下辽河平原玉米农田水肥交互作用研究

利用持续16年的长期田间试验与气象观测资料，对下辽河平原不同降水年景作物对施肥的增产反应及水分对肥料增产的促进作用、不同水肥条件下玉米对养分的吸收与分配以及玉米农田土壤养分收支进行了研究；并估算了该地区水肥交互作用对作物增产的贡献；同时，利用沈阳地区近50年气象与玉米单产历史资料，建立趋势—随机预测模型，以预测该地区不同气候年景玉米产量。 研究结果表明，该地区玉米蒸散耗水与其生育期内降水之间关系密切，且不同的施肥处理对玉米消耗水分量影响不大。过少或过多的降水均会降低玉米产量；在高肥力水平下平水年（降水400～550mm）玉米产量最高，水肥交互作用对作物增产的贡献亦达最大，可占总增产量的44.9%。 玉米体内养分浓度及养分在籽实与秸秆中的分配比例明显受施肥、降水及作物生长状况的影响。在平水年条件下，养分在籽实内累积的比例最高；同时，作物生长状况愈好，形成单位籽实产量所需养分量有减少的趋势，有利于提高作物体内养分的转化利用效率。 施肥条件差异可使玉米收获移出农田的养分量相差2～3倍。水分条件对养分移出量的作用不如施肥明显；N肥施用加剧了土壤P的赤字，而N、P肥施用可加剧土壤K收支赤字；水分条件的改善也会明显加快养分收支赤字过程。 通过对沈阳地区玉米单产与气象因子的分析，建立趋势—随机预测模型，发现热量因素对玉米产量形成有着重要作用；而养分均衡供给可提高玉米对不利气象条件的耐抗能力，具有稳产作用；同时，利用长期定位试验结果对模型加以验证，发现模型预测结果与长期定位试验结果非常吻合。

下辽宁省河平原稻田生态系统的NH_3挥发和N淋溶

在地处下辽河平原的中国科学院沈阳生态实验站潮棕壤上布置施N量分别为180、240和300kg·hm~(-2)，施P量分别为70、100和130kg·hm~(-2)的稻田田间试验。应用通气密闭室法和陶土渗滤管法，测定了稻田生态系统三个不同施肥期施用氮肥后的NH3挥发损失和N淋溶，结果表明：1．水稻生长季节施用氮肥后有明显NH3挥发，总挥发量为11.64kgN·hm~(-2)-34.01kgN·hm~(-2)，占施N量的4.66％-11.66％，主要发生在施用分孽肥后，每次NH3挥发高峰出现在施氮肥后的2-4d内。2．水分渗漏对NH3挥发损失有重要影响。田面积水条件下，NH3挥发损失量及其占施N量的比率都较大，不同施N处理间差异显著（P＜0.05），NH3挥发量随施N量增加而增加；田面不积水条件下，NH3挥发损失挥发量相对较小。3．氮肥用量、田面水NH4斗一浓度和田面水pH是影响NH3挥发重要因素；180kgN·hm~(-2)条件下，积水时不同P处理间NH3挥发差异不显著。4．水稻生长季节各次施用氮肥后，60cm和gocm深处渗漏液中NH4+-N含量都小于2mg·L~(-1)，各施氮肥处理与对照间差异不显著。但NO3-淋溶比较显著，多集中在3mgN·ul-15mgN·L~(-1)之间。NO3-的淋溶随施N量增加而增加。水分渗漏状况影响N03一在不同土层深度的累积，渗水越快NO3-淋溶深度越大。渗水快或者施N量高时NO3，淋溶浓度高于国际饮用水卫生标准10mgN·L~(-1)，已有污染浅层地下水的可能。5．施用基肥后灌水，NH_4~+、NO_3~-立即出现淋溶高峰，而两次追施氮肥的淋溶高峰出现在施肥后10d或更久；并且基肥时期的淋溶浓度也比较高。

Communities of gastrointestinal helminths of fish in historically connected habitats: habitat fragmentation effect in a carnivorous catfish Pelteobagrus fulvidraco from seven lakes in flood plain of the Yangtze River, China

Background: Habitat fragmentation may result in the reduction of diversity of parasite communities by affecting population size and dispersal pattern of species. In the flood plain of the Yangtze River in China, many lakes, which were once connected with the river, have become isolated since the 1950s from the river by the construction of dams and sluices, with many larger lakes subdivided into smaller ones by road embankments. These artificial barriers have inevitably obstructed the migration of fish between the river and lakes and also among lakes. In this study, the gastrointestinal helminth communities were investigated in a carnivorous fish, the yellowhead catfish Pelteobagrus fulvidraco, from two connected and five isolated lakes in the flood plain in order to detect the effect of lake fragmentation on the parasite communities. Results: A total of 11 species of helminths were recorded in the stomach and intestine of P. fulvidraco from seven lakes, including two lakes connected with the Yangtze River, i.e. Poyang and Dongting lakes, and five isolated lakes, i.e. Honghu, Liangzi, Tangxun, Niushan and Baoan lakes. Mean helminth individuals and diversity of helminth communities in Honghu and Dongting lakes was lower than in the other five lakes. The nematode Procamallanus fulvidraconis was the dominant species of communities in all the seven lakes. No significant difference in the Shannon-Wiener index was detected between connected lakes (0.48) and isolated lakes (0.50). The similarity of helminth communities between Niushan and Baoan lakes was the highest (0.6708), and the lowest was between Tangxun and Dongting lakes (0.1807). The similarity was low between Dongting and the other lakes, and the similarity decreased with the geographic distance among these lakes. The helminth community in one connected lake, Poyang Lake was clustered with isolated lakes, but the community in Dongting Lake was separated in the tree. Conclusion: The similarity in the helminth communities of this fish in the flood-plain lakes may be attributed to the historical connection of these habitats and to the completion of the life-cycles of this fish as well as the helminth species within the investigated habitats. The diversity and the digenean majority in the helminth communities can be related to the diet of this fish, and to the lacustrine and macrophytic characters of the habitats. The lake isolation from the river had little detectable effect on the helminth communities of the catfish in flood-plain lakes of the Yangtze River. The low similarities in helminth communities between the Dongting Lake and others may just be a reflection of its unique water environment and anthropogenic alterations or fragmentation in this lake.

Occurrence of Bothriocephalus acheilognathi in cyprinid fish from three lakes in the flood plain of the Yangtze River, China

Cyprinid fish, Hemiculter leucisculus, Cultrichthys erythropterus and Culter dabryi, were sampled from Liangzi, Honghu and Tangxun lakes in the flood plain of the Yangtze River. The cestode Bothriocephalus acheilognathi Yamaguti, 1934 was found in the 3 lakes, but C. erythropterus sampled from Liangzi lake was found uninfected due probably to the small sample size. Findings of the cestode in the 3 lakes represent the first record of the parasite in the flood plain of the Yangtze River, indicating that B. acheilognathi may be distributed much wider in China than previously recognized.

Diversity of intestinal helminth communities of carp from six lakes in the flood plain of the Yangtze river, China

The infra- and component communities of intestinal helminths of carp Cyprinus carpio were investigated in six lakes in the flood plain of the lower and middle reaches of the Yangtze River, China. Eight species of helminth parasites were recorded. The intestinal helminth communities were species rich in Niushan and Tonghu lakes where the digenean Asymphylodora japonica was the dominant species, whereas in Qinggang and Yanglan lakes a species-poor helminth community had only one species, Khawia sinensis. The degree of similarity within localities was highest in Qinggang and Yanglan lakes, and was high between communities where K. sinensis was the dominant species. The rich composition of these helminth communities may be because China is the heartland for carp while the poor helminth composition of those in Qinggang and Yanglan lakes may reflect the poor fauna there. It is suggested that species compositions of intestinal helminth communities of carp may be diversified in lakes in the hood plain of the Yangtze River. (C) 1999 The Fisheries Society of the British Isles.

Food web of benthic macro invertebrates in a large Yangtze River-connected lake: the role of flood disturbance

This Study was conducted in Lake Dongtinghu, a large river-connected lake on the Yangtze River flood-plain, China. Our goal was to determine trophic relationships among benthic macroinvertebrates, as well as the effects of flood disturbance on the benthic food web of a river-connected lake. Macroinvertebrates in the lake fed mainly on detritus and plankton (both zooplankton and phytoplankton). Food web Structure in Lake Dongtinghu was characterized by molluscs as the dominant group, low connectance, high level of omnivory. based oil detritus and primary production, and most ingestion concentrating on a few links. Our analyses showed that flood disturbance is an important factor affecting the benthic food web in Lake Dongtinghu. The numbers of species and functional feeding groups (FFGs), and the density and biomass of macroinvertebrates decreased significantly during flooding. Connectance was higher during the flood season than in other seasons, indicating that floods have a strong effect on connectance in this Yangtze River-connected lake. Flood effects on the benthic web were also evident in the decrease of niche overlaps within and anion, FFGs. Our results provide useful information regarding biodiversity conservation on the Yangtze floodplain. Reconstructing and maintaining natural and regular flow regimes between Yangtze lakes and the river is essential for restoration of macroinvertebrates on the floodplain.

Flux and fate of Yangtze river sediment delivered to the East China Sea

Numerous cores and dating show the Yangtze River has accumulated about 1.16 x 10(12) t sediment in its delta plain and proximal subaqueous delta during Holocene. High-resolution seismic profiling and coring in the southern East China Sea during 2003 and 2004 cruises has revealed an elongated (similar to 800 km) distal subaqueous mud wedge extending from the Yangtze River mouth southward off the Zhejiang and Fujian coasts into the Taiwan Strait. Overlying what appears to be a transgressive sand layer, this distal clinoform thins offshore, from similar to 40 in thickness between the 20 and 30 m water depth to < 1-2 in between 60 and 90 m water depth, corresponding to an across shelf distance of less than 100 km. Total volume of this distal mud wedge is about 4.5 x 10(11) m(3), equivalent to similar to 5.4 x 10(11) t of sediment. Most of the sediment in this mud wedge comes from the Yangtze River, with some input presumably coming from local smaller rivers. Thus, the total Yangtze-derived sediments accumulated in its deltaic system and East China Sea inner shelf have amounted to about 1.7 x 10(12) t. Preliminary analyses suggest this longshore and across-shelf transported clinoform mainly formed in the past 7000 yrs after postglacial sea level reached its mid-Holocene highstand, and after re-intensification of the Chinese longshore current system. Sedimentation accumulation apparently increased around 2000 yrs BP, reflecting the evolution of the Yangtze estuary and increased land erosion due to human activities, such as fanning and deforestation. The southward-flowing China Coastal Current, the northward-flowing Taiwan Warm Current, and the Kuroshio Current appear to have played critical roles in transporting and trapping most of Yangtze-derived materials in the inner shelf, and hence preventing the sediment escape into the deep ocean. (c) 2006 Elsevier B.V. All rights reserved.

Influences of the Fish-Mouth Project and the Groins on the Flow and Sediment Ratio of the Yangtze River Waterway

A depth-integrated two-dimensional numerical model of current, salinity and sediment transport was proposed and calibrated by the observation data in the Yangtze River Estuary. It was then applied to investigate the flow and sediment ratio of the navigati

Two-Dimensional Flood Simulation of the Lower Yellow River from Huayuankou to Jiahetan

黄河下游花园口至夹河滩河段系典型的游荡型河段.在该河段,黄河大堤内范围宽广,一般洪水频率年份,水流主要限制在主槽内,因此大堤内分布有不少居民点以及纵横交错的保护居民点的生产堤和不少高于地面的灌溉渠堤和公路,使洪水行洪范围受到了很大的限制.当洪峰流量很大时,洪水将造成生产堤溃决,极大地危害滩区居民的生活.因此,设计模拟模型计算网格时需要考虑大堤、生产堤、明显高于地面的道路等阻水建筑物的影响,使这些堤及公路成为计算格网的边.不规则四边形网格能够很好地拟合黄河这种复杂的计算域.数值模拟时采用有限体积法,为确保通量的单向性,文中使用Osher格式计算通量.通过对1982年洪水的模拟,模拟结果表明了模型的合理性.

Case Study: Influence Of Morphological Changes On Flooding In Jingjiang River

The middle reach of the Yangtze River, customarily called the Jingjiang River, together with its diversion channels and Dongting Lake, form a large complicated drainage system. In the last five decades, significant geomorphological changes have occurred in the drainage system, including the shrinkage of diversion channels, contraction of Dongting Lake, changes in the rating curve at the Luoshan station, and cutoffs of the lower Jingjiang River. These changes are believed to be the cause of the occurrence of abnormal floods in the Jingjiang River. Qualitative analyses suggest that the first three factors aggravate the flood situation in the lower Jingjiang River, while the last factor seems beneficial for flood prevention. To quantitatively evaluate these conclusions, a finite-volume numerical model was constructed. A series of numerical simulations were carried out to test the individual and combined effects of the aforementioned four factors, and these simulations showed that high flood stages in the Jingjiang River clearly are related to the geomorphological changes.

On the contact width in generalized plain strain JKR model for isotropic solids

Adhesive contact model between an elastic cylinder and an elastic half space is studied in the present paper, in which an external pulling force is acted on the above cylinder with an arbitrary direction and the contact width is assumed to be asymmetric with respect to the structure. Solutions to the asymmetric model are obtained and the effect of the asymmetric contact width on the whole pulling process is mainly discussed. It is found that the smaller the absolute value of Dundurs' parameter beta or the larger the pulling angle theta, the more reasonable the symmetric model would be to approximate the asymmetric one.