| Riparian plants can use nitrogen (N) from soil and river water, but the use of river water N might be limited in higher floodplain environments of the Chikuma River. The purpose of this study is to reveal the relationship between N uptake by riparian plants and the floodplain topography (relative height and distance from a river channel). We examined the hypothesis that surface sediment removal from the higher floodplain increases river water N uptake by riparian plants by using a stable isotope analysis. The d15N value of river water samples (ca. 8%) were significantly higher than those of the soil extracts (ca. 3%) in the study area. The d15N value of riparian plants increased from +3.0% (standard deviation, SD ±2.1%) before sediment removal to +9.6% (±2.1%) after sediment removal, although there was no significant change in the d15N value in N sources of soil and river water. The sediment removal enhanced frequency of flood disturbance, relative ground water level, and river water N uptake by riparian plants on the floodplain. |
