Abstract:A new freshwater phototrophic species of the dinoflagellate genus Peridiniopsis, P. niei sp. nov., is described based on morphology. The new species appeared during spring with densities up to 1.48 × 10 7 cells . L -1 in some tributaries and gullies of Three Gorge Reservoir and Lake Donghu, China, forming red tides. Peridiniopsis niei is a cyst-producing freshwater dinoflagellate that belongs to the group Penardii. The plate tabulation is po+x+4'+0a+6"+5c+5s+5'"+2"" and the plate pattern is symmetric. The cells of P. niei are pentagonal in ventral view, the epitheca is larger than the hypotheca, making up about 2/3 the length of the cell. Plate 3' is hexangular. The closest species to P. niei is P. penardii (Lemmermann) Bourrelly, but cells of the former are pentagonal, very compressed dorsoventrally, and the hypotheca is truncated with one transparent, robust spine on each antapical plate.

Benthic diatom assemblages on the natural substrata were investigated at 21 sites of the Ganhe River watershed (China) once per season and in addition, early spring in 2013. A total of 487 diatom taxa from 36 genera were identified during five investigations. The assemblages were dominated by Achnanthidium minutissimum (Kützing) Czarnecki and Cocconeis placentula in the rural reach, whereas Navicula, Nitzschia, and Gomphonema species were characteristic of urbanized sites. Our results suggest that biodiversity was positively related to high nutrient levels and strongly negatively related to diatom-based indices. The periphyton biomass (expressed as chlorophyll a and ash-free dry mass) was not related to water quality. Canonical correspondence analysis (CCA) showed that the nutrient concentration gradient was the most important factor that affected the diatom assemblage composition and species distribution. The diatom-based indices (specific pollution sensitivity index (IPS), biological diatom index (IBD), and trophic diatom index (TDI)) were significantly positively correlated with water quality and are adequate for use in China. Slight changes in the biodiversity and diatom-based indices followed a temporal pattern. The species composition was less related to the season or hydrological characteristics of the river but more strongly related to differences in the trophic status. In this region, urbanization masked the impact of rural land use on benthic diatoms. The research will expand the understanding of using benthic diatom assemblages for water quality monitoring in urban streams and improve watershed-scale management and conservation efforts in the Ganhe River, China.

The colonization characteristics of benthic microalgae communities on artificial substrata were analyzed in four shallow lakes of different trophic status. Colonizations in lower nutrient lakes with macrophytes (Niuchao Lake and Langzi Lake) had longer lag phases, lower peak biomasses, and had longer times to community maturity than the higher nutrient lakes without macrophytes (Nanhu Lake and Donghu Lake). Hypereutrophic Nanhu Lake was dominated by filamentous green algae Oedogonium spp. and the diatom Gomphonema parvulum. The diatoms Melosira varians and Synedra spp. dominated the community in eutrophic Donghu Lake. Achnanthes minutissima was dominant in most colonization periods, and some filamentous green algae appeared with prolonged colonization time in the lower nutrient lakes. Succession rates were higher at sites with higher nutrient concentrations.

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The response of periphyton biofilm and the submerged macrophyte tape grass (Vallisneria natans) to internal loading from eutrophic lake sediments were evaluated in microcosms. The sediments from the littoral zone and center of a lake were selected to carry out the microcosm experiment. To determine how the differences in the periphyton biofilm and V. natans growth alone or in combination, we measured changes in water quality, growth, and TP in the periphyton biofilm and V. natans in microcosms containing these sediments. The results showed that the average daily TN and TP removal rates were 32.6 and 35.4%, respectively, in the microcosms containing the lake center sediments by V. natans and the periphyton biofilm. The presence of the periphyton biofilm and V. natans increased the pH, dissolved oxygen, and redox potential and decreased the conductivity in the overlying water in all treatments. Compared to the state before the treatments, V. natans grew well, with a significant increase in biomass (3.1- to 5.5-fold growth) and TP amount (5.1- to 8.8-fold) in all treatments after 48 days. However, the growth of V. natans that combined with the periphyton biofilm was better than that of V. natans alone, as reflected by the dry weight, chlorophyll a content, malondialdehyde content, and TP amount. In conclusion, the periphyton biofilm was beneficial for the growth of V. natans, and the appropriate combination of V. natans and periphyton biofilm would be a potential method for the ecological restoration of eutrophic lakes.

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An annual investigation on periphytic diatoms and physicochemical parameters was performed in Donghu Lake, China, to explore a suitable method to differentiate the dominant and subordinate taxa, and how they responded to the change of environmental factors. The results showed that: (1) a combined consideration of species frequency of occurrence and relative abundance for defining the dominant index was more appropriate than using solely relative abundance; (2) the dominant taxa Fragilaria capucina var. vaucheriae (Kützing) Lange‐Bertalot and Melosira varians Agardh responded insensitively to the environmental factors, whereas the subordinate species Fragilaria capucina Desmazieres var. capucina, Nitzschia amphibia Grunow, Achnanthidium exiguum (Grunow) Czarnecki and Melosira italica (Ehrenberg) Kützing showed the potential to be indicators; F. capucina var. radians (Kützing) Lange‐Bertalot increased along the gradient of higher water temperature (WT) and nutrients concentration, however, Fragilaria bidens Heiberg and Cymbella affinis Kützing were affected in the opposite direction. Our findings revealed that periphytic diatoms varied seasonally and were useful for assessing water quality of different trophic status. Especially the subordinate species showed the potential to be better indicators than the dominant species in Donghu Lake.