Evolution of the sink and source of dissolved inorganic nitrogen with salinity as a tracer during summer in the Pearl River Estuary.

Mei-Lin Wu,You-Shao Wang,Jun-De Dong,Jian-Ping Yin,Yi-Guo Hong

doi:10.1038/srep36638

Abstract

In this study, we evaluated the sink and source of the surface water along the PRE using a mixing model method with salinity as tracer. The observational data showed that the decreasing of dissolved inorganic nitrogen (DIN) did not closely follow the physical mixing lines of freshwater and modified seawater. In the western part, DIN consumption by phytoplankton and bacteria uptake (ΔDIN)varied from 15.81 μmol L−1 to 88.53 μmol L−1. On the contrary, in the eastern part, ΔDIN varied from −63.66 μmol L−1 to −10.45 μmol L−1. DIN source in the eastern part may be mainly caused by organic matter decomposition, while DIN remove is strongly associated with phytoplankton growth and bacteria consumption. These differential behaviors of the estuary with respect to DIN are largely due to varying degrees of hydrodynamics due to different topography in the two areas. Sensitivity analysis indicated reduction strategies of DIN inputs to coastal waters may improve environment quality in the PRE, due to DIN changes in the freshwater end-member having a determined influence on biological activities (R). Our results indicate that the model may be a valuable way to address the sources and sink of DIN in the river-dominated estuaries.

Highlights

Biogeochemical processes vary spatially and temporarily, and highly depends on system-specific features
The simple model involved with Dissolved inorganic nitrogen (DIN) vs. salinity is useful way in understanding the sink and source of DIN across the estuarine salinity gradient
The sink and source of DIN in the Pearl River Estuary (PRE) provided the abundant information about DIN consumption and production during the physical mixing of freshwater and modified seawater

Summary

Introduction

Biogeochemical processes vary spatially and temporarily, and highly depends on system-specific features. Rapid removal of dissolved inorganic nutrients (especially P and Si) often occurs in the very low salinity (0~5) region of the estuary[12]. Guangzhou lies in the western and northern sides of the PRE (Fig. 1) This difference in the western and eastern sides of the PRE plays a key role in DIN biogeochemical processes. The mixing diagram (DIN vs salinity) was used to explore the sink and source of DIN involving with physical mixing and biological activities. This approach can afford the valuable way to understand quantification and mechanistic of DIN behaviors and may eventually allow for the forecasting of estuarine behavior

Methods

Results

Discussion

Conclusion