A simple approach to soil loss prediction: a revised Morgan–Morgan–Finney model

A revised version of the Morgan–Morgan–Finney model for prediction of annual soil loss by water is presented. Changes have been made to the way soil particle detachment by raindrop impact is simulated, which now takes account of plant canopy height and leaf drainage, and a component has been added for soil particle detachment by flow. When tested against the same data set used to validate the original version at the erosion plot scale, predictions made with the revised model gave slopes of a reduced major-axis regression line closer to 1.0 when compared with measured values. The coefficient of efficiency, for sites with measured runoff and soil loss, increased from 0.54 to 0.65. When applied to a new data set for erosion plots in Denmark, Spain, Greece and Nepal, very high coefficients of efficiency of 0.94 for runoff and 0.84 for soil loss were obtained. The revised version was applied to two small catchments by dividing them into land elements and routing annual runoff and sediment production over the land surface from one element to another. The results indicate that, when used in this way, the model provides useful information on the source areas of sediment, sediment delivery to streams and annual sediment yield.     

河漫滩沉积物中磷素沉积的研究进展

河流沉积物可以携带营养元素并沉积在河漫滩上:概述了沉积物在河漫滩上的沉积率、与之相伴随的磷素在河漫滩上的沉积、磷素在河漫滩上的存在形态及其对水体质量的影响。     

土壤和沉积物中烃类污染物的主要来源与识别标志

土壤、沉积物中烃类污染物的来源十分复杂,其输入方式主要包括矿物油直接输入、大气颗粒物沉降、通过水介质输入、工业固体废弃物、城市垃圾和生活废弃物排放及天然有机质生物化学降解产物等。不同来源的烃类污染物组成上存在一定的差别,可根据这些差别判识环境中烃类污染物的来源。介绍了不同污染源的烃类污染物中正构烷烃、类异戊间二烯烷烃、单甲基取代支链烷烃、烷基环己烷、甾萜烷烃及芳香烃类化合物的组成与分布特征,综合评述了不同污染源的分子标志物特征及主要识别标志。     

Multi-parameter fingerprinting of sediment deposition in a small gullied catchment in SE Australia

The determination of relative contributions of potential sediment sources is an important step in the development of management strategies to combat soil erosion. In a 1.2 km² gullied catchment in southeastern New South Wales, multi-parameter fingerprinting of sediment deposited in successive downstream pools has identified gully walls as the dominant sediment source when the grazed pasture surface was the only other potential source. The median fractional contributions remained relatively steady in the successive downstream pools, with the gully walls responsible for between 90% and 98% of the pool sediment. This result was achieved despite the ratio of the source areas varying considerably between successive nested subareas. Reliability bounds on the predictions, accounting for limited sampling of sources, were well constrained and varied between 5.4% and 13.8%. Downstream of an unsealed road crossing, sediment from the road source dominated the pool sediments such that contributions from the pasture surface and gully sources could not be determined.     

典型因素对泥沙特性影响的试验研究

泥沙颗粒在不同的浓度、颗粒大小以及絮凝剂的影响下,其絮凝结构以及沉降速度存在一定的差异,这些差异性对于研究泥沙特性来说具有重要的意义.为了直观演示其差异性,自行设计了试验,采用控制变量的方法,分为5组对比试验.结果表明,上述3种因素对其絮凝结构以及沉降速度有显著影响.     

Estimate of sediment yield in a basin without sediment data

In this study, three mathematical models for the estimate of sediment yield, due to soil and stream erosion, at the outlet of a basin are presented. Each model consists of three submodels: a rainfall-runoff submodel, a soil erosion submodel and a sediment transport submodel for streams. The rainfall-runoff and the stream sediment transport submodels are identical in the three mathematical models. The rainfall-runoff submodel that is used for the computation of the runoff in a sub-basin is a simplified water balance model for the soil root zone. For the estimate of soil erosion in a sub-basin, three different submodels are used alternatively, owing to the fact that erosion or sediment yield data are not available. The soil erosion submodels are (a) a modified form of the classical Universal Soil Loss Equation (USLE, [Foster, G.R., Meyer, L.D., Onstad, C.A., 1977. A runoff erosivity factor and variable slope length exponents for soil loss estimates. Transactions of the ASAE, 20 (4), 683–687]) taking into account both the rainfall erosion and the runoff erosion, (b) the relationships of Poesen [Poesen, J., 1985. An improved splash transport model. Zeitschrift für Geomorphologie, 29, 193–211] quantifying the splash detachment, as well as the upslope and downslope splash transport, (c) the relationships of Schmidt [Schmidt, J., 1992. Predicting the sediment yield from agricultural land using a new soil erosion model. Proceedings of the 5th International Symposium on River Sedimentation. Karlsruhe, Germany, pp. 1045–1051] including the momentum flux exerted by the droplets and the momentum flux exerted by the runoff. The sediment transport submodel for streams aims to estimate the sediment yield at the outlet of a sub-basin. This quantity results by comparing the available sediment amount in the main stream of a sub-basin with the sediment transport capacity by stream flow, which is computed by the relationships of Yang and Stall [Yang, C.T., Stall, J.B., 1976. Applicability of unit stream power equation. Journal of the Hydraulics Division, ASCE, 102, 559–568]. The mathematical models were applied to the basin of Kompsatos River, in northeastern Greece, with an area of about 565 km². The whole basin was divided into 18 natural sub-basins for more precise calculations. Monthly rainfall data were available for 27 years (1966–1992); therefore, the calculations were performed on a monthly basis. The deviation between the three mean annual values of sediment yield at the basin outlet, for 27 years, resulting from the three mathematical models is relatively small.     

滇池沉积物铵态氮的时空变化特征研究

沉积物在湖泊氮、磷循环和水体富营养化过程中起着重要作用。本研究应用GPS定位技术,于2003年5月至2004年5月,对滇池海埂、斗南、罗家村、新街、昆阳等5个代表性样点沉积物铵态氮含量进行为期1 a的动态监测,全面分析了滇池不同区域、不同层次、不同时期沉积物铵态氮的动态变化特征。结果表明,滇池沉积物铵态氮平均含量为74.57 mg kg-1,全湖沉积物铵态氮平均含量年变化范围是45.55~170.1mg kg-1。沉积物铵态氮因季节变化其变化幅度很大,各区域沉积物铵态氮含量总体趋势夏季高、冬季低,但不同位点变化高峰和趋势不同。不同层次沉积物铵态氮含量变化随季节而变化,夏季为表层(0~5 cm)中层(5~10 cm)底层(10~20 cm),冬季为中层表层和底层。表层、中层、底层沉积物铵态氮含量的变化范围分别为18.71~172.9mg kg-1、29.55~192.2mg kg-1、19.93~123.8mg kg-1。各区域沉积物铵态氮平均含量以罗家村最高,斗南最低。沉积物铵态氮与水体铵态氮、水体pH呈显著正相关,与沉积物有效磷呈显著负相关,暗示了沉积物铵态氮是水体氮的源和库,并影响着沉积物中磷的释放。     

鲁中山区小流域坡面土壤侵蚀产流、产沙及侵蚀方式变化过程的研究

采用模拟降雨的方法对鲁中山区坡面土壤降雨条件下产流、产沙和侵蚀方式的演变过程进行了研究,结果表明:产流量都是随时间递增最终达到稳定产流,但是各次降雨达到稳定产流的时间均随降雨强度和坡度的增大而递减。相同坡度条件下120mmh-1雨强产流较60mmh-1雨强先到稳态,而相同雨强条件下10°坡面则较5°坡面先达到稳态。产沙量呈递增趋势且逐渐达到稳定产沙,达到稳定产沙的时间随雨强和坡度的增大而递减。相同坡度条件下120mmh-1雨强处理较60mmh-1雨强处理先达到稳态,相同雨强条件下10°坡面比5°坡面产沙过程先达到稳定产沙状态;在降雨过程中坡面首先产生面蚀,后出现细沟侵蚀;面蚀率随降雨历时延长有减小趋势,但变幅较小,细沟侵蚀率随降雨时间先急剧增加后保持稳定。     

Coarse bed material patch evolution in low-order,ephemeral channels

In river channel beds composed of a wide range of grain sizes, the bed material is often arranged in discrete patches discernable by relative texture. These bed material patches are the primary source of entrainable coarse sediment within the channel system and their composition and size have been found to influence the composition and rate of sediment transport. Twelve coarse (gravel–cobble) sediment patches distributed throughout the channel network within a 4.53 ha watershed in southeastern Arizona were monitored for 2 years. Changes in patch area and grain size were measured and painted patch grains were monitored to confirm that patch grains were mobilized during flow. Individual coarse bed material patches exhibited variable persistence during flows with return frequencies ranging from approximately 1 year to 4.6 years. While no patch fully dispersed during the study period, two new patches formed. Most coarse patches remained relatively stable in area and grain-size distribution despite the entrainment of patch grains as lost grains were sufficiently replaced with sediment from upstream. Because of the grain replacement process and the effect of other sediment supply dynamics, the changes in patch area and grain-size distribution display a complex relationship with the magnitude of predicted grain mobilization within each patch. Results indicate that relative stability varies from patch to patch, influenced by the balance of patch grains transported out of the patch and the deposition of new grains into the patch. Predictive models of coarse sediment transport and yield that assume the channel bed is a fixed source of sediment supply may not adequately capture the sediment dynamics within patchy channel beds and should be used with caution when applied to these environments due to the possibility of patch instability as documented in this study.     

东苕溪中下游沉积物重金属污染特征与评价

于2009年10月和2010年5月在东苕溪中下游河段采集沉积物样品34个,测定了沉积物中As、Cd、Cr、Cu、Hg、Ni、Pb和Zn的含量,并用地积累指数法对沉积物中重金属污染进行评价分析。结果表明,Hg和Ni含量属于国家一级土壤标准;Cr、Cu、Pb、Zn含量基本属于国家一级至二级土壤标准;2009年As含量属于国家一级至二级土壤标准,2010年As含量属于国家二级至三级土壤标准;Cd污染最严重,属于国家三级土壤标准。采用地积累指数法对东苕溪中下游沉积物中重金属的污染状况进行评价,结果显示,Cd污染最严重,As次之,Cr污染最轻;东苕溪中下游河段76.5%的样品重金属浓度具有增大的趋势。