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1.

Purpose

Nitrate (NO 3 ? ) is often considered to be removed mainly through microbial respiratory denitrification coupled with carbon oxidation. Alternatively, NO 3 ? may be reduced by chemolithoautotrophic bacteria using sulfide as an electron donor. The aim of this study was to quantify the NO 3 ? reduction process with sulfide oxidation under different NO 3 ? input concentrations in river sediment.

Materials and methods

Under NO 3 ? input concentrations of 0.2 to 30?mM, flow-through reactors filled with river sediment from the Pearl River, China, were used to measure the processes of potential NO 3 ? reduction and sulfate (SO 4 2? ) production. Molecular biology analyses were conducted to study the microbial mechanisms involved.

Results and discussion

Simultaneous NO3 ? removal and SO4 2? production were observed with the different NO 3 ? concentrations in the sediment samples collected at different depths. Potentially, NO 3 ? removal reached 72 to 91?% and SO 4 2? production rates ranged from 0.196 to 0.903?mM?h?1. The potential NO 3 ? removal rates were linearly correlated to the NO 3 ? input concentrations. While the SO 4 2? production process became stable, the NO 3 ? reduction process was still a first-order reaction within the range of NO 3 ? input concentrations. With low NO 3 ? input concentrations, the NO 3 ? removal was mainly through the pathway of dissimilatory NO 3 ? reduction to NH 4 + , while with higher NO 3 ? concentrations the NO 3 ? removal was through the denitrification pathway.

Conclusions

While most of NO 3 ? in the sediment was reduced by denitrifying heterotrophs, sulfide-driven NO 3 ? reduction accounted for up to 26?% of the total NO 3 ? removal under lower NO 3 ? concentrations. The vertical distributions of NO 3 ? reduction and SO 4 2? production processes were different because of the variable bacterial communities with depth.  相似文献   

2.
High As groundwater normally contained high concentrations of Cl? and HCO 3 ? . This study examined the effects of Cl?, HCO 3 ? , and As species on As uptake by hyperaccumulator Pteris vittata. Plants were exposed hydroponically to 5.0?mg/L As(III) or As(V) in the presence of 0, 0.5, 1, 2, 5, 10, and 20?mM of Cl? or HCO 3 ? for 10?days. Addition of high Cl? concentrations (>10?mM) slightly inhibited P. vittata growth (biomass), while generally had no significant effect on plant As uptake. High solution pH resulted in reduced plant growth and As uptake, which attributed to the inhibitory effects in HCO 3 ? treatments with the high pH of the high HCO 3 ? concentration. It was speculated that addition of HCO 3 ? (<20?mM) would have no significant effect on plant growth and As uptake. The inhibitory effect of HCO 3 ? on As translocation was less apparent in the As(III) solutions than the As(V) solutions. For the high As groundwater with As(III) as the predominant species, high pH, instead of high concentrations HCO 3 ? and Cl?, was expected to inhibit As uptake. The results suggested that optimum plant growth and maximum As hyperaccumulation could be achieved by adjusting solution pH in the growth media (around 7.2).  相似文献   

3.

Purpose

In summer 2007, biweekly benthic fluxes of the biogenic elements carbon (C), nitrogen (N), silicon (Si), and phosphorus (P) were studied in the Se?ovlje saltern (salt-making facility) in the northern Adriatic Sea, Slovenia in order to determine the impact of stromatolite (??petola??) on the geochemical properties of saltern sediments.

Materials and methods

The brine and pore waters were analyzed for salinity, NH 4 + , NO 3 ? , PO 4 3? , SiO 4 4? , total dissolved nitrogen, total dissolved phosphorus, and fluorescent dissolved organic matter. The sediment was analyzed for organic carbon (OC), total nitrogen (TN), total and organic phosphorus (OP), and biogenic Si concentrations, as well as values of ?? 13COC and ?? 15NTN.

Results and discussion

Nutrient concentrations in brine water increased along the salinity gradient due to different processes, such as the evaporative concentrations of seawater, bacterial activity, more pronounced transformation and degradation of organic matter, and regeneration of nutrients. The petola from the Se?ovlje saltern, which is predominately composed of cyanobacterial and diatom communities, develops during the early evaporation stage and survives during high salinity and halite crystallization. Nitrogen fixation and P removal were the principal biogeochemical processes controlling dissolved inorganic N and P concentrations. At higher salinities, N limitation was more important. Microbes decomposed at higher salinities, and the remineralized N and P nutrients were released from surface pore waters to the brine. OP remineralization was also an important process influencing the distribution of PO 4 3? concentrations in pore waters deeper in the sediments. The increasing SiO 4 4? concentrations with increasing salinity in the brine waters were due to dissolution of diatom frustules, while the decrease in pore water SiO 4 4? was probably the consequence of microbial uptake.

Conclusions

This study provides a better understanding of nutrient cycling and the geochemical processes in the Se?ovlje saltern.  相似文献   

4.
The study aimed to determine the influence of catchment characteristics and flood type on the relationship between streamflow and a number of chemical characteristics of streamwater. These were specific electrical conductivity (SC), pH, the concentrations of main ions (Ca2+, Mg2+, Na+, K+, HCO 3 ? , SO 4 2? , and Cl?), and nutrients (NH 4 + , NO 2 ? , NO 3 ? , and PO 4 3? ). These relationships were studied in three small catchments with different geological structure and land use. Several flood types were distinguished based on the factors that initiate flooding and specific conditions during events. Geological factors led to a lower SC and main ion concentrations at a given specific runoff in catchments built of resistant sandstone versus those built of less resistant sediments. A lower concentration of nutrients was detected in the semi-natural woodland catchment versus agricultural and mixed-use catchments, which are strongly impacted by human activity. The strongest correlation between streamflow and the chemical characteristics of water was found in the woodland catchment. Different types of floods were characterized by different ion concentrations. In the woodland catchment, higher SC and higher concentrations of most main ions were noted during storm-induced floods than during floods induced by prolonged rainfall. The opposite was true for the agricultural and mixed-use catchments. During snowmelt floods, SC, NO 3 ? , and most main ion concentrations were higher when the soil was unfrozen in the agricultural and mixed-use catchments versus when the soil was frozen. In the case of the remaining nutrients, lower concentrations of NH 4 + were detected during rain-induced floods than during snowmelt floods. The opposite was true of PO 4 3? .  相似文献   

5.
A long-term hydrological and water chemistry research was conducted in three experimental microbasins differing in land cover: (1) a purely agricultural fertilized microbasin, (2) a forested microbasin dominated by Carpinus betulus (European hornbeam), and (3) a forested microbasin dominated by Picea abies (L.) (Norway spruce). The dissolved inorganic nitrogen (DIN: NH 4 + , NO 2 ? , NO 3 ? ) budget was examined for a period of 3 years (1991–1993). Mean annual loads of DIN along with sulfate SO 4 2? and base cations Ca2+, Mg2+, Na+, K+, and HCO 3 ? were calculated from ion concentrations measured in stream water, open-area rainfall, throughfall (under tree canopy), and streamwater at the outlets from the microbasins. Comparison of the net imported/exported loads showed that the amount of NO 3 ? leached from the agricultural microbasin is ～3.7 times higher (43.57 kg ha?1?a?1) than that from the spruce dominated microbasin (11.86 kg ha?1?a?1), which is a markedly higher export of NO 3 ? compared to the hornbeam dominated site. Our analyses showed that land cover (tree species) and land use practices (fertilization in agriculture) may actively affect the retention and export of nutrients from the microbasins, and have a pronounce impact on the quality of streamwater. Sulfate export exceeded atmospheric rainfall inputs (measured as wet deposition) in all three microbasins, suggesting an additional dry depositions of SO 4 2? and geologic weathering.  相似文献   

6.
Nitrogen emissions have grown in Spain during the last 15 years. As precipitation scavenges gases and aerosols from the atmosphere, an effect on rainwater concentrations can be expected. However, time-series studies on wet N concentrations in the Iberian Peninsula are very scarce. This paper aims to fill this gap by analysing weekly rainfall N concentrations at a set of rural sites in Catalonia (NE Spain) from 1995/1996 to 2007 and a forest site monitored from 1983 to 2007. The sites encompass a range of rural environments and climate conditions, from the inland pre-Pyrenees (Sort) to the Mediterranean coast (Begur) and from north (Sort and Begur) to central (Palautordera and La Castanya) and south Catalonia (La Senia). We found a 1-year cycle for concentrations of NH 4 + and NO 3 ? whereby higher values were reached at the end of spring–early summer, except at the easternmost coastal site of Begur. Weekly NH 4 + concentrations decreased with time at all sites (except at La Senia) whilst NO 3 ? concentrations increased at all sites during the same period. Rainfall SO 4 2? concentrations decreased with time at all sites. The opposite trends in NO 3 ? and SO 4 2? concentrations determined a shift in the relative acid contribution of those anions during the 12–13-year period. To interpret the increasing trend, mean annual NO 3 ? concentrations were regressed against NO2 Spanish emissions and to some indicators of local anthropogenic activity. The increase at Sort and Palautordera showed good correlation with local anthropogenic indicators. Wet inorganic N deposition ranged between 4.2 and 6.7 kg ha?1 year?1. When including estimates of dry deposition, total annual deposition rose up to 10–20 kg ha?1 year?1, values that have been found to initiate adverse effects on Mediterranean-type forest ecosystems.  相似文献   

7.
A constructed wetland composed of a pond- and a marsh-type wetland was employed to remove nitrogen (N) and phosphorus (P) from effluent of a secondary wastewater treatment plant in Korea. Nutrient concentrations in inflow water and outflow water were monitored around 50 times over a 1-year period. To simulate N and P dynamics in a pond- and a marsh-type wetland, mesocosm experiments were conducted. In the field monitoring, ammonium (NH 4 + ) decreased from 4.6 to 1.7 mg L?1, nitrate (NO 3 ? ) decreased from 6.8 to 5.3 mg L?1, total N (TN) decreased from 14.6 to 10.1 mg L?1, and total P (TP) decreased from 1.6 to 1.1 mg L?1. Average removal efficiencies (loading basis) for NO 3 ? , NH 4 + , TN, and TP were over 70%. Of the environmental variables we considered, water temperature exhibited significant positive correlations with removal rates for the nutrients except for NH 4 + . Results from mesocosm experiments indicated that NH 4 + was removed similarly in both pond- and marsh-type mesocosms within 1 day, but that NO 3 ? was removed more efficiently in marsh-type mesocosms, which required a longer retention time (2?C4 days). Phosphorus was significantly removed similarly in both pond- and marsh-type mesocosms within 1 day. Based on the results, we infer that wetland system composed of a pond- and a marsh-type wetland consecutively can enhance nutrient removal efficiency compared with mono-type wetland. The reason is that removal of NH 4 + and P can be maximized in the pond while NO 3 ? requiring longer retention time can be removed through both pond and marsh. Overall results of this study suggest that a constructed wetland composed of a pond- and a marsh-type wetland is highly effective for the removal of N and P from effluents of a secondary wastewater treatment plant.  相似文献   

8.
The influence of NTA, EDTA, STPP, Triton X100, PO inf4 sup3 and NO inf3 sup? on the mobilization of Pb, Cd, Cu, Cr and Mn from sediments of two rivers located in Northern Greece was studied. The release caused by all examined complexing agents was higher in deionized water than either Axios or Aliakmon river water due to the lack of competition of Ca and Mg cations with the heavy metals for the studied complexing agents, and the decrease of ionic strength. From all examined agents NTA and EDTA showed the greater mobilization ability. Copper showed the greater tendency for remobilization by all examined agents, (according to the order: EDTA?NTA, Triton X1004 PO inf4 sup3? > NO inf3 sup3? ?STPP) while Cr and Mn the smallest following the orders: NTA, PO inf4 sup3? >> NO inf3 sup? , Triton X1004 EDTA, STPP and STPP > EDTA > NTA > Triton X 100 ? PO inf4 sup3? NO3, respectively. An increase in mobilization was noticed with an increase of agent concentration and time of shaking.  相似文献   

9.
Brine shrimp excystment, although highly resistant, is severely inhibited by mmolar mercuric chloride. The presence of 100 mmolar NaCl largely prevents the toxic response. The chloride effect can be explained if the toxic Hg species, neutral HgCl2, is converted into HgCl inf3 sup2? and HgCl inf4 sup2? since charged species not likely to penetrate cyst walls. Other Hg antagonists include SO in3 su2? , SeO inf3 sup2? , TeO inf3 sup2? and TeO inf4 sup2? , but not SO inf4 sup2? and SeO inf4 sup2? . The activity of both Te species can be explained by ready reduction of Te(VI) to Te(IV). Significant anti-mercurial effects were seen in mmolar thiols, ethionine and organoselenium compounds. Thiamine and methionine were both active Hg antagonists at 10 to 30 mmolar levels. The activities of S, Se and Cl? compounds show that both geochemical and physiological modes of defense against and adaptation to high Hg levels exist.  相似文献   

10.
The present study was conducted in tropical Sal forest ecosystem of the Doon valley in the Indian Himalayas to assess the critical load of sulfur and nitrogen and their exceedances. The observed pattern of throughfall ionic composition in the study are Ca2+>K+>Mg2+>Cl?>?HCO3?>?Na+>NO 3 ? >?SO 3 2? ???NH 4 + >F?. The sum of cation studied is 412.29 ??eq l?1 and that of anions is 196.98 ??eq l?1, showing cation excess of 215.31 ??eq l?1. The cations, namely Ca2+, Mg2+, K+, Na+, and NH 4 + , made a contribution of about 67% of the total ion strength, where as anion comprising of SO 4 2? , Cl?, NO 3 ? , and HCO 3 ? contributed 33%. The chief acidic components were Cl?C (12%) and HCO 3 ? (8%), while the presence of SO 4 2? (5%) and NO 3 ? (6%), respectively. Percentage contribution of bole to total aboveground biomass was ??72.38% in comparison to 2.24?C2.93% of leaf biomass, 10.34?C10.96% of branch biomass and 13.21?C17.07% of bark biomass. There was high and significant variation (P?<?0.001) in the total aboveground biomass produced at different sites. The aboveground net primary productivity (ANPP) in these sites ranged between 2.09 and 9.22 t ha?1 year?1. The base cations and nitrogen immobilization was found to be maximum in bole. The net annual uptake of the base cations varied from 306.85 to 1,311.46 eq ha?1 year?1 and of nitrogen from 68.27 to 263.51 eq ha?1 year?1. The critical appraisal of soil showed that cation exchange capacity lied between 18.37 and 10.30 Cmol (p+) kg?1. The base saturation percentage of soil was as high as 82.43% in Senkot, whereas in Kalusidh it was just 44.28%. The local temperature corrected base cation weathering rates based on soil mineralogy, parent material class, and texture class varied from 484.15 to 627.25 eq ha?1 year?1, showing a weak potentiality of the system to buffer any incoming acidity and thus providing restricted acid neutralizing capacity to keep the ecosystem stable under increased future deposition scenarios in near future. The appreciable BS of the soil indicates the presence of intense nutrient phytorecycling forces within this climate and atmospheric deposition in replenishing base cations in the soil, which includes intrinsic soil-forming processes, i.e., weathering. The highest value of critical load for acidity was 2,896.50 eq ha?1 year?1 and the lowest was 2,792.45 eq ha?1 year?1. The calculated value of the minimum critical loads for nitrogen varied from 69.77 to 265.01 eq ha?1 year?1, whereas the maximum nitrogen critical load ranged between 2,992.63 and 4,394.45 eq ha?1 year?1. The minimum and the maximum critical loads of sulfur ranged between 2,130.49 and 3,261.64 eq ha?1 year?1 and 2,250.58 and 3,381.73 eq ha?1 year?1, respectively. The values of exceedance of sulfur and nitrogen were negative, implying that in the current scenario Sal forests of the Doon valley are well protected from acidification.  相似文献   

11.
The present work discusses the startup and operation of different biotrickling filters during the simultaneous removal of NH3, H2S, and ethyl mercaptan (EM) for odor control, focusing on (a) the impact of pH control in the stability of the nitrification processes during reactor startup and (b) the crossed effects among selected pollutants and their by-products. Two biotrickling filters were packed with poplar wood chips (R1 and R2A), while a third reactor was packed with polyurethane foam (R2B). R2A and R2B presented a pH control system, whereas R1 did not. Loads of 2?C10?g N?CNH3 m?3?h?1, 5?C16?g S?CH2S m?3?h?1, and 1?C6?g EM m?3?h?1 were supplied to the bioreactors. The presence of a pH control loop in R2A and R2B proved to be crucial to avoid long startup periods and bioreactors malfunctioning due to biological activity inhibition. In addition, the impact of the presence of different concentrations of a series of N species (NH 4 + , NO 2 ? , and NO 3 ? ) and S species (SO 4 2? and S2?) on the performance of the two biotrickling filters was studied by increasing their load to the reactors. Sulfide oxidation proved to be the most resilient process, since it was not affected in any of the experiments, while nitrification and EM removal were severely affected. In particular, the latter was affected by SO 4 2? and NO 2 ? , while nitrification was significantly affected by NH 4 + . The biotrickling filter packed with polyurethane foam was more sensitive to crossed effects than the biotrickling filter packed with poplar wood chips.  相似文献   

12.
A modeling study on fertilizer by-products fate and transport was performed in an unconfined shallow aquifer equipped with a grid of 13 piezometers. The field site was located in a former agricultural field overlying a river paleochannel near Ferrara (Northern Italy), cultivated with cereals rotation until 2004 and then converted to park. Piezometers were installed in June 2007 and were monitored until June 2009 via pressure transducer data loggers to evaluate the temporal and spatial variation of groundwater heads, while an onsite meteorological station provided data for recharge rate calculations via unsaturated zone modeling. The groundwater composition in June 2007 exhibited elevated nitrate (NO 3 ? ) and chloride (Cl?) concentrations due to fertilizer leaching from the top soil. The spatial distribution of NO 3 ? and Cl? was heterogeneous and the concentration decreased during the monitoring period, with NO 3 ? attenuation (below 10?mg/l) after 650?days. A transient groundwater flow and contaminant transport model was calibrated versus observed heads and NO 3 ? and Cl? concentrations. Cl? was used as environmental tracer to quantify groundwater flow velocity and it was simulated as a conservative species. NO 3 ? was treated as a reactive species and denitrification was simulated with a first order degradation rate constant. Model calibration gave a low denitrification rate (2.5e?3 mg-NO 3 ? /l/d) likely because of prevailing oxic conditions and low concentration of dissolved organic carbon. Scenario modeling was implemented with steady state and variable flow time discretization to identify the mechanism of NO 3 ? attenuation. It was shown that transient piezometric conditions did not exert a strong control on NO 3 ? clean up time, while transient recharge rate did, because it is the main source of unpolluted water in the domain.  相似文献   

13.
The effect of different anions on the balance of heavy metal cations in the soil-solution system has been assessed under model laboratory conditions. It has been found that the uptake of the Cu, Zn, and Pb cations by an ordinary chernozem from solutions of different salts is accompanied by the displacement of the exchangeable cations to the solution in the following order: Ca2+ > Mg2+ > Na+ > K+. The sum of the displaced exchangeable cations in most cases exceeds the amount of the adsorbed heavy metal cations. According to the effect of the anions on the displacing capacity of the metal cations, the following series are formed: for copper, SO 4 2? ? Cl? > OAc? > NO 3 ? ; for lead, Cl? ? NO 3 ? > OAc?; and, for zinc, SO 4 2? ? Cl? ? OAc? > NO 3 ? .  相似文献   

14.
Over 3 yr of particulate measurements were made at two high elevation sites in the southern Appalachian Mountains of Tennessee and Virginia. Both dichotomous samplers and filter packs were used to obtain day and night, week-long samples for subsequent elemental and ionic analysis. Total No inf3 sup? (HNO3 + No in3 sup? ) and SO inf4 sup2? averaged, respectively, 1.1 and 5.0 µg m?3 at Look Rock, Tennessee and 2.0 and 6.4 µg m?3 at Whitetop Mountain, Virginia. At Whitetop Mountain, the spring and summer seasons had the highest average SO inf4 sup2? concentrations. Seasonally, total N03 varied little. The diurnal variation of elements and SO inf4 sup2? was small. Only total NO inf3 sup? varied substantially with highest values during the day. The fine fraction (particle diameter < 2.5 µm) accounted for about 67% of the total mass. Fine mass and elemental concentrations were generally higher at Look Rock. The elements comprising the principal mass fraction of the coarse samples (2.5 gm < particle diameter < 10 to 15 µm) were of crustal origin (e.g., Al, Si, Ca, Fe) while the element comprising the principal mass fraction of the fine samples (i.e., S) was of manmade origin. Cluster analysis identified two groups of elements at Whitetop Mountain. These groups, in both the coarse and fine fraction, were associate with a soil and an automobile emission component. At Look Rock, only a soil component was obvious.  相似文献   

15.
The chemical composition of snowmelt, groundwater, and streamwater was monitored during the spring of 1991 and 1992 in a 200-ha subalpine catchment on the western flank of the Rocky Mountains near Steamboat Springs, Colorado. Most of the snowmelt occurred during a one-month period annually that began in mid-May 1991 and mid-April 1992. The average water quality characteristics of individual sampling sites (meltwater, streamwater, and groundwater) were similar in 1991 and 1992. The major ions in meltwater were differentially eluted from the snowpack, and meltwater was dominated by Ca2+, SO 4 2? , and NO 3 ? . Groundwater and streamwater were dominated by weathering products, including Ca2+, HCO 3 ? (measured as alkalinity), and SiO2, and their concentrations decreased as snowmelt progressed. One well had extremely high NO 3 ? . concentrations, which were balanced by Ca2+ concentrations. For this well, hydrogen ion was hypothesized to be generated from nitrification in overlying soils, and subsequently exchanged with other cations, particularly Ca2+. Solute concentrations in streamwater also decreased as snowmelt progressed. Variations in groundwater levels and solute concentrations indicate that most of the meltwater traveled through the surficial materials. A mass balance for 1992 indicated that the watershed retained H+, NH 4 + , NO 3 ? , SO 4 2? and Cl? and was the primary source of base cations and other weathering products. Proportionally more SO 4 2? was deposited with the unusually high summer rainfall in 1992 compared to that released from snowmelt, whereas NO 3 ? was higher in snowmelt and Cl? was the same. The sum of snowmelt and rainfall could account for greater than 90% of the H+ and NH 4 + retained by the watershed and greater than 50% of the NO 3 ? .  相似文献   

16.
A study on pH and chemical composition of precipitation was carried out in two Italian sites, one urban (site 1) and one rural (site 2), located approximately 30 km far from Bologna, during a 3-year period. No significative site variation was found. In both locations, bulk deposition pH ranged from slightly acid to slightly alkaline, despite the volume weighted mean concentration of acidic species, NO 3 ? and SO 4 2? (67.4 and 118.4 μeq l?1 in site 1 and 88.7 and 103.8 μeq l?1 in site 2), that were similar to those of typical acidic rainfall region. This might be ascribed to the neutralization reaction of the Ca2+, attributed to the calcareous soil and the frequent dusty air mass intrusion from the Sahara. The pair correlation matrix and the analysis of the main components suggested also ammonium and other crustal elements as neutralization agents. The depositional rate of SO 4 2? and NO 3 ? , chemical elements of agricultural interest, amounted to 38 and 28 and 32 and 35 kg ha?1 for site 1 and site 2, respectively. These supplies of nutrient were not negligible and had to be considered on cultivated lands. NH 4 + deposition rate on site 2 was 7 kg ha?1, 23% over site 1, probably due to nitrogen fertilization in the fields around the monitoring station. In site 1, SO 4 2? presented a seasonal trend, indicating that its principal source was the residential heating. Results emphasized that the entity of the bulk deposition acidification is linked not only to the ions local emission sources (fossil fuel combustions, heating, and fertilizers) but also to the surrounding territory and the prevalent wind that transports through kilometers air masses which may contain acidic and alkaline species.  相似文献   

17.
At Lange Bramke (Harz) soil solution and runoff concentrations of major elements were observed over 16 yr. During this period acid deposition was high but showed a marked decrease of H+ and SO 4 2? both in concentrations and fluxes over the last five years. Among others, this record reveals the following patterns: seasonality in the signals for SO 4 2? and NO 3 ? in runoff which are synchronous; an accumulation of SO 4 2? in the soil, initially up to 50% of the deposition fluxes; apparently no correlation between runoff and SO 4 2? concentration, and no long-term trend in runoff concentration of SO 4 2? . In this paper we use these patterns in the data set from Lange Bramke to test two established acidification models. The test criterion is that the algorithms employed by the SO 4 2? modules of these models must be able to reproduce these features. To that end, both models need not to be run as it can be shown that even with completely unrestricted parameter values the two algorithms are unable to match the observed SO 4 2? dynamics. The MAGIC model (Cosbyet al., 1985) is unable to reproduce, given the existence of net SO 4 2? accumulation, the constant SO 4 2? concentration in runoff during the last 16 years. The second model, BEM (Prenzel, 1986), is succesful in reconstructing the constant SC>4~ levels in runoff. However, on a monthly time scale BEM predicts a shift between the periodic maximum concentrations of SO 4 2? and NO 3 ? which is not observed in the data.  相似文献   

18.
The reversibility of acidification is being investigated in a full scale catchment manipulation experiment at Lake Gårdsjön on the Swedish west coast using isotopes as environmental tracers. A 6300 m2 roof over the catchment enables researchers to control depositional variables. Stable S isotope values were determined in bulk deposition, throughfall, runoff, groundwater and soil-extracted water during one year prior to and two years of experimental control. Data collected prior to experimental control suggest that the inorganic SO 4 2? pool within the catchment has a homogeneousδ 34S value of about+5.5‰. Sprinkling of water spiked with small amounts of sea-water derived SO 4 2? started in April 1991. Theδ 34S value of this SO 4 2? is around+19.5‰. Since April 1991, the SO 4 2? concentration in runoff has decreased by some 30%, however, theδ 34S value have increased by only 0.5‰. This suggests mixing of sprinkling water S with a large reservoir of S in the catchment. Oxygen isotopes in SO 4 2? suggest that less than one third of the SO 4 2? in runoff is secondary SO 4 2? formed within the soil profile. This is, however, no evidence for net mineralization of S. The SO 4 2? in runoff in the roofed catchment is a mixture of SO 4 2? previously adsorbed in the soil, mineralized organic S and SO 4 2? from the sprinkler water. Calculations based on isotope data indicate that the turnover time of S within the catchment is on the order of decades. Since SO 4 2? facilitates base cation flow, the acidification reversal will take a much longer time than concentration decreases of SO 4 2? would suggest.  相似文献   

19.
A 2 yr field study on the influence of N fertilization and rainfall on groundwater pollution was carried out in the sandy area of Belgium. The NO inf3 sup? -N and Cl? content of the groundwater at 0.5, 1.0, 1.5, and 2.0 m depths was monitored every two weeks on a field, grown with barley in 1980 and with maize in 1981. Turnips for cattle feed were grown in between the two crops. The total annual rainfall during the period under study was about 800 mm. The NO inf3 sup? -N content at all depths was at all times above 11.3 mg NO inf3 sup? -N dm?3, the WHO safe limit. Fluctuation of the NO inf3 sup? -N content occurred mainly at 0.5 and 1.0 m. The concentration at 1.5 and 2.0 m depths was higher most of the time than at 0.5 and 1.0 m. Leaching of NO inf3 sup? -N into deeper layers occurred when there was heavy rainfall. There was no important loss of NO inf3 sup? -N through denitrification at 1.5 and 2.0 m depths.  相似文献   

20.
We evaluated the differences in the use of a quartz filter and a polytetrafluoroethylene (PTFE) filter as a first (F0)-stage filter in a four-stage filter-pack method. A four-stage filter-pack method can completely collect sulfur species (SO2 and SO 4 2? ), nitrate species (HNO3 and NO 3 ? ), and ammonium species (NH3 and NH 4 + ) with little or no leakage irrespectively of the first-stage filter used. On the other hand, a seasonal variation was observed in the efficiency of collection between the quartz filter and the PTFE filter depending on the material to be collected. There was no seasonal variation in the efficiency of collection in sulfur species; in contrast, a clear seasonal variation was observed for the nitrate and ammonium species. As for NO 3 ? , the PTFE filter was more vulnerable than the quartz filter at air temperatures below 21°C, while the quartz filter was more vulnerable than the PTFE filter at air temperatures exceeding 21°C. A similar vulnerability for air temperature was observed for NH 4 + , although the threshold air temperature was 23°C for NH 4 + . Consequently, the evaporation loss of NO 3 ? would be mainly attributable to the volatilization of NH4NO3, although it is also partially due to the volatilization of NH4Cl.  相似文献   

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