FIG. 2.

Anaerobic ammonium oxidation coupled to nitrate reduction in anoxic marine sediments amended with ¹⁵N-ammonium and unlabeled nitrate (filled symbols), compared to controls with ¹⁵N-ammonium only (open symbols), from Skagerrak station S6 (A) and Aarhus Bay (B). Time courses of the combined concentrations of nitrate and nitrite (squares, right axis), ¹⁵N-ammonium (circles, left axis, Skagerrak S6 only), and ¹⁵N in N₂ (triangles, left axis). Nitrate and nitrite concentrations are only shown for nitrate-amended incubations. In incubations without nitrate addition, endogenous nitrate and nitrite were depleted at the first sampling time. Examples are from 1- to 4-cm and 0.8- to 1.3-cm depths at Skagerrak S6 and Aarhus Bay, respectively. Results in panel A are representative of three experiments, and the error bars in panel B represent the standard deviations of three parallel incubations.