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Wayne S. Gardner - One of the best experts on this subject based on the ideXlab platform.

  • assessing Nitrogen Dynamics throughout the estuarine landscape
    Estuaries and Coasts, 2013
    Co-Authors: Ashley R Smyth, Wayne S. Gardner, Suzanne P Thompson, Kaylyn Siporin, Mark J Mccarthy, Michael F Piehler
    Abstract:

    Assessing Nitrogen Dynamics in the estuarine landscape is challenging given the unique effects of individual habitats on Nitrogen Dynamics. We measured net N2 fluxes, sediment oxygen demand, and fluxes of ammonium and nitrate seasonally from five major estuarine habitats: salt marshes, seagrass beds (SAV), oyster reefs, and intertidal and subtidal flats. Net N2 fluxes ranged from 332 ± 116 μmol N-N2 m−2 h−1 from oyster reef sediments in the summer to −67 ± 4 μmol N-N2 m−2 h−1 from SAV in the winter. Oyster reef sediments had the highest rate of N2 production of all habitats. Dissimilatory nitrate reduction to ammonium (DNRA) was measured during the summer and winter. DNRA was low during the winter and ranged from 4.5 ± 3.0 in subtidal flats to 104 ± 34 μmol 15NH 4 + m−2 h−1 in oyster reefs during the summer. Annual denitrification, accounting for seasonal differences in inundation and light, ranged from 161.1 ± 19.2 mmol N-N2 m−2 year−1 for marsh sediments to 509.9 ± 122.7 mmol N-N2 m−2 year−1 for SAV sediments. Given the current habitat distribution in our study system, an estimated 28.3 × 106 mol of N are removed per year or 76 % of estimated watershed Nitrogen load. These results indicate that changes in the area and distribution of habitats in the estuarine landscape will impact ecosystem function and services.

  • Nitrogen Dynamics at the sediment–water interface in shallow, sub-tropical Florida Bay: why denitrification efficiency may decrease with increased eutrophication
    Biogeochemistry, 2009
    Co-Authors: Wayne S. Gardner, Mark J Mccarthy
    Abstract:

    Nitrogen (N) Dynamics at the sediment–water interface were examined in four regions of Florida Bay to provide mechanistic information on the fate and effects of increased N inputs to shallow, subtropical, coastal environments. Dissimilatory nitrate (NO_3 ^−) reduction to ammonium (DNRA) was hypothesized to be a significant mechanism retaining bioreactive N in this warm, saline coastal ecosystem. Nitrogen Dynamics, phosphorus (P) fluxes, and sediment oxygen demand (SOD) were measured in north-central (Rankin Key; eutrophic), north-eastern (Duck Key; high N to P seston ratios), north-western (Murray Key; low N to P ratios), and central (Rabbit Key; typical central site) Florida Bay in August 2004, January 2005, and November 2006. Site water was passed over intact sediment cores, and changes in oxygen (O_2), phosphate ( o -PO_4 ^3−), ammonium (NH_4 ^+), NO_3 ^−, nitrite (NO_2 ^−), and N_2 concentrations were measured, without and with addition of excess ^15NO_3 ^− or ^15NH_4 ^+ to inflow water. These incubations provided estimates of SOD, nutrient fluxes, N_2 production, and potential DNRA rates. Denitrification rates were lowest in summer, when SOD was highest. DNRA rates and NH_4 ^+ fluxes were high in summer at the eutrophic Rankin site, when denitrification rates were low and almost no N_2 came from added ^15NO_3 ^−. Highest ^15NH_4 ^+ accumulation, resulting from DNRA, occurred at Rabbit Key during a picocyanobacteria bloom in November. ^15NH_4 ^+ accumulation rates among the stations correlated with SOD in August and January, but not in November during the algal bloom. These mechanistic results help explain why bioreactive N supply rates are sometimes high in Florida Bay and why denitrification efficiency may decrease with increased NO_3 ^− inputs in sub-tropical coastal environments.

  • Nitrogen Dynamics at the sediment water interface in shallow sub tropical florida bay why denitrification efficiency may decrease with increased eutrophication
    Biogeochemistry, 2009
    Co-Authors: Wayne S. Gardner, Mark J Mccarthy
    Abstract:

    Nitrogen (N) Dynamics at the sediment–water interface were examined in four regions of Florida Bay to provide mechanistic information on the fate and effects of increased N inputs to shallow, subtropical, coastal environments. Dissimilatory nitrate (NO3 −) reduction to ammonium (DNRA) was hypothesized to be a significant mechanism retaining bioreactive N in this warm, saline coastal ecosystem. Nitrogen Dynamics, phosphorus (P) fluxes, and sediment oxygen demand (SOD) were measured in north-central (Rankin Key; eutrophic), north-eastern (Duck Key; high N to P seston ratios), north-western (Murray Key; low N to P ratios), and central (Rabbit Key; typical central site) Florida Bay in August 2004, January 2005, and November 2006. Site water was passed over intact sediment cores, and changes in oxygen (O2), phosphate (o-PO4 3−), ammonium (NH4 +), NO3 −, nitrite (NO2 −), and N2 concentrations were measured, without and with addition of excess 15NO3 − or 15NH4 + to inflow water. These incubations provided estimates of SOD, nutrient fluxes, N2 production, and potential DNRA rates. Denitrification rates were lowest in summer, when SOD was highest. DNRA rates and NH4 + fluxes were high in summer at the eutrophic Rankin site, when denitrification rates were low and almost no N2 came from added 15NO3 −. Highest 15NH4 + accumulation, resulting from DNRA, occurred at Rabbit Key during a picocyanobacteria bloom in November. 15NH4 + accumulation rates among the stations correlated with SOD in August and January, but not in November during the algal bloom. These mechanistic results help explain why bioreactive N supply rates are sometimes high in Florida Bay and why denitrification efficiency may decrease with increased NO3 − inputs in sub-tropical coastal environments.

  • Nitrogen Dynamics and microbial food web structure during a summer cyanobacterial bloom in a subtropical shallow well mixed eutrophic lake lake taihu china
    Hydrobiologia, 2007
    Co-Authors: Mark J Mccarthy, Peter J. Lavrentyev, Longyuan Yang, Lu Zhang, Yuwei Chen, Wayne S. Gardner
    Abstract:

    Nitrogen Dynamics and microbial food web structure were characterized in subtropical, eutrophic, large (2,338 km2), shallow (1.9 m mean depth), and polymictic Lake Taihu (China) in Sept–Oct 2002 during a cyanobacterial bloom. Population growth and industrialization are factors in trophic status deterioration in Lake Taihu. Sites for investigation were selected along a transect from the Liangxihe River discharge into Meiliang Bay to the main lake. Water column Nitrogen and microbial food web measurements were combined with sediment–water interface incubations to characterize and identify important processes related to system Nitrogen Dynamics. Results indicate a gradient from strong phosphorus limitation at the river discharge to Nitrogen limitation or co-limitation in the main lake. Denitrification in Meiliang Bay may drive main lake Nitrogen limitation by removing excess Nitrogen before physical transport to the main lake. Five times higher nutrient mineralization rates in the water column versus sediments indicate that sediment nutrient transformations were not as important as water column processes for fueling primary production. However, sediments provide a site for denitrification, which, along with Nitrogen fixation and other processes, can determine available nutrient ratios. Dissimilatory nitrate reduction to ammonium (DNRA) was important, relative to denitrification, only at the river discharge site, and Nitrogen fixation was observed only in the main lake. Reflecting Nitrogen cycling patterns, microbial food web structure shifted from autotrophic (phytoplankton dominated) at the river discharge to heterotrophic (bacteria dominated) in and near the main lake.

  • Effects of the zebra mussel on Nitrogen Dynamics and the microbial community at the sediment-water interface
    Aquatic Microbial Ecology, 2000
    Co-Authors: Peter J. Lavrentyev, Wayne S. Gardner, Longyuan Yang
    Abstract:

    A flow-through expenment was conducted on intact cores of sedunents from Saginaw Bay, Lake Huron, to examine how trophic interactions between filter-feeding bivalve mussels and microbial populations could affect Nitrogen Dynamics at the sediment-water interface. The zebra mussels used in this experiment removed a large proportion of protozoa and phytoplankton from the overlying water, particularly heterotrophic nanoplankton (up to 82 %), while bacterial population~ showed less change. A 3-fold decrease in the protozoan to bacterial carbon ratio corresponded to a 2.5-fold increase in relative ammonium removal rates as estimated from the dark loss of '5N-ammonium. Excretion by the bivalves also increased net ammonium flux to the water, thus elevating the total calculated area1 ammonium removal rates to about 6-fold over rates observed in the control treatment. These data suggest that filter-feedng bivalves may significantly affect Nitrogen transformation rates near the sediment-water interface by excreting ammonium and altering the microbial food web structure at the sediment-water interface.

Mark J Mccarthy - One of the best experts on this subject based on the ideXlab platform.

  • assessing Nitrogen Dynamics throughout the estuarine landscape
    Estuaries and Coasts, 2013
    Co-Authors: Ashley R Smyth, Wayne S. Gardner, Suzanne P Thompson, Kaylyn Siporin, Mark J Mccarthy, Michael F Piehler
    Abstract:

    Assessing Nitrogen Dynamics in the estuarine landscape is challenging given the unique effects of individual habitats on Nitrogen Dynamics. We measured net N2 fluxes, sediment oxygen demand, and fluxes of ammonium and nitrate seasonally from five major estuarine habitats: salt marshes, seagrass beds (SAV), oyster reefs, and intertidal and subtidal flats. Net N2 fluxes ranged from 332 ± 116 μmol N-N2 m−2 h−1 from oyster reef sediments in the summer to −67 ± 4 μmol N-N2 m−2 h−1 from SAV in the winter. Oyster reef sediments had the highest rate of N2 production of all habitats. Dissimilatory nitrate reduction to ammonium (DNRA) was measured during the summer and winter. DNRA was low during the winter and ranged from 4.5 ± 3.0 in subtidal flats to 104 ± 34 μmol 15NH 4 + m−2 h−1 in oyster reefs during the summer. Annual denitrification, accounting for seasonal differences in inundation and light, ranged from 161.1 ± 19.2 mmol N-N2 m−2 year−1 for marsh sediments to 509.9 ± 122.7 mmol N-N2 m−2 year−1 for SAV sediments. Given the current habitat distribution in our study system, an estimated 28.3 × 106 mol of N are removed per year or 76 % of estimated watershed Nitrogen load. These results indicate that changes in the area and distribution of habitats in the estuarine landscape will impact ecosystem function and services.

  • Nitrogen Dynamics at the sediment–water interface in shallow, sub-tropical Florida Bay: why denitrification efficiency may decrease with increased eutrophication
    Biogeochemistry, 2009
    Co-Authors: Wayne S. Gardner, Mark J Mccarthy
    Abstract:

    Nitrogen (N) Dynamics at the sediment–water interface were examined in four regions of Florida Bay to provide mechanistic information on the fate and effects of increased N inputs to shallow, subtropical, coastal environments. Dissimilatory nitrate (NO_3 ^−) reduction to ammonium (DNRA) was hypothesized to be a significant mechanism retaining bioreactive N in this warm, saline coastal ecosystem. Nitrogen Dynamics, phosphorus (P) fluxes, and sediment oxygen demand (SOD) were measured in north-central (Rankin Key; eutrophic), north-eastern (Duck Key; high N to P seston ratios), north-western (Murray Key; low N to P ratios), and central (Rabbit Key; typical central site) Florida Bay in August 2004, January 2005, and November 2006. Site water was passed over intact sediment cores, and changes in oxygen (O_2), phosphate ( o -PO_4 ^3−), ammonium (NH_4 ^+), NO_3 ^−, nitrite (NO_2 ^−), and N_2 concentrations were measured, without and with addition of excess ^15NO_3 ^− or ^15NH_4 ^+ to inflow water. These incubations provided estimates of SOD, nutrient fluxes, N_2 production, and potential DNRA rates. Denitrification rates were lowest in summer, when SOD was highest. DNRA rates and NH_4 ^+ fluxes were high in summer at the eutrophic Rankin site, when denitrification rates were low and almost no N_2 came from added ^15NO_3 ^−. Highest ^15NH_4 ^+ accumulation, resulting from DNRA, occurred at Rabbit Key during a picocyanobacteria bloom in November. ^15NH_4 ^+ accumulation rates among the stations correlated with SOD in August and January, but not in November during the algal bloom. These mechanistic results help explain why bioreactive N supply rates are sometimes high in Florida Bay and why denitrification efficiency may decrease with increased NO_3 ^− inputs in sub-tropical coastal environments.

  • Nitrogen Dynamics at the sediment water interface in shallow sub tropical florida bay why denitrification efficiency may decrease with increased eutrophication
    Biogeochemistry, 2009
    Co-Authors: Wayne S. Gardner, Mark J Mccarthy
    Abstract:

    Nitrogen (N) Dynamics at the sediment–water interface were examined in four regions of Florida Bay to provide mechanistic information on the fate and effects of increased N inputs to shallow, subtropical, coastal environments. Dissimilatory nitrate (NO3 −) reduction to ammonium (DNRA) was hypothesized to be a significant mechanism retaining bioreactive N in this warm, saline coastal ecosystem. Nitrogen Dynamics, phosphorus (P) fluxes, and sediment oxygen demand (SOD) were measured in north-central (Rankin Key; eutrophic), north-eastern (Duck Key; high N to P seston ratios), north-western (Murray Key; low N to P ratios), and central (Rabbit Key; typical central site) Florida Bay in August 2004, January 2005, and November 2006. Site water was passed over intact sediment cores, and changes in oxygen (O2), phosphate (o-PO4 3−), ammonium (NH4 +), NO3 −, nitrite (NO2 −), and N2 concentrations were measured, without and with addition of excess 15NO3 − or 15NH4 + to inflow water. These incubations provided estimates of SOD, nutrient fluxes, N2 production, and potential DNRA rates. Denitrification rates were lowest in summer, when SOD was highest. DNRA rates and NH4 + fluxes were high in summer at the eutrophic Rankin site, when denitrification rates were low and almost no N2 came from added 15NO3 −. Highest 15NH4 + accumulation, resulting from DNRA, occurred at Rabbit Key during a picocyanobacteria bloom in November. 15NH4 + accumulation rates among the stations correlated with SOD in August and January, but not in November during the algal bloom. These mechanistic results help explain why bioreactive N supply rates are sometimes high in Florida Bay and why denitrification efficiency may decrease with increased NO3 − inputs in sub-tropical coastal environments.

  • Nitrogen Dynamics and microbial food web structure during a summer cyanobacterial bloom in a subtropical shallow well mixed eutrophic lake lake taihu china
    Hydrobiologia, 2007
    Co-Authors: Mark J Mccarthy, Peter J. Lavrentyev, Longyuan Yang, Lu Zhang, Yuwei Chen, Wayne S. Gardner
    Abstract:

    Nitrogen Dynamics and microbial food web structure were characterized in subtropical, eutrophic, large (2,338 km2), shallow (1.9 m mean depth), and polymictic Lake Taihu (China) in Sept–Oct 2002 during a cyanobacterial bloom. Population growth and industrialization are factors in trophic status deterioration in Lake Taihu. Sites for investigation were selected along a transect from the Liangxihe River discharge into Meiliang Bay to the main lake. Water column Nitrogen and microbial food web measurements were combined with sediment–water interface incubations to characterize and identify important processes related to system Nitrogen Dynamics. Results indicate a gradient from strong phosphorus limitation at the river discharge to Nitrogen limitation or co-limitation in the main lake. Denitrification in Meiliang Bay may drive main lake Nitrogen limitation by removing excess Nitrogen before physical transport to the main lake. Five times higher nutrient mineralization rates in the water column versus sediments indicate that sediment nutrient transformations were not as important as water column processes for fueling primary production. However, sediments provide a site for denitrification, which, along with Nitrogen fixation and other processes, can determine available nutrient ratios. Dissimilatory nitrate reduction to ammonium (DNRA) was important, relative to denitrification, only at the river discharge site, and Nitrogen fixation was observed only in the main lake. Reflecting Nitrogen cycling patterns, microbial food web structure shifted from autotrophic (phytoplankton dominated) at the river discharge to heterotrophic (bacteria dominated) in and near the main lake.

K Lorenzen - One of the best experts on this subject based on the ideXlab platform.

  • Modeling Nitrogen Dynamics in intensive shrimp ponds: the role of sediment remineralization
    Aquaculture, 2004
    Co-Authors: M.a Burford, K Lorenzen
    Abstract:

    Abstract A mathematical model is used to investigate the role of sedimentation and remineralization in the sediment on Nitrogen (N) Dynamics in intensive shrimp culture ponds. The model describes the key processes involved in N cycling that underpin the Dynamics of total ammoniacal N (TAN), nitrate/nitrite (NOX) and chlorophyll a (CHL) concentrations and the sediment N pool. These parameters may, in high concentrations, impact negatively on the shrimp or the adjacent aquatic environment when water is discharged from ponds. The model was calibrated for an Australian commercial shrimp ( Penaeus monodon ) pond. Most N enters the pond system as TAN from shrimp excretion of dietary N and decomposition of wasted feed, and is subsequently taken up by phytoplankton, which, on senescence, is sedimented and remineralized. Sediment remineralization is the dominant source of TAN in the water column for all but the beginning of the production cycle. The remineralization rate of sedimented N was estimated at 6% day −1 . Nonetheless, sediment acts as a net sink of N throughout the production cycle. The effect of management strategies, including increased stocking densities, water exchange and sludge (=sedimented material) removal, on water quality was examined. Model outputs show that using current shrimp farming techniques, with water exchange rates of 7% day −1 , an increase in stocking densities above 60 animals m −2 would result in unacceptably high TAN concentrations. Both sludge removal and water exchange provide effective ways of reducing TAN and NOX concentrations and may allow substantially higher stocking densities. However, sludge removal may be the more acceptable option, given the need to meet strict regulatory requirements for discharge loads in some countries and the desire to reduce water intake to improve biosecurity.

  • Modeling Nitrogen Dynamics in intensive shrimp ponds: the role of sediment remineralization
    Aquaculture, 2004
    Co-Authors: M.a Burford, K Lorenzen
    Abstract:

    A mathematical model is used to investigate the role of sedimentation and remineralization in the sediment on Nitrogen (N) Dynamics in intensive shrimp culture ponds. The model describes the key processes involved in N cycling that underpin the Dynamics of total ammoniacal N (TAN), nitrate/nitrite (NOX) and chlorophyll a (CHL) concentrations and the sediment N pool. These parameters may, in high concentrations, impact negatively on the shrimp or the adjacent aquatic environment when water is discharged from ponds. The model was calibrated for an Australian commercial shrimp (Penaeus monodon) pond. Most N enters the pond system as TAN from shrimp excretion of dietary N and decomposition of wasted feed, and is subsequently taken up by phytoplankton, which, on senescence, is sedimented and remineralized. Sediment remineralization is the dominant source of TAN in the water column for all but the beginning of the production cycle. The remineralization rate of sedimented N was estimated at 6% day-1. Nonetheless, sediment acts as a net sink of N throughout the production cycle. The effect of management strategies, including increased stocking densities, water exchange and sludge (=sedimented material) removal, on water quality was examined. Model outputs show that using current shrimp farming techniques, with water exchange rates of 7% day-1, an increase in stocking densities above 60 animals m-2 would result in unacceptably high TAN concentrations. Both sludge removal and water exchange provide effective ways of reducing TAN and NOX concentrations and may allow substantially higher stocking densities. However, sludge removal may be the more acceptable option, given the need to meet strict regulatory requirements for discharge loads in some countries and the desire to reduce water intake to improve biosecurity.Griffith Sciences, Griffith School of EnvironmentFull Tex

M.a Burford - One of the best experts on this subject based on the ideXlab platform.

  • Modeling Nitrogen Dynamics in intensive shrimp ponds: the role of sediment remineralization
    Aquaculture, 2004
    Co-Authors: M.a Burford, K Lorenzen
    Abstract:

    Abstract A mathematical model is used to investigate the role of sedimentation and remineralization in the sediment on Nitrogen (N) Dynamics in intensive shrimp culture ponds. The model describes the key processes involved in N cycling that underpin the Dynamics of total ammoniacal N (TAN), nitrate/nitrite (NOX) and chlorophyll a (CHL) concentrations and the sediment N pool. These parameters may, in high concentrations, impact negatively on the shrimp or the adjacent aquatic environment when water is discharged from ponds. The model was calibrated for an Australian commercial shrimp ( Penaeus monodon ) pond. Most N enters the pond system as TAN from shrimp excretion of dietary N and decomposition of wasted feed, and is subsequently taken up by phytoplankton, which, on senescence, is sedimented and remineralized. Sediment remineralization is the dominant source of TAN in the water column for all but the beginning of the production cycle. The remineralization rate of sedimented N was estimated at 6% day −1 . Nonetheless, sediment acts as a net sink of N throughout the production cycle. The effect of management strategies, including increased stocking densities, water exchange and sludge (=sedimented material) removal, on water quality was examined. Model outputs show that using current shrimp farming techniques, with water exchange rates of 7% day −1 , an increase in stocking densities above 60 animals m −2 would result in unacceptably high TAN concentrations. Both sludge removal and water exchange provide effective ways of reducing TAN and NOX concentrations and may allow substantially higher stocking densities. However, sludge removal may be the more acceptable option, given the need to meet strict regulatory requirements for discharge loads in some countries and the desire to reduce water intake to improve biosecurity.

  • Modeling Nitrogen Dynamics in intensive shrimp ponds: the role of sediment remineralization
    Aquaculture, 2004
    Co-Authors: M.a Burford, K Lorenzen
    Abstract:

    A mathematical model is used to investigate the role of sedimentation and remineralization in the sediment on Nitrogen (N) Dynamics in intensive shrimp culture ponds. The model describes the key processes involved in N cycling that underpin the Dynamics of total ammoniacal N (TAN), nitrate/nitrite (NOX) and chlorophyll a (CHL) concentrations and the sediment N pool. These parameters may, in high concentrations, impact negatively on the shrimp or the adjacent aquatic environment when water is discharged from ponds. The model was calibrated for an Australian commercial shrimp (Penaeus monodon) pond. Most N enters the pond system as TAN from shrimp excretion of dietary N and decomposition of wasted feed, and is subsequently taken up by phytoplankton, which, on senescence, is sedimented and remineralized. Sediment remineralization is the dominant source of TAN in the water column for all but the beginning of the production cycle. The remineralization rate of sedimented N was estimated at 6% day-1. Nonetheless, sediment acts as a net sink of N throughout the production cycle. The effect of management strategies, including increased stocking densities, water exchange and sludge (=sedimented material) removal, on water quality was examined. Model outputs show that using current shrimp farming techniques, with water exchange rates of 7% day-1, an increase in stocking densities above 60 animals m-2 would result in unacceptably high TAN concentrations. Both sludge removal and water exchange provide effective ways of reducing TAN and NOX concentrations and may allow substantially higher stocking densities. However, sludge removal may be the more acceptable option, given the need to meet strict regulatory requirements for discharge loads in some countries and the desire to reduce water intake to improve biosecurity.Griffith Sciences, Griffith School of EnvironmentFull Tex

Longyuan Yang - One of the best experts on this subject based on the ideXlab platform.

  • Nitrogen Dynamics and microbial food web structure during a summer cyanobacterial bloom in a subtropical shallow well mixed eutrophic lake lake taihu china
    Hydrobiologia, 2007
    Co-Authors: Mark J Mccarthy, Peter J. Lavrentyev, Longyuan Yang, Lu Zhang, Yuwei Chen, Wayne S. Gardner
    Abstract:

    Nitrogen Dynamics and microbial food web structure were characterized in subtropical, eutrophic, large (2,338 km2), shallow (1.9 m mean depth), and polymictic Lake Taihu (China) in Sept–Oct 2002 during a cyanobacterial bloom. Population growth and industrialization are factors in trophic status deterioration in Lake Taihu. Sites for investigation were selected along a transect from the Liangxihe River discharge into Meiliang Bay to the main lake. Water column Nitrogen and microbial food web measurements were combined with sediment–water interface incubations to characterize and identify important processes related to system Nitrogen Dynamics. Results indicate a gradient from strong phosphorus limitation at the river discharge to Nitrogen limitation or co-limitation in the main lake. Denitrification in Meiliang Bay may drive main lake Nitrogen limitation by removing excess Nitrogen before physical transport to the main lake. Five times higher nutrient mineralization rates in the water column versus sediments indicate that sediment nutrient transformations were not as important as water column processes for fueling primary production. However, sediments provide a site for denitrification, which, along with Nitrogen fixation and other processes, can determine available nutrient ratios. Dissimilatory nitrate reduction to ammonium (DNRA) was important, relative to denitrification, only at the river discharge site, and Nitrogen fixation was observed only in the main lake. Reflecting Nitrogen cycling patterns, microbial food web structure shifted from autotrophic (phytoplankton dominated) at the river discharge to heterotrophic (bacteria dominated) in and near the main lake.

  • Effects of the zebra mussel on Nitrogen Dynamics and the microbial community at the sediment-water interface
    Aquatic Microbial Ecology, 2000
    Co-Authors: Peter J. Lavrentyev, Wayne S. Gardner, Longyuan Yang
    Abstract:

    A flow-through expenment was conducted on intact cores of sedunents from Saginaw Bay, Lake Huron, to examine how trophic interactions between filter-feeding bivalve mussels and microbial populations could affect Nitrogen Dynamics at the sediment-water interface. The zebra mussels used in this experiment removed a large proportion of protozoa and phytoplankton from the overlying water, particularly heterotrophic nanoplankton (up to 82 %), while bacterial population~ showed less change. A 3-fold decrease in the protozoan to bacterial carbon ratio corresponded to a 2.5-fold increase in relative ammonium removal rates as estimated from the dark loss of '5N-ammonium. Excretion by the bivalves also increased net ammonium flux to the water, thus elevating the total calculated area1 ammonium removal rates to about 6-fold over rates observed in the control treatment. These data suggest that filter-feedng bivalves may significantly affect Nitrogen transformation rates near the sediment-water interface by excreting ammonium and altering the microbial food web structure at the sediment-water interface.