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.

Purpose The organic phosphorus (OP) that is found in sediments influences the water quality of the overlying water. Accurate methods for OP extraction are important to identify phosphorus fractions in the sediments. We optimized the following: (1) the pH range of solutions after digestion; (2) the amounts of TP, H 2 SO 4 , and K 2 S 2 O 8 in the digestion; and (3) the digestion efficiency between acid K 2 S 2 O 8 and alkaline K 2 S 2 O 8 in total phosphorus (TP) and total nitrogen (TN) measurements. Moreover, we explained the related experimental phenomena and the results with an in-depth mechanism. Materials and methods Sediments samples were taken from three locations (Yellow Sea, Jiehe River, and Jiaolai River, China). Each sample was analyzed to optimize sequential OP extraction based on the Ivanoff method. Results and discussionWe focused on the digestion step and digestion efficiency between acidic K 2 S 2 O 8 and alkaline K 2 S 2 O 8 , total phosphorus (TP), and total nitrogen (TN) measurements. The results indicate that the optimal pH range of solutions after digestion is from 3 to 5.5. The TP digestion efficiency in combination withH 2 SO 4 + K 2 S 2 O 8 (acid) is, on average, 8% higher than that of NaOH+ K 2 S 2 O 8 (alkaline). However, the results for TN suggest the opposite. Optimal amounts of TP, H 2 SO 4 , and K 2 S 2 O 8 for digestion were also clearly determined. Conclusions The pH of solutions after digestion affects the color development necessary for effective phosphorus (P) determination. The TP and TN could be determined simultaneously using the alkaline K 2 S 2 O 8 digestion system under the experimental conditions. Finally, the optimal orthogonal combinations and mass ratios of P, K 2 S 2 O 8 , and H 2 SO 4 , respectively, were determined to be ~1.5 × 10

Identification of nitrogen (N) sources is important in water quality control and management. Nitrogen pollution can lead to eutrophication of waterbodies and high concentrations of nitrate in drinking water can pose potential health problems. The 15N isotope and nitrogen fluxes budget approach is useful for determining the source of to surface waters. In this study, mass balance and 15N isotope approaches and nitrogen flux budgets were applied to identify total nitrogen (TN) sources and nitrogen transformation processes in the Menlou Reservoir (MR), Jiaodong Peninsula, China. The different fractions of nitrogen and their 15N isotope signatures were analyzed in the reservoir water, river water, groundwater, soil, and atmospheric precipitation. The results indicate that surface runoff pollution (e.g., fertilizer and animal manure) is the main source of in MR. High concentrations of TN in MR are caused by low nitrogen self-purification (denitrification) rate, low sediment adsorption capacity, and the influx of rich groundwater.

The remediation of polluted coastal rivers is a global challenge in the environmental field. The objective of this study was to investigate the remediation feasibility of a high-salinity river using water spinach (WS) and sticky rice (SR) in hydroponic floating-bed systems. In this study, the total nitrogen (TN) removal rates were 89.7, 92.3, 85.1, and 75.2% in the WS floating-bed system and 81.2 and 78.9% in the SR floating-bed system under different salinities (2-31 psu). Additionally, the total phosphorus (TP) removal rates were 94.4, 96.4, 93.5, and 75.2% in the WS floating-bed system and 75.7 and 80.0% in the SR floating-bed system under different salinities. The results indicate that WS and SR significantly contributed to the remediation of a polluted tidal river. Additionally, increased salinity suppressed the removal of ammonium and phosphate by WS and SR. The salt tolerance of WS was greater than that of SR, which indicated that WS was a more appropriate choice for treating river contamination.