Carbon fluxes in a marine trout cage farm in the Gullmar Fjord, western Sweden, were measured to investigate how much of the carbon supplied to the farm was recovered in harvest, how much was lost to the environment, and the properties and fate of this environmental loss. The measured fluxes included fish food, juveniles, harvest, fish loss (death and escape), sedimentation from the cages, and benthc release measured with diver-operated flux chambers and a gas collection unit in situ. Carbon mass balances for the farm, based on the measured fluxes (flux method), were constructed for each of 2 consecutive growing seasons. Another mass balance (accumulation method) was based on the total carbon input with food and juveniles to the farm since it was started, the removal of carbon with harvested fish and fish loss, and the recovery of carbon in the sediment originating from the farm after 7 growing seasons. Some 21 to 22 % of the total carbon input to the farm was recovered in harvest, fish loss constituted 1 to 3 %, and 75 to 78 % (or 878 to 952 kg C per tonne of fish produced) was lost to the aquatic environment. On a seasonal basis and of the carbon input to the farm, solute release from the cages (probably CO2 produced during fish respiration and excreted urea) removed 4 to 49 %, sedimentation of faeces and excess food removed 29 to 71 %, flux from the farm sediment of dissolved and gaseous carbon (total carbonate [C,], methane and dissolved organic carbon) transferred 2 to 6 O/o back to the overlying water, and 23 to 69 % was accumulated in the sediment. (Ranges of values represent inter-seasonal variability.) The long-term (7 seasons) sediment accumulation of carbon amounted to 18 'Yo of the total carbon input to the farm. Of the carbon deposited on the sediment surface 3 to 20 '/o was released back to the overlying water seasonally. C, dominated the annual benthic fluxes. Loss to the environment of dissolved carbon [the sum of solute release from the cages and benthic flux) amounted to between 6 and 55 % of the carbon input to the farm (or 9 to 71 'X of the total environmental loss) on a seasonal basis, and 5 8 % (or 76% of the total environmental loss) on a long-term basis. This study constitutes the first step in an assessment of the eutrophication caused by the fish farm.

The influence of redox potential on dissimilatory nitrate reduction to ammonium was investigated on a marine bacterium, Pseudomonas putrefaciens. Nitrate was consumed (3.1 mmol liter-'), and ammonium was produced in cultures with glucose and without sodium thioglycolate. When sodium thioglycolate was added, nitrate was consumed at a lower rate (1.1 mmol liter-'), and no significant amounts of nitrite or ammonium were produced. No growth was detected in glucose media either with or without sodium thioglycolate. When grown on tryptic soy broth, the production of nitrous oxide paralleled growth. In the same medium, but with sodium thioglycolate, nitrous oxide was first produced during growth and then consumed. Acetylene caused the nitrous oxide to accumulate. These results and the mass balance calculations for different nitrogen components indicate that P. putrefaciens has the capacity to dissimilate nitrate to ammonium as well as to dinitrogen gas and nitrous oxide (denitrification). The dissimilatory pathway to ammonium dominates except when sodium thioglycolate is added to the medium.

Nitrification and dissimilatory reduction of nitrate to ammonium were measured concomitantly with nitrogen release from marine coastal sediment samples from 2 fjord sill stations. Dissimilatory ammonium production (DAP) and nitrification were measured using core injections of "NO; and H1"CO;, respectively. DAP was detected in all segments of the cores by tracing "NH: evolved from the added "NO;. 15NH: recovery increased with increasing core depth, ranging from 1.6 to 10 % for Stn H and from 0.3 to 2.9 % for Stn L. Nitrification activity at Stn L was in the order of 10 nmol cm-3 h-' in the upper 2 cm but was not demonstrated in deeper strata. Consequently, DAP was most pronounced in the upper few centimeters although it was anticipated that more than 97 % of the nitrate produced was denitnfied. Mean fluxes of ammonlum out of the sediment were 24 and 12 pm01 m-2 h-' for Stns H and L, respectively, and corresponding nitrate fluxes were 2 and -24 pm01 m-2 h-'.The sum of ammonium and nitrate release in the individual cores did not reach the rates expected from their oxygen consumption rates, which implies that inorganic nitrogen was lost, probably due to coupled nitrification and denitrification. This estimated loss was about half of the obtained nitrification rate at Stn L. Furthermore, the estimated loss was larger in cores with a rich macrofauna and especially with high numbers of Arnphiura spp. (brittlestars). It is suggested that these animals stimulate both nitrification and dissimilatory nitrate reduction.

The relationships among surface energy, adsorbed organic matter, and attached bacterial growth were examined by measuring the degradation of adsorbed ribulose-1,5-bisphosphate carboxylase (a common algal protein) by attached bacteria ( Pseudomonas strain S9). We found that surface energy (work of adhesion of water) determined the amount and availability of adsorbed protein and, consequently, the growth of attached bacteria. Percent degradation of adsorbed ribulose-1,5-bisphosphate carboxylase decreased with increasing hydrophobicity of the surface (decreasing work of adhesion). As a result, growth rates of attached bacteria were initially higher on hydrophilic glass than on hydrophobic polyethylene. However, during long (6-h) incubations, growth rates increased with surface hydrophobicity because of increasing amounts of adsorbed protein. Together with previous studies, these results suggest that the number of attached bacteria over time will be a complex function of surface energy. Whereas both protein adsorption and bacterial attachment decrease with increasing surface energy, availability of adsorbed protein and consequently initial bacterial growth rates increase with surface energy.