Distribution of Geochemical Species of P, Fe and Mn in Surface Sediments in the Eutrophic Estuary, Northern Taiwan

Tien-Hsi Fang,Cheng-Wen Wang

doi:10.3390/w13213075

Abstract

The Danshuei River Estuary (DRE) in northern Taiwan is a seriously eutrophic estuary due to the domestic effluent discharge. Surface sediment samples were collected from the DRE to study the concentrations and spatial distributions of different fractions of phosphorus through the five-step sequential extraction method which chemically divides the sedimentary P into five fractions: PSORB, PCDB, PCFA, PDET, and PORG. The Fe and Mn contents in the extracted solution were also determined. The total organic carbon (TOC) and grain size in sediment samples were analyzed as well. The sedimentary total P (TP) concentrations ranged within 537–1310 mg/kg and mostly exceeded 800 mg/kg, suggesting that the DRE sediments were moderately polluted by phosphorus. The PCDB was the dominant fraction of P, averagely contributing 58% of TP, followed by PDET 31%. The contributions of the PSORB and PCFA fractions to the TP were relatively minor. Two fractions, FeCDB and FeORG, of sedimentary Fe equally shared approximately 70% of total Fe, followed by FeDET with 22%. The contribution of different fractions of sedimentary Mn followed the sequence: MnCDB (36%) > MnCFA (29%) > MnORG (14.7%) > MnDET (14.5%) > MnSORB (5.3%). The sedimentary P, Fe, and Mn within the DRE are easily mobilized because they were mainly present in the reducible fraction. The concentrations of sedimentary TP positively correlated with the TOC contents and inversely negatively correlated with grain size, suggesting that the TOC and grain size play the crucial roles in influencing the distribution of sedimentary P within the DRE. Finally, the Fe(III) (hydro)oxides seems to play an important carriers to adsorb dissolved P because PCDB positively correlated with FeCDB.

Highlights

Phosphorus and nitrogen are the most important essential elements among the trace elements for marine organisms, especially for phytoplankton, and they control the primary productivity in the marine environment [1]
The concentrations of sedimentary total P (TP) positively correlated with the total organic carbon (TOC) contents and inversely negatively correlated with grain size, suggesting that the TOC and grain size play the crucial roles in influencing the distribution of sedimentary P within the Danshuei River Estuary (DRE)
The percentages of the four fractions of sediment grain sizes at each station obtained in the four surveys are plotted in Figure 5, and the percentage ranges of each fraction were as follows: MS, 0.5–94.5%; FS, 1.2–91.9%; VFS, 0.1–45.2%; and mud

Summary

Introduction

Phosphorus and nitrogen are the most important essential elements among the trace elements for marine organisms, especially for phytoplankton, and they control the primary productivity in the marine environment [1]. Both elements play a crucial role in influencing the marine carbon cycle and affect the global biogeochemical cycles [1,2,3]. The eutrophication in the aquatic environment, especially in estuaries, is recognized as a globally pertinent environmental issue [3,9]

Methods

Results

Discussion

Conclusion