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Landscape characteristics of twenty-eight sub-catchments within the Miyun reservoir watershed in Miyun County, northeast Beijing of China were examined to identify relationships with stream water chemistry. The influences of the entire catchment and 300 m buffer zone on water quality were compared using multiple regression analysis and redundancy analysis during three seasons. Results showed that strong seasonal differences in nitrate, nitrite and ammonium are observed whereas no difference in total phosphorus and conductivity. Landscape factors were significantly correlated to stream water quality. Residential area and stream density contributed markedly to river condition variability. Water quality was better explained by interactions with the landscape during and after rainy season. There was also a seasonal shift in the landscape factors that were the dominant explanatory variables. The relationships between landscape attributes and water quality on watershed scale were slightly different from those on riparian scale; however, landscape attributes may have stronger influences on water chemistry. [ABSTRACT FROM AUTHOR]

Miyun Reservoir is the major water source for Bijing, China. Currently, the water quality of Miyun reservoir is meso - trophict, mainly dur to the non-point source pollution (NPS) in the watershed. Phosphorus (P) is the limited factor. In this paper, Chaohe River basin, upstream of the Miyun Reservoir, is chosen as the study area, A modified P Index was developed to identify critical source areas (CSAs) of non-point source pollution by analyzing local hydrological and meteorological data, land use, soil, soil conservation, farmland management, population density, and livestock. The factors of livestock and population density are new factors added to the P Index system based on the actual local characteristics. It was found that the loss P from high-risk area accounts for only 7.95%. These areas are located mainly along streams. Livestock factor and the population density factor are most closely related to the CSAs downstream of Chaohe River basin. The management strategies are outlined according to the distribution characteristics of the critical source areas. [ABSTRACT FROM AUTHOR]

The Tembusu virus (TMUV) PS strain, derived by several passages and plaque purifications in BHK-21 cells, displays markedly lower virulence in Pekin ducklings relative to a natural isolate of TMUV, but the potential virulence determinants and the in vivo mechanisms for substantial virulence attenuation of the passage variant remain unknown. Here, we constructed a series of chimeric and mutant viruses and assessed their virulence using a 2-day-old Pekin duckling model. We showed that residue 304 in the envelope (E) protein is the molecular determinant of TMUV virulence. Further investigations with mutant and parental viruses demonstrated that acquisition of positive charges at E protein residue 304 plays a critical role in substantial attenuation of neurovirulence and neuroinvasiveness, which is linked to enhanced binding affinity for glycosaminoglycans (GAGs). In Pekin ducklings infected by subcutaneous inoculation, an Arg at residue 304 in the E protein was shown to contribute to more rapid virus clearance from the circulation, markedly reduced viremia, and significantly decreased viral growth in the extraneural tissues and the central nervous system, relative to a Met at the corresponding residue. These findings suggest that the in vivo mechanism of virulence attenuation of the TMUV passage variant closely resembles that proposed previously for GAG-binding variants of other flaviviruses. Overall, our study provides insight into the molecular basis of TMUV virulence and the in vivo consequences of acquisition of a GAG-binding determinant at residue 304 in the E protein of TMUV. [ABSTRACT FROM AUTHOR]