ALBERT

Notes: Abstract A sensitive method for estimating living biomass, based on a direct extraction of phospholipids, was applied to soil. The variation between replicate soil samples was generally below 10%. Recovery from soil was qualitative. Estimates of biomass from the phospholipid assay were not correlated with estimates from the chloroform fumigation-incubation method (CFIM). In non-fumigated soil a significant reduction (25–57%) of biomass, as determined from phospholipid analysis, was observed during the 10-day incubation. The concentration of phospholipids was reduced by 21–54% during the 24-h chloroform fumigation, decreasing further during the 10-day incubation. Phospholipid, carbon dioxide evolution and inorganic nitrogen were followed in a growth experiment with additions of glucose and glucose + ammonium. The conversion of phospholipids into biomass-C units is discussed in relation to the observed ratios of phospholipid to CFIM biomass-C, as well as to the ratios estimated from the growth experiment.

Notes: Abstract Processes involved in the C, N, S, and O cycles in a marine sediment were stimulated for a situation where most organic degradation occured in the top 2 mm and NO3− was not present in the overlying water. The effect of increasing organic loading was examined (degradation of C ? 7 to 107 mmol m−2 d−1). Increasing organic loading had the following results: (1) ? 50% of the dissolved organic nitrogen was lost by diffusion in all treatments; (2) the proportion of NH4++; flux increased, the proportion of nitrification increased slightly and then decreased; and (3) the proportion of NO3− of NO3− efflux.

Notes: Abstract  Pore water and solid phase distributions of C, N, P and Si in sediments of the Arctic Ocean (Svalbard area) have been investigated. Concentrations of organic carbon (Corg) in the solid phase of the sediment varied from 1.3 to 2.8% (mean 1.9%), with highest concentrations found at shallow stations south/southwest of Svalbard. Relatively low concentrations were obtained at the deeper stations north/northeast of Svalbard. Atomic carbon to nitrogen ratios in the surface sediment ranged from below 8 to above 10. For some stations, high C/N ratios together with high concentrations of Corg suggest that sedimentary organic matter is mainly of terrigenous origin and not from overall biological activity in the water column. Organic matter reactivity (defined as the total sediment oxygen consumption rate normalized to the organic carbon content of the surface sediment) correlated with water depth at all investigated stations. However, the stations could be divided into two separate groups with different reactivity characteristics, representing the two most dominant hydrographic regimes: the region west of Svalbard mainly influenced by the West Spitsbergen Current, and the area east of Svalbard where Arctic polar water set the environmental conditions. Decreasing sediment reactivity with water depth was confirmed by the partitioning between organic and inorganic carbon of the surface sediment. The ratio between organic and inorganic carbon at the sediment-water interface decreased exponentially with water depth: from indefinite values at shallow stations in the central Barents Sea, to approximately 1 at deep stations north of Svalbard. At stations east of Svalbard there was an inverse linear correlation between the organic matter reactivity (as defined above) and concentration of dissolved organic carbon (DOC) in the pore water. The more reactive the sediment, the less DOC existed in the pore water and the more total carbonate (Ct or ΣCO2) was present. This observation suggests that DOC produced in reactive sediments is easily metabolizable to CO2. Sediment accumulation rates of opaline silica ranged from 0.35 to 5.7 μmol SiO2 m-2 d-1 (mean 1.3 μmol SiO2 m-2 d-1), i.e. almost 300 times lower than rates previously reported for the Ross Sea, Antarctica. Concentrations of ammonium and nitrate in the pore water at the sediment-water interface were related to organic matter input and water depth. In shallow regions with highly reactive organic matter, a pool of ammonium was present in the pore water, while nitrate concentrations were low. In areas where less reactive organic matter was deposited at the sediment surface, the deeper zone of nitrification caused a build-up of nitrate in the pore water while ammonium was almost depleted. Nitrate penetrated from 1.8 to ≥5.8 cm into the investigated sediments. Significantly higher concentrations of “total” dissolved nitrogen (defined as the sum of NO3, NO2, NH4 and urea) in sediment pore water were found west compared to east of Svalbard. The differences in organic matter reactivity, as well as in pore water distribution patterns of “total” dissolved nitrogen between the two areas, probably reflect hydrographic factors (such as ice coverage and production/import of particulate organic material) related to the dominant water mass (Atlantic or Arctic Polar) in each of the two areas.

Notes: Abstract The distribution of nitrification potential (NP) with depth in sediment and season was investigated in a shallow sandy sediment (0.5 m water) and a deeper muddy sediment (17m water). In both sediments, nitrifying bacteria were present in the anoxic strata (oxygen penetration was 5 mm below the surface). The NP at 6–8 cm depth in the sediment was 50% and 10% of the surface NP at the sandy and muddy sediment, respectively. It is suggested that bioturbation and physical disturbance of the sediment were the most likely reasons for this distribution. The NP increased as sediment temperature decreased. This effect was less marked in the muddy sediment. It is concluded that during the summer, the numbers or specific activity of nitrifying bacteria diminished for the following reasons: There was decreased O2 penetration into the sediment and increased competition for O2 by heterotrophs; there was increased competition for NH4 + and there was inhibition by H2S. These effects counteracted the potentially higher growth rates and increased rates of NH4 + production at the elevated summer temperatures. The potential nitrification rates in the upper 1 cm, which were measured at 22°C, were converted to calculated rates at the in situ temperature (Q10=2.5) and in situ oxygen penetration. These calculated rates were shown to closely resemble the measured in situ rates of nitrification. The relationship between the in situ rates of nitrification and the nitrification potential is discussed.

Notes: Abstract Sediment cores containing different densities of Chironomus plumosus, ranging from 0 to 12 000 ind. m−2, were incubated in the laboratory, with 100 and 39% O2 saturation in the overlying water. Rates of O2 uptake, and fluxes of the various inorganic N species were measured after addition of 15NO inf3 su− to the overlying water. The animals enhanced O2 and NO inf3 su− uptake, due to irrigation. Denitrification of NO inf3 su− coming from the overlying water (Dw) and dissimilatory NO inf3 su− reduction to NH inf4 sup+ (DNRA) represented 20–30 and 4–10% of the NO inf3 su− uptake, respectively. Only 20–40% of the measured NH inf4 sup+ effluxes corresponded to DNRA, the rest was probably due to animal excretion. Nitrite production, mostly from dissimilatory NO inf3 sup− reduction, was detected at both 39 and 100% oxygen saturation. Higher rates of NO inf2 su− production at the lower oxygen concentrations, were probably due to a thinner oxic layer, compared to fully oxygenated waters. The presence of Chironomus plumosus increased nitrification rates, relative to non-inhabited microcosms. However, nitrification rates were low compared to Dw, probably due to low numbers of nitrifiers in the sediment. At 39% oxygen saturation, rates of nitrification and denitrification of NO inf3 su− generated within the sediment were not measurable.