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1. Freshwater Salinization Syndrome Alters Retention and Release of ‘Chemical Cocktails’ along Flowpaths:  from Stormwater Management to Urban Streams

   https://doi.org/10.1086/721469  

   Kaushal, Sujay; Reimer, Jenna E.; Mayer, Paul M.; Shatkay, Ruth R.; Maas, Carly; Nguyen, William D.; Boger, Walter L.; Yaculak, Alexis M.; Doody, Thomas R.; Pennino, Michael; et al (June 2022, Freshwater Science)

   Freshwater salinization syndrome (FSS) refers to the suite of interactive effects of salt ions on degradation of physical, biological,and social systems. Best management practices (BMPs), which are methods to effectively reduce runoff and nonpoint source pollution (stormwater, nutrients, sediments), do not typically consider management of salt pollution. We investigate impacts of FSS on mobilization of salts, nutrients, and metals in urban streams and storm water BMPs by analyzing original data on concentrations and fluxes of salts, nutrients, and metals from 7 urban watersheds in the Mid-Atlantic USA and synthesizing literature data. We also explore future critical research needs through a survey of practitioners and scientists. Our original data show 1) sharp pulses in concentrations of salt ions and metals in urban streams directly following both road salt events and stream restoration construction (e.g.,similar to the way concentrations increase during other soil disturbance activities); 2) sharp declines in pH (acidification) in response to road salt applications because of mobilization of H+ from soil exchange sites by Na+; 3) sharp increases inorganic matter from microbial and algal sources (based on fluorescence spectroscopy) in response to road salt applications, likely because of lysing cells and changes insolubility; 4) substantial retention (~30–40%) of Na+ in stormwater BMP sediments and floodplains in response to salinization; 5) increased ion exchange and mobilization of diverse salt ions (Na+, Ca2+, K+, Mg2+), nutrients(N, P), and trace metals(Cu, Sr) from stormwater BMPs and restored streams in response to FSS; 6) downstream increasing loads ofCl–, SO42–, Br–, F–,andI–along flowpaths through urbanstreams and P release from urban stormwater BMPs in response to salinization; and 7)a substantial annual reduction (>50%) in Na+concentrations in an urban stream when road salt applications were dramatically reduced, which suggests potential for ecosystem recovery. We compare our original results with published metrics of contaminant retention and release across a broad range of stormwater BMPs from North America and Europe.Overall, urban streams and stormwater BMPs consistently retain Na+ and Cl–but mobilize multiple contaminants based on salt types and salinity levels. Finally, we present our top 10 research questions regarding FSS impacts on urban streams and stormwater BMPs. Reducing diverse chemical cocktails of contaminants mobilized by freshwater salinization is a priority for effectively and holistically restoring urban waters. 

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2. Freshwater salinization syndrome: from emerging global problem to managing risks

   https://doi.org/10.1007/s10533-021-00784-w  

   Kaushal, Sujay S.; Likens, Gene E.; Pace, Michael L.; Reimer, Jenna E.; Maas, Carly M.; Galella, Joseph G.; Utz, Ryan M.; Duan, Shuiwang; Kryger, Julia R.; Yaculak, Alexis M.; et al (April 2021, Biogeochemistry)

   Abstract Freshwater salinization is an emerging global problem impacting safe drinking water, ecosystem health and biodiversity, infrastructure corrosion, and food production. Freshwater salinization originates from diverse anthropogenic and geologic sources including road salts, human-accelerated weathering, sewage, urban construction, fertilizer, mine drainage, resource extraction, water softeners, saltwater intrusion, and evaporative concentration of ions due to hydrologic alterations and climate change. The complex interrelationships between salt ions and chemical, biological, and geologic parameters and consequences on the natural, social, and built environment are called Freshwater Salinization Syndrome (FSS). Here, we provide a comprehensive overview of salinization issues (past, present, and future), and we investigate drivers and solutions. We analyze the expanding global magnitude and scope of FSS including its discovery in humid regions, connections to human-accelerated weathering and mobilization of ‘chemical cocktails.’ We also present data illustrating: (1) increasing trends in salt ion concentrations in some of the world’s major freshwaters, including critical drinking water supplies; (2) decreasing trends in nutrient concentrations in rivers due to regulations but increasing trends in salinization, which have been due to lack of adequate management and regulations; (3) regional trends in atmospheric deposition of salt ions and storage of salt ions in soils and groundwater, and (4) applications of specific conductance as a proxy for tracking sources and concentrations of groups of elements in freshwaters. We prioritize FSS research needs related to better understanding: (1) effects of saltwater intrusion on ecosystem processes, (2) potential health risks from groundwater contamination of home wells, (3) potential risks to clean and safe drinking water sources, (4) economic and safety impacts of infrastructure corrosion, (5) alteration of biodiversity and ecosystem functions, and (6) application of high-frequency sensors in state-of-the art monitoring and management. We evaluate management solutions using a watershed approach spanning air, land, and water to explore variations in sources, fate and transport of different salt ions (e.g.monitoring of atmospheric deposition of ions, stormwater management, groundwater remediation, and managing road runoff). We also identify tradeoffs in management approaches such as unanticipated retention and release of chemical cocktails from urban stormwater management best management practices (BMPs) and unintended consequences of alternative deicers on water quality. Overall, we show that FSS has direct and indirect effects on mobilization of diverse chemical cocktails of ions, metals, nutrients, organics, and radionuclides in freshwaters with mounting impacts. Our comprehensive review suggests what could happen if FSS were not managed into the future and evaluates strategies for reducing increasing risks to clean and safe drinking water, human health, costly infrastructure, biodiversity, and critical ecosystem services. 

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3. Low Temperature Molten Salt Production of Silicon Nanowires by Electrochemical Reduction of CaSiO₃

   https://doi.org/10.1002/anie.201707064  

   Dong, Yifan; Slade, Tylor; Stolt, Matthew J; Li, Linsen; Girard, Steven N; Mai, Liqiang; Jin, Song (October 2017, Angewandte Chemie International Edition)

   Silicon is an extremely important technological material, but the current industrial production of silicon by carbothermic reduction of SiO₂ is energy intensive and generates CO₂ emission. Here we developed a new and more sustainable method to produce silicon nanowires in bulk quantities via direct electrochemical reduction of CaSiO₃, an abundant and inexpensive silicon source soluble in molten salts, at a low temperature of 650 ⁰C by using low melting point ternary molten salts CaCl₂-MgCl₂-NaCl, which still retains high CaSiO₃ solubility, and a supporting electrolyte of CaO, which facilitates the transport of O²¯ anions, drastically improves the reaction kinetics and enables the electrolysis at low temperatures. The Si nanowire product can be used as high-capacity Li-ion battery anode materials with excellent cycling performance. This practical strategy at lower temperatures can be applied to other molten salt systems and also promising for waste glass and coal ash recycling. 

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4. Inorganic salts and organic matter effects on nanorod, nanowire, and nanoplate MoO ₃ aggregation, dissolution, and photocatalysis

   https://doi.org/10.1039/D0EN00708K  

   Fanourakis, Sofia K.; Peña-Bahamonde, Janire; Rodrigues, Debora F. (December 2020, Environmental Science: Nano)

   null (Ed.)

   Use of visible light photocatalytic nanomaterials in water treatment can be promising in treating contaminants. However, little research has been conducted examining the effects of more complex chemistries in the nanomaterial's performance. In this work, the effects of inorganic salts (NaCl and CaCl 2 ) and natural organic matter (NOM) such as humic acid (HA) and extracellular polymeric substances (EPS) on nanoparticle aggregation, dissolution, and ultimately on the photocatalytic properties of molybdenum trioxide (MoO 3 ), i.e. nanorods, nanowires, and nanoplates were examined. In the presence of NaCl, nanorod, nanowire, and nanoplate MoO 3 had similar critical coagulation concentrations, while the nanorods showed higher instability in CaCl 2 . Overall, the presence of inorganic salts caused high colloidal instability in the MoO 3 nanostructures in terms of aggregation behavior, but greatly aided in the reduction of MoO 3 dissolution. NOM presence decreased aggregation rates, albeit dissolution was not similarly affected in all three structures. Only the dissolution of the nanowire structures was reduced in the presence of HA or EPS. Furthermore, the photocatalytic activity of the nanowires and nanoplates was overall reduced when inorganic salts or natural organic matter were present. While the presence of natural organic matter alone did reduce photocatalytic effectiveness of the nanorod MoO 3 , the presence of salts seemed to negate the effects from the organic compounds. Furthermore, the presence of CaCl 2 resulted in a highly enhanced photocatalytic activity regardless of the presence of natural organic matter. The structural and chemical differences of the nanomaterials played a significant role in their aggregation, dissolution, and ability to photocatalytically degrade methylene blue in solution. This study demonstrates that a better understanding of water chemistry effects on nanomaterials is essential prior to their intended applications. 

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5. Freshwater salinization syndrome limits management efforts to improve water quality

   https://doi.org/10.3389/fenvs.2023.1106581  

   Maas, Carly M.; Kaushal, Sujay S.; Rippy, Megan A.; Mayer, Paul M.; Grant, Stanley B.; Shatkay, Ruth R.; Malin, Joseph T.; Bhide, Shantanu V.; Vikesland, Peter; Krauss, Lauren; et al (September 2023, Frontiers in Environmental Science)

   Freshwater Salinization Syndrome (FSS) refers to groups of biological, physical, and chemical impacts which commonly occur together in response to salinization. FSS can be assessed by the mobilization of chemical mixtures, termed “chemical cocktails”, in watersheds. Currently, we do not know if salinization and mobilization of chemical cocktails along streams can be mitigated or reversed using restoration and conservation strategies. We investigated 1) the formation of chemical cocktails temporally and spatially along streams experiencing different levels of restoration and riparian forest conservation and 2) the potential for attenuation of chemical cocktails and salt ions along flowpaths through conservation and restoration areas. We monitored high-frequency temporal and longitudinal changes in streamwater chemistry in response to different pollution events (i.e., road salt, stormwater runoff, wastewater effluent, and baseflow conditions) and several types of watershed management or conservation efforts in six urban watersheds in the Chesapeake Bay watershed. Principal component analysis (PCA) indicates that chemical cocktails which formed along flowpaths (i.e.,permanent reaches of a stream) varied due to pollution events. In response to winter road salt applications, the chemical cocktails were enriched in salts and metals (e.g.,Na⁺, Mn, and Cu). During most baseflow and stormflow conditions, chemical cocktails were less enriched in salt ions and trace metals. Downstream attenuation of salt ions occurred during baseflow and stormflow conditions along flowpaths through regional parks, stream-floodplain restorations, and a national park. Conversely, chemical mixtures of salt ions and metals, which formed in response to multiple road salt applications or prolonged road salt exposure, did not show patterns of rapid attenuation downstream. Multiple linear regression was used to investigate variables that influence changes in chemical cocktails along flowpaths. Attenuation and dilution of salt ions and chemical cocktails along stream flowpaths was significantly related to riparian forest buffer width, types of salt pollution, and distance downstream. Although salt ions and chemical cocktails can be attenuated and diluted in response to conservation and restoration efforts at lower concentration ranges, there can be limitations in attenuation during road salt events, particularly if storm drains bypass riparian buffers. 

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