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1.
Modeling nitrogen cycling in a coastal fresh water sediment 总被引:1,自引:0,他引:1
Increased nitrogen (N) loading to coastal marine and freshwater systems is occurring worldwide as a result of human activities.
Diagenetic processes in sediments can change the N availability in these systems, by supporting removal through denitrification
and burial of organic N (Norg) or by enhancing N recycling. In this study, we use a reactive transport model (RTM) to examine N transformations in a coastal
fresh water sediment and quantify N removal rates. We also assess the response of the sediment N cycle to environmental changes
that may result from increased salinity which is planned to occur at the site as a result of an estuarine restoration project.
Field results show that much of the Norg deposited on the sediment is currently remineralized to ammonium. A rapid removal of nitrate is observed in the sediment
pore water, with the resulting nitrate reduction rate estimated to be 130 μmol N cm−2 yr−1. A model sensitivity study was conducted altering the distribution of nitrate reduction between dissimilatory nitrate reduction
to ammonium (DNRA) and denitrification. These results show a 40% decline in sediment N removal as NO
3
−
reduction shifts from denitrification to DNRA. This decreased N removal leads to a shift in sediment-water exchange flux
of dissolved inorganic nitrogen (DIN) from near zero with denitrification to 133 μmol N cm−2 yr−1 if DNRA is the dominant pathway. The response to salinization includes a short-term release of adsorbed ammonium. Additional
changes expected to result from the estuarine restoration include: lower NO
3
−
concentrations and greater SO
4
2−
concentrations in the bottom water, decreased nitrification rates, and increased sediment mixing. The effect of these changes
on net DIN flux and N removal vary based on the distribution of DNRA versus denitrification, illustrating the need for a better
understanding of factors controlling this competition. 相似文献
2.
Sybil P. Seitzinger Lars Peter Nielsen Jane Caffrey Peter Bondo Christensen 《Biogeochemistry》1993,23(3):147-167
Measurements of denitrification using the acetylene inhibition,15N isotope tracer, and N2 flux methods were carried out concurrently using sediment cores from Vilhelmsborg sø, Denmark, in an attempt to clarify some of the limitations of each technique. Three experimental treatments of overlying water were used: control, nitrate enriched, and ammonia enriched water. The N2 flux and15N tracer experiments showed high rates of coupled nitrification/denitrification in the sediments. The acetylene inhibition method did not capture any coupled nitrification/denitrification. This could be explained by acetylene inhibition of nitrification. A combined15N tracer/acetylene inhibition experiment demonstrated that acetylene inhibition of N2O reduction was incomplete and the method, therefore, only measured approximately 50% of the denitrification due to nitrate from the overlying water. Similar rates of denitrification due to nitrate in the overlying water were measured by the N2 flux method and the acetylene inhibition method, after correcting for the 50% efficiency of acetylene inhibition. Rates of denitrification due to nitrate from the overlying water measured by the15N tracer method, however, were only approximately 35% or less of those measured by the acetylene inhibition or N2 flux methods. 相似文献
3.
Macrophyte presence is an indicator of enhanced denitrification and nitrification in sediments of a temperate restored agricultural stream 总被引:1,自引:0,他引:1
Stream macrophytes are often removed with their sediments to deepen stream channels, stabilize channel banks, or provide habitat
for target species. These sediments may support enhanced nitrogen processing. To evaluate sediment nitrogen processing, identify
seasonal patterns, and assess sediment processes relative to stream load, we measured denitrification and nitrification rates
in a restored third- to fourth-order agricultural stream, Black Earth Creek, Wisconsin, and estimated processing over a 10 km
reach. Our results show that sediments with submerged and emergent macrophytes (e.g., Potomageton spp. and Phalaris arudinacea) support greater denitrification rates than bare sediments (1.12 μmol N g−1 h−1 vs. 0.29). Sediments with macrophytes were not carbon limited and organic matter fraction was weakly correlated to denitrification.
The highest denitrification potential occurred in macrophyte beds (5.19 μmol N g−1 h−1). Nitrification rates were greater in emergent beds than bare sediments (1.07 μg N ml−1day−1 vs. 0.35) with the greatest nitrification rates during the summer. Total denitrification removal in sediments with macrophytes
was equivalent to 43% of the nitrate stream load (463.7 kg N day−1) during spring and nitrification in sediments with macrophytes was equivalent to 247% of summer ammonium load (3.5 kg N day−1). Although the in-channel connectivity to nitrogen rich water was limited, actual stream nitrogen loads could increase with
removal of macrophytes. Macrophyte beds and supporting fringing wetted areas are important if nitrogen management is a concern
for riparian stream restoration efforts. 相似文献
4.
Assessing Nitrification and Denitrification in the Seine River and Estuary Using Chemical and Isotopic Techniques 总被引:4,自引:0,他引:4
Mathieu Sebilo Gilles Billen Bernhard Mayer Daniel Billiou Micheline Grably Josette Garnier André Mariotti 《Ecosystems》2006,9(4):564-577
Downstream from metropolitan Paris (France), a large amount of ammonium is discharged into the Seine River by the effluents
of the wastewater treatment plant at Achères. To assess the extent of nitrification and denitrification in the water column,
concentrations and isotopic compositions of ammonium (δ15N–NH4+) and nitrate (δ15N–NO3−, δ18O–NO3−) were measured during summer low-flow conditions along the lower Seine and its estuary. The results indicated that most of
the ammonium released from the wastewater treatment plant is nitrified in the lower Seine River and its upper estuary, but
there was no evidence for water-column denitrification. In the lower part of the estuary, however, concentration and isotopic
data for nitrate were not consistent with simple mixing between riverine and marine nitrate. A significant departure of the
nitrate isotopic composition from what would be expected from simple mixing of freshwater and marine nitrates suggested coupled
nitrification and denitrification in the water, in spite of the apparent conservative behavior of nitrate. Denitrification
rates of approximately 0.02 mg N/L/h were estimated for this part of the estuary. 相似文献
5.
Spatial and Temporal Variability in Sediment Denitrification Within an Agriculturally Influenced Reservoir 总被引:2,自引:1,他引:1
Reservoirs are intrinsically linked to the rivers that feed them, creating a river–reservoir continuum in which water and
sediment inputs are a function of the surrounding watershed land use. We examined the spatial and temporal variability of
sediment denitrification rates by sampling longitudinally along an agriculturally influenced river–reservoir continuum monthly
for 13 months. Sediment denitrification rates ranged from 0 to 63 μg N2O g ash free dry mass of sediments (AFDM)−1 h−1 or 0–2.7 μg N2O g dry mass of sediments (DM)−1 h−1 at reservoir sites, vs. 0–12 μg N2O gAFDM−1 h−1 or 0–0.27 μg N2O gDM−1 h−1 at riverine sites. Temporally, highest denitrification activity traveled through the reservoir from upper reservoir sites
to the dam, following the load of high nitrate (NO3−-N) water associated with spring runoff. Annual mean sediment denitrification rates at different reservoir sites were consistently
higher than at riverine sites, yet significant relationships among theses sites differed when denitrification rates were expressed
per gDM vs. per gAFDM. There was a significant positive relationship between sediment denitrification rates and NO3−-N concentration up to a threshold of 0.88 mg NO3− -N l−1, above which it appeared NO3−-N was no longer limiting. Denitrification assays were amended seasonally with NO3−-N and an organic carbon source (glucose) to determine nutrient limitation of sediment denitrification. While organic carbon
never limited sediment denitrification, all sites were significantly limited by NO3−-N during fall and winter when ambient NO
3−-N was low. 相似文献
6.
To clarify the relationship between denitrification activity and dry–wet levels in the littoral wetland sediments of Lake
Biwa, Japan, denitrification rates and their regulating parameters (degree of dryness, redox potential, nitrate concentration)
were measured on different moisture sediments. Redox potential in sediments was higher in the exposed region in contact with
atmosphere than the flooded region covered with water. The nitrate concentration in interstitial waters was undetectable in
the flooded region. On the other hand, concentration in the exposed region increased with increase in the degree of sediment
dryness. The denitrification rate ranged from <0.001 to 0.88 μg N cm−3 h−1 in the exposed region and increased with the increase in the degree of dryness. In the flooded region, on the other hand,
no detectable rate (<0.001 μg N cm−3 h−1) was observed. This indicates that the rates in the exposed region were mainly influenced by nitrate concentration in the
interstitial waters accumulated by desiccation of sediments, whereas rates in the flooded region were strongly limited by
no accumulation of nitrate in the anaerobic conditions. The potential denitrification rate, under the application condition
of nitrate, ranged from 0.13 to 0.26 μg N cm−3 h−1 in the flooded region and from 0.77 to 1.5 μg N cm−3 h−1 in the exposed region. The potential rates in the flooded region had a tendency to be lower than those in the exposed region,
implying that the number of denitrifying bacteria in the flooded region was low due to inactivation of aerobic respiration
and denitrification in the denitrifying bacteria community. Kinetic parameters, maximum rate (V
max) and half-saturation constant (K
s) for denitrification were calculated on the experimental procedures of the wetting–drying cycles of sediments. Both parameters
decreased by the wetting treatment and increased by the drying treatment. The fluctuation of V
max values with wetting–drying cycles indicated that the number of denitrifying bacteria was influenced by aerobic respiration
and denitrification in the denitrifying bacteria community similar to the potential rates, and denitrifying enzyme was induced
by the nitrate supplied by nitrification accelerated through the drying process. On the other hand, the fluctuation of K
s values implied that members of denitrifying bacteria were shifted to members of high nitrate affinity by wetting treatment
and of low nitrate affinity by drying treatment. 相似文献
7.
Routing nitrate through backwaters of regulated floodplain rivers to increase retention could decrease loading to nitrogen
(N)-sensitive coastal regions. Sediment core determinations of N flux were combined with inflow–outflow fluxes to develop
mass balance approximations of N uptake and transformations in a flow-controlled backwater of the Upper Mississippi River
(USA). Inflow was the dominant nitrate source (>95%) versus nitrification and varied as a function of source water concentration
since flow was constant. Nitrate uptake length increased linearly, while uptake velocity decreased linearly, with increasing
inflow concentration to 2 mg l−1, indicating limitation of N uptake by loading. N saturation at higher inflow concentration coincided with maximum uptake
capacity, 40% uptake efficiency, and an uptake length 2 times greater than the length of the backwater. Nitrate diffusion
and denitrification in sediment accounted for 27% of the backwater nitrate retention, indicating that assimilation by other
biota or denitrification on other substrates were the dominant uptake mechanisms. Ammonium export from the backwater was driven
by diffusive efflux from the sediment. Ammonium increased from near zero at the inflow to a maximum mid-lake, then declined
slightly toward the outflow due to uptake during transport. Ammonium export was small compared to nitrate retention.
Handling editor: J. Padisak 相似文献
8.
Nitrification and denitrification response to varying periods of desiccation and inundation in a western Kansas stream 总被引:3,自引:0,他引:3
Changing environmental conditions and increased water consumption have transformed many historically perennial stream systems
into intermittent systems. Multiple drying and wetting events throughout the year might impact many stream processes including
nitrification and denitrification, key components of the nitrogen (N) cycle. During summer 2007, an experimental stream was
used to dry and then rewet stream sediments to determine the effects of desiccation and rewetting of stream sediment on nitrification
and denitrification potentials. Mean (±SE) nitrification and denitrification rates in sediment not dried (controls) were 0.431 ± 0.017 μg
NO3
−–N/cm2/h and 0.016 ± 0.002 μg N2O–N/cm2/h, respectively. As sediment samples dried, nitrification rates decreased. Rates in sediments dried less than 7 d recovered
to levels equal or greater than those in the controls within 1 d of being rewetted. Denitrification rates were not affected
by 1 d of drying, but samples dried greater than 1 d experienced reduced rates of denitrification. Denitrification in sediments
dried 7 d or less recovered by day seven of being rewetted. Nitrification and denitrification processes failed to fully recover
in sediments dried more than 7 d. These results demonstrate that alterations in stream’s hydrology can significantly affect
N-cycle processes. 相似文献
9.
Algesten G Sobek S Bergström AK Jonsson A Tranvik LJ Jansson M 《Microbial ecology》2005,50(4):529-535
We measured sediment production of carbon dioxide (CO2) and methane (CH4) and the net flux of CO2 across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were
made in situ under ambient light conditions. The flux of CO2 between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m−2 day−1 from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated
to dissolved organic carbon (DOC) concentration in the water (r2 = 0.61). The net flux of CO2 across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed
layer (r2 = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration.
Lakes with DOC concentrations <5.6 mg L−1 had net consumption of CO2 in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic
(<2.6 mg L−1) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In
addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water
column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources. 相似文献
10.
11.
Factors Controlling Sediment Denitrification in Midwestern Streams of Varying Land Use 总被引:1,自引:0,他引:1
We investigated controls on stream sediment denitrification in nine headwater streams in the Kalamazoo River Watershed, Michigan,
USA. Factors influencing denitrification were determined by using experimental assays based on the chloramphenicol-amended
acetylene inhibition technique. Using a coring technique, we found that sediment denitrification was highest in the top 5 cm
of the benthos and was positively related to sediment organic content. To determine the effect of overlying water quality
on sediment denitrification, first-order stream sediments were assayed with water from second- and third-order downstream
reaches, and often showed higher denitrification rates relative to assays using site-specific water from the first-order stream
reach. Denitrification was positively related to nitrate (NO3
−) concentration, suggesting that sediments may have been nutrient-limited. Using stream-incubated inorganic substrata of varying
size classes, we found that finer-grained sand showed higher rates of denitrification compared to large pebbles, likely due
to increased surface area per volume of substratum. Denitrification was measurable on both inorganic substrata and fine particulate
organic matter loosely associated with inorganic particles, and denitrification rates were related to organic content. Using
nutrient-amended denitrification assays, we found that sediment denitrification was limited by NO3
− or dissolved organic carbon (DOC, as dextrose) variably throughout the year. The frequency and type of limitation differed
with land use in the watershed: forested streams were NO3
−-limited or co-limited by both NO3
− and DOC 92% of the time, urban streams were more often NO3
−-limited than DOC-limited, whereas agricultural stream sediments were DOC-limited or co-limited but not frequently limited
by NO3
− alone. 相似文献
12.
Denitrification efficiency for defining critical loads of carbon in shallow coastal ecosystems 总被引:2,自引:2,他引:0
Denitrification efficiency [DE; (N2 − N/(DIN + N2 − N) × 100%)] as an indicator of change associated with nutrient over-enrichment was evaluated for 22 shallow coastal ecosystems
in Australia. The rate of carbon decomposition (which can be considered a proxy for carbon loading) is an important control
on the efficiency with which coastal sediments in depositional mud basins with low water column nitrate concentrations recycle
nitrogen as N2. The relationship between DE and carbon loading is due to changes in carbon and nitrate (NO3) supply associated with sediment biocomplexity. At the DE optimum (500–1,000 μmol m−2 h−1), there is an overlap of aerobic and anaerobic respiration zones (caused primarily by the existence of anaerobic micro-niches
within the oxic zone, and oxidized burrow structures penetrating into the anaerobic zone), which enhances denitrification
by improving both the organic carbon and nitrate supply to denitrifiers. On either side of the DE optimum zone, there is a
reduction in denitrification sites as the sediment loses its three-dimensional complexity. At low organic carbon loadings,
a thick oxic zone with low macrofauna biomass exists, resulting in limited anoxic sites for denitrification, and at high carbon
loadings, there is a thick anoxic zone and a resultant lack of oxygen for nitrification and associated NO3 production. We propose a trophic scheme for defining critical (sustainable) carbon loading rates and possible thresholds
for shallow coastal ecosystems based on the relationship between denitrification efficiency and carbon loading for 17 of the
22 Australian coastal ecosystems. The denitrification efficiency “optimum” occurs between carbon loadings of about 50 and
100 g C m−2 year−1. Coastal managers can use this simple trophic scheme to classify the current state of their shallow coastal ecosystems and
for determining what carbon loading rate is necessary to achieve any future state.
Guest editors: J. H. Andersen & D. J. Conley
Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of
Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark 相似文献
13.
Linkages between organic matter mineralization and denitrification in eight riparian wetlands 总被引:6,自引:4,他引:2
Sybil P. Seitzinger 《Biogeochemistry》1994,25(1):19-39
Denitrification (N2 production) and oxygen consumption rates were measured at ambient field nitrate concentrations during summer in sediments from eight wetlands (mixed hardwood swamps, cedar swamps, heath dominated shrub wetland, herbaceous peatland, and a wetland lacking live vegetation) and two streams. The study sites included wetlands in undisturbed watersheds and in watersheds with considerable agricultural and/or sewage treatment effluent input. Denitrification rates measured in intact cores of water-saturated sediment ranged from 20 to 260 mol N m-2 h-1 among the three undisturbed wetlands and were less variable (180 to 260 mol N M-2 h-1) among the four disturbed wetlands. Denitrification rates increased when nitrate concentrations in the overlying water were increased experimentally (1 up to 770 M), indicating that nitrate was an important factor controlling denitrification rates. However, rates of nitrate uptake from the overlying water were not a good predictor of denitrification rates because nitrification in the sediments also supplied nitrate for denitrification. Regardless of the dominant vegetation, pH, or degree of disturbance, denitrification rates were best correlated with sediment oxygen consumption rates (r
2 = 0.912) indicating a relationship between denitrification and organic matter mineralization and/or sediment nitrification rates. Rates of denitrification in the wetland sediments were similar to those in adjacent stream sediments. Rates of denitrification in these wetlands were within the range of rates previously reported for water-saturated wetland sediments and flooded soils using whole core15N techniques that quantify coupled nitrification/denitrification, and were higher than rates reported from aerobic (non-saturated) wetland sediments using acetylene block methods. 相似文献
14.
The River Seine, below Paris, receives the effluents from a large sewage treatment plant, increasing the ammonium concentration
up to 6 mgN.1− in late summer. Careful measurement of ammonium, nitrate and organic nitrogen during the downriver travel of the water masses
over 100 km below the outfall, along with direct determination of nitrification and benthic fluxes, allowed to establish a
budget of nitrogen transport and transformations in this reach of the river. Nitrification is shown to start after a distinct
period of several days required for the growth of a significant nitrifying bacterial population. Denitrification is active
in the upper layer of bottom sediments but absent from the water column. Comparison of our data with those published for the
period 1973–1976 shows that the nitrate load carried by the river has increased not only because of higher runoff of agricultural
nitrate in the upstream part of the watershed, but also as a result of the severe reduction in the rate of denitrification
processes, owing to the restoration of better oxygen conditions. 相似文献
15.
Pascal M. A. Boderie John J. G. Zwolsman Gijsbertus T. M. Van Eck Cornelis H. Van der Weijden 《Aquatic Ecology》1993,27(2-4):309-318
The Scheldt river drains a densely populated and industrialized area in northern France, western Belgium and the south-west Netherlands. Mineralization of the high organic load carried by the river leads to oxygen depletion in the water column and high concentrations of dissolved nitrogen and phosphorus compounds. Upon estuarine mixing, dissolved oxygen concentrations are gradually restored due to reaeration and dilution with sea water. The longitudinal redox gradient present in the Scheldt estuary strongly affects the geochemistry of nutrients. Dissolved nutrients in the water column and dissolved nitrogen species in sediment porewaters were determined for a typical summer and winter situation. Water column concentration-salinity plots showed conservative behaviour of dissolved Si during winter. During summer (and spring) dissolved Si may be completely removed from solution due to uptake by diatoms. The geochemistry of phosphorus was governed by inorganic and biological processes. The behaviour of nitrogen was controlled by denitrification in the anoxic fluvial estuary, followed by nitrification in the upper estuary (prior to oxygen regeneration). In addition, nitrogen was taken up during phytoplankton blooms in the lower estuary. Dissolved inorganic nitrogen species in porewaters from the upper 20 cm of sediments were obtained from a subtidal site in the middle of the lower estuary. Dissolved nutrient concentrations were low in the upper 10–15 cm of the sandy and organic poor (<1% POC) sediments mainly as a result of strong sediment mixing. The porewater profiles of ammonium and nitrate were evaluated quantitatively, using a one-dimensional steady-state diagenetic model. This coupled ammonium-nitrate model showed ammonification of organic matter to be restricted to the upper 4 to 7 cm of the sediments. Total nitrification ranged from 3.7–18.1 mmol m?2 d?1, converting all ammonium produced by ammonification. The net balance between nitrification and denitrification depended on the season. Nitrate was released from the sediments during winter but is taken up from the water column during summer. These results are in good agreement with data obtained from the independently calibrated water column model for the Scheldt Estuary (VAN GILSet al., 1993). 相似文献
16.
Hitoshi Iizumi Akihiko Hattori C.P. McRoy 《Journal of experimental marine biology and ecology》1980,47(2):191-201
The distribution of nitrate and nitrite in the interstitial water of the sediment of eelgrass (Zostera marina) bed of Izembek Lagoon, Alaska, were investigated. Their concentrations were relatively high (0 to 9.8 μg-at.N·1?1, average 4.8 for nitrate; 0 to 4.0 μ-at.N·1?1, average 1.9 for nitrite) although the sediments were anoxic and contained hydrogen sulphide. The rates of bacterial denitrification measured by 15N tracer technique ranged from 0.49×10?10 to 1.2 × 10?9 g-atN·g?1·h?1. When a steady state is maintained, the loss of nitrate and nitrite must be balanced by their production by bacterial nitrification. Experimentally determined rate of nitrification in the sediment was of the same order. A model experiment demonstrated that oxygen is transported from leaves to rhizomes and roots of eelgrass and released into the sediment. The oxygen is used for nitrification in the rhizosphere in anoxic sediments. 相似文献
17.
A one-dimensional model that couples water-column physics with pelagic and benthic biogeochemistry in a 50-m-deep water column
is used to demonstrate the importance of the sediment in the functioning of shallow systems, the eutrophication status of
the system, and the system’s resilience to oligotrophication. Two physical scenarios, a well-mixed and a stratified water
column, are considered and both are run along a gradient of increasing initial pelagic-dissolved inorganic nitrogen (DIN)
concentration. Where the mixed layer extends to the bottom, more nutrients and less light are available for growth. Under
low to moderately eutrophic conditions (pelagic DIN <30 mmol m−3), this leads to higher productivity in well-mixed waters, while the stratified system is more productive under highly eutrophic
conditions. Under stratification, the build-up of nitrate and depletion of oxygen below the mixed layer does not notably change
the functioning of the sediment as a sink for reactive nitrogen. In sediments underlying well-mixed waters, sedimentary denitrification,
fueled mainly by in situ nitrification, is slightly more important (8–15% of total benthic mineralization) than under stratified
waters (7–20%), where the influx of bottom-water nitrate is the most important nitrate source. As a consequence of this less
efficient removal of reactive nitrogen, the winter DIN concentrations are higher in the stratified scenario. The model is
used to estimate the long-term benefits of nutrient reduction scenarios and the timeframe under which the new steady-state
condition is approached. It is shown that a 50% reduction in external nitrogen inputs ultimately results in a reduction of
60–70% of the original pelagic DIN concentration. However, as the efflux of nitrogen from the sediment compensates part of
the losses in the water column, system oligotrophication is a slow process: after 20 years of reduced inputs, the pelagic
DIN concentrations still remain 2.7 mmol m−3 (mixed) and 3.9 mmol m−3 (stratified) above the ultimate DIN concentrations.
Guest editors: J. H. Andersen & D. J. Conley
Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of
Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark 相似文献
18.
Nitrification, denitrification, and nitrate ammonification in sediments of two coastal lagoons in Southern France 总被引:5,自引:3,他引:2
Summary Seasonal and diurnal variations in sediment-water fluxes of O2, NO
3
–
, and NH
4
+
as well as rates of nitrification, denitrification, and nitrate ammonification were determined in two different coastal lagoons of southern France: The seagrass (Zostera noltii) dominated tidal Bassin d'Arcachon and the dystrophic Etang du Prévost. Overall, denitrification rates in both Bassin d'Arcachon (<0.4 mmol m–2 d–1) and Etang du Prévost (<1 mmol m–2 d–1) were low. This was mainly caused by a combination of low NO
3
–
concentrations in the water column and a low nitrification activity within the sediment. In both Bassin d'Arcachon and Etang du Prévost, rates of nitrate ammonification were quantitatively as important as denitrification.Denitrification played a minor role as a nitrogen sink in both systems. In the tidal influenced Bassin d'Arcachon, Z. noltii was quantitatively more important than denitrification as a nitrogen sink due to the high assimilation rates of the plants. Throughout the year, Z. noltii stabilized the mudflats of the bay by its well- developed root matrix and controlled the nitrogen cycle due to its high uptake rates. In contrast, the lack of rooted macrophytes, and dominance of floating macroalgae, made nitrogen cycling in Etang du Prévost more unstable and unpredictable. Inhibition of nitrification and denitrification during the dystrophic crisis in the summer time increased the inorganic nitrogen flux from the sediment to the water column and thus increased the degree of benthic-pelagic coupling within this bay. During winter, however, benthic microalgae colonizing the sediment surface changed the sediment in the lagoon from being a nitrogen source to the over lying water to being a sink due to their high assimilation rates. It is likely, however, that this assimilated nitrogen is liberated to the water column at the onset of summer thereby fueling the extensive growth of the floating macroalgae, Ulva sp. The combination of a high nitrogen coupling between sediment and water column, little water exchange and low denitrification rates resulted in an unstable system with fast growing algal species such as phytoplankton and floating algae. 相似文献
19.
The short-term effects of sediment recolonisation by Nereis succinea on sediment-water column fluxes of oxygen and dissolved inorganic nitrogen, and rates of denitrification, were studied in microcosms of homogenised, sieved sediments. The added worms enhanced oxygen uptake by the sediments, due to the increased surface area provided by the burrow walls and the degree of stimulation was stable with time. Similarly, ammonium fluxes to the water column were stimulated by N. succinea, but declined over the 3 day incubation in all microcosms including the controls. Nitrate fluxes were generally greater in the faunated microcosms, but highly variable with time. Denitrification rates were positively stimulated by N. succinea populations, denitrification of water column nitrate was stimulated 10-fold in comparison to denitrification coupled to nitrification in the sediments. Rates of denitrification of water column nitrate were not significantly different from rates in undisturbed sediment cores with similar densities of N. succinea, whereas rates of coupled nitrification–denitrification were 3-fold lower in the experimental set-up. These results may reflect the relative growth rates of nitrifying and denitrifying bacteria, which allow more rapid colonisation of new burrow surfaces by denitrifier compared to nitrifier populations. The data indicate that recolonisation by burrowing macrofauna of the highly reduced sediments of the Sacca di Goro, Lagoon, Italy, following the annual dystrophic crisis, may play a significant role in the reoxidation and detoxification of the sediments. The increased rates of denitrification associated with the worm burrows, may promote nitrogen losses, but due to the low capacity of nitrifying bacteria to colonise the new burrow structures, these losses would be highly dependent upon water column nitrate concentrations. 相似文献
20.
Little is known on microbial activities in the sediments of large lowland rivers despite of their potentially high influence
on biogeochemical budgets. Based on field measurements in a variety of sedimentary habitats typical for a large lowland river
(Elbe, Germany), we present results on the abundance and production of sedimentary bacteria, the potential activity of a set
of extracellular enzymes, and potential nitrification and denitrification rates. A diving bell was used to access the sediments
in the central river channel, enabling us to sample down to 1 m sediment depth. Depth gradients of all measures of microbial
activity were controlled by sediment structure, hydraulic conditions, as well as by the supply with organic carbon and nitrogen.
Microbial heterotrophic activity was tightly coupled with the availability of carbon and nitrogen, whereas chemolithotrophic
activity (nitrification rate) was related to the available surface area of particles. In the central bed of the river, bacterial
production and extracellular enzyme activity remained high down to the deepest sediment layers investigated. Due to the large
inner surface area and their connectivity with the surface water, the shifting sediments in the central channel of the river
were microbially highly active There, vertically integrated bacterial production amounted to 0.95 g C m−3 h−1, which was 2.9 to 5.5 times higher than in the nearshore habitats. We conclude that carbon and nitrogen cycling in the river
is controlled by the live sediments of the central river channel, which thus represent a “liver function” in the river's metabolism. 相似文献