A framework for assessing the effects of afforestation and South-to-North Water Transfer on nitrogen and phosphorus uptake by plants in a critical riparian zone

Nitrogen removal in freshwater sediments of riparian zone: N-loss pathways and environmental controls

The riparian zone is an important location of nitrogen removal in the terrestrial and aquatic ecosystems. Many studies have focused on the nitrogen removal efficiency and one or two nitrogen removal processes in the riparian zone, and less attention has been paid to the interaction of different nitrogen transformation processes and the impact of in situ environmental conditions. The molecular biotechnology, microcosm culture experiments and 15N stable isotope tracing techniques were used in this research at the riparian zone in Weinan section of the Wei River, to reveal the nitrogen removal mechanism of riparian zone with multi-layer lithologic structure. The results showed that the nitrogen removal rate in the riparian zone was 4.14-35.19 μmol·N·kg-1·h-1. Denitrification, dissimilatory reduction to ammonium (DNRA) and anaerobic ammonium oxidation (anammox) jointly achieved the natural attenuation process of nitrogen in the riparian zone, and denitrification was the dominant process (accounting for 59.6%). High dissolved organic nitrogen and nitrate ratio (DOC:NO3-) would promote denitrification, but when the NO3- content was less than 0.06 mg/kg, DNRA would occur in preference to denitrification. Furthermore, the abundances of functional genes (norB, nirS, nrfA) and anammox bacterial 16S rRNA gene showed similar distribution patterns with the corresponding nitrogen transformation rates. Sedimentary NOX-, Fe(II), dissolved organic carbon (DOC) and the nitrogen transformation functional microbial abundance were the main factors affecting nitrogen removal in the riparian zone. Fe (II) promoted NO3- attenuation through nitrate dependent ferrous oxidation process under microbial mediation, and DOC promotes NO3- attenuation through enhancing DNRA effect. The results of this study can be used for the management of the riparian zone and the prevention and control of global nitrogen pollution.

Sustainability of water transfer projects: A systematic review

Inter-basin water transfer projects (IBTs) have significantly increased in number in recent decades due to the unremitting need to solve the problem of global water imbalance. However, given the complex challenges inherent in implementing and maintaining IBTs, there is a need to characterize the multi-faceted aspects of sustainability (or unsustainability) that result from these megaprojects. Through a systematic review of the literature, we sought to identify and characterize the positive and negative impacts that most often influence the sustainability of IBTs, focusing on impacts within the environmental, social, and economic pillars of sustainability. Based on an eligibility criterion, the systematic review selected 68 documents out of an initial total of 1567 for information quality analysis and content evaluation. The qualitative coding of the documents allowed us to characterize the landscape of impacts that result from IBTs across the three pillars of sustainability. The study findings revealed that the most frequently coded positive impacts related to the environmental pillar of sustainability, while the most frequently coded negative impacts related to both social and environmental pillars. In addition, the most frequently coded positive impact overall related to the economic benefits generated by the IBTs. Through a critical analysis of the study findings, we provide an assessment of future IBTs with a focus on the UN sustainable development goals.

Organic P transformations and release from riparian soils responding to water level fluctuation

To manage eutrophication of reservoirs, it is important to consider the potential for unexpected releases of organic phosphorus (OP) from areas around the reservoir where the water level fluctuates. In this study, we investigated the absorption and release of OP from a riparian soil/sediment from the Miyun Reservoir under fluctuating water levels using laboratory simulations. The total organic phosphorus (TOP) content in the soils/sediments ranged from 250.76 to 298.62 mg/kg, which accounted for between 5.6 and 38.5% of the total phosphorus (TP) content. We measured three OP fractions and found that the concentration of moderately labile OP (MLOP) was the highest, followed by labile OP (LOP), and the concentration of non-labile OP (NLOP) was the lowest. As the soils and sediments dried, they adsorbed phosphorus (P). The inorganic phosphorus (IP) contents were significantly and negatively correlated with the LOP and MLOP contents, indicating exchange between IP with these two fractions when the concentrations of bioavailable phosphorus in the soil are low. During flooding, the physicochemical properties varied at the sediment-water interface, inducing the release of Fe/Al-P. Some of the LOP and MLOP in the sediments were mineralized to IP. Our results suggest that when there are external P inputs, P may be released when sediments around a reservoir are subjected to wetting and drying as water levels fluctuate, which may cause P enrichment in reservoirs, especially in areas with poor water exchange.

Potentially Toxic Element Contaminations and Lead Isotopic Fingerprinting in Soils and Sediments from a Historical Gold Mining Site

Lead (Pb) isotopes have been widely used to identify and quantify Pb contamination in the environment. Here, the Pb isotopes, as well as the current contamination levels of Cu, Pb, Zn, Cr, Ni, Cd, As, and Hg, were investigated in soil and sediment from the historical gold mining area upstream of Miyun Reservoir, Beijing, China. The sediment had higher ²⁰⁶Pb/²⁰⁷Pb ratios (1.137 ± 0.0111) than unpolluted soil did (1.167 ± 0.0029), while the soil samples inside the mining area were much more variable (1.121 ± 0.0175). The mean concentrations (soil/sediment in mg·kg⁻¹) of Pb (2470/42.5), Zn (181/113), Cu (199/36.7), Cr (117/68.8), Ni (40.4/28.9), Cd (0.791/0.336), As (8.52/5.10), and Hg (0.168/0.000343) characterized the soil/sediment of the studied area with mean I_geo values of the potentially toxic element (PTE) ranging from −4.71 to 9.59 for soil and from −3.39 to 2.43 for sediment. Meanwhile, principal component analysis (PCA) and hierarchical cluster analysis (HCA) coupled with Pearson’s correlation coefficient among PTEs indicated that the major source of the Cu, Zn, Pb, and Cd contamination was likely the mining activities. Evidence from Pb isotopic fingerprinting and a binary mixing model further confirmed that Pb contamination in soil and sediment came from mixed sources that are dominated by mining activity. These results highlight the persistence of PTE contamination in the historical mining site and the usefulness of Pb isotopes combined with multivariate statistical analysis to quantify contamination from mining activities.

A novel comprehensive risk assessment method for sudden water accidents in the Middle Route of the South-North Water Transfer Project (China)

The Middle Route of the South-North Water Transfer Project in China consists of a long open canal and complex hydraulic structures. It provides drinking water for Beijing, Shijiazhuang, and other cities under extremely strict water quality requirements. In the recent decades, water pollution accidents have frequently occurred in water transfer projects. Scientific and effective risk assessment is needed to assess the impact on the overall emergency management, which should be considered to incorporate social, economic, and environmental issues in the timely response to and management of emergencies. In this study, we combine the Drivers-Pressures-State-Impact-Response model, fuzzy comprehensive evaluation method, and coordinated development degree model into a comprehensive risk assessment tool. This new approach was tested on an emergency drilling simulation related to a sudden MRP water pollution accident in 2016. Based on the combined integration weight ranking, "water delivery status," "pollution accident characteristics," "town size," and "public satisfaction" play prominent roles in the risk assessment. Especially, "town size" is identified as the most important influent factor. The Drivers-Pressures-State-Impact-Response model index system and comprehensive risk assessment method can be used to evaluate accidents more scientifically and versatile, which helps managers or experts to make faster and more efficient decisions.