| Originating from the Shennongjia Forest District, Gufu River is a tributary of Xiangxi River which is the largest tributary of Three Gorges Reservoir Area in Hubei Province, central China. It is the research hotspot of watershed ecology. The community structure characteristics of periphytic algae and14environmental factors (including altitude, pH value, water temperature, dissolved oxygen, velocity, conductivity, hardness, total nitrogen, nitrate nitrogen, ammoniacal nitrogen, total phosphorus, silicon dioxide, chemical oxygen demand, total organic carbon) were investigated at19sites in the Gufu River and its major tributaries (Zhuyuan River) once each two month from December2010to October2011. With methods of one-way ANOVA, partial and Pearson correlation analysis and discriminant analysis, the variation characteristics community structure of periphytic algae and environmental factors were found out. Two diatom indices of GDI (Generic Diatom Index) and PTI (Pollution tolerance index for diatoms) and one periphyton indices of P-IBI (Periphyton Index of Biological Integrity) were used to assess stream conditions of Gufu River Basin. The relationship between the evaluation index and environmental factors were discussed, and moreover, merit and deficiency of GDI, PTI and P-IBI in the assessment of stream conditions of Gufu River Basin were evaluated. Results were shown as follows:The periphyton species were diversity and the community structure were complex in Gufu River Basin. A total of136algae taxa were identified, belonging to6phyla,36families,63genera. The periphytic algal communities were mainly consisted of diatoms (71taxa, accounting for52.21%of the number of species), followed by green algae and blue algae (38and23taxa, accounting for27.94%and16.91%of the number of species respectively), and then were Euglenophyta, Xanthophyta and Dinophyta (2,1and1taxa respectively).The dominant species were defined as the species whose relative abundance were more than5%. The maximum of individual dominance was in April2011when the average relative abundance of the all dominant species was16.10%and the dominant species were Nitzschia frustulum, Synedra sp., Melosira varians, Cyclotella sp., Achnanthes lanceolata and the predominant species was Nitzschia frustulum.The minimum of individual dominance was in February2011when the average relative abundance of the all dominant species was9.02%and the dominant species were Cocconeis placentula, Achnanthes biasolettiana, Nitzschia frustulum-. Cymbella gracillis-. Navicula rhynchocephala and the predominant species was Cocconeis placentula. The dominant diatom were mainly species preferred living in clean water in upstream of Gufu River, while there were mainly species preferred living in polluted water in downstream of Gufu River and upstream of Zhuyuan River. Overall, the dominant species were mainly the types of indicating clean water, such as Cocconeis placentula、 Achnanthes lanceolata、Achnanthes hiasolettiana、Gomphonema angustatwn, and were the tolerance species indicating polluted water only in few individual sampling points, such as Nitzschia frustulum. Oligosaprobic to mesosaprobic diatoms species dominated in Gufu River basin, indicating that the river water quality were in oligo-trophic to meso-trophic.The Shannon-Wiener diversity index ranged between0.476and4.207with a mean of2.212. The algae density ranged between6.707×103and7.633×106ind./cm2with a mean of8.134×105ind./cm2. The chlorophyll a concentration ranged between0.286and88.113mg/m2with a mean of8.894mg/m2. The Shannon-Wiener diversity index was significantly positively correlated with the chlorophyll a concentration (P<0.001). The algae density was positively correlated with the chlorophyll a concentration (0.01<P<0.05). The results indicated that variation of Shannon-Wiener diversity index, the chlorophyll a concentration and the algae density were in consensus.The periphyton samples were collected from90sampling sites in Gufu River basin. Six sampling sites (GF01, GF02, GF04, GF06, GF12, and ZY03) were chose as the reference sites. Twenty eight candidate metrics on5categories (including species richness, sensitive groups, diversity index, relative abundance, ecotype and density and biomass) were evaluated stepwise by distributing range analysis, discriminatory power analysis and Pearson’s correlation analysis. Basing these analysis we obtained9core metrics (including Periphyton taxa number, The total number of diatom genus, The total number of blue algae genus, Evenness index, Achnanthes percentage, Oscillatoria percentage, Stipitate diatoms percentage. Chlorophyll a content, Periphyton density) to produce P-IBI evaluation. The1,4,7,10quarters method was used to assign the value of each metric. P-IBI was the sum of the value of9core metrics. Based on the25%percentile of P-IBI value in reference sites, the criteria of health ranking was determined. The distribution range above25%percentile was defined as Health. The distribution range below25%percentile was divided into4quarters, forming4grades:Good, Fair, Poor and Very poor. P-IBI criteria was:P-IBI>59.25, Health;59.25-44.43, Good;44.43-29.62, Fair;29.62-14.81, Poor;<14.81, Very poor. Results were shown as follows:In all90sampling sites,14sites were in Health,35sites were in Good,36sites were in Fair,4sites were in Poor, and1sites were in Very poor. The P-IBI ranged between12and72with a mean of45.88(Good grade), indicating that Gufu River aquatic ecosystem had a good biological integrity and were in health conditon overall.P-IBI presented significant temporal and spatial heterogeneity. As the temporal variation:P-IBI of winter and spring (from December to April) were more than that of summer and autumn (from June to October), which was mainly because the sites in winter and spring suffered a small degree of outside interference, such as stable water dynamic conditions, and little effect of residents production and living. As the spatial variation:P-I13I of the upstream of Gufu River (from GF0I to GF13sites) were more than that of the downstream of Gufu River (from GF15a to GF19sites); P-IBI of the upstream and downstream of Zhuyuan River were higher than that of the midstream. The water ecosystem health level of Gufu River was higher than that of Zhuyuan River (annual average of P-IBI were47.00and36.91, respectively). It was mainly because most of sites in Gufu River (from GF01-GF11sites) were located at the Shennongjia National Nature Reserve where forest vegetation coverage percentage was relatively high, while the upstream sites of Zhuyuan River was located at the large-scale phosphorite mining area where soil erosion and sewage pollution of the miners were serious. So, the algae growth environment were serious damage, and biological integrity were severely affected by the human interference.The results of stream condition assessment based on GDI, PTI and P-IBI were in consensus in Gufu River Basin. The results of stream condition assessment showed that upstream area of Gufu River were in excellent ecological integrity, while, the downstream area of Gufu River were in severe impairment; midstream area of Zhuyuan River were in excellent ecological integrity, while, upstream and downstream area of Zhuyuan River were in severe impairment. The results of Pearson’s correlation analysis showed that there were significant positive correlations among the scores of GDI, PTI and P-IBI in sample sites of Gufu River Basin. P-IBI was positively correlated with GDI (r=0.340,0.001<P<0.01); P-IBI was significantly positively correlated with PTI (r=0.503, P<0.001); GDI was significantly positively correlated with PTI (r=0.644, P<0.001). The results of Pearson’s correlation analysis between P-IBI and characteristics of water environment showed that:P-IBI were negatively correlated with total nitrogen, ammoniacal nitrogen and conductivity (0.001<P<0.01); P-IBI were negatively correlated with total phosphorus, nitrate nitrogen, hardness, and velocity to some extent(0.01<P<0.05); P-IBI was significantly positively correlated with altitude (P<0.001). The above correlation test confirmed the reliability of the ecosystem health assessment results based on P-IBI. |
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