沿岸用地状况对中小河道沉水植物定居光照强度的影响

河道沿岸用地状况对水环境质量和水生态系统健康产生重要影响，水体光衰减特征对沉水植物定居生长具有重要意义.通过以建设闲置区、居住商业区、非居住商业区等不同沿岸用地状况中小河道为研究对象，分析了上海市130个中小河道调查区段的水环境和水下光环境指标.结果表明，上海市中小河道调查区段水体光衰减系数（K_d（PAR））的分布范围为1.243~7.592 m^-1，河道沿岸不同用地状况对K_d（PAR）具有较大影响，建设闲置区显著大于非居住商业区和居住商业区.总固体悬浮物是导致上海市中小河道水体光衰减的主要因素，但不同沿岸用地状况之间引起水体光衰减的主导因子存在差异：因处在建设开发阶段或表土裸露状态，建设闲置区的水体光衰减主导因子为总固体悬浮物，而非居住商业区、居住商业区的水体K_d（PAR）则受到总固体悬浮物、有机污染和营养盐等共同影响.总体上，总磷和叶绿素a随总固体悬浮物浓度增加表现为先增加后降低趋势.沉水植物定居光环境的最大水深Z_macrophytes分布范围为0.462~2.821 m，结合中小河道水深判定水下光照强度不足严重制约沉水植物恢复，并且浊度与K_d（PAR）的相关性显著.建设闲置区、居住商业区、非居住商业区等沿岸用地状况水体浊度与K_d（PAR）的相关系数分别为0.785、0.738、0.646，可作为判定沉水植物定植光照强度及适宜生长区的易操作定量指标.

Effects of riparian land use on underwater light intensity of submerged macrophytes colonization in middle-small rivers

Different land use condition along the river course has a profound impact on the quality of water environment and the health of aquatic ecosystems. Light penetration in water bodies is a decisive factor in the settlement and the growth of submerged macrophytes. In this study, 130 small and middle-sized urban river sections in Shanghai were selected to investigate their water qualities and light penetration variables in water. Land use conditions are divided into idle areas for further constructions (IAC), residential commercial area (R&C), and non-R&C areas. The result shows that the distribution of the light penetration coefficient K_d(PAR) in our sampled sections are 1.243~7.592 m^-1. Different land use conditions have significant impacts on K_d(PAR), where IAC shows a stronger impact than that of non-R&C and R&C. Total suspended solid is the primary factor affecting the light penetration in Shanghai''s small and middle-sized rivers. But co-decisive factors will be changed along with different land use conditions. Due to the IAC development in terms of exposed topsoil, total suspended solid is the leading factor in water light penetrations. In R&C and non-R&C, the K_d(PAR) can be also jointly affected by biochemical oxygen demand and chlorophyll a. In general, total phosphorus and chlorophyll were given an increasing trend initially and then decreased with the total suspended solid concentrating. The distribution range ofZ_macrophytes for the settlement of submerged plants is 0.462~2.821 m. The range is judged based on the real depth of sampling rivers. We observe insufficient underwater light radiations greatly restrict submerged plant''s restoration. Turbidity in water has a strong positive correlation with K_d(PAR). Correlation coefficients of turbidity and K_d(PAR) for IAC, R&C, and non-R&C are 0.785, 0.738, 0.646. It is further recommend that turbidity and water depths, as easily-obtained indicators, can be applied for the justification of water light environments and suitable growth places for submerged macrophytes.