Carbon and nitrogen cycling in intertidal mud flat sediments in the Scheldt Estuary was studied using measurements of carbon dioxide, methane and nitrous oxide emission rates and pore- water profiles of Sigma CO2, ammonium and nitrate. A comparison between chamber measured carbon dioxide fluxes and those based on Sigma CO2 pore-water gradients using Fick's First law indicates that apparent diffusion coefficients are 2 to 28 times higher than bulk sediment diffusion coefficients based on molecular diffusion. Seasonal changes in gaseous carbon fluxes or Sigma CO2 pore water concentrations cannot be used directly, or in a simple way, to determine seasonal rates of mineralization, because of marked seasonal changes in pore- water storage and exchange parameters. The annual amount of carbon delivered to the sediment is 42 mol m(-2), of which about 42% becomes buried, the remaining being emitted as methane (7%) or carbon dioxide (50%). Each year about 2.6 mol N m(-2) of particulate nitrogen reaches the sediment; 1.1 mol m(- 2) is buried and 1.6 mol m(-2) is mineralized to ammonium. Only 0.42 mol m(-2) yr(-1) of the ammonium produced escapes from the sediments, the remaining being first nitrified (1.2 mol m(-2) yr(-1)) and then denitrified (1.7 mol m(-2) yr(-1)). Simple calculations indicate that intertidal sediments may account for about 14% and 30% of the total estuarine retention of nitrogen and carbon, respectively. [KEYWORDS: Carbon cycling; nitrogen cycling; estuarine sediments; methane; nitrous oxide; mineralization; carbon dioxide Coastal marine basin; organic-carbon; disturbed sediments; water interface; kinetic-models; diffusion; methane; sulfur; bay; diagenesis]
Original languageEnglish
Journal publication date1995

ID: 372889