Annual changes in periphyton communities and their diatom indicator species, in the littoral zone of a subtropical urban lake restored by submerged plants

Biological indicators of assessing surface waters depend on regionally based indices and sensitivity to environmental conditions. Periphytic algae often used as a potential biological assessment method for its environmental sensitivity characteristics. Here we studied the characteristics of the periphytic algae community and diatom species in the subtropical urban landscape lake known as West Lake, Hangzhou, China, which is in the process of ecological restoration. The changes in species composition, biomass and the community diversity of periphytic algae were determined. 71 taxa of 54 genera of periphytic algae were observed. The Bacillariophyta, Chlorophyta and Cyanophyta dominated in the community. The Bacillariophytes exhibited the highest species richness, whereas the Cyanophytes showed the highest cell density. Principal component analysis environmental variables showed that the TN was main nutrient factor to periphytic algae in the West Lake. In terms of the relatively high TN contents characteristics in subtropical urban landscape lake West Lake, the ecological optimum values and tolerance values of TN about diatom were calculated by weighted regression method. Synedra capitata, Achnanthes minutissima, Gomphonema acuminatum, Navicula graciloides were extracted as indicator species for environmental gradients of TN in the West Lake. Those findings provide a theoretical basis for the use of diatoms biological index to improve the effectiveness of monitoring and evaluating the nutritional level of TN in urban landscape lakes system. It would be significant to identify the nutritional status of the subtropical shallow water bodies and advise related management.