Modeling water quality to determine a safe distance between cities: a case study in China

Both the distance between the upstream and downstream cities and the capacity of urban water infrastructure would affect the water safety of the cities in the catchment. In this work, the concept of safe distance for urban growth was proposed. If the water quality between the upstream and the downstream cities can meet the functional requirements of the water environment, then the distance between the upstream and the downstream cities is safe. Taking two neighboring cities in the Yangtze River catchment as a case study, a distributed Cellular Automata (CA) model and a backpropagation (BP) neural network water quality model were used to discuss the safety distance between the two cities. The results provided some decision-making on urban sprawl control and rational urban development.

The changing abundance and distribution of Greater White-fronted Geese Anser albifrons in the Yangtze River floodplain: impacts of recent hydrological changes

SummaryCount data show that wintering Greater White-fronted Goose Anser albifrons numbers in their Chinese stronghold (the Yangtze River catchment) have fallen from about 140,000 in the late 1980s and early 1990s to c.18,000 now, despite increases in the overall flyway population (mostly wintering in South Korea and Japan). Declines have occurred in Jiangxi, but most markedly in Hunan (predominantly at East Dongting Lake) where the decline has been steady since 2003/2004, with few left from 2008/2009 onwards. Numbers have increased substantially in Anhui (predominantly at Shengjin Lake), which now supports more Greater White-fronted Geese than Jiangxi and Hunan combined. The species appears a habitat specialist in China, confined to grazing short-sward recessional Carex sedge meadows. At East Dongting Lake, reductions in Greater White-fronted Geese numbers correlated with declines in availability of suitable sedge swards, caused by earlier water table recession, which in recent years has meant swards were too tall for geese to utilise from their arrival in autumn. The hydrological changes are most probably due to the commissioning of the Three Gorges Dam in mid-2003. At Shengjin Lake, the increases may be due to recent stable first exposure dates and slow water recession rates which favour short Carex swards attractive to geese; high buffalo grazing density at this lake may also assist in maintaining suitable sward heights. These hypotheses require investigation.