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1.
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
2.
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
3.
Understanding how the concentration and chemical quality of dissolved organic matter (DOM) varies in soils is critical because
DOM influences an array of biological, chemical, and physical processes. We used PARAFAC modeling of excitation–emission fluorescence
spectroscopy, specific UV absorbance (SUVA254) and biodegradable dissolved organic carbon (BDOC) incubations to investigate the chemical quality of DOM in soil water collected
from 25 cm piezometers in four different wetland and forest soils: bog, forested wetland, fen and upland forest. There were
significant differences in soil solution concentrations of dissolved organic C, N, and P, DOC:DON ratios, SUVA254 and BDOC among the four soil types. Throughout the sampling period, average DOC concentrations in the four soil types ranged
from 9–32 mg C l−1 and between 23–42% of the DOC was biodegradable. Seasonal patterns in dissolved nutrient concentrations and BDOC were observed
in the three wetland types suggesting strong biotic controls over DOM concentrations in wetland soils. PARAFAC modeling of
excitation–emission fluorescence spectroscopy showed that protein-like fluorescence was positively correlated (r
2 = 0.82; P < 0.001) with BDOC for all soil types taken together. This finding indicates that PARAFAC modeling may substantially improve
the ability to predict BDOC in natural environments. Coincident measurements of DOM concentrations, BDOC and PARAFAC modeling
confirmed that the four soil types contain DOM with distinct chemical properties and have unique fluorescent fingerprints.
DOM inputs to streams from the four soil types therefore have the potential to alter stream biogeochemical processes differently
by influencing temporal patterns in stream heterotrophic productivity. 相似文献
4.
Riparian nitrogen dynamics in two geomorphologically distinct tropical rain forest watersheds: subsurface solute patterns 总被引:3,自引:3,他引:0
Nitrate, ammonium, dissolved organic N, and dissolved oxygen were measured in stream water and shallow groundwater in the
riparian zones of two tropical watersheds with different soils and geomorphology. At both sites, concentrations of dissolved
inorganic N (DIN; NH4
+- and NO3
−-N) were low in stream water (< 110 ug/L). Markedly different patterns in DIN were observed in groundwater collected at the
two sites. At the first site (Icacos watershed), DIN in upslope groundwater was dominated by NO3
−-N (550 ug/L) and oxygen concentrations were high (5.2 mg/L). As groundwater moved through the floodplain and to the stream,
DIN shifted to dominance by NH4
+-N (200–700 ug/L) and groundwater was often anoxic. At the second site (Bisley watershed), average concentrations of total
dissolved nitrogen were considerably lower (300 ug/L) than at Icacos (600 ug/L), and the dominant form of nitrogen was DON
rather than inorganic N. Concentrations of NH4
+ and NO3
− were similar throughout the riparian zone at Bisley, but concentrations of DON declined from upslope wells to stream water.
Differences in speciation and concentration of nitrogen in groundwater collected at the two sites appear to be controlled
by differences in redox conditions and accessibility of dissolved N to plant roots, which are themselves the result of geomorphological
differences between the two watersheds. At the Icacos site, a deep layer of coarse sand conducts subsurface water to the stream
below the rooting zone of riparian vegetation and through zones of strong horizontal redox zonation. At the Bisley site, infiltration
is impeded by dense clays and saturated flow passes through the variably oxidized rooting zone. At both sites, hydrologic
export of nitrogen is controlled by intense biotic activity in the riparian zone. However, geomorphology appears to strongly
modify the importance of specific biotic components. 相似文献
5.
Metal pollution, in combination with other environmental stressors such as acid deposition and climate change, may disturb
metal biogeochemical cycles. To investigate the influence of dissolved organic carbon, acidity and seasonality on metal geochemistry,
this study has described concentrations of 19 metals as they pass through an acidified forested catchment on the Precambrian
Shield in south-central Ontario, Canada. Metal, dissolved organic carbon (DOC) and sulphate (SO4
2−) concentrations fluctuate throughout the catchment compartments as the water passes through and interacts with vegetation,
soils and bedrock. Relationships among metals, DOC and SO4
2− are most pronounced in compartments where DOC and SO4
2− exhibit high variability, namely in the throughfall, organic horizon soil water, and wetland-draining stream. Metal, DOC
and SO4
2− concentrations varied seasonally in the streams, and temporal coherence occurred among metal, DOC and SO4
2− concentrations in the organic horizon soil water and the wetland-draining stream (PC1). In the wetland-draining stream, the
highest DOC, Cr, Cu, Fe, Pb, and V concentrations occur in the summer, whereas concentrations of SO4
2− and most other metals peak in the fall after a period of drought. Despite the rural location, provincial water quality objectives
for surface water were exceeded for many metals when the peak fall values occurred. 相似文献
6.
Marion Schrumpf Wolfgang Zech Johannes Lehmann Herbert V. C. Lyaruu 《Biogeochemistry》2006,78(3):361-387
Organic nutrients have proven to contribute significantly to nutrient cycling in temperate forest ecosystems. Still, little
is known about their relevance in the tropics. In the present study, organic C, N, S and P were analysed in rainfall, throughfall,
litter percolate and soil solution of a montane rainforest at Mt. Kilimanjaro, Tanzania. The aim was to determine the amounts
of organic nutrients in different water pathways and to assess the influence of forest disturbance on organic nutrients by
comparing mature forests, secondary forests and shrub vegetation in clearings. Concentrations of all studied elements increased
from rainfall to throughfall and litter percolate and then exhibited a rapid decrease in the mineral soil. Concentrations
of organic P were above the detection limit only in the litter percolate. Organic N (ON) as a fraction of total N increased
from 50% in rainfall (0.19 mg l−1) to 66% (0.45 mg l−1) in throughfall followed by a decline to 39% in the litter percolate (0.77 mg l−1) of the mature forest. Similarly, proportions of organic S and P amounted to 43 and 34%, respectively, in the litter percolate
in mature forest. For ON, this proportion further decreased to less than 10% in the soil solution. The latter was probably
attributable to a high sorption capacity of the studied Andisols, which led to overall low organic element concentrations
in the soil solution (OC: 1.2 mg l−1, ON: 0.05 mg l−1 at 1 m soil depth) as compared to other temperate and tropical forest ecosystems. Organic element concentrations were higher
in litter percolate and soil solution under the clearings, but there were no differences in the relative contribution of these
elements. Organic nutrient forms at Mt. Kilimanjaro appeared to be much less susceptible to leaching than their inorganic
forms. 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.
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
9.
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
10.
11.
During 1999–2001 the chemical composition and fluxes were measured in rainfall, throughfall, soil solution and stream water
in a remote forested site in the Italian Alps. The analysis of temporal patterns revealed the differential behaviour of nitrogen
and sulphur and suggested that different mechanisms controlled their flux. No important changes in sulphate concentration
and fluxes emerged as the solution passed through the various components of the forest ecosystem, and temporal variations
of SO4 in the soil solution and stream were likely driven by the physical process of dilution. The availability of nitrate and ammonia,
by contrast, was drastically reduced as throughfall water entered the soil and passed through the mineral layers, irrespective
of season. The calculated hydrochemical budget based on throughfall and soil solution N fluxes revealed that ~80% N retention
in the forest soil, corresponding to 12 kg ha−1 yr−1, despite a relatively high N deposition loading (15 kg ha−1 yr−1). Most of the leached nitrogen (90%) was in the organic form. Indicators of the N status of this ecosystem, such as C/N ratio
in solid and solution phase of the soil and N foliage content as well as land use history were examined. Despite the strong
N retention in the forested part of the catchment, the stream water N–NO3 levels were consistently above 10 μg l−1 suggesting that the Val Masino catchment as a whole was less efficient in processing atmospheric N inputs. This contrasting
N behaviour illustrates the role of landscape features, such as the soil cover and vegetation type, that is characteristic
of an alpine catchment. 相似文献
12.
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
13.
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
14.
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
15.
This study examined changes in dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) in coastal seawater
after exposure to sand along a high energy beach face over an annual cycle between April 2004 and July 2005. Dissolved organic
nitrogen, NO3
−, and NH4
+ were released from sand to seawater in laboratory incubation experiments clearly demonstrating that they are a potential
source of N to underlying groundwater or coastal seawater. DON increases in seawater, after exposure to surface sands in laboratory
experiments, were positively correlated with in situ water column DON concentrations measured at the same time as sand collection.
Increase in NO3
− and NH4
+ were not correlated with their in situ concentrations. This suggests that DON released from beach sands is relatively more
recalcitrant while NO3
− and NH4
+ are utilized rapidly in the coastal ocean. The release of N was seasonal with carbon to nitrogen ratios indicating that
recent primary productivity was responsible for the largest fluxes in summer while more degraded humic material contributed
to lower fluxes in winter. Fluxes of total dissolved nitrogen (DON and DIN) from surface sand (2.1 × 10−4 mol m−2 h−1) were similar to that of groundwater and more than an order of magnitude larger than rain deposition indicating the potential
importance of surface sand derived nitrogen to the coastal zone with a corresponding impact on primary productivity. 相似文献
16.
Response of Periphytic Algae to Gradients in Nitrogen and Phosphorus in Streamside Mesocosms 总被引:2,自引:1,他引:1
In this study we manipulated both nitrogen and phosphorus concentrations in stream mesocosms to develop quantitative relationships
between periphytic algal growth rates and peak biomass with inorganic N and P concentrations. Stream water from Harts Run,
a 2nd order stream in a pristine catchment, was constantly added to 36 stream-side stream mesocosms in low volumes and then
recirculated to reduce nutrient concentrations. Clay tiles were colonized with periphyton in the mesocosms. Nutrients were
added to create P and N concentrations ranging from less than Harts Run concentrations to 128 μg SRP l−1 and 1024 μg NO3-N l−1. Algae and water were sampled every 3 days during colonization until periphyton communities reached peak biomass and then
sloughed. Nutrient depletion was substantial in the mesocosms. Algae accumulated in all streams, even streams in which no
nutrients were added. Nutrient limitation of algal growth and peak biomass accrual was observed in both low P and low N conditions.
The Monod model best explained relationships between P and N concentrations and algal growth and peak biomass. Algal growth
was 90% of maximum rates or higher in nutrient concentrations 16 μg SRP l−1 and 86 μg DIN l−1. These saturating concentrations for growth rates were 3–5 times lower than concentrations needed to produce maximum biomass.
Modified Monod models using both DIN and SRP were developed to explain algal growth rates and peak biomass, which respectively
explained 44 and 70% of the variance in algal response. 相似文献
17.
Jennifer Lawson Knoepfle Peter T. Doran Fabien Kenig W. Berry Lyons V. F. Galchenko 《Hydrobiologia》2009,632(1):139-156
In perennially ice-covered lakes of Taylor Valley, Antarctica, “legacy”, a carryover of past ecosystem events, has primarily
been discussed in terms of nutrient and salinity concentrations and its effect on the current ecology of the lakes. In this
study, we determine how residual pools of ancient carbon affect the modern carbon abundance and character in the water columns
of Lakes Fryxell, Hoare, and Bonney. We measure the stable carbon isotopic compositions and concentrations of particulate
organic carbon (POC) and dissolved inorganic carbon (DIC) in the water column of these lakes over four seasons (1999–2002).
These data are presented and compared with all the previously published Taylor Valley lacustrine carbon stable isotopic data.
Our results show that the carbon concentrations and isotopic compositions of the upper water columns of those lakes are controlled
by modern processes, while the lower water columns are controlled to varying degrees by inherited carbon pools. The water
column of the west lobe of Lake Bonney is dominated by exceptionally high concentrations of DIC (55,000–75,000 μmol l−1) reflecting the long period of ice-cover on this lake. The east lobe of Lake Bonney has highly enriched δ13CDIC values resulting from paleo-brine evaporation effects in its bottom waters, while its high DIC concentrations provide geochemical
evidence that its middle depth waters are derived from West Lake Bonney during a hydrologically connected past. Although ancient
carbon is present in both Lake Hoare and Lake Fryxell, the δ13CDIC values in bottom waters suggest dominance by modern primary productivity-related processes. Anaerobic methanogenesis and
methanotrophy are also taking place in the lower water column of Lake Fryxell with enough methane, oxidized anaerobically,
to contribute to the DIC pool. We also show how stream proximity and high flood years are only a minor influence on the carbon
isotopic values of both POC and DIC. The Taylor Valley lake system is remarkably stable in both inter-lake and intra-lake
carbon dynamics.
Handling editor: K. Martens 相似文献
18.
Characterizing the dynamics of nitrogen (N) leaching from organic and conventional paddy fields is necessary to optimize fertilization and to evaluate the impact of these contrasting farming systems on water bodies. We assessed N leaching in organic versus conventional rice production systems of the Ili River Valley, a representative aquatic ecosystem of Central Asia. The N leaching and overall performance of these systems were measured during 2009, using a randomized block experiment with five treatments. PVC pipes were installed at soil depths of 50 and 180 cm to collect percolation water from flooded organic and conventional paddies, and inorganic N (NH4-N+NO3-N) was analyzed. Two high-concentration peaks of NH4-N were observed in all treatments: one during early tillering and a second during flowering. A third peak at the mid-tillering stage was observed only under conventional fertilization. NO3-N concentrations were highest at transplant and then declined until harvest. At the 50 cm soil depth, NO3-N concentration was 21–42% higher than NH4-N in percolation water from organic paddies, while NH4-N and NO3-N concentrations were similar for the conventional and control treatments. At the depth of 180 cm, NH4-N and NO3-N were the predominant inorganic N for organic and conventional paddies, respectively. Inorganic N concentrations decreased with soil depth, but this attenuation was more marked in organic than in conventional paddies. Conventional paddies leached a higher percentage of applied N (0.78%) than did organic treatments (0.32–0.60%), but the two farming systems leached a similar amount of inorganic N per unit yield (0.21–0.34 kg N Mg−1 rice grains). Conventional production showed higher N utilization efficiency compared to fertilized organic treatments. These results suggest that organic rice production in the Ili River Valley is unlikely to reduce inorganic N leaching, if high crop yields similar to conventional rice production are to be maintained. 相似文献
19.
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
20.
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