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1.
Fate and Transport of Organic Nitrogen in Minimally Disturbed Montane Streams of Colorado,USA 总被引:1,自引:0,他引:1
In two montane watersheds that receive minimal deposition of atmospheric nitrogen, 15–71% of dissolved organic nitrogen (DON)
was bioavailable in stream water over a 2-year period. Discharge-weighted concentrations of bulk DON were between 102 and
135 μg/l, and the C:N ratio differed substantially between humic and non-humic fractions of DON. Approximately 70% of DON export
occurred during snowmelt, and 40% of that DON was biologically available to microbes in stream sediments. Concentrations of
bioavailable DON in stream water were 2–16 times greater than dissolved inorganic nitrogen (DIN) during the growing season,
and bioavailable DON was depleted within 2–14 days during experimental incubations. Uptake of DON was influenced by the concentration
of inorganic N in stream water, the concentration of non-humic DON in stream water, and the C:N ratio of the non-humic fraction
of dissolved organic matter (DOM). Uptake of DON declined logarithmically as the concentration of inorganic N in stream water
increased. Experimental additions of inorganic N also caused a decline in uptake of DON and net production of DON when the
C:N ratio of non-humic DOM was high. This study indicates that the relative and absolute amount of bioavailable DON can vary
greatly within and across years due to interactions between the availability of inorganic nutrients and composition of DOM.
DOM has the potential to be used biotically at a high rate in nitrogen-poor streams, and it may be generated by heterotrophic
microbes when DIN and labile DOM with low relative nitrogen content become abundant. 相似文献
2.
This study considers the cycling of nitrogen in the waters of the North Sea, particularly focussing on organic nitrogen. Dissolved
inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and particulate organic nitrogen (PON) were measured in the North
Sea over a one-year period (autumn 2004–summer 2005). The surface water concentrations of nitrate, ammonium, DON and PON during
the present study ranged from <0.1–7.2 μM, <0.1–2.0 μM, 1.9–11.2 μM and 0.3–5.6 μM, respectively, with DON the dominant fraction
of total nitrogen at all times. These nutrients concentrations were significantly lower compared to previous studies in the
southern North Sea. The seasonal variations showed high mean surface concentrations of nitrate (4.7 ± 0.6 μM) and DON (8.9 ± 0.9 μM),
low ammonium (<0.1 μM) and PON (0.8 ± 0.1 μM) in winter, shifting to low nitrate (0.3 ± 0.3 μM) and DON (4.2 ± 1.2 μM) in
summer, with high ammonium (0.8 ± 0.4 μM) in autumn and PON (2.5 ± 1.2 μM) in spring. Highest mean surface DON concentration
was measured in winter and may be due to resuspension of the organic matter from the bottom sediments. For autumn and spring,
phytoplankton DON release was likely to be the most significant source of DON as shown by high concentrations of low molecular
weight (LMW) DON and its positive correlation to chlorophyll a. Low total and LMW DON concentrations during summer were likely to be due to the uptake of the LMW DON fraction by phytoplankton
and bacteria and the stratification of the water column. DON is therefore shown to be a potentially important source of nitrogen
in shelf seas especially after the spring bloom has depleted nitrate to limiting concentrations.
Handling editor: L. Naselli-Flores 相似文献
3.
Seasonal Variations of Dissolved Nitrogen and DOC:DON Ratios in an Intermittent Mediterranean Stream
Seasonal variations of dissolved inorganic nitrogen (DIN) (NO3–N and NH4–N) and dissolved organic nitrogen (DON) were determined in Fuirosos, an intermittent stream draining an unpolluted Mediterranean
forested catchment (10.5 km2) in Catalonia (Spain). The influence of flow on streamwater concentrations and seasonal differences in quality and origin
of dissolved organic matter, inferred from dissolved organic carbon to nitrogen ratios (DOC:DON ratios), were examined. During
baseflow conditions, nitrate and ammonium had opposite behaviour, probably controlled by biological processes such as vegetation
uptake and mineralization activity. DON concentrations did not have a seasonal trend. During storms, nitrate and DON increased
by several times but discharge was not a good predictor of nutrient concentrations. DOC:DON ratios in streamwater were around
26, except during the months following drought when DOC:DON ratios ranged between 42 and 20 during baseflow and stormflow
conditions, respectively. Annual N export during 2000–2001 was 70 kg km−1 year−1, of which 75% was delivered during stormflow. The relative contribution of nitrogen forms to the total annual export was
57, 35 and 8% as NO3–N, DON and NH4–N, respectively. 相似文献
4.
Simultaneous occurrence of denitrification and nitrate ammonification in sediments of the French Mediterranean Coast 总被引:6,自引:0,他引:6
Dissimilatory nitrate reductions in coastal marine sediment of Carteau Cove (French Mediterranean Coast) were studied between
April 1993 and July 1994. Simultaneous determination of denitrification and dissimilatory nitrate reduction to ammonium was
achieved by using a combination of acetylene blockage and 15N techniques. After short incubations (maximum 5 h), a part of
15N labelled nitrate added to the sediment was recovered as ammonium without incorporation in organic matter. The result indicate
that a fraction of nitrate was reduced to ammonium by a dissimilatory mechanism instead of denitrifying. Denitrifying and
nitrate ammonifying activities ranged from 0 to 19.8 μmol l-1 d-1 and from 2.3 to 83.2 μmol l-1 d-1, respectively. Denitrification
rates were highest in early spring whereas nitrate ammonification were highest in fall. The recovery of nitrate reduced as
N2O-N plus ammonium was between 40 and 100%, the highest nitrogen losses were recorded in July. Depending on the station and
time of year denitrification accounted for between 0 and 43% of the total nitrate reduction whereas dissimilatory nitrate
reduction to ammonium (DNRA) accounted for between 18 and 100%. The reduction rate data suggest that the pathway of nitrate
reduction to ammonium may be important in coastal sediments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
Y. Tanaka T. Miyajima A. Watanabe K. Nadaoka T. Yamamoto H. Ogawa 《Coral reefs (Online)》2011,30(2):533-541
Dissolved organic matter (DOM) concentrations in a fringing coral reef were measured for both carbon and nitrogen with the
analytical technique of high-temperature catalytic oxidation. Because of high precision of the analytical system, not only
the concentrations of dissolved organic carbon and nitrogen (DOC and DON, respectively) but the C:N ratio was also determined
from the distribution of DOC and DON concentrations. The observed concentrations of DOC and DON ranged 57–76 and 3.8–5.6 μmol l−1, respectively. The C:N ratios of the DOM that was produced on the reef flat were very similar between seagrass- and coral-dominated
areas; the C:N ratio was 10 on average. The C:N ratio of DOM was significantly higher than that of particulate organic matter
(POM) that was produced on the reef flat. Production rates of DOC were measured on the reef flat during stagnant periods and
accounted for 3–7% of the net primary production, depending on the sampling site. The production rate of DON was estimated
to be 10–30% of the net uptake of dissolved inorganic N in the reef community. Considering that the DOM and POM concentrations
were not correlated with each other, a major source of the reef-derived DOM may be the benthic community and not POM such
as phytoplankton. It was concluded that a widely distributed benthic community in the coral reef released C-rich DOM to the
overlying seawater, conserving N in the community. 相似文献
6.
The formation of14CO2 from 3 μg l−1 labelled chloroform was studied in anaerobic Dutch river sediments. All incubations were performed under anaerobic conditions.
The observed first order mineralization kinetics showed half-lives of 2–37 days at 20°C in 12 muddy sediments. In contrast
most of the sandy sediment samples did not show a mineralization of chloroform. Most probable number analysis revealed about
3.104 chloroform mineralizing bacteria per g of dry sediment in a muddy sediment and 1–2.103 chloroform mineralizing bacteria per g of dry sediment in a sandy sediment. Therefore the persistence of chloroform in sandy
sediments is not caused by the absence of chloroform mineralizing bacteria but by the inactivity of these bacteria. This inactivity
of the sandy sediments might allow chloroform from infiltrating river water to reach the groundwater. Mud samples from a relatively
unpolluted site showed a similar chloroform mineralization rate compared with the polluted sediments from the rivers Rhine
and Meuse. The data indicate that the reductive dechlorination of aliphatic compounds is not influenced at the polluted sites. 相似文献
7.
Abstract
The dissimilatory nitrate-reducing processes, denitrification, and dissimilatory nitrate-reduction to ammonium were studied
in freshwater lake sediments within healthy and degrading Phragmites australis (reed) stands. The samples from the healthy vegetation site contained roots and rhizomes. Cores were supplied with 1.9–5.2
μg 15N-NO3
− g−1 dry sediment in the laboratory and subsequently incubated for 8 h at 20°C, in the dark. The 15N compounds were determined before (natural percentage of 15N) and after 1 and 8 h of incubation.
The uptake of 15N by the roots and rhizomes in the healthy vegetation was 61%. Nitrogen losses, interpreted as denitrification, accounted
for 25 and 84% of the added 15N-NO3
− in sediment from the healthy and degrading vegetation sites, respectively. The percentages of nitrate reduced to ammonium
were 4 and 9% in sediment from the healthy vegetation and degrading vegetation sites, respectively. The percentage of 15N–total N in the sediment of the healthy vegetation site was 10%, whereas for the degrading vegetation site this percentage
was 7%. The percentage of nitrate reduced to ammonium could be potentially underestimated by the percentage of 15N measured in the sediment. In this case, in healthy and degenerating P. australis stands, the percentage of produced ammonium accounted for 14–16%.
The nitrate reduction rates were calculated based on an incubation period of one hour. The denitrification rate in sediment
from the degrading vegetation site was higher than from the healthy vegetation site. The rate of dissimilatory nitrate reduction
to ammonium was almost tenfold higher in sediment from the degrading vegetation site compared to sediment from the healthy
vegetation site. The significantly lower percentages of dissimilatory nitrate reduction to ammonium and denitrification in
the healthy stand compared to the degrading stand was probably due to the presence of roots and rhizomes. In the sediments
of healthy and degrading P. australis stands, denitrification was the main nitrate-reducing process.
Received: 24 July 1996; Accepted: 5 December 1996 相似文献
8.
Dalila Serpa Manuela Falcão Pedro Duarte Luís Cancela da Fonseca Carlos Vale 《Biogeochemistry》2007,82(3):291-304
During an annual cycle, overlying water and sediment cores were collected simultaneously at three sites (Tavira, Culatra and
Ramalhete) of Ria Formosa’s intertidal muddy and subtidal sandy sediments to determine ammonium, nitrates plus nitrites and
phosphate. Organic carbon, nitrogen and phosphorus were also determined in superficial sediments. Ammonium and phosphate dissolved
in porewater were positively correlated with temperature (P < 0.01) in muddy and sandy sediments, while the nitrogen-oxidized forms had a negative correlation (P < 0.02) in muddy sediments probably because mineralization and nitrification/denitrification processes vary seasonally. Porewater
ammonium profiles evidenced a peak in the top-most muddy sediment (380 μM) suggesting higher mineralization rate when oxygen
is more available, while maximum phosphate concentration (113 μM) occurred in the sub-oxic layer probably due to phosphorus
desorption under reduced conditions. In organically poor subtidal sandy sediments, nutrient porewater concentrations were
always lower than in intertidal muddy sediments, ranging annually from 20 μM to 100 μM for ammonium and from 0.05 μM to 16 μM
for phosphate. Nutrient diffusive fluxes predicted by a mathematical model were higher during summer, in both muddy (104 nmol cm−2 d−1––NH4+; 8 nmol cm−2 d−1––HPO4−2) and sandy sediments (26 nmol cm−2 d−1––NH4+; 1 nmol cm−2 d−1––HPO4−2), while during lower temperature periods these fluxes were 3–4 times lower. Based on simulated nutrient effluxes, the estimated
annual amount of ammonium and phosphate exported from intertidal areas was three times higher than that released from subtidal
areas (22 ton year−1––NH4+; 2 ton year−1––HPO4−2), emphasizing the importance of tidal flats to maintain the high productivity of the lagoon. Global warming scenarios simulated
with the model, revealed that an increase in lagoon water temperature only produces significant variations (P < 0.05) for NH4+ in porewater and consequent diffusive fluxes, what will probably affect the system productivity due to a N/P ratio unbalance. 相似文献
9.
Concentrations of soluble reactive phosphorus (SRP), nitrate, and soluble reactive silicon (SRSi) were monitored in 12 streams
draining small catchments (<10 km2) in the English Lake District. The catchments varied with respect to underlying geology,
soil type and land cover. Average concentrations of SRP were in the range 0.5–11.2 μg P l-1, and estimated loads ranged from
0.01 to 0.14 kg P ha-1 a-1. The higher concentrations and loads were associated with catchments containing improved pasture.
Mean streamwater concentrations of nitrate varied from 55 to 660 μg N l-1, while loads were in the range 0.8–9.6 kg N ha-1
a-1; no general dependence on catchment properties was discerned. Concentrations of SRSi were similar in all the streams (0.8–2
mg Si l-1), and annual loads were in the range 10–26 kg Si ha-1 a-1. Loads of all three nutrients were greatest during the
winter, because of higher discharges, but in some catchments containing improved pasture, considerable transport of P also
took place during the summer. Concentrations of nitrate in streams draining unimproved moorland catchments are approximately
twice those reported for samples taken from similar streams in 1973 and 1974, possibly because of increased atmospheric deposition
of inorganic nitrogen (ammonium and nitrate). Concentrations of SRP in such streams were similar to those reported for the
earlier samples. Comparisons of stream loads of SRP and nitrate with estimated inputs suggest that catchment soils retain
substantial amounts of these nutrients. Implications for surface water eutrophication of changes in P retention by soils are
discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
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
11.
Temporal and spatial distributions of dissolved organic carbon and nitrogen in two small lakes on the Southwestern China Plateau 总被引:6,自引:0,他引:6
Wen Li Fengchang Wu Congqiang Liu Pingqing Fu Jing Wang Yi Mei Liying Wang Jianyang Guo 《Limnology》2008,9(2):163-171
Temporal and spatial distributions of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), chlorophyll-a and inorganic nitrogen were investigated in two small mountainous lakes (Lake Hongfeng and Baihua), on the Southwestern China
Plateau, based on almost 2 years’ field observation. DOC concentrations ranged from 163 μM to 248 μM in Lake Hongfeng and
from 143 μM to 308 μM in Lake Baihua, respectively, during the study period. DON concentrations ranged from 7 μM to 26 μM
in Lake Hongfeng and from 14 μM to 47 μM in Lake Baihua. DOC showed vertical heterogeneity with higher concentrations in the
epilimnion than in the hypolimnion during the stratification period. The DON concentration profiles appeared to be more variable
than the DOC profiles. Apparent DON maxima occurred in the upper layer of water. In Lake Hongfeng, DOC concentration in the
surface water was highest at the end of spring and early summer. DON concentration was 2–5 μM higher in May 2003 and in June
2004 than in adjacent months. DOC and chlorophyll-a concentrations were significantly correlated (r = 0.79, P < 0.05). The period of highest concentrations of DOC in Lake Hongfeng was also the season of concentrated rainfall. Algae
activity and allochthonous input might result in an increase of DOC and DON concentrations together. In Lake Baihua, the maximum
concentrations of DOC and DON in the surface water occurred simultaneously in May 2003 and February 2004. DOC concentrations
were significantly correlated with DON (r = 0.90, P < 0.01), indicating the common sources. Allochthonous input, biological processes, stratification and mixing were the most
important factors controlling the distributions and cycling of dissolved organic matter (DOM) and inorganic nitrogen in these
two lakes. Inference from the corresponding vertical distributions of DOM and inorganic nitrogen indicated that DOM played
potential roles in the internal loading of nitrogen and metabolism in the water body in these small lakes. The carbon/nitrogen
(C/N) ratio showed a potential significance for tracing the source and biogeochemical processes of DOM in the lakes. These
results are of significance in the further understanding of biogeochemical cycling and environmental effects of DOM and nitrogen
in lake ecosystems. 相似文献
12.
13.
Luitgard Schwendenmann Rainer Riecke Rubén J. Lara 《Wetlands Ecology and Management》2006,14(5):463-475
Although water in mangrove sediments influences nutrient cycling in both, mangrove forest and estuary, little information
exists on seasonal and vertical distribution of dissolved organic and inorganic compounds in the sediment column. We studied
the influence of sediment texture and chemistry, permeability (K), tides, and rainfall on dissolved organic carbon (DOC) and nitrogen (DON), dissolved inorganic phosphate (DIP) and salinity
in creek and sediment waters of a mangrove in Pará, Brazil. Water samples were taken from boreholes and piezometers in the
mangrove forest and from an adjacent tidal creek at neap and spring tides, during the dry and rainy season. Forest sediment
was analysed for carbon (C), nitrogen (N), salinity and permeability. Clay, C and N decreased with depth. Sediment permeability
(K) was lowest (<0.1 m day−1) in the upper, clay-rich and crab-burrow-free mud layer. In the deeper, fine sand strata, K ranged from 0.7 to 1.8 m day−1. Tidal range in the creek was 3.5 and 5.5 m for neap and spring tides, respectively. Salinity, DOC, DON and DIP in creek
water were inversely related to tidal height. Piezometer data revealed significant water level changes in deeper, sandy sediment
layer, which followed, time-lagged, the tidal fluctuations. In contrast, tide did not affect the water level in the upper
sediment due to low permeability. Compared with creek water, sediment water was enriched in DOC, DON and DIP because of organic
matter input and mineralization. In deeper layers, solute concentration was most likely affected by sorption processes (DOC
and DIP) and reduction reactions (DIP). During the rainy season, DOC and DON in creek and sediment water were higher than
in the dry season. DIP appeared invariant to seasonal changes. In the rainy season, salt flushing from surface sediments resulted
in higher salinities at intermediate sediment depths, while in the deeper layers salinity was lower due to exchange with water
from the tidal creek. 相似文献
14.
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
15.
Fish kills of milkfish Chanos chanos and tilapia Oreochromis spp. now occur frequently in brackish, marine, and freshwater
farms (ponds, pens, and cages) in the Philippines. Aquafarms with high organic load, limited water exchange and circulation,
no aeration, and high stocking and feeding rates can become oxygen-depleted and allow sulfide from the sediments to appear
in the water column and poison free-swimming fish. The sulfide tolerance of 2–5 g milkfish and 5–8 g O. mossambicus was determined
in 25-liter aquaria with flow-through sea water (100 ml min-1) at 26–30 °C and sulfide stock solutions pumped in at 1ml min-1.
Total sulfide concentrations in the aquaria were measured by the methylene blue method and used in the regression against
the probits of % survival. Four experiments showed that the two species have similar sulfide tolerance. In sea water of pH
8–8.5, about 163 ± 68 μM or 5.2 ± 2.2 mg l-1 total sulfide (mean ± 2 se) or 10 μM or 313 μg l-1 H2S was lethal to 50% of the
fish in 4–8 h, and 61 ± 3 μM total sulfide or 4 μM H2S in 24–96 h (to convert all sulfide concentrations: 1 μM = 32 μg l-1).
Earthen pond bottoms had 0–382 μM total dissolved sulfide (mean ± sd = 54 ± 79 μM, n = 76); a tenth of the samples had >200
μM. The water column may have such sulfide levels under hypoxic or anoxic conditions. To simulate some of the conditions during
fish kills, 5–12 g milkfish were exposed to an abrupt increase in sulfide, alone or in combination with progressive respiratory
hypoxia and decreasing pH. The tests were done in the same flow-through set-up but with sulfide pumped in at 25 ml min-1.
The lethal concentration for 50% of the fish was 197 μM total sulfide or 12 μM H2S at 2 h, but 28–53 μM sulfide allowed fish
to survive 6–10 h. Milkfish in aquaria with no aeration nor flow-through sea water died of respiratory hypoxia in 5–8 h when
oxygen dropped from 6 to 1 mg l-1. Under respiratory hypoxia with 30–115 μM sulfide, the fish died in 2.5–4 h. Tests with
low pH were done by pumping a weak sulfuric acid solution at 25 ml min-1 into aquaria with flow-through sea water such that
the pH dropped from 8 to 4 in 5 h. Under these conditions, milkfish died in 7–9 h when the pH was 3.5. When 30–93 μM sulfide
was pumped in with the acid, the fish died in 2–6 h when the pH was still 4.5–6.3. Thus, sulfide, hypoxia, and low pH are
each toxic to milkfish at particular levels and aggravate each other's toxicity. Aquafarms must be well oxygenated to prevent
sulfide toxicity and fish kills.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
Experimental measurement of sediment nitrification and denitrification in Hamilton Harbour,Canada 总被引:1,自引:0,他引:1
This research examines the role of sediment nitrification and denitrification in the nitrogen cycle of Hamilton Harbour. The
Harbour is subject to large ammonia and carbon loadings from a waste-water treatment plant and from steel industries. Spring
ammonia concentrations rapidly decrease from 4.5 to 0.5 mg 1−1, while spring nitrate concentrations increase from 1 to 2 mg l−1, by mid-summer. A three-layer sediment model was developed. The first layer is aerobic; in it, oxidation of organics and
nitrification occurs. The second layer is for denitrification, and the third layer is for anaerobic processes. Ammonia sources
for nitrification include diffusion from the water column, sources associated with the oxidation of organics, sources from
denitrification and from anaerobic processes. Diffusion of oxygen, ammonia and nitrate across the sediment-water interface
occurs. Temperature effects are modelled using the Arrhenius concept. A combination of zero-order kinetics for nitrate or
ammonia consumption with diffusion results in a half-order reaction, with respect to the water column loss rate to sediments.
From experimental measurement, the rate of nitrification is 200 mg N 1−1 sediment per day, while that of denitrification is 85 mg N 1–1 sediment per day at 20 °C. The Arrhenius activation energy
is estimated as 15 000 cal/ mole-K and 17 000 cal/ mole-K for nitrification and denitrification, respectively, between 10
°C and 20 °C. Calculations of the flux of ammonia with the sediments, using the biofilm model, compare favourably with experimental
observations. The ammonia flux from the water column is estimated to account for 20% of the observed decrease in water column
stocks of ammonia, while the nitrate flux from the water column is estimated to account for 25% of the total nitrogen produced
by the sediments. 相似文献
17.
Carbon and nitrogen mineralized from soil under waterlogged conditions may come from the soil microbial biomass pool and potentially
could be used for biomass estimations.14C and15N labeled cells added to soil were monitored for decomposition under aerobic and anaerobic conditions. Under aerobic conditions
12–42% of the added organism C was mineralized and 1–30% of the N. Under waterlogged conditions 13–33% of the C and 4–13%
of the N was mineralized. The mineralized organism C as a percent of the total C evolved was consistent for both aerobic and
anaerobic conditions, however the nitrogen showed extreme variations 相似文献
18.
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
19.
Landscape Controls on Organic and Inorganic Nitrogen Leaching across an Alpine/Subalpine Ecotone,Green Lakes Valley,Colorado Front Range 总被引:5,自引:0,他引:5
Here we report measurements of organic and inorganic nitrogen (N) fluxes from the high-elevation Green Lakes Valley catchment
in the Colorado Front Range for two snowmelt seasons (1998 and 1999). Surface water and soil samples were collected along
an elevational gradient extending from the lightly vegetated alpine to the forested subalpine to assess how changes in land
cover and basin area affect yields and concentrations of ammonium-N (NH4-N), nitrate-N (NO3-N), dissolved organic N (DON), and particulate organic N (PON). Streamwater yields of NO3-N decreased downstream from 4.3 kg ha−1 in the alpine to 0.75 kg ha−1 at treeline, while yields of DON were much less variable (0.40–0.34 kg ha−1). Yields of NH4-N and PON were low and showed little variation with basin area. NO3-N accounted for 40%–90% of total N along the sample transect and was the dominant form of N at all but the lowest elevation
site. Concentrations of DON ranged from approximately 10% of total N in the alpine to 45% in the subalpine. For all sites,
volume-weighted mean concentrations of total dissolved nitrogen (TDN) were significantly related to the DIN:DON ratio (R
2 = 0.81, P < 0.001) Concentrations of NO3-N were significantly higher at forested sites that received streamflow from the lightly vegetated alpine reaches of the catchment
than in a control catchment that was entirely subalpine forest, suggesting that the alpine may subsidize downstream forested
systems with inorganic N. KCl-extractable inorganic N and microbial biomass N showed no relationship to changes in soil properties
and vegetative cover moving downstream in catchment. In contrast, soil carbon–nitrogen (C:N) ratios increased with increasing
vegetative cover in catchment and were significantly higher in the subalpine compared to the alpine (P < 0.0001) Soil C:N ratios along the sample transect explained 78% of the variation in dissolved organic carbon (DOC) concentrations
and 70% of the variation in DON concentrations. These findings suggest that DON is an important vector for N loss in high-elevation
ecosystems and that streamwater losses of DON are at least partially dependent on catchment soil organic matter stoichiometry.
Received 26 July 2001; accepted 6 May 2002. 相似文献
20.
Large Loss of Dissolved Organic Nitrogen from Nitrogen-Saturated Forests in Subtropical China 总被引:5,自引:0,他引:5
Yunting Fang Weixing Zhu Per Gundersen Jiangming Mo Guoyi Zhou Muneoki Yoh 《Ecosystems》2009,12(1):33-45
Dissolved organic nitrogen (DON) has recently been recognized as an important component of terrestrial N cycling, especially
under N-limited conditions; however, the effect of increased atmospheric N deposition on DON production and loss from forest
soils remains controversial. Here we report DON and dissolved organic carbon (DOC) losses from forest soils receiving very
high long-term ambient atmospheric N deposition with or without additional experimental N inputs, to investigate DON biogeochemistry
under N-saturated conditions. We studied an old-growth forest, a young pine forest, and a young mixed pine/broadleaf forest
in subtropical southern China. All three forests have previously been shown to have high nitrate (NO3−) leaching losses, with the highest loss found in the old-growth forest. We hypothesized that DON leaching loss would be forest
specific and that the strongest response to experimental N input would be in the N-saturated old-growth forest. Our results
showed that under ambient deposition (35–50 kg N ha−1 y−1 as throughfall input), DON leaching below the major rooting zone in all three forests was high (6.5–16.9 kg N ha−1 y−1). DON leaching increased 35–162% following 2.5 years of experimental input of 50–150 kg N ha−1 y−1. The fertilizer-driven increase of DON leaching comprised 4–17% of the added N. A concurrent increase in DOC loss was observed
only in the pine forest, even though DOC:DON ratios declined in all three forests. Our data showed that DON accounted for
23–38% of total dissolved N in leaching, highlighting that DON could be a significant pathway of N loss from forests moving
toward N saturation. The most pronounced N treatment effect on DON fluxes was not found in the old-growth forest that had
the highest DON loss under ambient conditions. DON leaching was highly correlated with NO3− leaching in all three forests. We hypothesize that abiotic incorporation of excess NO3− (through chemically reactive NO2−) into soil organic matter and the consequent production of N-enriched dissolved organic matter is a major mechanism for the
consistent and large DON loss in the N-saturated subtropical forests of southern China.
Dr. YT Fang performed research, analyzed data, and wrote the paper; Prof. WX Zhu participated in the initial experimental
design, analyzed data, and took part in writing the paper; Prof. P Gundersen conceived the study and took part in writing;
Prof. JM Mo and Prof. GY Zhou conceived study; Prof. M Yoh analyzed part of the data and contributed to the development of
DON model. 相似文献