Distribution Of Benthic Diatoms And Water Ecosystem Health Evaluation In The Main Stream Of Dongjiang River

Benthic diatom is widely distributed in river ecosystems and an important biological group of river biology monitoring.It has been widely used in aquatic ecosystem health evaluation.In this thesis,a monitoring program,covering benthic diatom,physical and chemical indicators for Dongjiang River in Pearl river system,provides the fundemental information of benthic diatoms and environmental variables,which improves the list of benthic diatoms and accumulates data of water quality for assessment of water ecological health.In this study,80 benthic diatom samples were collected in the main stream of the Dongjiang River in Guangdong Province from November 2015 to December 2016 during five surveys.The environmental variables,the benthic diatom community,the sizes of diatom valves,the distribution of teratological form diatoms were analyzed with a focues on the health evaluation based on benthic diatoms.The main conclusions as follows:1)A total of 364 species of 66 genera,belonging to 11 families of benthic diatom(included 26 species of 12 genera diatom of teratological forms)were detected among the 16 sampling sites(November 2015,and February,June,September,December 2016)in the Dongjiang River,there were 22 species of 8 genera in Centrica and 316 species of 58 genera in Pennatae.The average species numbers of benthic diatoms in all sampling sites in the water system were 48 in the dry seasons and 52 species in the wet seasons.Achnanthidium,Gomphonema and Nitzschia were dominant genera with higher frequency and relative abundance.2)The dissimilarity between benthic diatom communities was lower in the middle reaches and higher in the lower reaches.The diversity indexes of benthic diatoms,such as richness and true Shannon-Wiener diversity index showed higher spatial distribution characteristics of middle reaches,and lower of other reaches.The spatial variation of community structure was significant and the seasonal variation was extremely significant(p<0.01).The species richness of diatoms in the Dongjiang River shows a trend with the highest in the middle reaches and lower in the upper and down reaches with obvious gradient distribution.3)The benthic diatom valves lengths appeared in the range of 2-190 ?m and the dominant valves lengths were mainly in the narrow range of 13.1-26.5 ?m and difference in valves lengths was not significant between the sampling sites.4)Redundancy analysis showed that the multiple environmental factors could significantly explain the variation of benthic diatoms communities.Variation partitioning indicated that nutrient,dissolved silicon,nitrate nitrogen,nitrite nitrogen and conductivity,pH and dissolved oxygen together contributed high explanation percentage.5)IBD(Diatom Biological Index)is significantly lower in the middle and low reaches than in the upstream of the Dongjiang River.The overall water health level is between "moderate level" to "poor level".6)Diatom Biological Index(IBD)can better reflect the environmental information of the sampling sites,and IBD is suitable for the Dongjiang River water quality health evaluation.It is recommended for the professional researchers to use IBD for analysis and health assessment.Generic index of diatoms(GI)can be easily applied by public users without a special training for emergency simple water health assessment,but there are still some unstable controlling factors,for example,GI is easily affected by the diatom genera selected and instable factors such as the distribution of diatoms in the sampling sites.