The transport of Cu and Zn from agricultural soils to surface water in a small catchment

Long-term manure-borne copper and zinc inputs (18–324 mg Cu m⁻² yr⁻¹ and 100–800 mg Zn m⁻² yr⁻¹) to grassland soils resulted in their catchment in water concentrations that often exceeded the surface water quality criteria (2 μg Cu l⁻¹ and 5 μg Zn l⁻¹). This paper compares retention and release of Cu and Zn by two types of soil, a mineral soil (MS) and a dark colored soil rich in organic matter (OS). On the basis of dry soil mass, the OS has a higher retention/affinity for Cu and Zn than the MS, but much less Zn accumulated in the MS when compared on an areal basis. This is largely because of the much smaller bulk OS density and larger dissolved metal concentrations in the OS drainage than that for the MS. However, because of the greater water retention capacity of the OS, elevated metal concentrations in the soil solution do not necessarily cause greater loss to water. It is concluded that artificially drained OS can contribute significantly to the observed elevated Cu and Zn concentrations of the river, especially during relatively dry weather conditions when the contribution of water seeping from OS to the total river water discharge becomes increasingly important.     

Estimating net primary production and annual plant carbon inputs, and modelling future changes in soil carbon stocks in arable farmlands of northern Japan

Soil C sequestration in croplands is deemed to be one of the most promising greenhouse gas mitigation options for Japan's agriculture. In this context, changes in soil C stocks in northern Japan's arable farming area over the period of 1971-2010, specifically in the region's typical Andosol (volcanic ash-derived) and non-Andosol soils, were simulated using soil-type-specific versions of the Rothamsted carbon model (RothC). The models were then used to predict the effects, over the period of 2011-2050, of three potential management scenarios: (i) baseline: maintenance of present crop residue returns and green manure crops, as well as composted cattle manure C inputs (24-34 Mg ha⁻¹ yr⁻¹ applied on 3-55% of arable land according to crop), (ii) cattle manure: all arable fields receive 20 Mg ha⁻¹ yr⁻¹ of composted cattle manure, increased C inputs from crop residues and present C inputs from green manure are assumed, and (iii) minimum input: all above-ground crop residues removed, no green manure crop, no cattle manure applied. Above- and below-ground residue biomass C inputs contributed by 8 major crops, and oats employed as a green manure crop, were drawn from yield statistics recorded at the township level and crop-specific allometric relationships (e.g. ratio of above-ground residue biomass to harvested biomass on a dry weight basis). Estimated crop net primary production (NPP) ranged from 1.60 Mg C ha⁻¹ yr⁻¹ for adzuki bean to 8.75 Mg C ha⁻¹ yr⁻¹ for silage corn. For the whole region (143 × 10³ ha), overall NPP was estimated at 952 ± 60 Gg C yr⁻¹ (6.66 ± 0.42 Mg C ha⁻¹ yr⁻¹). Plant C inputs to the soil also varied widely amongst the crops, ranging from 0.50 Mg C ha⁻¹ yr⁻¹ for potato to 3.26 Mg C ha⁻¹ yr⁻¹ for winter wheat. Annual plant C inputs to the soil were estimated at 360 ± 45 Gg C yr⁻¹ (2.52 ± 0.32 Mg C ha⁻¹ yr⁻¹), representing 38% of the cropland NPP. The RothC simulations suggest that the region's soil C stock (0-30 cm horizon), across all soils, has decreased from 13.96 Tg C (107.5 Mg C ha⁻¹ yr⁻¹) in 1970 to 12.46 Tg C (96.0 Mg C ha⁻¹ yr⁻¹) in 2010. For the baseline, cattle manure and minimum input scenarios, soil C stocks of 12.13, 13.27 and 9.82 Tg C, respectively, were projected for 2050. Over the period of 2011-2050, compared to the baseline scenario, soil C was sequestered (+0.219 Mg C ha⁻¹ yr⁻¹) by enhanced cattle manure application, but was lost (−0.445 Mg C ha⁻¹ yr⁻¹) under the minimum input scenario. The effect of variations of input data (monthly mean temperature, monthly precipitation, plant C inputs and cattle manure C inputs) on the uncertainty of model outputs for each scenario was assessed using a Monte Carlo approach. Taking into account the uncertainty (standard deviation as % of the mean) for the model's outputs for 2050 (5.1-6.1%), it is clear that the minimum input scenario would lead to a rapid decrease in soil C stocks for arable farmlands in northern Japan.     

Rates of accumulation of cadmium and uranium in a New Zealand hill farm soil as a result of long-term use of phosphate fertilizer

In New Zealand, phosphate (P) fertilisers used in agriculture are the main sources of the potentially toxic elements cadmium (Cd) and uranium (U), which occur as unwanted contaminants. New Zealand is developing draft soil guideline values (SGV) for maximum concentrations of Cd. To assess when soils under pasture for sheep production might reach a particular SGV, we analysed archived soil samples from a 23 yr P fertiliser trial. The pasture sites were at Whatawhata, North Island, New Zealand, and had received P fertiliser at the rates of 0, 30, 50 and 100 kg P ha⁻¹ yr⁻¹. From 1983 to 1989, P was applied as single superphosphate, from 1989 to 2006, P was applied as triple superphosphate. Soils from replicate paddocks were sampled annually to a depth of 75 mm on easy (10-20°) and steep (30-40°) slope classes. Total P, Cd and U were analysed by ICP-MS after acid digestion. Data were analysed by fitting trend lines using linear mixed models for two slope classes and for two sampling periods 1983-1989 and 1989-2006 when the soil sampling method and fertiliser type had been changed.The changes in total P, Cd and U were directly related to the type and amount of P fertiliser applied, the control treatment showed no significant change in P, Cd or U. At 50 and 100 kg P ha⁻¹ yr⁻¹ there were generally linear increases in total P and total U, and the same trend line applied to both time periods, but the rate of increase in P was greater on the easy slope class. For Cd, a “broken stick” model was needed to explain the data. Pre-1989, Cd increased in the 50 and 100 kg P ha⁻¹ yr⁻¹ treatment (0.036-0.045 mg kg⁻¹ yr⁻¹, respectively): post 1988 the rate of increase declined markedly on those two treatments (0.005-0.015 mg kg⁻¹ yr⁻¹, respectively), and declined absolutely in the 30 kg P ha⁻¹ yr⁻¹ treatments. The maximum content of Cd was in the 100 kg P ha⁻¹ yr⁻¹ treatment which reached 0.931 mg Cd kg⁻¹ on the easy slope. For U there were steady linear increases for the 30, 50 and 100 kg P ha⁻¹ treatments, and no significant difference between the steep and easy slopes, nor the two sampling periods, the maximum concentration obtained was 2.80 mg U kg⁻¹ on the 100 kg P ha⁻¹ treatment. The results suggest that at rates of P fertiliser likely to be applied to hill farms (<50 kg P ha⁻¹ yr⁻¹), and using P fertiliser with low Cd content, then the Cd concentration in this soil will never reach a SGV of 1 mg kg⁻¹.     

Nitrogen leaching under corn cultivation stabilized after four years application of pig manure to red soil in subtropical China

The impact of long-term pig manure application to a red soil in subtropical China on nitrate leaching was investigated in a field lysimeter experiment from 2002 to 2009. Simultaneously, nitrate leaching was simulated by water and nitrogen management model (WNMM) basing on these observed data to determine the environmental threshold of manure application. Nitrate concentrations in the drainage and nitrate leaching under low manure application (150 kg N ha⁻¹ y⁻¹) did not increase during the study period. Interestingly, the nitrate concentrations in drainage water following high manure application (600 kg N ha⁻¹ y⁻¹) increased exponentially in the first four years and then remained at 13 mg l⁻¹ for the next four years. Addition of lime based on high manure application had no significant effect on nitrate concentrations or total nitrate leaching. WNMM simulated the variation in corn yields and nitrate leaching well. The environmentally safe threshold for long-term application of pig manure was 360 kg N ha⁻¹.     

Assessing the potential for greenhouse gas mitigation in intensively managed annual cropping systems at the regional scale

We predicted changes in yields and direct net soil greenhouse gas (GHG) fluxes from converting conventional to alternative management practices across one of the world's most productive agricultural regions, the Central Valley of California, using the DAYCENT model. Alternative practices included conservation tillage, winter cover cropping, manure application, a 25% reduction in N fertilizer input and combinations of these. Alternative practices were evaluated for all unique combinations of crop rotation, climate, and soil types for the period 1997-2006. The crops included were alfalfa, corn, cotton, melon, safflower, sunflower, tomato, and wheat. Our predictions indicate that, adopting alternative management practices would decrease yields up to 5%. Changes in modeled SOC and net soil GHG fluxes corresponded to values reported in the literature. Average potential reductions of net soil GHG fluxes with alternative practices ranged from −0.7 to −3.3 Mg CO₂-eq ha⁻¹ yr⁻¹ in the Sacramento Valley and −0.5 to −2.5 Mg CO₂-eq ha⁻¹ yr⁻¹ for the San Joaquin Valley. While adopting a single alternative practice led to modest net soil GHG flux reductions (on average −1 Mg CO₂-eq ha⁻¹ yr⁻¹), combining two or more of these practices led to greater decreases in net soil GHG fluxes of up to −3 Mg CO₂-eq ha⁻¹ yr⁻¹. At the regional scale, the combination of winter cover cropping with manure application was particularly efficient in reducing GHG emissions. However, GHG mitigation potentials were mostly non-permanent because 60-80% of the decreases in net soil GHG fluxes were attributed to increases in SOC, except for the reduced fertilizer input practice, where reductions were mainly attributed to decreased N₂O emissions. In conclusion, there are long-term GHG mitigation potentials within agriculture, but spatial and temporal aggregation will be necessary to reduce uncertainties around GHG emission reductions and the delivery risk of the associated C credits.     

An experimental and thermodynamic equilibrium investigation of the Pb, Zn, Cr, Cu, Mn and Ni partitioning during sewage sludge incineration

The effects of different chlorides and operational conditions on the distribution and speciation of six heavy metals (Pb, Zn, Cr, Cu, Mn and Ni) during sludge incineration were investigated using a simulated laboratory tubular-furnace reactor. A thermodynamic equilibrium investigation using the FactSage software was performed to compare the experimental results. The results indicate that the volatility of the target metals was enhanced as the chlorine concentration increased. Inorganic-Cl influenced the volatilization of heavy metals in the order of Pb > Zn > Cr > Cu > Mn > Ni. However, the effects of organic-Cl on the volatility of Mn, Pb and Cu were greater than the effects on Zn, Cr and Ni. With increasing combustion temperature, the presence of organic-Cl (PVC) and inorganic-Cl (NaCl) improved the transfer of Pb and Zn from bottom ash to fly ash or fuse gas. However, the presence of chloride had no obvious influence on Mn, Cu and Ni. Increased retention time could increase the volatilization rate of heavy metals; however, this effect was insignificant. During the incineration process, Pb readily formed PbSiO₄ and remained in the bottom ash. Different Pb compounds, primarily the volatile PbCl₂, were found in the gas phase after the addition of NaCl; the dominant Pb compounds in the gas phase after the addition of PVC were PbCl₂, Pb(ClO₄)₂ and PbCl₂O₄.     

The potential to increase soil carbon stocks through reduced tillage or organic material additions in England and Wales: A case study

Results from the UK were reviewed to quantify the impact on climate change mitigation of soil organic carbon (SOC) stocks as a result of (1) a change from conventional to less intensive tillage and (2) addition of organic materials including farm manures, digested biosolids, cereal straw, green manure and paper crumble. The average annual increase in SOC deriving from reduced tillage was 310 kg C ± 180 kg C ha⁻¹ yr⁻¹. Even this accumulation of C is unlikely to be achieved in the UK and northwest Europe because farmers practice rotational tillage. N₂O emissions may increase under reduced tillage, counteracting increases in SOC. Addition of biosolids increased SOC (in kg C ha⁻¹ yr⁻¹ t⁻¹ dry solids added) by on average 60 ± 20 (farm manures), 180 ± 24 (digested biosolids), 50 ± 15 (cereal straw), 60 ± 10 (green compost) and an estimated 60 (paper crumble). SOC accumulation declines in long-term experiments (>50 yr) with farm manure applications as a new equilibrium is approached. Biosolids are typically already applied to soil, so increases in SOC cannot be regarded as mitigation. Large increases in SOC were deduced for paper crumble (>6 t C ha⁻¹ yr⁻¹) but outweighed by N₂O emissions deriving from additional fertiliser. Compost offers genuine potential for mitigation because application replaces disposal to landfill; it also decreases N₂O emission.     

Soil fertility dynamics in runoff-capture agriculture, Canary Islands, Spain

In the extremely arid (∼150 mm yr⁻¹) eastern Canary Islands of Lanzarote, Fuerteventura and La Graciosa, agriculture has been sustained for decades by a traditional runoff-capture (RC) farming system known as “gavias”. Although the main goal of these systems is to increase water supply for crops, making unnecessary conventional irrigation, a secondary and equally important factor is that this system allows for sustainable agricultural production without addition of chemical or organic fertilizers. A field study was conducted to assess the impact of long-term agriculture (>50 yr) on soil fertility and to evaluate key factors affecting the nutrient sustainability of RC agricultural production. Soil fertility and nutrient dynamics were studied through chemical characterization of the arable layer (0-25 cm) of RC agricultural plots, adjacent natural soils (control) not affected by runoff and cultivation, and sediments contributed by a series of RC events. Results showed that RC soils have enhanced fertility status, particularly because they are less affected by salinity and sodicity (mean electrical conductivity = 1.8 dS m⁻¹ vs. 51.0 dS m⁻¹ in control soils; mean exchangeable sodium percentage = 11.1% vs. 30.6% in control soils), and have higher water and nutrient holding capacities (mean clay plus silt contents ≈87% vs. 69% in control soils). In general, sediments transported with the runoff and deposited in RC plots (average sediment yield ≈ 46 ton ha⁻¹ yr⁻¹), contain sufficient nutrients to prevent a progressive reduction of essential plant nutrients below natural levels in spite of nutrient uptake and removal by the harvested crop. Average additions of nitrogen, phosphorus and potassium with the runoff sediments were 33.6, 35.3 and 48.8 kg ha⁻¹ yr⁻¹, respectively. Results of this study show how a crop production system can be sustained in the long term by natural hydrological and biogeochemical catchment processes. This system maintains a nutrient balance that is not based on energy-intensive inputs of fertilizers, but is integrated in natural nutrient cycling processes, unlike other tropical farming agroecosystems.     

Entry and toxicity of organic pesticides and copper in vineyard streams: Erosion rills jeopardise the efficiency of riparian buffer strips

The present study was performed to characterise in-stream pesticide exposure within the Palatinate vineyard region in south-west Germany, evaluate the influence of buffer strip widths and identify mitigation measures for the relevant entry pathways. In-stream water and sediment samples that were taken at nine sampling sites of different buffer widths following intense rainfall, and edge-of-field runoff that were sampled in erosion rills were analysed regarding 28 active ingredients of pesticides including copper. In-stream samples contained a mix of 8 ± 4 pesticide compounds, resulting in total pesticide concentrations of 1.4-8.9 μg l⁻¹ for water and 16-670 μg kg⁻¹ dw for sediment. Following an exceptional rainfall event with a previous 34-day drought period, pesticide concentrations reached 7.0-83.4 μg l⁻¹. Fungicides were the most important pesticides found and were significantly correlated with the pesticide application frequency and rate. The calculated toxicity values per sample (TU_max) indicated that both organic pesticides and copper concentrations likely cause ecotoxicological effects in the field. The buffer strip width was of little importance for pesticide in-stream concentrations because pesticide entry occurred mainly via the field path network and erosion rills. Pesticide in-stream concentrations were significantly and positively correlated with the concentrations detected in erosion rills (R² = 0.56). As possible risk mitigation measures, we suggest the implementation of grassed field paths and vegetated ditches or wetlands.     

Metal release/accumulation during the decomposition of Potamogeton crispus in a shallow macrophytic lake

Changes in metal concentrations in the litter of Potamogeton crispus were monitored during a consecutive 40-day in situ decomposition experiment using the litterbag method.The accumulation index was calculated and used to indicate the changes in the metals in litter.The results showed that the concentrations of Al,Cd,Cr,Fe,Mn,and Pb in litter increased significantly during the decomposition,while Cu and Zn concentrations decreased dramatically.Significant positive correlations were found between the concentrations of Al,Cr,Fe,and Mn and between Cu and Zn.Moreover,Cu and Zn both negatively correlated with Al and Fe.The remaining dry mass was negatively correlated with Al and Fe concentrations but positively correlated with Cu and Zn concentrations.Generally the accumulation index values of metals other than Al were less than one,indicating that the litter of P.crispus acted as a source of metals to the surrounding water body.Al was the only metal that showed continuous net accumulation in litter.The net accumulation of Fe and Mn in litter during the last 10 days of the experiment may indicate the precipitation of Feand Mn-oxides.It was estimated that 160 g/m~2(dry weight)P.crispus was decomposed in40 days.This was equivalent to releasing the following amounts of metals:0.01 mg Cd,0.03 mg Cr,0.71 mg Cu,0.55 mg Mn,0.02 mg Pb and 13.8 mg Zn into surrounding water,and accumulating 149 mg Al and 11 mg Fe,in a 1 m~2 area.     

Denitrification on Andosols in an intensive dairy farming region of central Japan

Evaluation of denitrification capacities is necessary to develop a sustainable manure management system in order to reduce NO₃⁻ leaching and N₂O emissions from agricultural soils. Denitrification rates were measured using the acetylene inhibition technique on intact soil cores from eight Andosols under three different cropping systems in an intensive livestock catchment of central Japan. The N application rates ranged from 200 to 800 kg N ha⁻¹ yr⁻¹. The denitrification rates were highly variable across fields, and were influenced significantly by land uses and manure forms. Compared with upland fields, paddy rice fields had a greater denitrification rate up to 1380 and 85 mg N m⁻² day⁻¹ in the top 30-cm soil layer during flooding and non-flooding periods, respectively. In upland fields, the maximum value for the top 30-cm soils was 44 mg N m⁻² day⁻¹ and most of the rates were less than 10 mg N m⁻² day⁻¹. The greater denitrification rates were often associated with slurry application rather than composted dry manure. Overall, denitrification from Andosols in this study displayed a lower capacity than that of non-Andosols.     

Particle size distribution and characteristics of heavy metals in road-deposited sediments from Beijing Olympic Park

Due to rapid urbanization and industrialization, heavy metals in road-deposited sediments (RDSs) of parks are emitted into the terrestrial, atmospheric, and water environment, and have a severe impact on residents' and tourists' health. To identify the distribution and characteristic of heavy metals in RDS and to assess the road environmental quality in Chinese parks, samples were collected from Beijing Olympic Park in the present study. The results indicated that particles with small grain size (< 150 μm) were the dominant fraction. The length of dry period was one of the main factors affecting the particle size distribution, as indicated by the variation of size fraction with the increase of dry days. The amount of heavy metal (i.e., Cu, Zn, Pb and Cd) content was the largest in particles with small size (< 150 μm) among all samples. Specifically, the percentage of Cu, Zn, Pb and Cd in these particles was 74.7%, 55.5%, 56.6% and 71.3%, respectively. Heavy metals adsorbed in sediments may mainly be contributed by road traffic emissions. The contamination levels of Pb and Cd were higher than Cu and Zn on the basis of the mean heavy metal contents. Specifically, the geoaccumulation index (I_geo) decreased in the order: Cd > Pb > Cu > Zn. This study analyzed the mobility of heavy metals in sediments using partial sequential extraction with the Tessier procedure. The results revealed that the apparent mobility and potential metal bioavailability of heavy metals in the sediments, based on the exchangeable and carbonate fractions, decreased in the order: Cd > Zn ≈ Pb > Cu.     

Metals and metalloid bioconcentrations in the tissues of Typha latifolia grown in the four interconnected ponds of a domestic landfill site

The uptake of metals in roots and their transfer to rhizomes and above-ground plant parts (stems, leaves) of cattails (Typha latifolia L.) were studied in leachates from a domestic landfill site (Etueffont, France) and treated in a natural lagooning system. Plant parts and corresponding water and sediment samples were taken at the inflow and outflow points of the four ponds at the beginning and at the end of the growing season. Concentrations of As, Cd, Cr, Cu, Fe, Mn, Ni and Zn in the different compartments were estimated and their removal efficiency assessed, reaching more than 90% for Fe, Mn and Ni in spring and fall as well in the water compartment. The above- and below-ground cattail biomass varied from 0.21 to 0.85, and 0.34 to 1.24 kg dry weight/m², respectively, the highest values being recorded in the fourth pond in spring 2011. The root system was the first site of accumulation before the rhizome, stem and leaves. The highest metal concentration was observed in roots from cattails growing at the inflow of the system''s first pond. The trend in the average trace element concentrations in the cattail plant organs can generally be expressed as: Fe > Mn > As > Zn > Cr > Cu > Ni > Cd for both spring and fall. While T. latifolia removes trace elements efficiently from landfill leachates, attention should also be paid to the negative effects of these elements on plant growth.     

Deficit irrigation: An option to mitigate arsenic load of rice grain in West Bengal, India

Farmers in arsenic (As) contaminated areas of West Bengal, India grow rice during dry months (January to April) and use underground water for irrigation with As concentration above WHO defined critical (0.01 mg l⁻¹) limit. In each season they add 50-150 mg As per m² soil area. Thus growing rice under deficit irrigation in these areas will reduce As load in soil-root-shoot-leaf-grain continuum of rice ecosystem. Suitable deficit irrigation system has to be screened so that As load will decrease with insignificant reduction in grain yield. With this objective, rice grown under four irrigation regimes (i) continuous ponding (CP), (ii) intermittent ponding (IP), (iii) saturation (SAT) and (iv) aerobic (AER) was tested to assess the arsenic load in soil and various parts of rice on 45 and 80 days after transplanting (DAT). Conditions described in treatments ii, iii and iv were imposed during 15-45 DAT. Highest value (18.18 and 18.74 mg kg⁻¹) of soil arsenic was attained under CP followed by IP, SAT and AER. Root arsenic content under AER at 45 and 80 DAT was at the lowest level (6.14 and 20.54 mg kg⁻¹) and this was 31 and 7.0% lower as compared to CP. As content in leaf and grain attained the lowest values under IP. Grain yield insignificantly differed under IP (4.33 Mg ha⁻¹) over CP (4.69 Mg ha⁻¹). Compared to soil As, As added through irrigation showed stronger relationship with As status of various plant parts. Imposition of IP only during vegetative stage was found to be optimum in terms of reduction of As content in straw and grain respectively by 23 and 33% over farmers irrigation practice with insignificant decrease in grain yield.     

Comparison between background concentrations of arsenic in urban and non-urban areas of Florida

Arsenic contamination is of great environmental concern due to its toxic effects as a carcinogen. Knowledge of arsenic background concentrations is important for land application of wastes and for making remediation decisions. The soil clean-up target level for arsenic in Florida (0.8 and 3.7 mg kg⁻¹ for residential and commercial areas, respectively) lies within the range of both background and analytical quantification limits. The objective of this study was to compare arsenic distribution in urban and non-urban areas of Florida. Approximately 440 urban and 448 non-urban Florida soil samples were compared. For urban areas, soil samples were collected from three land-use classes (residential, commercial and public land) in two cities, Gainesville and Miami. For the non-urban areas, samples were collected from relatively undisturbed non-inhabited areas. Arsenic concentrations varied greatly in Gainesville, ranging from 0.21 to approximately 660 mg kg⁻¹ with a geometric mean (GM) of 0.40 mg kg⁻¹, which were lower than Miami samples (ranging from 0.32 to 112 mg kg⁻¹; GM=2.81 mg kg⁻¹). Arsenic background concentrations in urban soils were significantly greater and showed greater variation than those from relatively undisturbed non-urban soils (GM=0.27 mg kg⁻¹) in general.     

Distribution and assessment of heavy metals in the surface sediment of Yellow River, China

Large amounts of heavy metals discharged by industrial cities that are located along the middle reach of Yellow River, China have detrimental impacts on both the ecological environment and human health. In this study, fourteen surface sediment samples were taken in the middle reach of the Yellow River. Contents of Zn, Pb, Ni, Cu, Cr, Cd, As were measured, and the pollution status was assessed using three widely used pollution assessment methods, including the single factor index method, Nemerow pollution index method and potential ecological risk index. The concentrations of the studied heavy metals followed the order: Zn > Cr > Cu > Ni > Pb > As > Cd. Nearly 50% of sites had Cu and Cr accumulation. The concentration of Cu at the Yiluo River exceeded the secondary standard value of the Environmental quality standard for soils. Comparison of heavy metal concentrations between this study and other selected rivers indicated that Cu and Cr may be the major pollutants in our case. The single factor index indicated that many samples were at high levels of pollution for Cu and Cd; the Nemerow pollution index indicated that the Yihe River, Luohe River, Yiluo River and Huayuankou were polluted. According to the results of potential ecological risk assessment, Cd in the tributaries of Luo River, Yihe River, and Yiluo River showed high risk toward the ecosystem and human health, Cd in Huanyuankou and Cu in Yiluo River showed a middle level of risk and other samples were at a low level of risk.     

Decontamination of anaerobically digested slurry in a paddy field ecosystem in Jiaxing region of China

Anaerobic digestion has become increasing popular for managing biowastes in rural China as it has the advantage of generating biogas, a renewable energy. A new challenge, however, is minimizing the environmental pollution resulting from the anaerobically digested slurry (ADS). The aim of this study was to assess the feasibility of using a paddy field to remediate ADS while simultaneously cultivating rice. A field experiment was trialed using six treatments based on varying nitrogen loadings over the period of a rice-growing season. These treatments were adjusted to the content of the N within the ADS and had loadings of 270, 405, 540 and 1080 kg N ha⁻¹. These treatments were compared to a negative control (no fertilizer) and a positive control (chemical fertilizer) that consisted of urea applied at 270 kg N ha⁻¹. The effects of these N sources and slurry remediation were monitored using standard methods to measure water quality, soil properties and changes in rice production. Rice grain yields were generally higher for all ADS treatments than for the urea N treatment. Standing water quality in the field could reach national discharge standards for all treatments within 7-8 days after each ADS irrigation. Groundwater quality and heavy metal concentrations in both soil and the rice grain were not affected by the ADS treatments. We suggest that the quantities of ADS irrigated in 867-1734 m³ ha⁻¹ was not only safe for food quality (rice grain) and the receiving environment (water and soil), but also beneficial to soil fertility and rice grain yield.     

Photodegradation of methylmercury in Jialing River of Chongqing,China

Photodegradation (PD) of methylmercury (MMHg) is a key process of mercury (Hg) cycling in water systems, maintaining MMHg at a low level in water systems. However, we possess little knowledge of this important process in the Jialing River of Chongqing, China. In situ incubation experiments were thus performed to measure temporal patterns and influencing factors of MMHg PD in this river. The results showed that MMHg underwent a net demethylation process under solar radiation in the water column, which predominantly occurred in surface waters. For surface water, the highest PD rate constants were observed in spring (12 × 10^− 3 ± 1.5 × 10^− 3 m²/E), followed by summer (9.0 × 10^− 3 ± 1.2 × 10^− 3 m²/E), autumn (1.4 × 10^− 3 ± 0.12 × 10^− 3 m²/E), and winter (0.78 × 10^− 3 ± 0.11 × 10^− 3 m²/E). UV-A radiation (320–400 nm), UV-B radiation (280–320 nm), and photosynthetically active radiation (PAR, 400–700 nm) accounted for 43%–64%, 14%–31%, and 16%–45% of MMHg PD, respectively. PD rate constants varied substantially with the treatments that filtered the river water and amended it with chemicals (i.e., Cl⁻, NO₃⁻, dissolved organic matter (DOM), Fe(III)), which reveals that suspended particulate matter and water components are important factors in affecting the PD process. For the entire water column, the PD rate constant determined for each wavelength range decreased rapidly with water depth. UV-A, UV-B, and PAR contributed 27%–46%, 6.2%–12%, and 42%–65% to the PD process, respectively. PD flux was estimated to be 4.7 μg/(m²·year) in the study site. Our results are very important to understand the cycling characteristics of MMHg in the Jialing River of Chongqing, China.     

Composition and source apportionment of dust fall around a natural lake

The aim of this study was to determine the source apportionment of dust fall around Lake Chini, Malaysia. Samples were collected monthly between December 2012 and March2013 at seven sampling stations located around Lake Chini. The samples were filtered to separate the dissolved and undissolved solids. The ionic compositions(NO-3, SO2-4, Cl-and NH+4) were determined using ion chromatography(IC) while major elements(K, Na, Ca and Mg) and trace metals(Zn, Fe, Al, Ni, Mn, Cr, Pb and Cd) were determined using inductively coupled plasma mass spectrometry(ICP-MS). The results showed that the average concentration of total solids around Lake Chini was 93.49 ± 16.16 mg/(m2·day). SO2-4, Na and Zn dominated the dissolved portion of the dust fall. The enrichment factors(EF) revealed that the source of the trace metals and major elements in the rain water was anthropogenic, except for Fe. Hierarchical agglomerative cluster analysis(HACA) classified the seven monitoring stations and 16 variables into five groups and three groups respectively. A coupled receptor model, principal component analysis multiple linear regression(PCA-MLR), revealed that the sources of dust fall in Lake Chini were dominated by agricultural and biomass burning(42%),followed by the earth's crust(28%), sea spray(16%) and a mixture of soil dust and vehicle emissions(14%).     

Effect of liming on sulfate transformation and sulfur gas emissions in degraded vegetable soil treated by reductive soil disinfestation

Reductive soil disinfestation (RSD), namely amending organic materials and mulching or flooding to create strong reductive status, has been widely applied to improve degraded soils. However, there is little information available about sulfate (SO₄^2 −) transformation and sulfur (S) gas emissions during RSD treatment to degraded vegetable soils, in which S is generally accumulated. To investigate the effects of liming on SO₄^2 − transformation and S gas emissions, two SO₄^2 −-accumulated vegetable soils (denoted as S1 and S2) were treated by RSD, and RSD plus lime, denoted as RSD₀ and RSD₁, respectively. The results showed that RSD₀ treatment reduced soil SO₄^2 − by 51% and 61% in S1 and S2, respectively. The disappeared SO₄^2 − was mainly transformed into the undissolved form. During RSD treatment, hydrogen sulfide (H₂S), carbonyl sulfide (COS), and dimethyl sulfide (DMS) were detected, but the total S gas emission accounted for < 0.006% of total S in both soils. Compared to RSD₀, lime addition stimulated the conversion of SO₄^2 − into undissolved form, reduced soil SO₄^2 − by 81% in S1 and 84% in S2 and reduced total S gas emissions by 32% in S1 and 57% in S2, respectively. In addition to H₂S, COS and DMS, the emissions of carbon disulfide, methyl mercaptan, and dimethyl disulfide were also detected in RSD₁ treatment. The results indicated that RSD was an effective method to remove SO₄^2 −, liming stimulates the conversion of dissolved SO₄^2 − into undissolved form, probably due to the precipitation with calcium.