Purpose

The heavily forested Cache la Poudre (CLP) watershed in northern Colorado, USA, was impacted by the High Park wildfire in 2012. The wildfire burned land and vegetation immediately adjacent to the CLP River where blackened, ashy sediment samples were collected from five sites upstream of the City of Fort Collins drinking water intake to evaluate the spatial distribution and characteristics of burned sediments, along with quantifying and characterizing soluble compounds following a leaching experiment.

Materials and methods

At each site, samples were collected from three locations: (1) the edge of the bank adjacent to the water edge (downbank), (2) 1 m upslope of location 1 (midbank), and (3) 2 m upslope of location 1 (upperbank). All solid sediment samples were analyzed for elemental composition, and a subset of solid sediment samples were analyzed with ¹³C solid-state nuclear magnetic resonance spectroscopy. Sediments were mixed with the background CLP River water collected from upstream of the wildfire and allowed to leach for 6 and 24 h to determine the quantity and quality of water-soluble constituents. Filtered samples were analyzed for dissolved organic carbon (DOC), iron, manganese, and inorganic nutrient concentrations, by optical properties, and for disinfection byproduct (DBP) formation.

Results and discussion

Percent carbon and nitrogen content of the solid sediments were good predictors of leachate DOC concentration. The mean fluorescence index was higher for wildfire-impacted sediment leachates (1.50) compared to the background CLP River water (1.37), which may be due to changes in DOM molecular weight and oxidation of organic matter. All sediment leachates showed consistently higher haloacetonitrile and chloropicrin yields (DBP concentration/DOC concentration) compared to background CLP River water, whereas carbonaceous DBPs did not.

Conclusions

The collected sediments showed that burned material accumulated downstream near the river and was composed of inputs from burned soil and biomass along with the mobilization of unburned terrestrial material. The leachates of these sediments have different characteristics compared to the background CLP River water, indicating that DOM leached from sediments following a wildfire may increase aquatic DOC concentrations and N-DBP formation.

Purpose

In Japan, the excavated soils produced from constructions projects, which contain relatively low levels of arsenic (As), are considered as a potential concern if they could release significant amount of As to the environment. The aim of this study was to investigate the As leaching from excavated alkaline soils and, in particular, the influence of drying methods, pH of extracting solution, and consecutive washing on As leaching from these soils.

Materials and methods

Four excavated alkaline soils obtained from different construction sites in Tokyo, Japan, were used in this study. The soils were pretreated by three drying methods (air-dried, 40 °C-dried, and freeze-dried). Sequential extraction procedure was applied to partition As into five operationally defined chemical fractions. Batch leaching tests (initial pH-controlled leaching test and consecutive washing test) were conducted to investigate the As release under different leaching conditions.

Results and discussion

The As contents in the four soils were 9.22, 79.4, 6.75, and 11.7 mg kg^?1, respectively, and As was primarily associated with the residual phase. Arsenic leaching was strongly dependent on the extracting solution pH values. Strongly acidic extracting solution (pH 2) led to circumneutral leachates and limited As mobility, whereas the strong alkaline-extracting solution (pH 12) greatly enhanced the As release from these soils. The consecutive washing test results revealed a long-term release of As from these excavated soils. The pollution potential indices (PPIs) were successfully used to evaluate the pollution threat of As leaching from excavated soils. In addition, different drying methods resulted in variations in the short- and long-term release of As from these excavated soils.

Conclusions

The results revealed that the soil pretreatment and the leaching conditions should be considered if we want to use batch tests for the contamination assessment of excavated urban soils from construction projects. Different drying methods and single extraction may lead to misestimation of the As pollution level. High extraction efficiency with strong alkaline-extracting solution (pH 12) reveals that it could potentially be used to wash As from excavated alkaline soils.

Purpose

Concentrations and transformations of mercury were measured in river, estuarine, and marine sediments to determine factors affecting the fate of mercury entering the northern Adriatic Sea.

Materials and methods

Radiotracer methodology was used to compare rates of mercury methylation (²⁰³Hg), MeHg demethylation (¹⁴C), and sulfate reduction (³⁵S) in sediment depth profiles to concentrations of total and dissolved mercury species in the lower freshwater region of the Isonzo River, the coastal lagoons, and in the Gulf of Trieste, northern Adriatic Sea.

Results and discussion

Mercury was readily methylated and demethylated in all sediments, but the relative activity of these processes varied greatly with location. Methylation activity increased greatly from freshwater to the marine regions; however, demethylation was extremely high in the estuarine and lagoon sites. Ratios of methylation to demethylation were low in these coastal sites but increased further offshore in the gulf, which agreed with increased ratios of MeHg to total Hg (%MeHg) in gulf sediments. Comparisons of microbial activities indicated that sulfate reduction strongly controlled both methylation and demethylation. However, Hg methylation in coastal lagoon sediments was controlled by rapid demethylation and the bioavailability of Hg that was affected by Hg adsorption and precipitation. Methylation in offshore marine sites correlated with sulfate reduction but not the partitioning of Hg between pore water and solid phases. The decrease in sulfide production offshore exacerbated Hg methylation.

Conclusions

The freshwater to marine gradient in the Idrija/So?a/Isonzo/Adriatic region is dynamic, exhibiting horizontally variable rates of microbial activities and Hg transformations that create “hot spots” of MeHg accumulation that are controlled differently in each region.

Purpose

The low conductivity of sediments for mass and electron transport is the most severe limiting factor in sediment microbial fuel cells (SMFCs), so that sediment ameliorations yielded more remarkable effects than electrode improvements. The objective of this research was to enhance the electricity generation of SMFCs with amendments of biochar to freshwater sediments for conductivity enhancement.

Materials and methods

Laboratory-scale SMFCs were constructed and biochars were produced from coconut shells at different temperatures. Variations in the power output, electrode potential, internal resistance, total organic carbon (TOC) content, and microbial communities were measured.

Results and discussion

Amending with biochar reduced the charge transfer resistances of SMFCs and enriched the Firmicutes (mainly Fusibacter sp.) in the sediment, which improved the SMFC power generation by two- to tenfold and enhanced the TOC removal rate by 1.7- to fourfold relative to those without the amendment.

Conclusions

The results suggested that biochar amendment is a promising strategy to enhance SMFC power production, and the electrical conductivity of biochar should be considered important when interpreting the impact biochar has on the electrical performance of soil or freshwater sediment MFCs.

Purpose

Polycyclic aromatic hydrocarbons (PAHs) are unintentional products that are classified as persistent toxic substances. The goal of the present study was to generate data on the presence of 15 priority PAHs that are found in surface sediment and core sediment in the region of the Turvo/Grande watershed, São Paulo State, Brazil, which is an area of expanding sugarcane cultivation, and to correlate these data with the sources of these PAHs and the guiding values for sediment quality analysis.

Materials and methods

Surface sediments and sediment cores were sampled during the rainy and dry seasons in February and July 2010. The extraction of PAHs from sediments was performed using a Soxhlet extractor, and then the extract was cleaned according to the methods of the US EPA 3630C (US EPA 1996) using a silica gel column. Quantification was performed using high performance liquid chromatography with fluorescence detection.

Results and discussion

The concentrations of all 15 PAHs decreased as the depth of the sediment core increased. Overall, the concentrations decreased along the sediment core; however, the RTURARG (region predominantly used for planting sugarcane and livestock) during the rainy season and the CAPRP sampling site (located at part of the Preto River dam) during the dry season showed increased concentrations in the first few sediment fractions, and then the concentrations decreased. Higher concentrations were observed in urban locations, and the concentration of naphthalene was higher than the probable effect level (PEL) determined by the Canadian environmental agency. The obtained diagnostic ratios indicate that the sediment from areas with an abundance of sugarcane was a pyrolytic source of PAHs, which indicates a contribution from burning straw to the PAH concentrations in those areas.

Conclusions

For all sampling sites and all PAHs, we found a decreasing trend in PAH concentrations with increasing sediment core depth, and the locations, such as CAPRP, that experienced a higher level of human activity had the highest total concentrations of PAHs. These locations were the only areas in which the PAH naphthalene was found in higher concentrations than the PEL. The diagnostic ratios reveal that regions with sugarcane plantations had predominantly pyrolytic sources of PAHs, indicating the contribution of PAHs from sugarcane straw burning.

Purpose

Wood extractives in sediments originating from the wood industry may interfere with benthic biota in aquatic environments. The research area was the Äänekoski watercourse in Central Finland, which has been affected by the chemical wood industry for over a century. The goal was to determine the dissolution potency of resin acids (RAs) and their derivative, retene, in the sediment, and their current vertical and spatial stratification to assess the load due to potential erosion.

Materials and methods

Sediments were collected from two upstream reference sites and three lake-like basins, located as far as 33 km downstream from the mills. The dissolution potency was studied by two different agitation times and temperatures from sediment-water (1+4 v/v) elutriates. The vertical distribution of extractives was determined from the uppermost 20 cm of sediment. Using spatial interpolation, the distribution of extractives was estimated from two upper sediment layers (0–2 and 2–5 cm) downstream from the source. According to the interpolation, the total amount of dehydroabietic (DHAA) and isopimaric acids (IPA) were calculated as kg/ha in the whole sediment area.

Results and discussion

The total concentration of RAs in the surface sediment reached up to 168 µg/g dw, and they were found to desorb to water up to 77 µg/l. The concentrations of retene were low both in the sediment (<51 µg/g dw) and elutriate (<0.53 µg/l). Spatial interpolation showed that the highest calculated amounts of the most abundant RAs were in Kuhnamo basin, in the sediment layer 2–5 cm; the estimated amount of DHAA and IPA were approximately 440 and 85 kg/ha, respectively.

Conclusions

Disturbances may change the exposure situation, causing desorption of sediment-associated compounds in levels that may be harmful to aquatic animals. The amount of desorption varies depending on the concentration of contaminants in sediment, the nature of disturbance, and the sediment organic carbon content. Low retene concentrations can be explained by oxic conditions and low abundance of RAs in the sediments.

Purpose

Seasonal fluctuating water tables are common in sandy coastal plain soils, but their role in soil organic carbon dynamics is uncertain. Seasonal saturation influences biogeochemical processes that affect fate of organic matter and metals. A column study was conducted to test hypotheses that shallow water table (SWT) fluctuations reduce CO₂ loss (H1), increase leaching of dissolved organic C (DOC) and metals (Al and Fe) (H2), and result in greater net soil C storage (H3).

Materials and methods

The A- and E-horizon material of moderately well-drained sandy soils from five sites was collected for the study. Ten columns (two per site) of 90-cm height were packed to a thickness of 60 cm with E-horizon material, above which was packed 15 cm of A-horizon material from the same soil. Five columns were subjected to SWT treatments and five to deep water table (DWT) treatments. Upward CO₂ flux was measured using a NaOH (1 M) trap. Metal and DOC-C concentrations in leachates and in water sampled at the surface of columns were measured. Soil samples from the columns were collected by depth at 5–6-cm increments and tested for total and organic C, metals, and <50-μm material distribution by WT treatment.

Results and discussion

Upward flux of CO₂ was significantly less for SWT treatment. Higher DOC (for all events) and Fe concentrations (for first 18 days) were measured in SWT leachates as compared to DWT. Metal- and C concentrations were correlated (P?<?0.0001) for surface pore water samples of SWT but not for DWT. Net loss of C was significantly less under SWT condition. Results indicate significant water-table effects on magnitude and direction of C flux (solution or gaseous) and <50-μm particle distribution for sandy coastal plain soils materials.

Conclusions

Changes in water table depth can potentially alter not only net soil C storage but also the proportion of C converted to CO₂ versus DOC. Differences in the proportion would have consequences for C dynamics in ecosystems dominated by soils with fluctuating water tables such as occur extensively in the coastal plain of the SE USA and elsewhere.

Purpose

Cohesive sediment is able to flocculate and create flocs, which are larger than individual particles and less dense. The phenomenon of flocculation has an important role in sediment transport processes such as settling, deposition and erosion. In this study, laboratory experiments were performed to investigate the effect of key hydrodynamic parameters such as suspended sediment concentration and salinity on floc size and settling velocity. Results were compared with previous laboratory and field studies at different estuaries.

Materials and methods

Experimental tests were conducted in a 1-L glass beaker of 11-cm diameter using suspended sediment samples from the Severn Estuary. A particle image velocimetry system and image processing routine were used to measure the floc size distribution and settling velocity.

Results and discussion

The settling velocity was found to range from 0.2 to 1.2 mm s^?1. Settling velocity changed in the case of increasing suspended sediment concentration and was controlled by the salinity. The faster settling velocity occurred when sediment concentration is higher or the salinity is lower than 2.5. On the other hand, at salinities higher than 20, in addition to increasing SSC, it was found that the situation was reversed, i.e. the lower the sediment concentration, the faster the settling velocity.

Conclusions

Sediment flocculation is enhanced with increasing sediment concentration but not with increasing salinity.

Goal, Scope and Background

Distribution of hydrophobic organic contaminants in abiotic compartments is essential for describing their transfer and fate in aquatic ecosystems. Taihu Lake is the third largest freshwater lake in China. Water quality of Taihu Lake has deteriorated greatly during the last decades and has threatened the water supply. The aim of the present study was to investigate the partitioning of polycyclic aromatic hydrocarbons (PAHs) among overlying water, suspended particulate matter (SPM), sediments, and pore water in Meiliang Bay, Taihu Lake and to provide useful information for the ecological engineering in this area.

Materials and Methods

Overlying water and surface sediment were sampled from six sites in Meiliang Bay, Taihu Lake, China. Within 72 h of sampling, sediments were centrifuged to obtain the pore water. Overlying water samples were filtered to separate dissolved and SPM samples. After extraction, samples were purified following a clean-up procedure. PAH fraction was obtained by elution with a mixture of hexane: DCM (7:3, V/V) and analyzed by GC/MS.

Results

PAHs concentrations in overlying water varied from 37.5 ng/L to 183.5 ng/L. Concentrations of PAHs in pore water were higher than those in overlying water. The total concentrations of 16 priority PAHs in sediments ranged from 2091.8 ng/g-dw to 4094.4 ng/g-dw. PAHs concentrations on SPM were decreased with suspended solid concentrations (SSC). Total PAHs concentrations on SPM varied in the range of 3369.6 ng/g-dw to 7531.1 ng/g-dw. The partition coefficients between sediment and overlying water (log K _oc) for PAHs with log K _ow<5 were positively correlated with their octanol-water partition coefficients (log K _ow) (n=39, r=0.79, p<0.0001). Partition coefficients between sediment and pore water (log K _oc′) for all PAHs were also significantly correlated with their log K _ow values (n=48, r=0.82, p<0.0001).

Discussion

In general, PAHs derived from combustion sources tend to bind strongly to soot particles in natural sediment. Consequentially, K _oc values observed in the natural environment could be orders of magnitude higher than those predicted by linear correlation relationships under laboratory conditions. In the present study, the ratio of log K _oc values to log K _ow values falls consistently above 1, indicating that the sediment soot carbon in the bay was more attractive for PAHs than n-octanol. The log K _oc′ was also higher than that predicted under laboratory conditions, suggesting that the measured pore water PAH concentrations were lower than those predicted. That is to say, not all the sediment PAHs can be available to partition rapidly into sediment pore waters. A variation in soot content is a possible reason. Furthermore, concentrations of PAHs on SPM were higher than those in sediments. The compositions of PAHs on SPM and in sediments were similar, indicating the importance of re-suspension process of sediments in the partitioning process of the shallow lake.

Conclusions

The results indicated the equilibrium partitioning model could be used to predict PAHs distribution in various phases of a shallow lake in the stagnation period, but re-suspension processes should be considered to modify the relationship between log K _ocs and log K _ows.

Recommendations and Perspectives

Concentration, particle size and composition of resuspended particles could affect the relationship between log K _ocs and log K _ows. Further work should be done under field conditions, especially where a steady thermodynamic equilibrium state could be assumed.

Purpose

The present paper concerns the distribution and mobility of heavy metals (Cu, Pb, Zn and Fe) in the soils of some abandoned mine sites in Italy and their transfer to wild flora.

Materials and methods

Soils and plants were sampled from mixed sulphide mine dumps in different parts of Italy, and the concentrations of heavy metals were determined.

Results and discussion

The phytoremediation ability of Salix species (Salix eleagnos, Salix purpurea and Salix caprea), Taraxacum officinale and P?lantago major for heavy metals and, in particular, zinc was estimated. The results showed that soils affected by mining activities presented total Zn, Cu, Pb and Fe concentrations above the internationally recommended permissible limits. A highly significant correlation occurred between metal concentrations in soils.

Conclusions

The obtained results confirmed the environmental effects of mine waste; exploring wild flora ability to absorb metals, besides metal exploitation, proved a useful tool for planning possible remediation projects.

Purpose

Rivers in low plains in the subtropical regions of China, where the population is dense and economies are active and well-developed, might be a large terrestrial carbon pool. This present study of the Sanyang wetlands in Wenzhou, southeastern China, aims to quantitatively estimate the volume of sediments in this region’s polluted river systems and their carbon storage.

Materials and methods

The bathymetry of river sections were surveyed using an echo sounder equipped with a differential GPS. An underwater digital elevation model (DEM) was then developed using the anisotropic ordinary Kriging method. Sediment samples were collected and analyzed for carbon content and sediment properties. Carbon storage in sediments was calculated using bathymetric and sediment analysis data.

Results and discussion

The studied rivers have been receiving organic pollutants from local residences and industries for decades. Results from a river network of 1.2 km² revealed a total carbon storage of 46.7 million kg in the sediments which had a volume of 1.4 million m³, with the upper 20 cm depth of sediments contributing about one third of this carbon storage.

Conclusions

The present work demonstrated that GIS technologies can be used to create digital river sediment surfaces and assess sediment amounts as well as determine the spatial distribution of sediments and their components. This could provide further insight into river restoration planning and other options from a carbon-balance perspective.

Purpose

Chromium, a potentially harmful element, occurs commonly within the urban sediment cascade as a result of abundant industrial and transport-related sources. The risks that Cr-bearing particles pose to ecosystems and humans depend on the solid-phase chemical speciation of Cr and its environmental mobility. In this study, we adopt an integrated geochemical approach to investigate and determine the long-term fate of Cr in the urban sediment cascade.

Materials and methods

We use bulk chemical digests, sequential chemical extraction analysis, electron microscopy, electron microprobe and microfocus XANES analysis to describe the solid-phase speciation, geochemical characteristics and potential long-term behaviour of Cr in urban particulate matter from both aquatic sediment and road dust sediment (RDS) in Manchester, UK.

Results and discussion

Cr-bearing grains within RDS and aquatic sediment are predominantly iron oxides and alumino-silicate glass grains. Electron microprobe analysis indicates Cr concentrations up to 3300 and 133,400 μg g^?1 in the RDS and aquatic grains, respectively. XANES analysis indicates that Cr(III) is the dominant oxidation state, with only trace amounts of Cr(VI). Importantly, Cr speciation does not appear to have changed between sedimentary environments and the dominance of Cr(III) suggests limited bioavailability or toxicity under predominant environmental (anoxic and neutral pH) conditions in the aquatic sediment sink. Furthermore, geochemical analyses suggest the environmental mobility of Cr in the aquatic sediment sink is low (compared to other toxic metals) due to its association mainly with alumino-silicate glass grains and its inclusion as an integral part of the glass structure.

Conclusions

Industrial glass grains are a major component of urban sediment worldwide. The speciation and geochemical investigations performed in this study suggest most Cr within the urban sediment cascade may be resistant to environmental processes that could mobilise other toxic metals.

Purpose

This study aimed at evaluating the acute effects of arsenic and zinc to the warmwater aquatic oligochaete Branchiura sowerbyi. Relative sensitivity with the coldwater species Tubifex tubifex was compared. Implications for the use of B. sowerbyi in the risk assessment of sediments in the tropics are discussed.

Materials and methods

Water-only (96 h) and sediment (14 days) toxicity tests were conducted with both species evaluating a concentration series of arsenic and zinc. The tests were conducted considering the environmental conditions in the natural habitat of T. tubifex (predominantly temperate) and B. sowerbyi (predominantly tropical). Both lethal and sublethal endpoints (autotomy of the posterior body parts, abnormal behavior and appearance) were determined in the tests. The lethal (LC₁₀ and LC₅₀) and effect (EC₁₀ and EC₅₀) concentrations were also determined to assess metal sensitivity for both species.

Results and discussion

Both test species were more sensitive to Zn than As in water-only tests, which is in agreement with previous studies evaluating the toxicity of these metals to aquatic oligochaetes. Sublethal effects were generally noted at concentrations lower than those leading to mortality. The warmwater oligochaete B. sowerbyi was more sensitive to both metals tested than the coldwater species T. tubifex.

Conclusions

Study findings support the need for using indigenous tropical species in risk assessments in the tropics. In addition, sublethal effect parameters should be included in toxicity testing with aquatic oligochaetes.

Purpose

The El Granero reservoir is the last reservoir of the Rio Conchos before it joins the Rio Grande at the Mexico–USA border. This reservoir, together with the San Marcos reservoir, is located in the arid region of Chihuahua, Mexico. High, naturally occurring radioactivity levels, as well as high arsenic (As) concentrations, have been found in both reservoirs. The main goal of this research was to establish the spatial and temporal distribution of trace and radioactive elements in surface sediments and cores collected from these reservoirs.

Materials and methods

Sediment cores were dated using ²¹⁰Pb and ¹³⁷Cs measurements and applying the constant rate of supply (CRS) model. Major, trace, and radioactive elements were determined in surface samples and three sediment cores. Radioactive elements were determined by both alpha and gamma spectrometry. Major and trace elements were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using the EPA 3051a method. Enrichment factors (EF), contamination factors (CF), and pollution load indexes (PLI) were calculated in order to identify the human impact in both reservoirs, whereas the chemical index weathering (CIW) was used to assess differences in the degree of weathering.

Results and discussion

High uranium (U) enrichment (EFs?=?24.9–54.7) was observed in core layers at the San Marcos reservoir, while in surface sediments, this enrichment was lower. The high variability of lead (Pb) and As in sediment cores from the Granero reservoir was attributed to human influence. Arsenic and Pb enrichment differences between entry and exit sediment cores were explained by the filtering capabilities of the elongated shape, the topography, and the presence of plants on the reservoir’s bed. The highest PLI was found at the entrance core of the Granero reservoir.

Conclusions

The natural element concentration levels of As, Pb, and U were established at the Granero reservoir. High EFs for As and Pb suggest an anthropogenic origin of these pollutants at specific time intervals. High U concentrations in the San Marcos area are explained as naturally occurring. The concentrations of As in most of the studied sediments could pose a risk to human health by As ingestion, since they are above the probable effect level (PEL).

Purpose

Rivers feeding into the Loskop Dam, South Africa, pass through coal mining and heavily industrialised areas. Previous studies investigating mass mortalities of crocodile and fish in the river system, revealed the presence of organic compounds, including polycyclic aromatic hydrocarbons (PAHs), in their tissues.

Materials and methods

Samples were collected from nine sites within the dam in winter and summer. Liquid-liquid and microwave-assisted extraction was used for preconcentrating PAHs from water and sediment samples, respectively. Extracts were analysed by gas chromatography-mass spectrometry in the selected ion monitoring mode to determine the presence and levels of the 16 United States Environmental Protection Agency (US EPA)-priority PAHs.

Results and discussion

Significant levels of PAHs were found in both water and sediment samples. Concentrations were higher in sediments than in water, as well as in samples collected in winter. Levels of PAHs in sediments were generally higher than those reported by many researchers for other water bodies in industrialised areas. Zebrafish embryos were used to assess potential risks associated with the water and sediment, and to determine the effects of PAHs on aquatic life. Embryos, exposed to intact water and sediment samples, as well as to diluted sediment extracts, were monitored for 120 h post fertilisation. Sediment proved more toxic to zebrafish embryos than water, causing delayed embryo development and malformations.

Conclusions

These findings are alarming as they indicate that this water system is under stress. These findings can be typical of any water system situated in a coal mining and industrial region.

Purpose

Investigations of geochemical characteristics of sediments of the Zrmanja River estuary were done in order to determine the natural and anthropogenic factors influencing sediment composition in this area. For that purpose, spatial and temporal distribution of major and trace elements in the sediments and surrounding soils was studied.

Materials and methods

Sediment and soil samples, including one marl sample, were collected at 28 locations. All samples were subjected to total digestion and subsequently analysed by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) for total concentration of 20 elements (Ag, Al, As, Be, Ca, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Rb, Sb, Sn, Sr, Ti and Y). Obtained concentrations and their normalized counterparts were used for assessment of factors influencing sedimentation in the study area.

Results and discussion

The results of the analysis showed that the composition of sediments of the Zrmanja River estuary is primarily determined by the composition of bedrock, existing hydrodynamic conditions and the relative isolation of the studied basin. Nevertheless, anthropogenic influences were observed as well. The composition of the Zrmanja River sediments reflects the impact of the ex-alumina factory “Jadral” and transfer by wind of the material from its immediate surroundings to the water system of the Zrmanja River. In addition, sedimentation in the Zrmanja River was found to be influenced by the construction of reservoirs and the HE “Velebit”, hydroelectric power plant located in the Zrmanja watershed.

Conclusions

The geochemical composition of recent sediments of the Zrmanja River estuary is controlled primarily by natural factors, although the influence of anthropogenic activities is also evident.

Purpose

The aim of this study was to evaluate (i) the ability of two Technosols, prepared with gossan or sulfide-rich wastes plus mixtures of organic/inorganic amendments, to improve the characteristics of the wastes by the analysis of the variation of elemental concentrations in their simulated leachates, and (ii) the potential environmental risk of these Technosols evaluated through the concentrations of the elements leached from the tailings containing the two wastes, considering their mass in the São Domingos mine.

Materials and methods

Composite samples of two São Domingos mining wastes (gossan wastes—GW; sulfide-rich wastes—SW) were collected. Amendment mixtures, containing different organic/inorganic wastes (from green agriculture, distillation of Ceratonia siliqua and Arbutus unedo fruits, and limestone quarry), were applied at 12, 30, and 60 g/kg. Two sets of microcosm assays were performed under controlled conditions in greenhouse and monitored during 7 and 13 months for GW and SW, respectively. Materials from each pot/treatment (<5 cm of depth) were collected after 1, 4, 7, and 13 months of incubation and used to obtain simulated leachates (DIN extraction). The analytical parameters evaluated in the leachates were pH, electrical conductivity, and element concentrations using flame atomic absorption spectrometry for cations and graphite furnace atomic absorption spectrometry, ionic chromatography, and UV-VIS for elements that normally occur as anions in aqueous solution.

Results and discussion

Simulated leachates from SW had lower pH and higher concentrations of potentially hazardous elements than leachates from GW. The concentrations of As in leachates from GW-Technosols were higher than those in leachates from GW-control but <0.6 mg/kg. In GW-Technosols leachates, the pH and the concentrations of some nutrients (e.g., Ca and phosphates) also increased when compared to the control. In the SW-Technosols, the pH of the leachates increased only in the first month as long as limestone was present. In these leachates, a general decrease of the concentrations of some elements was observed (e.g., As, sulfate, Fe, Pb), especially in the first month. A clear influence of the dose and type of amendments was not observed during the experimental time span for both wastes.

Conclusions

The concentrations of elements like Al, Ca, Fe, and Pb in the leachates are controlled by both the pH of the solutions and the concentrations of phosphates and sulfates. The extensive mass of the studied mine wastes contribute to the release to the neighboring environment of considerable amounts of potentially hazardous elements. The rehabilitation of the mine wastes by the conception of Technosols, especially with sulfide-rich wastes, can reduce significantly their environmental impact.

Purpose

In a 6-year study, we investigated the effectiveness of blind inlets as a conservation practice in reducing pesticide losses compared to tile risers from two closed farmed depressional areas (potholes) in the US Midwest under a 4-year cropping rotation.

Materials and methods

In two adjacent potholes within the same farm and having similar soils, a conventional tile riser and blind inlet were installed. Each draining practice could be operated independent of each other in order to drain and monitor each depression with either practice. Sampling events (runoff events) were collected from the potholes from 2008 to 2013 using autosamplers. The samples were analyzed for atrazine, metolachlor, 2,4-D, glyphosate, and deethylatrazine.

Results and discussion

The results of this study demonstrated that the blind inlet reduced analyzed pesticide losses; however, the level of reduction was compound dependent: atrazine (57 %), 2,4-D (58 %), metolachlor (53 %), and glyphosate (11 %).

Conclusions

Results from this study corroborate previous research findings that blind inlets are an effective conservation practice to reduce discharge and pollutants, including pesticides from farmed pothole surface runoff in the US Midwest.

Purpose

A series of empirical and mechanistic geochemical models were developed to describe the solid-solution partitioning of copper (Cu) in typical fresh spiked Chinese soils.

Materials and methods

The influence of soil properties on Cu partitioning was assessed in a wide range of soils using multiple regression analysis. Geochemical models (WHAM VI and Visual MINTEQ) and simulation analyses in combination with experimental data (i.e., the bulk of soil properties and Cu contents) were performed in order to provide additional insight into the mechanisms controlling the Cu partitioning. Calculation of soluble Cu contents based on the two models was then simplified and optimized by adjusting input variables, and the calibrated outputs were used to produce reasonable predictions of soluble metal concentrations.

Results and discussion

The results of the multiple regression analyses presented in this paper show strong correlations between soluble Cu concentrations and soil Cu concentrations and properties, with adjusted coefficients of determination (R_adj²) ranging between 0.84 and 0.91. Soil organic carbon (OC) content was an insignificant factor in most cases, but the active fraction of dissolved organic matter was important in improving model estimates. The best fit of root mean square error (RMSE) varied between 0.42 and 0.77 for the WHAM VI model and between 0.28 and 0.57 for the Visual MINTEQ model across all pH categories.

Conclusions

The models presented in this paper are suitable for investigating and simulating Cu solid-solution partitioning in a wide range of Chinese soils.

Purpose

The critical shear stress of cohesive and mixed cohesive/non-cohesive sediments is affected by multiple interacting physical, chemical and biological parameters. There are various mathematical approaches in the scientific literature for computing critical shear stress. However, processes that influence sediment stability are still not fully understood, and available formulas differ considerably. These discrepancies in the literature arise from random system behaviour (natural variability of the sediments), different definitions of the critical shear stress, different measurement techniques and different model frameworks (scope of the parameters, undisturbed versus artificial sediment samples). While analytical approaches fail to address the involved uncertainties, fuzzy logic-based models integrate uncertainty and imprecision.

Materials and methods

With this in mind, a data-driven neuro-fuzzy model (ANFIS) was used to determine the critical shear stress based on sediment characteristics such as wet bulk density and grain size distribution. In order to select model predictors systematically, an automated stepwise regression algorithm was applied. The database for this analysis consisted of 447 measurements of the critical shear stress originating from 64 undisturbed sediment samples.

Results and discussion

The study identified clay content as the primarily controlling variable for erosion resistance. Depending on the characteristics of the sampling location, the bulk density was also selected as a model predictor. In comparison to analytical models that are available in the scientific literature, the fuzzy model achieved higher correlation coefficients between measured and predicted data.

Conclusions

The neuro-fuzzy-model includes uncertainties of input variables and their interactions directly. Thus, it provides a reliable method for the prediction of erosion thresholds of cohesive/non-cohesive mixtures. It was also shown that this approach requires fewer measured variables as well as fewer assumptions than the models it was compared to.