Utilization of nitrate stable isotopes of Chydorus sphaericus (OF Müller) to elucidate the hydrological characteristics of riverine wetlands in the Nakdong River, South Korea

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.