Sediment-water oxygen and nutrient exchanges along a depth gradient in the Baltic Sea

Abstract

Bottom water and sediment characteristics and net sediment-water fluxes of oxygen, nitrogen, phosphorus and hydrogen sulphide were measured under oxic and experimentally induced anoxic conditions along a depth gradient (47 to 130 m) during summer in the Baltic proper. Sediment organic content was much higher in sediments located beneath the permanent pycnocline (ca 65 m). Sediments at all stations were somewhat depleted in total N relative to total C (C:N approximately equals 10). Sediments at the shallow station (47 m) were highly enriched with total P relative to C or N (C:N:P approximately equals 18:2:1) but were somewhat depleted in P at the deeper stations (C:N:P approximately equals 120:12:1). Under oxic conditions oxygen fluxes ranged from 214 to 777 mu mol O/m super(2)/h and decreased with depth. Phosphorus and nitrite fluxes were always very small and were directed either into or out of the sediments. Ammonium fluxes were small (1 to 30 mu mol N/m super(2)/h) at all stations and did not exhibit a clear pattern with depth.