Distribution Pattern Of Benthic Diatom And Its Relationship To Environmental Factors In Yi-Shu-Si River Basin

Here we analyze the relationship between benthic diatoms and environmental factors based on investigating the species diversity and spatial distribution of benthic diatoms in Yi-Shu-Si River Basin. We discuss the assessing environmental conditions in Yi-Shu-Si River Basin with benthic diatoms and the influences of multi-scale environmental factors on benthic diatoms to provide basis for biological monitoring, assessment and restoration of river ecosystem. Main findings:1. Benthic diatoms and their spatial distribution were studied. In total 266 diatom taxa which belong to 3classes, 14 order, 30 families and 73 genera were identified in 64 sample sites. The average of taxa was 29, ranging from 9 to 49. The average of Shannon-Wiener index was 2.85, ranging from 0.51~4.29. The average of Simpson index was 0.72, ranging from 0.11~0.94. 8 dominant species were Achnanthidium mintissimum, Nitzschia frustulum, Navicula aitchelbee, Nitzschia palea, Gomphonema parvulum, Cyclotella meneghiniana, Eolimna subminuscula and Mayamaea atomus. Biological Diatom Index(BDI) and Trophic Diatom Index(TDI) showed a same trend that the water quality of upstream and downstream was superior to the water quality of midstream. Generally, the ecological status of rivers in Yi-Shu-Si River Basin was low and the water was eutrophic.2. The correlation between benthic diatoms and physic-chemical factors was analysed. There’s no significant correlation between diatom diversity and physic-chemical factors. Part of dominant species correlated significantly with physic-chemical factors. The higher the relative abundance of Achnanthidium mintissimum is, the cleaner water quality is. The results showed a positive correlation between physic-chemical factors and relative abundance of some dominant species including Nitzschia palea, Gomphonema parvulum, Cyclotella meneghiniana, Eolimna subminuscula, Mayamaea atomus. BDI showed a strong nagative correlation with TP and Turbidity and a positive correlation with N:P. TDI showed a significant positive correlation with TP, TN, COD and Turbidity.3. The distribution of benthic diatoms in different grade rivers and influencing factors was studied. With the increase of stream order, taxa and diversity index first increased and then decreased. Different grade rivers had different dominant species. Achnanthidium mintissimum which is a clean species is the first-dominant species in rivers which belong to first-order, fifth-order and sixth-order. Some other species which are indicator of polluted environment dominant the rivers which belong to second-order, third-order and fourth-order. BDI and TDI showed that the water quality of first-order rivers, fifth-order rivers and sixth-order rivers was superior to second-order rivers, third-order rivers and fourth-order rivers. The RDA analysis showed that TP was what affected the benthic diatoms the most.4. The impact of multi-scale environmental factors on benthic diatoms. Correlation analysis showed that land-use of catchment and reach were correlated significantly with index of nutrient and pollution. The land-use of buffer especially forest-land percentage had a greater impact on physic-chemical factors and characteristic of benthic diatoms. The influence of large-scale environmental factors on BDI was more important. CCA analysis showed that spatial distribution of benthic diatoms was affected by both large-scale and small-scale environmental factors. pCCA showed that small-scale environmental factors was main factor which influence distribution of benthic diatoms. Large-scale environmental factors can indirectly affect benthic diatoms by influencing small-scale environmental factors.