Spatial and temporal variations of water quality in Cao-E River of eastern China

Evaluation and analysis of water quality variations were performed wit h integrated consideration of water quality parameters, hydrological-meteorologi c and anthropogenic factors in Cao-E River, Zhejiang Province of China. Cao-E Ri ver system has been polluted and the water quality of some reaches are inferior to Grade V according to National Surface Water Quality Standard of China (GB2002 ). However, mainly polluted indices of each tributary and mainstream are differe nt. Total nitrogen (TN) and total phosphorus (TP) in the water are the main poll uted indices for mainstream that varies from 1.52 to 45.85 mg/L and 0.02 to 4.02 mg/L, respectively. TN is the main polluted indices for Sub-watershed I, II, IV and V (0.76 to 18.27 mg/L). BOD5 (0.36 to 289.5 mg/L), CODMn (0.47 to 78.86 mg/ L), TN (0.74 to 31.09 mg/L) and TP (0 to 3.75 mg/L) are the main polluted indice s for Sub-watershed Ⅲ. There are tow pollution types along the river including nonpoint source pollution and point source pollution types. Remarkably temporal variations with a few spatial variations occur in nonpoint pollution type reache s (including mainstream, Sub-watershed I and II) that mainly drained by arable f ield and/or dispersive rural dwelling district, and the maximum pollutant concen tration appears in flooding seasons. It implied that the runoff increases the po llutant concentration of the water in the nonpoint pollution type reaches. On th e other hand, remarkably spatial variations occur in the point pollution type re aches (include Sub-watershed III, IV and V) and the maximum pollutant concentrat ion appears in urban reaches. The runoff always decreases the pollutant concentr ation of the river water in the seriously polluted reaches that drained by indus trial point sewage. But for the point pollution reaches resulted from centralize d town domestic sewage pipeline and from frequent shipping and digging sands, ra infall always increased the concentration of pollutant (TN) in the river water t oo. Pollution controls were respectively suggested for these tow types according to different pollution causes.