Geochemistry of reduced inorganic sulfur, reactive iron, and organic carbon in fluvial and marine surface sediment in the Laizhou Bay region, China

Understanding the geochemical cycling of sulfur in sediments is important because it can have implications for both modern environments (e.g., deterioration of water quality) and interpretation of the ancient past (e.g., sediment C/S ratios can be used as indicators of palaeodepositional environment). This study investigates the geochemical characteristics of sulfur, iron, and organic carbon in fluvial and coastal surface sediments of the Laizhou Bay region, China. A total of 63 sediment samples were taken across the whole Laizhou Bay marine region and the 14 major tidal rivers draining into it. Acid volatile sulfur, chromium (II)-reducible sulfur and elemental sulfur, total organic carbon, and total nitrogen were present in higher concentrations in the fluvial sediment than in the marine sediment of Laizhou Bay. The composition of reduced inorganic sulfur in surface sediments was dominated by acid volatile sulfur and chromium (II)-reducible sulfur. In fluvial sediments, sulfate reduction and formation of reduced inorganic sulfur were controlled by TOC and reactive iron synchronously. High C/S ratios in the marine sediments indicate that the diagenetic processes in Laizhou Bay have been affected by rapid deposition of sediment from the Yellow River in recent decades

Influence of salinity on COD measurements in coastal water management

COD is an important parameter in water quality assessment. COD values by different determination methods were investigated in coastal rivers. The results show that there is no clear relationship between CODCr and CODMn in coastal areas. CODCr does not reflect the degree of pollution of coastal waters. As salinity increased, CODCr and acidic CODMn increased significantly, but there was little/no change observed for alkaline CODMn. Coastal zone water quality standards should be proposed to solve the connection problems between the marine quality standard and surface water quality standard

Phosphorus release from coastal sediments: Impacts of the oxidation-reduction potential and sulfide

The release of phosphorus (P) from benthic sediments can affect the P content, nutrient status and quality of overlying waters in coastal ecosystem. This study was carried out to investigate the influence of oxidation-reduction potential (ORP) and sulfide on P release from sediments in the coastal estuary of the Yuniao River, China. The results showed that ferric iron-bound P was the main P burial phase in the sediments. The P concentration in overlying water increased with ORP decrease and sulfide increase, displaying a significant linear correlation with the ORP and sulfide concentration. The results indicate that decreased ORP may elevate the zero equilibrium phosphorus concentration, enhancing the capability of P release. And increased sulfide may react or capture reactive iron in sediments, reducing the P adsorption capacity and accelerating P release. Therefore, the control of ORP and sulfide production is important in the sink/source conversion of P in coastal sediments. (C) 2016 Elsevier Ltd. All rights reserved

A combined application of different engineering and biological techniques to remediate a heavily polluted river

River pollution is becoming a serious problem worldwide. A field-scale experiment was undertaken to remediate a heavily polluted river using a combined engineering approach of aeration, microorganisms, biological aerated filtration, artificial biofilms and ecological floating beds. Prior to remediation, the river water was black, anoxic and highly sulfidic. With remediation, the chemical oxygen demand decreased from ~250 to ~50mgL-1, NH4+-N decreased from ~27 to ~4mgL-1, sulfide decreased from ~3 to ~0.3mgL-1, and total suspended solids decreased from ~270 to ~40mgL-1. At the same time, dissolved oxygen increased from ~0.1 to ~3.5mgL-1, and water clarity increased from ~6 to ~40cm. Furthermore, the unpleasant odor emanating from the polluted river was also stopped, and local farmers have begun using the water for irrigation. This field-scale experiment thus indicates the potential usefulness of this combined engineering approach to remediate heavily polluted rivers