Hypolimnetic anoxia and sediment oxygen demand during stratification in a drinking water reservoir

Journal of Soils and Sediments - Although hypolimnetic anoxia is a common occurrence in deep lakes and reservoirs, understanding the processes of oxygen depletion in water columns and sediment is...     

Grain legumes differ in nitrogen accumulation and remobilisation during seed filling

In grain legumes, the N requirements of growing seeds are generally greater than biological nitrogen fixation (BNF) and soil N uptake during seed filling, so that the N previously accumulated in the vegetative tissues needs to be redistributed in order to provide N to the seeds. Chickpea, field bean, pea, and white lupin were harvested at flowering and maturity to compare the relative contribution of BNF, soil N uptake, and N remobilisation to seed N. From flowering to maturity, shoot dry weight increased in all crops by approximately 50%, root did not appreciably change, and nodule decreased by 18%. The amount of plant N increased in all crops, however in field bean (17?g?m^?2) it was about twice that in chickpea, pea, and lupin. The increase was entirely due to seeds, whose N content at maturity was 26?g?m^?2 in field bean and 16?g?m^?2 in chickpea, pea, and lupin. The seed N content at maturity was higher than total N accumulation during grain filling in all crops, and endogenous N previously accumulated in vegetative parts was remobilised to fulfil the N demand of filling seeds. Nitrogen remobilisation ranged from 7?g?m^?2 in chickpea to 9?g?m^?2 in field bean, and was crucial in providing N to the seeds of chickpea, pea, and lupin (half of seed N content) but it was less important in field bean (one-third). All the vegetative organs of the plants underwent N remobilisation: shoots contributed to the N supply of seeds from 58% to 85%, roots from 11% to 37%, and nodules less than 8%. Improving grain legume yield requires either reduced N remobilisation or enhanced N supply, thus, a useful strategy is to select cultivars with high post-anthesis N₂ fixation or add mineral N at flowering.     

Physicochemical and ecotoxicological evaluation of estuarine water quality during a dredging operation

Purpose

Most of the information concerning the effects of contaminated sediments on estuarine organisms deals with the impacts of bed forming sediments. The ecotoxicological potential at the time of a dredging operation is more difficult to assess, and few studies have dealt specifically with resuspended contaminated sediments. The aim of this study was to determine whether release of contaminants through sediment resuspension during a dredging operation in the Itajaí-açu estuary (Brazil) changed the water quality classification and had an ecotoxicological impact on the near-field water column during the critical moment of this operation.

Materials and methods

Waters from two sites (control and dredged sites) were analyzed for physicochemical parameters before, during, and after a dredging operation. In parallel, a short-term, sensitive battery of biotests (bacteria, algae, and daphnids) was performed with water samples before and during this operation according to the ISO bioassay protocols.

Results and discussion

No short-term toxicity was observed with waters collected before or during the dredging operation. The results showed that desorption of contaminants from suspended particles of sediments with a low level of contamination during a dredging operation lowered the water quality in the near-field water column but that this did not promote significant acute toxicity effects on the organisms tested.

Conclusions

More detailed studies are needed (e.g., the question of the reliability of biotests under turbulent, particle-rich conditions) to fully understand this complex issue regarding water column ecotoxicity during the whole dredging operation and to support decisions on the management of dredging activities.

     

苹果浑浊汁贮藏过程中浑浊稳定性的研究

为考察苹果浑浊汁在贮藏中的浑浊稳定性，进行了在4、22和40℃贮藏果汁120 d的试验。采用了电子显微镜学、光学显微镜学、Zeta电位和粒径分布分析等技术，结合高效液相色谱(HPLC)分析酚类物质进行研究。结果发现，果汁中相对大尺寸的颗粒先聚集下沉，造成浊度的迅速下降。随着留在瓶上部的大的颗粒数目的减小，颗粒下沉的速率降低。总酚、表儿茶素、绿原酸和单宁的损失随着贮藏温度的升高和储藏时间的延长增大。添加0.006%的维生素C可抑制由酚类物质的氧化聚合产生的不溶性小颗粒的产生，使果汁浊度变化减小。悬浮颗粒的尺寸大于其电性质对浑浊稳定性的影响。     

Changes in the aroma of a strawberry drink during storage.

The flavor of a commercially available strawberry drink was investigated with special regard to the changes of the sensory properties during the shelf life of the product. The experiments were performed using gas chromatographic methods after liquid-liquid extraction and after solid-phase microextraction of the headspace. A trained sensory test panel was used to substantiate the results from instrumental analyses. The relative concentrations of several compounds were followed over a storage period of six weeks at elevated temperature (37 degrees C), which corresponds to about 12 months storage at room temperature. Significant concentration changes of several flavor compounds were determined after a short storage time. These results correlate highly with changes in the aroma observed by the sensory test panel. Further on, changes in the sensorial relevance of aroma active compounds were monitored by comparative aroma extract dilution analysis of extracts of the fresh product and the product at the end of the declared shelf-life time. The results showed a significant decrease in flavor dilution factors of compounds with characteristic fruity attributes.     

冬大麦花后穗部氮素积累及转移的研究

在大田条件下,以扬饲麦3、扬饲麦1、苏啤2号和扬农啤2号等4个品种为供试材料,在07、5、1502、25.kg/hm24个氮肥处理水平下,研究了大麦花后穗部氮积累及转移的规律。结果表明,在扬饲麦3、扬饲麦1、苏啤2号和扬农啤2号4个品种各氮肥处理的平均值中,开花期绿叶的含氮量依次为2.64%、2.76%、2.63%和2.45%,穗部含氮量依次为1.43%、1.83%、1.69%和1.51%。成熟期子粒含氮量分别为2.65%、2.63%、2.48%和2.14%。氮的花前积累量(NABF)依次为17.68、15.27、19.80和14.85.mg/plant,总积累量(NTA)分别为33.75、25.51、54.24和28.83mg/plant,花后积累量(NAAF)依次为16.061、0.25、34.45和13.98.mg/plant,转移量(NT)依次为12.60、10.551、3.48和9.54.mg/plant,转移效率(NTE)分别为71.49%、69.84%、68.42%和64.97%。收获指数(NHI)分别为84.91%、81.95%、88.47%和81.90%;随着施氮水平的提高,各品种的花前氮积累量、总积累量、花后积累量和氮转移量均呈上升趋势,而氮转移效率、氮转移对子粒的贡献(NCR)率则成下降趋势;大麦花后穗部氮积累过程可以用Richards方程W=A/(1+be-kt)m来描述,通径分析方程各特征参数与氮积累和转移的关系表明,影响大麦穗部氮积累和转移的主要因素是最大积累速率,其次是起始积累势,最大积累速率越高,起始积累势越小,越有利于氮的积累和转移。同时,积累中期和前期的积累速率和积累量对大麦穗部氮积累和转移的影响也较大。     

不同氮、钾配比对杂交水稻灌浆期直链淀粉积累的影响

选用4个不同系列的杂交水稻组合,通过施用不同量氮、钾底肥处理,对水稻开花后子粒淀粉积累、淀粉合成关键酶活性及其之间的关系进行了研究。分析不同氮、钾处理及基因型因素对直链淀粉含量的影响以及淀粉合成酶（GBSS）与直链淀粉积累的关系。结果显示:品种基因型和氮肥施用量是决定直链淀粉含量的主要因素,其他因素对子粒直链淀粉的含量影响也达到显著水平;不同因素对GBSS的影响与直链淀粉相似;GBSS活性与直链淀粉含量在灌浆期间显著正相关。不同品种最高直链淀粉含量的氮钾处理也不同,在本试验条件下各水稻品种直链淀粉含量的最佳氮钾组合为:B优827为N180K135;红优2009为N180K135; C优2009为N180K180;冈优725为N90K180。各品种中B优827直链淀粉含量最高。     

Changes in total, mineralizable and light fraction soil organic matter with cropping and tillage intensities in semiarid southern Alberta, Canada

There has been a trend toward increased cropping intensity and decreased tillage intensity in the semiarid region of the Canadian prairies. The impact of these changes on sequestration of atmospheric CO₂ in soil organic carbon (C) is uncertain. Our objective was to quantify the changes in total, mineralizable and light fraction organic C and nitrogen (N) due to the adoption of continuous cropping and conservation tillage practices. We sampled three individual long-term experiments at Lethbridge, Alberta, in September 1992: a spring wheat (Triticum aestivum L.)-fallow tillage study, a continuous spring wheat tillage study and a winter wheat rotation-tillage study. Treatments had been in place for 3–16 years. In the spring wheat-fallow study, different intensities (one-way disc > heavy-duty cultivator > blade cultivator) of conventional tillage (CT) were compared with minimum tillage (MT) and zero tillage (ZT). After 16 years, total organic C was 2.2 Mg ha⁻¹ lower in more intensively worked CT treatments (one-way disc, heavy-duty cultivator) than in the least-intensive CT treatment (blade cultivator). The CT with the blade cultivator and ZT treatments had similar levels of organic C. The CT treatments with the one-way disc and heavy-duty cultivator had light fraction C and N and mineralizable N amounts that were about 13–18% lower than the CT with the blade cultivator, MT or ZT treatments. In the continuous spring wheat study, 8 years of ZT increased total organic C by 2 Mg ha⁻¹, and increased mineralizable and light fraction C and N by 15–27%, compared with CT with a heavy-duty cultivator prior to planting. In the winter wheat rotation-tillage study, total organic C was 2 Mg ha⁻¹ higher in a continuous winter wheat (WW) rotation compared with that in a winter wheat-fallow rotation. The lack of an organic C response to ZT on the WW rotation may have been due to moldboard plowing of the ZT treatment in 1989 (6 years after establishment and 3 years before soil sampling), in an effort to control a severe infestation of downy brome (Bromus tectorum L.). Our results suggest that although relative increases in soil organic matter were small, increases due to adoption of ZT were greater and occurred much faster in continuously cropped than in fallow-based rotations. Hence intensification of cropping practices, by elimination of fallow and moving toward continuous cropping, is the first step toward increased C sequestration. Reducing tillage intensity, by the adoption of ZT, enhances the cropping intensity effect.     

Draft,construction and operation of a sequential rain sampler

Sequential sampling of rain on a volume basis presents fewer problems than sampling on a time basis. The optimum diameter of the collector opening depends on the rainfall statistics, the size of the sample needed for chemical analysis and the total number of samples that has to be collected. The sampler described here consists of a square polyethylene funnel of 0.64 m² and a fraction collector with 250 polypropylene tubes of 39 ml, which is activated by a rain detector. Each fraction corresponds to about 0.05 mm of rainfall. The funnel is covered by a roller blind that automatically rolls up when it starts to rain. Evaluation of the system leads to the conclusion that the collector opening can be made smaller (by 0.20 m²), that the measured rainfall rate depends on the averaging time, and that all other surfaces of the sampling set-up should be covered with inert material.     

Microbial properties and attributes of ecological relevance for soil quality monitoring during a chemical stabilization field study

Chemical stabilization is a soil remediation technique based on the incorporation of organic and/or inorganic amendments to metal contaminated soil in order to decrease metal bioavailability and improve soil quality. Consequently, the establishment of follow-up monitoring programmes is essential to ensure the long-term effectiveness of chemical stabilization in terms of both metal bioavailability reduction and soil quality improvement. In this study, three doses (20, 40 and 80 t ha⁻¹) of a lime-treated sewage sludge, that meets legal standards regarding metal contents, were added to a metalliferous mine soil and a variety of physicochemical and microbial indicators of soil quality were measured over time (immediately before treatment application and one and six months after such application). Soil CaCl₂-extractable and plant metal concentrations were also measured. We carried out a complementary interpretation of soil microbial properties through their grouping within a set of ecosystem attributes of ecological relevance: vigour, organization, stability, suppressiveness and redundancy. Sewage sludge addition led to an increase in soil pH, but this beneficial effect was transient. The addition of sewage sludge had a more pronounced effect on parameters used here to estimate soil vigour (dehydrogenase activity, basal and substrate-induced respiration). On the contrary, the addition of sewage sludge did not significantly alter the composition of soil microbial communities, as reflected by PCR-DGGE data. Chemical stabilization was only partly successful: it did improve soil quality but the expected reduction in soil metal bioavailability (as reflected by the values of CaCl₂-extractable metal concentration) was clearly observed only for Cd (not for Pb or Zn); however, SL addition led to a significant reduction in shoot metal concentration for the three metals under study. The assessment of soil quality at the attribute level has proven useful for the interpretation of the effect of chemical stabilization on soil functioning.     

装载机工作过程联合仿真与试验

为了分析装载机工作过程中的能量消耗情况,首先使用Pro/E软件建立了装载机工作装置的三维模型,将其导入Simulation X仿真软件中建立了装载机的动力学模型,同时使用该仿真软件建立了装载机工作装置液压系统模型,进一步建立了装载机联合仿真模型。然后针对正载和偏载2种典型工况中各个工作部件能量消耗情况进行了仿真和试验研究,通过比较仿真与试验结果,验证了所建立装载机工作装置机液联合仿真模型的准确性,获得了驱动工作装置液压系统在典型工况中的能量损失。结果表明:在正载工况下,多路阀的能量损失占49%;偏载工况下,多路阀的能量损失占52%。多路阀在一个工作循环中消耗能量最大,主要是中位卸荷损失。该研究为装载机液压控制系统节能设计提供了参考。     

Changes in the profile of genistein, daidzein, and their conjugates during thermal processing of tofu.

Profiles of genistein, daidzein, genistin, daidzin, and their acetyl- and malonyl-beta-glycosides were determined in tofu as affected by temperature and time. Tofu was heated in water at 80, 90, and 100 degrees C for 0 (control), 10, 20, 30, and 40 min, and the contents of the isoflavones of interest were quantified using reversed-phase HPLC. Total isoflavone content decreased most likely due to leaching of isoflavones into the water. Because the content of the isoflavones of the genistein series was little affected by the treatments, the decrease in the total isoflavone content was almost exclusively due to a decrease of the daidzein series. Changes in the profile of the daidzein series suggest little decarboxylation of the malonylglycoside to the acetylglycoside, but considerable de-esterification of the malonyl- and acetylglycoside to the beta-glucoside. Strongly temperature dependent decreases of the aglycon suggest possible thermal degradation of daidzein in addition to losses due to leaching.     

Changes in soil microbial and nematode communities during ecosystem decline across a long-term chronosequence

Following the creation of new land surfaces, there is an initial build-up phase, but in the prolonged absence of catastrophic disturbance an ecosystem decline phase has often been observed. While a number of studies have investigated the changes in soil biota that occur during the build-up phase, few studies have investigated how the soil food web changes during the ecosystem decline phase, even though such studies may assist our understanding of biotic factors that contribute to long-term ecosystem changes. We investigated the response of soil microbial and nematode communities to ecosystem decline by studying each of four stages of a long-term (280,000 year) forested chronosequence caused by uplift of marine terraces in the Waitutu region of Fiordland National Park, New Zealand. With increasing chronosequence age there were large increases in ratios of C to N, C to P, and N to P in both the organic layer and mineral soil layer, indicative of greater nutrient (notably P) limitation over time. Variables related to soil microbial biomass and activity were lower on the older terraces when expressed on a per unit soil C basis, reflecting that the quality of the soil organic matter, which is the resource that supports microbial metabolism, declined over time. This in turn had important consequences for population densities of soil nematodes and enchytraeids, including both microbe-feeding and predatory groups. There were significant increases in the fungal:bacterial biomass ratio and in the fungal-feeding:bacterial-feeding nematode densities. Taken collectively, our results suggest a decline in soil microbial activity and soil fauna, and an increase in the relative importance of the fungal-based (vs. bacterial-based) energy channel during long-term ecosystem development on terraces of marine origin. This corroborates the hypothesis that the studied sites represent a retrogressive shift in soil organic matter quality over a long-term chronosequence.     

Ammonium fertilization increases pearl millet yield by promoting early root growth,higher tillering,and water use during grain filling in a low P Sahelian soil

Background : Adaptation of pearl millet [Pennisetum glaucum (L.) R. Br.] to low soil phosphorus (P) at early seedling stages and efficient P fertilizer application are crucial for its survival in the West African Sahel. While addition of ${\mathrm{NH}}_4^{+}\text{-}N$ to P in the microdose technique has been reported to stimulate early growth of pearl millet, there is little information regarding root length (RL) at different timings. Aims : Our study aimed at assessing the effects of added ${\mathrm{NH}}_4^{+}\text{-}N$ and ${\mathrm{NO}}_3^{-}\text{-}N$ to P on (1) pearl millet agronomic traits such as root and shoot growth and (2) the water use dynamics during the cropping cycle. Methods : Twenty‐four “RhizoTubes” filled with P‐deficient soil were used to grow pearl millet under three treatments: (T1) placed P addition alone at 0.4 g per seed hole, P_placed, (T2) P_placed + ${\mathrm{NH}}_4^{+}\text{-}N$, and (T3) P_placed + ${\mathrm{NO}}_3^{-}\text{-}N$. At 2, 3, 4, and 5 weeks after sowing (WAS) we took non‐destructive measurements of RL. Water use (transpiration) was measured from 3.5 to 9 WAS. Results : At early growth, roots in the topsoil of T2 were longer than T3 and T1 roots (at 4 WAS: 129.3 cm for T2, 87.5 cm for T3, and 93.3 cm for T1, p < 0.05). Total RL at 2 WAS correlated positively with seedling height and final grain yield. Fertilization with ${\mathrm{NH}}_4^{+}\text{-}N$ reduced the time to flowering and increased the number of tillers and grain yield, whereas addition of ${\mathrm{NO}}_3^{-}\text{-}N$ increased vegetative dry matter at harvest and water use efficiency. Conclusions : Our findings suggest that fertilization with ${\mathrm{NH}}_4^{+}\text{-}N$ plays a critical root stimulating role at early growth stages, seemingly by increasing lateral root initiation, which carries through to a larger water use during grain filling and higher grain yield.     

短期连续光照下水培生菜品质指标变化及其关联性分析

以温室自然光照下水培20 d的生菜为试验材料, 研究其在72 h连续光照下叶片和叶柄中硝酸盐、可溶性糖及Vc含量的变化规律及其关联性。结果表明: 在72 h的连续光照下, 生菜叶片和叶柄中的硝酸盐含量大幅度降低, 但在不同光照时期降低速度各不相同, 叶片和叶柄中的硝酸盐含量分别在连续光照24 h和48 h后趋向于稳定; 而可溶性糖和Vc含量以近似恒定的速度快速提高, 其增速在72 h后并未表现出变缓趋势。可溶性糖在叶片和叶柄中的分布无显著差异, 但叶片中的Vc含量显著高于叶柄。无论是在叶片还是叶柄中, 硝酸盐含量与可溶性糖及Vc含量均呈极显著负相关。短期连续光照可实现生菜低硝酸盐与高可溶性糖及Vc的统一, 显著提高了生菜的综合品质。     

苹果幼果发育期果柄结构和Ca、Mg、K水平的变化

以富士、金冠苹果树为试材,分析了同一花序不同部位的果实重量,Ca、Mg、K含量和果柄结构的变化,以期探讨果柄发育和幼果Ca、Mg、K吸收之间的关系及其在幼果脱落中的作用。结果表明,随幼果的发育,单个幼果重量和Ca、Mg、K含量呈增加趋势;与发育不正常的边果相比,发育正常的中心果和边果的鲜重、干重、果柄直径、维管束数目、木质部厚度、韧皮部维管束面积和单果Ca、Mg、K总含量较高,而以干重为单位的果柄Ca、Mg含量较低。相关分析表明,苹果幼果的单果重和Ca、Mg、K含量与果柄的直径、维管束数目、木质部厚度、韧皮部维管束面积呈显著正相关,说明幼果发育与Ca、Mg、K吸收和果柄结构密切相关,Ca、Mg、K吸收率低和果柄发育不良可能是导致落果的重要原因。     

Changes in enzymic activity and distribution of acid-soluble,amino acid-nitrogen in soil during nitrogen immobilization and mineralization

During a period of immobilization of nitrate-¹⁵N and mineralization of organic N in a sandy-loam, changes were recorded in: (a) the concentration of an added carbon source, glucose-¹⁴C: (b) evolution of ¹⁴CO₂: (c) bacterial populations; (d) distribution and concentration of newly-synthesized, acid-soluble, amino acid-¹⁵N; and (e) distribution and activities of several oxidative and hydrolytic enzyme systems.Added glucose-¹⁴C was rapidly metabolized by the soil microflora. After 1.5 day's incubation, when only 3.6 per cent of the added glucose was present, 68 per cent of the ¹⁴C remained in the soil-microbial system. During this period there was a marked increase in viable bacterial numbers and an almost complete immobilization of nitrate-¹⁵N. On continued incubation, microbial metabolites were oxidized at decreasing rates, the more rapid phase corresponding to a period of net decline in the viable bacterial population.Soil was fractionated by a relatively mild procedure into components containing: (a) extractable proteins; (b) extractable amino acids and peptides; (c) particulate material containing microbial cells, cell debris and material bound to larger soil particles; and (d) microbial metabolites mainly bound to soil colloids. Although the total, acid-soluble, amino acid-¹⁵N remained relatively constant for about 50 days, there were marked changes in their concentration in different fractions, especially in the extracts and in the fraction containing fine colloidal material. However, the relatively large decline in labelled, acid-soluble, amino acid-¹⁵N occurred during the active phase of oxidation of microbial metabolites when little net mineralization of labelled compounds occurred.Increases in enzymic activities generally coincided with increased viable bacterial populations although there were some exceptions, notably casein and benzoyl arginine amide-hydrolysing enzymes. The stabilities of the newly-formed enzymes varied markedly. The greatest relative changes in activity occurred with the casein-hydrolysing enzymes. Their activity reached a maximal value after the main flush of bacterial growth, was short-lived and was to a large extent extractable. The formation and disappearance of this extracellular proteolytic activity coincided approximately with that of a secondary peak of extractable, newly-synthesized, protein-¹⁵N. In general however, changes in enzymic activity could not be identified with changes of protein-¹⁵N concentrations of the different fractions.