Methane (CH4) emission from pig slurry is a large contributor to the climate footprint of livesto... more Methane (CH4) emission from pig slurry is a large contributor to the climate footprint of livestock production. Acidification of excreta from livestock animals with sulfuric acid, reduce CH4 emission and is practiced at many Danish farms. Possible interaction effects with other acidic agents or management practices (e.g. frequent slurry removal and residual slurry acidification) have not been fully investigated. Here we assessed the effect of pig slurry acidification with a range of organic and inorganic acids with respect to their CH4 inhibitor potential in several batch experiments (BS). After careful selection of promising CH4 inhibitors, three continuous headspace experiments (CHS) were carried out to simulate management of manure in pig houses. In BS experiments, more than <99% CH4 reduction was observed with HNO3 treatment to pH 5.5. Treatments with HNO3, H2SO4, and H3PO4 reduced CH4 production more than acetic acid and other organic acids when acidified to the same initial...
Odour emission from intensive pig production is a major source of local nuisance and sulphur-cont... more Odour emission from intensive pig production is a major source of local nuisance and sulphur-containing odorants (e.g. hydrogen sulphide and methanethiol) have been recognized as key odorants. Biological air filter has emerged as a cost-effective technique to remove odorants from ventilation air. However, low removal efficiencies for sulphurous odorants have been observed when a large volume of air has been applied with low concentrations. Recent kinetic studies on full scale biological air filters indicate that the removal of odorants is related both to mass load and air load of odorants but the dependence of sulphurous odorants on loading rates are not clear due to the very low and highly varying removal efficiencies. In the present study, two inoculated biofilter columns were applied to test the dependence of sulphurous odorants (hydrogen sulphide, methanethiol and dimethylsulfide) removal on air loading rate, mass loading rate or concentration. Specially designed commercially av...
Bioavailability and chemical composition of dissolved organic nitrogen (DON) in marine pore water... more Bioavailability and chemical composition of dissolved organic nitrogen (DON) in marine pore water were followed and related to bacterial activity in a 14-d anoxic decomposition experiment. For the experiment 0.2-m filtered pore water from a coastal marine sediment was inoculated with native sediment bacteria. The initial composition of DON was characterized by a high contribution of dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA), and urea, which together accounted for 82% of the DON pool. During the experiment, 54% of the DON was used by bacteria, indicating that DON was readily available to bacterial degradation. The consumption of DFAA and DCAA accounted for more than half of the DON consumed. The unidentified DON pool accounted for 33% of the net DON consumption, and the unidentified DON pool was fully depleted by the end of the experiment. Systematic changes in the amino acid composition occurred with time of incubation, as demonstrated by use of a principal component analysis based on the mole percent contribution of amino acids. The results indicated that amino acids of both the DFAA and the DCAA pools were useful indicators of the diagenetic state of DON. The present study presents the first direct evidence of short-term (within 14 d) changes in DFAA and DCAA of the DON pool. These changes were similar to decompositional changes in the molecular composition of amino acids observed in traditional studies of bulk sediment diagenesis.
Methane (CH 4) emission from pig slurry is a large contributor to the climate footprint of livest... more Methane (CH 4) emission from pig slurry is a large contributor to the climate footprint of livestock production. Acidification of excreta from livestock animals with sulfuric acid, reduce CH 4 emission and is practiced at many Danish farms. Possible interaction effects with other acidic agents or management practices (e.g. frequent slurry removal and residual slurry acidification) have not been fully investigated. Here we assessed the effect of pig slurry acidification with a range of organic and inorganic acids with respect to their CH 4 inhibitor potential in several batch experiments (BS). After careful selection of promising CH 4 inhibitors, three continuous headspace experiments (CHS) were carried out to simulate management of manure in pig houses. In BS experiments, more than <99% CH 4 reduction was observed with HNO 3 treatment to pH 5.5. Treatments with HNO 3 , H 2 SO 4 , and H 3 PO 4 reduced CH 4 production more than acetic acid and other organic acids when acidified to the same initial pH of 5.5. Synergistic effects were not observed when mixing inorganic and organic acids as otherwise proposed in the literature, which was attributed to the high amount of acetic acid in the slurry to start with. In the CHS experiments, HNO 3 treatment reduced CH 4 more than H 2 SO 4 , but increased nitrous oxide (N 2 O) emission, particularly when the acidification target pH was above 6, suggesting considerable denitrification activity. Due to increased N 2 O emission from HNO 3 treatments, HNO 3 reduced total CO 2-eq by 67%, whereas H 2 SO 4 reduced CO 2-eq by 91.5% compared to untreated slurry. In experiments with daily slurry addition, weekly slurry removal, and residual acidification, HNO 3 and H 2 SO 4 treatments reduced CO 2-eq by 27% and 48%, respectively (not significant). More cycles of residual acidification are recommended in future research. The study provides solid evidence that HNO 3 treatment is not suitable for reducing CO 2-eq and H 2 SO 4 should be the preferred acidic agent for slurry acidification.
The degradation of an Ulva lactuca mat (0.2 kg dw m À2) was studied in a controlled flow-through ... more The degradation of an Ulva lactuca mat (0.2 kg dw m À2) was studied in a controlled flow-through mesocosm for 31 d. Sediment chambers without U. lactuca served as controls. Fluxes of P CO 2 , O 2 , inorganic nitrogen, and urea were determined during the incubation period in addition to sulfate reduction rates, POC and PON content, enumeration of specific bacterial populations and evaluation of the physiological state of the added U. lactuca thalli. After U. lactuca addition to the chambers, there was an immediate increase in the efflux of P CO 2 from 11 to 27 mmol-C m À2 d À1 and a concomitant increase in O 2 uptake from 11 to 23 mmol m À2 d À1. These effluxes remained elevated throughout the incubation period. In contrast, the NH 4 + efflux increased from 0.1 to 1.8 mmol NH 4 + m À2 d À1 during the first 3 d of incubation, followed by 6 d with a constant efflux rate, after which time it decreased gradually to 0.3 mmol NH 4 + m À2 d À1 by the end of the experiment. In total, NH 4 + accounted for 83% of the total nitrogen efflux after addition of U. lactuca. During the 31 d incubation period there was a continuous colonization of the thalli by bacteria. Sulfate reducers associated with the thalli accounted for 3% of the carbon oxidation on day 31. The molar C:N ratio in mineralization products (the ratio between the efflux of P CO 2 and NH 4 + + NO 2 À + NO 3 À) increased from 15 mol mol À1 at day 11 after U. lactuca addition to >80 mol mol À1 by the end of the incubation. Since the C:N ratio in the mineralization products was much higher than the original thallus material (8.9 mol mol À1) it is probable that a preferential incorporation of NH 4 + into the increasing bacterial biomass occurred. The nitrogen for bacterial growth was most likely obtained from degradation of U. lactuca thalli as there was no stimulation of urea-N turnover in the sediment during incubation. The net increase in bacteria cell number in the 18-mm thick thallus layer was estimated to be 7.6 Â 10 9 to 2.4 Â 10 10 bacterial cells cm À3. In contrast, the bacterial cell number remained constant in the ÀUlva incubations.
Journal of Experimental Marine Biology and Ecology, 2006
The benthic degradation of mussel tissue (Mytilus edulis) was studied in a continuous flow-throug... more The benthic degradation of mussel tissue (Mytilus edulis) was studied in a continuous flow-through system over a 32 day incubation period. Sediment chambers without mussels served as controls. The inflowing artificial seawater and the outflow water were analyzed for dissolved organic nitrogen (DON), short chain fatty acids (SCFA), dissolved inorganic nitrogen (DIN), ∑CO2 and O2 during the course of incubation. Sediment profiles of particulate organic carbon (POC), particulate organic nitrogen (PON), total hydrolyzable amino acids (THAA), pore water concentrations of DON and DIN and turnover rate of dissolved free amino acids (DFAA) were measured at four different times during the 32 day experiment. Immediately after the addition of mussel tissue, the chambers became completely anoxic and there was an increase in carbon oxidation and the efflux of DON, SCFA and NH4+ from the sediment+mussel layer to the overlaying water. During the first 9 days there was a net buildup of DON, and NH4+ in the sediment followed by a net consumption of the respective N-species during the remainder of the experiment. During the course of incubation 41% of the organic content of the added mussel tissue was released from the sediment as DON, whereas most of the other mussel-N effluxed the sediment as NH4+. Only 8% of the added mussel-N remained by the end of the experiment. There were indications of stimulated bacterial growth in both the mussel amended and the unamended sediments. This was measured as a net increase in THAA, which could only be explained by net bacterial growth and/or protein synthesis. During mussel decomposition both the estimated bacterial carbon incorporation efficiency and the C:N ratio of the substrates used by the bacteria were low. This resulted in a low bacterial nitrogen demand. As a consequence, almost all of the nitrogen mineralized within the sediment was released to the water column as NH4+.
The degradation of an Ulva lactuca mat (0.2 kg dw m À2) was studied in a controlled flow-through ... more The degradation of an Ulva lactuca mat (0.2 kg dw m À2) was studied in a controlled flow-through mesocosm for 31 d. Sediment chambers without U. lactuca served as controls. Fluxes of P CO 2 , O 2 , inorganic nitrogen, and urea were determined during the incubation period in addition to sulfate reduction rates, POC and PON content, enumeration of specific bacterial populations and evaluation of the physiological state of the added U. lactuca thalli. After U. lactuca addition to the chambers, there was an immediate increase in the efflux of P CO 2 from 11 to 27 mmol-C m À2 d À1 and a concomitant increase in O 2 uptake from 11 to 23 mmol m À2 d À1. These effluxes remained elevated throughout the incubation period. In contrast, the NH 4 + efflux increased from 0.1 to 1.8 mmol NH 4 + m À2 d À1 during the first 3 d of incubation, followed by 6 d with a constant efflux rate, after which time it decreased gradually to 0.3 mmol NH 4 + m À2 d À1 by the end of the experiment. In total, NH 4 + accounted for 83% of the total nitrogen efflux after addition of U. lactuca. During the 31 d incubation period there was a continuous colonization of the thalli by bacteria. Sulfate reducers associated with the thalli accounted for 3% of the carbon oxidation on day 31. The molar C:N ratio in mineralization products (the ratio between the efflux of P CO 2 and NH 4 + + NO 2 À + NO 3 À) increased from 15 mol mol À1 at day 11 after U. lactuca addition to >80 mol mol À1 by the end of the incubation. Since the C:N ratio in the mineralization products was much higher than the original thallus material (8.9 mol mol À1) it is probable that a preferential incorporation of NH 4 + into the increasing bacterial biomass occurred. The nitrogen for bacterial growth was most likely obtained from degradation of U. lactuca thalli as there was no stimulation of urea-N turnover in the sediment during incubation. The net increase in bacteria cell number in the 18-mm thick thallus layer was estimated to be 7.6 Â 10 9 to 2.4 Â 10 10 bacterial cells cm À3. In contrast, the bacterial cell number remained constant in the ÀUlva incubations.
Bioavailability and chemical composition of dissolved organic nitrogen (DON) in marine pore water... more Bioavailability and chemical composition of dissolved organic nitrogen (DON) in marine pore water were followed and related to bacterial activity in a 14-d anoxic decomposition experiment. For the experiment 0.2-m filtered pore water from a coastal marine sediment was inoculated with native sediment bacteria. The initial composition of DON was characterized by a high contribution of dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA), and urea, which together accounted for 82% of the DON pool. During the experiment, 54% of the DON was used by bacteria, indicating that DON was readily available to bacterial degradation. The consumption of DFAA and DCAA accounted for more than half of the DON consumed. The unidentified DON pool accounted for 33% of the net DON consumption, and the unidentified DON pool was fully depleted by the end of the experiment. Systematic changes in the amino acid composition occurred with time of incubation, as demonstrated by use of a principal component analysis based on the mole percent contribution of amino acids. The results indicated that amino acids of both the DFAA and the DCAA pools were useful indicators of the diagenetic state of DON. The present study presents the first direct evidence of short-term (within 14 d) changes in DFAA and DCAA of the DON pool. These changes were similar to decompositional changes in the molecular composition of amino acids observed in traditional studies of bulk sediment diagenesis.
The degradation of an Ulva lactuca mat (0.2 kg dw m À2 ) was studied in a controlled flow-through... more The degradation of an Ulva lactuca mat (0.2 kg dw m À2 ) was studied in a controlled flow-through mesocosm for 31 d. Sediment chambers without U. lactuca served as controls. Fluxes of P CO 2 , O 2 , inorganic nitrogen, and urea were determined during the incubation period in addition to sulfate reduction rates, POC and PON content, enumeration of specific bacterial populations and evaluation of the physiological state of the added U. lactuca thalli. After U. lactuca addition to the chambers, there was an immediate increase in the efflux of P CO 2 from 11 to 27 mmol-C m À2 d À1 and a concomitant increase in O 2 uptake from 11 to 23 mmol m À2 d À1 . These effluxes remained elevated throughout the incubation period. In contrast, the NH 4 + efflux increased from 0.1 to 1.8 mmol NH 4 + m À2 d À1 during the first 3 d of incubation, followed by 6 d with a constant efflux rate, after which time it decreased gradually to 0.3 mmol NH 4 + m À2 d À1 by the end of the experiment. In total, NH 4 + accounted for 83% of the total nitrogen efflux after addition of U. lactuca. During the 31 d incubation period there was a continuous colonization of the thalli by bacteria. Sulfate reducers associated with the thalli accounted for 3% of the carbon oxidation on day 31. The molar C:N ratio in mineralization products (the ratio between the efflux of P CO 2 and NH 4 + + NO 2 À + NO 3 À ) increased from 15 mol mol À1 at day 11 after U. lactuca addition to >80 mol mol À1 by the end of the incubation. Since the C:N ratio in the mineralization products was much higher than the original thallus material (8.9 mol mol À1 ) it is probable that a preferential incorporation of NH 4 + into the increasing bacterial biomass occurred. The nitrogen for bacterial growth was most likely obtained from degradation of U. lactuca thalli as there was no stimulation of urea-N turnover in the sediment during incubation. The net increase in bacteria cell number in the 18-mm thick thallus layer was estimated to be 7.6 Â 10 9 to 2.4 Â 10 10 bacterial cells cm À3 . In contrast, the bacterial cell number remained constant in the ÀUlva incubations. #
Methane (CH4) emission from pig slurry is a large contributor to the climate footprint of livesto... more Methane (CH4) emission from pig slurry is a large contributor to the climate footprint of livestock production. Acidification of excreta from livestock animals with sulfuric acid, reduce CH4 emission and is practiced at many Danish farms. Possible interaction effects with other acidic agents or management practices (e.g. frequent slurry removal and residual slurry acidification) have not been fully investigated. Here we assessed the effect of pig slurry acidification with a range of organic and inorganic acids with respect to their CH4 inhibitor potential in several batch experiments (BS). After careful selection of promising CH4 inhibitors, three continuous headspace experiments (CHS) were carried out to simulate management of manure in pig houses. In BS experiments, more than <99% CH4 reduction was observed with HNO3 treatment to pH 5.5. Treatments with HNO3, H2SO4, and H3PO4 reduced CH4 production more than acetic acid and other organic acids when acidified to the same initial...
Odour emission from intensive pig production is a major source of local nuisance and sulphur-cont... more Odour emission from intensive pig production is a major source of local nuisance and sulphur-containing odorants (e.g. hydrogen sulphide and methanethiol) have been recognized as key odorants. Biological air filter has emerged as a cost-effective technique to remove odorants from ventilation air. However, low removal efficiencies for sulphurous odorants have been observed when a large volume of air has been applied with low concentrations. Recent kinetic studies on full scale biological air filters indicate that the removal of odorants is related both to mass load and air load of odorants but the dependence of sulphurous odorants on loading rates are not clear due to the very low and highly varying removal efficiencies. In the present study, two inoculated biofilter columns were applied to test the dependence of sulphurous odorants (hydrogen sulphide, methanethiol and dimethylsulfide) removal on air loading rate, mass loading rate or concentration. Specially designed commercially av...
Bioavailability and chemical composition of dissolved organic nitrogen (DON) in marine pore water... more Bioavailability and chemical composition of dissolved organic nitrogen (DON) in marine pore water were followed and related to bacterial activity in a 14-d anoxic decomposition experiment. For the experiment 0.2-m filtered pore water from a coastal marine sediment was inoculated with native sediment bacteria. The initial composition of DON was characterized by a high contribution of dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA), and urea, which together accounted for 82% of the DON pool. During the experiment, 54% of the DON was used by bacteria, indicating that DON was readily available to bacterial degradation. The consumption of DFAA and DCAA accounted for more than half of the DON consumed. The unidentified DON pool accounted for 33% of the net DON consumption, and the unidentified DON pool was fully depleted by the end of the experiment. Systematic changes in the amino acid composition occurred with time of incubation, as demonstrated by use of a principal component analysis based on the mole percent contribution of amino acids. The results indicated that amino acids of both the DFAA and the DCAA pools were useful indicators of the diagenetic state of DON. The present study presents the first direct evidence of short-term (within 14 d) changes in DFAA and DCAA of the DON pool. These changes were similar to decompositional changes in the molecular composition of amino acids observed in traditional studies of bulk sediment diagenesis.
Methane (CH 4) emission from pig slurry is a large contributor to the climate footprint of livest... more Methane (CH 4) emission from pig slurry is a large contributor to the climate footprint of livestock production. Acidification of excreta from livestock animals with sulfuric acid, reduce CH 4 emission and is practiced at many Danish farms. Possible interaction effects with other acidic agents or management practices (e.g. frequent slurry removal and residual slurry acidification) have not been fully investigated. Here we assessed the effect of pig slurry acidification with a range of organic and inorganic acids with respect to their CH 4 inhibitor potential in several batch experiments (BS). After careful selection of promising CH 4 inhibitors, three continuous headspace experiments (CHS) were carried out to simulate management of manure in pig houses. In BS experiments, more than <99% CH 4 reduction was observed with HNO 3 treatment to pH 5.5. Treatments with HNO 3 , H 2 SO 4 , and H 3 PO 4 reduced CH 4 production more than acetic acid and other organic acids when acidified to the same initial pH of 5.5. Synergistic effects were not observed when mixing inorganic and organic acids as otherwise proposed in the literature, which was attributed to the high amount of acetic acid in the slurry to start with. In the CHS experiments, HNO 3 treatment reduced CH 4 more than H 2 SO 4 , but increased nitrous oxide (N 2 O) emission, particularly when the acidification target pH was above 6, suggesting considerable denitrification activity. Due to increased N 2 O emission from HNO 3 treatments, HNO 3 reduced total CO 2-eq by 67%, whereas H 2 SO 4 reduced CO 2-eq by 91.5% compared to untreated slurry. In experiments with daily slurry addition, weekly slurry removal, and residual acidification, HNO 3 and H 2 SO 4 treatments reduced CO 2-eq by 27% and 48%, respectively (not significant). More cycles of residual acidification are recommended in future research. The study provides solid evidence that HNO 3 treatment is not suitable for reducing CO 2-eq and H 2 SO 4 should be the preferred acidic agent for slurry acidification.
The degradation of an Ulva lactuca mat (0.2 kg dw m À2) was studied in a controlled flow-through ... more The degradation of an Ulva lactuca mat (0.2 kg dw m À2) was studied in a controlled flow-through mesocosm for 31 d. Sediment chambers without U. lactuca served as controls. Fluxes of P CO 2 , O 2 , inorganic nitrogen, and urea were determined during the incubation period in addition to sulfate reduction rates, POC and PON content, enumeration of specific bacterial populations and evaluation of the physiological state of the added U. lactuca thalli. After U. lactuca addition to the chambers, there was an immediate increase in the efflux of P CO 2 from 11 to 27 mmol-C m À2 d À1 and a concomitant increase in O 2 uptake from 11 to 23 mmol m À2 d À1. These effluxes remained elevated throughout the incubation period. In contrast, the NH 4 + efflux increased from 0.1 to 1.8 mmol NH 4 + m À2 d À1 during the first 3 d of incubation, followed by 6 d with a constant efflux rate, after which time it decreased gradually to 0.3 mmol NH 4 + m À2 d À1 by the end of the experiment. In total, NH 4 + accounted for 83% of the total nitrogen efflux after addition of U. lactuca. During the 31 d incubation period there was a continuous colonization of the thalli by bacteria. Sulfate reducers associated with the thalli accounted for 3% of the carbon oxidation on day 31. The molar C:N ratio in mineralization products (the ratio between the efflux of P CO 2 and NH 4 + + NO 2 À + NO 3 À) increased from 15 mol mol À1 at day 11 after U. lactuca addition to >80 mol mol À1 by the end of the incubation. Since the C:N ratio in the mineralization products was much higher than the original thallus material (8.9 mol mol À1) it is probable that a preferential incorporation of NH 4 + into the increasing bacterial biomass occurred. The nitrogen for bacterial growth was most likely obtained from degradation of U. lactuca thalli as there was no stimulation of urea-N turnover in the sediment during incubation. The net increase in bacteria cell number in the 18-mm thick thallus layer was estimated to be 7.6 Â 10 9 to 2.4 Â 10 10 bacterial cells cm À3. In contrast, the bacterial cell number remained constant in the ÀUlva incubations.
Journal of Experimental Marine Biology and Ecology, 2006
The benthic degradation of mussel tissue (Mytilus edulis) was studied in a continuous flow-throug... more The benthic degradation of mussel tissue (Mytilus edulis) was studied in a continuous flow-through system over a 32 day incubation period. Sediment chambers without mussels served as controls. The inflowing artificial seawater and the outflow water were analyzed for dissolved organic nitrogen (DON), short chain fatty acids (SCFA), dissolved inorganic nitrogen (DIN), ∑CO2 and O2 during the course of incubation. Sediment profiles of particulate organic carbon (POC), particulate organic nitrogen (PON), total hydrolyzable amino acids (THAA), pore water concentrations of DON and DIN and turnover rate of dissolved free amino acids (DFAA) were measured at four different times during the 32 day experiment. Immediately after the addition of mussel tissue, the chambers became completely anoxic and there was an increase in carbon oxidation and the efflux of DON, SCFA and NH4+ from the sediment+mussel layer to the overlaying water. During the first 9 days there was a net buildup of DON, and NH4+ in the sediment followed by a net consumption of the respective N-species during the remainder of the experiment. During the course of incubation 41% of the organic content of the added mussel tissue was released from the sediment as DON, whereas most of the other mussel-N effluxed the sediment as NH4+. Only 8% of the added mussel-N remained by the end of the experiment. There were indications of stimulated bacterial growth in both the mussel amended and the unamended sediments. This was measured as a net increase in THAA, which could only be explained by net bacterial growth and/or protein synthesis. During mussel decomposition both the estimated bacterial carbon incorporation efficiency and the C:N ratio of the substrates used by the bacteria were low. This resulted in a low bacterial nitrogen demand. As a consequence, almost all of the nitrogen mineralized within the sediment was released to the water column as NH4+.
The degradation of an Ulva lactuca mat (0.2 kg dw m À2) was studied in a controlled flow-through ... more The degradation of an Ulva lactuca mat (0.2 kg dw m À2) was studied in a controlled flow-through mesocosm for 31 d. Sediment chambers without U. lactuca served as controls. Fluxes of P CO 2 , O 2 , inorganic nitrogen, and urea were determined during the incubation period in addition to sulfate reduction rates, POC and PON content, enumeration of specific bacterial populations and evaluation of the physiological state of the added U. lactuca thalli. After U. lactuca addition to the chambers, there was an immediate increase in the efflux of P CO 2 from 11 to 27 mmol-C m À2 d À1 and a concomitant increase in O 2 uptake from 11 to 23 mmol m À2 d À1. These effluxes remained elevated throughout the incubation period. In contrast, the NH 4 + efflux increased from 0.1 to 1.8 mmol NH 4 + m À2 d À1 during the first 3 d of incubation, followed by 6 d with a constant efflux rate, after which time it decreased gradually to 0.3 mmol NH 4 + m À2 d À1 by the end of the experiment. In total, NH 4 + accounted for 83% of the total nitrogen efflux after addition of U. lactuca. During the 31 d incubation period there was a continuous colonization of the thalli by bacteria. Sulfate reducers associated with the thalli accounted for 3% of the carbon oxidation on day 31. The molar C:N ratio in mineralization products (the ratio between the efflux of P CO 2 and NH 4 + + NO 2 À + NO 3 À) increased from 15 mol mol À1 at day 11 after U. lactuca addition to >80 mol mol À1 by the end of the incubation. Since the C:N ratio in the mineralization products was much higher than the original thallus material (8.9 mol mol À1) it is probable that a preferential incorporation of NH 4 + into the increasing bacterial biomass occurred. The nitrogen for bacterial growth was most likely obtained from degradation of U. lactuca thalli as there was no stimulation of urea-N turnover in the sediment during incubation. The net increase in bacteria cell number in the 18-mm thick thallus layer was estimated to be 7.6 Â 10 9 to 2.4 Â 10 10 bacterial cells cm À3. In contrast, the bacterial cell number remained constant in the ÀUlva incubations.
Bioavailability and chemical composition of dissolved organic nitrogen (DON) in marine pore water... more Bioavailability and chemical composition of dissolved organic nitrogen (DON) in marine pore water were followed and related to bacterial activity in a 14-d anoxic decomposition experiment. For the experiment 0.2-m filtered pore water from a coastal marine sediment was inoculated with native sediment bacteria. The initial composition of DON was characterized by a high contribution of dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA), and urea, which together accounted for 82% of the DON pool. During the experiment, 54% of the DON was used by bacteria, indicating that DON was readily available to bacterial degradation. The consumption of DFAA and DCAA accounted for more than half of the DON consumed. The unidentified DON pool accounted for 33% of the net DON consumption, and the unidentified DON pool was fully depleted by the end of the experiment. Systematic changes in the amino acid composition occurred with time of incubation, as demonstrated by use of a principal component analysis based on the mole percent contribution of amino acids. The results indicated that amino acids of both the DFAA and the DCAA pools were useful indicators of the diagenetic state of DON. The present study presents the first direct evidence of short-term (within 14 d) changes in DFAA and DCAA of the DON pool. These changes were similar to decompositional changes in the molecular composition of amino acids observed in traditional studies of bulk sediment diagenesis.
The degradation of an Ulva lactuca mat (0.2 kg dw m À2 ) was studied in a controlled flow-through... more The degradation of an Ulva lactuca mat (0.2 kg dw m À2 ) was studied in a controlled flow-through mesocosm for 31 d. Sediment chambers without U. lactuca served as controls. Fluxes of P CO 2 , O 2 , inorganic nitrogen, and urea were determined during the incubation period in addition to sulfate reduction rates, POC and PON content, enumeration of specific bacterial populations and evaluation of the physiological state of the added U. lactuca thalli. After U. lactuca addition to the chambers, there was an immediate increase in the efflux of P CO 2 from 11 to 27 mmol-C m À2 d À1 and a concomitant increase in O 2 uptake from 11 to 23 mmol m À2 d À1 . These effluxes remained elevated throughout the incubation period. In contrast, the NH 4 + efflux increased from 0.1 to 1.8 mmol NH 4 + m À2 d À1 during the first 3 d of incubation, followed by 6 d with a constant efflux rate, after which time it decreased gradually to 0.3 mmol NH 4 + m À2 d À1 by the end of the experiment. In total, NH 4 + accounted for 83% of the total nitrogen efflux after addition of U. lactuca. During the 31 d incubation period there was a continuous colonization of the thalli by bacteria. Sulfate reducers associated with the thalli accounted for 3% of the carbon oxidation on day 31. The molar C:N ratio in mineralization products (the ratio between the efflux of P CO 2 and NH 4 + + NO 2 À + NO 3 À ) increased from 15 mol mol À1 at day 11 after U. lactuca addition to >80 mol mol À1 by the end of the incubation. Since the C:N ratio in the mineralization products was much higher than the original thallus material (8.9 mol mol À1 ) it is probable that a preferential incorporation of NH 4 + into the increasing bacterial biomass occurred. The nitrogen for bacterial growth was most likely obtained from degradation of U. lactuca thalli as there was no stimulation of urea-N turnover in the sediment during incubation. The net increase in bacteria cell number in the 18-mm thick thallus layer was estimated to be 7.6 Â 10 9 to 2.4 Â 10 10 bacterial cells cm À3 . In contrast, the bacterial cell number remained constant in the ÀUlva incubations. #
Uploads
Papers by Lise Guldberg