K.H. Tiedemann (Canada)
Time-series models, least squares regressions, maximum likelihood regressions, phosphorus levels, fertilizer management.
Eutrophication has emerged as a major water quality concern in China, particularly in the reservoirs and lakes of the Yangtze River, and phosphorous loadings appear to be a major determinant of eutrophication. This study provides an analysis of the determinants of phosphorus concentration levels and phosphorus flux in the lower Yangtze River. The study has four main findings. First, the Government of China has subsidized the use of commercial and organic fertilizer and irrigation water to increase agricultural yields, but it has paid less attention to the impact of increased phosphorus loadings on water quality. Second, annual fertilizer use per hectare has increased from an average of 84.8 kg for 1963-1969, to 125.8 kg for 1970-1979, and to 217.8 kg for 1980 to 1987. Third, average phosphorous concentration levels and average annual phosphorous fluxes have risen respectively from 8.30 mg/L and 9.21 million tonnes in 1963-1969, to 5.30 mg/L and 5.05 million tonnes in 1970 1979, and to 13.07 mg/L and to 12.38 million tonnes in 1980-1987. Fourth, agriculture phosphorous concentrations and phosphorous fluxes in the lower Yangtze River are statistically significantly driven by fertilizer loadings and by precipitation runoff.
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