| Periphyton is the primary basal food source of the fish species indigenous to the cross-border rivers of Xinjiang Uygur Autonomous Region (northwest China). The periphyton community is crucial for the fishery resources and characterizing the community structure is important for assessing the regional ecological environment. The periphyton community structure was investigated systematically in May, July, September and October of 2013 in the Yili River, originating in Mount Tianshan (China) and eventually flowing to Lake Balkhash (Kazakhstan). The investigation focused on species composition, dominant species, spatial and temporal distribution and the biodiversity index. Water quality in Yili River was also evaluated, based on the biodiversity index, periphyton community structure and physicochemical factors. Periphyton samples for qualitative and quantitative analysis were collected at eight sampling sites located in the main stem of the Yili River and its three primary tributaries; (1) Linggongli, (2) 71 Great Bridge, (3) Qiao’erma, (4) Nileke, (5) Zhaosu Liberation Bridge, (6) Tekesisanxiang, (7) Yamadu and (8) Yili River Bridge. Physicochemical parameters monitored included water temperature, transparency, depth, flow velocity, salinity, pH, conductivity, dissolved oxygen, total dissolved solids, total hardness, nitrate nitrogen, ammonia nitrogen, fluoride, calcium ion, total nitrogen and total phosphorus. A total of 145 periphyton species from 41 genera and five phyla were collected and Bacillariophyta dominated (113 species, 77.9% of total species), followed by Cyanophyta (14 species, 9.7%), Chlorophyta (13 species, 9.0%), Euglenophyta (4 species, 2.8%) and Cryptophyta (1 species, 0.7%). The dominant periphyton species were N. halophila, Cymbella naviculiformis, Diatoma vulgare and Phormidium corium from Bacillariophyta and Phormidium corium from Cyanophyta. Periphyton densities in May, July, September and October were, respectively, 1 177.4×106, 501.8×106, 1 812.9×106 and 1 669.2×106 ind/m2, with an average value of 1 331.7×106 ind/m2 and the biomasses were 1 816.2, 971.7, 2 428.1 and 2 350.7 mg/m2, with an average value of 1 908.5 mg/m2. Periphyton distribution also displayed spatial variation, with the highest density (1 648.6×106 ind/m2) observed at Yili River Bridge (8) and the highest biomass (2 613.0 mg/m2) at Zhaosu Liberation Bridge (5), with the lowest density (519.6×106 ind/m2) and biomass (813.9mg/m2) both occurring at Linggongli (1). Temporally, periphyton density and biomass were highest in September and lowest in July. Spatially, periphyton density and biomass in the main stem were higher than in the tributaries and downstream values were higher than upstream. The Simpson diversity index (D), Shannon-Wiener diversity index (H′), evenness index (J) and abundance index (d) of the Yili River periphyton community were, respectively, 0.73, 3.24, 0.60 and 3.91. Overall, the biodiversity indices (H′, D, J and d) gradually declined from upstream to downstream. Pearson correlation analysis gave a significant negative correlation between periphyton density and flow velocity and a significant positive correlation with total nitrogen, water temperature, salinity, fluoride, total hardness and calcium ion. The water quality assessment was based on biodiversity indices (Shannon-Wiener, Margalef, Pielou), indicator organisms and the pollution tolerance index for diatoms (PTI) and gave consistent results and indicate that water quality in the Yili river basin is generally good. Among the eight sampling sites, water quality at Zhaosu Liberation Bridge (5), Yamadu (7) and Yili River Bridge (8) was mesotrophic, while water quality at the other five sites was oligotrophic. |
