Spatial distribution pattern of nitrogen in marsh soils in Xianghai wetlands
向海沼泽湿地土壤氮素的空间分布格局

Wetlands serve as source, sink or transfer of nitrogen(N), and spatial distribution of N in wetlands also significantly influences most ecological processes of wetlands. Some researchers have testified that soil nutrients in wetlands had higher spatial heterogeneity. Geostatistics have been successfully used in soil science and become an efficient tool to research spatial heterogeneity of soils since the 1970s. Xianghai wetland is a one of international importance, which is located at the downstream of Huolin river catchment of semi-arid area and is a typical agriculture/pastoral ecotone and ecological fragibility zone in the west of Jilin province. Xianghai wetland has been the important factor keeping ecological balance and one of the natural barriers for eastern ecological environment in this region. At present, Xianghai wetlands are potentially threatened as a result of such human activities as overgrazing, building large-scale irrigation works and unreasonable reclamation. Spatial distribution pattern of total N and N forms in marsh soils during plant budding were studied using geostatistics of Xianghai wetlands in May, 2001. The results showed that, with the exception of ammonium N, other forms of N and total N were mainly distributed on surface soils, appearing a decreasing tendency gradually with the increase of soil depth; the total N and all forms of N contents had higher statistical variations; on surface soils, the statistical variation of the available N was the highest, but ammonium N the lowest, with variation coefficients of 65.64%and 49.51%, respectively. For other soil layers, soil organic N, total N and nitrate N had higher statistical variations, but available N and ammonium N had lower statistical variations. The spatial distribution pattern of total N was similar to that of organic N; it was highly consistent in distribution areas with higher or lower contents of N forms; with the except of the fact that available N concentrated on top soils, other forms of N appeared accumulation peaks in deeper layers of soil profiles. Both N behavioral processes and environmental factors controlled spatial distribution pattern of N, but quantifying their influences on spatial distribution pattern needed further studies.