From May 2005 to September 2006, the potential effects of marsh flooding regimes on the decomposition and nutrient (N, P) dynamics of Calamagrostis angustifolia litter were studied in the typical waterlogged depression in the Sanjiang Plain, Northeast China. The decomposition of C. angustifolia litter was related to four sites with different hydrologic regimes [F1 (perennial flooding, average water depth of 480 days was 40.14 ± 8.93 cm), F2 (perennial flooding 33.27 ± 6.67 cm), F3 (perennial flooding 23.23 ± 5.65 cm) and F4 (seasonal flooding 1.02 ± 1.09 cm)]. Results showed that flooding regimes had important effects on the litter decomposition, the decomposition rates differed among the four sites, in the order of F3 (0.001820d, and the values in the perennial flooding regimes were much higher. Flooding regimes also had significant effects on the N and P dynamics of litter in decomposition process. If the perennial flooding regimes were formed in C. angustifolia wetland due to the changes of precipitation in the future, the litter mass loss would increase 23.28-48.88%, the decomposition rate would increase 13.41-98.47%, and the t 0.95 would decrease 1.07 yr-4.50 yr. In the perennial flooding regimes, the net N accumulated in some periods, while the net P released at all times. This study also indicated that the changes of N and P content in the litter of the four flooding regimes were probably related to the C/N or C/P ratios in the litter and the N or P availability in the decomposition environment. If the nutrient status of the decomposition environment did not change greatly, the decomposition rates depended on the substrate quality indices of the litter. Conversely, if the nutrient status changed greatly, the decomposition rates might depend on the supply status of nutrient in the decomposition environment.

The action of freeze-thaw is one of the important influence factors which can cause the changes of soil physicochemical and biological characteristics. During the freeze-thaw period the variations of active organic matters in cropland black soil were studied through the in-situ monitoring and determining methods. The surface soil experienced a series of repeated freeze-thaw actions during the alternate from autumn to winter and from winter to spring. The soil active organic matter was in the trend of fluctuation increase from 8.68 mg kg-1to 9.81 mg kg-1 during the seasonal freeze-thaw period. The soil water soluble organic matter was also in a gradually increasing trend, which could increase 33.95% for the surface layer in early April of the next year when compared with that of January. The soil microorganism carbon content increased firstly and then decreased during the seasonal freeze-thaw period, which fluctuated at 912.51-1137.91 mg kg-1. The research showed that the freeze-thaw action could improve the active organic matter and strengthen the adaptability and activity of microorganism, which could promote the mineralization of organic matter.

The farmland soils around three typical livestock farms in Jilin province were studied to elucidate the impact of farms on heavy metal pollution in surrounding farmland soils. The results showed that the average content of Cd was maximal in the soils around cattle farm (0.29 mg kg-1); the average value of Pb was highest in the soils around the pig farm; and Cu, Zn, Ni and Cr were all highest in the soils around the chicken farm. The distribution of heavy metals in the soils around different livestock farms varied greatly. The contents of Cu, Zn, Ni and Cr decreased in the same order: chicken farm> pig farm > cattle farm, but Pb was pig farm> chicken farm> cattle farm, and Cd was cattle farm> pig farm> chicken farm. These results indicated that the livestock farms did not cause significant heavy metal pollution in its surrounding agricultural soils, but the accumulation of heavy metals caused by farms should arouse the attention.

ArcGIS analysis was applied to study the concentrations and spatial distribution characteristics of Cr and Ni in surface soil (0~20cm) of corn belt in Dehui—the typical area of black soil in Jilin province. The average concentrations of Cr and Ni were 49.85 mg·kg-1 and 20.85 mg·kg-1, which were both lower than the corresponding background value and thus in no pollution level. The trends for soil Cr and Ni were similar with higher concentrations trending N-S across the centre of the study area, while the other hotspots were located in the southwest of Dehui. There was prominent correlation between Cr and Ni in 0.01 level, indicating the close relationship of them. The method based on the geostatistical analysis in ArcGIS can exactly reflect the character of spatial distribution of heavy metals.