Significant and conservative long-range transport of dissolved organic nutrients in the Changjiang diluted water

Hyeong Kyu Kwon,Guebuem Kim,Jong Woo Park,Jeomshik Hwang,Weol Ae Lim,Tae-Hoon Kim

doi:10.1038/s41598-018-31105-1

Abstract

The Changjiang River is one of the main nutrient sources in the northwestern Pacific marginal seas. However, most of the previous studies have neglected the long-range transport (>200 km) of riverine nutrients since they are rapidly consumed. In this study, we examined the long-range transport (200–800 km) of nutrients in the surface layer during the summer of 2017. The plots of nutrients against salinity display that dissolved organic nitrogen (DON) was conservative over ~800 km, while more than 99% of the dissolved inorganic nitrogen (DIN) was removed within 200 km. As a result, in the study region, DON concentrations (avg. 7.0 ± 1.3 µM), which are minor in the river water, were much higher than DIN concentrations (avg. 0.28 ± 0.26 µM). Both nutrients, N and P, showed a similar pattern. Our results suggest that dissolved organic nutrients play a critical role on the long-range transport of riverine nutrients in surface waters and subsequent ecosystem changes.

Highlights

(200–800 km) of nutrients in the surface layer during the summer of 2017
The salinity distribution in the surface waters shows that the low-salinity (
In the study region (200–800 km), the concentrations of dissolved inorganic nitrogen (DIN) and DIP were lower than 1.3 μM and 0.22 μM, respectively, which were much lower than the concentrations of dissolved organic nitrogen (DON) (3.4–10.1 μM, avg. 7.0 ± 1.3 μM) and DOP (0.09–0.47 μM, avg. 0.24 ± 0.08 μM) (Figs. 2 and 3; Supplementary Table S1)

Summary

Introduction

(200–800 km) of nutrients in the surface layer during the summer of 2017. The plots of nutrients against salinity display that dissolved organic nitrogen (DON) was conservative over ~800 km, while more than. Our results suggest that dissolved organic nutrients play a critical role on the long-range transport of riverine nutrients in surface waters and subsequent ecosystem changes. Over the past 50 years, the riverine fluxes of DIN and DIP have increased approximately 6-fold due to the large-scale use of chemical fertilizers in the Changjiang River basin[12]. The long-range transport of dissolved organic nutrients in this region is poorly understood. In this study, we measured dissolved inorganic and organic nutrients in the downstream of the Changjiang estuary over a long distance (200–800 km) since most of the previous studies were conducted within 200 km[13,16,17,18,19,20]. We occupied our study region (200–800 km) twice in the same season, and all previous data within 800 km were included in this study in order to look at the general processes occurring in this region (Fig. 1)

Methods

Results

Conclusion