红壤有机碳流失特征及其与泥沙径流流失量的定量关系

通过野外微型径流小区模拟降雨试验,对坡面小区尺度水力侵蚀过程中物理运移土壤有机碳的规律进行研究。结果表明:2 m×5 m径流小区持续降雨30 min后,大雨强(1.64 mm min-1)和小雨强(0.58 mm min-1)降雨条件下泥沙携带流失的有机碳总量分别为56.09 g和3.18 g,溶解于径流流失的有机碳总量分别为13.55 g和2.81 g。降雨强度和持续时间对有机碳流失的过程特征有显著影响。降雨强度越大,泥沙携带及溶解于径流的有机碳流失速率和总量也越大。大雨强泥沙有机碳富集比在产流发生后的18min内大于1,随后降至1以下。小雨强泥沙有机碳富集比始终小于1。大雨强径流有机碳浓度与径流量呈立方关系,小雨强有机碳流失量随径流量增加呈线性递增趋势;大雨强泥沙有机碳含量与泥沙量之间具有明显的立方关系。     

Population size in stream-living juveniles of lake-migratory brown trout Salmo trutta L.: the importance of stream discharge and temperature

Abstract –  Based on the analysis of 17 successive year-classes, this investigation attempted to identify the factors determining year-to-year variation in population size of the stream-living juveniles of Lake Hald-dwelling brown trout Salmo trutta L. Population size appeared to be influenced chiefly by annual recruitment that in turn, was determined by stream discharge and temperature. These patterns matched those previously highlighted for a resident population located >2500 km apart and emphasised the importance of environmental (climatic) variability as a major regulating agent of population size in stream brown trout. However, distinctly shaped recruitment–discharge relationships between the two populations suggested different mechanisms in response to environmental variability and thus to persist in time.     

Accumulation, organic carbon and dry matter concentration of sediment in commercial channel catfish ponds

Sediment depth and organic carbon (OC) concentration were measured in sediment cores (n=675) collected from 45 commercial channel catfish ponds in northwest Mississippi from April to September in 1998 and 1999. Ponds had been in continuous catfish production from 14 days to 21 years. Sediment depth ranged from 1 to 95 cm and was heterogeneously distributed within ponds: least in the shallow end (26.3 cm) and greatest in deeper areas (33.7 cm). Mean sediment depth increased with pond age, although the rate of sediment accumulation was greatest in the first year (12.5 cm per year). Organic carbon concentration varied slightly within ponds ranging from 0.76 to 3.43% of dry matter (DM). Mean organic carbon concentration in the upper 2 cm of sediment (1.77%) was significantly greater than in the deeper sediment layer (1.55%). Mean dry matter content in the upper 2 cm of sediment averaged 24.2% of total wet weight. Mean dry matter for the lower sediment fraction was 37.8% of total wet weight. Despite large inputs of organic matter from feed and primary production, sediment organic carbon concentrations did not increase with pond age.     

Quantifying the contributions of sediment, sediment-P and fertiliser-P from forested, cultivated and pasture areas at the landuse and catchment scale using fallout radionuclides and geochemistry

In this paper we use a combination of fallout nuclides and geochemistry to determine the contributions of sediment and sediment bound phosphorus (sed-P) from the major diffuse sources in the Bundella Creek catchment (8700 ha), NSW, Australia. Sources include surface erosion from cultivated, pasture and steep forested land as well as subsoil erosion from channels and gullies. We determine these contributions to the <10 μm fraction of deposited sediments. Concentrations of P were higher in the surface soils of each landuse than the underlying subsoils, and erosion from these contributed more to offsite sediment-P (60%) than did subsoil erosion at the individual landuse scale. At the catchment outlet, the amount of surface sediment eroded from cultivated lands was a factor of 84 higher than from pastures; the steep forested lands contributed 9 times more than pastures. Sed-P eroded from cultivated land was 42 times higher than from pasturelands; the forests were 8 times greater than from pastures. At the catchment outlet the largest contribution of sediment (70%) and sed-P (62%) was from subsoil erosion of gullies and channels within and between the different landuse areas. There was little contribution of sediment or sed-P at the catchment scale from surface erosion of pastures. Concentrations of P were highest in ‘storm event’ suspended sediment samples taken from the pasture and cultivated areas without gullies. In a suite of samples selected for their high P contents, fertiliser P was detected in two storm event suspended sediment samples and one deposited sediment sample, using the ratio of Nd/P. This suggests fertiliser P may be transported-off landsurfaces with sediments and contribute to offsite sediment-P concentrations in some situations. However, the fertiliser contributions were episodic and variable; and probably influenced by particle size selectivity as well as timing of fertiliser application with respect to size and occurrence of subsequent rainfall.     

动力换档离合器充/放油特性仿真研究

为研究动力换档离合器换档过程中的充油和放油特性，基于动力换档离合器的工作原理，建立了动力换档离合器充油和放油两个过程的动态特性数学模型。应用动态仿真软件，将充/放油过程的动态特性以统一的仿真模型描述。通过仿真得到了对动力换档离合器充/放油过程的动态特性影响最大的离合器结构参数是充油油道直径。摩擦片间隙（离合器活塞行程）主要影响充/放油时间，而卸压孔直径的影响程度随着其值的增加而加大。在进行离合器设计、液压系统设计以及电控系统设计时，必须充分考虑油液温度的影响。试验结果验证了仿真方法及仿真模型的正确性和有效性。     

黄土丘陵区植被恢复与流域养分环境演变研究进展

针对在陕北黄土丘陵沟壑区实施的植被恢复及不同土地利用类型调整的政策,在小区和流域尺度上,就植被恢复对流域水土流失、养分流失、养分循环平衡影响方面的国内外研究概况进行了综述。指出植被恢复可减少流域水土流失和养分流失,使流域养分循环平衡能力加强、向良性循环方向发展,同时指出了在这方面需进一步研究的问题。     

Reservoirs' siltation measurments and sediment transport assessment in the Czech Republic, the Vrchlice catchment study

Sediment transport from agricultural land into rivers and reservoirs is a problem within the Czech Republic. This problem was highly accelerated almost 50 years ago during the communist period. At that time strong collectivization was undertaken leading to destruction of traditional landscape patterns, surface outflow, erosion processes intensification and surface water quality deterioration. Thirteen years after political changes erosion problems remain.At the Department of Irrigation, Drainage and Landscape Engineering at the CTU Prague there has been continuous research undertaken in the field of erosion and sediment transport assessment. There are several modelling tools available for this purpose. One of them—USLE (Universal Soil Loss Equation) is commonly used in the Czech Republic for many years at a plot-scale but modern GIS (geographical information systems) tools in computer science allow using it at larger scales. Very important is the validation of this model for two-dimensional topography and GIS routines. Moreover USLE produces only local erosion amount values and has to be completed by another tool to get sediment amounts. For this purpose SDR (sediment delivery ratio) is usually used, applying a lumped approach—total erosion of every watershed is reduced by SDR and by pond’s trapping efficiency. Another available approach is using the Watem/SEDEM model that puts together RUSLE (Revised USLE) and a distributive approach to sediment transport modelling. This has already been used for estimating sediment amount in several catchments of the Czech Republic, but has to be validated as well.At the Dept. of Drainage, Irrigation and Landscape Engineering there are datasets of sediment amount from different reservoirs available and other reservoirs are to be measured soon. As the dataset of various watersheds is expanded, a methodology for sediment amount measurements is needed. The main objective of this paper is to propose a simple methodology to measure the sediment amount within reservoirs as well as to present a review of available methods. The application of the methodology at Vrchlice Catchments (97 km²) case study is presented. Total sediment amounts between 125 000140 000 m³ were measured in Vrchlice reservoir and values of 110 976 m³ (using USLE), resp. 105833 m³ (using Watem/SEDEM) were predicted by the erosion models. For catchments of this scale it is a sufficient validation.     

Analysis of gully dimensions and sediment texture from southeast Australia for catchment sediment budgeting

Catchment scale sediment budgeting models are increasingly being used to target remediation works aimed at controlling erosion and improving water quality. Gully erosion is often a major sediment source and needs to be accounted for in such models in a manner consistent with the scale of analysis and available data. Using 130 measurements of gully cross-sectional area and 45 measurements of gully wall sediment texture, the variability in gully dimensions and particle size distribution for the Lake Burragorang catchment in Australia is examined. The distribution of gully cross-sectional area measurements is log-normally distributed and modelling indicates a representative value of 23 m² be used in catchment sediment budgeting applications. The proportion of gully eroded sediment contributing to the bedload budget (defined as particles > 63 μm diameter) of a river link is approximately half, though may be higher in igneous landscapes. A continental scale spatially distributed subsoil texture dataset provided limited capacity to predict the finer scale spatial variation in the proportion of sediment contributing to bedload from gully erosion within the Lake Burragorang catchment.     

Are rare species rare or just overlooked? Assessing the distribution of the freshwater bryozoan, Lophopus crystallinus

Given the widespread degradation of freshwater habitats, assessing the distributions of species that may be negatively or positively impacted should be of general interest. However, determining distributions of freshwater organisms that are small and patchily distributed and attached or sedentary is particularly problematic, as it is time consuming, inaccurate, and nearly impossible when the focal species is rare. Here we illustrate the use of indirect sampling approaches to survey the distribution of the rare freshwater bryozoan Lophopus crystallinus, a priority species in the UK Biodiversity Action Plan [Anonymous, 1999. UK Biodiversity Group Tranche 2 Action Plans. Invertebrates, vol. 4. Environment Agency, Peterborough, pp. 437-439.]. By utilising two complementary methods for sampling bryozoan propagules (statoblasts), namely the collection of debris samples and sediment cores, we achieved an efficient and integrative sampling of habitats across spatial and temporal scales. Analysis of 154 debris samples, encompassing 62 rivers and lakes, identified at least 16 new populations while analysis of 26 sediment cores provided evidence of current or very recent (in the last 10-20 years) occurrence in a further six localities. These results represent a more than 10-fold increase in the current recorded distribution of the species in the UK. Logistic regression analysis provided evidence that L. crystallinus is generally found in lowland sites and is tolerant of eutrophication. Our study exemplifies how integrative and indirect sampling approaches can greatly aid in assessing the conservation status of rare aquatic species and reveals, in this case, that the focal species is less rare than previously appreciated.     

BMBF Coordinated Research Project SEDYMO (2002-2006) - Sediment Dynamics and Pollutant Mobility in River Basins

-  DOI: http://dx.doi.org/10.1065/jss2005.08.002 Background and Scope   Characteristic dynamic features of sediment-related processes in rivers include (i) dramatic effects of stormwater events on particle transport, (ii) rapid and far-reaching effects of sulfide oxidation during resuspension, and (iii) biological accumulation and potential release of toxic chemicals. Pollutant mobility is the net result from stabilizing and mobilizing effects in both hydraulic and chemical fields. In practice, emphasis has to be given to fine-grained sediments and suspended matter, since these materials exhibit large surface areas and high sorption capacities. Discussion   Organic materials are highly reactive. Degradation of organic matter will induce depletion of oxygen and may enhance formation of flocs and biofilms. Study of variations of sediment and water chemistry should predominantly include changes of pH and redox conditions, competition of dissolved ions and processes such as complexation by organic substances. All these processes will influence solution/solid equilibrium conditions and have to be studied prior to modeling the overall effects of pollutants on the water body and aquatic ecosystems. Conclusion   The cooperative program SEDYMO ('Fine Sediment Dynamics on Pollutant Mobility in Rivers') is funded by the German Federal Ministry of Education and Research (BMBF) since May 2002. It comprises 13 research projects and its interdisciplinary approach focuses on the release of DOC, nutrients and pollutants into the open water due to hydrodynamic processes in rivers and estuaries. Three themes are studied: 'experimental techniques', 'processes and properties', 'development/validation of models'.