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Background This study aimed to identify NO3−-N sources using the stable isotope δ15N in Chydorus sphaericus (OF Müller), to investigate hydrological characteristics and nutrient states in artificial wetlands near the Nakdong River. Chydorus sphaericus is dominant in wetlands where aquatic plants are abundant, occurring in high density, and is sensitive to wetland water pollution, making it suitable for identification of NO3−-N sources. Results NO3−-N sources for each wetland were strongly dependent on hydrological characteristics. Wetlands with sewage or rainfall/groundwater as their main sources had high levels of NO3−-N, whereas wetlands with surface water as their main input had comparatively lower levels. Since wetlands with sewage and rainfall/groundwater as their main water sources were mostly detention ponds, their inputs from tributaries or the main river stream were limited and nutrients such as NO3−-N easily become concentrated. Changes in NO3−-N levels at each wetland were closely associated with δ15N of C. sphaericus. Interestingly, regression analysis also showed positive correlation between δ15N of C. sphaericus and NO3−-N level. Conclusions We conclude that the nitrate stable isotope (δ15N) of C. sphaericus can be used to elucidate the hydrological characteristics of riverine wetlands. This information is important for maintenance and conservation of artificial wetlands at the Nakdong River.

We collected zooplankton from May to October, 2011, with the aim of understandingthe zooplankton community distribution and food web interaction between the openwater and littoral (aquatic plants) zones in two small reservoirs with different landcovers(Sobudang, Myeongdong). Small-sized reservoirs are more abundant in SouthKorea, and a total of 51 and 65 species of zooplankton were identified at the twosmall reservoir (Sobudang and Myeongdong), where zooplankton densities weremore abundant in the littoral zone than in the open water zone. Cladocerans andcopepods densities were also higher in the littoral zone, in contrast, rotifers showedhigher densities in the open water zone (t-test

In this study, we investigated what environmental factors mainly influence the pattern of zooplankton communities in the regulated Nakdong River. Fifteen years of data (N = 629, 1994 to 2008) were used to analyze the patterns by means of self-organizing map (SOM), that is capable of extracting information through competitive and adaptive properties. A total of 34 variables (18 groups of zooplankton and 16 physicochemical parameters) were patterned onto the SOM, and then each variable was compared in accordance with three different annual rainfall patterns (i.e., dry, moderate, and wet). Finally, seven clusters were categorized according to Euclidian distance between the clusters on the SOM. Clear seasonal features for the variables were interpreted in five major categories, and two more subcategories were partitioned by a specific feature of zooplankton abundance and appearance. In the result, the patterns of zooplankton assemblage were mainly distinguished by water temperature, Secchi transparency, and river flow rate. In particular, the SOM result depicted a clear pattern of zooplankton assemblage clusters partitioned by annual precipitation, which accentuated the prolonged effect of dam regulation on plankton assemblage in a regulated river system.

Key-words: submerged macrophyte, macrophyte habitat, zooplankton, species diversity, shallow wetland Submerged macrophytes improve the structural heterogeneity of microhabitats in aquatic ecosystems, often providing an important habitat for zooplankton. However, excessive development of free-floating macrophytes on the water surface can reduce the biomass of submerged macrophytes and result in a relatively simple habitat structure. We hypothesized that controlling the development of free-floating macrophytes would result in a more complex habitat structure by promoting the development of submerged macrophytes. After applying three experimental treatments (NR, no removal; IR, intermediate removal; CR, complete removal of free-floating macrophytes), we found that CR of free-floating macrophytes improved the growth and development of submerged macrophytes and supported a large zooplankton assemblage. However, the largest zooplankton assemblage (in terms of abundance and diversity) was recorded after the IR treatment. Although submerged macrophytes were abundant in the CR treatment, the number, abundance, and density of zooplankton species were much lower than those in the IR treatment. Preferential selection of different macrophyte types by zooplankton presumably led to variation in plant utilization of niches, and the simultaneous presence of different macrophyte life forms created a complex microhabitat structure that induced high species diversity and zooplankton density.