Seasonal Variation Of Periphytic Diatom Communities In Two Small Streams, Guangdong Province, Southern China

For the study of the seasonal variation of diatom communities and the diatom speciesdiversity in the subtropical region, periphytic diatom assemblages were investigated fromJanuary to December,2011, in the streams of Zeng and Liuxihe River, southern China.Diversity indices and RDA (Redundancy analysis) were used to analyse the correlationsbetween the diatom community and environmental factors, and to understand the diatomseasonal variations and the main influencing factors. The seasonal diatom diversity in artificialsubstrates were investigated in the wet season (August), the normal water period (April) and thedry season (January) at three locations: Paitan, Xiaolou, and Shitan in Zeng River. The growthcharacteristics and succession characteristics of diatoms in the artificial substrates were alsoobserved at the estuary of a feeding stream to Liuxihe reservoir, from November,2011toJanuary,2012. Biomass (Chl a) was applied to estimate the period for the diatom to reachbiomass maximum and maintain stable community. The Shannon diversity index, Simpson'sindex, Pielou evenness index, Similarity index, and the Sorensen index were calculated toevaluate the succession of diatom communities on the artificial substrates.At Liangming, one site in a stream of Liuxihe River,103diatom species were identified,belonging to33genera. The dominant genera included Achnanthidium, Cyclotella,Gomphonema, Nativula and Nitzschia, but their relative abundance varied stronlgy between theseasons. During the normal water period (March and April), Gomphonema was the dominantgenus, making up for more than60%in the community, but at the wet season (July and August),Nitzschia became more prominent, with relative abundance of about60%. At Hanhu, the site ina stream of Zeng River, there were111diatom species, belonging to44genera; Achnanthidium,Cocconeis, Gomphonema, Nativula and Nitzschia. Achnanthidium were the dominant genera,but in the wet season the relative abundance of Nitzschia became about30%; Achnanthidiumbecame the main genus in the dry season again. RDA (Redundancy analysis) analysis showedthat the water temperature was the major factor regulating the community structure ofperiphytic diatoms both in Liangming and Hanhu. Especially at Hanhu, the water temperaturerevealed a strong positive correlation with diatom assemblages (p<0.01). At Liangming, NO₂--Nalso have positive correlation with the diatom assemblage (p<0.05).Settlement patterns of periphytic diatoms on five types of artificial substrates (wood, tile, grass, PVC, stone) in3locations of the Zeng River with different trophic states werecomparatively analyzed in January, April and August,2011, we found that there were244diatom species, belonging to62genera. The dominant genera included Achnanthidium,Gomphonema, Melosira, Navicula and Nitzschia. The biomass indicated that wood was themost favorable artificial substrate for periphytic diatom research. Tile and PVC also seemedfavorable substrates in this study. The similarity index indicated that the diatom assemblageswere not similar between the artificial and natural substrates (S′<0.75) except for Paitan duringthe dry season, but there were strong similarities between the artificial substrates.During the experiment of diatom growth characteristics and succession characteristics at theestuary of Liuxihe reservoir in the dry season, a total of229species, belonging to43generawere identified on the artificial stones, and27genera,181species on the natural stones.Achnanthidium rivulare, Achnanthidium catenata, Cocconeis placentula, Gomphonemaentolejum, Melosira varians, Navicula canalis, Navicula hintzii, Nitzschia palea andPsammothidium grischuum were the first colonized species into the artificial substrate.Thereafter, there were several dominant genera on the artificial substrates, such asAchnanthidium, Navicula, Nitzschia, Melosira, Gomphonema and Psammothidium, and thecommunity became more stable than before. The biomass (Chl a) indicates that it needs32daysto reach the peak. Chl a was up to62mg L^-1 cm^-2, after that it decreased. About38days later,the biomass became relatively stable, with the averaged Chl a concentration at41mg L^-1 cm^-2. Diversity indices showed that the diatom assemblages differed between natural andartificial substrates; the similarity index also showed that the diatom assemblages on artificialand natural substrates were not similar (S′<0.75).