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1.

Purpose

Factors such as organic matter can significantly influence the distribution of mercury (Hg) in aquatic environments. Recent studies in Arctic and sub-Arctic lakes in Canada have investigated whether scavenging of Hg by phytoplankton significantly affects distributions of Hg in sediments. This study examined the relationships between Hg and organic components in two contrasting lakes (Lakes Qinghai and Chenghai) in low and middle latitudes of China.

Materials and methods

Sediment cores from the less-polluted, oligotrophic Lake Qinghai (QH) and from the polluted, eutrophic Lake Chenghai (CH) were collected by a gravity corer. The cores were sectioned and transported on ice to the laboratory where they were stored at ?20 °C. Subsamples were dried in a vacuum freeze dryer and grounded with a mortar and pestle prior to analyses. Total concentrations of Hg were quantified using cold vapor atomic absorption spectrometry. Total organic carbon (TOC) was quantified using an elemental analyzer after removal of carbonate. The Rock-Eval 6 pyrolysis technique (Vinci Technologies, Rueil-Malmaison, France) was used to deconvolute TOC in sediments into S1, S2, and RC components; S2 was further separated into S2a and S2b.

Results and discussion

Different relationships between Hg and TOC were found in the two lakes, which suggest that different types of organic compounds might play completely different roles in the distribution of Hg in lakes. S1 (the soluble organic matter (SOM)) was found to significantly control distributions of Hg in sediments of both lakes, while S2 and S2a were not. Combining the synchronous fluctuations of Hg and the oxygen index in the QH sediment core and in recent sections of CH suggested that allochthonous SOM derived from the terrestrial environment had an important influence on the distribution of Hg in both lakes and a large portion of Hg that originated from the lake catchment.

Conclusions

This study provides further evidence that organic matter is one of the most important factors that influences distributions of Hg in lake sediments and that SOM was the primary form of carbon associated with sedimentation of Hg. The results also suggest that Hg in lake sediments might not accurately represent its pollution history as it could also be influenced by land use, such as agriculture or other human activities in the catchment.  相似文献   

2.

Purpose

Soil-plant transfer models are needed to predict levels of mercury (Hg) in vegetables when evaluating food chain risks of Hg contamination in agricultural soils.

Materials and methods

A total of 21 soils covering a wide range of soil properties were spiked with HgCl2 to investigate the transfer characteristics of Hg from soil to carrot in a greenhouse experiment. The major controlling factors and prediction models were identified and developed using path analysis and stepwise multiple linear regression analysis.

Results and discussion

Carrot Hg concentration was positively correlated with soil total Hg concentration (R 2?=?0.54, P?<?0.001), and the log-transformation greatly improved the correlation (R 2?=?0.76, P?<?0.001). Acidic soil exhibited the highest bioconcentration factor (BCF) (ratio of Hg concentration in carrot to that in soil), while calcareous soil showed the lowest BCF among the 21 soil types. The significant direct effects of soil total Hg (Hgsoil), pH, and free Al oxide (AlOX) on the carrot Hg concentration (Hgcarrot) as revealed by path analysis were consistent with the result from stepwise multiple linear regression that yielded a three-term regression model: log [Hgcarrot]?=?0.52log [Hgsoil]???0.06pH???0.64log [AlOX]???1.05 (R 2?=?0.81, P?<?0.001).

Conclusions

Soil Hg concentration, pH, and AlOX content were the three most important variables associated with carrot Hg concentration. The extended Freundlich-type function could well describe Hg transfer from soil to carrot.  相似文献   

3.

Purpose

Approximately 74 % of agricultural soils in Tunisia are affected by water erosion, leading to the siltation of numerous human-made reservoirs and therefore a loss of water storage capacity. The objective of this study was to propose a methodology for estimating the relative contributions of gully/channel bank erosion and surface topsoil erosion to the sediment accumulated in small reservoirs.

Materials and methods

We tested an approach based on the sediment fingerprinting technique for sediments collected from a reservoir (which has been in operation since 1994) at the outlet of a catchment (Kamech, 2.63 km2). Sampling concentrated on the soil surface (in both cropland and grassland), gullies and channel banks. A total of 17 sediment cores were collected along a longitudinal transect of the Kamech reservoir to investigate the origin of the sediment throughout the reservoir. Radionuclides (particularly caesium-137, 137Cs) and nutrients (total phosphorus, total nitrogen and total organic carbon (TOC)) were analysed as potential tracers.

Results and discussion

The applications of a mixing model with 137Cs alone or 137Cs and TOC provided very similar results: The dominant source of sediment was surface erosion, which was responsible for 80 % of the total erosion within the Kamech catchment. Additionally, we showed that the analysis of a single composite core provided information on the sediment origin that was consistent with the analysis of all sediment layers in the core. We demonstrated the importance of the core sampling location within the reservoir for obtaining reliable information regarding sediment sources and the dominant erosion processes.

Conclusions

The dominance of surface erosion processes indicates that conservation farming practices are required to mitigate erosion in the agricultural Kamech catchment. Based on the results from 17 sediment cores, guidelines regarding the number and location of sampling cores to be collected for sediment fingerprinting are proposed. We showed that the collection of two cores limited the sediment source apportionment uncertainty due to the core sampling scheme to <10 %.  相似文献   

4.
The deposition of strong acids is one of many threats to forest ecosystems and viable forestry. Several counteractions against acidification have been launched, e.g. changes in forestry management and the introduction of chemicals. The inter-institutional programme “Counteractions Against Acidification in Forest Ecosystems” was established in 1993 to evaluate existing knowledge and run experimental and fullscale field experiments. A total of 240 metric tons of coarse dolomite powder was spread by helicopter in September 1994 on 84 ha forest catchment dominated by pine (Pinus sylvestris) and Norway spruce (Picea abies). Potential desirable and undesirable effects after this carbonate application may be less pronounced than recorded at other sites due to the relatively moderate dose (3 tons ha?1). Pre-liming stream water quality (mean values for May 1993-September 1994) was as follows: pH 4.8; Ca 1.13 mg L?1; reactive Al (RAl) 248 μg L?1; inorganic monomeric Al (Al) 72 μg L?1. The reference station was slightly higher in Ca and slightly lower in both RAl and Al. Dolomite application resulted in a significant increase in pH to 5.7 as mean value for the post-liming period (September 1994-April 1995). Both Ca and Mg increased significantly after liming, and both RAl and Al, declined significantly. The rapid detoxification of stream-water may be explained by dissolution of dolomite particles in both streams and catchment, a resulting pH increase and change in Al species composition. Retention of Al in the catchment probably explains the reduction in RAl. No increase in NO3, total N, total P or TOC was recorded the first seven months.  相似文献   

5.

Purpose

The best method for determining soil organic carbon (SOC) in carbonate-containing samples is still open to debate. The objective of this work was to evaluate a thermal gradient method (ThG), which can determine simultaneously inorganic carbon (SIC) and SOC in a wide range of soil samples.

Materials and methods

The determination of SOC by ThG (SOCThG) was compared to the following widespread standard methods: (1) acidification (ACI) as pretreatment and subsequent dry combustion (SOCACI) and (2) volumetric quantification of SIC by a calcimeter (CALC) and subtraction of the total carbon content as determined by dry combustion (SOCCALC). Precision (F test) and bias (t test) were tested on a subset of seven samples (n?=?3). Comparison of the ThG and CALC methods was performed by regression analysis (n?=?76) on samples representing a wide range of SOC (5.5 to 212.0 g kg?1) and SIC (0 to 59.2 g kg?1) contents.

Results and discussion

Tests on the replicated subset showed that the precision of ThG was not significantly different from ACI or CALC (F values?<?39, n?=?3) for SOC and SIC measurements. However, SOCACI and SOCCALC contents were systematically and significantly lower compared to SOCThG contents. The positive bias for SOCThG relative to SOCCALC contents appeared also in the regression analysis (given numbers?±?standard errors) of the whole data set (y?=?(4.67?±?0.70)?+?(0.99?±?0.01)x, R 2?=?0.99, n?=?76). When performing a regression with carbonate-free samples, the bias between the methods was negative (?2.90?±?0.63, n?=?29) but was positive in the set with carbonate-containing samples (3.95?±?1.41, n?=?47). This observation corroborated the suspicion that the use of acid for carbonate decomposition can lead to an underestimation of SOC.

Conclusions

All methods were suitable for differentiation between SIC and SOC, but the use of acid resulted in lower estimates of SOC contents. When comparing soil samples with different carbonate concentrations, the use of the ThG method is more reliable.  相似文献   

6.

Purpose

The aim of the present study was to investigate the differences of methylmercury (MeHg) formation and distribution between mariculture (aquaculture) sediments (MS) and reference sediments (RS) collected from a site in Hong Kong.

Materials and methods

The MS and RS samples were split into four batches, three of which were spiked with HgCl2 aqueous solution to a concentration of 0.8, ,2 and 8 mg k g?1 in sediment samples SP1, SP2, and SP3, respectively, while the rest served as a control batch (referred to as C).

Results and discussion

The results showed that the highly Hg-polluted sediment produced greater amounts of MeHg. During the culture period, MeHg concentrations in sediments decreased over time. The decreasing percentage increased in the order of SP3?<?SP2?<?SP1, which might be due to the inhibition of MeHg degradation by high Hg concentrations. The mean value of MeHg concentrations and %MeHg of the total Hg (THg) in MS was significantly lower than those in RS, possibly due to the complexation of Hg with organic ligands, leading to lower Hg bioavailability for methylation bacteria. The distribution coefficient of THg (KdT) was relatively high in MS compared to RS, indicating that the former had a greater number of binding sites for Hg adsorption.

Conclusions

Methylmercury formation was inhibited in MS, probably due to increased complexation of Hg2+ with organic matter and adsorption of Hg to MS. Furthermore, the mean value of KdT in MS was relatively high when compared to RS, which illustrates that MS sediments have more binding sites than RS for adsorption of Hg.  相似文献   

7.

Purpose

Determining the dynamics of silicon in lakes, one of the essential nutrients for diatoms, is valuable for understanding aquatic environmental problems. The dissolved silicon (DSi) and biogenic silicon (BSi) budgets in Lake Kasumigaura, a shallow eutrophic lake in Japan, during the last three decades were assessed based on the analysis of dated sediment cores and a water quality database.

Materials and methods

Sediment cores (100?cm long) were taken at the center of Lake Kasumigaura in 2005, 2007, and 2009 and at two other sites in 2007. BSi contents of the dated sediments were determined by wet alkaline digestion. The net sedimentation rates of BSi were defined as the difference between the DSi load from inflowing rivers and the DSi and BSi loads from the outflow of the lake, calculated using DSi concentrations and diatom abundances in the lake from 1980 to 2007 and DSi concentrations of the inflowing rivers during 1994, 2007, and 2009. The gross sedimentation rates of BSi were estimated by multiplying BSi concentrations in lake water by the diatom sinking rate reported by previous studies.

Results and discussion

Budgetary calculations based on the database showed that 60?C70?% of DSi inputs from the inflowing rivers during the 27?years could ultimately be accumulated as diatom frustules in bottom sediments in the lake. The sediment analysis revealed that the amount of BSi accumulated in the lake from 1980 to 2007 was 2.0?C2.6?×?1011?g, similar to the amount based on the database of 1.3?C2.4?×?1011?g. Although the gross sedimentation rates of BSi likely increased, the net sedimentation rates of BSi decreased significantly from 6?C10?×?109?g?year?1 in the 1980s to 2?C6?×?109?g?year?1 in the 2000s, suggesting a fast recycling of BSi in recent years caused by an increase in sediment resuspension and regeneration.

Conclusions

The sediment core information and the water quality database can be used for calculating the long-term silicon budgets in Lake Kasumigaura. An increase in the DSi release rates was identified, which is consistent with recent sediment resuspension. Comparing the sediment core information with the database suggests the long-term dissolution of sediment BSi; however, analysis of the BSi content in sediment cores representing a much longer time period is needed to confirm this.  相似文献   

8.

Purpose

In this study, a soil-washing process was investigated for arsenic (As) and pentachlorophenol (PCP) removal from polluted soils. This research first evaluates the use of chemical reagents (HCl, HNO3, H2SO4, lactic acid, NaOH, KOH, Ca(OH)2, and ethanol) for the leaching of As and PCP from polluted soils.

Materials and methods

A Box–Behnken experimental design was used to optimize the main operating parameters for soil washing. A laboratory-scale leaching process was applied to treat four soils polluted with both organic ([PCP] i ?=?2.5–30 mg kg?1) and inorganic ([As] i ?=?50–250 mg kg?1, [Cr] i ?=?35–220 mg kg?1, and [Cu] i ?=?80–350 mg kg?1) compounds.

Results and discussion

Removals of 72–89, 43–62, 52–68, and 64–98 % were obtained for As, Cr, Cu, and PCP, respectively, using the optimized operating conditions ([NaOH]?=?1 N, [cocamidopropylbetaine] i ?=?2 % w w?1, t?=?2 h, T?=?80 °C, and PD?=?10 %).

Conclusions

The use of NaOH, in combination with the surfactant, is efficient in reducing both organic and inorganic pollutants from soils with different levels of contamination.  相似文献   

9.

Purpose

The content and composition of dissolved organic matter (DOM) in sediment directly affect nutrient cycling and material exchange in lake ecosystems. This study investigated the content and composition of DOM and its fractions in sediments, as well as the relationship between the different parameters and nitrogen (N) forms in DOM. The main aim of this study was to evaluate the compositional characteristics of DOM, hydrophobic bases (HOB), hydrophobic acids (HOA), hydrophobic neutral fractions (HON), and hydrophilic matter (HIM) in sediments from Erhai Lake, China.

Materials and methods

Seven surface sediment samples with different environmental characteristics were collected. The DOM in the sediment was fractionated into HOB, HOA, HON, and HIM using XAD-8 resin based on compound hydrophobicity. The contents of DOM and its fractions were measured using a TOC analyzer. The structural characteristics of DOM and its fractions were investigated using fluorescence spectroscopy and UV–Vis absorbance. Correlation analyses were carried out to better understand the relationships between the parameters of the spectral characteristics and the contents of the different N forms in DOM and its fractions.

Results and discussion

The content, spatial distribution and structure of DOM and its fractions in Erhai Lake sediment were affected by water depth and aquatic plants. The DOM content in sediment ranged from 0.2 to 0.5 g kg?1. HON accounted for 41.3 to 85.7 % of DOM, whereas HIM constituted 15.0 to 58.7 % and was significantly negatively correlated with HON (R 2 ?=?0.856, P?Conclusions (1) Hydrophobic fractions are the major components of DOM in the sediments from the seven sites in Erhai Lake. (2) DOM and its fractions mainly originated from microbial sources. (3) The A 253/A 203 ratio is useful for evaluating the contents of N forms. The structure of DOM and its fractions are important in affecting the contents of DON. Nitrate (NO3-N) contributes to eutrophication, and thus cannot be ignored from studies of Erhai Lake sediment.  相似文献   

10.

Purpose

Middle-European floodplain soils are often contaminated with mercury (Hg) and periodically flooded. In this study, the influence of a flooding event and subsequent dewatering on the volatilization of elemental Hg and methylated species was investigated in a laboratory experiment.

Material and methods

Undisturbed soil cores were taken from a topsoil (12.1?±?0.75 mg kg?1 Hg) at the Elbe River in Lower Saxony, Germany. Soil columns were incubated at 20 °C with varying soil moisture (water-saturated for 2 weeks, 95 and 90 % water content for 1 week each), and the redox potential (EH) was recorded. The gaseous Hg that accumulated in the headspace of the flux chamber of the columns was pumped over cooled traps filled with adsorber material and analyzed by gas chromatography/inductively coupled plasma mass spectrometry for the various Hg species.

Results and discussion

The watering of the soil resulted in a rapid decrease in the EH and the achievement of strongly reducing conditions (EH??1 Hg at the beginning to 5.78 μg L?1 Hg at the end of the experiment. Species analyses revealed that exclusively elemental Hg volatilized. The volatilization rate was between 1.73 and 824 ng m?2 h?1 Hg, which is consistent with other studies at the Elbe River.

Conclusions

Even when flooded for a longer period of time, floodplain soils should show neither emission of methylated Hg nor exceptionally high volatilization of elemental Hg.  相似文献   

11.

Purpose

Information about phosphorus (P) losses from agricultural catchments in Mediterranean environments is scarce. In this work, P losses in overland flow from two representative small Mediterranean catchments, one dominated by Alfisols and the other by Vertisols, were studied.

Materials and methods

At the lowest level of each catchment, overland flow was measured and several runoff samples taken in each runoff event during two growing seasons (2001–2002 and 2002–2003). After centrifugation, total P in sediments and total and molybdate reactive P in supernatant were determined. Different chemical extraction methods were used to quantify the forms of P in soils and sediments.

Results and discussion

Total P losses in the studied catchments ranged between 0.5 and 3.2 kg ha?1 year?1, losses higher than 2 kg P ha?1 being observed in one event. Phosphorus was mainly lost in the sediments, the ratio of total dissolved P to particulate P being higher in the Alfisol than in the Vertisol catchment. Phosphorus concentration in sediments from the Vertisol catchment was similar to that in the source soils, whereas sediments in the Alfisol catchment had 2.1 times more inorganic P and 9 times more organic P (OP) than the source soils. In the latter catchment, there was an enrichment in the more labile inorganic P forms in the sediments relative to the source soils, which corresponds to a relative enrichment in iron (Fe) oxides by a factor of 2.4. Alfisols had lower TP contents and exhibited lower erosion rates than Vertisols in the studied period but they posed a greater environmental risk than the latter soils because their sediments were richer in P and had a higher proportion of P in forms bound to the Fe oxides compared to the source soils—these P forms can be easily released with the onset of reducing conditions at the bottom of waterbodies.

Conclusions

A study of the P enrichment ratios and the dominant P forms in eroded sediments is therefore necessary to predict the impact of P losses from soils on the ecological quality of waterbodies.  相似文献   

12.

Purpose

Ichkeul National Park, NW Tunisia, is a UNESCO Biosphere Reserve. Garaet El Ichkeul Lake is known for its seasonal variability in water level and salinity. In recent decades, the waterbody has been affected by the construction of new hydraulic structures. To reduce the impacts of dams and to maintain the sustainability of the ecosystem, a sluice was built at the outlet of the lake, and it operated for the first time in 1996. This paper describes an investigation of recent sedimentation dynamics in Ichkeul Lake, determined by radiometric dating of sediment cores.

Materials and methods

A sediment core was collected with a UWITEC gravity corer at the deepest, central part of the lake in August 2009. Specific activities of unsupported lead-210 (210Pb) and caesium-137 (137Cs) were measured in the core, enabling calculation of recent sediment accumulation rates (SAR). Published radiometric data from nearby sediment cores, collected in 1997 and 1982, provide a comparison.

Results and discussion

The measured excess 210Pb inventory was 5300?±?500?Bq?m?2, leading to an estimation of constant flux of 165?±?16?Bq?m?2?yr?1, a value higher than the best estimate for local atmospheric fluxes (123?±?12?Bq?m?2?yr?1) and the flux estimated from the core collected in 1982 (48?Bq?m?2?yr?1). The 137Cs inventory was 3550?±?120?Bq?m?2, two times higher than the historical 137Cs atmospheric deposition in the area. The 137Cs profile displayed a distinct peak, but the 137Cs depth-distribution did not follow the pattern expected from atmospheric deposition. Application of the constant rate of supply (CRS) model, with the reference point method, produced a chronology and SAR values comparable to those found in previous work. The whole 137Cs profile was quantitatively reconstructed from the historical records of atmospheric deposition, using the system-time-averaged (STA) model.

Conclusions

The CRS and STA models provide consistent sediment accumulation results for the whole data set, considering the time resolution of the chronology (~6?years) and analytical uncertainties. Results from cores sampled in 1982, 1997 and 2009 reveal an increasing SAR trend, from ~0.25?g?cm?2?yr?1 in the early 1940s to ~0.67?g?cm?2?yr?1 at present. In the 13?years since installation of sluice gates at Tinja, SAR in the central Ichkeul Lake has not declined. Thus, if siltation continues at the present rate, shallowing of the lake will seriously affect the hydromorphology and ecology of this important lake.  相似文献   

13.
Lacustrine sediment cores from depositional areas have frequently been used to estimate pre-industrial rates of atmospheric Hg deposition. However, this approach tends to result in overestimates, partly because of Hg inputs from the catchment, partly because of a horizontal redistribution of sediments within lakes. Peat core studies may suffer from a vertical migration of Hg due to water table fluctuations. A natural Hg deposition rate around 2 μg m?2 y?1 is suggested to be more realistic than values of 3 to 12 μg m?2 y?1 reported from recent studies. The anthropogenic impact on the present Hg deposition may have been underestimated accordingly.  相似文献   

14.

Purpose

Heavy metals often occur as co-contaminants with polycyclic aromatic hydrocarbons (PAHs) and reportedly have adverse effects on biodegradation. In this study, the development of 14C-phenanthrene mineralisation in soil co-contaminated with aged or freshly added Al or Fe amendment was assessed.

Materials and methods

14C-phenanthrene mineralisation was assessed using respirometry; respirometers incorporated a Teflon-lined screw-capped CO2 trap containing 1-M NaOH within a glass scintillation vial. The production of 14CO2 was assessed by the addition of Ultima Gold liquid scintillation fluid to the CO2 traps and subsequent liquid scintillation counting. Enumeration of phenanthrene-degrading bacteria was achieved by counting the colony forming unit count using the spread plate method.

Results and discussion

This investigation considered the effects of Al and Fe (50, 100, 250 and 500 mg/kg) on 14C-phenanthrene biodegradation in soil over 63-day contact time. Fresh Al amendments at lower concentrations (50 and 100 mg/kg) stimulated phenanthrene catabolism (p <0.05) at t?=?21 and 42 days which may reflect an ‘Arndt–Schulz’ effect, but phenanthrene catabolism was significantly reduced (p <0.05) in 500 mg/kg aged Al this could be due to Al toxicity to phenanthrene degraders. Phenanthrene mineralisation was stimulated in the highest Fe concentration (500 mg/kg) in aged and fresh Fe amendments at t?=?21 days. This could be because Fe is an essential requirement for microbial growth.

Conclusions

The impact of Al or Fe on the catabolism of 14C-phenanthrene was dependent on incubation time and Al was more toxic than Fe to soil PAH catabolic activity. This could be because Al is a non-essential microbial requirement. Bioremediation of soils co-contaminated with PAH and heavy metal is a complex problem; therefore, studies on the impact of metals on PAHs biodegradation highlight the risks and biodegradation potential in contaminated soil.  相似文献   

15.

Background, aim, and scope

The Mecklenburg Bight (Western Baltic Sea) near Luebeck, Germany was historically used to dump industrial waste at sea and, thus, sediments in some regions are highly polluted at present. While earlier studies identified hot spots of chemical pollution, little is known about biological activities and impacts on exposed marine organisms. This study aimed to assess the pollution in the Mecklenburg Bight to determine the degree of contamination with sediment-bound polycyclic aromatic hydrocarbons (PAHs) as well as biological activities.

Materials and methods

Sediment cores with a depth of 30 cm were sampled at a dumping site and at a reference site, sliced in distinct layers, freeze-dried, and processed using the accelerated solvent extraction method. Sediment was characterized measuring total organic carbon (TOC) and soot contents. Concentrations of the 16 EPA-PAHs were determined with chemical analysis (gas chromatography–mass spectroscopy) in each sediment slice and referred to the determined TOC content. Further on, in vitro biotests were applied to determine toxic effects of contaminants in the sediment. The acute neutral red retention assay indicated no specific cytotoxic effects. Arylhydrocarbon receptor (AhR)-mediated activities were measured using the mechanism-specific 7-ethoxyresorufin-O-deethylase induction assay. Both biotests were performed with rainbow trout (Oncorhynchus mykiss) liver cells (RTL-W1). Analyzed compound concentrations and biological activities were given in toxicological equivalent concentrations (chem- and bio-TEQs) to determine shares of analyzed EPA-PAHs to the overall activity.

Results

TOC and soot contents indicated a significant alteration through the sediment core at the dumping site. EPA-PAH concentrations were referred to TOC and indicated elevated concentrations at the dumping site. Maximum PAH concentrations (14 to 16 cm depth; 5.44 µg/g TOC) were 300-fold increased at the dumping site, compared to the reference site (4 to 6 cm depth; 0.017 µg/g TOC). Cytotoxicity as determined in the neutral red retention assay was elevated in some layers at the dumping site (maximum in 4 to 6 cm depth; NR50?=?14 mg/ml), but not correlated with TOC or soot contents. Ah receptor agonist activities were clearly elevated in highly PAH-loaded layers at both sites. At the dumping site, maximum activities were determined reflected by a bio-TEQ of 223,000 pg/g (19 to 22 cm), in contrast to a bio-TEQ of 41,000 pg/g (6 to 8 cm) at the reference site. Further on, shares of EPA-PAHs to the overall activity were determined and contributed >40% at the dumping site and between 4% and 17% at the reference site. Chem-TEQs were found to exceed bio-TEQs in a depth of 11 to 22 cm, indicating the presence of Ah receptor antagonistic or inhibitive compounds.

Discussion

Sediments from the dumping site were determined to be highly contaminated and caused toxic effects in depths that are known to be influenced by dumping activities. In contrast, the reference sediment indicated only near to surface layers to be minor contaminated. In comparison with highly polluted sediments from other marine sites, the contamination of the dumping site could be ranked as elevated. Chem-TEQs exceeding bio-TEQs in a depth of 11 to 22 cm seem to be caused by AhR antagonistic compounds in the dumped material. Furthermore, particle-bound PAH concentrations assessed in this study were discussed against freely dissolved concentrations in interstitial water, as determined in a different study with the same sediment core.

Conclusions

Sediments in the inner Mecklenburg Bight could be shown to be highly contaminated, at least with PAHs, causing articulate increased Ah receptor-mediated activities. Marine organisms may be exposed to these contaminants, in particular when inhabiting the sediment.

Recommendations and perspectives

Further research activities should extend the range of chemically analyzed pollutants and applied biotests and endpoints. Monitoring should close the gap between analytical methods in the laboratory and the field to determine possible impacts on organisms at site.  相似文献   

16.

Purpose

In this study, we quantified soil organic carbon (SOC) stocks and analyzed their relationship with biophysical factors and soil properties.

Materials and methods

The study region was Veracruz State, located in the eastern part of Mexico, covering an area of 72,410 km2. A soil database that contains physicochemical analyses of soil horizons such as carbon concentration data was the source of information used in this study. The database consisted of 163 soil profiles representing 464 genetic horizons. Statistical analysis was used to investigate the effect of each factor (climate, altitude, slope) on SOC stock to 0.50 m depth and to assess differences in the distribution of SOC stock in terms of soil depth (0.0–0.20, 0.20–0.40, 0.40–0.60, 0.60–0.80, 0.80–1.0 m) and land use. In order to compute the spatial distribution of SOC stock to 0.50 m depth based on the soil sampling location, the kriging method was used.

Results and discussion

Results indicated that SOC stock (0.50 m depth) ranged between 0.44 and 41.2 kg C m?2. Regression analysis showed that SOC stocks (0.50 m depth) are negatively correlated with temperature (r?=??0.38; P?<?0.001) and positively correlated with altitude (r?=?0.40; P?<?0.001) and slope (r?=?0.40; P?<?0.001). In addition, by multiple regression, temperature combined with precipitation explained more SOC stock variations (r?=?0.43; P?<?0.001) than the regression model with precipitation (r?=?0.13; P?=?0.16) alone. Also, slope combined with temperature and precipitation explained more SOC stock variations (r?=?0.46; P?<?0.001) than the regression model with slope alone. Forest lands, grasslands, and croplands have higher SOC stocks in the 0.0–0.20-m soil layer than in deeper layers. On average, forest lands, grasslands, croplands, and other lands (wetland and dunes) had a SOC stock of 13.6, 14.6, 15.1, and 8.5 kg C m?2 at 1 m depth, respectively. Soil color correlated (?0.25 ≤ r ≤ ?0.89) with SOC content.

Conclusions

Overall, these results indicate the influence of major interactions between biophysical factors and SOC stocks. This research indicated that SOC stock decreased with soil depth, but with slight variations depending on land use. Thus, there remains a need for more SOC data that include an improved distribution of soil sampling points in order to entirely understand the contributions of biophysical factors to SOC stocks in Veracruz State.  相似文献   

17.

Purpose

The extensive use of chemical pesticides on farmlands during the last several decades in China has led to a rapid deterioration of environmental water quality in recent years. The aims of this study were to: reconstruct the history of pesticide residues, determine the input load and residual load of dichlorodiphenyltrichloroethane (DDT) pesticides, and assess the risk of pesticide residues to aquatic ecosystem and human health.

Materials and methods

Caesium-137 was used to date sediment cores collected from ponds representing four land use types of an agricultural watershed with high-yield grain production and characterized by multipond systems in the Yangtze-Huaihe region of China. These ponds were selected to establish the historic pattern of DDT pesticide residues.

Results and discussion

(1) The mean total concentration of DDT residues including p,?p?′-dichlorodiphenyldichloroethylene (p,p′-DDE), p,?p?′-dichlorodiphenyldichloroethane ( p,p′-DDD), o,p′-DDT, and p,p′-DDT in sediment in the watershed was 82 μg kg?1, ranging from under the detection limit to 457 μg kg?1, which was mostly contributed by p,?p′-DDE (57 μg kg?1 on average). Spatially, total concentrations of DDT residues in farmland pond sediment were the highest, reaching as high as 457 μg kg?1. Temporally, an inflection point appeared in the 1970s, prior to which DDT contents increased with time, after which concentrations showed a decreasing trend. (2) In total, 323 kg DDT pesticide was applied to the Liuchahe Watershed since 1955. The total retention of four DDT residues in the multipond system was 14 kg (～4 % of the input), and most DDT pesticide was degraded to p,?p?′-DDE. (3) More than 80 % of sediment DDT residues exceeded their interim freshwater sediment quality guidelines, and the percentages of DDT,DDD, and DDE residues exceeding probable effect limit (PEL) values were 57, 29, and 70 %, respectively, which indicated a moderate to high ecological risk of DDT in this watershed.

Conclusions

Our results clearly reveal that the extensive use of pesticides has resulted in significant pesticide residual pollution in this watershed, which could severely deteriorate water quality and threaten aquatic ecosystem and human health in the watershed and, thus, remain a cause for concern.  相似文献   

18.

Purpose

Closed erosion plots have been used extensively to investigate soil loss and its spatial variation within a watershed. However, erosion rates measured on closed plots at various locations within a watershed may not reflect the “real world” conditions due to plot boundary problems. The purpose of this study was to identify runoff and sediment sources in a semi-arid, complex terrain catchment by using the data collected from open plots, nested catchments, and tunnel systems.

Materials and methods

The study catchment, in the Loess Plateau of China, was partitioned into various-level geomorphic units. Runoff and sediment discharges were measured from 55 storm events between 1963 and 1968 on open plots and nested catchments. Storm flows were also monitored in 14 rainfall events from the tunnel systems between 1989 and 1990. This study combined the data collected from the two periods to investigate runoff and sediment sources from the different geomorphic units of the catchment.

Results and discussion

On the four open plots (S1, S2, S3, and S4) of the hill slope, total runoff depths of 128.5 mm (S1), 84.3 mm (S2), 101.92 mm (S3), and 141.73 mm (S4) were recorded from all the events over the first period, which correspondingly produced total sediment yields of 3.056 kg m?2 (S1), 9.058 kg m?2 (S1), 42.848 kg m?2 (S3), and 97.256 kg m?2 (S4). The number of runoff events also varied due to a non-uniformity in runoff generation among the different geomorphic units of the catchment. Tunnel flows generally had higher mean sediment concentrations than catchment outflows. Three nested catchments located from the headwaters (C1) to the mouth of the catchment (C3) generated total runoff depths of 120.02 mm (C1), 143.92 mm (C2), and 149.43 mm (C3), and correspondingly produced sediments yields of 62.01 kg m?2 (C1), 144.02 kg m?2 (C2), and 123.92 kg m?2 (C3) for the first period.

Conclusions

Significant variations in runoff and erosion existed within the catchment. The spatial variation of runoff generation on the hill slopes resulted from the variation of soil infiltration. Sediment produced from the lower hill slope zone was disproportionally higher than that from the upper hill slope zone. Nevertheless, a significant portion of the sediment eroded on the lower slope zone was caused by runoff generated from the upper slope zone. Tunnel erosion also played a significant role in sediment production.  相似文献   

19.
Surficial sediments were sampled with a light-weight gravity corer at 175 sites in 73 Ontario and Québec lakes and Zooplankton was collected with a 225 μm mesh size net in 24 lakes. Hg concentrations in surficial sediments (0–2 cm) ranged from 3 to 267 ng g?1 dry weight with a mean of 80 ng g?1 dry weight for all sites. A regression model including organic content of sediments and the ratio of the catchment area/lake surface explained 60% of the variation in sediments Hg concentrations. Hg in Zooplankton ranged from about 25 to 377 ng g?1 dw with a mean of 108 ng g?1 dw and was weakly correlated with catchment area, primary productivity and TOC. Our data indicate that an important fraction of Hg originates from the catchments, but do not show a clear west-east regional gradient for Hg concentrations in surficial sediments or in zooplankton.  相似文献   

20.
Mercury concentrations were measured in samples of peat soils, sediments and clams (Rangia cuneata) from a peatland region of the Albemarle-Panlico Peninsula of North Carolina. Total Hg concentrations in peat cores ranged from 40 to 193 ng g?1 (dw); no depth-related trends were noted. Mercury concentrations in surface sediments from canals draining the peatlands and from the Pungo River that receives this drainage ranged from 8 to 20 ng g?1 (dw). Selective extractions of these peat and sediment samples revealed that the bulk of the Hg was associated with organic matter-associated fractions (particularly humic/fulvic acid bound and organic-sulfide bound fractions). No Hg was detected in the relatively mobile and bioavailable water-soluble or ion-exchangeable fractions. Total Hg concentrations in the soft tissues of clams from the Pungo River ranged from 25 to 32 ng g?1 (ww). No concentrations of methyl Hg above the detection limit of a 25 ng g?1 were measured in soils, sediments, or clams. These data indicate that Hg concentrations in this region are at the low end of the distribution of levels reported for uncontaminated systems and that mining of these peatlands is unlikely to significantly elevate Hg concentrations in the receiving estuarine system.  相似文献   

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