COMMUNITY STRUCTURE OF DIATOM IN NANCHONG SECTION OF JIALING RIVER AND ANALYSIS OF ITS WATER ENVIRONMENT

Abstract

In order to understand the diatom community structure and reveal the pollution status and water quality in Nanchong section of Jialing River,15 diatom samples and water quality samples in five cites or counties of Nanchong city,were collected according to normal methods,in dry season,level season and rainy season,respectively.Chemical indices including COD,TN and TP were measured.The diatom community structure including diatom species composition,cell densities,Shannon-Weaver diversity index and Lloyd-Ghelardi evenness index were analysed,and the water quality was evaluated combined with chemical index.The results showed that:(1) 136 taxa,which belonged to 2 class,10 family and 26 genera were observed(including variety and form).Pennatae diatom species numbers were richer than that of centriate diatom.The percentage of Pennatae diatoms and centriate diatoms were 94.52% and 5.48% to the total diatoms,respectively.Langzhong section had the highest species numbers with 86 and Nanchong section had the lowest species numbers with the number of 48;The cell densities of diatom was in the range of 4500—39000 ind/L with the mean value of 18213 ind/L.Langzhong section had the lowest cell densities of diatom with the value of 12600 ind/L and Nanchong section had the highest cell densities of diatom with the value of 23700 ind/L.The diversity index was in the range of 1.05—3.30,with the mean value of 2.44.Langzhong section had the highest diversity index with the value of 2.85 and Nanchong section had the lowest diversity index with the value of 1.80;the evenness index was in the range of 0.22—0.66 with the mean value of 0.47.Langzhong section had the highest evenness index with the value of 0.55 and Nanchong section had the lowest evenness index with the value of 0.35.(2) The diatom species numbers,cell densities,diversity and evenness index took on noticeable seasonal and horizontal distribution distinction.To seasonal change,the diatom community structure had similarities in level season and dry season,with more species numbers,higher cell densities,diversity and indices evenness indices than those in rainy season.To horizontal distribution change,from upstream to downstream,the diatom species numbers decreased and diversity index and evenness index declined gradually,however,cell densities of diatom increased gradually.The sampling sites at upstream of the city had more species numbers,lower cell densities and higher diversity indices and evenness indices than those at downstream.(3) Species diversity index and evenness index as well as chemical items were used to evaluate the water quality in Nanchong section of Jialing River.The results consistently indicated that the water quality in Nanchong section of Jialing River belonged to β-mesosaprobic Zone all in all and the water body possessed certain self-purification ability.The water quality of Langzhong section was the best of all,which belonged to Oligosaprobid Zone;those of Nanbu,Xinzheng and Peng'an sections were between β-mesosaprobic Zone and Oligosaprobid Zone,which of Nanchong section was the worst of all,belonging to α-mesosaprobic Zone.To improve and protect the water quality of Jialing River,some prevention and cure measures and suggestions were given in the paper.