMI were analyzed. The crop grains were measured between September 2013 and May 2018.
Results and discussionBetween 2013 and 2018, rice and wheat grain yields under SM were comparable to CK, except there were higher rice yields in 2016 and higher wheat yields in 2017 under SM. The soil organic carbon decreased as soil depth increased in both treatments. Soil TOC, POC, and KMnO4-C concentrations at 0–5 and 5–10 cm, CPMI at 0–5 and 5–10 cm, and DOC at 0–5, 5–10, and 10–20-cm soil depths were significantly greater under SM than under CK, whereas the MBC at 0–5 and 5–10 cm under SM was lower than CK. The POC/TOC, KMnO4-C/TOC, and DOC/TOC ratios were greater under SM in the 0–5 and 5–10 cm, 0–5 cm, and 5–10 and 10–20-cm layers than CK, respectively, whereas the MBC/TOC ratio decreased under SM at 0–5, 5–10, and 10–20-cm depths.
ConclusionsThe results showed that straw mulching should be adopted when a no-till rice-wheat cropping system is used in southwestern China because it leads to effective improvements in SOC sequestration while still maintaining normal crop yields.
相似文献Characterizations of soil aggregates and soil organic carbon (SOC) losses affected by different water erosion patterns at the hillslope scale are poorly understood. Therefore, the objective of this study was to quantify how sheet and rill erosion affect soil aggregates and soil organic carbon losses for a Mollisol hillslope in Northeast China under indoor simulated rainfall.
Materials and methodsThe soil used in this study was a Mollisol (USDA Taxonomy), collected from a maize field (0–20 cm depth) in Northeast China. A soil pan with dimensions 8 m long, 1.5 m wide and 0.6 m deep was subjected to rainfall intensities of 50 and 100 mm h?1. The experimental treatments included sheet erosion dominated (SED) and rill erosion dominated (RED) treatments. Runoff with sediment samples was collected during each experimental run, and then the samples were separated into six aggregate fractions (0–0.25, 0.25–0.5, 0.5–1, 1–2, 2–5, >?5 mm) to determine the soil aggregate and SOC losses.
Results and discussionAt rainfall intensities of 50 and 100 mm h?1, soil losses from the RED treatment were 1.4 and 3.5 times higher than those from the SED treatment, and SOC losses were 1.7 and 3.8 times greater than those from the SED treatment, respectively. However, the SOC enrichment ratio in sediment from the SED treatment was 1.15 on average and higher than that from the RED treatment. Furthermore, the loss of <?0.25 mm aggregates occupied 41.1 to 73.1% of the total sediment aggregates for the SED treatment, whereas the loss of >?0.25 mm aggregates occupied 53.2 to 67.3% of the total sediment aggregates for the RED treatment. For the organic carbon loss among the six aggregate fractions, the loss of 0–0.25 mm aggregate organic carbon dominated for both treatments. When rainfall intensity increased from 50 to 100 mm h?1, aggregate organic carbon loss increased from 1.04 to 5.87 times for six aggregate fractions under the SED treatment, whereas the loss increased from 3.82 to 27.84 times for six aggregate fractions under the RED treatment.
ConclusionsThis study highlights the effects of sheet and rill erosion on soil and carbon losses at the hillslope scale, and further study should quantify the effects of erosion patterns on SOC loss at a larger scale to accurately estimate agricultural ecosystem carbon flux.
相似文献The purpose of the study was to determine the levels of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD/F), two types of persistent organic pollutant (POP), in an urban retention reservoir located in an industrial zone within a coal-mining region. It also assesses the potential ecological risk of the PCDDs/Fs present in bottom sediments and the relationship between their content and the fraction of organic matter.
Materials and methodsThe sediment samples were collected from Rybnik Reservoir, located in the centre of the Rybnik Coal Region, Silesia, one of Poland’s major industrial centres. Seventeen PCDD/F congeners in the surface of the sediments were analysed using high-resolution gas chromatography and high-resolution mass spectrometry (HRGC/HRMS).
Results and discussionThe toxic equivalency (TEQ) of the PCDDs/Fs in the sediments ranged from 1.65 to 32.68 pg TEQ g?1. PCDDs constituted 59–78% of the total PCDDs/Fs, while the PCDFs accounted for 22–41%. The pattern of PCDD/F congeners in the sediments was dominated by OCDD. However, the second-most prevalent constituents were OCDF and ∑HpCDFs in the low TOC sediment (< 10 g TOC kg?1), but HpCDD in the rich TOC samples (> 10 g TOC kg?1). PCDD/F concentrations in the sediment samples were 2- to 38-fold higher than the sediment quality guidelines limit, indicating high ecological risk potential. Although a considerable proportion of PCDDs/Fs in the bottom sediments from the Rybnik Reservoir were derived from combustion processes, they were also obtained via transport, wastewater discharge, high-temperature processes and thermal electricity generation. The PCDD/F concentrations were significantly correlated with all fractions of organic matter; however, the strongest correlation coefficients were found between PCDDs/Fs and humic substances. Besides organic matter, the proportions of silt/clay fractions within sediments played an important role in the transport of PCDDs/Fs in bottom sediments.
ConclusionsThe silt/clay fraction of the bottom sediments plays a dominant role in the movement of PCDDs/Fs, while the organic matter fraction affects their sorption. The results indicate that the environmental behaviour of PCDDs/Fs is affected by the quantity and quality of organic matter and the texture of sediments.
相似文献Analysis of sediment transport is an effective approach for identifying sediment sources and for catchment management. However, a long-term analysis of sediment variability at multiple time scales is less available, especially in mountainous catchments. This study aims to determine sediment sources and to identify sediment transport dynamics, as well as the influencing factors, through analyzing long-term sediment fluxes at different time scales.
Materials and methodsIn this paper, 32 years of sediment flux in an instrumented mountainous catchment in eastern Zhenjiang Province, China, was investigated at multiple time scales (i.e., monthly, seasonal, annual, and event). Sediment yields (SYs) during three time periods (i.e., 1964–1977, 1978–1989, and 2010–2015) were first classified by the Mann-Kendall and cumulative anomaly tests, and then sediment fluxes for each period were investigated and compared at multiple time scales.
Results and discussionAnnual SYs ranged from 29 to 308 t year?1 during the recording period and were significantly influenced by several high magnitude flood events. The mean annual SYs decreased from 153.82 t year?1 in 1964–1977, to 97.79 t year?1 in 1978–1989, and to 91.08 t year?1 in 2010–2015 due to improved soil conservation measures and increased reservoirs. At the seasonal scale, over 92% of the sediment was transported in spring and summer over the recording period. Heterogeneous sediment sources, partial areal distribution of rainfalls, and other factors led to complex suspended sediment concentration versus water discharge hysteresis loop patterns at the event and monthly scales.
ConclusionsThe improved soil conservation measures and increased reservoirs over the recent decades decreased sediment availability, and the number and the magnitude of flood events from 1964 onward. However, the flood sediment fluxes in a few months were still high due to extreme precipitation events in recent years. The work can provide guidance for addressing sediment problems in this and/or other similar catchments.
相似文献Recent research suggests that Swedish organic arable soils have been under-recognized as a potential source of phosphorus (P) loading to water bodies. The aim of this study was to compare P losses through leaching from organic and high-fertility mineral soils. In addition, the effectiveness of a magnesium-salt-coated biochar applied below the topsoil as a mitigation strategy for reducing P losses was evaluated.
Materials and methodsPhosphorus leaching was measured from four medium- to high-P arable soils, two Typic Haplosaprists (organic 1 and 2), a Typic Hapludalf (sand), and an unclassified loam textured soil (loam), in a 17-month field study utilizing 90-cm-long lysimeters. A magnesium-salt-coated biochar was produced and characterized using X-ray powder diffraction (XPD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and X-ray adsorption (XANES) spectroscopy, and its phosphate adsorption capacity was determined at laboratory scale. It was also applied as a 3-cm layer, 27 cm below the soil surface of the same lysimeters and examined as a mitigation measure to reduce P leaching.
Results and discussionTotal-P loads from the 17-month, unamended lysimeters were in the order of organic 2 (1.2 kg ha?1)?>?organic 1 (1.0 kg ha?1)?>?sand (0.3 kg ha?1)?>?loam (0.2 kg ha?1). Macropore flow, humic matter competition for sorption sites, and fewer sorption sites likely caused higher P losses from the organic soils. Analysis by XRD and SEM revealed magnesium was primarily deposited as periclase (MgO) on the biochar surface but hydrated to brucite (Mg(OH)2) in water. The Langmuir maximum adsorption capacity (Qmax) of the coated biochar was 65.4 mg P g?1. Lysimeters produced mixed results, with a 74% (P?<?0.05), 51% (NS), and 30% (NS) reduction in phosphate-P from the organic 1, organic 2, and sand, respectively, while P leaching increased by 230% (NS) from the loam.
ConclusionsThe findings of this study indicate that P leached from organic arable soils can be greater than from mineral soils, and therefore, these organic soils require further investigation into reducing their P losses. Metal-enriched biochar, applied as an adsorptive layer below the topsoil, has the potential to reduce P losses from medium- to high-P organic soils but appear to be less useful in mineral soils.
相似文献While organic waste amendments can initially improve soil physicochemical properties, including nutritional benefits to plants and increased microorganism activity, long-term application of excessive amounts of organic wastes can cause accumulation of heavy metals (HMs). Thus, the current study examined the accumulation of HMs in agricultural soil profiles following organic waste application.
Materials and methodsThree common organic sludge, including municipal sewage sludge (MSS), industrial sewage sludge (ISS), and leather sludge (LS), were applied annually to an agricultural soil under field conditions over 7 years (1994–2000) at a rate of 25 and 50 t ha?1 year?1. Subsequently, when organic sludge amendments were ceased, the experimental plots were cultivated without any treatments for another 12 years (2001–2012) and the changes in HM concentrations along the soil depth profile were monitored together with soil pH, dissolved organic carbon (DOC), and dehydrogenase activity (DHA).
Results and discussionSignificant increases in Cu, Pb, and Zn concentrations were observed down to a depth of 80 cm in soils treated with ISS and LS, where sludge application also increased the levels of Cd, Cr, Pb, and Zn and their movement down the soil profile. However, with the exception of Cu, no significant changes in HM concentrations were observed following treatment with MSS. At a depth of 80 cm, soils which had received 25 and 50 t ha?1 LS showed, respectively, 4 and 14 times higher Cr levels than the control soil.
ConclusionsOrganic sludge induced changes in soil pH and soil DOC concentration which were the key factors influencing HM movement and accumulation following organic sludge treatment.
相似文献Currently, the distribution characteristics and transport processes of the radionuclides 137Cs and 239?+?240Pu in the sediments of estuaries are still a controversial issue. Thus, in the present study, we investigated the distribution characteristics, sources and migration path of 137Cs and 239?+?240Pu in sediment cores of the Liao River estuary (LRE), China, and evaluated the relative contributions of the Pacific Proving Grounds (PPG) and riverine sources of Pu for the sediments in this area. We used 137Cs and Pu isotopes for dating the sediments and estimated the sedimentation rates by the two radionuclides in the LRE.
Materials and methodsSeven sediment samples were collected using a box corer from the Liao River estuarine wetland and tidal flat in the LRE in October 2012 and April 2015, respectively. The activities of 137Cs in the various samples were determined by γ spectrometry using HP-Ge detectors with 60% relative counting efficiency. Approximately 2–5 g of sediment were spiked with 242Pu (ca. 1 mBq) as a chemical yield tracer for Pu isotopic analysis at the School of Radiation Medicine and Protection, Soochow University. The measurement of Pu isotopes (239Pu, 240Pu, 242Pu) was performed by a sector field ICP-MS. In order to quantitatively differentiate the relative proportions of global fallout and PPG, we employed a two-end member mixing model to estimate their contributions.
Results and discussionThe average values of 137Cs, 239?+?240Pu activity concentrations, and 240Pu/239Pu atom ratios in the surface sediment samples of the LRE were 6.727?±?0.251 mBq g?1, 0.294?±?0.024 mBq g?1, and 0.188?±?0.049 (1σ), respectively. The average 240Pu/239Pu atom ratios ranged from 0.180?±?0.034 to 0.199?±?0.021 in sediment cores from the east and west sides of the LRE. For core LT-2 values for 137Cs and 239?+?240Pu concentrations were from below the detection limit: 3.380?±?0.414 and 0.036?±?0.007 to 0.105?±?0.007 mBq g?1. The mean 240Pu/239Pu atom ratio 0.217?±?0.050 (1σ) in sediment core LT-2 lies between the global fallout and PPG close-in fallout.
ConclusionsWe found that atmospheric fallout is the main source of Pu in sediment cores from the east and west sides of the LRE. For core LT-2, atmospheric fallout and riverine input (~?73.4%) are the major sources of Pu with the source of the rest of Pu (~?26.6%) attributed to the PPG via the Tsushima Warm Current and the coastal water of the East China Sea. The sedimentation rates (means 0.62–0.8 cm year?1) estimated by the two radionuclides were in good agreement and without any statistically significant difference.
相似文献Identification of phosphorus (P) species is essential to understand the transformation and availability of P in soil. However, P species as affected by land use change along with fertilization has received little attention in a sub-alpine humid soil of Tibet plateau.
Materials and methodsIn this study, we investigated the changes in P species using Hedley sequential fractionation and liquid-state 31P-NMR spectroscopy in soils under meadow (M) and under cropland with (CF) or without (CNF) long-term fertilization for 26 years in a sub-alpine cold-humid region in Qinghai–Tibet plateau.
Results and discussionLand-use change and long-term fertilization affected the status and fractions of P. A strong mineralization of organic P (OP) was induced by losing protection of soil organic matter (SOM) and Fe and Al oxides during land-use change and resulted in an increase of orthophosphate (from 56.49 mg kg?1 in M soils to 130.07 mg kg?1 in CNF soils) and great decreases of orthophosphate diesters (diester-P, from 23.35 mg kg?1 in M soils to 10.68 mg kg?1 in CNF soils) and monoesters (from 336.04 mg kg?1 in M soils to 73.26 mg kg?1 in CNF soils). Long-term fertilization boosted P supply but failed to reclaim soil diester-P (from 10.68 mg kg?1 in CNF soils to 7.79 mg kg?1 in CF soils). This may be due to the fragile protection from the combination of SOM with diester-P when long-term fertilization had only improved SOM in a slight extent.
ConclusionsThese results suggest that SOM plays an important role in the soil P cycling and prevents OP mineralization and losses from soil. It is recommended that optimization of soil nutrient management integrated with SOM was required to improve the P use efficiency for the development of sustainable agriculture.
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.
相似文献Several interactions between Al and the solid phase of soil influence Al buffering in soil solution. This work evaluated soils cultivated with Pinus taeda L. to determine Al forms in organic and mineral horizons using various extraction methods and to relate acidity with clay mineralogy.
Materials and methodsOrganic and mineral horizons of 10 soil profiles (up to 2.1 m deep) in southern Brazil were sampled. Organic horizons were separated into fresh, aged, and fermented/humified litter. The following Al extraction methods were utilized: 0.5 mol L?1 pH 2.8 CuCl2–Al complexed in organic matter; 1.0 mol L?1 KCl–exchangeable Al; water–Al soluble in soil solution; HF concentrated?+?HNO3 concentrated?+?H2O2 30% (v/v)–total Al. Six sequential extractions were carried out to isolate different forms of amorphous minerals that can buffer Al on soil solution: 0.05 and 0.1 mol L?1 sodium pyrophosphate; 0.1 and 0.2 mol L?1 ammonium oxalate; 0.25 and 0.5 mol L?1 NaOH. Samples of clay were also analyzed by XRD.
Results and discussionThere was a clear effect of litter age on increasing total Al concentration. In the aged litter and fermented and/or humified litter, levels of total Al were 1.4 to 3.8 and 1.5 to 7.8 times greater than in fresh litter, respectively. The CuCl2 method had higher Al extraction capacity than the KCl method for litter. The lowest Al–pyrophosphate values were observed in the Oxisol, which also had a predominance of gibbsite and the lowest levels of Al–KCl and Al–CuCl2. There was an inverse relationship between degree of soil weathering and soluble and exchangeable Al in soils. Available Al increased with higher Si proportion in minerals of the clay fraction (2:1?>?1:1?>?0:1).
ConclusionsThe worst scenario was soils with the combination of high soluble and exchangeable Al levels and high concentrations of amorphous forms of Al minerals. The best predictors of Al accumulation in the youngest litter horizon were extractions of amorphous minerals with pyrophosphate and NaOH. These extractors are normally used to predict the level of Al buffering in soils. Organic matter had less influence on Al dynamics in soils.
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Biochar has agronomic potential but currently is too expensive for widespread adoption. New methodologies are emerging to reduce the cost such as enriching biochar with nutrients that match crops and soil requirements. However, the effects of biochar-based fertilisers on plant yield and soil nutrient availability have not been widely examined. This study investigated the effects of a novel organo-mineral biochar fertiliser in comparison to organic and commercial biochar fertiliser on ginger (Zingiber officinale Canton).
Materials and methodsThere were four treatments: (1) commercial organic fertiliser (5 t ha?1), as the control; (2) commercial biochar-based fertiliser (5 t ha?1); (3) organo-mineral biochar fertiliser at low rate (3 t ha?1); and (4) organo-mineral biochar fertiliser at high rate (7.5 t ha?1). A replicated pot trial was established with black dermosol soil and ten replicate pots for each treatment. Ginger was planted and grown for 30 weeks. Plant growth, biomass, foliar nutrients and water extractable soil nutrients including phosphorus (P), potassium (K) and calcium (Ca) were examined.
Results and discussionHigh rate organo-mineral biochar fertiliser increased soil P and K availability at week 30 (harvest) after planting, compared to all other treatments and low rate organo-mineral biochar fertiliser performed similarly to the organic control for P and K. High rate organo-mineral biochar fertiliser increased total foliar nutrient content at week 30 in P, K and Ca compared to commercial biochar fertiliser. High rate organo-mineral biochar fertiliser improved the commercial value of ginger (+?36%) due to a shift in the proportion of higher grade rhizomes. Low rate organo-mineral biochar fertiliser plants displayed similar yield, total dry and aboveground biomass to commercial organic fertiliser. Commercial biochar fertiliser had significantly lower biomass measures compared with other treatments as the rate applied had lower nutrient concentrations.
ConclusionsOur results show organo-mineral biochar fertilisers could be substituted for commercial organic fertilisers at low rates to maintain similar yield or applied at high rates to increase commercial value where economically feasible.
相似文献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Stripping contaminants from sediments with granular activated carbon (GAC) is a promising remediation technique in which the effectiveness depends on the rate of contaminant extraction from the sediment by the GAC. The purpose of the present study was to investigate the effect of mixing intensity on the short-term extraction rate of polycyclic aromatic hydrocarbons (PAHs) from contaminated sediment.
Materials and methodsPAH desorption from sediment at a wide range of rotational speeds (min?1; rotations per minute (rpm)) was monitored by uptake in Tenax polymeric resins using a completely mixed batch reactor. Desorption data were interpreted using a radial diffusion model. Desorption parameters obtained with the radial diffusion model were correlated with particle size measurements and interpreted mechanistically.
Results and discussionFast desorption rate constants, D e /r 2, with D e the effective diffusion coefficient and r the particle radius, ranged from 3.7 × 10?3 to 1.1 × 10?1 day?1 (PHE) and 6 × 10?6 to 1.9 × 10?4 day?1 (CHR), respectively, and increased with the intensity of mixing. The D e /r 2 values would correspond to D e ranges of 1.8 × 10?14–1.2 × 10?16 m2 × day?1 and 1.8 × 10?12–3.7 × 10?15 m2 × day?1, assuming fast desorption from the measured smallest particle size (9 μm) classes at 200 and 600 rpm, respectively.
ConclusionsDesorption of PAHs was significantly accelerated by a reduction of particle aggregate size caused by shear forces that were induced by mixing. The effective intra-particle diffusion coefficients, D e , were larger at higher mixing rates.
相似文献In this study, we analyzed the effects of different maize varieties with nitrogen utilization efficiency, fertilizer type, and rate on the ammonia volatilization emission of farmland. Aimed to seek the best matching method to improve grain yield and fertilizer utilization efficiency of summer maize simultaneously.
Materials and methodsIn field experiments, we choose two maize varieties with different nitrogen utilization efficiency (Zhengdan958, Z and Lainong14, L) as material. Set four different fertilizer treatments (200 kg N hm?2 inorganic fertilizer (U1), 100 kg N hm?2 inorganic fertilizer (U2), 200 kg N hm?2 organic fertilizer (M1), and 100 kg N hm?2 organic fertilizer (M2) to study their effect on NH3 emission and loss, maize grain yield, and nitrogen accumulation.
Results and discussionAmmonia volatilization accounted for 8.61–21.68% of applied N. Under the same variety, ammonia volatilization accumulation after fertilization was as follows: U1 > U2 > M1 > M2. Ammonia volatilization rates increased first and then gradually decreased after the fertilization. The ammonia volatilization loss and cumulative loss increased due to increased nitrogen fertilizer application rate. The average nitrogen accumulation and harvest index of 200 kg N hm?2 N treatments were higher than 100 kg N hm?2 N treatments, and the difference between the inorganic fertilizer and organic fertilizer was not significant. In 2016 and 2017, the average yield of Zhengdan958 was 11,758.79 kg hm?2, which was 15.78% higher than that of Lainong14, and the difference between the two fertilizer types was not significant. The average yield of 200 kg N hm?2 N treatment was 11,959.42 kg hm?2, which was 20.13% higher than those of 100 kg N hm?2 N treatment.
ConclusionsBy changing the type of fertilizer, replacing chemical fertilizers with organic fertilizer can reduce the loss of ammonia volatilization and promote the synergistic improvement to yield and resource utilization efficiency. Among them, using nitrogen-efficient varieties and using organic fertilizer instead of chemical fertilizer was beneficial to reduce the loss of ammonia volatilization, increase the accumulation of nitrogen, and promote the growth of maize to obtain high yield.
相似文献This study investigated the concentrations of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), zinc (Zn), and polycyclic aromatic hydrocarbons (PAHs) in sediments collected from gully pots for road drainage in Hong Kong. The presence and intensity of anthropogenic contamination of road gully sediments were assessed. Identifications of potential sources of trace elements and PAHs were performed to help understand the situation for future control of pollution to the land and aquatic environments.
Materials and methodsGully sediment samples were collected from gully pots of 18 roads that are potentially exposed to different pollution sources in Hong Kong. The selection of roads considered different road features, adjacent land uses, and traffic volumes. Composite samples were collected for the analysis of trace elements (Cd, Cr, Cu, Pb, Ni, and Zn) and PAHs by an accredited environmental testing laboratory. Geo-accumulation index (Igeo), contamination factor (Cf), modified degree of contamination (mCd), ecological risk factor (Er), and pollution load index (PLI) were used to assess the level of ecological risk of trace element contamination. Positive matrix factorization (PMF) and PAH diagnostic ratios were applied to identify the sources of trace elements and PAHs.
Results and discussionElevated trace element concentrations were commonly found in gully sediments. The concentrations of Zn (267–3700 mg kg?1) were the highest compared to the other trace elements. Noticeable high concentrations of Cu (27–1020 mg kg?1), Pb (21–332 mg kg?1), and Cr (14–439 mg kg?1) were found in all samples. The PAH contents were moderate to high (0.6 to 24.7 mg kg?1). Commercial/industrial emissions and road features that cause frequent acceleration-deceleration and turning events showed important influences on the contaminant levels. Strong correlations between the concentrations of Cd, Cr, Pb, and Zn were identified, implying that these trace elements are likely from common sources. The contamination assessment indices reflect significant sediment pollution. The ecological risk ranges from the considerable/moderate-risk class to over the high-risk class.
ConclusionsThe collected gully sediments are identified as highly contaminated and need to be isolated from the environment upon final disposal. Through the comprehensive analysis of the collected data, this study provides a detailed insight into the contaminant levels of road gully sediments and potential sources of contamination. Disposal of gully sediments and potential impacts due to release of contaminants into the downstream aquatic environment during rainstorm events should receive attention and need further investigation.
相似文献Rare earth elements have been used as sediment tracers in river, estuarine and coastal environments but rarely applied as fluvial tributary tracers. Lanthanides (Ln) and yttrium (Y) were quantified in fluvial sediments of the Minho River lower course (NW Iberian Peninsula), where the catchment contains heterogeneous lithologies, to define the characteristic imprints of tributaries and their relevance in the riverine system.
Materials and methodsSurface sediments were sampled at 36 points in the lower Minho riverbed and its nine main tributaries.The <?2-mm fraction was sieved and ground, and ≈?100 mg was completely acid-digested with HF and aqua regia in closed Teflon bombs at 100 °C for 1 h. The residue was evaporated, re-dissolved with HNO3 and Milli-Q water, heated 20 min at 75 °C and diluted to 50 cm3 with Milli-Q water. Lanthanides and yttrium were determined using a quadrupole ICP-MS equipped with a Peltier impact bead spray chamber and a concentric Meinhard nebuliser. Blanks accounted for less than 1% of the element concentrations in the samples. The precision and accuracy of the analytical procedures were controlled through reference materials AGV-1 and MAG-1.
Results and discussionContents ranged from 22 to 153 mg Ln kg?1 and 1.5–22.9 mg Y kg?1 and ES-normalised light-heavy Ln fractionation, (LN/HN), varied between 0.6 and 2.6. These wide ranges, together with Eu and Ce anomalies and element-by-element Ln, varied with changes in parental rocks of the lower Minho basin. Minho sediments showed negative Ce anomalies (0.81?±?0.29) and positive Eu anomalies (1.23?±?0.18). Sediments received traces of granitic pegmatites and gneissic peralkaline rocks from two tributaries: the Gadanha (22.9 mg Y kg?1; 83 mg Ln kg?1; 0.60 LN/HN; 0.51 Eu/Eu*; 0.88 Ce/Ce*) and the Louro (15.9 mg Y kg?1; 110 mg Lnkg?1; 0.97 LN/HN; 0.69 Eu/Eu*; 1.49 Ce/Ce*). The Tamuxe tributary, flowing through a slate and quartzite fault, provided the lowest source (1.6 mg Y kg?1; 28 mg Ln kg?1; 2.48 LN/HN; 1.01 Eu/Eu*; 0.55 Ce/Ce*).
ConclusionsLanthanide and Y signatures in sediments may be used to trace land-tributary-river influences. The imprints are observed downstream of fluvial confluences but not in all cases, responding to basin lithological changes, particularly for pegmatites and peralkaline rocks. The general REE trend is described using Y contents only. Tributaries, which are responsible for one-fifth of the Minho water load, provide one-half of their sediments. Non-homogeneous sediment patterns may be magnified in dammed rivers such as the Minho.
相似文献The suppression effect of a sandy soil interlayer on topsoil enrichment of salt ions was investigated. However, whether this suppression effect was enhanced by surface mulching was little documented. The objectives of this study were to compare the suppression effects under different materials mulching, and to investigate an innovative method to suppress the soil salt ions down-to-top enrichment.
Materials and methodsIn this study, the sandy soil layer was pre-positioned at 60–100 cm depth in a salt-contaminated site in advance, achieving the suppression effect on surface enrichment of salt components as expected. Three treatments were herein designed as bare field (CK), plastic film mulching (PM), and maize straw mulching (SM) to examine the dynamics of water and salt movement across soil profiles during the summer with strong evaporation.
Results and discussionsResults showed that total salt content was increased by 21.3 and 8.0% in CK and SM respectively, while decreased by 24.9% in PM at the end of strong evaporation period, comparing with the beginning. Thus, surface mulching further strengthened this suppression effect, but PM displayed better performance than SM did. The data also demonstrated that vertical transport of soil water was much restrained in PM and SM, accordingly inhibiting upward transfer of salt ions. Particularly, sodium adsorption ratio (SAR) ranged from 14.3–265.7, 17.9–147.1, 38.4–147.2 mmol1/2 kg?1/2 at a shallow soil layer (0–60 cm) in CK, PM, and SM, respectively.
ConclusionsThe results suggested that sandy soil interlayer settings with plastic mulching are a critical technical strategy for salt-contaminated land reutilization and management.
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