共查询到20条相似文献,搜索用时 31 毫秒
1.
Rosa Gómez M. Isabel Arce J. Javier Sánchez M. del Mar Sánchez-Montoya 《Hydrobiologia》2012,679(1):43-59
Mediterranean climates predispose aquatic systems to both flood and drought periods, therefore, stream sediments may be exposed
to desiccation periods. Changes in oxygen concentrations and sediment water content influence the biotic processes implicated
in nitrogen dynamics. The objectives of this study were to identify (1) the changes of inorganic nitrogen in stream sediments
during the transition from wet to dry conditions, and (2) the underlying processes in N dynamics and its regulation. Extractable
sediment NO3
−-N and NH4
+-N, organic matter and extractable organic carbon content were assessed during natural desiccation in microcosms with sediments
from an intermittent Mediterranean stream. In agreement with our initial hypothesis, our results showed how the NO3
−-N content of the sediment was enhanced during the first 10 days of sediment drying, whereas NH4
+-N was lost by 14 days post-drying. During the first 10 days, sediment desiccation seemed to stimulate the net N-mineralization
and net nitrification from sediments. Afterwards, the extractable NO3
−-N concentration sharply dropped, which may be attributed to lower ammonium-oxidation rates as ammonium and organic matter
are depleted, and to an increase in NO3
−-N consumption by microbial populations. Denitrification was inhibited, with a significant decrease as % water-filled pore
space lowered. We hypothesize that the sediment inorganic N content enhanced during sediment desiccation could be released
as part of the N pulse observed after sediment rewetting. However, the stream N availability after rewetting dried sediments
would differ depending on desiccation period duration. 相似文献
2.
Contrasting nutrient exports from a forested and an agricultural catchment in south-eastern Australia 总被引:1,自引:0,他引:1
Dissolved organic carbon (DOC) and total and inorganic nitrogen and phosphorus concentrations were determined over 3 years
in headwater streams draining two adjacent catchments. The catchments are currently under different land use; pasture/grazing
vs plantation forestry. The objectives of the work were to quantify C and nutrient export from these landuses and elucidate
the factors regulating export. In both catchments, stream water dissolved inorganic nutrient concentrations exhibited strong
seasonal variations. Concentrations were highest during runoff events in late summer and autumn and rapidly declined as discharge
increased during winter and spring. The annual variation of stream water N and P concentrations indicated that these nutrients
accumulated in the catchments during dry summer periods and were flushed to the streams during autumn storm events. By contrast,
stream water DOC concentrations did not exhibit seasonal variation.
Higher DOC and NO3
− concentrations were observed in the stream of the forest catchment, reflecting greater input and subsequent breakdown of
leaf-litter in the forest catchment. Annual export of DOC was lower from the forested catchment due to the reduced discharge
from this catchment. In contrast however, annual export of nitrate was higher from the forest catchment suggesting that there
was an additional NO3
− source or reduction of a NO3
− sink. We hypothesize that the denitrification capacity of the forested catchment has been significantly reduced as a consequence
of increased evapotranspiration and subsequent decrease in streamflow and associated reduction in the near stream saturated
area. 相似文献
3.
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
4.
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
5.
Jonathan M. O’Brien Walter K. Dodds Kymberly C. Wilson Justin N. Murdock Jessica Eichmiller 《Biogeochemistry》2007,84(1):31-49
We conducted 15NO3− stable isotope tracer releases in nine streams with varied intensities and types of human impacts in the upstream watershed
to measure nitrate (NO3−) cycling dynamics. Mean ambient NO3− concentrations of the streams ranged from 0.9 to 21,000 μg l−1 NO3−–N. Major N-transforming processes, including uptake, nitrification, and denitrification, all increased approximately two
to three orders of magnitude along the same gradient. Despite increases in transformation rates, the efficiency with which
stream biota utilized available NO3−-decreased along the gradient of increasing NO3−. Observed functional relationships of biological N transformations (uptake and nitrification) with NO3− concentration did not support a 1st order model and did not show signs of Michaelis–Menten type saturation. The empirical
relationship was best described by a Efficiency Loss model, in which log-transformed rates (uptake and nitrification) increase
with log-transformed nitrate concentration with a slope less than one. Denitrification increased linearly across the gradient
of NO3− concentrations, but only accounted for ∼1% of total NO3− uptake. On average, 20% of stream water NO3− was lost to denitrification per km, but the percentage removed in most streams was <5% km−1. Although the rate of cycling was greater in streams with larger NO3− concentrations, the relative proportion of NO3− retained per unit length of stream decreased as NO3− concentration increased. Due to the rapid rate of NO3− turnover, these streams have a great potential for short-term retention of N from the landscape, but the ability to remove
N through denitrification is highly variable. 相似文献
6.
The influence of land use on potential fates of nitrate (NO3
−) in stream ecosystems, ranging from denitrification to storage in organic matter, has not been documented extensively. Here,
we describe the Pacific Northwest component of Lotic Intersite Nitrogen eXperiment, phase II (LINX II) to examine how land-use
setting influences fates of NO3
− in streams. We used 24 h releases of a stable isotope tracer (15NO3-N) in nine streams flowing through forest, agricultural, and urban land uses to quantify NO3
− uptake processes. NO3
− uptake lengths varied two orders of magnitude (24–4247 m), with uptake rates (6.5–158.1 mg NO3-N m−2 day−1) and uptake velocities (0.1–2.3 mm min−1) falling within the ranges measured in other LINX II regions. Denitrification removed 0–7% of added tracer from our streams.
In forest streams, 60.4 to 77.0% of the isotope tracer was exported downstream as NO3
−, with 8.0 to 14.8% stored in wood biofilms, epilithon, fine benthic organic matter, and bryophytes. Agricultural and urban
streams with streamside forest buffers displayed hydrologic export and organic matter storage of tracer similar to those measured
in forest streams. In agricultural and urban streams with a partial or no riparian buffer, less than 1 to 75% of the tracer
was exported downstream; much of the remainder was taken up and stored in autotrophic organic matter components with short
N turnover times. Our findings suggest restoration and maintenance of riparian forests can help re-establish the natural range
of NO3
− uptake processes in human-altered streams. 相似文献
7.
We evaluated (1) the longitudinal pattern of stream chemistry and (2) the effects of the riparian zone on this longitudinal
pattern for nitrate (NO3
−), dissolved organic carbon (DOC), and total dissolved iron (Fe). We selected two small watersheds; the “southern watershed”
had an extending riparian wetland and the “northern watershed” had a narrow riparian area. Stream NO3
− concentrations decreased from the spring to outlet of both watersheds. In the southern watershed, stream DOC concentration
decreased from the spring to midstream and then increased to the outlet. Stream Fe concentration in the southern watershed
longitudinally increased. On the other hand, the northern watershed exhibited no longitudinal pattern for DOC and Fe concentrations.
In both watersheds, while NO3
− concentrations in the soil and ground water were lower than those in the stream waters, DOC and Fe concentrations exhibited
the opposite patterns. The longitudinal decreases of NO3
− concentrations in both streams and increase of stream Fe in the southern watershed mainly resulted from the inflow of the
soil and ground water to the stream. The decrease in stream DOC from the spring to midstream in the southern watershed was
due to the deep groundwater having low DOC, while the subsequent increase to the surrounding soil and ground water. Moreover,
considerations of stream solute flow with soil and ground water chemistry suggested other mechanisms adding NO3
− and removing/diluting DOC and Fe, especially for the northern watershed; coexistence of oxidizing and reducing conditions
in the riparian zone might control the longitudinal concentration change in the stream water chemistry. 相似文献
8.
Nitrate reduction in sediments of lowland tropical streams draining swamp forest in Costa Rica: An ecosystem perspective 总被引:2,自引:1,他引:1
Nitrate reduction and denitrification were measured in swamp forest streams draining lowland rain forest on Costa Rica's Atlantic slope foothills using the C2H2-block assay and sediment-water nutrient fluxes. Denitrification assays using the C2H2-block technique indicated that the full suite of denitrifying enzymes were present in the sediment but that only a small fraction of the functional activity could be expressed without adding NO3
–. Under optimal conditions, denitrification enzyme activity averaged 15 nmoles cm–3 sediment h–1. Areal NO3
– reduction rates measured from NO3
– loss in the overlying water of sediment-water flux chambers ranged from 65 to 470 umoles m–2 h–1. Oxygen loss rates accompanying NO3
– depletion averaged 750 umoles m–2 h–1. Corrected for denitrification of NO3
– oxidized from NH4
+ in the sediment, gross NO3
– reduction rates increase by 130 umoles m–2 h–1, indicating nitrification may be the predominant source of NO3
– for NO3
– reduction in swamp forest stream sediments. Under field conditions approximately 80% of the increase in inorganic N mass along a 1250-m reach of the Salto River was in the form of NO3
– with the balance NH4
+ . Scrutiny of potential inorganic N sources suggested that mineralized N released from the streambed was a major source of the inorganic N increase. Despite significant NO3
– reduction potential, swamp forest stream sediments appear to be a source of inorganic N to downstream communities. 相似文献
9.
CLAY P. ARANGO JENNIFER L. TANK JAMIE L. SCHALLER TODD V. ROYER MELODY J. BERNOT MARK B. DAVID 《Freshwater Biology》2007,52(7):1210-1222
1. Anthropogenic activities have increased reactive nitrogen availability, and now many streams carry large nitrate loads to coastal ecosystems. Denitrification is potentially an important nitrogen sink, but few studies have investigated the influence of benthic organic carbon on denitrification in nitrate‐rich streams. 2. Using the acetylene‐block assay, we measured denitrification rates associated with benthic substrata having different proportions of organic matter in agricultural streams in two states in the mid‐west of the U.S.A., Illinois and Michigan. 3. In Illinois, benthic organic matter varied little between seasons (5.9–7.0% of stream sediment), but nitrate concentrations were high in summer (>10 mg N L−1) and low (<0.5 mg N L−1) in autumn. Across all seasons and streams, the rate of denitrification ranged from 0.01 to 4.77 μg N g−1 DM h−1 and was positively related to stream‐water nitrate concentration. Within each stream, denitrification was positively related to benthic organic matter only when nitrate concentration exceeded published half‐saturation constants. 4. In Michigan, streams had high nitrate concentrations and diverse benthic substrata which varied from 0.7 to 72.7% organic matter. Denitrification rate ranged from 0.12 to 11.06 μg N g−1 DM h−1 and was positively related to the proportion of organic matter in each substratum. 5. Taken together, these results indicate that benthic organic carbon may play an important role in stream nitrogen cycling by stimulating denitrification when nitrate concentrations are high. 相似文献
10.
Urban streams often contain elevated concentrations of nitrogen (N) which can be amplified in systems receiving effluent from
wastewater treatment plants (WWTP). In this study, we evaluated the importance of denitrification in a stream draining urban
Greensboro, NC, USA, using two approaches: (1) natural abundance of 15N–NO3− in conjunction with background NO3−–N concentrations along a 7 km transect downstream of a WWTP; and (2) C2H2 block experiments at three sites and at three habitat types within each site. Overall lack of a longitudinal pattern of δ15N–NO3− and NO3−–N, combined with high concentrations of NO3−–N suggested that other factors were controlling NO3−–N flux in the study transect. However, denitrification did appear to be significant along one portion of the transect. C2H2 block experiments showed that denitrification rates were much higher downstream of the WWTP compared to upstream, and showed
that denitrification rates were highest in erosional and depositional areas downstream of the WWTP and in erosional areas
upstream of the plant. Thus, the combination of the two methods for evaluating denitrification provided more insight into
the spatial dynamics of denitrification activity than either approach alone. Denitrification appeared to be a significant
sink for NO3−–N upstream of the WWTP, but not downstream. Approximately 46% of the total NO3−–N load was removed via denitrification in the upstream, urban section of the stream, while only 2.3% of NO3−–N was lost downstream of the plant. This result suggests that controlling NO3−–N loading from the plant could result in considerable improvement of downstream water quality. 相似文献
11.
Since 1987 we have studied weekly change in winter (December–April) precipitation, snowpack, snowmelt, soil water, and stream
water solute flux in a small (176-ha) Northern Michigan watershed vegetated by 65–85 year-old northern hardwoods. Our primary
study objective was to quantify the effect of change in winter temperature and precipitation on watershed hydrology and solute
flux. During the study winter runoff was correlated with precipitation, and forest soils beneath the snowpack remained unfrozen.
Winter air temperature and soil temperature beneath the snowpack increased while precipitation and snowmelt declined. Atmospheric
inputs declined for H+, NO3−, NH4+, dissolved inorganic nitrogen (DIN), and SO42−. Replicated plot-level results, which could not be directly extrapolated to the watershed scale, showed 90% of atmospheric
DIN input was retained in surface shallow (<15 cm deep) soils while SO42− flux increased 70% and dissolved organic carbon (DOC) 30-fold. Most stream water base cation (CB), HCO3−, and Cl− concentrations declined with increased stream water discharge, K+, NO3−, and SO42− remained unchanged, and DOC and dissolved organic nitrogen (DON) increased. Winter stream water solute outputs declined or
were unchanged with time except for NO3− and DOC which increased. DOC and DIN outputs were correlated with the percentage of winter runoff and stream discharge that
occurred when subsurface flow at the plot-level was shallow (<25 cm beneath Oi). Study results suggest that the percentage
of annual runoff occurring as shallow lateral subsurface flow may be a major factor regulating solute outputs and concentrations
in snowmelt-dominated ecosystems. 相似文献
12.
Timothy J. Hoellein Jennifer L. Tank John J. Kelly Emma J. Rosi-Marshall 《Hydrobiologia》2010,649(1):331-345
Humans have increased the availability of nutrients including nitrogen and phosphorus worldwide; therefore, understanding
how microbes process nutrients is critical for environmental conservation. We examined nutrient limitation of biofilms colonizing
inorganic (fritted glass) and organic (cellulose sponge) substrata in spring, summer, and autumn in three streams in Michigan,
USA. Biofilms were enriched with nitrate (NO3
−), phosphate (PO4
3−), ammonium (NH4
+), NO3
− + PO4
3−, NH4
+ + PO4
3−, or none (control). We quantified biofilm structure and function as chlorophyll a (i.e., primary producer biomass) and community respiration on all substrata. In one stream, we characterized bacterial and
fungal communities on cellulose in autumn using clone library sequencing and denaturing gradient gel electrophoresis to determine
if community structure was linked to nutrient limitation status. Despite oligotrophic conditions, primary producer biomass
was infrequently nutrient limited. In contrast, respiration on organic substrata was frequently limited by N + P combinations.
We found no difference between biofilm response to NH4
+ versus NO3
− enrichment, although the response to both N-species was positively related to water column PO4
3− concentrations and temperature. Molecular analysis for fungal community composition suggested no relationship to nutrient
limitation, but the dominant members of the bacterial community on cellulose were different on NO3
−, PO43, and NO3
− + PO4
3− treatments relative to control, NH4
+, and NH4
+ + PO4
3− treatments, which matched patterns for biofilm respiration rates from each treatment. Our results show discrete patterns
of nutrient limitation dependent upon substratum type and season, and imply changes in bacterial community structure and function
may be linked following nutrient enrichment in streams. 相似文献
13.
Nathaniel B. Weston William P. Porubsky Vladimir A. Samarkin Matthew Erickson Stephen E. Macavoy Samantha B. Joye 《Biogeochemistry》2006,77(3):375-408
Porewater equilibration samplers were used to obtain porewater inventories of inorganic nutrients (NH4+, NOx, PO43−), dissolved organic carbon (DOC) and nitrogen (DON), sulfate (SO42−), dissolved inorganic carbon (DIC), hydrogen sulfide (H2S), chloride (Cl−), methane (CH4) and reduced iron (Fe2+) in intertidal creek-bank sediments at eight sites in three estuarine systems over a range of salinities and seasons. Sulfate
reduction (SR) rates and sediment particulate organic carbon (POC) and nitrogen (PON) were also determined at several of the
sites. Four sites in the Okatee River estuary in South Carolina, two sites on Sapelo Island, Georgia and one site in White
Oak Creek, Georgia appeared to be relatively pristine. The eighth site in Umbrella Creek, Georgia was directly adjacent to
a small residential development employing septic systems to handle household waste. The large data set (>700 porewater profiles)
offers an opportunity to assess system-scale patterns of porewater biogeochemical dynamics with an emphasis on DOC and DON
distributions. SO42− depletion (SO42−)Dep was used as a proxy for SR, and (SO42−)Dep patterns agreed with measured (35S) patterns of SR. There were significant system-scale correlations between the inorganic products of terminal metabolism
(DIC, NH4+ and PO43−) and (SO42−)Dep, and SR appeared to be the dominant terminal carbon oxidation pathway in these sediments. Porewater inventories of DIC and
(SO42−)Dep indicate a 2:1 stoichiometry across sites, and the C:N ratio of the organic matter undergoing mineralization was between
7.5 and 10. The data suggest that septic-derived dissolved organic matter with a C:N ratio below 6 fueled microbial metabolism
and SR at a site with development in the upland. Seasonality was observed in the porewater inventories, but temperature alone
did not adequately describe the patterns of (SO42−)Dep, terminal metabolic products (DIC, NH4+, PO43−), DOC and DON, and SR observed in this study. It appears that production and consumption of labile DOC are tightly coupled
in these sediments, and that bulk DOC is likely a recalcitrant pool. Preferential hydrolysis of PON relative to POC when overall
organic matter mineralization rates were high appears to drive the observed patterns in POC:PON, DOC:DON and DIC:DIN ratios.
These data, along with the weak seasonal patterns of SR and organic and inorganic porewater inventories, suggest that the
rate of hydrolysis limits organic matter mineralization in these intertidal creek-bank sediments. 相似文献
14.
Abstract
Sugar maple (Acer saccharum Marsh.)-dominated northern hardwood forests of the Great Lakes Region commonly receive elevated levels of atmospheric nitrate
(NO3−) deposition, which can alter belowground carbon (C) cycling. Past research has demonstrated that chronic experimental NO3− deposition (3 g N m−2 y−1 above ambient) elicits a threefold increase in the leaching loss of dissolved organic carbon (DOC). Here, we used DOC collected
from tension-cup lysimeters to test whether increased DOC export under experimental NO3− deposition originated from forest floor or mineral soil organic matter (SOM). We used DOC radiocarbon dating to quantify
C sources and colorimetric assays to measure DOC aromaticity and soluble polyphenolic content. Our results demonstrated that
DOC exports are primarily derived from new C (<50-years-old) in the forest floor under both ambient and experimental NO3− deposition. Experimental NO3− deposition increased soluble polyphenolic content from 25.03 ± 4.26 to 49.19 ± 4.23 μg phenolic C mg DOC−1, and increased total aromatic content as measured by specific UV absorbance. However, increased aromatic compounds represented
a small fraction (<10%) of the total observed increased DOC leaching. In combination, these findings suggest that experimental
NO3− deposition has altered the production or retention as well as phenolic content of DOC formed in forest floor, however exact
mechanisms are uncertain. Further elucidation of the mechanism(s) controlling enhanced DOC leaching is important for understanding
long-term responses of Great Lakes forests to anthropogenic N deposition and the consequences of those responses for aquatic
ecosystems. 相似文献
15.
Denitrification activity and oxygen dynamics in Arctic sea ice 总被引:1,自引:0,他引:1
Søren Rysgaard Ronnie N. Glud Mikael K. Sejr Martin E. Blicher Henrik J. Stahl 《Polar Biology》2008,31(5):527-537
Denitrification and oxygen dynamics were investigated in the sea ice of Franklin Bay (70°N), Canada. These investigations
were complemented with measurements of denitrification rates in sea ice from different parts of the Arctic (69°N–85°N). Potential
for bacterial denitrification activity (5–194 μmol N m−2 day−1) and anammox activity (3–5 μmol N m−2 day−1) in melt water from both first-year and multi-year sea ice was found. These values correspond to 27 and 7%, respectively,
of the benthic denitrification and anammox activities in Arctic sediments. Although we report only potential denitrification
and anammox rates, we present several indications that active denitrification in sea ice may occur in Franklin Bay (and elsewhere):
(1) despite sea ice-algal primary production in the lower sea ice layers, heterotrophic activity resulted in net oxygen consumption
in the sea ice of 1–3 μmol l−1 sea ice per day at in situ light conditions, suggesting that O2 depletion may occur prior to the spring bloom. (2) The ample organic carbon (DOC) and NO3
− present in sea ice may support an active denitrification population. (3) Measurements of O2 conditions in melted sea ice cores showed very low bulk concentrations, and in some cases anoxic conditions prevailed. (4)
Laboratory studies using planar optodes for measuring the high-resolution two-dimensional O2 distributions in sea ice confirmed the very dynamic and heterogeneous O2 distribution in sea ice, displaying a mosaic of microsites of high and low O2 concentrations. Brine enclosures and channels were strongly O2 depleted in actively melting sea ice, and anoxic conditions in parts of the brine system would favour anaerobic processes. 相似文献
16.
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
17.
Wetlands are often highly effective nitrogen (N) sinks. In the Lake Waco Wetland (LWW), near Waco, Texas, USA, nitrate (NO3−) concentrations are reduced by more than 90% in the first 500 m downstream of the inflow, creating a distinct gradient in
NO3− concentration along the flow path of water. The relative importance of sediment denitrification (DNF), dissimilatory NO3− reduction to ammonium (DNRA), and N2 fixation were examined along the NO3− concentration gradient in the LWW. “Potential DNF” (hereafter potDNF) was observed in all months and ranged from 54 to 278 μmol N m−2 h−1. “Potential DNRA” (hereafter potDNRA) was observed only in summer months and ranged from 1.3 to 33 μmol N m−2 h−1. Net N2 flux ranged from 184 (net denitrification) to −270 (net N2 fixation) μmol N m−2 h−1. Nitrogen fixation was variable, ranging from 0 to 426 μmol N m−2 h−1, but high rates ranked among the highest reported for aquatic sediments. On average, summer potDNRA comprised only 5% (±2%
SE) of total NO3− loss through dissimilatory pathways, but was as high as 36% at one site where potDNF was consistently low. Potential DNRA
was higher in sediments with higher sediment oxygen demand (r
2 = 0.84), and was related to NO3− concentration in overlying water in one summer (r
2 = 0.81). Sediments were a NO3− sink and accounted for 50% of wetland NO3− removal (r
2 = 0.90). Sediments were an NH4+ source, but the wetland was often a net NH4+ sink. Although DNRA rates in freshwater wetlands may rival those observed in estuarine systems, the importance of DNRA in
freshwater sediments appears to be minor relative to DNF. Furthermore, sediment N2 fixation can be extremely high when NO3− in overlying water is consistently low. The data suggest that newly fixed N can support sustained N transformation processes
such as DNF and DNRA when surface water inorganic N supply rates are low. 相似文献
18.
A portion of nitrate (NO
3
−
), a final breakdown product of nitrogen (N) fertilizers, applied to soils and/or that produced upon decomposition of organic
residues in soils may leach into groundwater. Nitrate levels in water excess of 10 mg L−1 (NO3–N) are undesirable as per drinking water quality standards. Nitrate concentrations in surficial groundwater can vary substantially
within an area of citrus grove which receives uniform N rate and irrigation management practice. Therefore, differences in
localized conditions which can contribute to variations in gaseous loss of NO
3
−
in the vadose zone and in the surficial aquifer can affect differential concentrations of NO3–N in the groundwater at different points of sampling. The denitrification capacity and potential in a shallow vadose zone
soil and in surficial groundwater were studied in two large blocks of a citrus grove of ‘Valencia’ orange trees (Citrus sinensis
(L.) Obs.) on Rough lemon rootstock ( Citrus jambhiri (L.)) under a uniform N rate and irrigation program. The NO3–N concentration in the surficial groundwater sampled from four monitoring wells (MW) within each block varied from 5.5- to
6.6-fold. Soil samples were collected from 0 to 30, 30 to 90, or 90 to 150 cm depths, and from the soil/groundwater interface
(SGWI). Groundwater samples from the monitoring wells (MW) were collected prior to purging (stagnant water) and after purging
five well volumes. Without the addition of either C or N, the denitrification capacity ranged from 0.5 to 1.53, and from 0.0
to 2.25 mg N2O–N kg−1 soil at the surface soil and at the soil/groundwater interface, respectively. The denitrification potential increased by
100-fold with the addition of 200 mg kg−1 each of N and C. The denitrification potential in the groundwater also followed a pattern similar to that for the soil samples.
Denitrification potential in the soil or in the groundwater was greatest near the monitor well with shallow depth of vadose
zone (MW3). Cumulative N2O–N emission (denitrification capacity) from the SGWI soil samples and from stagnant water samples strongly correlated to
microbial most probable number (MPN) counts (r2 = 0.84 – 0.89), and dissolved organic C (DOC) (r2 = 0.96 – 0.97). Denitrification capacity of the SGWI samples moderately correlated to water-filled pore space (WFPS) (r2 = 0.52). However, extractable NO3-N content of the SGWI soil samples poorly (negative) correlated to denitrification capacity (r2 = 0.35). However, addition C, N or both to the soil or water samples resulted in significant increase in cumulative N2O emission. This study demonstrated that variation in denitrification capacity, as a result of differences in denitrifier
population, and the amount of readily available carbon source significantly (at 95% probability level) influenced the variation
in NO3–N concentrations in the surficial groundwater samples collected from different monitoring wells within an area with uniform
N management.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
19.
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
20.
We examined the effect of sustained stream bank seepage during base flow conditions on the pore water nitrogen biogeochemistry
of two riparian zones in lowland agricultural areas in southern Ontario, Canada. Nitrate, ammonium and dissolved oxygen concentrations
in riparian subsurface water over a two-year period showed well-organized spatial patterns along stream bank seepage flow
paths that extended seasonally up to 25 m inland. High levels of dissolved oxygen and NO3− in stream inflow were depleted rapidly at the stream bank interface suggesting the occurrence of aerobic microbial respiration
followed by denitrification. A zone of NH4+ accumulation persisted in more anaerobic sediments inland from the bank margin, although the magnitude and intensity of the
pattern varied seasonally. A bromide tracer and NO3− co-injection at the stream bank interface indicated that bank seepage occurred along preferential flow paths in a poorly
sorted gravel layer in the two riparian zones. Depletion of NO3− in relation to co-injected bromide confirmed that the bank margin was a hot spot of biogeochemical activity within the riparian
zone. Conceptual models of humid temperate riparian zones have focused on nitrogen biogeochemistry in relation to hillslope
to stream hydrologic flow paths. However, our results suggest that sustained stream bank inflow during low flow conditions
can exert a dominant control on riparian nitrogen cycling in lowland landscapes where level riparian zones bounded by perennial
streams receive limited subsurface inflows from adjacent slopes. 相似文献