首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
We used the dual isotope method to study differences in nitrate export in two subwatersheds in Vermont, USA. Precipitation, soil water and streamwater samples were collected from two watersheds in Camels Hump State Forest, located within the Green Mountains of Vermont. These samples were analyzed for the δ15N and δ18O of NO3. The range of δ15N–NO3 values overlapped, with precipitation −4.5‰ to +2.0‰ (n = 14), soil solution −10.3‰ to +6.2‰ (n = 12) and streamwater +0.3‰ to +3.1‰ (n = 69). The δ18O of precipitation NO3 (mean 46.8 ± 11.5‰) was significantly different (P < 0.001) from that of the stream (mean 13.2 ± 4.3‰) and soil waters (mean 14.5 ± 4.2‰) even during snowmelt periods. Extracted soil solution and streamwater δ18O of NO3 were similar and within the established range of microbially produced NO3, demonstrating that NO3 was formed by microbial processes. The δ15N and δ18O of NO3 suggests that although the two tributaries have different seasonal NO3 concentrations, they have a similar NO3 source.  相似文献   

2.
Although they drain remarkably similar forest types, streams of the Hubbard Brook Experimental Forest (HBEF) vary widely in their NO3 concentrations during the growing season. This variation may be caused by differences in the terrestrial systems they drain (for example, varying forest age or composition, hydrology, soil organic matter content, and so on) and/or by differences between the streams themselves (for example, contrasting geomorphology, biotic nitrogen [N] demand, rates of instream nitrogen transformations). We examined interstream variation in N processing by measuring NH4 + and NO3 uptake and estimating nitrification rates for 13 stream reaches in the HBEF during the summers of 1998 and 1999. We modeled nitrification rates using a best-fit model of the downstream change in NO3 concentrations following short-term NH4 + enrichments. Among the surveyed streams, the fraction of NH4 + uptake that was subsequently nitrified varied, and this variation was positively correlated with ambient streamwater NO3 concentrations. We examined whether this variation in instream nitrification rates contributed significantly to the observed variation in NO3 concentrations across streams. In some cases, instream nitrification provided a substantial portion of instream NO3 demand. However, because there was also substantial instream NO3 uptake, the net effect of instream processing was to reduce rather than supplement the total amount of NO3 exported from a watershed. Thus, instream rates of nitrification in conjunction with instream NO3 uptake were too low to account for the wide range of streamwater NO3 . The relationship between streamwater NO3 concentration and rates of instream nitrification may instead be due to a shift in the competitive balance between heterotrophic N uptake and nitrification when external inputs of NO3 are relatively high. Received 11 October 2000; accepted 14 December 2001.  相似文献   

3.
A manipulated increase in acid deposition (15 kg S ha−1), carried out for three months in a mature Scots pine (Pinus sylvestris) stand on a podzol, acidified the soil and raised dissolved Al at concentrations above the critical level of 5 mg l−1 previously determined in a controlled experiment with Scots pine seedlings. The induced soil acidification reduced tree fine root density and biomass significantly in the top 15 cm of soil in the field. The results suggested that the reduction in fine root growth was a response not simply to high Al in solution but to the depletion of exchangeable Ca and Mg in the organic layer, K deficiency, the increase in NH4:NO3 ratio in solution and the high proton input to the soil by the acid manipulation. The results from this study could not justify the hypothesis of Al-induced root damage under field conditions, at least not in the short term. However, the study suggests that a short exposure to soil acidity may affect the fine root growth of mature Scots pine.  相似文献   

4.
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   

5.
Paramasivam  S.  Alva  A. K.  Prakash  O.  Cui  S. L. 《Plant and Soil》1999,208(2):307-319
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   

6.
Nitrogen fertilization is a key factor for coffee production but creates a risk of water contamination through nitrate (NO3) leaching in heavily fertilized plantations under high rainfall. The inclusion of fast growing timber trees in these coffee plantations may increase total biomass and reduce nutrient leaching. Potential controls of N loss were measured in an unshaded coffee (Coffea arabica L.) plot and in an adjacent coffee plot shaded with the timber species Eucalyptus deglupta Blume (110 trees ha−1), established on an Acrisol that received 180 kg N ha−1 as ammonium-nitrate and 2,700 mm yr−1 rainfall. Results of the one year study showed that these trees had little effect on the N budget although some N fluxes were modified. Soil N mineralization and nitrification rates in the 0–20 cm soil layer were similar in both systems (≈280 kg N ha−1 yr−1). N export in coffee harvest (2002) was 34 and 25 kg N ha−1 yr−1 in unshaded and shaded coffee, and N accumulation in permanent biomass and litter was 25 and 45 kg N ha−1 yr−1, respectively. The losses in surface runoff (≈0.8 kg mineral N ha−1 yr−1) and N2O emissions (1.9 kg N ha−1 yr−1) were low in both cases. Lysimeters located at 60, 120, and 200 cm depths in shaded coffee, detected average concentrations of 12.9, 6.1 and 1.2 mg NO3-N l−1, respectively. Drainage was slightly reduced in the coffee-timber plantation. NO3leaching at 200 cm depth was about 27 ± 10 and 16 ± 7 kg N ha−1 yr−1 in unshaded and shaded coffee, respectively. In both plots, very low NO3 concentrations in soil solution at 200 cm depth (and in groundwater) were apparently due to NO3 adsorption in the subsoil but the duration of this process is not presently known. In these conventional coffee plantations, fertilization and agroforestry practices must be refined to match plant needs and limit potential NO3 contamination of subsoil and shallow soil water.  相似文献   

7.
Summary The effects of aluminium (Al3+) on the growth of four cultivars of white clover dependent upon NO3 −N were examined. Plants were grown in flowing solution culture with carefully maintained low concentrations (0, 12.5, 25 and 50 mmolm−3) of Al, and with P and pH (4.5) also held constant and appropriately low. A three-week treatment period resulted in major effects on the growth and elemental composition of shoots and roots at all concentrations of added Al. There were inherent differences between the cultivars in growth but the relative effects of Al were similar in each case. Examination by S.E.M. and x-ray microanalysis of one cultivar grown at 50 mmolm−3 Al, indicated that Al in the roots was associated with P, especially in old, outer epidermal cells. Aluminium reduced NO3 uptake and there were significant effects of Al on nitrate reductase activity (NRA). In contrast to the other characteristics, there were differential effects between the cultivars in NRA, both in the presence and absence of Al.  相似文献   

8.
Nitrate removal from drinking water using a membrane-fixed biofilm reactor   总被引:4,自引:0,他引:4  
Biological treatment of drinking water is a cost-effective alternative to conventional physico/chemical processes. A new concept was tested to overcome the main disadvantage of biological denitrification, the intensive post-treatment process to remove microorganisms and remnant carbon source. The biological reaction zone and carbon supply were separated from the raw water stream by a nitrate-permeable membrane. Denitrification takes place in a biofilm, which is immobilized at the membrane. In a series of bench-scale runs, different types of membranes and reactor configurations were investigated. The best denitrification rates achieved were 1230 mg NO3 -N m−2 day−1. In one run, raw water containing 100 mg NO3 l−1 was completely freed from nitrate. The membrane and the attached biofilm also represent a barrier against the passage of the C source and nutrients into the raw water. At concentrations of 20 mg l−1 ethanol and 15 mg l−1 phosphate in the bioreactor no diffusion through the membrane into the treated water was observed. Without any post-treatment, the effluent met nearly all the relevant criteria for drinking water; only the colony count was slightly increased. Received: 18 December 1996 / Received last revision: 14 April 1997 / Accepted: 19 April 1997  相似文献   

9.
The modification of large areas of tropical forest to agricultural uses has consequences for the movement of inorganic nitrogen (N) from land to water. Various biogeochemical pathways in soils and riparian zones can influence the movement and retention of N within watersheds and affect the quantity exported in streams. We used the concentrations of NO3 and NH4 + in different hydrological flowpaths leading from upland soils to streams to investigate inorganic N transformations in adjacent watersheds containing tropical forest and established cattle pasture in the southwestern Brazilian Amazon Basin. High NO3 concentrations in forest soil solution relative to groundwater indicated a large removal of N mostly as NO3 in flowpaths leading from soil to groundwater. Forest groundwater NO3 concentrations were lower than in other Amazon sites where riparian zones have been implicated as important N sinks. Based on water budgets for these watersheds, we estimated that 7.3–10.3 kg N ha−1 y−1 was removed from flowpaths between 20 and 100 cm, and 7.1–10.2 kg N ha−1 y−1 was removed below 100 cm and the top of the groundwater. N removal from vertical flowpaths in forest exceeded previously measured N2O emissions of 3.0 kg N ha−1 y−1 and estimated emissions of NO of 1.4 kg N ha−1 y−1. Potential fates for this large amount of nitrate removal in forest soils include plant uptake, denitrification, and abiotic N retention. Conversion to pasture shifted the system from dominance by processes producing and consuming NO3 to one dominated by NH4 +, presumably the product of lower rates of net N mineralization and net nitrification in pasture compared with forest. In pasture, no hydrological flowpaths contained substantial amounts of NO3 and estimated N removal from soil vertical flowpaths was 0.2 kg N ha−1 y−1 below the depth of 100 cm. This contrasts with the extent to which agricultural sources dominate N inputs to groundwater and stream water in many temperate regions. This could change, however, if pasture agriculture in the tropics shifts toward intensive crop cultivation.  相似文献   

10.
Anaerobic bioreactors that can support simultaneous microbial processes of denitrification and methanogenesis are of interest to nutrient nitrogen removal. However, an important concern is the potential toxicity of nitrate (NO3 ) and nitrite (NO2 ) to methanogenesis. The methanogenic toxicity of the NOx compounds to anaerobic granular biofilms and municipal anaerobic digested sludge with two types of substrates, acetate and hydrogen, was studied. The inhibition was the severest when the NOx compounds were still present in the media (exposure period). During this period, 95% or greater inhibition of methanogenesis was evident at the lowest concentrations of added NO2 tested (7.6–10.2 mg NO2 -N l−1) or 8.3–121 mg NO3 -N l−1 of added NO3 , depending on substrate and inoculum source. The inhibition imparted by NO3 was not due directly to NO3 itself, but instead due to reduced intermediates (e.g., NO2 ) formed during the denitrification process. The toxicity of NOx was found to be reversible after the exposure period. The recovery of activity was nearly complete at low added NOx concentrations; whereas the recovery was only partial at high added NOx concentrations. The recovery is attributed to the metabolism of the NOx compounds. The assay substrate had a large impact on the rate of NO2 metabolism. Hydrogen reduced NO2 slowly such that NO2 accumulated more and as a result, the toxicity was greater compared to acetate as a substrate. The final methane yield was inversely proportional to the amount of NOx compounds added indicating that they were the preferred electron acceptors compared to methanogenesis.  相似文献   

11.
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   

12.
Based on data from three German forest ecosystems severely disturbed by windthrow events, correlation patterns between NO3 and SO4 2− dynamics in the soil solution are described. Each of the correlation types was related to site-specific SO4 2− retention processes. The relative importance of SO4 2− adsorption/desorption and precipitation/dissolution was found to be different for the studied soils depending on their contents of SO4 2− -adsorbing sesquioxides and of A1 hydroxy sulfate minerals. Enhanced NO3 concentrations in the soil solution resulting from excess nitrification promoted either SO4 2− adsorption or the dissolution of Al hydroxy sulfates. Both processes result in different ecological consequences: Whereas the former reaction reduces anion concentration peaks in the soil solution, the latter increases them. Thus, a prediction of cation export from soil ecosystems subjected to excess nitrification has to regard site-specific interrelationships between NO3 and SO4 2−. As a third type of conelation the independence of NO3 and SO4 2− concentrations in the soil solution is presented. This type is suggested to be typical for soils with low SO4 2−. adsorption capacity and absence of A1 hydroxy sulfates.  相似文献   

13.
Rapid Nitrate Loss and Denitrification in a Temperate River Floodplain   总被引:3,自引:0,他引:3  
Nitrogen (N) pollution is a problem in many large temperate zone rivers, and N retention in river channels is often small in these systems. To determine the potential for floodplains to act as N sinks during overbank flooding, we combined monitoring, denitrification assays, and experimental nitrate (NO3 -N) additions to determine how the amount and form of N changed during flooding and the processes responsible for these changes in the Wisconsin River floodplain (USA). Spring flooding increased N concentrations in the floodplain to levels equal to the river. As discharge declined and connectivity between the river and floodplain was disrupted, total dissolved N decreased over 75% from 1.41 mg l−1, equivalent to source water in the Wisconsin River on 14 April 2001, to 0.34 mg l−1 on 22 April 2001. Simultaneously NO3 -N was attenuated almost 100% from 1.09 to <0.002 mg l−1. Unamended sediment denitrification rates were moderate (0–483 μg m−2 h−1) and seasonally variable, and activity was limited by the availability of NO 3 -N on all dates. Two experimental NO3 -N pulse additions to floodplain water bodies confirmed rapid NO3 -N depletion. Over 80% of the observed NO 3 -N decline was caused by hydrologic export for addition #1 but only 22% in addition #2. During the second addition, a significant fraction (>60%) of NO3 -N mass loss was not attributable to hydrologic losses or conversion to other forms of N, suggesting that denitrification was likely responsible for most of the NO3 -N disappearance. Floodplain capacity to decrease the dominant fraction of river borne N within days of inundation demonstrates that the Wisconsin River floodplain was an active N sink, that denitrification often drives N losses, and that enhancing connections between rivers and their floodplains may enhance overall retention and reduce N exports from large basins.  相似文献   

14.
We conducted 15NO3 stable isotope tracer releases in nine streams with varied intensities and types of human impacts in the upstream watershed to measure nitrate (NO3) cycling dynamics. Mean ambient NO3 concentrations of the streams ranged from 0.9 to 21,000 μg l−1 NO3–N. Major N-transforming processes, including uptake, nitrification, and denitrification, all increased approximately two to three orders of magnitude along the same gradient. Despite increases in transformation rates, the efficiency with which stream biota utilized available NO3-decreased along the gradient of increasing NO3. Observed functional relationships of biological N transformations (uptake and nitrification) with NO3 concentration did not support a 1st order model and did not show signs of Michaelis–Menten type saturation. The empirical relationship was best described by a Efficiency Loss model, in which log-transformed rates (uptake and nitrification) increase with log-transformed nitrate concentration with a slope less than one. Denitrification increased linearly across the gradient of NO3 concentrations, but only accounted for ∼1% of total NO3 uptake. On average, 20% of stream water NO3 was lost to denitrification per km, but the percentage removed in most streams was <5% km−1. Although the rate of cycling was greater in streams with larger NO3 concentrations, the relative proportion of NO3 retained per unit length of stream decreased as NO3 concentration increased. Due to the rapid rate of NO3 turnover, these streams have a great potential for short-term retention of N from the landscape, but the ability to remove N through denitrification is highly variable.  相似文献   

15.
Streamwater chemistry was measured at 100-m intervals in all streams of the Hubbard Brook Valley, NH during ‘spring’ (May–July) and during ‘fall’ (October–December) 2001. Overall, streamwater chemistry was very similar during these two periods, but fall median concentrations were consistently higher than spring values, except for ANC, pH, NO3 and PO43−, which had lower values in fall. Median concentrations for NH4+ were approximately the same in spring and fall. Stream chemistry varied throughout the Hubbard Brook Valley by elevation, channel length, drainage area and type of drainage, but most of the variability in stream chemistry was subtle and relatively small. Overall, there were relatively large (two- to 10-fold) changes in chemistry with longitudinal distance of wetted channel, elevation and/or size of drainage area in some streams and for some elements (e.g., H+, Aln+, DOC), but other chemical concentrations changed relatively little (e.g., Cl, dissolved Si). The main Hubbard Brook, a fifth-order stream at the mouth of the Valley, was remarkably constant in chemistry throughout its length, except where human disturbance near the mouth changed the chemistry. Differences in vegetation, geologic substrates and wetland areas were related to changes in pattern of streamwater chemistry throughout the Valley.  相似文献   

16.
Experimental and theoretical work emphasize the role of plant nutrient uptake in regulating ecosystem nutrient losses and predict that forest succession, ecosystem disturbance, and continued inputs of atmospheric nitrogen (N) will increase watershed N export. In ecosystems where snowpack insulates soils, soil-frost disturbances resulting from low or absent snowpack are thought to increase watershed N export and may become more common under climate-change scenarios. This study monitored watershed N export from the Hubbard Brook Experimental Forest (HBEF) in response to a widespread, severe soil-frost event in the winter of 2006. We predicted that nitrate (NO3 ) export following the disturbance would be high compared to low background streamwater NO3 export in recent years. However, post-disturbance annual NO3 export was the lowest on record from both reference (undisturbed) and treated experimental harvest or CaSiO3 addition watersheds. These results are consistent with other studies finding greater than expected forest NO3 retention throughout the northeastern US and suggest that changes over the last five decades have reduced impacts of frost events on watershed NO3 export. While it is difficult to parse out causes from a complicated array of potential factors, based on long-term records and watershed-scale experiments conducted at the HBEF, we propose that reduced N losses in response to frost are due to a combination of factors including the long-term legacies of land use, process-level alterations in N pathways, climate-driven hydrologic changes, and depletion of base cations and/or reduced soil pH due to cumulative effects of acid deposition.  相似文献   

17.
Sampling spatial and temporal variation in soil nitrogen availability   总被引:18,自引:0,他引:18  
There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part, this is due to methodological difficulties associated with sampling the same spatial locations repeatedly over time. We describe the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in space fluctuate over time. We used this method to examine spatial patterns of soil ammonium (NH+ 4) and nitrate (NO 3) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in time, we also measured soil NH+ 4 and NO 3 concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH+ 4 and NO 3 concentrations increased with the age of the dune, whereas coefficients of variation for NH+ 4 and NO 3 concentrations decreased with the age of the dune. Soil NO 3 concentration showed strong spatial structure, but soil NH+ 4 concentration was not spatially structured. Plant-available NH+ 4 and NO 3 showed relatively little spatial structure: only NO 3 availability in the second sampling period had significant patch structure. Spatial maps of NH+ 4 and NO 3 availability changed greatly over time, and there were few significant correlations among soil nitrogen availability at different points in time. NO 3 availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO 3 concentrations, providing some evidence that patches of plant-available NO 3 may reappear at the same spatial locations at irregular points in time. Received: 20 February 1998 / Accepted: 23 November 1998  相似文献   

18.
Wilden  R.  Schaaf  W.  Hüttl  R. F. 《Plant and Soil》1999,213(1-2):231-240
Due to a large reclamation (recultivation) demand in the Lusatian lignite mining district, efficient strategies for the rehabilitation of abandoned mine sites are needed. A field study was conducted for comparing the effects of three different fertilizer treatments (mineral fertilizer, sewage sludge and compost) on soil solution chemistry of both a lignite and pyrite containing spoil as well as a lignite and pyrite free spoil. The lignite and pyrite containing spoil was ameliorated with fly ash from a lignite power plant (17–21 t ha−1 CaO), whereas the lignite and pyrite free site received 7.5 t ha−1 CaO in form of limestone. Fertilizer application rates were: mineral fertilizer 120 N, 100 P and 80 K kg ha−1. 19 t ha−1 sewage sludge and 22 t ha−1 compost were applied. Soil solution was sampled in 20, 60 and 130 cm depth for the period of 16 months. Solution was collected every fortnight and analysed for pH, EC, Ca2+, Mg2+, K+, Na+, Fen+, Aln+, Mn2+, Zn2+, NO3 , NH4 +, SO4 2−, Cl, PO4 3−, Cinorg and DOC. Lignite and pyrite containing spoil differed clearly from lignite and pyrite free spoil regarding soil solution concentrations and composition. Acidity (H+) produced by pyrite oxidation led to an enhanced weathering of minerals and, therefore, to at least 10 fold higher soil solution concentrations compared to the lignite and pyrite free site. Major ions in solution of the lignite and pyrite containing site were Ca2+, Mg2+, Fen+, Aln+ and SO4 2−, whereas soil solution at the lignite and pyrite free site was dominated by Ca2+, Mg2+ and SO4 2−. At both sites application of mineral fertilizer led to an immediate but short term (about 1 month) increase of NO3 , NH4 + and K+ concentrations in soil solution down to a depth of 130 cm. Application of sewage sludge caused a long term (about 16 months) increase of NO3 3 in the topsoil, whereas NO3 concentrations in the subsoil were significantly lower compared to the mineral fertilizer plot. Compost application resulted in a strong long-term increase of K+ in soil solution, whereas NO3 concentrations did not increase. Concentrations of PO4 3− in soil solution depend on solution pH and were not correlated with any treatment. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

19.
The effects of three S deposition scenarios — 50% reduction, no change, and 100% increase — on the cycles of N, P, S, K, Ca, and Mg in a mixed deciduous forest at Coweeta, North Carolina, were simulated using the Nutrient Cycling model (NuCM). The purpose of this exercise was to compare NuCM's output to observed soil and streamwater chemical changes and to explore NuCM's response to varying S deposition scenarios. Ecosystem S content and SO4 2– leaching were controlled almost entirely by soil SO4 2– adsorption in the simulations, which was in turn governed by the nature of the Langmuir isotherm set in the model. Both the simulations and the 20-year trends in streamwater SO4 2– concentration suggest that the ecosystem is slowly becoming S saturated. The streamwater data suggest S saturation is occurring at a slower rate than indicated by the simulations, perhaps because of underestimation of organic S retention in the model. Both the simulations and field data indicated substantial declines in exchangeable bases in A and BA soil horizons, primarily due to vegetation uptake. The correspondence of model output with field data in this case was a result of after-the-fact calibration (i.e. setting weathering rates to very low values) rather than prediction, however. Model output suggests that soil exchangeable cation pools change rapidly, undergoing annual cycles and multi-decade fluctuations.Varying S deposition had very little effect upon simulated vegetation growth, nutrient uptake, or N cycling. Varying S deposition strongly affected simulated Ca2+. Mg2+, K+, and P leaching but caused little change in soil exchangeable pools of Ca2+ K+, or P because soil exchangeable pools were large relative to fluxes. Soil exchangeable Mg2+ pools were reduced by high rates of S deposition but remained well above levels sufficient for tree growth. Although the total soil pools of exchangeable Ca2+ and K+ were only slightly affected by S deposition, there was a redistribution of Ca2+ and K+ from upper to lower horizons with increasing S deposition, causing increased base saturation in the deepest (BC) horizon. The 100% increased S deposition scenario caused increasing peaks in simulated Al3+ concentrations in A horizons after 25 years as a result of large seasonal pulses of SO4 2– and lowered base saturation. Simulated soil solution Al3+ concentrations remained well below toxicity thresholds for selected tree species at the site.  相似文献   

20.
We examined the hydrologic controls on nitrogen biogeochemistry in the hyporheic zone of the Tanana River, a glacially-fed river, in interior Alaska. We measured hyporheic solute concentrations, gas partial pressures, water table height, and flow rates along subsurface flowpaths on two islands for three summers. Denitrification was quantified using an in situ 15NO3 push–pull technique. Hyporheic water level responded rapidly to change in river stage, with the sites flooding periodically in mid−July to early−August. Nitrate concentration was nearly 3-fold greater in river (ca. 100 μg NO3–N l−1) than hyporheic water (ca. 38 μg NO3–N l−1), but approximately 60–80% of river nitrate was removed during the first 50 m of hyporheic flowpath. Denitrification during high river stage ranged from 1.9 to 29.4 mg N kg sediment−1 day−1. Hotspots of methane partial pressure, averaging 50,000 ppmv, occurred in densely vegetated sites in conjunction with mean oxygen concentration below 0.5 mgOl−1. Hyporheic flow was an important mechanism of nitrogen supply to microbes and plant roots, transporting on average 0.41 gNO3–N m−2 day−1, 0.22 g NH4+–N m−2 day−1, and 3.6 g DON m−2 day−1 through surface sediment (top 2 m). Our results suggest that denitrification can be a major sink for river nitrate in boreal forest floodplain soils, particularly at the river-sediment interface. The stability of the river hydrograph and the resulting duration of soil saturation are key factors regulating the redox environment and anaerobic metabolism in the hyporheic zone.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号