Applied Geochemistry (v.83, #C)

Urban Geochemistry by Christopher B. Gardner; David T. Long; W. Berry Lyons (1-2).

An odyssey of environmental pollution: The rise, fall and remobilisation of industrial lead in Australia by Louise Jane Kristensen; Mark Patrick Taylor; Arthur Russell Flegal (3-13).
The use of lead as an additive in petrol resulted in more than 240,000 tonnes of lead being emitted to the Australian environment over a 70-year period from 1932, until lead additives in petrol were eliminated in 2002. The consequences of Australia's protracted industrial lead emissions and subsequent depositions caused widespread contamination of urban and peri-urban aerosols, soils, plants, animals, and humans. This paper charts the impact of those lead emissions via environmental archives and proxies and examines the extent of recovery from one of the biosphere's most pervasive and persistent environmental pollutants. The remobilisation of industrial lead is examined by analysis of Sydney air filters that bracket wildfires between 1994 and 2004. Proxy atmospheric measurements of historical wine, lichen and fungi samples extending up to 150 years bp show how both lead concentration and isotopic composition values shifted in the middle to late 20th century to reflect petrol emissions and then recovered rapidly at the end of the century as leaded petrol was phased out. Lead isotopic composition of aerosol filters from Adelaide and Sydney show that air lead composition shifted from values that approximate Broken Hill type ores, the predominant lead source used in petrol (206Pb/207Pb = 1.04; 208Pb/207Pb = 2.32), towards ratios that more closely match local uncontaminated soil and bedrock values in Adelaide (206Pb/207Pb = 1.21; 208Pb/207Pb = 2.52) and Sydney (206Pb/207Pb = 1.14; 208Pb/207Pb = 2.44). However, the recovery from that historic industrial lead contamination is incomplete. Measurements of contemporary surface soils, ash produced from wildfires and aerosols demonstrate legacy industrial lead depositions are declining but are still subject to remobilisation.
Keywords: Environmental archive; Lead petrol; Metal contamination; Mining and smelting; Wildfires;

Case studies and evidence-based approaches to addressing urban soil lead contamination by Mark A.S. Laidlaw; Gabriel M. Filippelli; Sally Brown; Jorge Paz-Ferreiro; Suzie M. Reichman; Pacian Netherway; Adam Truskewycz; Andrew S. Ball; Howard W. Mielke (14-30).
Urban soils in many communities in the United States and internationally have been contaminated by lead (Pb) from past use of lead additives in gasoline, deterioration of exterior paint, emissions from Pb smelters and battery recycling and other industries. Exposure to Pb in soil and related dust is widespread in many inner city areas. Up to 20–40% of urban children in some neighborhoods have blood lead levels (BLLs) equal to or above 5 μg per decilitre, the reference level of health concern by the U.S. Centers for Disease Control. Given the widespread nature of Pb contamination in urban soils it has proven a challenge to reduce exposure. In order to prevent this exposure, an evidence-based approach is required to isolate or remediate the soils and prevent children and adult's ongoing exposure. To date, the majority of community soil Pb remediation efforts have been focused in mining towns or in discrete neighborhoods where Pb smelters have impacted communities. These efforts have usually entailed very expensive dig and dump soil Pb remediation techniques, funded by the point source polluters. Remediating widespread non-point source urban soil contamination using this approach is neither economical nor feasible from a practical standpoint. Despite the need to remediate/isolate urban soils in inner city areas, no deliberate, large scale, cost effective Pb remediation schemes have been implemented to isolate inner city soils impacted from sources other than mines and smelters. However, a city-wide natural experiment of flooding in New Orleans by Hurricane Katrina demonstrated that declines in soil Pb resulted in major BLL reductions. Also a growing body of literature of smaller scale pilot studies and programs does exist regarding low cost efforts to isolate Pb contaminated urban soils. This paper reviews the literature regarding the effectiveness of soil Pb remediation for reducing Pb exposure and BLL in children, and suggests best practices for addressing the epidemics of low-level Pb poisoning occurring in many inner city areas.
Keywords: Soil; Lead; Remediation; Abatement; Blood; Lead; Poisoning;

A series of leaching and partitioning tests (Toxicity Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure (SPLP), Controlled Acidity Leaching Protocol (CALP), Acid Neutralization Capacity (ANC), and sequential extraction) were applied to three different soils to study the potential mobility of metals into groundwater. Two of these soils were lead (Pb)-contaminated soils (Hotspot 1 and Hotspot 2) collected from an urban site associated with lead smelting and other industrial operations. The third sample (Stockpile) was soil affected by previous contamination in the area, removed from residential properties, stockpiled, and selected to be used as fill material in the studied site. The TCLP and CALP showed that Pb could be released from both hotspots, but were not released in the acidic rainfall extraction fluid of the SPLP. The sequential extraction showed that Pb in the hotspot soils was associated with the carbonate fraction, while As was associated with the Fe and Mn oxides. The stockpile released traces of Pb or As in the TCLP and CALP, but the ANC only released Pb under acidic conditions and the SPLP did not release Pb or As. Overall, the projected repository with Stockpile would not pose imminent danger to groundwater because, under the expected environmental conditions, Pb and As tend to remain in the solid phase.
Keywords: Arsenic; Metals leaching; Sustainability; Repository;

Contamination of heavy metals and isotopic tracing of Pb in intertidal surface sediments of Jinjiang River Estuary, SE China by Ruilian Yu; Gongren Hu; Chengqi Lin; Qiuli Yang; Chenchen Zhang; Xiaoming Wang (41-49).
Contamination of 14 heavy metals and isotopic tracing of Pb were studied in the intertidal surface sediments of Jinjiang River Estuary, southeast China. Concentrations of the heavy metals in the sediments decrease as Fe > Ti > Mn > Zn > Cu > Cr > Pb > V > Ni > Sn > Co > Sb > Cd > Hg. Except Fe, Ti and V, the other elements show higher concentrations than their background values at most sampling sites. The assessment results of geo-accumulation index and potential ecological risk index indicate that the intertidal surface sediments are polluted by some heavy metals (Cd, Hg, Cu, Mn, Zn, Sb, Sn, Pb, Cr, Ni and Co) and show very high ecological risk with the main contributors of Cd and Hg. Results of multivariate statistic analysis suggest that Fe, V, Ti and Cr are mainly influenced by natural sources; Cu, Ni, Sn and Mn are mainly influenced by mining industries and the combustion of fossil fuel; Pb and Hg are mainly influenced by coal combustion and Pb-Zn ore; Zn, Cd, Co and Sb are mainly influenced by agricultural activities. The results of Pb isotope tracing show that total Pb in the sediments is mainly from parent material (44.0%–50.0%), Pb-Zn ore (35.8%–41.7%) and vehicle exhaust (7.8%–18.2%).Display Omitted
Keywords: Heavy metals; Pollution assessment; Pb isotopes; Surface sediment; Jinjiang River Estuary;

Vehicular wash-off introduces toxic heavy metals into riverine environments, but the delivery patterns of such contaminants are normally difficult to observe. This study examines the spatial and temporal heterogeneity in metal loading of riverbed sediments at two river fords in the Mill Creek Watershed located in suburban Philadelphia, Pennsylvania. Riverbed sediment samples were collected over the course of the 2015 driving season (April to December) upstream and downstream of the two fords, which greatly differ in traffic density, and analyzed for their trace metal concentrations (As, Cd, Cu, Ni, Pb, Zn) and percent particulate organic carbon (%POC). Overall, metal concentrations were in the upper range of literature values for road-derived sediments. Comparing the sites, the more heavily trafficked ford had significantly higher concentrations, confirming the role of traffic density on metal accumulation. Highly enriched concentrations of Cu and Zn coupled with diagnostic metal:Cu ratios points to the strong influence of brake lining dust. While an increase in metal concentration was observed over the driving season, the highly variable spatial and temporal signal suggests other factors such as local geomorphological and hydrological conditions also play a role in metal accumulation and dispersal. Metal concentrations in excess of levels known to impact aquatic ecosystems, coupled with strong correlations between metal concentrations and the %POC content of the sediments, suggest vehicular-derived metals may play a role in the historically observed decrease in macroinvertebrate diversity in the watershed. These findings add to a growing body of literature highlighting the potential for vehicular and road-sourced metals to persist and potentially impact riverine environments.

Changes in the size partitioning of metals in storm runoff following wildfires: Implications for the transport of bioactive trace metals by Paulina Pinedo-Gonzalez; Bridget Hellige; A. Joshua West; Sergio A. Sañudo-Wilhelmy (62-71).
Mountainous areas affected by natural wildfires and highly urbanized settings both have been identified as sources of pollutants to receiving waters. In this study, the partitioning of metals between the colloidal (0.02–0.2 μm) and soluble (<0.02 μm) phases in storm-runoff was evaluated in three different environments: (i) a catchment affected by the 2012 Williams Fire (2–13 September 2012) in the San Gabriel Mountains, (ii) a neighboring control catchment in the San Gabriels, and (iii) three rivers draining the Los Angeles County area. Results from each region were compared to each other in order to gain information about potential sources of soluble (i.e., bioavailable) elements that are delivered to receiving waters. Results show that in runoff from recently burned areas, 58% and 24% of the total dissolved (<0.2 μm) Pb and Fe, respectively, was present in the soluble pool. In contrast, runoff from urban and natural unburned areas carried less than 17% and 8% of the total dissolved Pb and Fe, respectively, in the soluble pool. These results suggest that storm runoff from burned landscapes has the previously unrecognized potential to supply a greater proportion of trace elements in bioactive soluble form, compared to runoff from urban or unburned areas, potentially increasing the impact of wildfire-delivered metals on receiving waters.
Keywords: Trace metals; Partitioning; Colloids; Soluble metals; Wildfires; Urban runoff;

Soil as a reservoir for road salt retention leading to its gradual release to groundwater by Heather K. Robinson; Elizabeth A. Hasenmueller; Lisa G. Chambers (72-85).
Road salt application elevates Na and Cl concentrations throughout the year in many surface water and groundwater systems. This study explores the role of soils in extending the lag time between road salt application and the delivery of Na and Cl to shallow groundwater in a temperate environment. Intact soil cores were collected near karst springs at both an urban and a rural site at distances of 1 m, 5 m, and 13 m from nearby roads that experience winter salting. Cores were manipulated in the lab to simulate various field conditions; treatments included irrigation with: 1) deionized (DI) water (DI group) as a control, 2) NaCl solution (salt group) to mimic prolonged exposure to road salt, or 3) NaCl followed by DI water (recovery group) to mimic winter road salting followed by dilute rainfall in spring. In the first NaCl irrigation of the salt and recovery groups, soils retained 62% of the applied Cl and 66% of the applied Na on average, which was largely stored in the porewater. Throughout the 5 week study, Ca, Mg, and K were elevated and the pH was depressed in leachate from salt group compared to DI group cores due to cation exchange. Likewise, cation exchange enhanced Na retention so that salt and recovery group cores retained half of the applied Na at the end of the experiment, compared to a quarter of the Cl. Na and Cl retention were greater for soils from the rural site, which is characterized by higher organic matter (OM) and sand content, faster infiltration, and lower bulk density than for the urban site, which has higher bulk density and more silt and clay. Furthermore, extractable Cl in untreated field soils was positively correlated with soil water content, OM, and sand content, suggesting that these properties may control retention. We assume Cl retention to be the result of porewater retention, microbial uptake, and chlorination of soil OM. After the addition of 2000 mg Cl to the salt group cores, non-conservative Cl behavior ceased because the retention capacity of the soils had been exhausted. Recovery rates during DI flushes of recovery group cores indicate that these soils slowly release Na and Cl for at least 2.5–5 months following salt application. This gradual release from soils helps to explain the year-round persistence of high salt concentrations in some surface waters and groundwaters.
Keywords: Soil geochemistry; Urban soils; Contaminant transport; Road salt; Chloride;

Urban areas are thought to possess different geochemical characteristics than more natural regions due to large human population densities and intensified human activities that produce large quantities of waste products. In this work we have analyzed a number of urban streams in Columbus, Ohio, the 15th largest city in the U.S., for their dissolved trace metal concentrations. The three streams have subtle but measurably different land use patterns. Although, in general, the dissolved metal values observed are higher than global average river concentrations, there were no statistically different values between the streams. This suggests that urbanization may help to homogenize trace metal sources and fluxes, even on the small watershed scale, or that dissolved trace metals are not a variable that can be discriminated by land use subtype.

Concentration – discharge (c-q) hysteresis loops are used to qualitatively understand solute transport pathways to streams. The majority of c-q studies involve non-urban areas in environmental settings such as the subtropics, mountains, and high latitude rivers. Only a few involve urban or urban salted watersheds. In this study, we explore c-q hysteresis plots and pollutographs for a variety of inorganic solutes (Cl, Na+, K+, SiO2, NO3 ), dissolved organic carbon and an indicator of the aromatic fraction (SUVA254), and a microbiological indicator (E. coli) in an urban salted watershed. The major hydrologic events are snow melts. The overarching hypothesis is that the hysteresis behavior can be explained by extending the pathway analysis (i.e., relative importance of storm event water, CSE; groundwater CG; and soil water, CSO) from the Evans-Davis classification scheme that describes six behaviors to account for differences in source locations and the biogeochemical behavior of the solutes along these pathways. Data sets for the years 2013, 2014, and 2015 were assembled from a series of undergraduate and graduate research projects performed over this period. The results of these studies indicate that: 1) Cl and Na+ exhibit a combination of C2 (CSE > CSO > CG) and C3 (CG > CSE > CSO) behavior during salting season and A1 (CSO > GG > CSE) and A2 (CSO > CSE > CG) behavior in non-salting times; 2) SiO2 shows A3 (CG > CSO > CSE) behavior in all events, 3) K+ changes from C2 to C1 (CSE > CG > CSO) with concentration depletion over subsequent events; 4) NO3 changes from A2 to C1 or C2 with concentration depletion over subsequent events; 5) DOC and SUVA254 exhibit C2 and A1 behavior, respectively; 6) E. coli changes from C2 to A2 over subsequent storms; 7) Cland Na+ peak before the rising limb with a slight lag in the Na+ peak and 8) E. coli does not exhibit first-flush behavior. An integrative pollutograph for a snow melt event shows, 1) K+ and DOC peak together three times, unrelated to any additional event such as rain; 2) DOC becomes more aliphatic at its first peak, and 3) NO3 has a concentration decrease at the second DOC/K+ peak and peaks on the declining limb after the third DOC/K+ peak. These observations can be explained in terms of the c-q plots (e.g., importance of event water), environmental behavior (e.g., conservative solute), the nature of the urban landscape (e.g., pavement), and season (e.g., damped microbial activity). We interpret the multiple concentration peaks to indicate water masses originating from different compartments in the watershed are reaching the stream at different times and with different chemistries. These results extend the work of previous studies and may serve to help develop a fingerprint of solute behavior that can be used to more fully explore early season biogeochemical dynamics in an urban, salted, snow-melt dominated watershed.
Keywords: Hysteresis; Integrative pollutograph; Solutes; E. coli; Snow melt;

Limitations on the role of the hyporheic zone in chromium natural attenuation in a contaminated urban stream by Barbara Palumbo-Roe; Vanessa J. Banks; Helen C. Bonsor; Elliott M. Hamilton; Michael J. Watts (108-120).
The urban hyporheic zone may offer natural attenuation potential for contaminants. This potential is contaminant-specific and may be spatially and temporally variable. The aim of this study was the assessment of the natural attenuation potential of the hyporheic zone of an urban stream receiving hexavalent chromium (Cr)-rich effluents from the historical land disposal of chromite ore processing residue (COPR) in Glasgow, Scotland. The evidence based approach involved the use of a network of multilevel piezometers for best capturing potential anoxic field conditions and fine-scale spatial gradients in solute concentrations of surface water and porewater. In-situ porewater sampling was integrated with sediment sampling and reach-scale monitoring of stream water quality. The results show a sharp decrease of total dissolved (filtered <0.45 μm) Cr concentrations at the surface water – sediment boundary in all profiles, from Cr mean values of 1100 μg l−1 in surface water to 5 μg l−1 in porewater. Chromium speciation analysis indicates that no Cr(VI) was detectable in the neutral pH, moderately reducing porewater, while it was the dominant species in surface water. Evidence of historical COPR detrital grains contributed to the total Cr concentrations (size fraction <150 μm) up to 8800 mg kg−1 in the streambed sediment. The abundance in the porewater of Fe (mean value = 1700 μg l−1), mainly as Fe(II), a natural electron donor for Cr(VI) reduction to Cr(III), indicates a high natural attenuation potential of the hyporheic zone for downwelling dissolved Cr, through Cr(VI) reduction to Cr(III) and the formation of Cr(III) solids of low solubility. Authigenic Cr-rich rims on particles also documented active Cr precipitation from solution in the fine sediments. Large short-term changes of stream stage and stream water composition were not reflected in the hyporheic conservative (chloride) and reactive solute composition. This result indicates only limited surface water infiltration and suggests that small advective exchange might limit the effectiveness of the hyporheic zone for enhancing Cr surface water quality at the reach-scale. This is supported by further evidence from preliminary surface water quality synoptic sampling which shows only moderate to low downstream decrease in surface water Cr concentrations. The surface water investigation needs to be supported by combined water quality-flow monitoring and to be extended to a wider range of temporal and spatial scales to corroborate the reach-scale findings.

Human-accelerated weathering increases salinization, major ions, and alkalinization in fresh water across land use by Sujay S. Kaushal; Shuiwang Duan; Thomas R. Doody; Shahan Haq; Rose M. Smith; Tamara A. Newcomer Johnson; Katie Delaney Newcomb; Julia Gorman; Noah Bowman; Paul M. Mayer; Kelsey L. Wood; Kenneth T. Belt; William P. Stack (121-135).
Human-dominated land uses can increase transport of major ions in streams due to the combination of human-accelerated weathering and anthropogenic salts. Calcium, magnesium, sodium, alkalinity, and hardness significantly increased in the drinking water supply for Baltimore, Maryland over almost 50 years (p < 0.05) coinciding with regional urbanization. Across a nearby land use gradient at the Baltimore Long-Term Ecological Research (LTER) site, there were significant increases in concentrations of dissolved inorganic carbon (DIC), Ca2+, Mg2+, Na+, SO4 2−, Si, and pH with increasing impervious surfaces in 9 streams monitored bi-weekly over a 3–4 year period (p < 0.05). Base cations in urban streams were up to 60 times greater than forest and agricultural streams, and elemental ratios suggested road salt and carbonate weathering from impervious surfaces as potential sources. Laboratory weathering experiments with concrete also indicated that impervious surfaces increased pH and DIC with potential to alkalinize urban waters. Ratios of Na+ and Cl suggested that there was enhanced ion exchange in the watersheds from road salts, which could mobilize other base cations from soils to streams. There were significant relationships between Ca2+, Mg2+, Na+, and K+ concentrations and Cl, SO4 2-, NO3 and DIC across land use (p < 0.05), which suggested tight coupling of geochemical cycles. Finally, concentrations of Ca2+, Mg2+, DIC, and pH significantly increased with distance downstream (p < 0.05) along a stream network draining 170 km2 of the Baltimore LTER site contributing to river alkalinization. Our results suggest that urbanization can dramatically increase major ions, ionic strength, and pH over decades from headwaters to coastal zones, which can impact integrity of aquatic life, infrastructure, drinking water, and coastal ocean alkalinization.Display Omitted

Stream hydrology and geochemistry along a rural to urban land use gradient by Elizabeth A. Hasenmueller; Robert E. Criss; William E. Winston; Andrew R. Shaughnessy (136-149).
High frequency monitoring of water quality and stable isotopes quantify large hydrological and geochemical differences across a rural to urban land use gradient that includes three watersheds and two of their subbasins. Following precipitation events, floods on a rural stream feature hydrographs with low peak discharges and long lag times, high baseflow contributions, and small geochemical variations. In contrast, the flows of an urban stream and its tributary respond in a flashy manner, with average lag times decreasing by at least 55% compared to the rural stream. We also observed that baseflow contributions during floods decreased by an average of 40% in the urban streams. Importantly, we find that reduced baseflow as a function of increasing impervious surface area is not a linear trend among the streams, and suburban streams are less impacted than would be predicted by impervious surface area alone. The urban streams also exhibit large variations in water quality parameters during flooding events, often with five times the variability of the rural end-member. These differences are observed among all physical and geochemical characteristics that were monitored, including flow magnitude, stable isotope ratios, temperature, dissolved oxygen (DO), pH, turbidity, specific conductivity, concentrations of Cl and nutrients, and bacterial loads. The great variability of urban streams following storms is paralleled by their larger diurnal and seasonal oscillations. Collectively, the extreme variations in the physical and geochemical character of urban streams have negative consequences to environmental quality and aquatic life.
Keywords: Urban streams; Stream chemistry; Land use/land cover; Flooding; Isotope hydrology; Hydrograph separations;

Photodegradation of UV filters oxybenzone and sulisobenzone in wastewater effluent and by dissolved organic matter by Molly C. Semones; Charles M. Sharpless; Allison A. MacKay; Yu-Ping Chin (150-157).
Organic UV-filters are key ingredients found in sunscreens, cosmetics and plastic goods. Concerns have been raised about potential ecological and human health effects of certain organic UV filters that are currently FDA approved for use in the United States. Here, we investigate the photochemical fate of two of these compounds, oxybenzone and sulisobenzone. Both oxybenzone and sulisobenzone have previously been detected in surface waters, seawater, and treated wastewater effluent. Direct photolysis is found to be unimportant for these compounds, however, enhanced photodegradation of oxybenzone and sulisobenzone was observed under simulated solar irradiation in solutions of International Humic Substance Society standards (Pony Lake fulvic acid and Suwannee River natural organic matter), filtered wastewater effluent (Southerly Wastewater Treatment Plant in Lockbourne, OH), and Scioto River water (Columbus, OH) at pH 7. Quenching experiments with isopropanol revealed that the main pathway for degradation appears to be reaction with the hydroxyl radical (OH•). Observed degradation rates were 2–3 times slower than estimates calculated using literature reported second-order rate constants and measured hydroxyl radical steady-state concentrations for Suwannee River natural organic matter, Pony Lake fulvic acid and Scioto waters. The Southerly sample, however, exhibited nearly identical expected and observed rate constants, which we take to indicate the presence of unidentified reactive species that can react with oxybenzone and sulisobenzone. Values obtained in this work were used to calculate second-order rate constants for oxybenzone and sulisobenzone with the hydroxyl radical, as well as to estimate environmental half-lives for these compounds. Near surface 24-h averaged half-lives of 3.0 and 4.0 days were calculated for oxybenzone and sulisobenzone, respectively. When extrapolated to an environmentally representative water column, these same 24-h averaged half-lives increased to 2.4 and 3.5 years, respectively.
Keywords: Oxybenzone (benzophenone-3); Sulisobenzone (benzophenone-4); UV-Filters; Sunscreen; Dissolved organic matter; Wastewater effluent; Hydroxyl radical (OH)•; Endocrine disruptors;

Impact of anthropogenic disturbance on the chemistry of a small urban pond by Susan A. Welch; Brandon C. McAdams; Steven T. Goldsmith; Annette M. Trierweiler; Justin M. Von Bargen; Kelly Deuerling; Anne E. Carey (158-170).
Mirror Lake, one of the scenic locations on The Ohio State University's campus, experiences an intense bioturbation event as part of an annual tradition revolving around the rivalry football game against the University of Michigan. This tradition involves thousands of students jumping into the lake over one night in the week leading up to the football game.Water samples were collected from several locations in the lake before, during, and after the Mirror Lake Jump to determine the impact of this event on lake water chemistry. There were significant and systematic increases in the concentrations of Na+, K+, Cl, total nitrogen, ammonia, and dissolved organic carbon (DOC) associated with the jump, especially in the eastern side of the lake where most of the students entered. Over the 3-h period from 10 p.m. to 1 a.m. on the eastern side of the lake, Na+, K+, and Cl concentrations increased by about 2–4 ppm, 1.5–3 ppm, and 4–6 ppm, respectively. The total nitrogen concentration increased about five to six fold, from 450–500 ppb to 2300–2800 ppb over the height of the event on the eastern side of the lake. Similar increases were observed for DOC, increasing from 3.6 to 18 ppm. This DOC increase was coincident with a 5‰ shift in δ13C, from a mean of around −28‰ in the early hours of the evening to a maximum of −23‰, implying a large influx of isotopically heavy carbon into the lake. Ammonia concentrations varied substantially from year to year, but always showed a systematic increase in concentration during the event. Smaller changes in major ion and nutrient concentrations were observed in the middle and western side of the lake, where fewer students entered the lake.The changes in concentration and the timing and spatial distribution of these changes are primarily attributed to anthropogenic input from jumpers in the form of bodily fluids (e.g., evaporated sweat, sebum and urine). Over a single night, these anthropogenic event inputs represent roughly 10% of the annual nitrogen budget of the lake, emphasizing the direct impact humans can have on urban water bodies on short time scales.

Characterization of the δ13C signatures of anthropogenic CO2 emissions in the Greater Toronto Area, Canada by Stephanie C. Pugliese; Jennifer G. Murphy; Felix Vogel; Douglas Worthy (171-180).
In urban environments, carbon dioxide (CO2) is emitted from a variety of anthropogenic and biogenic sources. The isotopic ratio δ13CO2 has been widely used to source apportion CO2 as different sources have distinct isotopic fingerprints; the disadvantage of this technique is that δ13CO2 signatures are often spatially and temporally specific. We present a study characterizing the δ13CO2 signatures of the dominant anthropogenic sources of CO2 in the Greater Toronto Area (GTA). Refined gasoline and diesel fuel were sampled from various stations around the GTA in three separate campaigns (April, July and November 2015) to assess the variability of their δ13CO2 signatures. Mean winter δ13CO2 signatures for refined gasoline were measured to be −27.58 ± 0.52 ‰ and −28.12 ± 0.43 ‰ (uncertainties represent the standard deviation in sample signatures) in April and November respectively while the mean summer signature was measured to be −28.09 ± 0.34 ‰. Diesel fuel samples δ13CO2 signatures from the same campaign periods were measured to be −29.09 ± 0.34 ‰, −29.47 ± 0.29 ‰, and −29.28 ± 0.21 ‰, respectively. We hypothesize that inter-seasonal variability in signatures is likely a result of the use of different parent crude petroleum. We found no significant impacts from octane grade, fuel distributor or municipality the fuel was purchased from on the measured δ13CO2 signatures. Other transportation fuels that were measured include dyed-diesel (δ13CO2 signature = −29.3 ± 0.20 ‰) and jet fuel (δ13CO2 signature = −29.5 ± 0.20 ‰), which were both different than measurements made for the same fuels in other locations globally. To account for emissions from residential and commercial heating and electricity production, a variety of fuels were characterized in this study. The primary heating fuel used in the GTA, natural gas, was measured to have a δ13CH4 signature of −44.2 ± 0.20 ‰. Anthracite coal (a fuel that was used prior to 2014 for electricity) was measured to have a δ13CO2 signature of −23.8 ± 0.20 ‰, which is fairly consistent with coal samples measured elsewhere. With the transition in Ontario from coal to biomass-fueled power generation, softwood, hardwood and mixed wood pellets were sampled from two distributors in the GTA and measured δ13CO2 signatures were −25.0 ± 0.20 ‰, −26.8 ± 0.20 ‰, and −25.8 ± 0.20 ‰, respectively. Using these measured signatures, we performed a sensitivity analysis to quantify the precision required for continuous ambient measurements to separately identify fuel type using δ13CO2 as the sole tracer. The local signatures were also used in a mass balance calculation to quantify the relative contribution of two end-members (with the signatures of −44 ‰ and −28 ‰) to total measured CO2 in the GTA in 2014.
Keywords: Anthropogenic carbon dioxide; Carbon isotopes; Source apportionment; Urban pollution; Keeling plots; Mass balance;