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1.
Land surface evapotranspiration (ET) plays an important role in energy and water balances. ET can significantly affect the runoff yield of a basin and the available water resources in mountainous areas. The existing models to estimate ET are typically applicable to plains, and excessive data are required to calculate the surface fluxes accurately. This study established a simple and practical model capable of depicting the surface fluxes, while using relatively less parameters. Considering the complex terrain, solar radiation was corrected by importing a series of topographic factors. The water deficit index, a measure of land surface wetness, was calculated by applying the fc (vegetation fractional cover)‐Trad (land surface temperature) framework in the two‐source trapezoid model for evapotranspiration model to mountainous areas after corrections of temperature based on altitude variations. The model was successfully applied to the Kaidu River Basin, a basin with few gauges located in the east Tien Shan Mountains of China. Based on the time scale extensions, ET was analyzed at different time scales from 2000 to 2013. The results demonstrated that the corrected solar radiation and water deficit index were reasonably distributed in space and that this model is applicable to ungauged catchments, such as the Kaidu River Basin.  相似文献   

2.
Lake‐water quality is highly dependent on the landscape characteristics in its respective watershed. In this study, we investigated the relationships between lake‐water quality and landscape composition and configuration within the watershed in the Yangtze River basin of China. Water quality variables, including pH, electrical conductivity (EC), dissolved oxygen (DO), Secchi depth (SD), NO2?, NO3?, NH4+, TN, TP, chemical oxygen demand (CODMn), chlorophyll‐a (Chl‐a), and trophic state index (TSI), were collected from 16 lakes during the period of 2001–2003. Landscape composition (i.e. the percentage of vegetation, agriculture, water, urban, and bare land) and landscape configuration metrics, including number of patches (NP), patch density (PD), largest patch index (LPI), edge density (ED), mean patch area (MPA), mean shape index (MSI), contagion (CONTAG), patch cohesion index (COHESION), Shannon's diversity index (SHDI), and aggregation index (AI), were calculated for each lake's watershed. Results revealed that the percentage of agriculture was negatively related to NO2?, TN, TP, Chl‐a concentrations, and TSI, while the percentage of urban was significantly correlated with EC, NH4+, and CODMn concentrations. Among landscape‐level configuration metrics, only ED showed significant relationships with TN, TP concentrations, and TSI. However, at the class level, the PD, LPI, ED, and AI of agriculture and urban land uses were significantly correlated with two or more water quality variables. This study suggests that, for a given total area, large and clustered agricultural or urban patches in the watershed may have a greater impact on lake‐water quality than small and scattered ones. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

3.
Groundwater is a very significant water source used for irrigation and drinking purposes in the karst region, and therefore understanding the hydrogeochemistry of karst water is extremely important. Surface water and groundwater were collected, and major chemical compositions and environmental isotopes in the water were measured in order to reveal the geochemical processes affecting water quality in the Gaoping karst basin, southwest China. Dominated by Ca2+, Mg2+, HCO3? and SO42?, the groundwater is typically characterized by Ca? Mg? HCO3 type in a shallow aquifer, and Ca? Mg? SO4 type in a deeper aquifer. Dissolution of dolomite aquifer with gypsiferous rocks and dedolomitization in karst aquifers are important processes for chemical compositions of water in the study basin, and produce water with increased Mg2+, Ca2+ and SO42? concentrations, and also increased TDS in surface water and groundwater. Mg2+/Ca2+ molar ratios in groundwater decrease slightly due to dedolomitization, while the mixing of discharge of groundwater with high Mg2+/Ca2+ ratios may be responsible for Mg2+/Ca2+ ratios obviously increasing in surface water, and Mg2+/Ca2+ ratios in both surface water and groundwater finally tending to a constant. In combination with environmental isotopic analyses, the major mechanism responsible for the water chemistry and its geochemical evolution in the study basin can be revealed as being mainly from the water–rock interaction in karst aquifers, the agricultural irrigation and its infiltration, the mixing of surface water and groundwater and the water movement along faults and joints in the karst basin. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

4.
Abstract

Changes in development and use of water resources over the last 30 years have led to significant environmental and hydrological degradation of the River Heihe basin in the People's Republic of China. Water discharge of the lower reaches has been seriously compromised and more than 30 tributaries and terminal lakes have dried up. The water output of springs has dropped significantly. Also water quality problems have been observed, in both surface waters and groundwater. Hydrological changes have resulted in a marked degradation of aquatic habitats, and have caused substantial, and expanding, land salinization and desertification. Solving these problems, which have been largely caused by human activities, requires massive and long-lasting concerted efforts.  相似文献   

5.
Natural ecosystems in the region of the lower Tarim River in northwestern China strongly deteriorated since the 1950s due to an expanding desertification. As a result, the downstream Tarim River reaches became permanently dry land. This historical evolution in land‐use change is typically the result of the anthropogenic impact on natural ecosystems. On the basis of a spatially distributed hydrological catchment model bidirectionally linked with a fully hydrodynamic MIKE11 river model, land‐use changes characterized by historical changes in leaf area index (LAI) of vegetation, as well as the evolution of irrigated surface areas, can be causally related to changes in water resources (groundwater storage and surface water resources). An increased surface area of irrigated (agricultural) land, together with a majority of inefficient irrigation methods, did lead to a strong increase of water resources consumption of the farmlands located in the upper Tarim River area. Evidently, this evolution influenced available water resources downstream in the Tarim basin. As a result, farmland has been gradually relocated to the upstream regions. This has led to reduced flows from the upper Tarim stream, which subsequently accelerated the dropping of the groundwater level downstream in the basin. This study moreover demonstrates that land surface biomass changes (cumulative LAI) along the lower Tarim River are strongly related to the changes in groundwater storage. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

6.
土地利用结构与景观格局对鄱阳湖流域赣江水质的影响   总被引：4，自引：0，他引：4  
徐启渝  王鹏  王涛  舒旺  张华  齐述华 《湖泊科学》2020,32(4):1008-1019
于2015年1月和7月采集赣江干流及支流34个采样点水样,测定电导率、水化学离子、无机氮等水质指标.利用赣江流域2014年30 m分辨率的土地利用数据,以流域景观类型占比表征土地利用结构,景观指数表征景观格局;采用Pearson相关分析、Bioenv分析、Mantle检验与方差分解等方法分析流域土地利用结构与景观格局对赣江水质的影响.结果表明:上游Cl~-、Na~+浓度最高,中游电导率、Cl~-、Na~+、K~+、Ca~(2+)等水质指标最低,下游电导率、HCO_3~-、SO_4~(2-)、Mg~(2+)、Ca~(2+)、NO_3~--N等水质指标最高.居民建设用地是对水质影响最显著的单一土地利用类型.林地、水田与居民建设用地是对水质影响最显著的土地利用类型组合.平均最近邻体指数是对水质影响最显著的单一景观指数,斑块个数、斑块聚集度指数、平均最近邻体指数是对水质影响最显著的景观指数组合.枯水期土地利用结构和景观格局对水质的贡献率分别为41.1%和17.2%,景观格局对水质的贡献率(17.2%)均为和土地利用结构的交互作用,无独立贡献部分;丰水期二者对水质贡献率分别为51%、53%,交互作用部分为37%.以上结果表明,土地利用结构与景观格局都对赣江水质有较大影响,二者的交互作用在该影响中占有重要地位,且枯水期景观格局对水质的影响涵盖在与土地利用结构的交互作用中.  相似文献   

7.
Tropical rivers display profound temporal and spatial heterogeneity in terms of environmental conditions. This aspect needs to be considered when designing a monitoring program for water quality in rivers. Therefore, the physico-chemical composition and the nutrient loading of the Upper Mara River and its two main tributaries, the Amala and Nyangores were monitored. Initial daily, and later a weekly monitoring schedule for 4 months spanning through the wet and dry seasons was adopted. Benthic macro-invertebrates were also collected during the initial sampling to be used as indicators of water quality. The aim of the current study was to investigate the physico-chemical status and biological integrity of the Upper Mara River basin. This was achieved by examining trends in nutrient concentrations and analyzing the structure, diversity and abundance of benthic macro-invertebrates in relation to varying land use patterns. Sampling sites were selected based on catchment land use and the level of human disturbance, and using historical records of previous water quality studies. River water pH, dissolved oxygen, electrical conductivity (EC), temperature, and turbidity were determined in situ. All investigated parameters except iron and manganese had concentration values within allowable limits according to Kenyan and international standards for drinking water. The Amala tributary is more mineralized and also shows higher levels of pH and EC than water from the Nyangores tributary. The latter, however, has a higher variability in both the total phosphorus (TP) and total nitrogen (TN) concentrations. The variability in TP and TN concentrations increases downstream for both tributaries and is more pronounced for TN than for TP. Macro-invertebrate assemblages responded to the changes in land use and water quality in terms of community composition and diversity. The study recommends detailed continuous monitoring of the water quality at shorter time intervals and to identify key macro-invertebrate taxa that can be used to monitor changes of the water quality in rivers of the Mara basin as a result of anthropogenic changes.  相似文献   

8.
The influence of land use patterns on water quality in a river system is scale‐dependent. In this study, a four‐order hierarchical arrangement method was used to select water sampling sites and to delineate sub‐basins in the Daliao River Basin, China. The 20 sub‐basins were classified into four spatial scales that represented four different stream orders. Pearson correlation analysis was used to quantify relationships between land use composition and the river's physical‐chemical variables for all samples collected. This analysis showed that the presence of forest cover was associated with higher water quality at the scale of the whole basin. The scale effects of land use patterns on water quality were then examined using stepwise multiple regression analysis that compared different land use types with water quality variables. The results from this analysis showed that urban areas, as opposed to forest areas, became the most significant contributors of water pollutants when scale effects were considered. The influence of urban land cover on water pollution was significantly higher at larger scales. The lack of a significant regression correlation for the forest land use type at smaller scales revealed that forest located upstream of the Daliao River Basin did not provide a buffer for improved water quality. Further analysis showed that this result could be because of disproportionate spatial distributions for forest and urban land use types. The topographic characteristics of sub‐basins, such as average slope (S) and size (A), were determined to be secondary explanatory variables that affected land use impacts on stream water quality. Areas with steep slopes were associated with increased water oxygenation, whereas areas with flatter slopes were associated with higher concentrations of pollutants. These results are significant because they can provide a better understanding of the appropriate spatial scale required for effective river basin management in the future. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

9.
Jun Xiao  Fei Zhang  Zhangdong Jin 《水文研究》2016,30(25):4855-4869
Hydrochemistry methods were used to decipher the weathering and geochemical processes controlling solute acquisition of river waters in the dry season in the middle Loess Plateau (MLP), one of the most severely eroded areas and turbid riverine systems in the world. River waters were neutral to slightly alkaline with pH varying from 7.6 to 9.6. The total dissolved solids decreased from northwest to southeast with a mean value of 804 mg/l, much higher than the global average and other large rivers in China. Ternary diagram showed that river waters were dominated by Na+, HCO3?, and Cl? with the main water‐type of HCO3?–Cl?–Na+. Saturation index values, Mg2+, Ca2+, and HCO3? analyses indicated the preferential Ca2+ removal by calcite precipitation. Gibbs plots and stoichiometry plots indicated that the dissolved solutes were mainly derived from rock weathering with minor anthropogenic and atmospheric inputs. Samples in the northwestern basin are also influenced by evaporation. A forward model of mass budget calculation showed that, owing to high soluble characteristics, evaporite dissolution was a major feature of river waters and contributed 41% to the total dissolved cations on average, while carbonate and silicate weathering contributed 28%,and 25% on average, respectively. Besides evaporite dissolution, cation exchange is also responsible for the high concentrations of Na+ in river water. Spatial variations showed that evaporite dissolution and silicate weathering were higher in the northern basin, whereas carbonate weathering was higher in the southern basin. Different from most rivers in the world, the physical erosion rates (varying from 117.7 to 4116.6 t/km2y) are much higher than the chemical weathering rates (varying from 3.54 to 6.76 t/km2y) in the MLP because of the loose structure of loess and poor vegetation in the basin. In the future, studies on comparison of water geochemistry in different seasons and on influence of different types of land use and soil salinization on water geochemistry, denudation rates, and water quality should be strengthened in the MLP. These results shed some lights on processes responsible for modern loess weathering and also indicate the importance of time‐series sampling strategy for river water chemistry. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

10.
Abstract

Water resources management should cover both blue water and green water. For green-water management at the river drainage basin scale, the green-water coefficient (C gw) is adopted, defined as the ratio of annual green water to annual precipitation. Based on data from the Middle Yellow River basin, China, for the period 1950 to 2007, we studied the temporal variation in C gw in response to some influencing factors. A decreasing trend in C gw was found. The influence of changes in land management on C gw, reflected by an increase in the area (A sw) of soil and water conservation measures, is emphasized. Using multiple regression analysis, the contributions of A sw and the 5-year moving averages of annual precipitation and air temperature were estimated as 51, 37 and 12%, respectively. The results may provide useful information for better management of water resources, including green and blue water flows in the Yellow River basin.

Editor Z.W. Kundzewicz; Associate editor D. Gerten

Citation Xu, J.-X., 2013. Effects of climate and land-use change on green-water variations in the Middle Yellow River, China. Hydrological Sciences Journal, 58 (1), 1–12.  相似文献   

11.
郑达燕  刘睿  张柳柳  郑财贵  张静 《湖泊科学》2023,35(4):1343-1358
三峡库区拥有目前世界上规模最大的水利枢纽工程,自投入使用以来,为长江流域提供了丰富的水源及电力,促进了经济的发展,但同时也对该区域的生态环境造成了严重的冲击。澎溪河流域作为三峡库区长江流域干流的典型回水区和消落带,是众多学者研究三峡库区生态环境变化的重点区域。为探究不同时空尺度下土地利用对河流溶解性有机质（DOM）的影响,以澎溪河流域为研究对象,基于紫外-可见光谱分析和三维荧光光谱矩阵-平行因子分析,结合河段缓冲区、河岸带缓冲区及子流域3种空间尺度的二级土地利用类型,解析了旱雨季水体DOM的组成及来源特征,并采用相关分析和冗余分析方法探讨了3种空间尺度下土地利用方式对旱雨季水体DOM的多时空尺度影响。结果表明：（1）旱季水体DOM荧光组分以陆源类腐殖质所占比例更大,雨季水体DOM荧光组分以富里酸贡献为主。（2）流域内陆源输入和内源产生对水体DOM丰度均有贡献,雨季较旱季水体DOM的陆源性更强,自生源特征较弱。（3）土地利用在雨季和子流域尺度下对水体DOM的影响更显著,其中,雨季子流域尺度下,土地利用指数对水体DOM参数的解释率为90.35%。（4）不同土地利用方式对水体DOM产生的影响...  相似文献   

12.
土地利用/覆被变化对明晰气候变化和人类活动对湖泊水环境的影响有重要作用.以北方典型农牧交错的岱海流域为研究对象,基于遥感解译技术、马尔可夫转移矩阵、综合污染指数法等方法,对2000-2018年岱海流域土地利用/覆被和湖泊水质的变化进行分析,并结合冗余分析法和计量分析模型探究长时间序列尺度下土地利用/覆被变化对湖泊水质的影响.结果表明:近20年来,岱海流域的土地利用/覆被类型以耕地和草地为主,其变化特征主要是草地和林地转化为耕地,水域转化为季节性河流,岱海转化为内陆滩涂、沼泽草地和灌丛沼泽;岱海湖泊水质因子高锰酸盐指数、五日生化需氧量、总磷和总氮浓度存在不同程度的超标现象;岱海、湿地、林地对水质具有积极的改善作用,耕地、草地、建设用地是加剧水质污染的主要原因.该研究为岱海湖泊流域土地资源合理利用、湖泊水质改善和生态保护提供了一定的科学理论依据.  相似文献   

13.
To identify the groundwater flow system in the North China Plain, the chemical and stable isotopes of the groundwater and surface water were analysed along the Chaobai River and Yongding River basin. According to the field survey, the study area in the North China Plain was classified hydrogeologically into three parts: mountain, piedmont alluvial fan and lowland areas. The change of electrical conductance and pH values coincided with groundwater flow from mountain to lowland areas. The following groundwater types are recognized: Ca? HCO3 and Ca? Mg? HCO3 in mountain areas, Ca? Mg? HCO3 and Na? K? HCO3 in piedmont alluvial fan areas, and HCO3? Na in lowland areas. The stable isotope distribution of groundwater in the study area also has a good corresponding relation with other chemical characteristics. Stable isotope signatures reveal a major recharge from precipitation and surface water in the mountain areas. Chemical and stable isotope analysis data suggest that mountain and piedmont alluvial fan areas were the major recharge zones and the lowland areas belong to the main discharge zone. Precipitation and surface water were the major sources for groundwater in the North China Plain. Stable isotopic enrichment of groundwater near the dam area in front of the piedmont alluvial fan areas shows that the dam water infiltrated to the ground after evaporation. As a result, from the stable isotope analysis, isotope value of groundwater tends to deplete from sea level (horizontal ground surface) to both top of the mountain and the bottom of the lowland areas in symmetrically. This suggests that groundwater in the study area is controlled by the altitude effect. Shallow groundwater in the study area belongs to the local flow system and deep groundwater part of the regional flow system. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

14.
In this paper, general relationships of riverine bicarbonate concentrations and fluxes as a function of drainage basin mineral content and runoff are examined using a database of the 25 largest rivers in the world. Specific HCO3− flux normalized to unit basin area, which peaks in the mid latitudes, was found to be strongly correlated with the carbonate mineral content of river basins, while river HCO3− concentration was related to the balance of precipitation and evaporation. Within this global context, the weathering patterns of CO2 in a few large rivers (Changjiang, Huanghe, Pearl, and Mississippi rivers) were examined in further detail. The Zhujiang (Pearl River), especially its largest branch (Xijiang), was characterized by the highest specific weathering rate among all the world's large rivers due to an exceptionally high carbonate mineral content (over 80%) in its drainage basin and its warm and wet environment. It has a moderate level of HCO3− concentration, however, due to dilution by relatively high precipitation in the watershed. In stark contrast, the Huanghe (Yellow River) has one of the lowest specific weathering rates because of low carbonate mineral content and a dry climate. However, it has a high HCO3− concentration due largely to the concentrating effects of high evaporative water loss, as a result of arid weather and the agricultural use of water through irrigation systems, as well as carbonate-containing surficial deposits (i.e., loess). The strong correlation between specific HCO3− fluxes and discharge in all four rivers with different discharge seasonality suggests that higher precipitation in drainage basins promotes higher weathering rates.  相似文献   

15.
The assessment of surface water resources (SWRs) in the semi‐arid Yongding River Basin is vital as the basin has been in a continuous state of serious water shortage over the last 20 years. In this study, the first version of the geomorphology‐based hydrological model (GBHM) has been applied to the basin over a long period of time (1956–2000) as part of an SWR assessment. This was done by simulating the natural hydrological processes in the basin. The model was first evaluated at 18 stream gauges during the period from 1990 to 1992 to evaluate both the daily streamflows and the annual SWRs using the land use data for 1990. The model was further validated in 2000 with the annual SWRs at seven major stream gauges. Second, the verified model was used in a 45‐year simulation to estimate the annual SWRs for the basin from 1956 to 2000 using the 1990 land use data. An empirical correlation between the annual precipitation and the annual SWRs was developed for the basin. Spatial distribution of the long‐term mean runoff coefficients for all 177 sub‐basins was also achieved. Third, an additional 10‐year (1991–2000) simulation was performed with the 2000 land use data to investigate the impact of land use changes from 1990 to 2000 on the long‐term annual SWRs. The results suggest that the 10‐year land use changes have led to a decrease of 8·3 × 107 m3 (7·9% of total) for the 10‐year mean annual SWRs in the simulation. To our knowledge, this work is the first attempt to assess the long‐term SWRs and the impact of land use change in the semi‐arid Yongding River Basin using a semi‐distributed hillslope hydrological model. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

16.
Chahardouly basin is located in the western part of Iran and is characterized by semi‐arid climatic conditions and scarcity in water resources. The main aquifer systems are developed within alluvial deposits. The availability of groundwater is rather erratic owing to the occurrence of hard rock formation and a saline zone in some parts of the area. The aquifer systems of the area show signs of depletion, which have taken place in recent years due to a decline in water levels. Groundwater samples collected from shallow and deep wells were analysed to examine the quality characteristics of groundwater. The major ion chemistry of groundwater is dominated by Ca2+ and HCO3?, while higher values of total dissolved solids (TDS) in groundwater are associated with high concentrations of all major ions. An increase in salinity is recorded in the down‐gradient part of the basin. The occurrence of saline groundwater, as witnessed by the high electrical conductivity (EC), may be attributed to the long residence time of water and the dissolution of minerals, as well as evaporation of rainfall and irrigation return flow. Based on SAR values and sodium content (%Na), salinity appears to be responsible for the poor groundwater quality, rendering most of the samples not suitable for irrigation use. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

17.
It is important to understand the link between land surface/soil properties and shallow groundwater quality. To that end, soil properties and near‐water‐table groundwater chemistry of a shallow, unconfined aquifer were measured on a 100‐m grid on a 64‐ha irrigated field in southeastern North Dakota. Soil properties and hydrochemistry were compared via multivariate analysis that included product‐moment correlations and factor analysis/principal component analysis. Topographic low areas where the water table was in close proximity to the soil surface generally had higher apparent electrical conductivity (ECa) and higher percent silt and clay than higher positions on the landscape. The majority of the groundwater was characterized by Ca‐ and Mg‐HCO3 type water and was associated with topographic high areas with lower ECa and net groundwater recharge. Small topographic depressions were areas of higher ECa (net groundwater discharge) where salts that precipitated via evapotranspiration and evaporative discharge dissolved and leached to the groundwater during short‐term depression‐focused recharge events. At this site, groundwater quality and soil ECa were related to surface topography. High‐resolution topography and ECa measurements are necessary to characterize the land surface/soil properties and surficial groundwater quality at the field‐scale and to delineate areas where the shallow groundwater is most susceptible to contamination.  相似文献   

18.
Groundwater is an important source of freshwater for domestic, agricultural and industrial uses in Iran. Groundwater quality assessment and environmental evaluation are considered as critical issues in recent years. Intensive human activities have resulted in significant changes in environment leading to serious groundwater contamination. This research proposes a two-part systematic approach to tackle heavy metals contamination problem in Rayen Basin (southeast Iran). The first part consists of determining geochemical characteristics and evaluating groundwater quality through application of water quality index and heavy metal pollution indices (i.e. HPI and MI). The second part includes ranking sampling stations based on heavy metals concentration in groundwater using linear assignment method. Six types of water could be identified according to the dominant cations and anions in samples: Ca–HCO3, Ca–SO4, Na–Cl, Na–HCO3, Na–SO4 and mixed water type. Calculation of indices revealed that natural and anthropogenic activities are playing a vital role in degrading groundwater quality in the study area. The proposed methodology can help in groundwater resource management and preventative activities by identifying risk factors and recognizing their pollution level. The results of this research provide useful and effective information for water pollution control and management and can be used in environmental studies in order to protect groundwater resources in the future.  相似文献   

19.
《水文科学杂志》2013,58(1):124-134
Abstract

The three-route South-to-North Water Diversion Project (SNWDP), transferring water from the water-rich Yangtze River and its tributaries to the much drier area of North China for irrigation, industrial and domestic use, has been implemented in China since 2002. Thus, water quality in the Danjiangkou Reservoir, the water source area of the SNWDP's Middle Route, is of great concern. We investigate its water quality from 2004 to 2006 by monitoring some important physical (T, turbidity and SPM) and chemical (DO, pH, alkalinity, TDS, SpCond, ORP, CODMn and BOD) parameters and nutrient (nitrogen and phosphorus) contents. Consequently, their spatial and temporal patterns in the reservoir were examined. The results indicate that the water of the reservoir is of a Ca and HCO3 type, and the major pollutants are nitrogen and CODMn. Comparisons among the sampling sites show that water quality increases downstream, implying the self-purification capacity of the reservoir. The reservoir in general has better water quality in the dry season than in the wet season. Integrated basin management would be critical of the water quality in the Danjingkou Reservoir for the interbasin water transfer project.  相似文献   

20.
An Erratum has been published for this article in Hydrological Processes 16(5) 2002, 1130–1131. Humid tropical regions are often characterized by extreme variability of fluvial processes. The Rio Terraba drains the largest river basin, covering 4767 km2, in Costa Rica. Mean annual rainfall is 3139±419sd mm and mean annual discharge is 2168±492sd mm (1971–88). Loss of forest cover, high rainfall erosivity and geomorphologic instability all have led to considerable degradation of soil and water resources at local to basin scales. Parametric and non‐parametric statistical methods were used to estimate sediment yields. In the Terraba basin, sediment yields per unit area increase from the headwaters to the basin mouth, and the trend is generally robust towards choice of methods (parametric and LOESS) used. This is in contrast to a general view that deposition typically exceeds sediment delivery with increase in basin size. The specific sediment yield increases from 112±11·4sd t km?2 year?1 (at 317·9 km2 on a major headwater tributary) to 404±141·7sd t km?2 year?1 (at 4766·7 km2) at the basin mouth (1971–92). The analyses of relationships between sediment yields and basin parameters for the Terraba sub‐basins and for a total of 29 basins all over Costa Rica indicate a strong land use effect related to intensive agriculture besides hydro‐climatology. The best explanation for the observed pattern in the Terraba basin is a combined spatial pattern of land use and rainfall erosivity. These were integrated in a soil erosion index that is related to the observed patterns of sediment yield. Estimated sediment delivery ratios increase with basin area. Intensive agriculture in lower‐lying alluvial fans exposed to highly erosive rainfall contributes a large part of the sediment load. The higher elevation regions, although steep in slope, largely remain under forest, pasture, or tree‐crops. High rainfall erosivity (>7400 MJ mm ha?1 h?1 year ?1) is associated with land uses that provide inadequate soil protection. It is also associated with steep, unstable slopes near the basin mouth. Improvements in land use and soil management in the lower‐lying regions exposed to highly erosive rainfall are recommended, and are especially important to basins in which sediment delivery ratio increases downstream with increasing basin area. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

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