Atmospheric Environment 42 (2008) 6088– 6097

ARTICLE IN PRESS

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Atmospheric Environment

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Local to regional emission sources affecting mercury ﬂuxes to New York lakes$

Revital Bookman a,Ã, Charles T. Driscoll a, Daniel R. Engstrom b, Steven W. Efﬂer c a Department of Civil and Environmental Engineering, Syracuse University, 151 Link Hall, Syracuse, NY 13244, USA b St. Croix Watershed Research Station, Science Museum of Minnesota, Marine on St. Croix, MN 55047, USA c Upstate Freshwater Institute, P.O. Box 506, Syracuse, NY 13214, USA article info abstract

Article history: Lake-sediment records across the Northern Hemisphere show increases in atmospheric Received 19 December 2007 deposition of anthropogenic mercury (Hg) over the last 150 years. Most of the previous Received in revised form studies have examined remote lakes affected by the global atmospheric Hg reservoir. In 4 March 2008 this study, we present Hg flux records from lakes in an urban/suburban setting of central Accepted 7 March 2008 New York affected also by local and regional emissions. Sediment cores were collected from the Otisco and Skaneateles lakes from the Finger Lakes region, Cross Lake, a Keywords: hypereutrophic lake on the Seneca River, and Glacial Lake, a small seepage lake with a Mercury watershed that corresponds with the lake area. Sediment accumulation rates and dates 210Pb dating were established by 210Pb. The pre-anthropogenic regional atmospheric Hg flux was Atmospheric deposition 2 1 Sediment cores estimated to be 3.0 mgm yr from Glacial Lake, which receives exclusively direct Northeastern US atmospheric deposition. Mercury fluxes peaked during 1971–2001, and were 3 to more than 30 times greater than pre-industrial deposition. Land use change and urbanization in the Otisco and Cross watersheds during the last century likely enhanced sediment loads and Hg fluxes to the lakes. Skaneateles and Glacial lakes have low sediment accumulation rates, and thus are excellent indicators for atmospheric Hg deposition. In these lakes, we found strong correlations with emission records for the Great Lakes region that markedly increased in the early 1900s, and peaked during WWII and in the early 1970s. Declines in modern Hg fluxes are generally evident in the core records. However, the decrease in sediment Hg flux at Glacial Lake was interrupted and has increased since the early 1990s probably due to the operation of new local emission sources. Assuming the global Hg reservoir tripled since the pre-industrial period, the contribution of local and regional emission sources to central New York lakes was estimated to about 80% of the total atmospheric Hg deposition. & 2008 Elsevier Ltd. All rights reserved.

1. Introduction

Mercury (Hg) contamination is pervasive in aquatic $ This is contribution No. 254 of the Upstate Freshwater Institute. We ecosystems and has potential severe health consequences dedicate this paper to our colleague and principal investigator Geoffrey O. Seltzer who was a great scholar and person. He will be missed by the for wildlife and humans (United States Environmental Earth Sciences community. Protection Agency, 1997; National Academy of Sciences, Ã Corresponding author. Currently at: Leon H. Charney School for 2000). Both direct point source pollution and atmospheric Marine Sciences, University of Haifa, Haifa 31905, Israel. emissions have been historically important in delivering Tel.: +972 4 8288131. Hg to water bodies. Their relative influence is proportional E-mail addresses: [email protected] (R. Bookman), [email protected] (C.T. Driscoll), [email protected] (D.R. Engstrom), to the Hg load emitted to the atmosphere or discharged sweffl[email protected] (S.W. Effler). to water, and the proximity to the pollution sources

R. Bookman et al. / Atmospheric Environment 42 (2008) 6088–6097 6089

(Iverfeldt, 1991; Keeler et al., 1994). The main sources for 210Pb dated lacustrine cores. Most previous studies on Hg atmospheric Hg emissions, since the onset of the deposition in lakes have been conducted in relatively Industrial Revolution are medical waste incineration, remote locations affected by the global long distance municipal waste combustion, metal smelting, chlor-alkali transport Hg reservoir or in urban lakes affected by direct facilities, and coal combustion for electricity generation. discharges and highly developed watersheds (Swain et al., These sources contribute to contemporary Hg deposition 1992; Engstrom et al., 1994; Lorey and Driscoll, 1999; in New York state and originate from emissions from the Engstrom and Swain, 1997; Pirrone et al., 1998; Kamman state (9–25%), the contiguous United States (25–50%) and and Engstrom, 2002; Perry et al., 2005; Lamborg et al., Asia, the largest contributing continent other than North 2002a, b; Balogh et al., 1999). In this research, we studied America (11–20%; Seigneur et al., 2003). The first attempt four lakes influenced by different watershed character- to control effectively industrial emissions in the United istics, ranging from an agriculture and urban disturbed States started with the 1970 Amendments of the Clean Air watershed to a lake with almost no watershed area which Act (Driscoll et al., 2001). Over the past 35 years a variety receives Hg inputs directly from the atmosphere. of Hg emission sources have been controlled through the Clean Air Act. In addition, discussions are underway on 2. Site descriptions controls of Hg emissions from electric utilities, the largest currently unregulated source (United States Environmen- The lakes selected for this study are located in central tal Protection Agency, 2005; Driscoll et al., 2007). New York (Fig. 1). The lakes, Otisco, Skaneateles, Glacial, Anthropogenic emissions to the atmosphere occur as and Cross, are part of the Seneca River watershed that elemental Hg (Hg0), reactive gaseous Hg (RGM), and drains about 8960 km2 to the Oswego River, and subse- particulate Hg (Hg )(Mason et al., 1994). The predomi- (p) quently Lake Ontario. They exhibit a wide range of nant form of atmospheric Hg is Hg0, with an atmospheric watershed and limnological characteristics (Table 1), but lifetime of about 0.5–1 year (Schroeder and Munthe, are all hardwater alkaline systems. Land cover of the 1998). In this form, Hg is well mixed hemispherically, and watersheds has changed over the last two centuries. The can be considered a global pollutant (Fitzgerald et al., first settlers in the region established agricultural com- 1998). Oxidized Hg associated with gases or aerosols has a munities and by the 19th century most of the forestland shorter lifetime of a few days to a few weeks, and was cleared. In the last century agriculture has diminished generally impacts local to regional areas (Olmez et al., greatly, the forested area has recovered, and urban areas 1998; Ames et al., 1998). In the northeast US in 2002, the have developed further (Bloomfield, 1978). major emission sources are municipal waste combustion Skaneateles Lake and Otisco Lake are the eastern most (23%) and utility coal burners (16%) (Northeast States for of the Finger Lakes. They occupy long narrow glacial- Coordinated Air Use Management, 2005). Mercury also origin basins positioned in a north–south direction can be directly discharged to aquatic ecosystems from (Bloomfield, 1978). Both lakes are used for water supply; direct point sources, which under certain circumstances their watersheds are under land protection programs. can dominate the atmospheric inputs (e.g., Glass et al., Mercury inputs are from direct atmospheric deposition to 1990; Bloom and Effler, 1990). the surface of the lakes as well as export from their Mercury that is deposited to the lake’s watershed can be watersheds. Cross Lake is a culturally hypereutrophic lake subsequently transported to the lake. Mercury accumula- characterized by high nutrient content and productivity. tion in the lake depends on the ratio of the watershed to The lake is located on the Seneca River, which contributes lake surface area (Swain et al., 1992), and on variations in approximately 98% of its inflow. The river receives both sediment accumulation rates (Engstrom et al., 1994). The agricultural runoff and municipal wastewater discharge, processes regulating retention and release of Hg in soils and is high in suspended solids (Effler et al., 2004). Cross and wetlands can influence the Hg transport from the Lake receives atmospheric Hg inputs, but is undoubtedly watershed (Lorey and Driscoll, 1999), and cause significant also impacted by land use and wastewater discharge in inputs to a lake long after the actual deposition (Yang et al., the watershed. Glacial is a meromictic seepage lake, 2002). Once in the lake-watershed, Hg can follow several located in the Clark Reservation State Park southeast of pathways: reduction and subsequent evasion to the atmo- the city of Syracuse (Effler et al., 1981). The watershed of sphere, methylation and/or demethylation, soil phase the lake is approximately equal to the lake surface area particle scavenging and retention, and transport with and it has no outlet. Mercury inputs to the lake are almost drainage water (Watras et al., 1994). Methylation of Hg entirely derived from direct atmospheric deposition. This and subsequent transport to surface waters is a health lake is critically important since its record is an excellent concern (Watras et al., 1994; Matilainen, 1995; Porcella, reference of atmospheric Hg flux adjacent to the urban 1994). Methylmercury is taken up by aquatic organisms area of central New York. and bioaccumulates through the food chain, resulting in high concentrations in fish (Driscoll et al., 1994). Exposure of humans and wildlife is largely through consumption of 3. Methods fish. Sedimentation is an effective removal mechanism from water; after deposition and burial, remobilization is 3.1. Sediment core collection generally very limited (Fitzgerald et al., 1998). The objective of this study was to evaluate changes in Sediment cores were collected during 2003 and historical Hg fluxes by measuring Hg concentrations from 2004 by a gravity corer designed for unconsolidated ARTICLE IN PRESS

6090 R. Bookman et al. / Atmospheric Environment 42 (2008) 6088–6097

CR1 Seneca River

CR2-CR4

43°00’

SK1 SK2 GL1 OT3 GL2 OT1 OT2 OT4

SK3 SK4

0 5 10Km 76°20’

Fig. 1. Location map of the study lakes and coring sites. Cores dated by 210Pb are underlined.

Table 1 Characteristics for the Central New York study lakes

Lake Watershed area Surface area Watershed area/ lake Max. Mean Volume (km2) (km2) surface area depth (m) depth (m) (106 m3)

Otisco (OT) 93.8 7.6 12.3 20.1 10.2 77.8 Skaneateles (SK) 154 35.9 922 90.5 43.5 1562.8 Cross (CR) 8300 9 4.3 17 5.5 50.8 Glacial (GL) 0.025 0.025 1 16.2 6.2 0.154

fine-grained sediments (Glew et al., 2001). Core location water content. Samples were homogenized with a mortar and sampling depths (Fig. 1; Table 1 in Supplementary and pestle. data) were chosen based on prior knowledge on the bathymetry and sediment loads. High sediment accumulation rates and deep bathymetry may prevent the 3.2. 210Pb dating recovery of the full sediment inventory since pre-industrial times, as the corer is limited in its sediment Chosen cores from each lake were dated using 210Pb as penetration and is designed to operate in shallow the geochronological tracer. The samples were measured lacustrine environments. Therefore, in Cross Lake we at 1–3 cm intervals through its granddaughter product avoided core collection near the Seneca River inlet due 210Po, with added 209Po as an internal yield tracer. The Po to high sediment accumulation rates (Effler and Carter, isotopes were distilled from 0.08 to 1.3 g dry sediment at 1987), and in Skaneateles, which is a deep lake (Table 1) 550 1C following pretreatment with concentrated HCl and collection was limited to the northern and southern plated directly onto silver planchets from a 0.5N HCl shallower areas (Fig. 1). solution (Eakins and Morrison, 1978). Total 210Pb activity A total of 14 cores were collected from the lakes (Fig. 1; was measured for 1–12 days with an EG&G Nuclear alpha Table 1 in Supplementary data). Inspection of the cores at spectroscopy system. The total activity is the sum of in situ the time of collection indicated the sediment–water production of 210Pb from 226Ra in eroded mineral particles interface was recovered intact, except core GL1. The cores (supported 210Pb) and excess 210Pb that is supplied by were collected in 2.5-in polycarbonate tubes and sec- atmospheric 210Pb fallout (unsupported 210Pb). The un- tioned vertically in the field at 1–2 cm increments. The supported fraction is used to determine sediment chron- samples were kept refrigerated in the laboratory at 4 1C ology in accordance with the 210Pb half-life of 22.3 years until analysis. Small aliquots of wet samples were (Oldfield and Appelby, 1984). The unsupported 210Pb weighted, freeze-dried, and reweighed to determine the activity was calculated by subtracting supported activity ARTICLE IN PRESS

R. Bookman et al. / Atmospheric Environment 42 (2008) 6088–6097 6091 from the total activity measured at each level. Supported period due to their proximity to the Seneca River inlet and 210Pb was estimated from the asymptotic activity at depth its high sediment load. These cores demonstrate similar (the mean of the lowermost samples in the core). Lake profiles of recent decreasing concentrations from bottom sediment material below the depth of unsupported 210Pb to top and most likely correlate in time to the upper 20 cm was dated by assuming constant mass accumulation rates of core CR1. The cores from Glacial Lake showed an up- equal to that of the average of the lowermost dateable core increase in Hg concentrations. The 6.2-fold higher sections. The constant rate of supply (CRS) model was concentration of GL1 compared to GL2 may reflect a used to calculate the sediment accumulation rate and age focusing effect from the slope to the deeper part of the of each section with errors estimated from first-order basin. The modern decline in concentration depicted in analysis of counting uncertainty (Appleby, 2001). The core GL2 was not evident in core GL1 since the upper part dating analysis was preformed at the Science Museum of of the record was lost during sediment collection. Minnesota’s St. Croix Watershed Research station.

4.2. 210Pb dating and sediment accumulation rates 3.3. Mercury analysis

210Pb activity was measured in cores for all four lakes Mercury concentration in the sediments was deter- (Fig. 2; Table 2). Supported 210Pb concentrations ranged mined by cold vapor atomic absorption spectrometry from 0.24 to 1.10 pCi g1, and the number of lower samples (LECO AMA254 Advanced Mercury Analyzer) at the Center from which supported 210Pb was estimated ranged from 2 for Environmental Systems Engineering at Syracuse Uni- to 9. Inventories of cumulative unsupported 210Pb range versity. Freeze-dried and homogenized sediment aliquots from 11.15 to 21.96 pCi cm2, which is equivalent to 210Pb of 0.01–0.1 g were weighted and measured for each fluxes of 0.38–0.70 pCi cm2 yr1. These values are similar sample analysis. A calibration curve was determined to the atmospheric 210Pb fallout in regions of the northern by measuring a standard reference material (National hemisphere dominated by continental air masses (Binford Institute of Standards and Technology—1633b). Blanks et al., 1993). The cores from the southern Skaneateles Lake and standards were analyzed before and after all sample had substantially lower cumulative unsupported 210Pb runs and every tenth sample. No analysis was undertaken and unsupported fluxes (Table 2; Fig. 2 in Supplementary unless the associated standard measurement was with data), which likely indicates resuspension and focusing of 90–110% of its known concentration. The analytical fine-grained sediments (and associated 210Pb) into deeper accuracy of the Hg data, estimated as relative percent parts of the lake (Engstrom et al., 1994), as discussed difference between triplicates, was 3.7% (n ¼ 28). Random above. samples in each analysis were spiked with the standard The calculated sediment accumulation rates ranged reference material. Analytical precision, estimated as the from 0.01 to 0.18 g cm2 yr1 (Fig. 2). Sediment accumula- mean % recovery for matrix spikes, was 100.5% (n ¼ 32). tion rates in the Cross and Otisco cores increased with Mercury fluxes were calculated using the 210Pb-derived time, consistent with changes in land use and develop- sediment accumulation rates of the dated cores. Back- ment in the watersheds during the last century. The ground fluxes were calculated using the average sediment average accumulation rate in the northern portion of accumulation rates of the lowermost dateable sections. Skaneateles Lake was 0.09 g cm2 yr1 (Fig. 2), while the southern portion of the lake had an average sediment 4. Results and discussion accumulation rate nearly fivefold lower (0.02 g cm2 yr1; Fig. 2 in Supplementary data). Glacial Lake had a 4.1. Hg concentrations nearly constant sediment accumulation flux around 0.02 g cm2 yr1 (Fig. 2), which is consistent with its minimal The concentrations of Hg in the central New York lake watershed and lack of substantive changes in primary sediments ranged from 3.6 to 87.4 ng g1 in the deeper production. portions of the cores. Concentrations of Hg increased with The range of sediment accumulation rates and fluctua- decreasing sediment depth at different levels in most of tions in sediment supply reflect the different watershed the cores. Peak concentration values were in the range of conditions. Glacial Lake represents one end member, 29.9–467.2 ng g1 (Fig. 1 in Supplementary data). which is influenced by low and stable accumulation rates All four cores in Otisco Lake (OT1–4) had similar Hg with no major human-induced watershed impact, making profiles. The Hg concentrations in Skaneateles Lake it an excellent record for direct atmospheric Hg flux. Cross differed between the northern (SK1–2) and the southern Lake is the other end member, where a 15-fold increase in (SK3–4) locations. In the south, Hg concentrations sediment accumulation rates over a period of a few increased sharply only in the upper sediments, and were decades reflects a watershed controlled lake. Deposition approximately three times higher in the deeper core conditions in Cross Lake represent a highly disturbed (SK4), probably reflecting the focusing of fine-grained landscape, and are likely affected and even controlled by sediments into deeper parts in the lake. In Cross Lake only the change in land use (i.e., agriculture, urbanization). The the northern core (CR1) showed an Hg concentration two Finger Lakes, Skaneateles, and Otisco experienced profile increase and then a gradual decrease along the smaller changes in sedimentation rate. The threefold depth core. The other cores in Cross Lake (CR2–4) were too increase in sediment accumulation of Otisco Lake prob- short to cover the full record since the pre-industrial ably represents the development along the lakes shores ARTICLE IN PRESS

6092 R. Bookman et al. / Atmospheric Environment 42 (2008) 6088–6097

Cross Lake Otisco Lake Skaneateles lake Glacial Lake 0 0 0 0 5 5 5 5 10 10 10 15 15 10 20 15 20 25 20 25 15 30 25

Depth in core (cm) 30 35 20 30 35 40 40 45 25 35 0 12340 2468 02 4 6 84810 012 16 Total 210Pb activity (pCi g-1)

Cross Lake Otisco Lake Skaneateles lake Glacial Lake 2000 2000 2000 2000

1950 1950 1950 1950

1900 1900 1900 1900 Pb date 210

1850 1850 1850 1850

1800 1800 1800 1800 0.00 0.050.10 0.15 0.20 0.000.050.10 0.15 0.20 0.000.050.10 0.15 0.20 0.000.05 0.10 0.15 0.20 Sediment accumulation rate (g cm-2 yr-1)

Fig. 2. Total 210Pb activity, by depth down core, and sediment accumulation rates (calculated using the CRS dating model) vs. 210Pb inferred dates for the central New York lakes.

Table 2 210Pb data, Hg ﬂuxes, and Hg peak ﬂux ratios for the dated sediment cores from Central New York lakes

Core no. Supported Cumulative Unsupported Modern Hg fluxa Peak Hg fluxb Pre-industrial Peak 210Pb (pCi g1) unsupported 210Pb flux (mgm2 yr1) (mgm2 yr1) fluxc ratiod 210Pb (pCi cm2 yr1) (mgm2 yr1) (pCi cm2)

Otisco Lake OT2/3 1.1070.05 20.05 0.64 77.7 124.6 (1972) 42.2 (1722–1890) 3.0

Skaneateles Lake SK1 0.3570.03 21.96 0.70 77.0 114.4 (1971) 10.3 (1836–1868) 11.1 SK3e 0.2470.01 0.97 0.03 4.0 4.0 (1979) 0.8 (1104–1824) 5.4 SK4e 0.3470.05 5.41 0.17 20.7 20.7 (1995) 4.8 (1252–1795) 4.3

Cross Lake CR1 0.9770.03 11.15 0.38 248.8 307.2 (2001) 9.7 (1639–1755) 33.9

Glacial Lake GL2 0.2570.01 11.76 0.38 16.6 (1988), 23.5 (2002) 59.0 (1971) 3.0 (1803–1839) 19.5

a Hg flux at the surface layer. b In parenthesis year of occurrence. c In parenthesis years used to estimate pre-industrial flux. d Ratio of peak to pre-industrial Hg flux. e See supplementary data for 210Pb activity profiles. ARTICLE IN PRESS

R. Bookman et al. / Atmospheric Environment 42 (2008) 6088–6097 6093 for residence and recreation characterizing the last sediment focusing away from the core site into deeper century. A decrease in sediment accumulation in Skanea- parts of the basin (Fig. 3 in Supplementary data). Glacial teles Lake since 1950s may be linked to reforestation and Lake, which receives its Hg almost exclusively from direct effective land protection programs (City of Syracuse atmospheric deposition and thus likely represents the Department of Water, 2005). regional pre-industrial flux, had a background average flux of 3.0 mgm2 yr1, which is within the range of atmo- 4.3. Hg fluxes spheric deposition estimated for pre-industrial Hg fluxes in the mid continental North America (Swain et al., 1992) Mercury concentration profiles can be affected by and the nearby Adirondacks (Lorey and Driscoll, 1999). sedimentation rates. Concentrations are diluted when Otisco Lake had a rather high pre-industrial Hg flux sedimentation rates are elevated, and enriched under compared to the other lakes. This flux may point to early periods of reduced sedimentation (Engstrom and Wright, agriculture and deforesting in the lake watershed by the 1983). Multiplying the Hg concentration with the sedi- first European settlers in the region. ment accumulation rates determined from the 210Pb dating normalizes this covariance and enables the 4.3.2. Increase in Hg deposition and the watershed influence comparison among cores and lakes. We were able to The increase in Hg deposition started as early as 1850 calculate Hg fluxes for each lake only from the dated in Glacial Lake and 1870 in Skaneateles Lake (Fig. 3). In cores. Lakes may exhibit large spatial differences in both lakes the increase was gradual, but by the 1890s sediment accumulation and Hg concentrations across deposition increased sharply. In Otisco Lake and Cross the basin as evident from the lakes in this study. Due to Lake the increase in Hg deposition started in the 1920s spatial heterogeneity, the most accurate determination of and 1940s, respectively (Fig. 3). Spatial differences in whole basin Hg fluxes requires coring and dating of atmospheric Hg deposition could have influenced this multiple cores from each lake (Engstrom et al., 1994). temporal pattern. However, since Otisco and Cross lakes However, a single to a few cores can provide reliable have much larger watershed area to lake surface area information on temporal trends and the magnitude of ratios (Table 1) the delayed response to atmospheric change in atmospheric deposition (EPRI, 1996). Mercury pollution is more likely indicative of Hg retention and/or flux calculations from all lakes reveal an increase in Hg soil disturbance in these watersheds. inputs from pre-industrial times to the modern period. Glacial and Skaneateles lakes had a similar pattern of However, trends were not similar across the lakes in the Hg deposition over the last century, although the timing of increase, peak value, and magnitude (Fig. 3). magnitude of increase was different (Fig. 4). The similarity These differences are most likely due to the watershed in pattern emphasizes that these lakes are receiving their characteristics and disturbance. Hg flux from similar atmospheric sources, and that the watershed influence did not mask the atmospheric 4.3.1. Pre-industrial Hg fluxes signature. The difference in magnitude probably repre- The pre-industrial fluxes ranged from 0.8 to 42.2 mg sents the different watershed to lake surface area ratio m2 yr1 (Table 2). The lowest fluxes, which were of each lake (1, and 4.3, respectively). The Hg flux recovered from the southern Skaneateles cores, very from Glacial Lake is almost entirely derived from direct likely underestimate atmospheric Hg deposition due to atmospheric deposition. The additional flux of Hg to

Hg Concentration (ng g-1) 0 60 120 180 24000 30 60 90 120 40 80 1200 50 100 150 200 2000 Otisco Lake

1950

1900 Pb date 210

1850

Cross Lake Skaneateles Lake Glacial Lake 1800 0 100 200 300 400 0 30 60 90 120 0 40 80 1200 20 40 60 Hg flux (μg m-2 yr-1)

Fig. 3. Total Hg ﬂuxes and concentration for sediment cores from central New York lakes. Closed symbols are Hg ﬂuxes and open symbols are Hg concentrations. ARTICLE IN PRESS

6094 R. Bookman et al. / Atmospheric Environment 42 (2008) 6088–6097

140 140 Hg emissions 150 R2 = 0.94 -1 Great Lakes

yr 100

120 -2 120 50 g m μ 0 100 050100150 100 T yr-1

-1 80 80 80 R2 = 0.74 -1 -1

yr Skaneateles lake yr -2

-2 40 Hg sediment flux Ton yr g m g m 60 60 μ μ 0 050100150 -1 40 T yr 40

Glacial lake 20 Hg sediment flux 20

0 0 1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000

Fig. 4. Trends in Hg emissions (t Hg yr1) from anthropogenic sources in the Great Lakes region (Pirrone et al., 1998), and Hg ﬂuxes (mgHgyr1 m2)in Skaneateles Lake and Glacial Lake. In the inset, the linear relationships between the Great Lakes emission records and Hg sediment ﬂuxes from Skaneateles Lake (A) and Glacial Lake (B).

Skaneateles Lake beyond direct atmospheric deposition is )

transported from its watershed. We would expect the Hg -1

transported from the Skaneateles Lake watershed to be in yr proportion to the watershed to surface lake ratio, meaning -2 200 g m

at least four times greater than the Glacial Lake flux. μ However, during most of the period less Hg was deposited y = 0.1775x + 66.616 in Skaneateles Lake than expected reflecting possible R2 = 0.7562 watershed-specific and temporally varying lags between Hg deposition to the watershed and the eventual trans- 100 port to the lake. When multiplying the Glacial Lake flux, which represents the direct atmospheric fallout, with the watershed to surface lake ratio of Skaneateles Lake, we y = 1.1575x -19.607 2 estimate the expected flux to the lake assuming all Hg was R = 0.721 Skaneateles Lake Flux ( transported from its watershed. The linear relationship 0 between the recorded flux (measured from the core) and 0 100 200 the calculated expected flux shows a 1:1 relationship only Expected Flux (Glacial Lake Flux ∗ 4.3, μg m-2 yr-1) until the 1920s (Fig. 5). After that period relative Hg deposition to Skaneateles Lake sediments diverged and Fig. 5. Skaneateles Lake Hg flux calculated from core SK1 vs. the declined. Reforestation in the Finger Lakes area began at expected Hg flux according to a watershed to surface area ratio of 4.3. The expected Hg flux is the flux we would anticipate from the direct Hg that period after a century of forest clearance for logging deposition over the lake and deposition over its watershed, which is and agriculture (Bloomfield, 1978). The decline in Hg transported into the lake. The direct atmospheric flux is estimated from transport from the watershed most likely points to Glacial Lake that receives only direct atmospheric fallout. increased Hg watershed retention associated with the change in land cover. This creates a lag period between the concentration with the sediment accumulation rate time of Hg deposition to the watershed and its transport provides an accurate representation of the Hg flux. This to the lake. Mercury retention in the Skaneateles wa- deviation between the concentration and flux, not evident tershed is also consistent with the decline in sediment in Skaneateles and Glacial lakes (Fig. 3) due to relatively accumulation rate in the lake (Fig. 2). constant sediment flux, is evidence for watershed dis- In Otisco Lake and especially Cross Lake, Hg deposition turbance and urban development in the Otisco and Cross is influenced, or even controlled, by the sediment load to Lake watersheds. the lakes. This phenomenon is evident by comparing the Hg flux and concentration (Fig. 3). Sediment Hg concentrations have declined in the last century, despite 4.3.3. Peak and modern Hg fluxes increases in atmospheric Hg deposition through to the Maximum fluxes in three of the records, Otisco 1970s (e.g., Perry et al., 2005). This characteristic is a Lake (125 mgm2 yr1), northern Skaneateles Lake (114 mg result of an increase in sediment load to the lakes m2 yr1), and Glacial Lake (59 mgm2 yr1), peaked that diluted the Hg concentration. Multiplying the Hg synchronously in the early 1970s (Fig. 3). The close ARTICLE IN PRESS

R. Bookman et al. / Atmospheric Environment 42 (2008) 6088–6097 6095 correspondence in timing among the records shows again interruption in this trend in the early 1990s. Since the that Hg transported from the watershed or changes in early 1990s, the Hg flux has increased by approximately sediment accumulation rates did not obscure the atmo- 40%. This abrupt increase is uncharacteristic of recent spheric signature in these lakes, at least during the peak in sediment Hg deposition as reported in many studies atmospheric Hg deposition. The peak flux in across eastern North America (Lorey and Driscoll, 1999; the Cross Lake core (307 mgm2 yr1) dates to the current Engstrom and Swain, 1997; Kamman and Engstrom, 2002; decade (i.e., 2001), and is delayed compared to the other Perry et al., 2005). This unusual trend was only evident in records. This maximum Hg flux is almost certainly Glacial Lake and could be due to emissions from new controlled by the sediment load to the lake from Seneca nearby sources. A possible recent Hg source is a local River, which has overwhelmed the atmospheric signature municipal waste incinerator and its emissions and of Hg. Agricultural and urban runoff discharging from the associated deposition of oxidized species of Hg. The Seneca River drainage area contributed to the increase in incinerator, located 2.5 km upwind from Glacial Lake, Hg flux into Cross Lake. has had yearly Hg emissions averaging 15.3 kg Hg yr1 Peak flux ratios were determined as the ratio of peak to since the beginning of its operation in 1994 (D. Grasso, pre-industrial Hg fluxes (Table 2). Peak values are the Covanta Energy Corporation, personal communication). maximum Hg flux in each dated core as presented above, while the pre-industrial flux is an average of the fluxes 4.3.4. The contribution of local and regional sources to Hg before the increase of the industrial period. The peak flux deposition ratio for Skaneateles Lake and Glacial Lake was 11.1 and Increases in Hg accumulation in lake sediments can be 19.5, respectively. These ratios are substantially higher used as an indicator of airborne Hg pollution (Fitzgerald et than the flux ratio of 2–7 reported in other studies for al., 1998), although the relative contribution of local vs. small remote lakes in the Adirondacks, NY (Lorey and global sources to an individual lake system can be difficult Driscoll, 1999), the Midwestern US (Swain et al., 1992), to determine. Skaneateles Lake, which has relatively and Canada (Lockhart et al., 1995), and are likely due to constant sediment accumulation rate, and especially local and regional sources of Hg emissions in addition to Glacial Lake that receives Hg inputs almost entirely from the deposition from the global long-range transport direct atmospheric deposition, provide an opportunity to atmospheric Hg reservoir and/or enhanced Hg deposition examine correlation with Hg emission records. Compar- due to local air quality (i.e., increases in Hg0 oxidation due ison with records of Hg atmospheric emissions in North to elevated ozone or chloride concentrations). The Otisco America, and in particular the Great Lakes (Pirrone et al., Lake peak flux ratio was 4.4 when the lowest pre- 1998) showed strong correlations with the Hg sediment industrial value (deepest in the core) is used for calcula- deposition fluxes (Fig. 4). Mercury emissions increased tion, and decreases to 3 when the average of the entire dramatically at the period between 1880s and 1920s, period before 1900s is used. Although the lake is in close peaked during World War II, and again in the 1960–1970s. proximity to Skaneateles Lake (5 km) and its watershed Air-pollution regulations in the early 1970s gradually is adjacent to the Skaneateles watershed, it shows a much eliminated Hg emission sources, leaving coal combustion lower flux ratio. Otisco Lake has a three times greater for electric generation as the most significant source still watershed to lake area ratio (Table 1) compared to contributing Hg through atmospheric deposition in the Skaneateles Lake, suggesting that much of the deposition United States (EPA, 2003; Driscoll et al., 2007). The strong of Hg to the watershed is retained in soil. The Cross Lake linear relationships between the Great Lakes emission peak flux ratio is 33.9 and this elevated value is an records (Pirrone et al., 1998) and Hg sediment fluxes from additional signature for the influence of sediment load Skaneateles Lake (R2 ¼ 0.94) and Glacial Lake (R2 ¼ 0.74) from the watershed to the Hg flux. High Hg fluxes and (Fig. 4), and the high peak flux ratios (11.1 and 19.5, peak flux ratios are characteristic of lakes with disturbed respectively; Table 2) implies that a substantial fraction of watersheds influenced by agriculture, industrial, and the Hg atmospheric deposition is transported from urban development (Pirrone et al., 1998; Balogh et al., regional to local sources. 1999). Remote and rural sites tend to show atmospheric Hg Modern declines in Hg fluxes are evident in the levels largely dominated by the global reservoir unless core records (Fig. 3) and consistent with declining samples are taken downwind of an emission source rates of atmospheric inputs as observed in other sediment (Valente et al., 2007). However, urban areas can contribute cores from the northern United States (Engstrom and significantly to atmospheric Hg deposition as shown from Swain, 1997; Kamman and Engstrom, 2002). In Skanea- measurements at an urban site in Michigan (Lyman and teles Lake, the Hg flux decreased gradually from the Keeler, 2005). The local to regional Hg deposition early 1970 to the present (surface layer) by 33%. Recent component can be estimated by subtracting the global declines in sediment Hg deposition were evident also deposition increase from the increase in Hg sediment in Otisco and Cross Lake (38% and 19%, respectively). deposition found in Glacial Lake, which receives direct This pattern might also point to the decrease in sedi- atmospheric inputs. The atmospheric global Hg reservoir ment erosion due to watershed soil protection efforts in the Northern Hemisphere is estimated to have especially in the lakes that are affected by disturbed increased by threefold since the onset of the industrial watersheds. period (Lamborg et al., 2002a; Mason and Sheu, 2002). In Glacial Lake, the sediment Hg flux decreased by Pre-industrial atmospheric Hg deposition in Glacial Lake 72% from the peak value in the early 1970s until an has increased from 3 to 59 mgm2 yr1 in the early 1970s ARTICLE IN PRESS

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(Table 2). Assuming the global reservoir tripled during the Appendix A. Supporting data same period (Lamborg et al., 2002a; Mason and Sheu, 2002), global Hg emissions account roughly for a deposition flux of Supplementary data associated with this article can be 9 mgm2 yr1 in central New York. This value is in accordance found in the online version at doi:10.1016/j.atmosenv. with modern values of atmospheric wet deposition in a 2008.03.045 remote forested site upstate New York (Huntington Forest MDN site) that was 7 mgm2 yr1 for the period 2000–2004 (National Atmospheric Deposition Program), realizing dry deposition increases this value somewhat (e.g., 25% of wet References deposition; Selvendiran et al., in review). Subtracting the global deposition flux from the peak flux in Glacial Lake 2 1 Ames, M., Gullu, G., Olmez, I., 1998. Atmospheric mercury in the vapor gives a flux of 50 mgm yr . This analysis suggests that phase, and in fine and coarse particulate matter at Perch River, New about 80% of the total Hg deposition was derived from local York. Atmospheric Environment 32, 865–872. and regional sources. Sources of Hg emissions from the Great Appleby, P.G., 2001. Chronostratigraphic techniques in recent sediments. In: Last, W.M., Smol, J.P. (Eds.), Tracking Environmental Change Using Lakes area include a variety of industries (Pirrone et al., 1998; Lake Sediments. Basin Analysis, Coring, and Chronological Techni- Cohen et al., 2004). The Syracuse metropolitan area is highly ques, vol. 1. Kluwer Academic Publishers, Dordrecht, pp. 171–201. industrialized since the 19th century. Natural resources and Balogh, S.J., Engstrom, D.R., Almendinger, J.E., Meyer, M.L., Johnson, D.K., 1999. History of mercury loading in the upper Mississippi River early transportation infrastructure lead to the development reconstructed from the sediments of Lake Pepin. 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