yones khaledian * , farshad kiani and sohaila ebrahimi ,

1. Potential Impacts of Urbanization On Active Soil Organic Carbon Contents Along Natural Forest of Ziarat Watershed, Golestan Province, Iran. yoneskhaledian*, farshadkiani and sohailaebrahimi, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Yones.khaledian@gmail.com Iran Abstract Understanding soil carbon fractions and their responses to the urbanization and changed land use is important for improving soil carbon management of natural altitudinal forest ecosystem. In this study, the contents of soil total organic carbon (SOC), soil labile organic carbon (LOC), Soil microbial respiration (SMR), electrical conductivity (EC) and particle size distribution in soil upper layers (0–30 cm) and analysis of them were taken by completely randomized split-plot in the four land uses forest, pasture, cultivated and urban in Ziarat watershed and with two the north and west slope geography, and five replication designed. The results showed that under natural conditions the contents of SOC and LOC were largest in the forest, moderate in pasture and cultivated land uses, and smallest in the villa building area. MBC contents in different land uses decreased in the order of urbanization, deforestation and changed land use. The EC increased the most amounts in the urban, cultivated, pasture respectively with respect to the forest. In addition, the responses of SOC, LOC, and SMR to changing land use were decrease significant in the forest, pasture, cultivated and urban respectively and also In addition, there were strong correlations among particle size distribution, LOC, SMR and SOC. Due of Ziarat watershed is above Gorgan, center of Golestan province, this study demonstrated that trend of degradation and mis management increase hazard of urban floods, sediment problem and human health due to water pollution in main city of province.  Keywords Urbanization, labile carbon, Soil microbial respiration, organic carbon