Spatial Distribution of Carbon, Nitrogen and Phosphorus within Surface Sediments in the Lower Lancang River: Pollution Assessment Related to Dams

Hongjun Lu,Kaidao Fu,Xiaorui Song,Baiyun He,Liyuan Wang,Ting Dong,Wanhui Peng

doi:10.4236/jep.2018.913083

Abstract

Surface sediment is one of the main sources of nutrients in overlying water environments, and these can also indirectly reflect the degree of eutrophication. In this paper, the spatial distribution characteristics of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in the surface sediments of 11 sections in the lower Lancang River during flood season are analyzed, as well as the distribution of phosphorus in different forms. The main sources of TOC and its correlation with TN and TP are discussed and, finally, the pollution levels of the surface sediments are evaluated. The results show that the average content of TOC in the surface sediments of the lower Lancang River is 9003.75 mg/kg. The average TN content is 893.79 mg/kg, while the average TP content is 521.35 mg/kg. The TOC in the surface sediments of the lower Lancang River is derived mainly from algae and plankton in the river, and the TN and TP have similar sources. The total phosphorus in the surface sediments of the lower Lancang River is composed mainly of calcium-bound phosphorus (Ca-P). The evaluations of the organic pollution index and comprehensive pollution index show that the surface sediment pollution degree at the upper sections of the Nuozhadu and Jinghong Dams are more serious than those below the dams. Furthermore, the tributary sections are all slightly polluted, with the exception of the Mengyang River, which is considered moderately polluted.

Highlights

Sediment is an essential component of every river ecosystem [1] and the source of nutrient elements, such as carbon, nitrogen and phosphorus, which are of great significance to the migration and transformation of river biogenic elements
The spatial distribution findings suggest that the concentrations of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in the surface sediments of the lower reaches of Lancang River are influenced by both human activities and dam interception
The results of this study show the average content of TOC, TN and TP in the surface sediments of the lower Lancang River to be 0.675% - 1.336%, 0.063% - 0.122% and 367.99 - 736.13 mg/kg, respectively

Summary

Introduction

Sediment is an essential component of every river ecosystem [1] and the source of nutrient elements, such as carbon, nitrogen and phosphorus, which are of great significance to the migration and transformation of river biogenic elements. The migration and transformation of nitrogen and phosphorus with river sediments can affect the bioavailability of these nutrients in the water [3] Additional elements, such as calcium, aluminum and iron in the sediments, are adsorbed with phosphorus to form different patterns of phosphorus [4]. The difficulty of their release directly affects the quality of the river water environment and, the pollution status of river sediments indirectly reflects the extent of pollution in overlying water environments [5]. Of great scientific significance that the contents of carbon, nitrogen and phosphorus in river sediments and their spatial distribution are studied and the pollution status of sediments are evaluated, as these factors contribute substantially to the control of river eutrophication and improvement of the environmental quality of river water

Methods

Results

Discussion

Conclusion