Insights into community-based bioassessment of environmental quality status using microphytobenthos in estuarine intertidal ecosystems

The feasibility of community-based bioassessment of environmental quality status was studied using microphytobenthos（MPB） in estuarine intertidal ecosystems.The sediment samples of MPB were collected monthly during a 1-year cycle（September 2006-August 2007） at four sampling stations in the Nakdong River Estuary,Korea.Environmental variables,such as salinity,radiation,grain size of sediment,Si（OH）4（Si）,nitrate（NO3^-）,nitrite（NO2^-）,ammonium（NH4~＋） and phosphates（PO4^（3-））,were measured synchronously for comparison with biotic parameters.The statistical analyses were carried out for assessment the relationship between biotic and environmental parameters.The results showed that：（1） the MPB community structures were significant differences among four sampling stations;（2） spatial variation in the MPB communities were significantly correlated with environmental variables,especially the nutrient NH4＋ in combination with salinity and grain size;（3） three species（Navicula lacustris,Pleurosigma anglulatum and Fragilaria sp.1） were significantly correlated with nutrients and/or Si;and（4） the species richness and diversity were significantly correlated with the grain size.It is suggested that MPB communities may be used as a potentially robust bioindicator for assessing environmental quality status in estuarine intertidal ecosystems.

Dynamic genetic features of eukaryotic plankton diversity in the Nakdong River estuary of Korea

Estuaries are environments where freshwater and seawater mix and they display various salinity profiles.The construction of river barrages and dams has rapidly changed these environments and has had a wide range of impacts on plankton communities.To understand the dynamics of such communities,researchers need accurate and rapid techniques for detecting plankton species.We evaluated the diversity of eukaryotic plankton over a salinity gradient by applying a metagenomics tool at the Nakdong River estuary in Korea.Environmental samples were collected on three dates during summer and autumn of 2011 at the Eulsukdo Bridge at the mouth of that river.Amplifying the 18 S rDNA allowed us to analyze 456 clones and 122 phylotypes.Metagenomic sequences revealed various taxonomic groups and cryptic genetic variations at the intra-and inter-specific levels.By analyzing the same station at each sampling date,we observed that the phylotypes presented a salinity-related pattern of diversity in assemblages.The variety of species within freshwater samples reflected the rapid environmental changes caused by freshwater inputs.Dinophyceae phylotypes accounted for the highest proportion of overall diversity in the seawater samples.Euryhaline diatoms and dinoflagellates were observed in the freshwater,brackish and seawater samples.The biological data for species composition demonstrate the transitional state between freshwater and seawater.Therefore,this metagenomics information can serve as a biological indicator for tracking changes in aquatic environments.