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12C ratios in marine sediments from the New York Bight
Estuarbze and Coastal 31arine Science (x98o) Ix, 6o5-61 x
Effect of Ocean Dumping on 3C/'2C Ratios in Marine Sediments from the New York Bight
William C. Burnett Department of Oceanography, The Florida State University, Tallahassee, Florida 323o6, U.S.A.
and Oliver A. Schaeffer Department of Earth and Space Sciences, State University of New York, Stony Brook, Nezo York H794, U.S.A. Received 3J August z979 and in revised form e8 dYanuary x98o
Keywords: carbon; isotope ratlos; sewage disposal; dumping; sediments; New York Bight In order to evaluate the influence of the ocean dumping of sewage sludge upon the organic carbon fraction of sediments of the New York Bight, a study of carbon isotopic variations in surface sediments from the area has been completed. On the basis of our a3C/I:C measurements, it appears that: (x) sewage is depleted in 13C as compared to average marine organic sedimentary carbon, and (2) ~l~C values from sediments of the New York Bight show systematic variations which are a direct consequence of the sludge disposal. Based on assumptions regarding inputs of sedimentary carbon to the sea floor in this area, we have modeled these ~sCp2C variations in terms of progressive dilution of normal marine carbon with carbon derived from the ocean dumping of wastewater sludges. The isotopic composition of carbon in sediments from the New York Bight may serve as a quantitative tracer of sewage sludge components.
Introduction The Apex of the New York Bight has been a repository for man's wastes for many years. Gross (I972) has discussed the history of waste disposal in the New York metropolitan region and mentions regulations governing these activities dating back to x684. NIaterial currently being dumped in this area include dredge spoils, construction and demolition rubble, waste chemicals, and sewage sludge. Approximately 76% of all solids discharged into the New York Bight between i964 and x968 consisted of dredged wastes, while only 4"3% was derived from sewage sludge (Gross, x972 ). Although the bulk weight of sludge is low relative to other materials, the volume being dumped is tremendous. PararasCarayannis (I973) estimates, for example, that approximately 3.2• xo6 m 3 of sludge were dumped annually into the New York Bight during the period ]965-I97o. "/'he purpose of this paper is to assess the possibility of using variations in the isotopic composition of carbon as a quantitative index of sewage contamination in the sediments from the dump site area. It is hoped that these data will complement and extend the results of workers who 6o5 o3o2-3524/8o/z 20605 + 07 $o2.oo[o
9 z080 Academic Pre.q-qInt'_ tl ar~ndnnX I .tA
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have investigated other parameters (heavy metals, radionuclides, fecal steroids, etc9 in terms of delineating man's impact on this portion of the continental shelf (Charnell, i975; Williams et al., I978; Hatcher & McGillivary, i979). For this investigation, we analysed x8 surficial samples from the New York Bight Apex (Figure ,) and one core sampled at closely-spaced intervals from the Hudson Shelf Valley9 All the surface sediment samples are in the vicinity of the sewage sludge dump site located approximately 24 km from the entrance to New York Harbor. Our intention in analysing these samples is to make an evaluation of whether stable carbon isotope data is useful for assessing such factors as distribution, transport paths and ultimate sites of deposition of carbon-bearing pollutants in the New York Bight. Our core from the Hudson Shelf Valley ~s about 60 km south-east of the disposal area, and will be used as a control for baseline values. In order to isotopically characterize the carbon being derived by ocean dumping, wastewater sludges were collected directly from the holding tanks of two of New York's largest sewage treatment plants (Newtown Creek and Ward's Island). The tanks from which our samples were collected are the same tanks from which sewage barges load their holds for disposal at sea. The composition of these sludges has been described by Duedall et al, 0975). M a t e r i a l s and m e t h o d s Grab samples from 15 stations in the New York Bight Apex were obtained in late March, I976 by the Sandy Hook Marine Laboratory (Highlands, New Jersey). All samples were
~ NEW YORK HARBOR
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Figure x. Index map of New York Bight Apex showing locations of surficial sediment samples used in this study. Symbol ' @' designates the sewage sludge dump site centered at 4o~ 73~ since x924. The solid contour represents t'o% organic carbon in dried sediments (redrawn from Charnell, *975). Lines A-A' and B-B' represent the data profiles shown in Figure 2.
Effect of ocean dumping on 1~C/~2C ratios
607
frozen within a few hours after recover), to prevent bacterial degradation of the organic fraction. Prior to analysis, samples were dried at less than xoo ~ for a few days and then digested in warm 2 ~ HCI to destroy any carbonates. The samples were then repeatedly washed with distilled water to remove the acid. After a final drying, the samples were combusted in a quartz tube in a stream of pure oxygen at approximately 90o ~ The evolved gases from this combustion were then passed through cupric oxide maintained at 50o ~ to ensure complete oxidation of all the carbon. The gases were then passed through a series of chemical scrubbers (silver nitrate, potassium permanganate, and potassium dichromate combined with sulfuric acid) to remove halogens, oxides of sulfur and nitrogen, and water. The resulting CO 2 was condensed into cold traps maintained at liquid nitrogen temperature. After passing the gas over dry ice several times for further drying, an aliquot of the gas was taken for mass spectrometric analysis. Isotope ratios were measured on a Nuclide isotope ratio mass spectrometer at the LamontDoherty Geological Observatory. Results are expressed as ~oo deviations (613C) from the carbon isotope ratio of PDB (Chicago standard). Our values have been corrected for instrumental effects and for differences in the 170 content of the samples relative to the standard (Craig, x957). Replicate samples had isotope mass ratios which agreed to within q-o.25~oo. Results and discussion Sediment samples from the Bight Apex vary considerably in color, texture and organic content. Sediments in proximity to the sewage dump site are dark muddy silts with high contents of organics and water. Stations closer to shore are tan, light-colored, very coarse sands with an extremely low organic content. A more detailed description of the surficial sediments of the New York Bight area may be found in Stubblefield et aL (I977). Optical and X-ray studies of core HSV 53 have shown that silt to fine-sand sized quartz, feldspar and accessory minerals are the major inorganic components. There were no apparent systematic variations in the relative amounts of the inorganic phases as a function of depth in this core. It was found, however, that siliceous skeletal materials (diatom frustules, sponge spicules, etc.) increased greatly in the upper few centimeters of the core. Results of our isotopic measurements, as well as water and organic carbon contents, are presented in Table I. The most interesting aspect of our data concerns the aerial distribution of :3C/12C ratios in the surficial sediments of the Bight Apex. Two profiles (Figure 2) of ~13C across the sewage sludge disposal area show that the carbon isotopic composition becomes significantly lighter, i.e. more depleted in 13C, as the dump site is approached. Sediments from stations further from the disposal area progressively approach a more 'normal' ~13C value for continental shelf sediments of approximately --2Z~oo relative to PDB. What results, then, is a unique ~513C pattern with values becoming more negative in a seaward direction, reaching a minimum, and then reversing its trend by becoming less negative seaward of the sewage disposal area. Further verification that this pattern results from the input of wastewater sludge is provided by direct stable isotopic analyses of sludge samples from the Newtown Creek and Ward's Island treatment plants (Table x). The sludges collected from these two plants were determined to have ~513Cvalues of --25. 7 and --26"o~oo respectively. These values agree very closely with those measured from the stations immediately adjacent to the disposal site (Stations 3 z and 33). Systematic variations in the isotopic composition of carbon from sediments have been described before for continental shelf environments. Sackett & Thompson (I963) , for example, showed that ~ C values became less negative when proceeding from river through
IV. C. Burnett& O. A. Schaeffer
608
"I'^nLE x. Analytical data on surficial sediment samples from the New York Bight. The designations G-I and G-2 refer to two separate lowerings of the grab sampler at the same station. Values for HSV 53 are averages and ranges of I3 determinations down the 62 cm length of the core. The core was sampled in x973 at 4o~ 73~ in 68 m water depth. All other samples recovered in March x976 Station no.
Depth (m)
HtO (%)
Cot= (%)
9"7 x7"7 8"2 9"1 26-2 24"4 32"6 33"5 33"5 27"4 27"4 3"0 20"7 24"4 36"6 45"7 45"7 x8"3
x9 20 x7 x6 34 24 40 48 54 58 ~ 22 x8 z6 4x 32 49 15
o'x7 o.xo 0"07 0.02 x'x9 0"5 t 2"33 X'68 2"79 2"87 o'72 0"08 o.x6 o'o2 !.8o x.x6 2"09 0"08 27"x 4t'I o'5z (o'3I to 0"76)
x x2
x6 t9 23 32 33 34 G---X 34 G--2 35 G--x 35 G--2 40 42 43 45 56 G--x 56 G--2 64 Newtown Creek Ward's Island Core H S V 53
--
--
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~ 34 (29 to 39)
lsC/l=C,,mp,= a (~13C~oo
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-270
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-
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--
--21"6 --23"0 --24"I --24"3 --23"9 "--23"9 --24"2 --25"7 --26"0 --22"x (--21"4 to --22-8)
o 25 50 60 5~ 50 55 --
-o
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6t~C--51:Cm X Ioo = per cent sewage sludge contained within organic 51aC __5~aC= fraction of sediment. See explanation in text.
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Figure 2. Data profiles over the New York Bight Apex showing variations of 613C as a function of location. The symbol ' ( ~ ' gives the mean 5t3C value determined in sludge samples from two of New York City's largest treatment plants. The symbol is shown at the center of the designated ocean disposal area. Vertical bars indicate analytical precision based on replicate determinations. (a) Profile A-A" showing 5~3C variations in an east-west profile through the New York Bight Apex. (b) Profile B - B ' showing 6t3C variations in a north-south profile.
Effect of ocean dumping on xsC]ltC ratios
609
lagoonal to open marine environments in the Gulf of Mexico. They attributed this systematic variation to a mixing of land and marine plant derived organic materials which differ in isotopic composition. Newman et al. (i973) studied stable carbon isotopes in cores of Quaternary sediment from the Gulf of Mexico and concluded that the major parameter affecting the 513C values of organic carbon from marine sediments is the relative amount of terrestrial material present in the sediment. Hunt (I968) suggests that on the shelf of the Atlantic coast the major contribution to organic carbon is from marine organic matter resulting in 513C values more typical of deep sea sediments. Terrestrial organic matter is dominant in river sediments only to the mouth of narrow rivers in this region. If 5aaC values of organic carbon in continental shelf sediments are assumed to be a function of mixing of varying amounts of terrestrial and marine organic carbon, then an isotopic mixing equation can be formulated to calculate the relative amounts of each type of carbon contained in the samples, l'~ewman et aL (x973) and Shultz & Calder (I976) used this approach for estimating the extent of the influx of terrestrial carbon into Gulf of ]Vle.xico sediments. It is necessary to assume or have measured the values for the two end members in the mixing equation, i.e. ~taC in marine and terrestrial carbon from the region under study. We can use the same approach here for estimating what the approximate contribution of the sludge component is to the organic carbon content of each of our surficial sediment samples. The appropriate equation would be as follows:
F s ~---
5~C--513C~ 513C,--513C=
X I00
where F. = per cent sewage sludge, 51sC = 513C of organic carbon in sample, 613C., = 81~C of normal continental shelf marine carbon in this region (--22~oo), 5x3C, = ~ia3C of sewage sludge (--26~oo). The 51~C, value comes directly from our measurements of wastewater sludge (average of two measurements=--25.8~oo) while 5a3C,, will be estimated by using the mean value --2a'o~oo for our core from the Hudson Shelf Valley (HSV 53). As mentioned earlier, this core is believed to be far enough out on the shelf that it has not been affected by waste disposal or other forms of pollution. The relatively constant values of 51~C down the length of the core (zz.x+o.4~oo) indicates that this is probably a fairly good assumption. Our estimate also agrees well with measurements reported by Hunt (1968) for 513C values on the Atlantic sheff near Nantucket and off Delaware. g~[ost of his values are close to --2X~oo, even near the mouths of large estuaries. Our estimates for the percentages of sludge particles contained within the total organic content of our sediment samples are given in Table x. Because of the uncertainties involved, we have reported all values to the nearest 5%. Although we don't claim that the absolute magnitudes of these values are well known, we do feel that the dominent trend in the data is a direct result of the input of isotopicaUy lighter carbon by sludge dumping. Although our per cent contamination values are somewhat higher, the pattern is essentially the same as that reported by Hatcher & McGillivary (x979) who used a fecal steroid as an indicator. It might be argued that our values have little meaning because we have neglected the input of normal terrestrial organic carbon onto the shelf in this region. The input of terrigenous material to the New York Bight is probably small 0Heade, x969) , however, and
6to
IV. C. Burnett ~ O. A. Schaeffer
should not greatly affect our results. It should also be pointed out that the organic fraction of the sediments in the lower reaches of the Hudson are also contaminated with sludge particles (Simpson et al., x98o). Any addition, then, of riverborne particles will also contribute sludge carbon. Actually, the mixing that we are describing is a mixture of terrestrial organic carbon (in the form of wastewater sludge) with the marine carbon produced by productivity. The main feature of our data which makes it unique is that we have observed a pattern developed in the sediments of the Bight Apex which owes its origin completely to man's impact. The only stations which apparently have not been affected by sewage disposal are Stations x2, x6 and 4 o, all of which are in nearshore shallow locations. As expected, the stations displaying the greatest input of sewage are those located immediately adjacent to the disposal site (Stations 3z and 33). One unanticipated result is the relatively high sludge component found at Station 64, the furthest south of our stations. Because of the distinctive pattern of 13C/12C ratios developed in the sediments of the New York Bight as a result of sludge disposal, we feel that more detailed 61~C surveys would greatly assist in the delineation of transport paths and ultimate sites of deposition of sludge after its disposal at sea. Other parameters which have been mentioned as possible tracers for sewage sludge in the marine environment include heavy metals, total organic carbon, the ratio of carbohydrates to total organic carbon (Charnell, x975) and fecal steroids (Hatcher & McGillivary, x979). Although high concentrations of some metals and organic carbon are characteristic of wastewater sludge, their presence in high levels in marine sediments does not necessarily indicate that sludge components are present. High trace elements and organic carbon contents have been reported as occurring in marine sediments from many areas where sewage sludge is not a contaminant. Although more promising, the carbohydrate content normalized to total organic carbon may still lead to some ambiguity in interpretation. Tlae fact that this ratio will change as the result of progressive degradation of the organics (with the carbohydrates persisting longer) makes its use limited to qualitative assessments. The concentration of the fecal steroid coprostanol, normalized to total steroids, can be used in a quantitative sense to determine amounts of sewage-derived materials according to the recent work of Hatcher & iV/cGillivary (I979). Their results from the New York Bight showed basically the same pattern as reported here with maximum values of sewage sludge occurring in the Christiaensen Basin at the mouth of the Hudson Shelf Valley. We feel that our 13C/12C measurements have great potential as quantitative tracers for sludge components in the coastal marine environment. This should prove to be extremely valuable in assessing the extent of environmental impact of ocean dumping of wastewater sludges.
Acknowledgements Thanks are extended to J. Pierce and L. Rogers (Sandy Hook Marine Laboratory) for providing us with the surficial sediment samples. Our core from the Hudson Shelf Valley was sampled by the Atlantic Oceanographic and Meteorological Laboratories of the National Oceanic and Atmospheric Administration (AOML/NOAA). L. ~,filler and J. Lawrence assisted in the use of the Nuclide mass spectrometer which was made available at LamontDoherty Geological Observatory. H. Noels assisted in the chemical preparation laboratory. Financial support for this study was provided by grant o462244oi 3 from the National Oceanographic and Atmospheric Agency (Marine Ecosystems Analysis Program--New I York Bight Project).
Effect of ocean dumping on a'C]*'C ratios
6x x
References Charnell, R. L. x975 Assessment of offshore dumping; technical background: Physical Oceanography, Geological Oceanography, Chemical Oceanography. National Oceanic and Atmospheric Administration (NOAA) Technical ]~Iemorandum I, Environmental Research Laboratories (ERL), l~,iarine Ecosystems Analysis Program (MESA), Boulder, Colorado, 83 pp. Craig, H. x957 Isotopic standards for carbon and oxygen and correction factors for mass-spectrometrlc analysis of carbon dioxide. Geochlmica et Cosmochimica Acta x2~ x33-x49. Duedall, I. W., O'Connors, H. B. & Irwin, B. x975 Fate of waste-water sludge in the New York Bight Apex. Journal of the Water Pollution Control Federation 47, 2702-27 ~ Gross, M. G. x972 Geologic aspects of waste solids and marine waste deposits, New York metropolitan region. Geological Society of America Bulletb, 83, 3t63-3x76. Hatcher, P. G. & McGillivary, P. A. x979 Sewage contamination in the New York Bight. Coprostanol a s an indicator. Environmental Science and Technology I3~ x225-x229. Hunt, J. M. x968 The significance of carbon isotope variations in marine sediments. In Carbon in Biochemistry (Hobson, G. D., ed.). Pergamon Press. pp. 27-35. l~Ieade, R. It. x969 Landward transport of bottom sediments in estuaries of the Atlantic Coastal Plain. ffournal of Sedimentary Petrology 39, 222-234. Newman, J. W., Parker, P. L. & Behren, E. x,V. x973 Organic carbon isotope ratios in Quaternary cores from the Gulf of Mexico. Geochbnlca et Cosmochimica Acta 37, 225-238. Pararas-Carayannis, G. x973 Ocean dumping in the New York Bight; An assessment of environmental studies. Tedmical 3Iemorandum No. 39, Coast Engineering Research Center, U.S. Army Corps of Engineers. Saekett, W. M. & Thompson, R. R. x963 Isotopic organle carbon composition of recent continental 9 derived elastic sediments of eastern Gulf Coast, Gulf of Mexico. Bulletin of the American Assoclatlon of Petroleum Geologists 47, 525-53 x. Simpson, H. J., Peng, "P. H., Olsen, C. R. & Williams, S. C. x98o The radiocarbon chronology of Hudson River estuary sediment. Unpublished manuscript. Shultz, D. J. & Calder, J. A. x976 Organic carbon asC/X~C variations in estuarine sediments. Geochlmlca et Cosmochlmica Acta 4o~ 38x-385. Stubblefield, W. L., Permenter, R. W. & Swift, D. J. P. x977 Time and space variation in the surficlal sediments of the New York Bight Apex. Estuarine and Coastal 3larine Science 5, 597--607. Williams, S. C., Simpson, H. J., Olsen, C. R. & Bopp, R. F. x978 Sources of heavy metals in sediments of the Hudson River Estuary. Marine Chemistry 6, x95-2t3.
Effect of Ocean Dumping on 3C/'2C Ratios in Marine Sediments from the New York Bight
William C. Burnett Department of Oceanography, The Florida State University, Tallahassee, Florida 323o6, U.S.A.
and Oliver A. Schaeffer Department of Earth and Space Sciences, State University of New York, Stony Brook, Nezo York H794, U.S.A. Received 3J August z979 and in revised form e8 dYanuary x98o
Keywords: carbon; isotope ratlos; sewage disposal; dumping; sediments; New York Bight In order to evaluate the influence of the ocean dumping of sewage sludge upon the organic carbon fraction of sediments of the New York Bight, a study of carbon isotopic variations in surface sediments from the area has been completed. On the basis of our a3C/I:C measurements, it appears that: (x) sewage is depleted in 13C as compared to average marine organic sedimentary carbon, and (2) ~l~C values from sediments of the New York Bight show systematic variations which are a direct consequence of the sludge disposal. Based on assumptions regarding inputs of sedimentary carbon to the sea floor in this area, we have modeled these ~sCp2C variations in terms of progressive dilution of normal marine carbon with carbon derived from the ocean dumping of wastewater sludges. The isotopic composition of carbon in sediments from the New York Bight may serve as a quantitative tracer of sewage sludge components.
Introduction The Apex of the New York Bight has been a repository for man's wastes for many years. Gross (I972) has discussed the history of waste disposal in the New York metropolitan region and mentions regulations governing these activities dating back to x684. NIaterial currently being dumped in this area include dredge spoils, construction and demolition rubble, waste chemicals, and sewage sludge. Approximately 76% of all solids discharged into the New York Bight between i964 and x968 consisted of dredged wastes, while only 4"3% was derived from sewage sludge (Gross, x972 ). Although the bulk weight of sludge is low relative to other materials, the volume being dumped is tremendous. PararasCarayannis (I973) estimates, for example, that approximately 3.2• xo6 m 3 of sludge were dumped annually into the New York Bight during the period ]965-I97o. "/'he purpose of this paper is to assess the possibility of using variations in the isotopic composition of carbon as a quantitative index of sewage contamination in the sediments from the dump site area. It is hoped that these data will complement and extend the results of workers who 6o5 o3o2-3524/8o/z 20605 + 07 $o2.oo[o
9 z080 Academic Pre.q-qInt'_ tl ar~ndnnX I .tA
606
W. C, Burnett & O. A. Schaeffer
have investigated other parameters (heavy metals, radionuclides, fecal steroids, etc9 in terms of delineating man's impact on this portion of the continental shelf (Charnell, i975; Williams et al., I978; Hatcher & McGillivary, i979). For this investigation, we analysed x8 surficial samples from the New York Bight Apex (Figure ,) and one core sampled at closely-spaced intervals from the Hudson Shelf Valley9 All the surface sediment samples are in the vicinity of the sewage sludge dump site located approximately 24 km from the entrance to New York Harbor. Our intention in analysing these samples is to make an evaluation of whether stable carbon isotope data is useful for assessing such factors as distribution, transport paths and ultimate sites of deposition of carbon-bearing pollutants in the New York Bight. Our core from the Hudson Shelf Valley ~s about 60 km south-east of the disposal area, and will be used as a control for baseline values. In order to isotopically characterize the carbon being derived by ocean dumping, wastewater sludges were collected directly from the holding tanks of two of New York's largest sewage treatment plants (Newtown Creek and Ward's Island). The tanks from which our samples were collected are the same tanks from which sewage barges load their holds for disposal at sea. The composition of these sludges has been described by Duedall et al, 0975). M a t e r i a l s and m e t h o d s Grab samples from 15 stations in the New York Bight Apex were obtained in late March, I976 by the Sandy Hook Marine Laboratory (Highlands, New Jersey). All samples were
~ NEW YORK HARBOR
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Figure x. Index map of New York Bight Apex showing locations of surficial sediment samples used in this study. Symbol ' @' designates the sewage sludge dump site centered at 4o~ 73~ since x924. The solid contour represents t'o% organic carbon in dried sediments (redrawn from Charnell, *975). Lines A-A' and B-B' represent the data profiles shown in Figure 2.
Effect of ocean dumping on 1~C/~2C ratios
607
frozen within a few hours after recover), to prevent bacterial degradation of the organic fraction. Prior to analysis, samples were dried at less than xoo ~ for a few days and then digested in warm 2 ~ HCI to destroy any carbonates. The samples were then repeatedly washed with distilled water to remove the acid. After a final drying, the samples were combusted in a quartz tube in a stream of pure oxygen at approximately 90o ~ The evolved gases from this combustion were then passed through cupric oxide maintained at 50o ~ to ensure complete oxidation of all the carbon. The gases were then passed through a series of chemical scrubbers (silver nitrate, potassium permanganate, and potassium dichromate combined with sulfuric acid) to remove halogens, oxides of sulfur and nitrogen, and water. The resulting CO 2 was condensed into cold traps maintained at liquid nitrogen temperature. After passing the gas over dry ice several times for further drying, an aliquot of the gas was taken for mass spectrometric analysis. Isotope ratios were measured on a Nuclide isotope ratio mass spectrometer at the LamontDoherty Geological Observatory. Results are expressed as ~oo deviations (613C) from the carbon isotope ratio of PDB (Chicago standard). Our values have been corrected for instrumental effects and for differences in the 170 content of the samples relative to the standard (Craig, x957). Replicate samples had isotope mass ratios which agreed to within q-o.25~oo. Results and discussion Sediment samples from the Bight Apex vary considerably in color, texture and organic content. Sediments in proximity to the sewage dump site are dark muddy silts with high contents of organics and water. Stations closer to shore are tan, light-colored, very coarse sands with an extremely low organic content. A more detailed description of the surficial sediments of the New York Bight area may be found in Stubblefield et aL (I977). Optical and X-ray studies of core HSV 53 have shown that silt to fine-sand sized quartz, feldspar and accessory minerals are the major inorganic components. There were no apparent systematic variations in the relative amounts of the inorganic phases as a function of depth in this core. It was found, however, that siliceous skeletal materials (diatom frustules, sponge spicules, etc.) increased greatly in the upper few centimeters of the core. Results of our isotopic measurements, as well as water and organic carbon contents, are presented in Table I. The most interesting aspect of our data concerns the aerial distribution of :3C/12C ratios in the surficial sediments of the Bight Apex. Two profiles (Figure 2) of ~13C across the sewage sludge disposal area show that the carbon isotopic composition becomes significantly lighter, i.e. more depleted in 13C, as the dump site is approached. Sediments from stations further from the disposal area progressively approach a more 'normal' ~13C value for continental shelf sediments of approximately --2Z~oo relative to PDB. What results, then, is a unique ~513C pattern with values becoming more negative in a seaward direction, reaching a minimum, and then reversing its trend by becoming less negative seaward of the sewage disposal area. Further verification that this pattern results from the input of wastewater sludge is provided by direct stable isotopic analyses of sludge samples from the Newtown Creek and Ward's Island treatment plants (Table x). The sludges collected from these two plants were determined to have ~513Cvalues of --25. 7 and --26"o~oo respectively. These values agree very closely with those measured from the stations immediately adjacent to the disposal site (Stations 3 z and 33). Systematic variations in the isotopic composition of carbon from sediments have been described before for continental shelf environments. Sackett & Thompson (I963) , for example, showed that ~ C values became less negative when proceeding from river through
IV. C. Burnett& O. A. Schaeffer
608
"I'^nLE x. Analytical data on surficial sediment samples from the New York Bight. The designations G-I and G-2 refer to two separate lowerings of the grab sampler at the same station. Values for HSV 53 are averages and ranges of I3 determinations down the 62 cm length of the core. The core was sampled in x973 at 4o~ 73~ in 68 m water depth. All other samples recovered in March x976 Station no.
Depth (m)
HtO (%)
Cot= (%)
9"7 x7"7 8"2 9"1 26-2 24"4 32"6 33"5 33"5 27"4 27"4 3"0 20"7 24"4 36"6 45"7 45"7 x8"3
x9 20 x7 x6 34 24 40 48 54 58 ~ 22 x8 z6 4x 32 49 15
o'x7 o.xo 0"07 0.02 x'x9 0"5 t 2"33 X'68 2"79 2"87 o'72 0"08 o.x6 o'o2 !.8o x.x6 2"09 0"08 27"x 4t'I o'5z (o'3I to 0"76)
x x2
x6 t9 23 32 33 34 G---X 34 G--2 35 G--x 35 G--2 40 42 43 45 56 G--x 56 G--2 64 Newtown Creek Ward's Island Core H S V 53
--
--
-68
~ 34 (29 to 39)
lsC/l=C,,mp,= a (~13C~oo
F, --
-270
'
'
'
=
13C/l'~C
__x.ioS
PDB
~sC= (%0) -
F', t'
-
-
--22-x --22-0 --22-8 --24"0 ~25"8 --26"2 --25"3 --25"2 --24"7
-
o o 20 50 95 ZOO 80 80 70
--
--
--21"6 --23"0 --24"I --24"3 --23"9 "--23"9 --24"2 --25"7 --26"0 --22"x (--21"4 to --22-8)
o 25 50 60 5~ 50 55 --
-o
]
6t~C--51:Cm X Ioo = per cent sewage sludge contained within organic 51aC __5~aC= fraction of sediment. See explanation in text.
'
'
'Dump site
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Figure 2. Data profiles over the New York Bight Apex showing variations of 613C as a function of location. The symbol ' ( ~ ' gives the mean 5t3C value determined in sludge samples from two of New York City's largest treatment plants. The symbol is shown at the center of the designated ocean disposal area. Vertical bars indicate analytical precision based on replicate determinations. (a) Profile A-A" showing 5~3C variations in an east-west profile through the New York Bight Apex. (b) Profile B - B ' showing 6t3C variations in a north-south profile.
Effect of ocean dumping on xsC]ltC ratios
609
lagoonal to open marine environments in the Gulf of Mexico. They attributed this systematic variation to a mixing of land and marine plant derived organic materials which differ in isotopic composition. Newman et al. (i973) studied stable carbon isotopes in cores of Quaternary sediment from the Gulf of Mexico and concluded that the major parameter affecting the 513C values of organic carbon from marine sediments is the relative amount of terrestrial material present in the sediment. Hunt (I968) suggests that on the shelf of the Atlantic coast the major contribution to organic carbon is from marine organic matter resulting in 513C values more typical of deep sea sediments. Terrestrial organic matter is dominant in river sediments only to the mouth of narrow rivers in this region. If 5aaC values of organic carbon in continental shelf sediments are assumed to be a function of mixing of varying amounts of terrestrial and marine organic carbon, then an isotopic mixing equation can be formulated to calculate the relative amounts of each type of carbon contained in the samples, l'~ewman et aL (x973) and Shultz & Calder (I976) used this approach for estimating the extent of the influx of terrestrial carbon into Gulf of ]Vle.xico sediments. It is necessary to assume or have measured the values for the two end members in the mixing equation, i.e. ~taC in marine and terrestrial carbon from the region under study. We can use the same approach here for estimating what the approximate contribution of the sludge component is to the organic carbon content of each of our surficial sediment samples. The appropriate equation would be as follows:
F s ~---
5~C--513C~ 513C,--513C=
X I00
where F. = per cent sewage sludge, 51sC = 513C of organic carbon in sample, 613C., = 81~C of normal continental shelf marine carbon in this region (--22~oo), 5x3C, = ~ia3C of sewage sludge (--26~oo). The 51~C, value comes directly from our measurements of wastewater sludge (average of two measurements=--25.8~oo) while 5a3C,, will be estimated by using the mean value --2a'o~oo for our core from the Hudson Shelf Valley (HSV 53). As mentioned earlier, this core is believed to be far enough out on the shelf that it has not been affected by waste disposal or other forms of pollution. The relatively constant values of 51~C down the length of the core (zz.x+o.4~oo) indicates that this is probably a fairly good assumption. Our estimate also agrees well with measurements reported by Hunt (1968) for 513C values on the Atlantic sheff near Nantucket and off Delaware. g~[ost of his values are close to --2X~oo, even near the mouths of large estuaries. Our estimates for the percentages of sludge particles contained within the total organic content of our sediment samples are given in Table x. Because of the uncertainties involved, we have reported all values to the nearest 5%. Although we don't claim that the absolute magnitudes of these values are well known, we do feel that the dominent trend in the data is a direct result of the input of isotopicaUy lighter carbon by sludge dumping. Although our per cent contamination values are somewhat higher, the pattern is essentially the same as that reported by Hatcher & McGillivary (x979) who used a fecal steroid as an indicator. It might be argued that our values have little meaning because we have neglected the input of normal terrestrial organic carbon onto the shelf in this region. The input of terrigenous material to the New York Bight is probably small 0Heade, x969) , however, and
6to
IV. C. Burnett ~ O. A. Schaeffer
should not greatly affect our results. It should also be pointed out that the organic fraction of the sediments in the lower reaches of the Hudson are also contaminated with sludge particles (Simpson et al., x98o). Any addition, then, of riverborne particles will also contribute sludge carbon. Actually, the mixing that we are describing is a mixture of terrestrial organic carbon (in the form of wastewater sludge) with the marine carbon produced by productivity. The main feature of our data which makes it unique is that we have observed a pattern developed in the sediments of the Bight Apex which owes its origin completely to man's impact. The only stations which apparently have not been affected by sewage disposal are Stations x2, x6 and 4 o, all of which are in nearshore shallow locations. As expected, the stations displaying the greatest input of sewage are those located immediately adjacent to the disposal site (Stations 3z and 33). One unanticipated result is the relatively high sludge component found at Station 64, the furthest south of our stations. Because of the distinctive pattern of 13C/12C ratios developed in the sediments of the New York Bight as a result of sludge disposal, we feel that more detailed 61~C surveys would greatly assist in the delineation of transport paths and ultimate sites of deposition of sludge after its disposal at sea. Other parameters which have been mentioned as possible tracers for sewage sludge in the marine environment include heavy metals, total organic carbon, the ratio of carbohydrates to total organic carbon (Charnell, x975) and fecal steroids (Hatcher & McGillivary, x979). Although high concentrations of some metals and organic carbon are characteristic of wastewater sludge, their presence in high levels in marine sediments does not necessarily indicate that sludge components are present. High trace elements and organic carbon contents have been reported as occurring in marine sediments from many areas where sewage sludge is not a contaminant. Although more promising, the carbohydrate content normalized to total organic carbon may still lead to some ambiguity in interpretation. Tlae fact that this ratio will change as the result of progressive degradation of the organics (with the carbohydrates persisting longer) makes its use limited to qualitative assessments. The concentration of the fecal steroid coprostanol, normalized to total steroids, can be used in a quantitative sense to determine amounts of sewage-derived materials according to the recent work of Hatcher & iV/cGillivary (I979). Their results from the New York Bight showed basically the same pattern as reported here with maximum values of sewage sludge occurring in the Christiaensen Basin at the mouth of the Hudson Shelf Valley. We feel that our 13C/12C measurements have great potential as quantitative tracers for sludge components in the coastal marine environment. This should prove to be extremely valuable in assessing the extent of environmental impact of ocean dumping of wastewater sludges.
Acknowledgements Thanks are extended to J. Pierce and L. Rogers (Sandy Hook Marine Laboratory) for providing us with the surficial sediment samples. Our core from the Hudson Shelf Valley was sampled by the Atlantic Oceanographic and Meteorological Laboratories of the National Oceanic and Atmospheric Administration (AOML/NOAA). L. ~,filler and J. Lawrence assisted in the use of the Nuclide mass spectrometer which was made available at LamontDoherty Geological Observatory. H. Noels assisted in the chemical preparation laboratory. Financial support for this study was provided by grant o462244oi 3 from the National Oceanographic and Atmospheric Agency (Marine Ecosystems Analysis Program--New I York Bight Project).
Effect of ocean dumping on a'C]*'C ratios
6x x
References Charnell, R. L. x975 Assessment of offshore dumping; technical background: Physical Oceanography, Geological Oceanography, Chemical Oceanography. National Oceanic and Atmospheric Administration (NOAA) Technical ]~Iemorandum I, Environmental Research Laboratories (ERL), l~,iarine Ecosystems Analysis Program (MESA), Boulder, Colorado, 83 pp. Craig, H. x957 Isotopic standards for carbon and oxygen and correction factors for mass-spectrometrlc analysis of carbon dioxide. Geochlmica et Cosmochimica Acta x2~ x33-x49. Duedall, I. W., O'Connors, H. B. & Irwin, B. x975 Fate of waste-water sludge in the New York Bight Apex. Journal of the Water Pollution Control Federation 47, 2702-27 ~ Gross, M. G. x972 Geologic aspects of waste solids and marine waste deposits, New York metropolitan region. Geological Society of America Bulletb, 83, 3t63-3x76. Hatcher, P. G. & McGillivary, P. A. x979 Sewage contamination in the New York Bight. Coprostanol a s an indicator. Environmental Science and Technology I3~ x225-x229. Hunt, J. M. x968 The significance of carbon isotope variations in marine sediments. In Carbon in Biochemistry (Hobson, G. D., ed.). Pergamon Press. pp. 27-35. l~Ieade, R. It. x969 Landward transport of bottom sediments in estuaries of the Atlantic Coastal Plain. ffournal of Sedimentary Petrology 39, 222-234. Newman, J. W., Parker, P. L. & Behren, E. x,V. x973 Organic carbon isotope ratios in Quaternary cores from the Gulf of Mexico. Geochbnlca et Cosmochimica Acta 37, 225-238. Pararas-Carayannis, G. x973 Ocean dumping in the New York Bight; An assessment of environmental studies. Tedmical 3Iemorandum No. 39, Coast Engineering Research Center, U.S. Army Corps of Engineers. Saekett, W. M. & Thompson, R. R. x963 Isotopic organle carbon composition of recent continental 9 derived elastic sediments of eastern Gulf Coast, Gulf of Mexico. Bulletin of the American Assoclatlon of Petroleum Geologists 47, 525-53 x. Simpson, H. J., Peng, "P. H., Olsen, C. R. & Williams, S. C. x98o The radiocarbon chronology of Hudson River estuary sediment. Unpublished manuscript. Shultz, D. J. & Calder, J. A. x976 Organic carbon asC/X~C variations in estuarine sediments. Geochlmlca et Cosmochlmica Acta 4o~ 38x-385. Stubblefield, W. L., Permenter, R. W. & Swift, D. J. P. x977 Time and space variation in the surficlal sediments of the New York Bight Apex. Estuarine and Coastal 3larine Science 5, 597--607. Williams, S. C., Simpson, H. J., Olsen, C. R. & Bopp, R. F. x978 Sources of heavy metals in sediments of the Hudson River Estuary. Marine Chemistry 6, x95-2t3.