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1.
To identify the controls on dissolved organic carbon (DOC) production, we incubated soils from 18 sites, a mixture of 52 forest
floor and peats and 41 upper mineral soil samples, at three temperatures (3, 10, and 22°C) for over a year and measured DOC
concentration in the leachate and carbon dioxide (CO2) production from the samples. Concentrations of DOC in the leachate were in the range encountered in field soils (<2 to >50 mg l−1). There was a decline in DOC production during the incubation, with initial rates averaging 0.03–0.06 mg DOC g−1 soil C day−1, falling to averages of 0.01 mg g−1 soil C day−1; the rate of decline was not strongly related to temperature. Cumulative DOC production rates over the 395 days ranged from
less than 0.01 to 0.12 mg g−1 soil C day−1 (0.5–47.6 mg g−1 soil C), with an average of 0.021 mg g−1 soil C day−1 (8.2 mg g−1 soil C). DOC production rate was weakly related to temperature, equivalent to Q10 values of 0.9 to 1.2 for mineral samples and 1.2 to 1.9 for organic samples. Rates of DOC production in the organic samples
were correlated with cellulose (positively) and lignin (negatively) proportion in the organic matter, whereas in the mineral
samples C and nitrogen (N) provided positive correlations. The partitioning of C released into CO2–C and DOC showed a quotient (CO2–C:DOC) that varied widely among the samples, from 1 to 146. The regression coefficient of CO2–C:DOC production (log10 transformed) ranged from 0.3 to 0.7, all significantly less than 1. At high rates of DOC production, a smaller proportion
of CO2 is produced. The CO2–C:DOC quotient was dependent on incubation temperature: in the organic soil samples, the CO2–C:DOC quotient rose from an average of 6 at 3 to 16 at 22°C and in the mineral samples the rise was from 7 to 27. The CO2–C:DOC quotient was related to soil pH in the organic samples and C and N forms in the mineral samples. 相似文献
2.
Mark S. Johnson Johannes Lehmann Eduardo Guimarães Couto João Paulo Novães Filho Susan J. Riha 《Biogeochemistry》2006,81(1):45-57
Organic and inorganic carbon (C) fluxes transported by water were evaluated for dominant hydrologic flowpaths on two adjacent headwater catchments in the Brazilian Amazon with distinct soils and hydrologic responses from September 2003 through April 2005. The Ultisol-dominated catchment produced 30% greater volume of storm-related quickflow (overland flow and shallow subsurface flow) compared to the Oxisol-dominated catchment. Quickflow fluxes were equivalent to 3.2 ± 0.2% of event precipitation for the Ultisol catchment, compared to 2.5 ± 0.3% for the Oxisol-dominated watershed (mean response ±1 SE, n = 27 storms for each watershed). Hydrologic responses were also faster on the Ultisol watershed, with time to peak flow occurring 10 min earlier on average as compared to the runoff response on the Oxisol watershed. These different hydrologic responses are attributed primarily to large differences in saturated hydraulic conductivity (K
s). Overland flow was found to be an important feature on both watersheds. This was evidenced by the response rates of overland flow detectors (OFDs) during the rainy season, with overland flow intercepted by 54 ± 0.5% and 65 ± 0.5% of OFDs for the Oxisol and Ultisol watersheds respectively during biweekly periods. Small volumes of quickflow correspond to large fluxes of dissolved organic C (DOC); DOC concentrations of the hydrologic flowpaths that comprise quickflow are an order of magnitude higher than groundwater flowpaths fueling base flow (19.6 ± 1.7 mg l−1 DOC for overland flow and 8.8 ± 0.7 mg l−1 DOC for shallow subsurface flow versus 0.50 ± 0.04,mg l−1 DOC in emergent groundwater). Concentrations of dissolved inorganic C (DIC, as dissolved CO2–C plus HCO3−–C) in groundwater were found to be an order of magnitude greater than quickflow DIC concentrations (21.5 mg l−1 DIC in emergent groundwater versus 1.1 mg l−1 DIC in overland flow). The importance of deeper flowpaths in the transport of inorganic C to streams is indicated by the 40:1 ratio of DIC:DOC for emergent groundwater. Dissolved CO2–C represented 92% of DIC in emergent groundwater. Results from this study illustrate a highly dynamic and tightly coupled linkage between the C cycle and the hydrologic cycle for both Ultisol and Oxisol landscapes: organic C fluxes strongly tied to flowpaths associated with quickflow, and inorganic C (particularly dissolved CO2) transported via deeper flowpaths. 相似文献
3.
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
4.
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
5.
M. J. Mitchell K. B. Piatek S. Christopher B. Mayer C. Kendall P. Mchale 《Biogeochemistry》2006,78(2):217-246
Understanding the effects of climate change including precipitation patterns has important implications for evaluating the
biogeochemical responses of watersheds. We focused on four storms in late summer and early fall that occurred after an exceptionally
dry period in 2002. We analyzed not only the influence of these storms on episodic chemistry and the role of different water
sources in affecting surface water chemistry, but also the relative contributions of these storms to annual biogeochemical
mass balances. The study site was a well studied 135-ha watershed in the Adirondack Park of New York State (USA). Our analyses
integrated measurements on hydrology, solute chemistry and the isotopic composition of NO3−(δ15N and δ18O) and SO42−(δ34S and δ18O) to evaluate how these storms affected surface water chemistry. Precipitation amounts varied among the storms (Storm 1:
Sept. 14–18, 18.5 mm; Storm 2: Sept. 21–24, 33 mm; Storm 3: Sept. 27–29, 42.9 mm; Storm 4: Oct. 16–21, 67.6 mm). Among the
four storms, there was an increase in water yields from 2 to 14%. These water yields were much less than in studies of storms
in previous years at this same watershed when antecedent moisture conditions were higher. In the current study, early storms
resulted in relatively small changes in water chemistry. With progressive storms the changes in water chemistry became more
marked with particularly major changes in Cb (sum of base cations), Si, NO3−, and SO42−, DOC and pH. Analyses of the relationships between Si, DOC, discharge and water table height clearly indicated that there
was a decrease in ground water contributions (i.e., lower Si concentrations and higher DOC concentrations) as the watershed
wetness increased with storm succession. The marked changes in chemistry were also reflected in changes in the isotopic composition
of SO42− and NO3−. There was a strong inverse relationship between SO42− concentrations and δ34S values suggesting the importance of S biogeochemical redox processes in contributing to SO42− export. The isotopic composition of NO3− in stream water indicated that this N had been microbially processed. Linkages between SO42− and DOC concentrations suggest that wetlands were major sources of these solutes to drainage waters while the chemical and
isotopic response of NO3− suggested that upland sources were more important. Although these late summer and fall storms did not play a major role in
the overall annual mass balances of solutes for this watershed, these events had distinctive chemistry including depressed
pH and therefore have important consequences to watershed processes such as episodic acidification, and the linkage of these
processes to climate change. 相似文献
6.
We examined patterns of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) loading to a small urban stream
during baseflow and stormflow. We hypothesized that lower DOC and TDN contributions from impervious surfaces would dilute
natural hydrologic flowpath (i.e., riparian) contributions during storm events in an urban watershed, resulting in lower concentrations
of DOC and TDN during storms. We tested these hypotheses in a small urban watershed in Portland, Oregon, over a 3-month period
during the spring of 2003. We compared baseflow and stormflow chemistry using Mann–Whitney tests (significant at p<0.05). We also applied a mass balance to the stream to compare the relative significance of impervious surface contributions
versus riparian contributions of DOC and TDN. Results showed a significant increase in stream DOC concentrations during stormflows
(median baseflow DOC = 2.00 mg l−1 vs. median stormflow DOC = 3.46 mg l−1). TDN streamwater concentrations, however, significantly decreased with stormflow (median baseflow TDN = 0.75 mg l−1 vs. median stormflow TDN = 0.56 mg l−1). During storms, remnant riparian areas contributed 70–74% of DOC export and 38–35% of TDN export to the stream. The observed
pattern of increased DOC concentrations during stormflows in this urban watershed was similar to patterns found in previous
studies of forested watersheds. Results for TDN indicated that there were relatively high baseflow nitrogen concentrations
in the lower watershed that may have partially masked the remnant riparian signal during stormflows. Remnant riparian areas
were a major source of DOC and TDN to the stream during storms. These results suggest the importance of preserving near-stream
riparian areas in cities to maintain ambient carbon and nitrogen source contributions to urban streams. 相似文献
7.
The Ferrous Wheel Hypothesis (Davidson et al. 2003) postulates the abiotic formation of dissolved organic N (DON) in forest floors, by the fast reaction of NO2
− with dissolved organic C (DOC). We investigated the abiotic reaction of NO2
− with dissolved organic matter extracted from six different forest floors under oxic conditions. Solutions differed in DOC
concentrations (15–60 mg L−1), NO2
− concentrations (0, 2, 20 mg NO2
−-N L−1) and DOC/DON ratio (13.4–25.4). Concentrations of added NO2
− never decreased within 60 min, therefore, no DON formation from added NO2
− took place in any of the samples. Our results suggest that the reaction of NO2
− with natural DOC in forest floors is rather unlikely. 相似文献
8.
J. Alan Yeakley David C. Coleman Bruce L. Haines Brian D. Kloeppel Judy L. Meyer Wayne T. Swank Barry W. Argo James M. Deal Sharon F. Taylor 《Ecosystems》2003,6(2):0154-0167
We investigated the effects of removing near-stream Rhododendron and of the natural blowdown of canopy trees on nutrient export to streams in the southern Appalachians. Transects were instrumented
on adjacent hillslopes in a first-order watershed at the Coweeta Hydrologic Laboratory (35°03′N, 83°25′W). Dissolved organic
carbon (DOC), K+, Na+, Ca2+, Mg2+, NO3
−-N, NH4
+-N, PO4
3−-P, and SO4
2− were measured for 2 years prior to disturbance. In August 1995, riparian Rhododendron on one hillslope was cut, removing 30% of total woody biomass. In October 1995, Hurricane Opal uprooted nine canopy trees
on the other hillslope, downing 81% of the total woody biomass. Over the 3 years following the disturbance, soilwater concentrations
of NO3
−-N tripled on the cut hillslope. There were also small changes in soilwater DOC, SO4
2−, Ca2+, and Mg2+. However, no significant changes occurred in groundwater nutrient concentrations following Rhododendron removal. In contrast, soilwater NO3
−-N on the storm-affected hillslope showed persistent 500-fold increases, groundwater NO3
−-N increased four fold, and streamwater NO3
−-N doubled. Significant changes also occurred in soilwater pH, DOC, SO4
2−, Ca2+, and Mg2+. There were no significant changes in microbial immobilization of soil nutrients or water outflow on the storm-affected hillslope.
Our results suggest that Rhododendron thickets play a relatively minor role in controlling nutrient export to headwater streams. They further suggest that nutrient
uptake by canopy trees is a key control on NO3
−-N export in upland riparian zones, and that disruption of the root–soil connection in canopy trees via uprooting promotes
significant nutrient loss to streams.
Received 30 January 2001; accepted 25 July 2002. 相似文献
9.
Fifteen-year Change in Forest Floor Organic and Element Content and Cycling at the Turkey Lakes Watershed 总被引:11,自引:0,他引:11
To assess the long-term effects of atmospheric deposition on forest floor chemical composition, we took quantitative samplings
of L-(Oi), F-(Oe), and H-(Oa) layers at an old-growth sugar maple–yellow birch stand on a till soil at the Turkey Lakes Watershed
near Lake Superior, Ontario, Canada, in 1981 and 1996. We then assessed these samples for contents of organic matter (OM),
total N, K, Ca, Mg, S, and Na, and exchangeable NH4
+, NO3
−, K+, Ca2+, Mg2+, SO4
2−, and Na+. Over the 15-year period, total OM and element contents remained unchanged, with the exception of N, which increased significantly
from 61.3 kmol/ha in 1981 to 78.4 kmol/ha in 1996. On an area basis, there were significant increases in exchangeable Ca2+ (from 3.8 to 4.6 kmol/ha) and Na+ (from 0.05 to 0.08 kmol/ha) and decreases in exchangeable NH4
+-N (from 1.41 to 0.95 kmol/ha) and SO4
2−-S (from 1.29 to 0.96 kmol/ha). There were no significant differences in average annual litterfall OM, N, Ca, Mg, S or Na
inputs between 1980 and 1985 and between 1992 and 1997. Average annual wet-only SO4
2−-S deposition during 1981–86 was 0.30; during 1992–97, it was 0.21 kmol/ha. Annual wet-only NO3
−-N averaged 0.33 kmol/ha during 1981–86 and was similar during 1992–97. Throughfall was less rich in SO4
2− and Ca2+, Mg2+, and Na+ during 1992–97 than earlier. Throughfall NH4
+ and NO3
− fluxes were unchanged. Efflux of cations from the forest floor reflected reduced throughput of SO4
2−. Overall, the results suggest that in spite of atmospheric inputs, active biological processes—including litter input, fine-root
turnover, and tree uptake—serve to impart stability to the mineral composition of mature sugar maple forest floor.
Received 5 October 1999; accepted 25 October 2000. 相似文献
10.
G. V. M. Gupta V. V. S. S. Sarma R. S. Robin A. V. Raman M. Jai Kumar M. Rakesh B. R. Subramanian 《Biogeochemistry》2008,87(3):265-285
Studies on biogeochemical cycling of carbon in the Chilka Lake, Asia’s largest brackish lagoon on the east coast of India,
revealed, for the first time, strong seasonal and spatial variability associated with salinity distribution. The lake was
studied twice during May 2005 (premonsoon) and August 2005 (monsoon). It exchanges waters with the sea (Bay of Bengal) and
several rivers open into the lake. The lake showed contrasting levels of dissolved inorganic carbon (DIC) and organic carbon
(DOC) in different seasons; DIC was higher by ∼22% and DOC was lower by ∼36% in premonsoon than in monsoon due to seasonal
variations in their supply from rivers and in situ production/mineralisation. The DIC/DOC ratios in the lake during monsoon
were influenced by physical mixing of end member water masses and by intense respiration of organic carbon. A strong relationship
between excess DIC and apparent oxygen utilisation showed significant control of biological processes over CO2 production in the lake. Surface partial pressure of CO2 (pCO2), calculated using pH–DIC couple according to Cai and Wang (Limnol and Oceanogr 43:657–668, 1998), exhibited discernable gradients during monsoon through northern (1,033–6,522 μatm), central (391–2,573 μatm) and southern
(102–718 μatm) lake. The distribution pattern of pCO2 in the lake seems to be governed by pCO2 levels in rivers and their discharge rates, which were several folds higher during monsoon than premonsoon. The net CO2 efflux, based on gas transfer velocity parameterisation of Borges et al. (Limnol and Oceanogr 49(5):1630–1641, 2004), from entire lake during monsoon (141 mmolC m−2 d−1 equivalent to 2.64 GgC d−1 at basin scale) was higher by 44 times than during premonsoon (9.8 mmolC m−2 d−1 ≈ 0.06 GgC d−1). 15% of CO2 efflux from lake in monsoon was contributed by its supply from rivers and the rest was contributed by in situ heterotrophic
activity. Based on oxygen and total carbon mass balance, net ecosystem production (NEP) of lake (−308 mmolC m−2 d−1 ≈ −3.77 GgC d−1) was found to be almost in consistent with the total riverine organic carbon trapped in the lake (229 mmolC m−2 d−1 ≈ 2.80 GgC d−1) suggesting that the strong heterotrophy in the lake is mainly responsible for elevated fluxes of CO2 during monsoon. Further, the pelagic net community production represented 92% of NEP and benthic compartment plays only a
minor role. This suggests that Chilka lake is an important region in biological transformation of organic carbon to inorganic
carbon and its export to the atmosphere. 相似文献
11.
Michael R. McHale Douglas A. Burns Gregory B. Lawrence Peter S. Murdoch 《Biogeochemistry》2007,84(3):311-331
The 24 ha Dry Creek watershed in the Catskill Mountains of southeastern New York State USA was clearcut during the winter
of 1996–1997. The interactions among acidity, nitrate (NO3−), aluminum (Al), and calcium (Ca2+) in streamwater, soil water, and groundwater were evaluated to determine how they affected the speciation, solubility, and
concentrations of Al after the harvest. Watershed soils were characterized by low base saturation, high exchangeable Al concentrations,
and low exchangeable base cation concentrations prior to the harvest. Mean streamwater NO3− concentration was about 20 μmol l−1 for the 3 years before the harvest, increased sharply after the harvest, and peaked at 1,309 μmol l−1 about 5 months after the harvest. Nitrate and inorganic monomeric aluminum (Alim) export increased by 4−fold during the first year after the harvest. Alim mobilization is of concern because it is toxic to some fish species and can inhibit the uptake of Ca2+ by tree roots. Organic complexation appeared to control Al solubility in the O horizon while ion exchange and possibly equilibrium
with imogolite appeared to control Al solubility in the B horizon. Alim and NO3− concentrations were strongly correlated in B-horizon soil water after the clearcut (r
2 = 0.96), especially at NO3− concentrations greater than 100 μmol l−1. Groundwater entering the stream from perennial springs contained high concentrations of base cations and low concentrations
of NO3− which mixed with acidic, high Alim soil water and decreased the concentration of Alim in streamwater after the harvest. Five years after the harvest soil water NO3− concentrations had dropped below preharvest levels as the demand for nitrogen by regenerating vegetation increased, but groundwater
NO3− concentrations remained elevated because groundwater has a longer residence time. As a result streamwater NO3− concentrations had not fallen below preharvest levels, even during the growing season, 5 years after the harvest because
of the contribution of groundwater to the stream. Streamwater NO3− and Alim concentrations increased more than reported in previous forest harvesting studies and the recovery was slower likely because
the watershed has experienced several decades of acid deposition that has depleted initially base-poor soils of exchangeable
base cations and caused long-term acidification of the soil. 相似文献
12.
Stream dissolved organic matter bioavailability and composition in watersheds underlain with discontinuous permafrost 总被引:1,自引:0,他引:1
Kelly L. Balcarczyk Jeremy B. JonesJr. Rudolf Jaffé Nagamitsu Maie 《Biogeochemistry》2009,94(3):255-270
We examined the impact of permafrost on dissolved organic matter (DOM) composition in Caribou-Poker Creeks Research Watershed
(CPCRW), a watershed underlain with discontinuous permafrost, in interior Alaska. We analyzed long term data from watersheds
underlain with varying degrees of permafrost, sampled springs and thermokarsts, used fluorescence spectroscopy, and measured
the bioavailabity of dissolved organic carbon (DOC). Permafrost driven patterns in hydrology and vegetation influenced DOM
patterns in streams, with the stream draining the high permafrost watershed having higher DOC and dissolved organic nitrogen
(DON) concentrations, higher DOC:DON and greater specific ultraviolet absorbance (SUVA) than the streams draining the low
and medium permafrost watersheds. Streams, springs and thermokarsts exhibited a wide range of DOC and DON concentrations (1.5–37.5 mgC/L
and 0.14–1.26 mgN/L, respectively), DOC:DON (7.1–42.8) and SUVA (1.5–4.7 L mgC−1 m−1). All sites had a high proportion of humic components, a low proportion of protein components, and a low fluorescence index
value (1.3–1.4), generally consistent with terrestrially derived DOM. Principal component analysis revealed distinct groups
in our fluorescence data determined by diagenetic processing and DOM source. The proportion of bioavailable DOC ranged from
2 to 35%, with the proportion of tyrosine- and tryptophan-like fluorophores in the DOM being a major predictor of DOC loss
(p < 0.05, R
2 = 0.99). Our results indicate that the degradation of permafrost in CPCRW will result in a decrease in DOC and DON concentrations,
a decline in DOC:DON, and a reduction in SUVA, possibly accompanied by a change in the proportion of bioavailable DOC. 相似文献
13.
Response of Oxidative Enzyme Activities to Nitrogen Deposition Affects Soil Concentrations of Dissolved Organic Carbon 总被引:10,自引:0,他引:10
Recent evidence suggests that atmospheric nitrate (NO
3
−
) deposition can alter soil carbon (C) storage by directly affecting the activity of lignin-degrading soil fungi. In a laboratory
experiment, we studied the direct influence of increasing soil NO
3
−
concentration on microbial C cycling in three different ecosystems: black oak–white oak (BOWO), sugar maple–red oak (SMRO),
and sugar maple–basswood (SMBW). These ecosystems span a broad range of litter biochemistry and recalcitrance; the BOWO ecosystem
contains the highest litter lignin content, SMRO had intermediate lignin content, and SMBW leaf litter has the lowest lignin
content. We hypothesized that increasing soil solution NO
3
−
would reduce lignolytic activity in the BOWO ecosystem, due to a high abundance of white-rot fungi and lignin-rich leaf litter.
Due to the low lignin content of litter in the SMBW, we further reasoned that the NO
3
−
repression of lignolytic activity would be less dramatic due to a lower relative abundance of white-rot basidiomycetes; the
response in the SMRO ecosystem should be intermediate. We increased soil solution NO
3
−
concentrations in a 73-day laboratory incubation and measured microbial respiration and soil solution dissolved organic carbon
(DOC) and phenolics concentrations. At the end of the incubation, we measured the activity of β-glucosidase, N-acetyl-glucosaminidase,
phenol oxidase, and peroxidase, which are extracellular enzymes involved with cellulose and lignin degradation. We quantified
the fungal biomass, and we also used fungal ribosomal intergenic spacer analysis (RISA) to gain insight into fungal community
composition. In the BOWO ecosystem, increasing NO
3
−
significantly decreased oxidative enzyme activities (−30% to −54%) and increased DOC (+32% upper limit) and phenolic (+77%
upper limit) concentrations. In the SMRO ecosystem, we observed a significant decrease in phenol oxidase activity (−73% lower
limit) and an increase in soluble phenolic concentrations (+57% upper limit) in response to increasing NO
3
−
in soil solution, but there was no significant change in DOC concentration. In contrast to these patterns, increasing soil
solution NO
3
−
in the SMBW soil resulted in significantly greater phenol oxidase activity (+700% upper limit) and a trend toward lower DOC
production (−52% lower limit). Nitrate concentration had no effect on microbial respiration or β-glucosidase or N-acetyl-glucosaminidase
activities. Fungal abundance and basidiomycete diversity tended to be highest in the BOWO soil and lowest in the SMBW, but
neither displayed a consistent response to NO
3
−
additions. Taken together, our results demonstrate that oxidative enzyme production by microbial communities responds directly
to NO
3
−
deposition, controlling extracellular enzyme activity and DOC flux. The regulation of oxidative enzymes by different microbial
communities in response to NO
3
−
deposition highlights the fact that the composition and function of soil microbial communities directly control ecosystem-level
responses to environmental change. 相似文献
14.
Donald R. Zak William E. Holmes Matthew J. Tomlinson Kurt S. Pregitzer Andrew J. Burton 《Ecosystems》2006,9(2):242-253
Sugar maple (Acer saccharum Marsh.)-dominated northern hardwood forests in the upper Lakes States region appear to be particularly sensitive to chronic
atmospheric NO3− deposition. Experimental NO3− deposition (3 g NO3− N m−2 y−1) has significantly reduced soil respiration and increased the export of DOC/DON and NO3− across the region. Here, we evaluate the possibility that diminished microbial activity in mineral soil was responsible for
these ecosystem-level responses to NO3− deposition. To test this alternative, we measured microbial biomass, respiration, and N transformations in the mineral soil
of four northern hardwood stands that have received 9 years of experimental NO3− deposition. Microbial biomass, microbial respiration, and daily rates of gross and net N transformations were not changed
by NO3− deposition. We also observed no effect of NO3− deposition on annual rates of net N mineralization. However, NO3− deposition significantly increased (27%) annual net nitrification, a response that resulted from rapid microbial NO3− assimilation, the subsequent turnover of NH4+, and increased substrate availability for this process. Nonetheless, greater rates of net nitrification were insufficient
to produce the 10-fold observed increase in NO3− export, suggesting that much of the exported NO3− resulted directly from the NO3− deposition treatment. Results suggest that declines in soil respiration and increases in DOC/DON export cannot be attributed
to NO3−-induced physiological changes in mineral soil microbial activity. Given the lack of response we have observed in mineral
soil, our results point to the potential importance of microbial communities in forest floor, including both saprotrophs and
mycorrhizae, in mediating ecosystem-level responses to chronic NO3− deposition in Lake States northern hardwood forests. 相似文献
15.
R. Thomas James Wayne S. Gardner Mark J. McCarthy Stephen A. Carini 《Hydrobiologia》2011,669(1):199-212
Total nitrogen (TN) in Lake Okeechobee, a large, shallow, turbid lake in south Florida, has averaged between 90 and 150 μM
on an annual basis since 1983. No TN trends are evident, despite major storm events, droughts, and nutrient management changes
in the watershed. To understand the relative stability of TN, this study evaluates nitrogen (N) dynamics at three temporal/spatial
levels: (1) annual whole lake N budgets, (2) monthly in-lake water quality measurements in offshore and nearshore areas, and
(3) isotope addition experiments lasting 3 days and using 15N-ammonium (15NH4
+) and 15N-nitrate (15NO3
−) at two offshore locations. Budgets indicate that the lake is a net sink for N. TN concentrations were less variable than
net N loads, suggesting that in-lake processes moderate these net loads. Monthly NO3
− concentrations were higher in the offshore area and higher in winter for both offshore and nearshore areas. Negative relationships
between the percentage of samples classified as algal blooms (defined as chlorophyll a > 40 μg l−1) and inorganic N concentrations suggest N-limitation. Continuous-flow experiments over intact sediment cores measured net
fluxes (μmol N m−2 h−1) between 0 and 25 released from sediments for NH4
+, 0–60 removed by sediments for NO3
−, and 63–68 transformed by denitrification. Uptake rates in the water column (μmol N m−2 h−1) determined by isotope dilution experiments and normalized for water depth were 1,090–1,970 for NH4
+ and 59–119 for NO3
−. These fluxes are similar to previously reported results. Our work suggests that external N inputs are balanced in Lake Okeechobee
by denitrification. 相似文献
16.
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
17.
To determine the chemical and physicochemical characteristics of dissolved organic carbon in the Ado River and the Yasu River,
the main rivers flowing into Lake Biwa, the adsorption behavior onto hydrous iron oxide (HIO) and the reactivity to KMnO4 oxidant were investigated in parallel with measurement of the distribution profiles of dissolved organic carbon (DOC) along
the rivers. In one year of observation at the mouths of the two rivers, DOC concentrations were found to vary in the Ado over
the range 0.28–1.21 mg C l−1 and in the Yasu over the range 1.01–2.68 mg C l−1. Act-DOC, one of the fractions separated from the total DOC by its adsorption-active character onto HIO at pH 4, was thought
primarily to control the variation of total DOC, as in Lake Biwa. The int-DOC, another fraction separated by its adsorption-inert
or -inactive character onto HIO, remained at almost a steady value around 0.18 ± 0.07 mg C l−1 in the Ado, which was lower than that (0.35 ± 0.05 mg C l−1) in Lake Biwa. The act-DOC in river waters was reactive to KMnO4 oxidant, showing a linear relation with the amount of permanganate consumed for the reaction (chemical oxygen demand: COD).
In river waters, the relation can be approximated by a straight line expressed as COD (mg O2 l−1) = 0.64 × act-DOC (mg C l−1) − 0.02. In contrast, in the lake water the relation was COD (mg O2 l−1) = 0.97 × act-DOC (mg C l−1) − 0.50.
Received: March 3, 1999 / Accepted: December 2, 1999 相似文献
18.
Leaching losses of inorganic N and DOC following repeated drying and wetting of a spruce forest soil
Forest soils are frequently subjected to dry–wet cycles, but little is known about the effects of repeated drying and wetting
and wetting intensity on fluxes of , and DOC. Here, undisturbed soil columns consisting of organic horizons (O columns) and organic horizons plus mineral soil
(O + M columns) from a mature Norway spruce stand at the Fichtelgebirge; Germany, were repeatedly desiccated and subsequently
wetted by applying different amounts of water (8, 20 and 50 mm day−1) during the initial wetting phase. The constantly moist controls were not desiccated and received 4 mm day−1 during the entire wetting periods. Cumulative inorganic N fluxes of the control were 12.4 g N m−2 (O columns) and 11.4 g N m−2 (O + M columns) over 225 days. Repeated drying and wetting reduced cumulative and fluxes of the O columns by 47–60 and 76–85%, respectively. Increasing (0.6–1.1 g N m−2) and decreasing fluxes (7.6–9.6 g N m−2) indicate a reduction in net nitrification in the O + M columns. The negative effect of dry–wet cycles was attributed to
reduced net N mineralisation during both the desiccation and wetting periods. The soils subjected to dry–wet cycles were considerably
drier at the final wetting period, suggesting that hydrophobicity of soil organic matter may persist for weeks or even months.
Based on results from this study and from the literature we hypothesise that N mineralisation is mostly constrained by hydrophobicity
in spruce forests during the growing season. Wetting intensity did mostly not alter N and DOC concentrations and fluxes. Mean
DOC concentrations increased by the treatment from 45 mg l−1 to 61–77 mg l−1 in the O tlsbba columns and from 12 mg l−1 to 21–25 mg l−1 in the O + M columns. Spectroscopic properties of DOC from the O columns markedly differed within each wetting period, pointing
to enhanced release of rather easily decomposable substrates in the initial wetting phases and the release of more hardly
decomposable substrates in the final wetting phases. Our results suggest a small additional DOC input from organic horizons
to the mineral soil owing to drying and wetting. 相似文献
19.
Atmospheric Deposition to the Turkey Lakes Watershed: Temporal Variations and Characteristics 总被引:3,自引:0,他引:3
We investigated the atmospheric concentrations and deposition fluxes of major ions to the Turkey Lakes Watershed (TLW) between
1980 and 1996. During that time, daily SO4
2− concentrations in precipitation decreased markedly, while NO3
−, NH4
+, and H+ concentrations remained roughly constant. It appears that precipitation acidity did not decrease in spite of declining SO4
2− concentrations due to a concurrent and counterbalancing decrease in the concentrations of Ca2+, Mg2+, and K+ in precipitation. The reasons for the decline in base cations are unknown, but this decline is probably related to decreasing
emissions of soil-derived particles from agricultural, industrial, and road sources. A similar situation was seen during the
same period in other parts of Canada, the eastern United States, and Europe. Wet, dry, and total (wet + dry) deposition fluxes
of sulphur (S) and nitrogen (N) were estimated annually for the years 1980–96. The 17-year mean annual total (wet + dry) deposition
of S to the watershed was estimated at 38.5 mmol m−2 y−1 (range 24.3–50.3). Total S deposition decreased by 35% from the early 1980s (1982–84) to the mid-1990s (1994–96), a decline
consistent with the 23% decline in annual SO2 emissions in eastern North America during the same period. In contrast, the annual total (wet + dry) deposition of oxidized
N ranged from 39.8 to 60.4 mmol m−2 y−1, with a 15-year mean of 50.1 mmol m−2 y−1 and a net increase of 10% between the early 1980s (1983–85) and the mid-1990s (1994–96). This is in keeping with a 10% increase
in NOx emissions in eastern North America during the same period. For both S and N (oxidized), wet deposition dominated over dry
deposition as the major mechanism for atmospheric input to the watershed. Annually, wet deposition accounted for approximately
two-thirds of the total atmospheric deposition of both S and N. Dry S deposition was due more to gaseous SO2 deposition (two-thirds of dry S deposition) than to particulate SO4
2− deposition (one-third of dry S deposition). Dry deposition of oxidized N, however, was dominated (95%) by gaseous HNO3 deposition, with minimal input from particulate NO3
− deposition. Compared to several selected watershed/forest sites in Canada, the United States, and Europe, the estimated total
deposition of S and N at the TLW was relatively high during the measurement period.
Received 5 October 1999; accepted 1 March 2001. 相似文献
20.
Mark S. Castro Keith N. Eshleman Louis F. Pitelka Geoff Frech Molly Ramsey William S. Currie Karen Kuers Jeffrey A. Simmons Bob R. Pohlad Carolyn L. Thomas David M. Johnson 《Biogeochemistry》2007,84(3):333-348
The objective of this study was to evaluate the nitrogen (N) biogeochemistry of an 18–22 year old forested watershed in western
Maryland. We hypothesized that this watershed should not exhibit symptoms of N saturation. This watershed was a strong source
of nitrate (NO3
−) to the stream in all years, with a mean annual export of 9.5 kg N ha−1 year−1 and a range of 4.4–18.4 kg N ha−1 year−1. During the 2001 and 2002 water years, wet deposition of inorganic N was 9.0 kg N ha−1 year−1 and 6.3 kg N ha−1 year−1, respectively. Watershed N export rates in 2001 and 2002 water years were 4.2 kg N ha−1 year−1 and 5.3 kg N ha−1 year−1, respectively. During the wetter water years of 2003 and 2004, the watershed exported 15.0 kg N ha−1 year−1 and 18.4 kg N ha−1 year−1, rates that exceeded annual wet deposition of N by a factor of two (7.5 kg N ha−1 year−1 in 2003) and three (5.5 kg N ha−1 year−1 in 2004). Consistent with the high rates of N export, were high concentrations (2.1–3.3%) of N in foliage, wood (0.3%) and
fine roots, low C:N ratios in the forest floor (17–24) and mineral soil (14), high percentages (83–96%) of the amount of mineralized
N that was nitrified and elevated N concentrations (up to 3 mg N l−1) in soil solution. Although this watershed contained a young aggrading forest, it exhibited several symptoms of N saturation
commonly observed in more mature forests. 相似文献