[Comparison of Available Nitrogen and Phosphorus Characteristics in the Land-Water Transition Zone of Different Watersheds and Their Environmental Significance].

In order to explore the characteristics and environmental significance of available nitrogen and phosphorus in different land-water transition zones, soil and sediment samples from three study areas, including the upstream watershed of Minjiang River (MJU), western watershed of Hongze Lake (HZW), and western watershed of Taihu Lake (THW), were collected and analyzed. The results showed that the contents of total nitrogen and phosphorus in THW were higher than those of other two study areas. The contents of nitrogen and phosphorus in sediments were higher than those in soils of HZW. The distribution trend of available nitrogen and available phosphorus was generally consistent with the distribution trend of total nitrogen and phosphorus. The proportions of available nitrogen and phosphorus in THW and HZW were much higher than those in MJU, and the proportions of available nitrogen and phosphorus in sediments were higher than those in soils. The physiochemical properties such as pH value, organic matter, and iron and aluminum oxides were related to the available nitrogen and phosphorus in the soil and sediment, but correlations between them were complex. The distribution patterns of available nitrogen and phosphorus in the soil and sediments of the land-water transition zone reflect the impacts of the natural environment and human activities, particularly those of the latter.

[Effects of Biochar Input on Changes of Available Nutrient Elements in Riparian Soils with Different Landuse Types].

Biochar, as a new environmentally friendly material, has been used to improve soil quality and for pollution remediation. Biochar input has a significant impact on available nutrients in the soil. Based on the different land use types (forestland, grassland, cultivated land, and barren land) in the riparian zone of Taihu Lake, the effects of biochar application on the available content of nutrients in different land use types of soil were compared, and the dynamics of nutrient change was also discussed. Results show that the addition of biochar can significantly affect the available nutrient content in riparian soil, however the influential degrees for carbon, nitrogen, and phosphorus were different. After the input of biochar, dissolved organic carbon in riparian soils showed a clear downward trend, while the available nitrogen increased slightly, and the available phosphorus increased significantly. For woodland, grassland, arable land and wasteland soils, the contents of dissolved organic carbon decreased by 33.3%, 27.4%, 29.5%, and 51.4%, while the contents of available nitrogen increased by 10.8%, 18.2%, 16.4%, and 15.2%, and the contents of available phosphorus increased by 40.0%, 50.2%, 34.0%, and 43.6%, respectively. Compared with the concentrations between the control group soil (CK) and the biochar additive group soil (BC), the concentrations of dissolved organic carbon and available phosphorus exhibited large differences between the two groups regarding available nitrogen concentrations. Among the four types of riparian soils, the effects of biochar on the availability of different nutrients were different.

[Spatial Distribution of Organic Phosphorus in Sediment and Its Environmental Implication in the Upper Stream of Minjiang River].

In order to explore the effect of land use pattern on phosphorus distribution and the potential release capacity of stream sediment in the upper Minjiang River, this paper presented organic phosphorus forms and their spatial distribution characteristics of sediments in the upper Minjiang River by using the IVANOFF method and discussing the effects of physicochemical properties of sediments on the distribution of organic phosphorus forms. The results show that:①nitrogen and phosphorus contents of sediments in Jianxi and Shaxi catchments are higher than those in the Futunxi catchment, probably related to the large number of farmland runoff and municipal sewage near the Jianxi and Shaxi catchments and the large forest area around the Futunxi catchment;②contents in the sediments from three catchments and TP contents in the sediments from Jianxi and Futunxi catchments showed the order of upper reaches < middle reaches < lower reaches, which may be caused by the mountainous and forested areas in the upper reaches and the intensive human activities in the middle and lower reaches;③nitrogen phosphorus in sediments of the three catchments were mainly non-active organic phosphorus, which indicated that upper reaches of the Minjiang river were generally less affected by external pollution, and the relative proportion of organic phosphorus in the sediments of different catchments was relatively large, while the change in different sections of the same river was relatively small;④physicochemical properties of sediments had a significant impact on the morphology and distribution of organic phosphorus, among which the effects of organic matter, TP, and TN were the most obvious, but the effects on sediments in different river basins were different. Therefore, to protect the water quality of the upper Minjiang River, it is necessary to strengthen the control of the living and agricultural pollution sources near the catchments.