Evaluating the influence of forest roads on shallow landsliding

This study investigates how subsurface flowpaths are altered by forest roads and how these changes influence shallow landsliding susceptibility in steep, forested landscape. A simple conceptual model of the effect of forest roads on hillslope subsurface flow is developed. The model is incorporated into a hydro-geomechanical, threshold-based model for slope instability. In the model, the occurrence of shallow landsliding is evaluated in terms of drainage areas, ground slope and soil properties (i.e., hydraulic conductivity, bulk density, and friction angle). Model results allow to quantify the influence of roads on shallow landsliding hazard across a landscape and to generate hypotheses about the broader geomorphic effect of roads.Modelling results are compared with field data collected in four sites located in north-eastern Italy. Observed landslide patterns are broadly consistent with model estimates, a finding that underscores the utility of this simple approach for predicting the geomorphic effects of forest roads constructed on steep slopes. The approach used in this study may be useful for defining criteria for road design that reduce the effects of roads on geomorphic processes.     

雷州桉树人工林小集水区地形分析与静态水文学模拟

利用小集水区生态水文学模型-Topog模型对雷州半岛桉树人工林纪家示范小集水区进行了地形分析和静态水文学模拟。地形分析表明，该集水区地表较为平坦，集水区总面积为0．63km^2，夏季、冬季与春（秋）分平均太阳辐射值分别为44MJ.m^-2．d^-1、25MJ.m^-2．d^-1和34MJ.m^-2．d^-1。在考虑太阳辐射影响与不考虑太阳辐影响两种情况下进行了集水区土壤含水量指数（WI）静态模拟。设定不同的静态壤中流参数值，Topog模型模拟结果表明，静态壤中流越大，在集水区内高WI的分布范围越大，也即土壤含水量越高。在考虑太阳辐射影响的条件下，分别设置不同的土壤导水率（T）、地表阴蔽系数（Es）、平均降雨最（R）进行了模拟。模拟结果表明，WI分布依各参数的不同而变化。T越大，在集水区内的WI重新分布越快；T越小，在集水区内WI趋向于平均分布。Es越大，集水区土壤所保持的含水量越高。集水区WI随R增大而有升高趋势。     

SWAT parameterization for the identification of critical diffuse pollution source areas under data limitations

For lowering sediment, nitrogen (N) and phosphorus (P) pollution of surface water bodies at the catchment scale, environmental legislation require programs of pollution abatement measures. To be able to ensure the cost-effectiveness of such programs we first need to identify high risk areas, which give rise to increased pollutant runoff. Process-based GIS models provide the opportunity to identify such critical areas and hence better target diffuse pollution abatement actions. However, these models are data intensive and their spatially-distributed parameterization in poorly monitored catchments is not feasible without extensive input data pre-processing and significant simplifying assumptions. This study implements the widely-used SWAT river basin model (Soil Water Assessment Tool) to study a medium-sized Greek catchment with the typical data limitations met at the national level, in order to identify critical diffuse pollution source areas that may serve as the key areas for meeting the objective of ‘good ecological status’ of water bodies set by the European Water Framework Directive (WFD). Model parameterization and evaluation are presented along with the decisions made to overcome problems related to data representation in the catchment, in an effort to provide guidance on SWAT modeling in areas with similar characteristics. The results show that sediments and nutrients could be adequately reproduced in large time steps (monthly or seasonal) and that even with the current data limitations, the seasonal variation and the most critical areas of pollutant losses to waters could be adequately identified. The study proposes a transparent modeling approach under data limitations without neglecting possible deficiencies; however, it maintains that the SWAT model, if appropriately parameterized with respect to the land-use and soil differentiation within a limited-gauged catchment, can still facilitate the selection and placement of suitable practices across the landscape for a cost-effective diffused pollution management.     

Comparison of a simple and a spatially distributed hydrologic model for the simulation of a lowland catchment in Northern Germany

This paper describes the application of two simple models for runoff simulation of the Kielstau, a small wetland catchment in Northern Germany. The first one is SIMPEL, a one-dimensional spreadsheet model for soil water balance and runoff for small catchments; the second one is KIDS, Kielstau discharge simulation model, which is written in the PCRaster dynamic modelling language. KIDS uses the algorithms of SIMPEL, but applies them to a spatial database.The basic version of both models fails to reproduce the measured hydrograph for a flat region in Northern Germany with ca. 30% wetlands. Additionally, the water balance of the region cannot be closed, the relative discharge is lower than in the neighbouring catchments which means that ET must be higher. After the creation of an additional wetland compartment module where ETa equals ETp, the hydrographs could be matched. In a second step, we used inverse modelling with the SIMPEL model to evaluate the range of input parameters and possible sources of the low outflow of the catchment. We found that the low discharge can only be modelled if the evaporation is increased substantially. A wetland fraction of 0.3 produced the best results in inverse modelling runs, this value was also estimated based on the available maps.     

密云县密云水库流域坡耕地养分流失特征

于2005年和2006年连续2 a对密云水库流域坡耕地进行水土流失小区试验,并完全按照当地农民习惯进行农事管理.试验结果表明:(1)降雨后坡耕地产生的地表径流量、泥沙量随坡度增大而增加,并与坡度正弦值呈一定的线性关系;(2)坡度对雨后地表径流和泥沙中养分含量影响不明显,但对泥沙养分流失量有明显影响;(3)养分流失以泥沙携带为主要途径,且通过泥沙携带途径流失的养分量占流失养分总量的比例随坡度增加而增加;(4)水库周边区域内坡耕地流失养分的主要来源为施用于坡耕地的化学肥料.(5)调整水库流域内坡耕地的种植结构、对坡耕地实施改造以截留或减少泥沙流失和控制化学肥料投入等措施对于治理流域内农业非点源污染、保护水源地水质显得尤为迫切.     

基于水土流失的景观格局分析方法

景观格局和生态过程是景观生态学研究的重要内容,但是很多研究只重视景观格局的研究,而忽略了生态过程的研究。文章针对水土流失这一重要生态过程,提出了基于水土流失过程的景观坡度指数和景观空间负荷对比指数,并对黄土高原泾河流域15个子流域的景观格局进行了分析,认为泾河流北部各子流域主要以水土流失的＂源＂景观为主,景观坡度指数大,空间负荷指数小,水土流失风险大;流域南部各子流域上游以＂汇＂景观为主,坡度指数大,中下游以＂源＂景观为主,景观空间分布不均衡,存在一定的水土流失风险;流域东部局部子流域主要以水土流失的＂汇＂景观为主,＂源＂景观相对较小,＂源＂-＂汇＂景观空间分布均衡,水土流失风险小。     

Modelling the effects of land-use modifications to control nutrient loads from an agricultural catchment in Western Australia

The estuary of the Swan and Canning Rivers in Western Australia is becoming increasingly prone to algal blooms, fish deaths and other biochemical problems that are thought to be associated with increasing eutrophication. Phosphorus and nitrogen enrichment are seen as the two most common causes of such eutrophication, with both elements being transported in streamflow and with concentrations strongly dependent upon land-use in the catchment. Many of the efforts to prevent and control eutrophication in the estuary are focused on managing land-use within the catchment. In this paper, the large-scale catchment model (LASCAM) is applied to Ellen Brook, a rural catchment located within the Swan River catchment, to simulate catchment exports of phosphorus and nitrogen, under a range of land cover scenarios that are designed to control the eutrophication. The scenarios, which are related to different management options for the catchment, are: (i) reforestation of agricultural land; (ii) reduction in fertiliser application; and (iii) urbanisation following a highway development. The model results show that: (i) full reforestation of agricultural land is expected to reduce phosphorus and nitrogen export by 50 and 85%, respectively; (ii) a proportionally greater reduction of phosphorus and nitrogen export occurs for smaller areas of reforestation than for larger areas; (iii) reduction in phosphorus fertiliser application produces a linear response with respect to phosphorus export; (iv) urbanisation increases runoff due to the larger impermeable areas causing an increase of overland flow during storms; and (v) phosphorus and nitrogen loads are expected to increase about 4 and 12%, respectively, during the 10 years following urbanisation.     

Integrated effects of slope aspect and land use on soil nutrients in a small catchment in a hilly loess area,China

This study addressed the integrated effect of slope aspect and land use on soil nutrients in a loess hilly catchment in the western Loess Plateau of China. Soil samples were collected from five land-use types: wasteland, cropland, woodland, shrubland and abandoned cropland, at two depths (0–20 and 20–40 cm) in the middle slope position of both north-facing and south-facing slopes. Soil nutrient changes and the relationships between soil nutrients and slope aspect were investigated, based on statistical analysis and expert knowledge. Soil organic matter, total N, total P, nitrate nitrogen and available K of the 0–20 cm soil layer differed significantly between land uses and slope aspects. Soil nutrients in the north-facing slope were better than in the south-facing slope. Revegetation has an enrichment effect, especially on soil organic matter, total N, total P, nitrate nitrogen and available K. Planting of trees, shrubs and grasses could improve soil fertility and favours a policy of revegetation and sustainable land use in the hilly loess area of China. Conversion of slope farmlands into more sustainable land uses, such as shrubland or grassland is a cost-efficient way to achieve soil conservation and ecological restoration. Terracing and the use of agro-techniques for soil conservation, such as furrow-ridging tillage and leaving crop residues on fields, can increase the input of C to soils. Growing crops in rotation with alfalfa and beans could be a promising choice for the sustainability of agriculture and the environment.     

上海城市降水径流营养盐氮负荷及空间分布

在野外采样和室内化学分析的基础上，研究了上海市区，郊区各不同功能区内降水径流中营养元素氮的含量水平及其空间分布差异，研究结果表明，城市降水径流中营养元素氮具有较高的含量水平，其中TIN，NH4－N，NO3－N的均值含量分别为7．45，3．14，2．98和1．33mg/L，与同期河流水体中氮含量相比，降水径流中营养元素氮对河流水中氮含量水平具有重要的贡献，反映城市降水径流是一种不容忽略的非点污染源，从城市降水径流中营养元素氮负荷的空间分布来看，在工业区，交通要道，氮含量普遍偏高，而在居民居住区和商业区，氮含量普遍较低，此外，市区和郊区相比，在市区内氮含量普遍比郊区高。     

Application of a water quality model in the White Cart water catchment,Glasgow, UK

Water quality models of urban systems have previously focused on point source (sewerage system) inputs. Little attention has been given to diffuse inputs and research into diffuse pollution has been largely confined to agriculture sources. This paper reports on new research that is aimed at integrating diffuse inputs into an urban water quality model. An integrated model is introduced that is made up of four modules: hydrology, contaminant point sources, nutrient cycling and leaching. The hydrology module, T & T consists of a TOPMODEL (a TOPography-based hydrological MODEL), which simulates runoff from pervious areas and a two-tank model, which simulates runoff from impervious urban areas. Linked into the two-tank model, the contaminant point source module simulates the overflow from the sewerage system in heavy rain. The widely known SOILN (SOIL Nitrate model) is the basis of nitrogen cycle module. Finally, the leaching module consists of two functions: the production function and the transfer function. The production function is based on SLIM (Solute Leaching Intermediate Model) while the transfer function is based on the flushing hypothesis which postulates a relationship between contaminant concentrations in the receiving water course and the extent to which the catchment is saturated. This paper outlines the modelling methodology and the model structures that have been developed. An application of this model in the White Cart catchment (Glasgow) is also included.     

Hierarchical regulation of nitrogen export from urban catchments: interactions of storms and landscapes.

In urban catchments of arid central Arizona, we investigate how the export of mineral and organic nitrogen (N) in storm runoff is regulated by interactions between local landscape characteristics and broader scale storm features. First, we test whether N export is more a function of (1) processes that affect N concentration in runoff or (2) the propensity of the catchment to convey rainfall as runoff. With data pooled across catchments, the mass of N in export (load) is determined by processes regulating runoff N concentration. There are exceptions when catchments are examined individually, where N load from some catchments is determined by the hydrologic responsiveness of the catchment. Second, we investigate the relationship between N export and catchment features. Loads per catchment area were greater from more impervious catchments, probably because impervious catchments held more N in a mobilizable phase and conveyed more rainfall as overland flow. Loads per area were lower from larger catchments, possibly owing to more N-retention hot spots in larger catchments. Catchments with the greatest N exports were those with commercial land use, and loads decreased as development became less prevalent or as residential replaced industrial land use. Third, we investigated how catchment features moderated direct responses of N export to storms. Export was less correlated with storm features in catchments that were larger, more pervious, and less industrial. Results support an "N build and flush" hypothesis, which purports that there is little biotic processing of N deposited to arid, urban surfaces with little organic matter. The rate and duration of deposition determine the size of the mobile N pool. Any amount of rainfall capable of generating overland flow would entrain nearly all mobilizable N and export it from the catchment. Nonetheless, these results suggest that, even with daunting seasonal and interannual variability in storm conditions, material export can be reduced by managing intrinsic catchment features.     

A model of rainfall redistribution in terraced sandy grassland landscapes

A simple model of rainfall redistribution within a terraced sandy grassland landscape has been developed. The model assumes that rainfall redistribution is driven by rainfall impulses and is controlled by characteristic field capacity of soils. When the rainfall intensity is large enough to render soil water content greater than its characteristic field capacity, the excessive soil water can drain very quickly by means of large amounts of non-capillary pores of sandy soils or by means of surface runoff. Exponential distribution of rainfall impulses was assumed and tested with measured daily rainfall at two meteorological stations in the sandy grassland area of north China. The model was solved to give the equivalent rainfall at each terrace in the landscape.     

Pollution of River Mahaweli and farmlands under irrigation by cadmium from agricultural inputs leading to a chronic renal failure epidemic among farmers in NCP, Sri Lanka

Chronic renal failure (CRF) associated with elevated dietary cadmium (Cd) among farming communities in the irrigated agricultural area under the River Mahaweli diversion scheme has reached a significantly higher level of 9,000 patients. Cadmium, derived from contaminated phosphate fertilizer, in irrigation water finds its way into reservoirs, and finally to food, causing chronic renal failure among consumers. Water samples of River Mahaweli and its tributaries in the upper catchment were analyzed to assess the total cadmium contamination of river water and the possible source of cadmium. Except a single tributary (Ulapane Stream, 3.9?μg?Cd/l), all other tested tributaries carried more than 5?μg?Cd/l, the maximum concentration level accepted to be safe in drinking water. Seven medium-sized streams carrying surface runoff from tea estates had 5.1-10?μg?Cd/l. Twenty larger tributaries (Oya), where the catchment is under vegetable and home garden cultivation, carried 10.1-15?μg?Cd/l. Nine other major tributaries had extremely high levels of Cd, reaching 20?μg?Cd/l. Using geographic information system (GIS), the area in the catchment of each tributary was studied. The specific cropping system in each watershed was determined. The total cadmium loading from each crop area was estimated using the rates and types of phosphate fertilizer used by the respective farmers and the amount of cadmium contained in each type of fertilizer used. Eppawala rock phosphate (ERP), which is mostly used in tea estates, caused least pollution. The amount of cadmium in tributaries had a significant positive correlation with the cadmium loading of the cropping system. Dimbula Tea Estate Stream had the lowest Cd loading (495.9?g/ha/year), compared with vegetable-growing areas in Uma Oya catchment with 50,852.5?g?Cd/ha/year. Kendall's τ rank correlation value of total Cd loading from the catchment by phosphate fertilizer used in all crops in the catchment to the Cd content in the tributaries was +0.48. This indicated a major contribution by the cropping system in the upper catchment area of River Mahaweli to the eventual Cd pollution of river water. Low soil pH (4.5-5.2), higher organic matter content (2-3%), and 18-20?cmol/kg cation exchange capacity (CEC) in upcountry soil have a cumulative effect in the easy release of Cd from soil with the heavy surface runoff in the upcountry wet zone. In view of the existing water conveyance system from upcountry to reservoirs in North Central Province (NCP) through diversion of River Mahaweli, in addition to their own nonpoint pollution by triple superphosphate fertilizer (TSP), this demands a change in overall upper catchment management to minimize Cd pollution through agriculture inputs to prevent CRF due to elevated dietary cadmium among NCP farmers.     

A review of source tracking techniques for fine sediment within a catchment

Excessive transport of fine sediment, and its associated pollutants, can cause detrimental impacts in aquatic environments. It is therefore important to perform accurate sediment source apportionment to identify hot spots of soil erosion. Various tracers have been adopted, often in combination, to identify sediment source type and its spatial origin; these include fallout radionuclides, geochemical tracers, mineral magnetic properties and bulk and compound-specific stable isotopes. In this review, the applicability of these techniques to particular settings and their advantages and limitations are reviewed. By synthesizing existing approaches, that make use of multiple tracers in combination with measured changes of channel geomorphological attributes, an integrated analysis of tracer profiles in deposited sediments in lakes and reservoirs can be made. Through a multi-scale approach for fine sediment tracking, temporal changes in soil erosion and sediment load can be reconstructed and the consequences of changing catchment practices evaluated. We recommend that long-term, as well as short-term, monitoring of riverine fine sediment and corresponding surface and subsurface sources at nested sites within a catchment are essential. Such monitoring will inform the development and validation of models for predicting dynamics of fine sediment transport as a function of hydro-climatic and geomorphological controls. We highlight that the need for monitoring is particularly important for hilly catchments with complex and changing land use. We recommend that research should be prioritized for sloping farmland-dominated catchments.     

风沙土不同有机组分对氨氮的解吸特征影响

采用平衡解吸法研究了风沙土不同有机组分对氨氮的解吸特征影响。结果表明,去除腐殖质后的风沙土氨氮解吸比例增加（由0.58增加到0.68）,同时,解吸迟滞性指数显著降低（由0.067降低到0.021）,说明腐殖质是影响风沙土氨氮解吸特征的重要因素;氨氮在轻组有机组分上的表面分配作用吸附是导致解吸比例增大,解吸迟滞性指数减小的原因;重组有机组分中的紧结态腐殖质（胡敏素）对氨氮的解吸起关键作用,它不但解吸比例较低（Dr=0.23）,而且解吸迟滞性指数较大（TⅡ=0.458）;氨氮在紧结态和稳结态腐殖质所形成的团聚体颗粒微孔隙中的不可逆吸附是导致解吸比例降低、解吸迟滞性指数增大的根本原因;考查土壤对氨氮的解吸特征不但要考虑有机质的含量,更要考虑有机质的存在形态,它也是影响土壤氨氮解吸特征的重要因素,轻组有机组分、重组有机组分及重组有机组分中的稳结态加紧结态腐殖质（HⅡ＋HⅢ组）和紧结态腐殖质（HⅢ组）携载的吸附态氨氮进入水体后,对上覆水体的扩散通量可分别按其饱和吸附量的0.94、0.58、0.33和0.23倍估算。     

尾巨桉人工林小流域降水产流特征分析

研究尾巨桉(E.urophylla×E.grandis)生长阶段(林龄3.5—5.5 a)所处小流域的降水产流特征,有助于了解桉树生长过程的生态水文效应,对修订桉树人工林经营方案中注重提高生态系统的水源涵养能力有重要参考意义。以广西南宁桉树森林生态系统定位观测研究站(南宁桉树生态站)的闭合尾巨桉林小流域为试验区,在小流域出水口建设1个测流堰,在测流堰附属房的测定池安放1个自动水位计,定位观测小流域2013年5月—2015年4月的地表径流,使用生态站的自动气象观测系统观测降水量和土壤体积含水量,建立降水、土壤含水量和径流的函数关系,分析土壤前期含水量对径流形成和持续的影响。小流域年均降水量1300 mm,以小雨为主,两个年度小雨共计191场,占降水强度等级总场数74%;降水年内分布不均,雨季集中在季夏,占全年降水量的60%以上,冬季降水最少,属于干旱季节;降水产流现象在降水集中的月份才可能出现,2013年5月—2014年4月的径流深为81 mm,径流系数6%,2014年5月—2015年4月的径流深只有9 mm,径流系数仅为0.7%;径流初始时间明显滞后于降水初始,滞后时间与前期土壤含水量密切相关;径流递增率与降水历时呈线性函数关系,径流递减率与径流消退时间呈对数函数关系;降水产流过程经历径流递增期、稳定期和递减期3个阶段。     

环太湖丘陵地区农田氮素随地表径流输出特征

对环太湖丘陵地区农田氮素随地表径流的输出特征进行了研究,结果表明,地表径流中TN浓度随径流量而变化,浓度峰值出现时间滞后于径流量峰值;径流发生前期,NH3 N和NO-3 N浓度水平相当,后期NO-3 N浓度缓慢抬升,而NH3 N含量缓慢下降;NO-2 N浓度相对较低,随时间快速下降;对于TN和NO-3 N而言,溶解态含量高于悬浮态,而溶解态和悬浮态NH3 N的浓度相当;无机氮平均浓度高于有机氮,有机氮尤其是悬浮态有机氮浓度表现出随径流量而变化的特点。     

皖南低山丘陵地区流域氮磷径流输出特征

通过对安徽南部宣城地区梅村小流域的定位监测,研究了该小流域地表径流中氮磷输出特征。结果表明:氮输出以NO-3N为主,占氮素输出总量的60%,磷输出以悬浮颗粒结合态磷(PAP)为主,占磷输出总量的92%;各类形态氮素输出量间存在极显著线性正相关关系;PAP随悬浮颗粒输出量的增加而增加,PAP与水溶性磷(DP)输出量间存在着极显著的对数关系;氮磷输出具有明显的季节性变化规律,夏季输出量最大,其次是春季,再次是秋季,冬季最少,这是由降雨量的季节性变化所引起的。而且暴雨对氮磷输出的贡献率极大,因此控制雨季土壤侵蚀是有效控制氮磷通过径流输出的最重要方式。     

喀斯特小流域复杂景观中水质状况

以红枫湖流域周边一个受人为活动严重影响的农田源头溪流-王家寨小流域为研究对象,设置11个监测点研究硝酸盐（NO3-N）、氨态氮（NH4＋-N）、溶解性无机磷（PO4--P）、总磷（TP）和总悬浮物（TSS）在复杂景观中的变化状况。降雨后采样水中氮、磷含量明显低于雨后的地表积水,地表积水受各种影响,水质降低。水塘型湿地,其丰水期的PO43--P、TP、SS高于枯水期,与水循环条件较好的流水溪流还是存在明显的区别。从平均值来看,枯水期地表水和地下水TP都超过5级水质标准。水质与＂源＂景观的关系不明显,说明喀斯特小流域中复杂的景观结构对氮磷的截留作用。     

白盆珠水库库区坡面径流侵蚀规律初步研究

在对白盆珠水库库区开展水土流失实地调查的基础上,选择库区典型的侵蚀地貌类型与植被类型进行降雨-径流-产沙规律的初步研究.通过6个径流小区试验对比,分析了在不同植被条件下产流、产沙的差异,结果表明缺乏地表草本植被的纯飞播造林的水土保持效益十分有限;库区降雨径流产沙是白盆珠水库淤积的重要来源.