Global nitrogen (N) emission and deposition have been increased rapidly due to massive mobilization of N which may have longreaching impacts on ecosystems.Many agricultural and forest ecosystems have been identified as secondary N sources.In the present study,the input-output budget of inorganic N in a small forested watershed of subtropical China was investigated.Inorganic N wet deposition and discharge by stream water were monitored from March,2007 to February,2009.The concentrations and fluxes of inorganic N in wet precipitation and stream water and net retention of N were calculated.Global N input by dry deposition and biological fixation and N output by denitrification for forested watersheds elsewhere were reported as references to evaluate whether the studied forested watershed is a source or a sink for N.The results show that the inorganic N output by the stream water is mainly caused by NO 3-N even though the input is dominated by NH 4 +-N.The mean flux of inorganic N input by wet precipitation and output by stream water is 1.672 and 0.537 g N/(m 2 ·yr),respectively,which indicates that most of inorganic N input is retained in the forested watershed.Net retention of inorganic N reaches 1.135 g N/(m 2 ·yr) considering wet precipitation as the main input and stream water as the main output.If N input by dry deposition and biological fixation and output by denitrification are taken into account,this subtropical forested watershed currently acts as a considerable sink for N,with a net sink ranging from 1.309 to 1.913 g N/(m 2 ·yr) which may enhance carbon sequestration of the terrestrial ecosystem.
The vertical distribution and migration of Cu,Zn,Pb,and Cd in two forest soil profiles near an industrial emission source were investigated using a high resolution sampling method together with reference element Ti.One-meter soil profile was sectioned horizontally at 2 cm intervals in the first 40 cm,5 cm intervals in the next 40 cm,and 10 cm intervals in the last 20 cm.The migration distance and rate of heavy metals in the soil profiles were calculated according to their relative concentrations in the profiles,as calibrated by the reference element Ti.The enrichment of heavy metals appeared in the uppermost layer of the forest soil,and the soil heavy metal concentrations decreased down the profile until reaching their background values.The calculated average migration rates of Cd,Cu,Pb,and Zn were 0.70,0.33,0.37,and 0.76 cm year-1,respectively,which were comparable to other methods.A simulation model was proposed,which could well describe the distribution of Cu,Zn,Pb,and Cd in natural forest soils.
Pedogenetic soil horizons are one of the fundamental building blocks of modern soil classification;however,in soils of urban areas which are often strongly disturbed by human activities,horizons are diffcult to distinguish but substitutive morphological layers may be identified.To identify the characteristic soil layers in an urban environment,224 soil layers of 36 in-situ pedons were examined and described in urban and suburban Nanjing,and 27 variables were extracted for multivariate analysis.Three groups and six subdivisions were identified by TwoStep cluster analysis combined with hierarchical cluster analysis based on factor scores.Soil forming factors and soil forming processes could be interpreted from the principal component analysis(PCA) of variables,cluster analysis of soil layers,and discriminant analysis of soil layer groups and their subdivisions.Parent materials,moisture regimes,organic matter accumulation,and especially nutrient accumulation were the main causes of characteristic soil layer formations.The numerical approaches used in this study were useful tools for characteristic soil layer identification of urban soils.
