流域次降雨侵蚀产沙的BP神经网络模拟

在分析黄土高原韭园沟流域多年观测资料的基础上,应用BP神经网络建模方法,建立了流域次降雨侵蚀产沙的神经网络模型。通过输入模型变量流域次降雨量、平均降雨强度、径流深和洪峰流量模数,对流域次降雨侵蚀产沙量进行了训练和预测。预测结果表明,所建BP神经网络模型预测精度较高,可近似揭示复杂非线性流域次降雨侵蚀产沙系统的产沙规律,为建立较高预报精度的黄土高原流域次降雨侵蚀产沙预报模型提供了依据。     

黄土丘陵区不同降雨强度对农地土壤侵蚀的影响

采用人工模拟降雨的方法，对仪器自身性能进行了测试，并分设5种不同的降雨强度分别研究半干旱区林地、草地、人工草地和耕地的产流产沙特征。模拟天然降雨最大雨强5．05mm／min，雨量118．2～300．3mm／h；雨滴落地速度、雨滴动能等降雨特征值与天然降雨特征值是一致的；不同立地条件下径流量、侵蚀模数随雨强的增加而增加，并与降雨强度呈指数函数或幂函数关系。     

Regional Sediment Deficits in the Dutch Lowlands: Implications for Long-Term Land-Use Options (8 pp)

Background, Aim and Scope   Coastal and river plains are the surfaces of depositional systems, to which sediment input is a parameter of key-importance. Their habitation and economic development usually requires protection with dikes, quays, etc., which are effective in retaining floods but have the side effect of retarding sedimentation in their hinterlands. The flood-protected Dutch lowlands (so-called dike-ring areas) have been sediment-starved for up to about a millennium. In addition to this, peat decomposition and soil compaction, brought about by land drainage, have caused significant land subsidence. Sediment deficiency, defined as the combined effect of sediment-starvation and drainage-induced volume losses, has already been substantial in this area, and it is expected to become urgent in view of the forecasted effects of climate change (sea-level rise, intensified precipitation and run-off). We therefore explore this deficiency, compare it with natural (Holocene) and current human sediment inputs, and discuss it in terms of long-term land-use options. Materials and Methods: We use available 3D geological models to define natural sediment inputs to our study area. Recent progress in large-scale modelling of peat oxidation and compaction enables us to address volume loss associated with these processes. Human sediment inputs are based on published minerals statistics. All results are given as first-order approximations. Results: The current sediment deficit in the diked lowlands of the Netherlands is estimated at 136 ± 67 million m3/a. About 85% of this volume is the hypothetical amount of sediment required to keep up with sea-level rise, and 15% is the effect of land drainage (peat decomposition and compaction). The average Holocene sediment input to our study area (based on a total of 145 km3) is ~14 million m3/a, and the maximum (millennium-averaged) input ~26 million m3/a. Historical sediment deficiency has resulted in an unused sediment accommodation space of about 13.3 km3. Net human input of sediment material currently amounts to ~23 million m3/a. Discussion: As sedimentary processes in the Dutch lowlands have been retarded, the depositional system's natural resilience to sea-level rise is low, and all that is left to cope is human countermeasure. Preserving some sort of status quo with water management solutions may reach its limits in the foreseeable future. The most viable long-term solutions therefore seem a combination of allowing for more water in open country (anything from flood-buffer zones to open water) and raising lands that are to be built up (enabling their lasting protection). As to the latter, doubling or tripling the use of filling sand in a planned and sustained effort may resolve up to one half of the Dutch sediment deficiency problems in about a century. Conclusions: Conclusions, Recommendations and Perspectives. We conclude that sediment deficiency – past, present and future – challenges the sustainable habitation of the Dutch lowlands. In order to explore possible solutions, we recommend the development of long-term scenarios for the changing lowland physiography, that include the effects of Global Change, compensation measures, costs and benefits, and the implications for long-term land-use options. Recommendations and Perspectives: -     

无定河粗泥沙产沙量的变化及其原因

 为了解决黄河治理中迫切需要解决的粗泥沙来源和数量问题,依据大量实测资料,运用统计方法对无定河粗泥沙产沙量进行研究。结果表明:无定河流域d>0.05 mm粗泥沙产沙量呈现出减少趋势,这种减少与年降水量、年沙尘暴频率的减少和水土保持面积的增大有一定的因果关系;估算出最大30d降雨量和年沙尘暴频率的变化对d>0.05mm粗泥沙产沙量变化的贡献率分别为66.5%和33.5%,即沙尘暴特征的变化对粗泥沙产沙量变化的贡献率相当于暴雨特征的变化贡献率的1/2。建立了粗泥沙年产沙量与最大30d降雨量、年沙尘暴频率和水土保持措施面积之间的回归方程,表明粗泥沙年产沙量随最大30d降雨量、年沙尘暴频率的减小而减小,随水土保持面积的增大而减小。因此,20世纪50年代以来暴雨的减弱、沙尘暴的减弱和水土保持措施面积的增大是无定河流域粗泥沙产沙量减少的原因。     

水土保持对偏关河径流和泥沙的影响分析

 偏关河流域水土保持面积从1959年的1万1593hm2增加到1996年的5万5338hm2,占流域面积的28.90%。年径流量、常水径流量与年份和各类水土保持措施之间,均呈极显著负相关,年径流量与年降水量、汛期降水量和有效降水量,均呈显著正相关,而常水流量与年降水量、汛期降水量和有效降水量关系很弱;偏关河流域小型蒸发器测定的蒸发量与年份呈显著负相关,但径流和泥沙变化并没有增加,说明水土保持是引起径流量和泥沙量变化的主要原因。洪水径流量、年输沙量和洪水输沙量变化一致,与年降水量、汛期降水量和有效降水量均呈显著正相关,而与水土保持措施面积呈不显著的负相关。     

科尔沁沙地不同下垫面风沙流结构与变异特征

对流动、半流动、半固定和固定沙地 4种不同下垫面 0～ 2 0 cm气流层的风沙流结构与变异特征研究表明 :(1 )不同退化沙地在总输沙量及各层输沙量上存在明显的差异 ,在 5月 1 5日的测定中 ,流动沙地的总输沙量是 83 .1g/ cm2 .h,分别是半流动、半固定和固定沙地的 2 .1倍、9.2倍和 33 .9倍 ;而在 5月 1 5日的测定中 ,流动沙地的总输沙量 1 0 5.7g/ cm2 .h,分别是半流动、半固定和固定沙地的 5.6倍、1 4.1倍和 75.6倍。(2 )总输沙量的 60以上分布在 1 0cm的高度内 ,随高度的增加 ,输沙量呈负指数函数下降。(3)风蚀物中粗粒 (粒径 1 .0～ 0 .5mm )与极细颗粒 (粒径0 .1～ 0 .0 5mm)和粉、粘粒 (<0 .0 5mm)的含量均很低 ,而细颗粒 (粒径 0 .2 5～ 0 .1 mm)的含量很高 ,占风蚀物的73 %～ 91 %,说明近地表层沙粒的运动以跃移为主。随高度的增加 ,风蚀物中中颗粒 (粒径 0 .5～ 0 .2 5mm)的含量下降 ,而极细颗粒和粉、粘粒含量增加 ,但其增幅因下垫面不同而异。(4) 0～ 2 0 cm总输沙量及各层输沙量与植被盖度呈显著负相关 ,与植株高度、地表紧实度和地表粗糙度长度呈微弱负相关     

滨岸排污口对潮滩沉积物中重金属的影响研究

通过对排污口附近及对照点的潮滩沉积物中重金属Zn ,Cu ,Cr和Pb的含量分析发现:各采样点沉积物中的重金属含量均高于环境背景值,平均含量约为环境背景值的2～3倍,排污口附近潮滩沉积物中重金属的含量明显高于对照点潮滩沉积物中的含量;各采样点的柱状沉积物中重金属的含量随深度的变化呈现出一定的变化规律;在垃圾填埋场附近高中低潮滩由于距离排污口的远近不同,表层沉积物中重金属的含量依次降低;对各采样点沉积物中重金属含量的相关性分析发现各点沉积物中累积的重金属的来源有所不同:在排污口附近潮滩的沉积物中重金属主要来源于排污口排放的污水,而对照点朝阳农场潮滩沉积物中重金属主要来源于自然的本底输入或海水外源输入     

流域侵蚀产沙的尺度变异规律研究

 侵蚀产沙的尺度变异规律,是当今土壤侵蚀研究的前沿,它涉及的研究范围广泛,小到土壤颗粒,大到全球气候变化与碳循环过程。特别是不同尺度流域之间侵蚀产沙和输移,究竟有什么样的内在联系,小流域所获得的研究成果是否能推广应用到大中流域,已成为迫切需要解决的重要科学问题。有关流域侵蚀产沙与输移过程随流域尺度复杂变化的研究,国际上刚刚开始,国内有关流域尺度研究主要涉及于水文学领域的一些尺度研究,关于流域侵蚀产沙与输移过程随流域尺度复杂变化的研究不多。作者对国外当前土壤侵蚀模型的最新进展进行了综述,并对侵蚀产沙的尺度变异规律进行了分析。由于具有GIS强大的空间数据管理和分析能力,它将在流域侵蚀产沙尺度变异这一侵蚀产沙的问题研究中发挥重要作用。     

A Novel Particle Contact Assay with the Yeast Saccharomyces cerevisiae (8 pp)

Goal, Scope and Background   Numerous xenobiotics released into surface waters are transferred to suspended particulate matter and finally attached to sediments. Aquatic organisms may be exposed to them by direct particle feeding, by physical contact with contaminated surfaces as an exposure route, and by the uptake of dissolved contaminants after equilibration via the free water phase. In order to assess potential sediment toxicity, each of these exposure routes has to be addressed. This paper presents a newly developed particle contact assay that uses the fermentation performance of a specific Saccharomyces cerevisiae strain for the assessment of toxic effects in sediments. The test procedure is based on the characteristic feature of growing yeast cells to attach to sediment particles, which are also relevant for the accumulation of contaminants. The physical contact with lipophilic contaminants mirrors an exposition pathway for the direct uptake into the cells. In order to quantitatively characterize the toxic effects of particle attached pollutants on the fermentation performance, unpolluted native reference sediment was spiked with representatives for widely distributed anthropogenic contaminants. Methods   Saccharomyces cerevisiae was established as sensitive eukaryotic microorganism for the ecotoxicological assessment of particle attached anthropogenic contaminants in freshwater sediments. For this purpose, yeast cells were cultivated in sediment samples and the resulting fermentation performance was continuously measured. Sediments artifically spiked with HCB, PCB, g-HCH, DDT, and benzo(a)pyrene and solutions of each contaminant were comparatively investigated by means of their adverse effects on yeast fermentation performance. Additionally, four native river sediments characterized by increasing levels of pollution were assessed by the yeast particle contact assay, and simultaneously by standard aquatic tests with algae, daphniae, and luminescent bacteria using pore water and elutriates. Results of the bioassays were related to specific sediment contamination with respect to metals and organic priority pollutants. Results and Discussion   In sediments spiked with PCB and benzo(a)pyrene fermentation, performance was affected extensively below concentrations inhibiting fermentation in contaminant solutions. This suggests a high efficiency of the exposure route by physical contact. The fermentation performance was only slightly affected by single lipophilic pollutants, whereas mixtures of individually spiked sediments caused critically reduced fermentation performance suggesting additive synergistic effects. Native river sediments modestly to critically polluted by hazardous organic compounds lead to a slightly to dangerously reduced fermentation performance in the yeast contact assay. These inhibitory effects were much less pronounced in the standard bioassays conducted with algae, daphniae and luminescent bacteria, applying pore waters and elutriates as sample matrices. Using pore water, inhibition was measured only in the most polluted sediment, elutriates lead to a slight inhibition of the algal growth in the undiluted sample only. These results indicate an improved sensitivity of the yeast particle contact assay compared to the standard assays, due to uptake and physical cell contact as additional routes of exposure. Conclusion   The yeast particle contact assay is a valuable tool for the assessment of ecotoxicological potential in freshwater sediments. Since the assay addresses physical contact as an exposure route, it indicates bioavailability of lipophilic compounds in sediments. Outlook   The sensitive indication of bioavailable contaminants associated to sediment particles by the newly developed yeast particle contact assay recommends it as a complementary microbial bioassay in a test battery for assessing major pathways of contaminants in whole sediments.     

Prognosis of Methane Formation by River Sediments (9 pp)

Background   Under anoxic conditions typically prevailing in disposal sites for dredged sediment, methanogenesis is the terminal step during microbial degradation of sediment organic matter. Sediment gas production may pose several problems to site management and post-closure utilisation. Depending on the magnitude of gas/methane formation and the intended utilisation of the site, countermeasures will have to be effected during and after deposition of the dredged material. For this purpose it may be of interest to pre-estimate the extent of gas formation from simple sediment variables. Therefore, the aim of the investigations presented here was to analyse the interrelations between gas formation and sediment physical, chemical and biological qualities. Methods   Freshly sampled riverbed sediment from nine German federal waterways was analysed for standard solid physical and chemical parameters, pore water composition, cell counts of methanogenic and sulfate-reducing bacteria, and gas formation over a period of 500 days. Particle size and density fractionation were carried out in order to characterise organic matter quality. Correlations between methane formation and sediment chemical, physical and microbiological characteristics were tested using linear and multiple correlation analysis. Results and Discussion   The selected sediments, including two with marine influence, differed strongly regarding texture, chemical parameters, pore water composition, and methanogen cell counts. The course of methane formation was found to follow distinct phases. The commencement of methane formation was preceded by a lag phase of variable duration. The lag phase was followed by a strong increase of the methane formation rate up to a sediment-characteristic maximum of 5–30 nmol CH4 h–1 g dw–1. Eventually, the rate of methane formation decreased and reached a more stable, long-term level. The extent and amplitude of each phase varied strongly between sediments and could be correlated well with only a few standard analytical parameters, despite the strong heterogeneity of sediment with respect to chemical, physical, and biological characteristics. Lag phase duration depended strongly on the content of inorganic electron acceptors and also on the number of methanogens present at the beginning of the experiment. Maximum and steady state methanogenesis were mainly determined by sediment total nitrogen. As analysis of sediment density fractions revealed that total nitrogen reflected the share of readily degradable macroorganic matter. Conclusion and Outlook   The results imply that the observed methane formation is a function of the temporally changing balance of the availability of electron acceptors and H2, and the share of easily degradable organic matter. For fresh riverbed sediments, the latter may be deduced from total nitrogen content. Overall, the results showed that methane formation by freshly dredged material may well be pre-estimated from standard analytical data within the first few years of deposition. However, the differently degradable organic matter pools will change over time with respect to size, chemical nature and association with the sediment mineral phase. It can thus be expected that the correlations found in this study will not be readily transferable to older materials. Further studies on the gas formation and organic matter quality by older sediments, e.g. from older dredged material disposal sites of known age, should be conducted and results should be combined with existing organic matter degradation models in order to improve the prediction of sediment gas formation over time.