Coagulation pH appeared to be a determining factor for maximum NOM removal.Several bench‐scale studies were conducted to evaluate the effectiveness of enhanced coagulation for controlling chlorination by‐products and to assess the impace of coaqulation pH preadjustment on total organic carbon (TOC) removal and plant operating costs. Tests were conducted on a variety of surface water sources with TOC values ranging from 2 to 1 mg/L. An iron‐based coagulant, such as ferric chloride, was consisitently more effective than alum in removing natural organic matter (NOM). Coagulation pH appeared to be a determining factor for maximum NOM removal when ferric chloride was used as a primary coagulant. Typically, preadjustment of pH at a value of 6.0 ± 0.2 increased NOM overall removal to as much as 65 percent and reduced the coagulant dose by as much as 60 precent. Enhanced coagulation led to higher overall operating costs, but preadjustment of pH with sulfuric acid reduced costs, by lowering the coagulant dosage as well as sludge production.
The Greenland Ice Sheet is losing mass at a remarkable rate as a result of climatic warming.This mass loss coincides with the export of dissolved organic matter (DOM) in glacial meltwaters. However, little is known about how the source and composition of exported DOM changes over the melt season, which is key for understanding its fate in downstream ecosystems. Over the 2015 ablation season, we sampled the outflow of Leverett Glacier, a large land-terminating glacier of the Greenland Ice Sheet. Dissolved organic carbon (DOC) concentrations and DOM fluorescence were analyzed to assess the evolution of DOM sources over the course of the melt season. DOC concentrations and red-shifted fluorescence were highly associated (R 2 > 0.95) and suggest terrestrial inputs from overridden soils dominated DOM early season inputs before progressive dilution with increasing discharge. During the outburst period, supraglacial drainage events disrupted the subglacial drainage system and introduced dominant protein-like fluorescence signatures not observed in basal flow. These results suggest that subglacial hydrology and changing water sources influence exported DOC concentration and DOM composition, and these sources were differentiated using fluorescence characteristics. Red-shifted fluorescence components were robust proxies for DOC concentration. Finally, the majority of DOM flux, which occurs during the outburst and postoutburst periods, was characterized by protein-like fluorescence from supraglacial and potentially subglacial microbial sources. As protein-like fluorescence is linked to the bioavailability of DOM, the observed changes likely reflect seasonal variations in the impact of glacial inputs on secondary production in downstream ecosystems due to shifting hydrologic regimes.
A case study of Denver, Colorado explores the roles of three social actors-individual users, infrastructure designer-operators, and policy actors-in near-term greenhouse gas (GHG) mitigation in U.S. cities. Energy efficiency, renewable energy, urban design, price- and behavioral-feedback strategies are evaluated across buildings-facilities, transportation, and materials/waste sectors in cities, comparing voluntary versus regulatory action configurations. GHG mitigation impact depends upon strategy effectiveness per unit, as well as societal participation rates in various action-configurations. Greatest impact occurs with regulations addressing the vast existing buildings stock in cities, followed by voluntary behavior change in electricity use/purchases, technology shifts (e.g., to teleconferencing), and green-energy purchases among individual users. A portfolio mix of voluntary and regulatory actions can yield a best-case maximum of ~1% GHG mitigation annually in buildings and transportation sectors, combined. Relying solely on voluntary actions reduces mitigation rates more than five-fold. A portfolio analysis of climate action plans in 55 U.S. cities reveals predominance of voluntary outreach programs that have low societal participation rates and hence low GHG impact, while innovative higher-impact behavioral, technological, and policy/regulatory strategies are under-utilized. Less than half the cities capitalize on cross-scale linkages with higher-impact state-scale policies. Interdisciplinary field research can help address the mis-match in plans, actions, and outcomes.
Glaciated environments have been highlighted as important sources of bioavailable nutrients, with inputs of glacial meltwater potentially influencing productivity in downstream ecosystems. However, it is currently unclear how riverine nutrient concentrations vary across a spectrum of glacial cover, making it challenging to accurately predict how terrestrial fluxes will change with continued glacial retreat. Using 40 rivers in Chilean Patagonia as a unique natural laboratory, we investigate how glacial cover affects riverine Si and Fe concentrations, and infer how exports of these bioessential nutrients may change in the future. Dissolved Si (as silicic acid) and soluble Fe (<0.02 μm) concentrations were relatively low in glacier-fed rivers, whereas concentrations of colloidal-nanoparticulate (0.02-0.45 μm) Si and Fe increased significantly as a function of glacial cover. These colloidal-nanoparticulate phases were predominately composed of aluminosilicates and Fe-oxyhydroxides, highlighting the need for size-fractionated analyses and further research to quantify the lability of colloidal-nanoparticulate species. We also demonstrate the importance of reactive particulate (>0.45 μm) phases of both Si and Fe, which are not typically accounted for in terrestrial nutrient budgets but can dominate riverine exports. Dissolved Si and soluble Fe yield estimates showed no trend with glacial cover, suggesting no significant change in total exports with continued glacial retreat. However, yields of colloidal-nanoparticulate and reactive sediment-bound Si and Fe were an order of magnitude greater in highly glaciated catchments and showed significant positive correlations with glacial cover. As such, regional-scale exports of these phases are likely to decrease as glacial cover disappears across Chilean Patagonia, with potential implications for downstream ecosystems. Glacial weathering processes have been identified to be particularly important in the generation of potentially bioavailable iron (Fe) (
An annually laminated succession in Crawford Lake, Ontario, Canada is proposed as the Global boundary Stratotype Section and Point (GSSP) for the Anthropocene as a series/epoch with a base dated at 1950 CE. Varve couplets of organic matter capped by calcite precipitated each summer in alkaline surface waters reflect environmental change at global to local scales. Spheroidal carbonaceous particles and nitrogen isotopes record an increase in fossil fuel combustion in the early 1950s, coinciding with fallout from nuclear and thermonuclear testing—239+240Pu and 14C:12C, the latter more than compensating for the effects of old carbon in this dolomitic basin. Rapid industrial expansion in the North American Great Lakes region led to enhanced leaching of terrigenous elements by acid precipitation during the Great Acceleration, and calcite precipitation was reduced, producing thin calcite laminae around the GSSP that is marked by a sharp decline in elm pollen (Dutch Elm disease). The lack of bioturbation in well-oxygenated bottom waters, supported by the absence of fossil pigments from obligately anaerobic purple sulfur bacteria, is attributed to elevated salinities and high alkalinity below the chemocline. This aerobic depositional environment, unusual in a meromictic lake, inhibits the mobilization of 239Pu, the proposed primary stratigraphic guide for the Anthropocene.
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