CHAPTER 29
Benthic Fluxes of Oxygen, Ammonium and Nitrate and
Coupled-uncoupled Denitrification Rates within Communities
of Three Different Primary Producer Growth Forms
M. BartolP, G. CastaldellP, D. Nizzoli 1 , L.G. Gatif2, and P. ViaroliI
ABSTRACT
Inorganic nitrogen and oxygen fluxes together with coupled-uncoupled denitrification were
studied in sediments covered by different primary producers (benthic microalgae, the floating
macroalga U/va rigida, and the rooted phanerogam Ruppia cirrhosa). High DIN (Dissolved
Inorganic Nitrogen) assimilation rates were measured for all the primary producers and resulted
in low denitrification rates, in particular at the Ulva and Ruppia colonised sites. The competition
for NH/ and N0 3 - between phototrophic organisms and nitrifiers-denitrifiers was particularly
strong when DIN concentrations in the water column were low. Despite algal uptake denitrification rates were appreciable (>200 llmol N m- 2 h- 1 ) in the site covered by benthic diatoms due
to high availability of NO)- in the water column and efficient coupling between nitrification and
denitrification. In the sites with macrophytes losses of N due to coupled-uncoupled denitrification were negligible compared to assimilation rates. Most of the organic nitrogen pool in the
Ulva biomass is probably recycled in the water column while a consistent part of the N stored in
Ruppia may be buried in the sediment.
Introduction
In estuaries and shallow water impoundments
primary producers can markedly affect Ncycling in many direct and indirect ways. Benthic
micro algae can control at the sediment-water
interface the diffusion of combined nitrogen to
or from the sediment through their assimilation
activity and thus compete with nitrifiers and
denitrifiers for inorganic nitrogen. The influence
of benthic microalgae on N-cycling at the sediment-water interface can be attributed to a combination of factors including: ammonium limitation, high pH and 02 concentrations, COzlimitation and organic excretion products (Henriksen
and Kemp 1988; Sundback and Graneli 1988;
Nielsen et al. 1990; Nielsen and Sloth 1994).
Photosynthesis at the sediment-water interface
can expand the horizon of oxic sediment
(Revsbech et al. 1981) with a positive effect on
nitrifiers-denitrifiers but conversely remove
NH/ and CO 2 from the porewater and increase
the pH to values up to 9-10 units, thus inhibiting
the activity of nitrifiers and consequently denitrifiers (Rasmussen et al. 1983; Focht and
Verstraete 1977; Henriksen et al.1984).
Floating macro algae have very high primary
production rates which are sustained by significant amounts of DIN (Dissolved Inorganic
Nitrogen) (Sand-Jensen and Borum 1991; Borum
1996). Whilst, part of the nitrogen requirement
of macro algal biomass production is probably
due to internal recycling of N) most of it comes
from the water column. Macroalgal mats can
strongly influence the pool of DIN in the water
column and may act as a significant sink of inorganic nitrogen during the growth season.
Assimilation of N0 3 - is considered to be a much
more important sink for N compared to denitrification. in particular where macroalgal mats
attain biomass values over 200-300 gdwm-2 (Naldi
1994). Although, macroalgal uptake can be a
major sink for DIN it is likely that the biomass
becomes aN-source for the system when it is
decomposed and during the frequent collapses
occurring in summer, the so called "dystrophic
crises" (Viaroli et al. 1996a).
Rooted macrophytes can control sediment1 Dipartimento di Sdenze Ambientali, Universit1t di Parma, Parco Area delle Sdenze 33A. 43100 Parma, Italy
2 Dipartimento di Biologia Evolutiva, Universita di Ferrara, Via Borsari, 44100 Ferrara, Italy
F.M. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag Italia 2001
Benthic Fluxes of Oxygen, Ammonium and Nitrate and
Coupled-uncoupled Denitrification Rates within Communities
of Three Different Primary Producer Growth Forms
M. BartolP, G. CastaldellP, D. Nizzoli 1 , L.G. Gatif2, and P. ViaroliI
ABSTRACT
Inorganic nitrogen and oxygen fluxes together with coupled-uncoupled denitrification were
studied in sediments covered by different primary producers (benthic microalgae, the floating
macroalga U/va rigida, and the rooted phanerogam Ruppia cirrhosa). High DIN (Dissolved
Inorganic Nitrogen) assimilation rates were measured for all the primary producers and resulted
in low denitrification rates, in particular at the Ulva and Ruppia colonised sites. The competition
for NH/ and N0 3 - between phototrophic organisms and nitrifiers-denitrifiers was particularly
strong when DIN concentrations in the water column were low. Despite algal uptake denitrification rates were appreciable (>200 llmol N m- 2 h- 1 ) in the site covered by benthic diatoms due
to high availability of NO)- in the water column and efficient coupling between nitrification and
denitrification. In the sites with macrophytes losses of N due to coupled-uncoupled denitrification were negligible compared to assimilation rates. Most of the organic nitrogen pool in the
Ulva biomass is probably recycled in the water column while a consistent part of the N stored in
Ruppia may be buried in the sediment.
Introduction
In estuaries and shallow water impoundments
primary producers can markedly affect Ncycling in many direct and indirect ways. Benthic
micro algae can control at the sediment-water
interface the diffusion of combined nitrogen to
or from the sediment through their assimilation
activity and thus compete with nitrifiers and
denitrifiers for inorganic nitrogen. The influence
of benthic microalgae on N-cycling at the sediment-water interface can be attributed to a combination of factors including: ammonium limitation, high pH and 02 concentrations, COzlimitation and organic excretion products (Henriksen
and Kemp 1988; Sundback and Graneli 1988;
Nielsen et al. 1990; Nielsen and Sloth 1994).
Photosynthesis at the sediment-water interface
can expand the horizon of oxic sediment
(Revsbech et al. 1981) with a positive effect on
nitrifiers-denitrifiers but conversely remove
NH/ and CO 2 from the porewater and increase
the pH to values up to 9-10 units, thus inhibiting
the activity of nitrifiers and consequently denitrifiers (Rasmussen et al. 1983; Focht and
Verstraete 1977; Henriksen et al.1984).
Floating macro algae have very high primary
production rates which are sustained by significant amounts of DIN (Dissolved Inorganic
Nitrogen) (Sand-Jensen and Borum 1991; Borum
1996). Whilst, part of the nitrogen requirement
of macro algal biomass production is probably
due to internal recycling of N) most of it comes
from the water column. Macroalgal mats can
strongly influence the pool of DIN in the water
column and may act as a significant sink of inorganic nitrogen during the growth season.
Assimilation of N0 3 - is considered to be a much
more important sink for N compared to denitrification. in particular where macroalgal mats
attain biomass values over 200-300 gdwm-2 (Naldi
1994). Although, macroalgal uptake can be a
major sink for DIN it is likely that the biomass
becomes aN-source for the system when it is
decomposed and during the frequent collapses
occurring in summer, the so called "dystrophic
crises" (Viaroli et al. 1996a).
Rooted macrophytes can control sediment1 Dipartimento di Sdenze Ambientali, Universit1t di Parma, Parco Area delle Sdenze 33A. 43100 Parma, Italy
2 Dipartimento di Biologia Evolutiva, Universita di Ferrara, Via Borsari, 44100 Ferrara, Italy
F.M. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag Italia 2001