| Periphyton acts as the primary basal food resource of indigenous and unique fishes in the cross-border rivers of Xinjiang Uygur Autonomous Region(northwest China), and are of great importance for the protection of fishery resources and assessment of ecological environment in this region. For this purpose, the community structure of periphyton was investigated systematically in May, July, September and October 2013 for Yili River, and May, July, August and September 2015 for Irtish River. We studied the characteristics of community structure in the two rivers,including the species composition, dominant species, density, biomass and the spatiotemporal pattern. Furthemore, we compared the community structure of periphyton on the artificial substrate and natural substrate. Based on four evaluation methods of water quality, we evaluated the health status of the two rivers. Moreover,we analyzed the ecological stoichiometry characteristics of four foodweb components in the Irtish River. The main results were shown as follows:Our study indicated that the periphyton assemblage was composed of 145 algae species in total and grouped into five taxonomic phylum in the Yili River. Specifically,Bacillariophyta exhibited the highest number of taxa(113 species, 77.9%), followed by Cyanophyta(14 species, 9.7%), Chlorophyta(13 species, 9.0%), Euglenophyta(4species, 2.8%) and Cryptophyta(1 species, 0.7%). In the present study, predominant species of periphyton was composed of Bacillariophyta(Navicula halophila,Cymbella naviculiformis, Diatoma vulgare and Phormidium corium) and Cyanophyta(Phormidium corium). The periphyton assemblage was composed of 102 algae species in total and grouped into five taxonomic phylum in the Irtish River.Specifically, Bacillariophyta exhibited the highest number of taxa(67 species, 65.7%),followed by Chlorophyta(20 species, 19.6%), Cyanophyta(6 species, 5.9%),Euglenophyta(6 species, 5.9%), Cryptophyta(2 species, 2.0%) and Cryptophyta(1species, 1.0%). In the present study, predominant species of periphyton was composed of Bacillariophyta(Cyclotella meneghiniana, Gomphonema angustatum, Cymbella naviculiformis and Navicula cincta) and Cyanophyta(Phormidium corium).During the study period, the averaged cell density and biomass in the Yili River were 1331.7×106 ind/m2 and 1908.5 mg/m2, respectively. Seasonal and spatial trends in the density and biomass were shown by normal season > wet season > dry season and mainstream > tributary, respectively. The averaged cell density and biomass in the Irtish River were 1572.0×106 ind/m2 and 2785.3 mg/m2, respectively. Seasonal and spatial trends in the density and biomass were shown by wet season > normal season > dry season and mainstream > tributary, respectively. The species composition and dominant species of periphyton on the artificial substrate and natural substrate were similar, in whicn most of dominant species were Bacillariophyta. And we found that the density and biomass of periphyton on the artificial substrate and natural substrate were statistically different. The averaged cell density and biomass of periphyton on the artificial substrate were respectively 1351.3 ind/m2 and 2069.6mg/m2; while the averaged cell density and biomass of periphyton on the natural substrate were respectively 2199.9 ind/m2 and 3228.9 mg/m2.The means of diversity indices(H ′, D), evenness(J) and abundance(d) of periphyton in the Yili River were 3.24, 0.73, 0.60 and 3.91, respectively. Averaged diversity indices(H′, D), evenness(J) and abundance(d) of periphyton in the Irtish River were 3.52, 0.73, 0.64 and 3.30, respectively. Pearson correlation analysis showed that the density of periphyton in the Yili River was correlated significantly negatively with flow velocity, but correlated positively with water temperature,salinity. The biomass of periphyton was correlated negatively with flow velocity, but positively with water temperature. The density of periphyton in the Irtish River was correlated significantly positively with dissolved oxygen, and the biomass of periphyton was correlated positively with electrical conductivity, salinity and total dissolved solids.Based on the biodiversity indices(Shannon-Wiener, Margalef, Pielou), the method of indicator organism, the pollution tolerance index for diatoms and the algal saprobic index the water quality assessment showed that water quality in the Yili River basin was in good condition except for several sampling sites(Zhaosu liberation bridge, Yamadu and Yili River bridge). Overall, the Yili river basin showed a better status of water quality currently. The water quality assessment showed that water quality in the Irtish River basin was in a good condition except for several sampling sites(Chonghuer bridge, Tuohongtai reservoir, Bieliezeke). Overall, the Irtish river basin showed a better status of water quality currently.C/N/P elemental compositions were measured in macrozoobenthos, fish musculature, periphyton and hydrophyte in the Irtish River. The carbon(C), nitrogen(N) and phosphorous(P) of macrozoobenthos, fish musculature, periphyton POM and hydrophyte ranged from 39.9%-52.7%, 8.5%-9.5% and 0.6%-0.7%; 40.2%-48.3%,10.7%-13.0% and 0.8%-1.4%;1.3%-2.0% and 0.2%-0.3%;33.5%-39.6%, 1.9%-2.1%and 0.1%-0.2%, respectively. The lowest N/P ratio of macrozoobenthos was found in July, and P contentwas correlated negatively with N/P ratio and variation in N/P ratio change was determined by the P content. So, we speculated that the growth rate of macrozoobenthos was more fast in July than those in other seasons. The lowest N/P ratio of fish muscle was found in May, and the P content was correlated negatively with N/P ratio, while N content was correlated positively with N/P ratio, possibly suggesting a fast growth rate of fish in May. The lowest N/P of hydrophyte was found in May, and C content was correlated positively with N/P ratio, suggesting fast growth rate of hydrophyte in May. |
