Interstitial water chemistry of anoxic Long Island Sound sediments. 2. Nutrient regeneration and phosphate removal 1

The stoichiometry of nutrient regeneration in anoxic Long Island Sound sediments is examined through changes in the concentration of dissolved sulfate, ammonia, reactive phosphate, and other chemical species with depth in interstitial waters. In offshore sediments the mean ΔSO4:ΔNH4:Δ∑P ratio is —53:4.6:0.37; in shallow harbor sediment it is −53:19:3.3 and ΔNH4:Δ∑P ratios are half the offshore ratio. These indicated shoreward changes probably reflect more rapid deposition, and thus less preferential stripping of P and N from organic material before burial in shallow water harbor sediments, or selective stripping in the heavily bioturbated upper sediment layers offshore, or both. The effects of differential diffusion and adsorption of ammonia and phosphorus are considered. Phosphate concentration maxima in ammonia‐ and phosphate‐rich shallow harbor sediments yield evidence for possible equilibrium with respect to vivianite, Fe3(PO4)2·8H2O, and struvite, MgNH4PO4·6H2O.