Determining factors for the occurrence and richness of submerged macrophytes in major Korean rivers

The natural flow regime in Korean rivers is approaching that of a lentic environment, and submerged macrophytes have become widely distributed throughout the river systems. To manage river ecosystems, it is important to identify the key environmental factors that affect species occurrence and richness of submerged macrophytes. Here, we examined the environmental factors that affect species occurrence and richness of submerged macrophytes after the major rivers project in Korea. We collected data for species presence/absence and species richness from 197 surveyed sites (from 2014 to 2015) along the five major rivers in Korea. Water environmental variables were obtained from the Ministry of Environment's national water quality measurement network (from January 2012 to October 2015). We used a boosted regression model and generalized additive model to identify the crucial water environmental factors related to occurrence and diversity of submerged macrophytes. The boosted regression model indicated that submerged macrophytes were abundant in waters with low concentrations of suspended solids and chlorophyll a. The generalized additive model showed that suspended solids, chlorophyll a, and water current velocity had the greatest effects on species richness, which declined with increasing water turbidity and flow velocity. Our results confirm observations in other impacted river systems and ask for a better understanding of the underlying environmental factors affecting macrophytes abundance and species richness.