Identifying key environmental factors influencing spatial variation of water quality in upper Shitoukoumen Reservoir Basin in Jilin Province, China

Based on the observed data in monitored drainage areas and GIS spatial analysis tools, watershed basic database of Shitoukoumen Reservoir Basin was built. The multivariate analysis and redundancy analysis (RDA) were used to analyze the spatial and temporal variations of water quality, identify the key environmental factors and their patterns influencing the spatial variation of water quality, and determine the main types and forms of the non-point source (NPS) pollutant export controlled by the key environmental factors. The results show that different patterns of environmental factors lead to great changes in water quality at spatial and seasonal scales. All selected environmental factors explain 64.5% and 68.2% of the spatial variation of water quality over dry season and rainy season, respectively, which shows clear seasonal difference. Over dry season, residential land is the most important environmental factor, which possesses 35.4% of the spatial variation, and drainage area is the second key environmental factor, which possesses 17.0% of spatial variation in the total variance. Over rainy season, slope length and drainage area are the key environmental factors, which possess 29.3% of the spatial variation together. Residential land influences nitrogen export by changing NH₄ ⁺-N and particulate organic nitrogen (PON) discharge over dry season, and drainage area controls phosphorus export by regulating dissolved phosphorus (DP) drainage over dry season and phosphorus associated particulate (PAP) loss over rainy season, respectively. Although slope length is an important environmental factor, it does not influence NPS pollutant export. It is interesting that soil organic matter, as a minor environmental factor, highly determines phosphorus and nitrogen export by enhancing the DP, PAP and PON loss.     

融合土地覆盖和土壤水分产品的近地表空气温度空间化方法

空气温度是评价人居环境的重要指标,与人类的生产生活息息相关;其观测对于水文、环境、生态和气候变化等方面的研究具有重要意义。传统的大范围空气温度观测数据一般通过气象站点获取,但由于气象观测站点空间分布离散稀疏的特点,所获取的数据不能精确描述空间连续的空气温度变化情况。因此,实现基于遥感数据的近地表空气温度精准估算具有重要的现实意义。本研究基于精细的地表覆盖类型、空间连续的土壤水分、地表温度（LST）数据,并结合其他辅助数据,构建了近地表空气温度空间化模型,并对近地表空气温度影响因子进行评估,发现地表覆盖类型对近地表空气温度的影响最大,土壤水分为最活跃的影响因素,经验证,模型精度较高,R²接近0.85,RMSE为0.5℃。本研究获取的精确空间连续的近地表空气温度信息,能够充分表达其空间异质性,为农业气象灾害灾变过程监测、农作物生长过程模拟、区域气候变化分析等研究提供良好的近地表空气温度数据支撑。     

南方山地丘陵土地利用类型的地形影响GIS分析——以江西省为例

分布广泛的山地丘陵,地形复杂多样,生态环境脆弱,不合理的土地利用方式会造成生态环境的破坏,导致严重的水土流失。分析山地丘陵区土地利用的地形控制机制,对于山地丘陵区土地利用开发与水土保持等生态保护之间权衡提供科学依据而具有重要现实意义。因此,本文以南方山地丘陵分布较广泛的江西省为例,在SRTM数字高程模型(DEM)的支持下,利用中国资源环境数据中心基于Landsat遥感解译的2000年土地利用数据,分析了江西省土地利用结构与高程、坡度和坡向等地形因子的关系。结果表明地形因子是影响江西省土地利用方式的一个重要因素,具体表现在:(1)随着高程和坡度的增加,耕地面积及占土地总面积的比例都呈下降趋势,南坡耕地面积和比例都大于北坡的耕地面积和比例;(2)在低海拔区,林地面积占土地总面积比例随着海拔高程的增加而增加,当海拔高于400米时,基本稳定;(3)居民点和工矿用地受高程和坡度的影响较大,受坡向影响较小;(4)草地的面积随着海拔的增加呈下降趋势,但其面积比随着高程增加呈缓慢增加,受坡度和坡向的影响较小。     

Spatial variability of soil carbon to nitrogen ratio and its driving factors in Ili River valley,Xinjiang, Northwest China

Soil carbon to nitrogen(C/N) ratio is one of the most important variables reflecting soil quality and ecological function,and an indicator for assessing carbon and nitrogen nutrition balance of soils.Its variation reflects the carbon and nitrogen cycling of soils.In order to explore the spatial variability of soil C/N ratio and its controlling factors of the Ili River valley in Xinjiang Uygur Autonomous Region,Northwest China,the traditional statistical methods,including correlation analysis,geostatistic alanalys and multiple regression analysis were used.The statistical results showed that the soil C/N ratio varied from 7.00 to 23.11,with a mean value of 10.92,and the coefficient of variation was 31.3%.Correlation analysis showed that longitude,altitude,precipitation,soil water,organic carbon,and total nitrogen were positively correlated with the soil C/N ratio(P 0.01),whereas negative correlations were found between the soil C/N ratio and latitude,temperature,soil bulk density and soil p H.Ordinary Cokriging interpolation showed that r and ME were 0.73 and 0.57,respectively,indicating that the prediction accuracy was high.The spatial autocorrelation of the soil C/N ratio was 6.4 km,and the nugget effect of the soil C/N ratio was 10% with a patchy distribution,in which the area with high value(12.00–20.41) accounted for 22.6% of the total area.Land uses changed the soil C/N ratio with the order of cultivated land grass land forest land garden.Multiple regression analysis showed that geographical and climatic factors,and soil physical and chemical properties could independently explain 26.8%and 55.4% of the spatial features of soil C/N ratio,while human activities could independently explain 5.4% of the spatial features only.The spatial distribution of soil C/N ratio in the study has important reference value for managing soil carbon and nitrogen,and for improving ecological function to similar regions.     

Effects of temperature, algae biomass and ambient nutrient on the absorption of dissolved nitrogen and phosphate by Rhodophyte Gracilaria asiatica

Gracilaria asiatica,being highly efficient in nutrient absorption,is cultivated in sea cucumber ponds to remove nutrients such as nitrogen and phosphate.It was cultured in a laboratory simulating field conditions,and its nutrient absorption was measured to evaluate effects of environmental conditions.Ammonia nitrogen(AN),nitrate nitrogen(NN),total inorganic nitrogen(TIN),and soluble reactive phosphorus(SRP) uptake rate and removal efficiency were determined in a 4×2 factorial design experiment in water temperatures(T) at 15℃ and 25℃,algae biomass(AB) at 0.5 g/L and 1.0 g/L,total inorganic nitrogen(TIN) at 30 μmol/L and 60 μmol/L,and soluble reactive phosphorus(SRP) at 3 and 6 μmol/L.AB and ambient TIN or SRP levels significantly affected uptake rate and removal efficiency of AN,NN,TIN,and SRP(P<0.001).G.asiatica in AB of 0.5 g/L showed higher uptake rate and lower removal efficiency relative to that with AB of 1.0 g/L.Nitrogen and phosphorus uptake rate rose with increasing ambient nutrient concentrations;nutrient removal efficiency decreased at higher environmental nutrient concentrations.The algae preferred to absorb AN to NN.Uptake rates of AN,NN,and SRP were significantly affected by temperature(P<0.001);uptake rate was higher for the 25℃ group than for the 15℃ group at the initial experiment stage.Only the removal efficiency of AN and SRP showed a significant difference between the two temperature groups(P<0.01).The four factors had significant interactive effects on absorption of N and P,implying that G.asiatica has great bioremedial potential in sea cucumber culture ponds.     

Soil organic carbon and nutrients along an alpine grassland transect across Northern Tibet

Soil carbon and nutrient contents and their importance in advancing our understanding of biogeochemical cycling in terrestrial ecosystem, has motivated ecologists to find their spatial patterns in various geographical area. Few studies have focused on changes in the physical and chemical properties of soils at high altitudes. Our aim was to identify the spatial distribution of soil physical and chemical properties in cold and arid climatic region. We also tried to explore relationship between soil organic carbon (SOC) and total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), available phosphorus (AP), soil particle size distribution (PSD). Samples were collected at 44 sites along a 300 km transect across the alpine grassland of northern Tibet. The study results showed that grassland type was the main factor influencing SOC, TN and TP distribution along the Gangdise Mountain-Shenzha-Shuanghu Transect. SOC, TN and TP contents were significantly higher in alpine meadow than alpine steppe ecosystems. SOC, TN, TP and AN contents in two soil layers (0-15 cm and 15-30 cm) showed no significant differences, while AP content in top soil (0-15 cm) was significantly higher than that in sub-top soil (15-30 cm). SOC content was correlated positively with TN and TP content (r = 0.901 and 0.510, respectively). No correlations were detected for clay content and fractal dimension of particle size distribution (D). Our study results indicated the effects of vegetation on soil C, N and P seem to be more important than that of rocks itself along latitude gradient on the northern Tibetan Plateau. However, we did not found similar impacts of vegetation on soil properties in depth. Inaddition, this study also provided an interesting contribution to the global data pool on soil carbon stocks.     

Impact factors identification of spatial heterogeneity of herbaceous plant diversity on five southern islands of Miaodao Archipelago in North China

Herbaceous plants are widely distributed on islands and where they exhibit spatial heterogeneity. Accurately identifying the impact factors that drive spatial heterogeneity can reveal typical island biodiversity patterns. Five southern islands in the Miaodao Archipelago, North China were studied herein. The spatial distribution of herbaceous plant diversity on these islands was analyzed, and the impact factors and their degree of impact on spatial heterogeneity were identified using CCA ordination and ANOVA. The results reveal 114 herbaceous plant species, belonging to 94 genera from 34 families in the 50 plots sampled. The total species numbers on different islands were significantly positively correlated with island area, and the average α diversity was correlated with human activities, while the β diversity among islands was more affected by island area than mutual distances. Spatial heterogeneity within islands indicated that the diversities were generally high in areas with higher altitude, slope, total nitrogen, total carbon, and canopy density, and lower moisture content, pH, total phosphorus, total potassium, and aspect. Among the environmental factors, pH, canopy density, total K, total P, moisture content, altitude, and slope had significant gross effects, but only canopy density exhibited a significant net effect. Terrain affected diversity by restricting plantation, plantation in turn influenced soil properties and the two together affected diversity. Therefore, plantation was ultimately the fundamental driving factor for spatial heterogeneity in herbaceous plant diversity on the five islands.     

Effects of gully erosion and gully filling on soil degradation in the black soil region of Northeast China

Gully erosion has caused soil degradation and even reduced soil productivity.However,only few studies on the effects of gully erosion and artificial controlling measures on soil degradation in the Black Soil Region of Northeast China are available.Thus,this study explores the relationships between gully erosion,gully filling and soil parameters.Two sets of soil samples were collected in the field at:(1) 72 sample points in the gully erosion study area,60 sample points in the ephemeral and classical gully erosion area(3,518 m2),12 sample points in the deposition zone(443 m2),(2)10 reference points along a slope unaffected by gully erosion representing the original situation before the gully was formed.All soil samples were analyzed for gravel content(GC),soil organic matter(SOM),total nitrogen(TN),available nitrogen(AN),available phosphorus(AP),and available potassium(AK).The soil property values on unaffected slope were fitted by the polynomial curves as the reference values in no gully erosion area.The interpolated soil property values in gully eroded study area were compared with these polynomial curves,respectively,and then,changes of soil property values were analyzed.Gully erosion caused an increase in GC and a decrease in SOM,TN,AN,AP and AK.The change of GC,SOM,TN,AN,AP,AK was 8.8%,-9.04 g kg-1,-0.92 g kg-1,-62.28 mg kg-1,-29.61 mg kg-1,-79.68 mg kg-1.The soil property values in the study area were below optimal values.Thus,we concluded that gully erosion and gully filling caused both on-site and off-site soil degradation.Soil degradation area was 0.65 % of the cultivated land.In addition,it was proved that gully filling were an improper soil and water conservation measure,which seems to exacerbate the problem.Thus,it is suggested that soil where soil is deep is moved to fill the gully,and then the area around the filled gullies should be covered by grass for preventing the formation and development of the gully.     

Community characteristics of wild fruit forests along elevation gradients and the relationships between the wild fruit forests and environments in the Keguqin Mountain region of Iii

In this paper,the quantitative relationship between the wild fruit communities and direct environmental factors is discussed on the basis of detailed data on landscape scale habitats obtained through field vegetation investigation.The results from TWINSPAN and DCCA showed that:1) In the distribution sections of the wild fruit forest in the Keguqin Mountain region,the basic patterns characteristic of the different habitats are due to topographic factors,nutrients and moisture conditions;2) The elevation affected the most basic differentiation of plant communities in the study area,indicating that the elevation condition was the most important factor restricting the distribution of the wild fruit communities in the study area;3) The close relationship between the moisture content in the upper soil layer and the elevation reflected the influence of moisture conditions on both wild fruit and herb-layer communities;4) Nutrient differences not only indicated that the habitat conditions were different in themselves but also showed that the present nutrient conditions of the habitats were seriously affected by human activities.In summary,under complicated mountainous topographic conditions,the habitat conditions for the communities differed very significantly,and the combination of elevation,soil moisture content,total nitrogen,slope aspect,and pH value influenced and controlled the formation of community distribution patterns in the study area.     

Scaling of soil carbon,nitrogen, phosphorus and C:N:P ratio patterns in peatlands of China

Inspired by the importance of Redfield-type C:N:P ratios in global soils,we looked for analogous patterns in peatlands and aimed at deciphering the potential affecting factors.By analyzing a suite of peatlands soil data(n = 1031),mean soil organic carbon(SOC),total nitrogen(TN) and total phosphorous(TP) contents were 50.51%,1.45% and 0.13%,respectively,while average C:N,C:P and N:P ratios were 26.72,1186.00 and 46.58,respectively.C:N ratios showed smaller variations across different vegetation coverage and had less spatial heterogeneity than C:P and N:P ratios.No consistent C:N:P ratio,though with a general value of 1245:47:1,was found for entire peatland soils in China.The Northeast China,Tibet,Zoigê Plateau and parts of Xinjiang had high soil SOC,TN,TP,and C:P ratio.Qinghai,parts of the lower reaches of the Yangtze River,and the coast zones have low TP and N:P ratio.Significant differences for SOC,TN,TP,C:N,C:P and N:P ratios were observed across groups categorized by predominant vegetation.Moisture,temperature and precipitation all closely related to SOC,TN,TP and their pairwise ratios.The hydrothermal coefficient(RH),defined as annual average precipitation divided by temperature,positively and significantly related to C:N,C:P and N:P ratios,implying that ongoing climate change may prejudice peatlands as carbon sinks during the past 50 years in China.     

Application of matter-element model in soil nutrient evaluation of ecological fragile region

On the basis of the soil environment investigation in Da'an City, Jilin Province, China, 40 soil samples from main land use types were obtained and tested by standard method. Soil organic matter (SOM), total N (TN), total P (TP), total K (TK), available N (AN), available P (AP) and available K (AK) were chosen as the evaluation factors. A regional soil nutrient evaluation model was developed based on the matter-element model. The results show that the soil samples with nutrient grade Ⅱ-Ⅴ respectively account for 10%, 30%, 32.5% and 27.5%, and those with grade Ⅳ and Ⅴ account for 60% in all samples. The relationship between soil nutrients and land types indicates that the nutrients of farmland are relatively good, with 41.7% of soil samples with the nutrient grade Ⅳ and Ⅴ. The nutrients of saline-alkali land and sandy land are the worst, with 100% of soil samples with the nutrient grade Ⅳ and Ⅴ. And the ratios of soil samples grade Ⅳ and Ⅴ in grassland and wasteland are respectively 62.5 % and 54.55%. Generally speaking, the soil nutrients status in Da'an City is poor, 60% of soil samples are in poor and extremely poor conditions, indicating that the soil has been severely eroded. Being a relatively superior evaluation method with more accurate resuits and spatial distribution consistency, matter-element analysis is more suitable for regional soil nutrient evaluation than previous models.     

高时间分辨率遥感在土壤质地空间变化识别中的应用

在土壤信息推测研究中,遥感技术通常被作为辅助手段,用来提供地形和植被数据,并利用它们与土壤之间的关系推导土壤空间信息。然而,在平原等地形平缓的农业区,易于观测的地形和植被等环境因素,通常与土壤的协同程度较低,不能有效用于推测土壤质地等属性的空间变化。对于这类地区,如何寻找新的易于获取的变量,以准确地揭示土壤属性的空间变化,是需要解决的问题。本文提出了利用高时间分辨率遥感捕捉这类地区土壤质地空间变化的方法。采用光谱-时间响应线对多时相的光谱数据进行组织表达,使用光谱信息散度定量刻画不同光谱-时间响应线之间的差异。结果显示,在相同的地形和植被条件下,土壤质地相同的区域,其地表动态反馈模式明显相似;土壤质地不同的区域,其反馈模式也明显不同;土壤质地越相似,反馈模式也呈相似趋势。这表明,高时间分辨率遥感获取的地表动态反馈能够有效地指示土壤质地的空间差异。本文的工作表明了高时间分辨率遥感在土壤空间变化识别方面的应用潜力。     

Spatial variability and its main controlling factors of the permafrost soil-moisture on the northern-slope of Bayan Har Mountains in Qinghai-Tibet Plateau

The soil moisture movement is an important carrier of material cycle and energy flow among the various geo-spheres in the cold regions. Thus, this research takes the north slope of Bayan Har Mountains in Qinghai-Tibet Plateau as a case study. The present study firstly investigates the change of permafrost moisture in different slope positions and depths. Based on this investigation, this article attempts to investigate the spatial variability of permafrost moisture and identifies the key influence factors in different terrain conditions. The method of classification and regression tree (CART) is adopted to identify the main controlling factors influencing the soil moisture movement. The relationships between soil moisture and environmental factors are revealed by the use of the method of canonical correspondence analysis (CCA). The results show that: 1) Due to the terrain slope and the freezing-thawing process, the horizontal flow weakens in the freezing period. The vertical migration of the soil moisture movement strengthens. It will lead to that the soil-moisture content in the up-slope is higher than that in the down-slope. The conclusion is contrary during the melting period. 2) Elevation, soil texture, soil temperature and vegetation coverage are the main environmental factors which affect the slope-permafrost soil-moisture. 3) Slope, elevation and vegetation coverage are the main factors that affect the slope-permafrost soil-moisture at the shallow depth of 0-20 cm. It is complex at the middle and lower depth.     

Shrub Communities and Environmental Variables Responsible for Species Distribution Patterns in an Alpine Zone of the Qilian Mountains,Northwest China

Understanding the factors that drive variation in species distribution is a central theme of ecological research. Although several studies focused on alpine vegetation, few efforts have been made to identify the environmental factors that are responsible for the variations in species composition and richness of alpine shrublands using numericalmethods. In the present study, we investigated vegetation and associated environmental variables from 45 sample plots in the middle Qilian Mountains of the northwestern China to classify different community types and to elucidate the speciesenvironment relationships. We also estimated the relative contributions of topography and site conditions to spatial distribution patterns of the shrub communities using the variation partitioning. The results showed that four shrub community types were identified and striking differences in floristic composition were found among them. Species composition greatly depended on elevation, slope,shrub cover, soil p H and organic carbon. The important determinants of species richness were soil bulk density and slope. No significant differences in species richness were detected among the community types. Topography and site conditions had almost equal effects on compositional variation. Nonetheless,a large amount of the variation in species composition remained unexplained.     

THE DRIVING FORCES OF LAND USE/COVER CHANGE INTHE UPSTREAM AREA OF THE NENJIANG RIVER

IINTRODUCTION niques in China（ZHANG。t al，1999； CHEN et al，2000b）．Since the early 1990s，he acceleration of land With its abundant forest，land and water re－use／cover change（LUL乙）has spurred renewed con－sources，the area of the Nenjlang River valley Is one ofcerns about the role ofland use change Indrlvingmany the lmpoFtant lumber products and commodity grainenvironmental problems．Research on the causes and ba…     

The influence of seasonal snow on soil thermal and water dynamics under different vegetation covers in a permafrost region

Seasonal snow is one of the most important influences on the development and distribution of permafrost and the hydrothermal regime in surface soil. Alpine meadow, which constitutes the main land type in permafrost regions of the Qinghai-Tibet Plateau, was selected to study the influence of seasonal snow on the temperature and moisture in active soil layers under different vegetation coverage. Monitoring sites for soil moisture and temperature were constructed to observe the hydrothermal processes in active soil layers under different vegetation cover with seasonal snow cover variation for three years from 2010 to 2012. Differences in soil temperature and moisture in areas of diverse vegetation coverage with varying levels of snow cover were analyzed using active soil layer water and temperature indices. The results indicated that snow cover greatly influenced the hydrothermal dynamics of the active soil layer in alpine meadows. In the snow manipulation experiment with a snow depth greater than 15 cm, the snow cover postponed both the freeze-fall and thawrise onset times of soil temperature and moisture in alpine LC （lower vegetation coverage） meadows and of soil moisture in alpine HC （higher vegetation coverage） meadows; however, the opposite response occurred for soil temperatures of alpine HC meadows,where the entire melting period was extended by advancing the thaw-rise and delaying the freeze-fall onset time of the soil temperature. Snow cover resulted in a decreased amplitude and rate of variation in soil temperature, for both alpine HC meadows and alpine LC meadows, whereas the distinct influence of snow cover on the amplitude and rate of soil moisture variation occurred at different soil layers with different vegetation coverages. Snow cover increased the soil moisture of alpine grasslands during thawing periods. The results confirmed that the annual hydrothermal dynamics of active layers in permafrost were subject to the synergistic actions of both snow cover and vegetation coverage.     

Source-sink landscape spatial characteristics and effect on non-point source pollution in a small catchment of the Three Gorge Reservoir Region

The source and sink landscape patterns refer to landscape types or units that can either promote positive evolvement of non-point source (NPS) pollution process, or can prevent/defer the ecological process, respectively. Therefore, the role of a catchment landscape pattern in nutrient losses can be identified based on the spatial arrangement of source and sink landscapes. To reveal the relations between landscape spatial characteristics and NPS pollution in small catchment, a case study was carried out in a Wangjiagou small catchment of the Three Gorges Reservoir Region (TGRR), China. Google earth imagery for 2015 were processed and used to differentiate source and sink landscape types, and six subcatchments were selected as sample regions for monitoring nitrogen and phosphorus nutrients. Relative elevation, slope gradient and relative flow length was used to construct the Lorenz curves of different source and sink landscape types in the catchment, in order to assess the source and sink landscape spatial characteristics. By calculating the location-weighted landscape indices of each subcatchment and total catchment, the landscape spatial load characteristics affecting the NPS pollution was identified, with a further Pearson correlation analysis for location-weighted landscape indices and nitrogen-phosphorus monitoring indicators. The analysis of Lorenz curve has revealed that the obtained distribution trend of Lorenz curve and curve area quantified well the spatial characteristics of source and sink landscape pattern related to the relative elevation, slope gradient and relative flow length in small catchment. Results of Pearson correction analysis indicated that location-weighted landscape index (LWLI) combining of terrain and landscape type factor did better in reflecting the status of nitrogen and phosphorus loss than the indices related to relative elevation, slope gradient and relative flow length.     

多年平均气温空间化BP神经网络模型的模拟分析

气温数据空间化是插补无站地区温度、使气温数据便于综合分析的重要技术手段.理想情况下,气温的空间化分布受经度、纬度和海拔高度的影响,呈现规律性的空间分布态势.但是,各种微观因子如坡度、坡向、地形起伏、地表覆被等的存在,在一定程度上扰乱并弱化了这种规律性的分布态势.本文基于Matlab平台,利用BP神经网络研究了多年平均气...     

A methodological approach for weighting factors in land suitability assessment: a tool for facilitating spatial planning

The increasing demand for infrastructural facilities in hill areas needs efficient spatial planning at the local level through land suitability assessment,which is influenced by a number of factors. There has been little systematic empirical work for identification and evaluation of the factors affecting spatial planning decisions in hill areas. The present study focuses on identifying the critical factors for land suitability assessment at the local level in hill areas and determining their percentage influence, which has been done in two stages. In the first stage, the comprehensive list of 21 factors from the reported literature was prepared which was further condensed to the critical factors. In the second stage, the percentage influence of the critical factors was calculated by analyzing the experts' opinions collected through a questionnaire survey. Analytic Hierarchy Process(AHP) was used for the analysis of the questionnaire for weighting the critical factors. The slope was identified with the highest weight followed by aspect, surface runoff, elevation, and vegetation,whereas groundwater table, existing utilities,accessibility, soil type, and land use have comparatively less weights. The results of the study were used for the identification of locations for builtup facilities of an educational campus located in hill areas of Himachal Pradesh, India.     

Soil organic carbon pools in particle-size fractions as affected by slope gradient and land use change in hilly regions, western Iran

This study was conducted to explore the effects of topography and land use changes on particulate organic carbon(POC),particulate total nitrogen(PTN),organic carbon(OC) and total nitrogen(TN) associated with different size primary particle fractions in hilly regions of western Iran.Three popular land uses in the selected site including natural forest(NF),disturbed forest(DF) and cultivated land(CL) and three slope gradients(0-10 %,S1,10-30 %,S2,and 30-50%,S3) were employed as the basis of soil sampling.A total of 99 soil samples were taken from the 0-10 cm surface layer in the whole studied hilly region studied.The results showed that the POC in the forest land use in all slope gradients was considerably more than the deforested and cultivated lands and the highest value was observed at NF-S1 treatment with 9.13%.The values of PTN were significantly higher in the forest land use and in the down slopes(0.5%) than in the deforested and cultivated counterparts and steep slopes(0.09%) except for the CL land use.The C:N ratios in POC fraction were around 17-18 in the forest land and around 23 in the cultivated land.In forest land,the silt-associated OC was highest among the primary particles.The enrichment factor of SOC,EC,was the highest for POC.For the primary particles,EC of both primary fractions of silt and clay showed following trend for selected land uses and slope gradients:CL> DF> NF and S3 > S2> S1.Slope gradient of landscape significantly affected the OC and TN contents associated with the silt and clay particles,whereas higher OC and TN contents were observed in lower positions and the lowest value was measured in the steep slopes.Overall,the results showed that native forest land improves soil organic carbon storage and can reduce the carbon emission and soil erosion especially in the mountainous regions with high rainfall in west of Iran.