ORGANIC-N LOSS BY EFFLUX AND BURIAL ASSOCIATED WITH A LOW EFFLUX OF INORGANIC N AND WITH NITRATE ASSIMILATION IN ARCTIC SEDIMENTS (SVALBARD, NORWAY)

Sediments were sampled at water depths from 170 to 2577 m at 17 statio ns adjacent to Svalbard. In general, with increasing water depth there was decreasing NH4+ with increasing NO3- in the sediment pore water, increasing depth of O-2 penetration, decreasing NH4+- and increasing N O3--efflux rates, decreasing nitrification and denitrification rates, and decreasing rates of organic nitrogen burial. Most sediments had in significant rates of nitrogen mineralisation (0 to 0.34 mmol m(-2) d(- 1)); there was a very high C:N ratio (mean 68) in the measured efflux products. Efflux and consumption rates of NO3-, calculated from pore w ater profiles, were generally higher than the measured rates, but thes e calculated rates also predicted high C:N mineralisation ratios. The high ratios demanded that the particulate organic substrate must also have had a low nitrogen content. The high measured efflux of dissolved organic nitrogen (mean 0.93 mmol m(-2) d(-1)) from the sediment sugge sted that fresh detritus (C:N 13) might reach the sediment surface, an d be hydrolysed with efflux loss of dissolved nitrogen-rich organic ma tter (e.g. C:N 6) and with subsequent mineralisation (C:N similar to 6 8) or burial (C:N similar to 10) of the transformed material. High C:N ratios in the products of sediment mineralisation are commonly report ed, indicating the prevalence of preferential nitrogen loss from detri tus in the water column and probably also at the sediment-water interf ace. The retention of nitrogen by the sediment can explain the discrep ancy between measured and calculated NO3- fluxes: NO3- did not escape from the sediment to the water because it was assimilated by bacteria utilising high C:N substrate. It is likely that some NO3- which diffus ed downward was also assimilated rather than denitrified. Many of thes e sediments had a sub-surface zone of NH4+ production associated with nitrification. Above and below this zone of net production were zones of NH4+ and NO3- disappearance.