Abstract
The C/N and stable C and N isotope ratios (delta(13)C, delta(15)N) of sedimentary and suspended particulate matter were determined in the Schelde Estuary. Suspended matter was divided into 2 to 5 size fractions by centrifugation. Four major pools of organic matter were recognized: riverine, estuarine, marine and terrestrial materials. Terrestrial organic matter (delta(13)C approximate to -26%, delta(15)N approximate to 3.5%, C/N approximate to 21) is important for the sedimentary pool, but suspended matter is dominated by the marine (delta(13)C approximate to -18%, delta(15)N approximate to 9%, C/N approximate to 8), riverine (delta(13)C approximate to -30%, delta(15)N approximate to 9%, C/N approximate to 7.5) and estuarine (delta(13)C approximate to -29%, delta(15)N approximate to 15%, C/N approximate to 8) end-members. In the upper estuary, the suspended matter size fractions vary systematically in their carbon and nitrogen biogeochemistry, with the small particles having low C/N ratios, depleted delta(13)C and enriched delta(15)N values relative to large particles. Moreover, sedimentary and suspended matter differ significantly in terms of C/N ratios (17 vs. 8.9), delta(13)C (-26.3 vs. -28.9%) and delta(15)N (+ 6.9 vs. 12.0%). In the lower estuary, suspended matter fractions are similar and sedimentary and suspended organic matter differ only in terms of delta(13)C (-23.5 vs. -20.1%). Our data indicate that autochthonous organic matter contributes significantly to the total suspended matter and that the suspended organic matter composition cannot be explained in terms of conservative mixing of riverine and terrestrial sources on the one hand and marine sources on the other hand. [KEYWORDS: Scheldt River; suspended materials; estuaries; stable isotopes; carbon; nitrogen Ecosystem model moses; organic-matter; westerschelde estuary; natural abundance; tidal estuaries; sw netherlands; n-15; river; indicator; fluxes]
Published Version
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