The degradation threshold of water quality associated with urban landscape component
城市景观组分影响水质退化的阈值研究

It is one of the key topics in landscape pattern and ecological process analysis to combine landscape pattern analysis and water quality monitoring, so as to assess the impact of urban landscape change on water quality. Moreover, to realize the harmonization between urban development and water quality protection, it is in great need for the quantitative analysis of the relationship between urban landscape change and water quality degradation. Unfortunately, there is no enough scientifically understanding on the very relationship so far. One of the solutions is to quantify the degradation threshold of urban landscape change impact on water quality. In this research, nonlinear regression was used to analyze the relationship between urban landscape change and water quality degradation, and a new method was developed to estimate the threshold based on cross-section statistics. Impervious Surface Area (ISA) was conducted to monitor the urbanization degree in the watershed, and chemical indicators were used to analyze the water quality. All of 31 sample sites and watersheds were selected in Shenzhen. Watershed and buffer zone scale of urban landscape change was quantified with the application of Linear Spectral Mixture Method using Landsat TM images, and water quality was monitored 12 times a year using 15 water quality indicators. Both were collected in 2005. The results indicated that, when stream buffer zone was set at 100-200m, there was the highest significance of the impact of urban landscape change on water quality, with the P value less than 0.001. Furthermore, the exponential relationships between such water quality indicators as DO, S2-, CGB and F- and urban landscape change were significant when the flow path distance was accepted, with the significantly exponential relationships for CODMn, BOD5, NH3-N, TP, TN, Zn, Pb, VP, Oils, ANC and SO42- in Euclidean distance. The exponential relationships between oxygen consumption, eutrophication of water quality and impervious component indicated that urban landscape change was the most important influencing factor, which interpreted about 50-60% of water quality degradation. However, for other water quality indicators, such as heavy metals and toxicity, their changes could only be interpreted by urban landscape change for 30%-40%, which meant urban landscape change was no longer a significant influencing factor compared with other factors such as point source pollution input to stream ecosystem. These results agreed with that urbanization degree of riparian was of great significance to chemical water quality of stream. Furthermore, with the exception of Zn, F-, Pb and Oils, the degradation threshold level of water quality associated with landscape change was between 38.2% and 50%. The minimum value of 38.2% meant if the ratio of watershed imperviousness area reached this level, water quality degradation would began and the water quality would be prone to be hardly recovered. The results showed that