Assessing Se cycling and toxicity in aquatic ecosystems

Toxic substances exert impacts on ecosystems at several levels: biogeochemical, toxicological, and populations/communities. Integrating exposure (biogeochemistry) and effects (toxicology) into an ecological context requires models as a necessary step to prediction and assessment of effects on populations and their interactions. To this end, research is being conducted to develop techniques for predicting the effects of Se on aquatic ecosystems. The objective is to develop mechanistic models to predict biogeochemical cycling, toxicological processes, and toxic effects on population and community dynamics. Earlier research demonstrated that different chemical forms of Se have different toxicological properties. Biogeochemical research culminated with a dynamic model of the Se cycle. In ongoing research, experiments are being conducted on microorganisms, phytoplankton, microzooplankton, zooplankton, benthic invertebrates, and fish to measure uptake, biotransformation, and depuration kinetics of different chemical forms of Se, transfer through the food web, and effects on growth, reproduction, community interactions, and survival. This information will provide the basis for the ecosystem effects model.     

Nitrogen accumulation, cycling and the restoration of ecosystems on derelict land

Abstract. Nitrogen deficiency is the major problem in the creation of new ecosystems on most derelict land. Initially there is insufficient nitrogen in the wastes to drive the new systems, and nitrogen accumulation is, therefore, required. The most cost-effective way of providing this nitrogen is to use leguminous species which fix nitrogen from the atmosphere. Once nitrogen starts to accumulate in the soil management should aim to promote efficient cycling. Maintaining a near-neutral soil pH and a sward with a small C:N ratio helps to increase the mineralization of nitrogen in dead plant residues, and grazing animals also reduce nitrogen accumulation in dead vegetation.     

A model framework for assessing the effects of selenium on aquatic ecosystems

Water, Air, & Soil Pollution - A model framework is being developedto assess the effects of Se toxicity on aquatic ecosystems. The framework integrates several types of model components...     

Sulfur cycling in five forest ecosystems

The cycling and retention of sulfur were studied in five forest ecosystems: a chestnut oak and yellow poplar stand on Walker Branch Watershed, Tennessee; a mixed oak stand on Camp Branch Watershed, Tennessee; and a red alder and Douglas-fir stand at the Thompson site, Washington. Calculations from foliage sulfur turnover indicate that about one-half of total sulfur input was dry in the Tennessee sites, whereas only one-tenth was dry in the Washington sites. Atmospheric sulfur inputs exceeded forest sulfur requirements in all cases, but three sites (chestnut oak, mixed oak, and red alder) showed a net ecosystem retention of atmospherically deposited sulfur. Net ecosystem sulfur retention was consistent with laboratory-determined sulfate adsorption isotherms within a given location (Walker Branch, Thompson site) but not between locations because of differing deposition histories and consequent differing degrees of soil sulfate saturation. No consistent relationships between soil sulfate adsorption capacity and other soil properties (pH, base saturation, iron, and aluminum oxides) were found.     

Bioaccumulation of selenium by floating aquatic plants

The degree to which floating aquatic plants concentrate Se in tissues was determined for four species grown in solutions containing various levels of Se. Results of this greenhouse study showed that all four plant species, Azolla caroliniana, Eichhornia crassipes, Salvinia rotundi folia, and Lemna minor absorbed Se quickly upon exposure to Se in water as concentrated as 2.5 g Se mL^–1, and attained maximum tissue concentrations within 1 to 2 weeks. Azolla absorbed Se to the highest tissue concentration (about 1000 g Se g^–1 dry matter) from the 2.5 g Se mL^–1 solution, followed by Salvinia (700 g Se g^–1), Lemna (500 g Se g^–1),and Eichhornia (300 g Se g^–1). Plant growth appeared unaffected by solution Se concentrations lower than about 1.25 g mL^–1. These results indicate potential for rapid Se movement from water into aquatic food chains, and for use of aquatic plants for Se removal in wastewater treatment systems.     

Effects of acid mine wastes on aquatic ecosystems

The Cedar Creek Basin (39th N parallel 92nd W meridian) was studied for the period June 1952 through August 1954 to observe the effects of both continuous and periodic acid effluent flows on aquatic communities. The acid strip-mine effluent contained ferric and ferrous Fe, Cu, Pb, Zn, Al, Mg, titratable acid, and elevated H ion concentration, and was toxic to many of the aquatic organisms. In the areas of Cedar Creek, subjected to continuous acid flow, planktonic and benthic species had become adapted to the severe conditions and varied in abundance and diversity. No fishes were observed in the continuous acid effluents area. Downstream, where periodic mineral acid conditions changed drastically during an excessive effluent flow, planktonic and benthic communities had high diversity but low density. The populations of fishes were variable in this stream reach. The chemical basis of water quality variability was shown to be time-related, and statistically related to the aquatic communities. Physical, chemical and biological conditions of acid lakes formed by surface mining were reviewed. In addition to apparent physical and chemical differences in lakes, due in part to variable solar absorbance due to suspended oxides of Fe, chemical variability related to organic composition was reviewed. It is quite probable that degradation of such lakes can be reversed.     

金线莲施硒的吸收与积累规律

为探究金线莲的硒吸收、转化及生长效应,通过种苗繁殖培养基、移栽基质、林下腐殖土添加与叶面喷施等方式进行亚硒酸钠(Se4+)施用试验,检测分析金线莲植株形态、主要成分、植株及器官总硒与有机硒、生长量等指标与硒施用量关系。结果表明,施硒能极显著提高金线莲植株含硒量,硒吸收利用率最高为繁殖培养基添加方式,为13.09%,其他依次为叶面喷施、基质添加和林下腐殖土添加方式,分别为6.81%、6.36%和2.79%。植株干品总硒含量随施用浓度提高而增加,有机硒含量为81.8%～92.1%,硒有机转化率不受施用浓度影响。植株各器官硒含量为根>叶>茎,硒有机转化率为叶>根>茎。根部适宜浓度施用硒能促进金线莲植株生长,过高浓度施用抑制生长。叶面喷施硒对金线莲植株生长量无显著影响。施硒对金线莲植株主要成分含量无显著影响。金线莲的硒最佳经济施用量分别为培养基添加4.75 mg/L、叶面喷施0.168 mg/株、基质添加8.00 mg/L、林下腐殖土添加9.50 mg/L。综合各种施用方式效果来看,以种苗繁殖培养基添加硒方式可获得最佳吸收利用率和最佳产量     

白洋淀芦苇湿地生态系统中植硅体的产生和积累研究

植硅体(phytoliths),又称植物蛋白石,存在于大部分植物组织细胞中,主要是依靠植物的根系吸取土壤溶液中的可溶性二氧化硅,在植物细胞或细胞内沉淀硅化而形成的一种固体的非晶质含水二氧化硅颗粒物[1].植硅体主要组成部分是二氧化硅(67％～95％)、水(1％～12％)、碳(0.1％～6％)及少量的无机元素Na、K、 Ca、 Fe、 AL、 Ti等[2],由于其具有较强的抗分解、抗腐蚀和耐高温等特性,可以长时间较稳定地保存在一些岩石和土壤中[3-5],在硅的生物地球化学循环中有着重要的作用,是全球硅循环的重要参与者[6].虽然植硅体作为生物硅的重要组成部分,在全球硅的生物地球化学循环中占据着重要地位,但在湿地生态系统中植硅体产生和积累研究则鲜见报道[7].     

Acid precipitation and its influence upon aquatic ecosystems — An overview

The impact of acid precipitation reflects a usually deleterious balance between good and bad effects which may lead to serious and sometimes extreme degradation of aquatic as well as terrestrial ecosystems, particularly around metal smelters. Addition of H ions as H₂SO₄, HNO₃, and HCl can alter and impoverish the species composition of biotic communities, and lead to severe leaching of beneficial metal cations such as Ca from ecosystems. Heavy metals and other trace elements which accompany acid precipitation may reach toxic levels, particularly where acid fallout leaches additional amounts from the soil into streams and lakes. Complex and often toxic hydrocarbons also comprise a little known organic component of acid precipitation. Alternatively, acid precipitation usually is enriched in plant nutrients such as nitrate- and ammonia-nitrogen, K, Ca, and S; and at certain concentrations some of the associated trace elements may also be beneficial. Moreover the initial effect of soil leaching by acid fallout may be to enrich aquatic ecosystems in metal cations such as Ca. Basic materials in air pollution, biogenic NH₃ from the soil, dust fall from arid regions, and soils rich in adsorbed metal cations or in carbonates may neutralize some of the harmful effects of acid precipitation upon ecosystems. However, associated heavy metals, other trace elements, and toxic hydrocarbons may still constitute serious problems in many environments.     

Effects of pH and selenium oxidation state on the selenium accumulation and yield of alfalfa

Experiments were performed in greenhouse sand culture to determine the effect of pH and Se oxidation state on the tissue composition and yield of alfalfa (Medicago sativa L.). Alfalfa was planted and irrigated with nutrient solution containing 0, 0.25, 0.5, 1.0 or 3.0 mg Se L^‐1 as Na₂SeO₃ or Na₂SeO_l4. The solution pH was maintained at 7.0 ± 0.2 or 4.5±0.2. Three harvests were made and the shoots and roots weighed and analyzed for total Se. At the levels tested, additions of Se to the treatment solutions increased the tissue Se concentrations and depressed alfalfa shoot growth regardless of Se oxidation state or pH. Root growth was reduced in the presence of Se(VI) but was unaffected by Se(IV). Selenium was accumulated to higher concentrations in the shoot when supplied as Se(VI) compared to Se(IV) and accumulated to higher concentrations in the root when added as Se(IV) compared to Se(VI). Relative shoot yields were depressed more by Se(IV) then Se(VI) at pH 7, but there was no difference between Se(IV) and Se(VI) at pH 4.5. Relative root yields were depressed by Se(VI) but not by Se(IV).     

黑麦草对硒的吸收、分配与累积

用营养液培养方法研究了黑麦草(Lolium.multiflorum,Lamaubada)对硒的吸收、分配和累积特征以及硒对黑麦草生物量的影响,以探讨黑麦草对硒的吸收和利用规律。结果表明,不同SeO32--Se浓度处理的黑麦草在不同生育期的硒含量大小顺序均表现为分蘗期拔节期抽穗期苗期,且其差异在低硒浓度([Se4+]0.05.mg／L)时表现不明显,在非中毒范围内,黑麦草体内含硒量随供硒水平的提高而增加。在不同硒浓度处理中,黑麦草不同器官的硒含量大小顺序均为根叶茎,黑麦草吸收的SeO32--Se大部分在根部累积,少部分转移到茎与叶中,SeR／SeL3,SeR／Ses4。当营养液中加入低浓度硒([Se4+]=0-0.1.mg／L)时促进了黑麦草的生长,其生物量随外源硒浓度的增大而增加;高浓度硒([Se4+]1.0.mg／L)时抑制黑麦草的生长甚至引起中毒死亡。抽穗期黑麦草对硒的阶段累积率最大,达40.42％。     

水稻子粒硒累积机制研究

采用溶液培养方法研究了富硒与非富硒两品种水稻（秀水48和丙9652）对硒的转运差异及其子粒硒积累机制。结果表明,水稻子粒灌浆开始后停止供硒,其根系硒浓度随着时间的推移而表现下降的趋势。秀水48根系硒含量下降幅度大于丙9652;秀水48根系中硒更加容易转运出去。剑叶是水稻的功能叶,在水稻整个生育期内剑叶中硒含量逐渐下降。秀水48剑叶硒含量下降幅度大于丙9652,两者差异显著。从硒的积累量看,秀水48剑叶硒积累量下降幅度大于丙9652,剑叶硒的转移将有助于硒在水稻子粒中的积累。     

Difference in selenium accumulation in shoots of two rice cultivars

Two japonica rice （Oryza sativa L.） cultivars, Xiushui 48 and S. Andrea, differing in their ability to accumulate Se in the grain （as high as a three-fold difference）, were compared for selenium （Se） accumulation in their shoots when their growth media was supplied with different forms of Se. Results indicated that when treated with 0.25μmol L^-1 Na2SeO3, Xiushui 48 accumulation of Se in the shoots was significantly more rapid （P〈0.05） than S. Andrea, probably because of greater Se uptake and transport in Xiushui 48. Xiushui 48 rice seedlings had a higher shoot-Se accumulation rate and absorbed selenocysteine （Se-Cys） more rapidly than S. Andrea seedlings. However, when treated with Se as 0.25μmol L^-1 selenomethionine （Se-Met）, the S. Andrea seedlings＇ accumulation rate was significantly greater （P〈0.05） than that of Xiushui 48. Possibly, the high Se accumulation rate of Xiushui 48 seedling shoots compared to S. Andrea shoots was the result of a higher capacity of Xiushui 48 to transform selenite to organic Se compounds and a higher selenite uptake rate.     

紫甘薯对硒的吸收和累积特征

以紫甘薯为试验材料,采用盆栽试验的方法研究了基施硒酸钠[Se(VI)]和亚硒酸钠[Se(IV)]条件下,紫甘薯对外源硒的吸收累积规律,并比较了施用两种不同价态硒的紫甘薯富硒效果。结果表明:两种硒源均可显著提高紫甘薯各器官含硒量,且紫甘薯含硒量均随施硒量的增加而增大。当土壤施硒量为Se 8 mg/kg时,施用硒酸钠、亚硒酸钠收获期薯块的硒含量(干基)分别达到6.69、0.88 mg/kg。紫甘薯生育期40 d时各器官硒含量叶茎薯块,130 d时硒含量叶薯块茎。当硒酸钠施用量为Se 4 mg/kg时,紫甘薯薯块中的硒累积量最高达923.81μg/株,硒在紫甘薯块根中的分配率可达67%~70%,硒酸钠处理下,紫甘薯对硒的吸收利用率远远高于亚硒酸钠处理。综合紫甘薯含硒量和施硒量对生长的影响结果分析,施用硒酸钠和亚硒酸钠均能增加紫甘薯薯块的硒含量,紫甘薯对硒酸钠敏感性高于亚硒酸钠,生产过程中应充分考虑施用硒酸钠对作物造成的毒害。     

Effects of nitrogen deposition on the acidification of terrestrial and aquatic ecosystems

The concentration of ammonium and nitrate in precipitation has increased during this century. The deposition of N compounds (wet + dry) is reaching 30 to 40 kg ha^?1yr^?1 in many areas in Central Europe and above 20 kg in the southern parts of Scandinavia. In extreme situations throughfall data indicate depositions above 60 kg ha^?1yr^?1 in Central Europe and above 40 kg ha^?1yr^?1 in south Sweden. Very high depositions are observed on slopes at forest edges and adjacent to areas with animal farms and manure spreading. In areas with low N deposition almost all deposited N (>95%) will be absorbed in the tree canopies or in the soil. In areas with high deposition an increased outflow is observed which in some cases reach 10 to 15 kg ha-lyr-1. The increased output is an indication of N saturation of the ecosystem and it leads to acidification effects in soils, soilwater, groundwater and surface waters.     

Assessing significant harm to terrestrial ecosystems from contaminated land

Abstract. Terrestrial ecosystem risk assessment remains in its infancy by comparison with the aquatic discipline, yet it is advancing quickly in response to increasing concerns surrounding soil quality and the sustainable use of soil. Several international frameworks have been developed during the last decade to aid decision-makers as the need for scientifically derived tools for determining ecological risk from land contamination has been recognized. From the regulatory viewpoint, the priority is establishing what to protect in order to prevent ecological harm. This is a complex issue requiring clear objectives in a risk assessment context. The most important factor in assessing ecological harm is whether or not ecosystem function is altered as a result of land contamination and, if it is, judging the significance. A consensus is developing that ecological risk assessment should aim to protect populations rather than individuals. This paper critically reviews recent developments in risk assessment for terrestrial ecosystems and land contamination in the UK, with emphasis on deriving a measure of ecological harm to assess ecosystem function. We seek to further justify the use of earthworms as a favoured indicator species for protecting ecological function. Guidance on how to measure harm in relation to ecological function is, however, still lacking.     

硒对苦荞硒、总黄酮和芦丁含量、分布与累积的影响

采用盆栽试验探讨土壤施硒对苦荞硒、总黄酮和芦丁含量、分布与累积的影响。结果看出,在土壤施硒0.5～2.0 mg/kg范围,苦荞根在苗期（40 d）大量吸收并累积硒,全生育期各器官硒含量极显著提高;在生长中后期(60～80 d) 硒的累积最快,累积量最多。硒在苦荞各器官中的分布为:在40 d时,根＞叶＞茎;60 d时Se0.0处理为叶＞根＞花＞茎,施硒各处理则为花＞根＞叶＞茎;80 d时Se0.0处理以花＞根＞叶＞茎＞子粒,Se0.5处理以花＞叶＞子粒＞茎＞根,施硒≥1.0 mg/kg的处理则为花＞叶＞茎＞根＞子粒。土壤施硒≤1.0 mg/kg促进苦荞生长,提高地上部各器官干重和植株总干重以及各器官总黄酮和芦丁含量与累积量,不改变总黄酮和芦丁的器官分布,增加苦荞中后期对总黄酮的累积;以Se0.5处理效应最佳,各差异达显著水平。过量的硒（Se1.5～2.0 mg/kg）显著抑制苦荞生长,降低各器官干重、总黄酮和芦丁含量与累积,不利于硒在子粒中富集和总黄酮在子粒中分布。表明在低硒土壤上栽培苦荞,土壤施硒以不超过1.0 mg/kg为宜,既能最大限度的提高苦荞各器官硒、总黄酮和芦丁含量和累积量,又可降低施用硒肥的成本和减少硒肥对环境的影响。     

Influence of selenium on carbohydrate accumulation in developing wheat grains

The present investigation reports the effects of different doses of sodium selenate and sodium selenite on its uptake, carbohydrate composition, and sucrose and starch metabolizing enzymes in flag leaf and developing grains of wheat grown under greenhouse conditions. Selenium (Se) concentration increased significantly in leaves and developing grains of Se-treated plants compared to control at different intervals post-anthesis. Total soluble sugars and sucrose concentrations in developing grains increased due to various Se treatments. Different selenite treatments increased sucrose synthase activity from 10 to 20 days post-anthesis and increased starch accumulation compared to control plants. Lower starch accumulation in selenate than control and selenite treatments was observed. The activities of α, β and total amylase, invertase and sucrose synthase increased whereas sucrose phosphate synthase declined. Results indicated that Se accumulation causes disturbances in carbohydrate metabolism that is dependent on Se concentration, form and the development stage of the plant.     

Enriched accumulation and biotransformation of selenium in the edible seaweed Laminaria japonica

Accumulations of selenium in kelp Laminaria japonica cultured in seawater was achieved by adding selenite (Na2SeO3) with or without N-P (NaNO3 + NaH2PO4) nutrients at different concentrations. Biotransformation of selenium in the kelp was investigated through measuring the selenium of biological samples and different biochemical fractionations. The results showed that the optimal selenite-enrichment concentration is 200 mg L(-1), which can allow the kelp to accumulate a total selenium content from 0.51 +/- 0.15 to 26.23 +/- 3.12 microg g(-1) of fresh weight (fw). Selenium composition analysis of kelp (control group) showed that selenium is present as organic selenium, which is up to 86.22% of the total selenium, whereas inorganic selenium is barely 4.85%. When L. japonica was exposed for 56 h in seawater containing 200 mg L(-1) Na2SeO3, the organic selenium was 16.70 microg g(-1) of fw (68.23%) and inorganic selenium was 4.71 microg g(-1) of fw (19.26%). The capability of accumulation of selenium was further enhanced by adding N-P nutrients to the selenite-enriched medium. Total selenium is increased to be 33.65 microg g(-1) of fw at optimal concentration of N-P nutrient (150 mg L(-1) NaNO3 and 25 mg L(-1) NaH2PO4), whereas the inorganic selenium was not increased and remained at 4.597 microg g(-1) of fw (13.36%), and the increased part of selenium was organic selenium. This implied that kelp L. japonica could effectively transform inorganic selenium into organic selenium through metabolism.