Evaluation of relationship between environmental factors and diatom assemblages at genus and species levels in the Taizi River Basin, China

Abstract

Benthic diatoms are generally used to assess stream conditions, however most of the methods and diatom indices are based on the identification at species levels, which requires a lot of training because of its extreme diversity. Compared with species level, identification at genus level can save amount of time and money to assess river pollution, however it may lose some ecological information. In this paper, we investigated 67 samples sites in the Taizi River basin to investigate the relationship between diatom assemblages and environmental characteristics at both species and genus levels. Ten diatom assemblage attributes: relative abundance, richness, Shannon-Wiener diversity index, Pielou diversity index, Margalef diversity index, Berger-Parker diversity index, Simpson diversity index, Hill diversity index and Mackintosh diversity index were chosen to evaluate concordance correlations between genus and species level. We assessed relationship between diatom assemblages and environment base on the Pearson Correlation Test, Mantel-Test, Canonical Correspondence Analysis and Diatom Bioassessment Index. The results showed that 15 genera and 141 species of diatoms were observed in the Taizi River basin. The most abundant species was Navicula, followed by Nitzschia, presenting 32.6% and 13.5% of the sample sites, respectively. The Diploneis and Stauroneis were represented by a single species. Genus richness ranged from 2 to 13 and the species richness ranged from 3 to 40. The relative abundance and richness had strong correlations between species and genus resolution. Eight biology diversity indexes had strong correlations between species and genus resolution, of which the strongest coefficient was Mackintosh diversity index. Moreover the Berger-Parke diversity index was no related with the other biology diversity indexes. Both genus and species richness exhibited strong correlations with the suspended solid, total dissolved solid, total nitrogen, Cl-, NH+4-N, PO3-4, sand, total phosphorus, biochemical oxygen demand, chemical oxygen demand and permanganate index. Dissolved oxygen and NO-3-N variables were significantly correlated with genus richness, however there were no significant correlation between species richness and dissolved oxygen or NO-3-N. Correlations between major-ions, nutrients and organic matter with species relative abundance were significant, which was also observed at genus level. Based on principal component analysis, dissolved oxygen, conductivity, suspended solid, NO-2-N and biochemical oxygen demand were the main environmental factors in Taizi River basin. Canonical correspondence analysis showed that suspended solid had significant influence on the community structure of genus and species diatom in Taizi River basin. Assessment of river condition was made using the Diatom Bioassessment Index (DBI) at species and genus levels. The results at both levels (species and genus) showed same trend, indicating that upstream area of Taizi River basin was in excellent and good ecological integrity, while the stream condition of downstream area was in severe pollution. In conclusion, genus resolution may be used to replace the species resolution to evaluate the river conditions in China.