Black Carbon in Estuarine and Coastal Ocean Dissolved Organic Matter

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  • Black Carbon in Estuarine and Coastal Ocean Dissolved Organic MatterAuthor(s): Antonio Mannino and H. Rodger HarveySource: Limnology and Oceanography, Vol. 49, No. 3 (May, 2004), pp. 735-740Published by: American Society of Limnology and OceanographyStable URL: http://www.jstor.org/stable/3597790 .Accessed: 14/06/2014 13:06

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  • Limnol. Oceanogr., 49(3), 2004, 735-740 ? 2004, by the American Society of Limnology and Oceanography, Inc.

    Black carbon in estuarine and coastal ocean dissolved organic matter

    Antonio Mannino1 and H. Rodger Harvey Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, P.O. Box 38, Solomons, Maryland 20688

    Abstract We measured black carbon (BC) in ultrafiltered, high-molecular weight dissolved organic matter (UDOM) in

    surface waters of Delaware Bay, Chesapeake Bay, and the adjacent Atlantic Ocean (U.S.A.) to investigate the importance of riverine and estuarine dissolved organic matter (DOM) as a source of BC to the ocean. BC was 5- 72% of UDOM-C (27 ? 17%), which corresponds to 8.9 ? 6.5% of dissolved organic carbon (DOC), with higher values in the heavily urbanized midbay region of the Delaware Estuary and lower yields in the river and coastal ocean. The spatial and seasonal distributions of BC along the salinity gradient of Delaware Bay suggest that the elevated levels of BC in surface water UDOM originate from localized sources, possibly from atmospheric depo- sition or release from resuspended sediments. BC in UDOM made up 4-7% of the DOC in the coastal Atlantic Ocean, revealing that river-estuary systems are important exporters of colloidal BC to the ocean. The annual flux of BC from Delaware Bay UDOM to the Atlantic Ocean was estimated at 2.4 X 1010 g BC yr-~, supporting the

    hypothesis that the DOC pool is an important contributor of BC to the ocean.

    Dissolved organic matter (DOM) in the ocean constitutes one of the largest pools of organic carbon in the biosphere, yet much of its composition remains uncharacterized. In coastal waters, inputs of marine, terrestrial, and anthropo- genic organic matter contribute to the complexity of DOM composition. Observations of black carbon (BC) particles in the atmosphere, ice, rivers, soils, and marine sediments sug- gest that this material is ubiquitous in the environment (Goldberg 1985; Schmidt and Noack 2000; Masiello and Druffel 2001; Mitra et al. 2002). The contribution of BC to the ocean's DOM pool, however, is not known.

    BC represents a refractory and chemically complex prod- uct of incomplete combustion of fossil fuels and biomass, including vegetation burns and forest fires. BC is defined as a "continuum of partly charred plant material through char and charcoal to graphite and soot particles recondensed from the gas phase" (Seiler and Crutzen 1980, p. 207). Multiple mechanisms introduce BC to the ocean, including atmo- spheric deposition of land-derived BC aerosols, material transported by river-estuary systems, and marine diesel en- gine exhaust. Although most BC is deposited near the site of production, long-range transport of BC through rivers and the atmosphere is also possible (Goldberg 1985). BC accu- mulates in sediments, making up 10-50% of sedimentary organic carbon (Gustafsson et al. 1997; Middelburg et al. 1999) and is much older (2,400-13,900 yr older) than non-

    To whom correspondence should be addressed. Present address: NASA Goddard Space Flight Center, Laboratory for Hydrospheric Processes, Mail Stop 971.1, Greenbelt, Maryland 20771 (anto- nio.mannino@nasa.gov).

    Acknowledgments We thank two anonymous reviewers and Elizabeth Canuel for

    their constructive comments and Mike Behrenfeld for critiquing an earlier draft of this manuscript. This work was supported by the Chemical Oceanography Program of the National Science Foun- dation and National Oceanic and Atmospheric Association through the ECOHAB program. A.M. acknowledges support from the USGS Mendenhall Postdoctoral Program and NASA. Contribution 3716, University of Maryland Center for Environmental Science.

    BC material in deep ocean settings (Masiello and Druffel 1998). The radiocarbon age differences between sedimentary BC and other sedimentary organic matter present an unre- solved issue on whether the BC that ultimately resides in marine sediments ages primarily within the oceanic dis- solved organic carbon (DOC) pool or in soils (Masiello and Druffel 1998).

    In an effort to understand the importance of riverine and estuarine DOM as a source of BC to the ocean, the BC component of ultrafiltered, high-molecular weight DOM (UDOM) was measured in surface waters of the Delaware Estuary and Chesapeake Bay (mid-Atlantic, U.S.A.). We present evidence that BC comprises a significant fraction of marine DOM, accounting for a substantial fraction of DOC that has previously remained elusive to chemical character- ization.

    Methods

    Study sites-The Delaware Estuary is a highly urbanized coastal plain estuary, extending 215 km from the mouth of the bay to Trenton, New Jersey, the upstream limit of tidal influence (Fig. 1). Freshwater entering the estuary, with a mean annual discharge of 550 m3 s-1, originates largely from the Delaware (-58%; 320 m3 s-1) and Schuylkill (-14%; 78 m3 s-1) rivers, with minor contributions from other in- dividual sources (Lebo and Sharp 1993). Chesapeake Bay, also a coastal plain estuary, discharges more freshwater (mean annual discharge of 2,280 m3 s-l; Schubel and Prit- chard 1986) than any other river-estuary system along the U.S. Atlantic coast. The Susquehanna River, which flows into the head of Chesapeake Bay, contributes about half of the total freshwater discharge within the estuary.

    Sampling and analyses-Size-fractionated DOM was col- lected at five to seven sites (1 m depth) along the salinity gradient from the Delaware River to the coastal Atlantic Ocean in June 1996, September 1996, March 1997, and May-June 1997 (Fig. 1; Table 1; Mannino and Harvey 2000;

    735

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  • Mannino and Harvey

    Fig cludin

    -780 -770 -760 -750 -740 -730 Harvey and Mannino 2001). Single samples were collected Delaware trenton from the headwaters of Chesapeake Bay and beyond the

    1o- PA Philadelphia iver 200km Chesapeake Bay mouth in May-June 1997 (Table 1). DOM

    Schuylkill River 4? . . - 40?

    Susquehanna Wilmington y from filtered water (99% for the S10N1 filter (Mannino and Har-

    Longitude vey 2000). The three DOC size fractions accounted for 83- 111 % of total DOC, which compares well with previous re- . 1. Map of the Delaware Estuary and Chesapeake Bay, in- sults using similar instrumentation and procedures (Guo and

    ig station locations and designation of urban areas (triangles). Santschi 1996; Benner et al. 1997). BC was measured only in the 1-30-kDa fraction (UDOM), which constitutes, on average, 35 + 15% of DOC (Harvey and Mannino 2001). The 30-kDa to 0.2-,am fraction typically accounted for only 1-3% of DOC.

    Table 1. Sampling locations, salinity, and ultrafiltered high-molecular-weight dissolved organic matter (UDOM; 1-30 kDa DOM) carbon concentrations in Delaware Bay, Chesapeake Bay (CB), and adjacent coastal ocean.

    Date

    06Jun96 07Jun96 07Jun96 09Jun96 08Jun96 08Jun96 08Jun96 04Sep96 04Sep96 05Sep96 05Sep96 05Sep96 14Mar97 14Mar97 15Mar97 15Mar97 15Mar97 29May97 31May97 01Jun97 03Jun97 10Jun97 10Jun97 11Jun97 11Jun97 12Jun97

    Latitude

    40?7.67'N 39?37.0'N 39022.0'N 39012.75'N 39?5.46'N 38041.61'N 38024.01'N 40?7.67'N 39037.0'N 39?22.0'N 3905.46'N 38046.77'N 4007.67'N 39?37.0'N 39?12.62'N 39?5.46'N 38?55.0'N 38?48.47'N 36?51.97'N 38?23.44'N 39?25.01 'N 39?4.685'N 38?23.97'N 4007.73'N 39037.24'N 39021.86'N

    Longitude

    74049.33'W 75?34.84'W 75027.17'W 75?17.05'W 75?11.41'W 74054.95'W 74049.50'W 74?49.33'W 75?34.84'W 75027.17'W 75?11.41'W 74?57.62'W 74049.33'W 75?34.84'W 75?26.87'W 75011.41'W 7506.4"W 7504.84'W 75?56.95'W 74031.03'W 76?1.82'W 75?10.63'W 74049.44'W 74049.18'W 75?34.83'W 75?26.87'W

    Station

    2 16 20 22 24 P3 P1

    2 16 20 24 28

    2 16 21 24 26

    MAB-1 MAB-26 MAB-42 MAB-75

    24 P1

    2 16 20

    Distance upstream

    (km)

    197 100 66.4 45 28.4

    -16.3 -51.5 197.1 100.2 66.4 28.4

    -19.3 197.1 100.2 56.6 28.4 9.4

    -5.6 CB

    -70.4 CB 28.4

    -51.5 197.1 100.2 66.4

    Salinity

    0.11 0.67 9.07

    13.19 22.58 29.42 29.48

    0.116 2.72

    11.7 23.52 29.6

    0.070 0.181 4.44

    18.10 26.60 28.65 23.76 31.71 0.492

    21.03 31.21 0.099 1.75 9.01

    UDOM (Ijmol C L-

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