Evaluation and analysis of water quality variations were performed with integrated consideration of water quality parameters, hydrological-meteorologic and anthropogenic factors in Cao-E River, Zhejiang Province of China. Cao-E River 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 different. Total nitrogen （TN） and total phosphorus （TP） in the water are the main polluted 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 indices 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 reaches （including mainstream, Sub-watershed Ⅰ and Ⅱ） that mainly drained by arable field and/or dispersive rural dwelling district, and the maximum pollutant concentration appears in flooding seasons. It implied that the runoff increases the pollutant concentration of the water in the nonpoint pollution type reaches. On the other hand, remarkably spatial variations occur in the point pollution type reaches （include Sub-watershed Ⅲ, Ⅳ and Ⅴ） and the maximum pollutant concentration appears in urban reaches. The runoff always decreases the pollutant concentration of the river water in the seriously polluted reaches that drained by industrial point sewage. But for the point pollution reaches resulted from centralized town domestic sewage pipeline and from frequent shipping and digging sands, rainfall always increased the concentration of pollutant （TN） in the river water too
The distribution of different nitrogen forms and their spatial and temporal variations in different pollution types of tributaries or reaches were investigated. Based on the catchments characteristics the tributaries or reaches can be classified into 4 types, including headwater in mountainous areas （type Ⅰ）, agricultural non-point source （NPS） pollution in rural areas （type Ⅱ）, municipal and industrial pollution in urban areas （type Ⅲ）, and combined pollution in main stream （type IV）. Water samples were collected monthly from July 2003 to June 2006 in the Cao-E River Basin in Zhejiang, eastern China. The concentrations of NO3^--N, NH4^＋ -N, and total nitrogen （TN） were measured. The mean concentrations of NO3^- -N were decreased in the sequence type IV 〉 type Ⅱ〉 type Ⅲ 〉 type Ⅰ, whereas, NH4^＋-N, total organic nitrogen （TON）, and TN were in the sequence： type Ⅲ〉 type Ⅳ 〉 type Ⅱ〉 type Ⅰ. In headwater and rural reaches, CNO^-2-N was much higher than Crea^＋ 4-N. In urban reaches, TON and NH4^＋ -N were the main forms, accounting for 54.7% and 32.1% of TN, respectively. In the whole river system, Crea^＋ 4--N decreased with increasing distance from cities, and CNo^-3 -N increased with the increasing area of farmland in the catchments. With increased river flow, CNO^-3 N increased and Crea4^＋-N decreased in all types of reaches, while the variations of CTON and CTN were different. For TN, the concentration may be decreased with the increase of river flow, but the export load always increased.
JIN ShuquanLU JunCHEN DingjiangSHEN YenaSHI Yiming
