[Risk assessment of nitrogen and phosphorus export in upper reach of Daliao river watershed].

With the development of point pollution control, non-point source pollution has become an important environmental and water quality management problem. Land cover composition across a watershed is a dominant factor in controlling the amount of nitrogen and phosphorus exported from a watershed. Generally, urban and agricultural land covers are considered as principal sources of excess loads of nitrogen (N) and phosphorous (P) in receiving waters. A well developed literature of nutrient export coefficients by land-cover class was used to model the risk of equaling or exceeding specified levels of nutrient export in drainage basin of Dahuofang Reservoir. The model was applied to about 513 comparatively small watersheds mapped for the drainage basin of Dahuofang Reservoir for environmental analysis and planning. The results suggest that the probabilities of risk are 19.31% and 8.95% for N and P nutrient respectively. As the spatial distribution concerned, risk estimates generally differed with different slope degrees and districts. Risk estimates generally increased from the places where lies near the rivers to the places where are far from the river, but numerous areas of high variability were evident.

[Regional environment risk assessment and probability distribution of topsoil PAHs in Tianjin area].

Based on some foreign standards of soil PAHs assessment, regional environment risk assessment of topsoil PAHs in Tianjin Area was discussed using the method of indicator Kriging. The results using different standards are also compared. It is shown that Bap is the only one component which exceeds the preliminary remedial goals and risk based concentration of U.S. in Tianjin area and the regions of exceeding standards are about 8.12% and 2.34% respectively. Most components of soil PAHs in Tianjin area are exceed the standard of Holland. The regions of exceeding standard are mostly 90% except the components of Ant (5.26%) and Bas (68.42%). Otherwise, the regions of exceeding Canada standard are mostly under 5% except Nap (97.89%), Phe (56.84%) and Pyr (47.65%). Based on the Soil Plan Zealand of Denmark, Nap is the only one component which exceeds the standard in Tianjin area and the region is about 9.26%. Comparing these risk distribution maps and spatial distribution maps of PAHs, it is found that the areas with high risk are mainly fallen in the areas with high concentrations of PAHs. The probability maps of PAHs risk are helpful for regional environmental management and planning.