Soil Extraction of Readily Soluble Heavy Metals and As with 1 M NH4NO3-Solution - Evaluation of DIN 19730 (6 pp)

Background, Aims and Scope   The German DIN 19730 (1997) describes a method for the extraction of readily available trace elements from soil by shaking the soil with 1 M NH4NO3-solution. Based on this method trigger and action values for the transfer of heavy metals and arsenic from soils to plants have been published in the German Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV 1999). The chemical mechanisms involved in this soil extraction procedure were evaluated in some detail to create requirements to improve environmental risk assessment for soil contaminations.Methods   The chemical mechanisms involved when soil is extracted with 1 M NH4NO3-solution were evaluated. This was followed by a laboratory experiment to quantify the formation of soluble metal ammine complexes during the extraction. Cd, Zn, Ni, Cu, Co and Hg were extracted from 16 soils by 1 M NH4NO3, 1 M KNO3 and water. pH was adjusted in 5 steps between 5.0 to 7.5. The potassium cation (K+) and the ammonium cation (NH4+) behave similarly when cations from soil surfaces are desorbed, because they have almost identical ion radii (e.g. 0.133 and 0.143 nm). K+ does not form ammine complexes with other ions, whereas, due to the increasing formation of NH3 from NH4 by dissociation with rising pH, metal ammine complex formation is an important process in soil extraction when using ammonium salt solutions. A difference in the extraction efficiency of 1 M NH4NO3- and 1 M KNO3-solution for a given soil can therefore be attributed to the formation of soluble metal ammine complexes. Conclusion   Our experiments resulted in considerably higher extraction rates of Cu, Cd and Hg by 1 M NH4NO3-solution as compared to 1 M KNO3-solution. This effect, caused by the formation of soluble metal ammine complexes, was only evident in soils with higher readily soluble heavy metal contents and a soil pH above 6 – 6.5 for Cu and 7 – 7.5 for Cd. Further chemical mechanisms involved when soils are extracted with 1 M NH4NO3 are a moderate decrease in pH and an increase in ionic strength. Most of the colloids and parts of soluble metal-organic complexes are precipitated due to the high ionic strength. High ionic strength also decreases the activity of metal-OH+ species and the electrostatic potential of the particle surfaces, which in turn, increases the desorption of heavy metal cations from negatively charged soil surfaces. In contrast, the adsorption of anions like arsenate is favoured by the decreasing electrostatic potential. The prediction of heavy metal uptake by plants from the results of the 1 M NH4NO3-solution extraction fits well for elements, which are mainly bound by low strength electrostatic forces to the soils. Such conditions are found in acidic soils for Cd and Tl, which have a low tendency for hydrolysis compared to other heavy metals. The correlation between 1 M NH4NO3 soil extraction and plant uptake is less significant for Ni and Zn. Only low positive correlation coefficients have been found for Pb, As, Hg and for the Cu-uptake by wheat. Imprecise prediction of plant uptake of heavy metals by the extraction with 1 M NH4NO3-solution is mainly caused by conditions leading to an overestimation of plant availability such as elements are strongly bound to soils, or low soluble trace element contents in soils. Neutral to alkaline soil pH can also lead to imprecise prediction due to increasing formation of soluble metal-organic (Cu, Pb, Hg) and metal ammine (Hg, Cu, Cd) complexes and less importantly due to the formation of colloids. Therefore, at low 1 M NH4NO3-extractable soil contents usually no high plant contents are to be expected. Recommendation and Outlook   Extraction of soil with 1 M NH4NO3-solution is a suitable method for the determination of readily soluble and plant available trace element contents. The chemical soil extraction process may cause misleading predictions of the transfer of trace elements to plants for some soil properties. This knowledge should be used to improve risk assessment of soil contaminations. It has to be considered, that the processes involved in plant uptake of trace elements are too complex to expect that just one soil extraction method can always guarantee a correct prognosis of toxicological significant element contents in plants. Soil analyses may be used for the preliminary examination of suspicious areas and the demarcation of contaminated areas. The results of soil analyses should be checked additionally by plant analyses especially under conditions with a high probability for misleading results by the 1 M NH4NO3-extraction. Alternatively, extraction with 1 M KNO3-solution can be performed to exclude the effect of metal ammine complex formation.     

Fate of N and C from labelled plant material: Recovery in perennial ryegrass–clover mixtures and in pore water of the sward

The belowground C and N dynamics leading to organic and inorganic N leaching from perennial ryegrass–clover mixtures are not well understood. Based on the hypothesis that four different plant materials would degrade differently, a 16 months field experiment was conducted to determine (i) the source strength of labelled plant residues in dissolved inorganic N (DIN) and dissolved organic N (DON) in pore water from the plough layer, and (ii) the plant uptake of organically bound N. Litterbags containing ¹⁴C- and ¹⁵N-labelled ryegrass or clover roots or leaves were inserted into the sward of a ryegrass–clover mixture in early spring. The fate of the released ¹⁴C and ¹⁵N was monitored in harvested biomass, roots, soil, and pore water percolating from the plough layer. No evidence of plant uptake of dual-labelled organic compounds from the dual-labelled residues could be observed. N in pore water from the plough layer during autumn and winter had a constant content of dissolved organic N (DON) and an increasing content of dissolved inorganic N (DIN). A positive correlation between aboveground clover biomass harvested in the growth season and total-N in pore water indicated that decaying roots from the living clover could be a major source of the 10 kg N ha⁻¹ being lost with pore water during autumn and winter. The presence of ¹⁵N in pore water shifted from the DON fraction in autumn to the DIN fraction in late winter, with strong indications that ¹⁵N originated from the living ryegrass. However, ¹⁵N in pore water originating from plant residues only constituted 1.5% of the total dissolved N from the plough layer.     

五垒岛湾海域无机氮、无机磷的时空分布和氮磷比值变化

根据2012-2014年5月、10月的调查数据,分析了五垒岛湾海水中无机氮、无机磷的时空分布特征和N/P比值的变化。结果表明,该海域水体中无机氮、无机磷平均含量分别为0.202mg/L和0.011mg/L,达国家二类水质标准,均表现出逐年增加的趋势;空间分布上表现出近岸水域含量大于远岸的变化趋势,原因可能是受陆源物质输入的影响所致;除少数站位外,该海域N/P比值接近16∶1,并表现出逐年增大的趋势,但春季可能受到赤潮的威胁。     

凡纳滨对虾精养池养殖水体的富营养状况时空差异

监测了凡纳滨对虾养殖全过程精养虾池养殖水体中溶解态无机氮(DIN)、溶解态活性磷酸盐(DIP)、水体的化学需氧量(COD)、pH、溶解氧(DO)、营养状态综合指数(E)等理化指标的变化,以及养殖后期水体中各理化因子的水平、垂直分布。结果表明:在凡纳滨对虾养殖过程中,DIN质量浓度为(0.093±0.076)～(1.736±1.134)mg·L–1,DIP质量浓度为(0.062±0.271)～(0.380±0.276)mg·L–1,COD质量浓度为(0.940±0.934)～(9.653±1.317)mg·L–1,E:(1.198±4.250)～(1267.537±68.534),富营养化程度随着养殖时间的增加逐渐增强,20d时各项指标均达到较大值,之后逐渐降低,到养殖后期又逐渐增强,营养状态综合指数(E)达到最大值;养殖后期,富营养化程度在水平方向随着靠近排污口的方向逐渐增强,营养状态综合指数(E):(343.230±1.659)～(2786.072±55.241),在垂直方向随着靠近池底的方向逐渐增强,营养状态综合指数(E):(2046.687±5.568)～(2789.524±7.166)。     

FieldStar精细农业系统DIN9684接口的试验研究

消化吸收发达国家先进技术是开展我国精细农业研究的当务之急。本文对引进的FieldStar精细农业系统DIN9684接口进行试验研究,实现FieldStar与PC机的通信,从DIN9684接口将在FieldStar系统的CAN总线上传输的数据通过CAN接口卡接入PC机,并对接收到的数据进行简单分析。本文最后总结了本研究的结果,并提出了进一步消化FieldStar系统核心技术的建议。     

长江口及邻近海域富营养化指标原因变量参照状态的确定

河口区参照状态的确定是营养盐基准制定的核心步骤.采用参照点或观测点指标频数分布曲线法,利用长江口及邻近海域1992-2010年的调查数据,针对长江口外海区及舟山海区富营养化指标的原因变量,即无机氮和活性磷酸盐,进行参照状态值的确定.经分析,长江口外海区无机氮各季节参照状态可确定如下:春季为0.317mg/L、夏季为0.273 mg/L、秋季为0.211mg/L,活性磷酸盐各季节参照状态:春季为0.014mg/L、夏季为0.009 mg/L、秋季为0.018 mg/L;舟山海区无机氮各季节参照状态确定如下:春季为0.372mg/L、夏季为0.273 mg/L、秋季为0.441 mg/L,活性磷酸盐各季节参照状态:春季为0.020mg/L、夏季为0.018 mg/L、秋季为0.029 mg/L.     

FieldStar精细农业系统DIN9684接口的试验研究

消化吸收发达国家先进技术是开展我国精细农业研究的当务之急。本文对引进的FieldStar精细农业系统DIN9684接口进行试验研究,实现FieldStar与PC机的通信,从DIN9684接口将在FieldStar系统的CAN总线上传输的数据通过CAN接口卡接入PC机,并对接收到的数据进行简单分析。总结了本研究的结果,并提出了进一步消化FieldStar系统核心技术的建议。     

In situ carbon and nitrogen dynamics in ryegrass-clover mixtures: Transfers, deposition and leaching

Carbon (C) and nitrogen (N) dynamics in a third production year ryegrass-clover mixture were investigated in the field. Cylinders (diameter 29.7 cm) were installed to depths of 20, 40 and 60 cm and equipped with suction cups to collect percolating pore water. Ryegrass and clover leaves were cross-labelled with ¹⁴C- and ¹⁵N-enriched urea and the fate of the two tracers was studied for 3 months during summer. Transfer of ¹⁴C occurred mainly from ryegrass to clover, whereas the largest transfer of ¹⁵N was in the opposite direction. The average transfer of N from clover was 40% (SE±3.1, n=9) of N in ryegrass, whereas the fraction of N in clover donated by ryegrass was 5% (±1.2, n=9). The amount of ¹⁴C transferred from ryegrass to clover was 1.7% (±0.1, n=9) of the ¹⁴C-activity in the total above-ground plant biomass found in the unlabelled clover and with a transfer from clover to ryegrass being 0.4% (±0.1, n=9). ¹⁵N-enriched compounds were not detected in percolating pore water, which may be caused by either dilution from irrigation or low availability of leachable N compounds. ¹⁴C was found solely as ¹⁴CO₂ in the pore water indicating that dissolved organic carbon (DOC) did not originate from fresh root deposits. Transfer of ¹⁴C between the two species in the mixed crop alongside with high transfer of ¹⁵N despite a large percolation of pore water indicates that part of the N transfer occurred in non-leachable N-forms. The amount of N transferred between the two species was found to depend on the ratio between dry matter accumulated in the donating and receiving species, the ¹⁴C-allocation within the receiving species and the root turnover rate in the soil.     

A three-dimensional numerical model for a mariculture nitrogen cycle: case study in Shizugawa Bay, Japan

A numerical model is developed for mariculture management, which consists of: (1) calculation of spatial distribution of PON (particulate organic nitrogen) using simulated current, (2) calculation of spatial distribution of DO (dissolved oxygen), (3) calculation of DON (dissolved organic nitrogen), (4) calculation of spatial distribution of DIN (dissolved inorganic nitrogen), and (5) calculation of the horizontal distribution of accumulated matter which is supplied by deposits from the mariculture of fish. This model is capable of calculating the detailed spatial distribution of PON, DON, DIN and DO by dividing the bay into many grid points. It also takes into consideration the effects of feed and fish in each raft, and the loading of DIN from rivers. The model is applied to Shizugawa Bay, in Miyagi Prefecture, Japan. The model elucidated the oxygen cycle among ecological compartments. The amount of dissolved oxygen supplied by photosynthesis is much greater than the consumption through respiration by fish and all other conditions for mariculture of fish are favourable in this bay.