High salinisation risks in a typical semi-arid river network in northern China

The objective of this study was to investigate the salinisation characteristics of a semi-arid river network in northern China and highlight the influencing factors and risks. The Ziya River Basin, a typical semi-arid river network located in the North China Plain, is studied herein. Overlying water, surface sediment and riparian soil samples were collected in July and December of 2014 in the Ziya River Basin. The results showed that the average concentrations of salt content in the overlying water and surface sediment of 10 rivers in the Ziya River Basin were 1105.64 and 2159.35 mg/L, respectively. High level of salinisation was found in most rivers not only in overlying water, but also in surface sediment. The impact of the salinisation of overlying water on riparian soil diminished with distance away from the shore and had no impact beyond 15 m from the shore. Heavy pollution can contribute greatly to the salinisation of the water column and can cause significant impacts on river sediment and riparian soil. Salinisation in the overlying water affects the sediment and riparian soil, and reveals that the high risk of salinisation in the Ziya River Basin has been underestimated.</p

³¹P-NMR spectra for different extracts of the river sediments (A: 0.5 M NaOH and 100 mM EDTA; B: 0.25 M NaOH and 50 mM EDTA; C: 0.25 M NaOH; D: 1 M NaOH and 50 mM EDTA).

<p>³¹P-NMR spectra for different extracts of the river sediments (A: 0.5 M NaOH and 100 mM EDTA; B: 0.25 M NaOH and 50 mM EDTA; C: 0.25 M NaOH; D: 1 M NaOH and 50 mM EDTA).</p

Characteristics and Distribution of Phosphorus in Surface Sediments of Limnetic Ecosystem in Eastern China

<div><p>Phosphorus (P) is an essential nutrient for aquatic organisms; however, excessive P inflow to limnetic ecosystems can induce eutrophication. P concentrations in the rivers, wetlands and lakes of Eastern China have been amplified by fertilizer and sewage inputs associated with the development of industry and agriculture. Yet, knowledge of the distribution and speciation of P is lacking at the regional scale. We determined the distribution and speciation of P in limnetic ecosystems in Eastern China using Standards, Measurements and Testing (SMT) and phosphorus nuclear magnetic resonance (³¹P-NMR). The results indicate that P pollution in surface sediments was serious. Inorganic P (Pi) was the primary drive of variation in total P (TP) among different river systems, and Pi accounted for 71% to 90% of TP in surface sediment in Eastern China. Also, the concentrations of TP and Pi varied among watersheds and Pi primarily drove the variation in TP in different watersheds. Sediments less than 10-cm deep served as the main P reservoir. Environmental factors affect the speciation and origin of P. NaOH-Pi, HCl-Pi and organic P (Po) were related to pH accordingly at the regional scale. The physicochemical properties of sediments from different limnetic ecosystems affect the P speciation. HCl-Pi was higher in wetland sediments than in riverine and lake sediments in Eastern China. Conversely, NaOH-Pi was lowest in wetland sediments. Total Po concentration was lower in riverine sediments than in other sediments, but Mono-P was higher, with an average concentration of 48 mg kg⁻¹. Diesters-P was highest in lake sediments. By revealing the regional distribution of TP, Pi and Po, this study will support eutrophication management in Eastern China.</p></div

Properties of the sediment used in this study.

<p>Properties of the sediment used in this study.</p

Recovery in Dissolved Oxygen Levels in Chinese Freshwater Ecosystems in the Past Three Decades

Deoxygenation is a serious problem in oceanic waters, but few studies have documented dissolved oxygen (DO) changes in freshwater systems. In this study, the changes in DO at the national scale were analyzed in the past 30 years. The results showed that the proportion of sites with DO greater than 5 mg L–1 increased from 29.1% in 2002 to 87.45% in 2020, and the proportion of sites with DO less than 2 mg L–1 decreased from 44% in 2001 to 0.2% in 2020. There was a change point in the DO levels in 2007. DO levels can recover benefit from reduction in the pollution load. Meanwhile, further improvement in DO is challenged by global warming and inefficiency of pollutant collection and treatment. There is no doubt that the Chinese freshwater system has basically crossed the first stage of pollution control and treatment, laying a foundation for entering the stage of ecological restoration

Sediment characteristics in different freshwater ecosystems in Eastern China.

<p>Sediment characteristics in different freshwater ecosystems in Eastern China.</p

The total P (TP) and organic P (Po) concentrations found using different extractant solutions.

<p>The total P (TP) and organic P (Po) concentrations found using different extractant solutions.</p

Location of the 89 sampling sites in Eastern China.

Sites were distributed throughout Heilongjiang, Liaoning, Hebei, Shandong, Jiangsu, Anhui, Hubei and Guangdong provinces, as well as Beijing, Tianjin and Shanghai municipalities. River, wetland and lake systems, prominent ecosystems in the Eastern China, are represented.</p

The total P (TP) and organic P (Po) concentrations in the re-dissolved extracts after lyophilization.

<p>The total P (TP) and organic P (Po) concentrations in the re-dissolved extracts after lyophilization.</p

P components in surface sediment determined by SMT fractionation and ³¹P-NMR.

<p>DNA-P: deoxyribonucleic acids (orthophosphate diesters); Lipids-P: phospholipids (orthophosphate diesters); Mono-P: orthophosphate monoesters; Ortho-P: orthophosphate; Phon-P: phosphonates; Pyro-P: pyrophosphates.</p