Nitrogen cycling in Estuarine and Nearshore Sediments

Nitrogen (N) availability is frequently cited as the factor limiting primary production in marine systems over annual time scales (Capone and Kiene, 1988; Ryther and Dunstan, 1971; Vitousek and Howarth, 1991) though phosphorus (P), silica (Si) limitation or co-limitation by N, P, and/or Si sometimes occur on seasonal time scales (Conley et al., 1993; Malone et al., 1996; Officer and Ryther, 1980). In offshore waters, the presence of bioavailable iron can also regulate primary productivity, particularly that by diatoms (Coale et al., 1996; Hutchins and Bruland, 1998; Martin et al., 1994). Sediment N pools reflect a balance between inputs (external or internal) and outputs (sedimentation, denitrification (DNF), long-term burial, or export), and this balance is affected by a variety of environmental and physiological factors ( Joye, 2002). Within the sediment, N is cycled primarily by microbiallymediated redox reactions between more highly oxidized forms (nitrate, NO3
, or nitrite, NO2
) and more reduced forms (ammonium, NH4