Sulfur and oxygen isotope ratios in sulfate during an acidification reversal study at Lake Gårdsjön,Western Sweden

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.     

Deposition of air pollutants in a wind-exposed forest edge

The atmospheric deposition of air pollutants at a forest edge was studied by means of monitoring canopy throughfall at the edge and at five different parallel lines in the forest behind the edge. The investigation was carried out at a pine forest on the Swedish west coast. Throughfall and bulk deposition samples were analyzed for volume, SO ₄ ^2? , NO ₃ ^? , Cl^?, NH ₄ ⁺ , Na⁺, K⁺, Mg²⁺, Ca²⁺, and for pH. The results show that the throughfall flow at the edge was increased substantially for most ions. The ratios in throughfall flows between the edge and the line 50 m into the forest were for SO ₄ ^2? , 1.5, NO ₃ ^? 2.9, NH ₄ ⁺ 2.7, and Na⁺ 3.1. Since this effect is not only valid for forest edges but also for hillsides, hilltops, and edges between stands of different age, etc., there might be substantial areas which get much larger total deposition than the normally considered closed forest.     

Long-term sulfate dynamics at lange bramke (Harz) used for testing two acidification models

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.     

Trends in surface water acidification at ecological monitoring sites in southeastern Canada (1981–1993)

Atmospheric deposition and surface water chemistry have been monitored intensively at 5 geologically “sensitive” sites in southeastern Canada. The sites receive differing acid inputs that span the entire range found in Canada. Surface water data collected at 9 stations from 1981 to 1993 for SO ₄ ^2? , NO ₃ ^? , Alkalinity, DOC, pH, Ca²⁺ and Mg²⁺ have been analyzed to detect monotonic trends. Similarities between the temporal patterns and trends for SO ₄ ^2? in deposition and surface water suggest that they are strongly linked at our sites. Our 13-year datasets showed significant negative SO ₄ ^2? trends at the 3 Ontario sites and a positive trend in Nova Scotia. A climatically-induced SO ₄ ^2? increase in northwestern Ontario has been reversed. Mobilization and export of adsorbed SO ₄ ^2? and/or reoxidized S from the basins of central Ontario sites is delaying their recovery. Two of our 9 stations (in Quebec and central Ontario) are continuing to acidify. The 2 Nova Scotia stations have the highest DOC levels and both exhibit a decreasing trend. Ionic compensation for declining SO ₄ ^2? varies from station to station, sometimes involving an Alk increase, sometimes a base cation decrease, and sometimes more complex combinations. Additional factors (e.g. climatic variation) also influence variable trends, and data records longer than those presently available will be needed to unequivocally verify acidification recovery.     

Sulfur isotope dynamics in a high-elevation catchment,West Glacier lake,Wyoming

Stable isotopes of S are used in conjunction with dissolved SO ₄ ^2? concentrations to evaluate the utility ofδ ³⁴S ratios in tracing contributions of bedrock-derived S to SO ₄ ^2? in runoff. Water samples were collected over the annual hydrograph from two tributaries in the West Glacier Lake, Wyoming, catchment. Concentrations of SO ₄ ^2? ranged from 12.6 to 43.0 Μeq L^?1;δ ³⁴S ratios ranged from ?1.8‰ to +4.9‰ Theδ ³⁴S value of atmospherically derived SO ₄ ^2? is about +5.6%c.; four samples of pyrite from the bedrock hadδ ³⁴S ratios that ranged from +0.7 to +4.1‰ Concentrations of SO ₄ ^2? were inversely related toδ ³⁴S and discharge. The data for the tributary with the higher SO ₄ ^2? concentrations were reasonably consistent with mixing between atmospheric S and S from a bedrock source with aδ ³⁴S ratio of about ?4.5‰. The difference from the measured bedrock values presumably indicates that S isotopes in the bedrock pyrite are heterogeneously distributed. The data from the tributary with lower SO ₄ ^2? concentrations did not follow a two-component mixing line. Deviation from a two-component mixing line is most likely caused by preferential elution of SO ₄ ^2? from the snowpack during the early stages of snowmelt, although microbially mediated fractionation of S isotopes in the soil zone also may cause the deviation from the mixing line. Sulfur isotopes are useful in identifying whether or not there is a substantial contribution of bedrock S to runoff, but quantifying that contribution is problematic.     

The geographical distribution and temporal variations of acidic deposition in Eastern North America

Data from two national precipitation chemistry monitoring networks, and several regional air and precipitation chemistry networks are used to describe some broad-scale features of acidic deposition in eastern North America. In northeastern North America, the coefficient of variation is shown to increase from 10–16% for annual averages to nearly 100% for daily values. There is a strong annual cycle in H⁺, SO _inf4 ^sup= and NH _inf4 ^sup+ deposition and some of the other ions although these cycles are not all in phase. The wet NO _inf3 ^sup? deposition contributes relatively more than SO _inf4 ^sup= to the acidity of snow as compared to rain. Wet deposition is highly “episodic” with about 50% to 70% of the total annual deposition of SO _inf4 ^sup= and NO _inf3 ^sup? accumulating in the highest 20% of the days. Estimates made in various ways indicate that, over eastern North America as a whole, dry deposition is approximately equal to wet for both SO _inf4 ^sup= and NO _inf3 ^sup? . Dry may exceed wet in the high emissions zone but drops to about 20% of the total deposition in more remote areas. Deposition via fog or low cloud impaction is an important input to high elevation forests, but more data are required to quantify the magnitude and regional extent of this.     

Inorganic and organic sulfur profiles in nine Sphagnum peat bogs in the United States and Czechoslovakia

Depth profiles of total S, organic S, soluble SO ₄ ^2? -S, FeS, and FeS₂ were characterized for Sphagnum-derived peat cores collected from 9 sites. Marcell S-2 Bog (MN), Tamarack Swamp (PA), Cranesville Swamp (MD/WV), and Big Run Bog (WV) receive water from precipitation and upland runoff; atmospheric S deposition is 13, 47, 54, and 114 mmol m^?2, yr^?1, respectively. McDonald's Branch Swamp (NJ) is predominantly groundwater fed. Tub Run Bog (WV) and Allegheny Mining Bog (MD) receive augmented SO ₄ ^2? inputs through acid coal mine drainage. Jezerní slat' and Bo?í Dar Bog in Czechoslovakia receive atmospheric S inputs of 33 and 243 mmol m^?2 yr^?1, respectively. In the peat from all sites except Allegheny Mining Bog, where the substantially augmented SO ₄ ^2? input was reflected in an unusually high dissolved SO ₄ ^2? pool in the surface peat, organic S (probably mostly carbon bonded S) was the dominant S fraction; FeS₂ was generally the dominant inorganic S fraction. Subsurface peaks in total S, organic S and FeS₂-S in peat from the runoff water fed sites were interpreted as indicative of depth-dependent patterns in S reduction/oxidation and in S immobilization/mineralization. Unless SO ₄ ^2? inputs to a site are tremendously augmented (e.g., Allegheny Mining Bog), the rapid turnover of the dissolved SO ₄ ^2? pool combined with the relative stability of the other inorganic and organic S pools, apparently functions as an effective buffer against site differences in S inputs, leading to a general similarity in vertical S profiles in the peat deposits.     

Mesoscale spatial variability of sulfate in air and rainwater at St. Louis

Sulfate concentrations in rainwater and in air measured on four summer days at St. Louis were highly variable, both spatially or temporally. Maximum/minimum ratios of aerosol SO _inf4 ^sup? varied by up to a factor of 9, and those in rainwater by a factor of 3 on the average. Generally, SO _inf4 ^sup? concentration patterns in air and rainwater were similar, and consistent with wind direction and the location of sources. Direct relationships between SO _inf4 ^sup? in air and in water were evident on two of the individual days, but not for all days together. The non-uniformity of the SO _inf4 ^sup? pattern plus consideration of possible sources of SO _inf4 ^sup? suggests that nucleation of SO _inf4 ^sup? particles must be a major cause of S scavenging, with some possible influence from sub-cloud impaction.     

Ion mass budgets for small forested catchments in Finland

Ion mass and H⁺ budgets were calculated for three pristine forested catchments using bulk deposition, throughfall and runoff data. The catchments have different soil and forest type characteristics. A forest canopy filtering factor for each catchment was estimated for base cations, H⁺, Cl^? and SO ₄ ^2? by taking into account the specific filtering abilities of different stands based on the throughfall quality and the distribution of forest types. Output fluxes from the catchments were calculated from the quality and quantity of the runoff water. Deposition, weathering, ion exchange, retention and biological accumulation processes were taken into account to calculate catchment H⁺ budgets, and the ratio between external (anthropogenic) and internal H⁺ sources. In general, output exceeded input for Na⁺, K⁺, Ca²⁺, Mg²⁺, HCO ₃ ^? (if present) and A^? (organic anions), whereas retention was observed in the case of H⁺, NH ₄ ⁺ , NO ₃ ^? and SO ₄ ^2? . The range in the annual input of H⁺ was 22.8–26.3 meq m^?2 yr^?1, and in the annual output, 0.3–3.9 meq m^?2 yr^?1. Compared with some forested sites located in high acid deposition areas in southern Scandinavia, Scotland and Canada, the catchments receive rather moderate loads of acidic deposition. The consumption of H⁺ was dominated by base cation exchange plus weathering reactions (41–79 %), and by the retention of SO ₄ ^2? (17–49 %). The maximum net retention of SO ₄ ^2? was 87% in the HietajÄrvi 2 catchment, having the highest proportion of peatlands. Nitrogen transformations played a rather minor role in the H⁺ budgets. The ratio between external and internal H⁺ sources (excluding net base cation uptake by forests) varied between 0.74 and 2.62, depending on catchment characteristics and acidic deposition loads. The impact of the acidic deposition was most evident for the southern Valkeakotinen catchment, where the anthropogenic acidification has been documented also by palaeolimnological methods.     

Mercury antagonists: Effects of sodium chloride and sulfur group (VIa) compounds on excystment of the brine shrimp artemia

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.     

Nitrate reduction coupled with microbial oxidation of sulfide in river sediment

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.     

δ34S, δ18O, δ D in shallow groundwater: Tracing anthropogenic sulfate and accompanying ground water/rock interactions

The objectives of this study are to assessδ ³⁴S as a tracer of anthropogenic SO ₄ ^2? in groundwater and to document geochemical interactions that take place as a result of industrial SO ₄ ^2? loading. During four separate sampling excursions, groundwater samples were obtained from 13 piezometers which surround the elemental S storage blocks at a processing facility for sour (H₂S) natural gas in Alberta, Canada. Each sample was analyzed forδ ³⁴S_sulfate,δ ¹⁸O_sulfate,δ ¹⁸O_water,δD_water, major aqueous species, alkalinity, pH, temperature and dissolved O₂. Hydraulic head measurements were taken to define the groundwater flow field. In the study area, anthropogenic SO ₄ ^2? has aδ ³⁴S of approximately +18‰ (CDT), while natural groundwater SO ₄ ^2? is depleted to about ?12%. Low activity of sulfate reducing bacteria in the groundwater at this site assures thatδ ³⁴S is a conservative tracer. Groundwater SO ₄ ^2? concentrations increase asδ ³⁴S approaches +18‰, suggesting that elevated SO ₄ ^2? concentrations are due to S released by sour gas processing. Acidic waters generated by the oxidation of industrial S from the gas plant are neutralized by rock-water reactions.     

Nutrient Fluxes in Planted Norway Spruce Stands of Different Age in Southern Poland

The fluxes of N–NO ₃ ^? , N–NH ₄ ⁺ , S–SO ₄ ^2? , Na⁺, K⁺, Ca²⁺ and Mg²⁺ from bulk precipitation to throughfall, stemflow and soil water surface flows were studied during 1999–2003 in planted Norway spruce forest stands of different ages (11, 24, 91 and 116 years in 1999). Also, runoff from the corresponding Potok Dupniański Catchment in the Silesian Beskid Mts was studied. N deposition was above the critical load for coniferous trees. The interception increased with stand age as well as leaf area index and so did the leaching from the canopy of almost all the analysed elements, but especially S–SO ₄ ^2? , H⁺ and K⁺. The nutrient fluxes varied with age of the spruce stands. Throughfall showed a high amount of S and of the strong acids (S–SO ₄ ^2? and N–NO ₃ ^? ) deposited to the soil, especially in older spruce age classes. Decomposition of organic matter caused a rise in water acidity and an increase in the concentrations of all the analysed ions; the leaching of minerals, however, was low (under 1%). The horizontal soil water flow showed an increase in the amount of water and amount of ions and contributed to a further decrease of pH at the soil depth of 20 cm. Element concentrations and their amounts increased with water penetrating vertically and horizontally on the slopes. Considerable amounts of ions, especially S and alkaline cations, were carried beyond the reach of the root system and then left the catchment. In the long term, these mineral losses will adversely affect health and growth of the spruce stands, and the increased acidity with stand age will presumably have negative effects on the runoff water ecosystem.     

A method for evaluation of acidic sulfate and nitrate in precipitation

A simple method is presented and used to estimate the portions of SO _inf4 ^sup2? and NO _inf? ^sup3 that contribute to the strong acidity in weekly precipitation samples collected at three NADP sites in the eastern United States. The method assumes that, in general, the difference between SO _inf4 ^sup2? and NH _inf+ ^sup4 represents acidic sulfate and the difference between NO _inf? ^sup3 and soil-derived materials (the sum of Ca²⁺, Mg²⁺, and K⁺) represents acidic nitrate. Acidic sulfate and nitrate are considered to be the predominant source of H⁺ (determined from laboratory pH) in the weekly precipitation samples. Most of the acidity for all three sites was attributed to acidic sulfate. The highest fraction of acidic SO _inf4 ^sup2? to H⁺ wet deposition values was for the east-central Tennessee site (0.95) and the northeastern Illinois site (0.90), and the lowest fraction occurred at the central Pennsylvania site (0.75). The Tennessee site had the greatest acidic fraction of sulfate (0.84) and the Pennsylvania site had the greatest acidic fraction of nitrate (0.59).     

Analysis of Decadal Time Series in Wet N Concentrations at Five Rural Sites in NE Spain

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.     

Biotic and abiotic processes controlling water chemistry during snowmelt at rabbit ears pass,Rocky Mountains,Colorado, U.S.A.

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 ^? .     

Mid-term trends in acid precipitation,streamwater chemistry and element budgets in the strengbach catchment (Vosges Mountains,France)

In the Vosges Mountains (NE of France), integrated plot-catchment studies have been carried out since 1985 in the Strengbach basin to study the influence of acid atmospheric inputs on surface water quality and element budgets. In this paper, available mid-term time series (1985–1991) have been considered to detect obvious trends, if any, in surface water chemistry and element budgets. Air quality data showed a slight decline for SO₂, whereas NO₂ slightly increased over the period, but these trends are not very significant. This is in agreement with increased N concentration (mainly as NH ₄ ⁺ ) and with the stability of SO ₄ ^2? in open field precipitation. Because of a significant decrease in rainfall amount over the period, only inputs of NH ₄ ⁺ increased significantly whereas H⁺ and SO ₄ ²⁺ inputs declined. In spring and streamwaters, pH and dissolved Si concentration increased mainly as a result of a reduced flow. Na⁺, K⁺, Cl^? and HCO-3~^? concentrations remained stable whereas Ca²⁺, Mg²⁺ and SO ₄ ²⁺ concentrations declined significantly. Only NO ₃ ^? concentration increased significantly in springwaters. The catchment budgets revealed significant losses of base cations, Si and SO ₄ ^2? . These losses decreased over the period. Nitrogen was retained in the ecosystem. However, a longer record is needed to determine whether or not changes in surface water chemistry have resulted from short-term flow reductions or long-term changes in input-output ion budgets. This is specially true with N because the decline in SO ₄ ^2? output was accompanied by N accumulation.     

An estimation of atmospheric deposition input of sulphur and nitrogen oxides to the Kejimkujik watershed : 1979–1987

Daily measurements of the concentrations of major ions in ambient air and in precipitation at Kejimkujik National Park, Nova Scotia, Canada over the period May 1979 to December 1987 are used to estimate the wet, dry and total deposition to the watershed. Variations on three time-scales are apparent. The strongest variation, of up to two orders of magnitude occurs on a day to day basis resulting in a coefficient of variation in the range of 110 to 140%. Deposition is highly episodic with the highest 20% of the daily events accounting for 55 to 60% of the long-term deposition. The most systematic variation is the annual cycle observed for many of the species. The air concentration of SO₂ has the most pronounced cycle with a winter maximum and a summer minimum. The SO _inf4 ^sup= air concentrations show a smaller amplitude and are out-of-phase with SO₂, showing a summer maximum. Air concentrations of HNO₃ and particulate N0 _inf3 ^sup- also have an out-of-phase annual cycle, with a summer maximum and summer minimum respectively. Wet deposition of SO _inf4 ^sup= shows a broad maximum through the summer months, but for NO _inf3 ^sup- no systematic cycle is evident. On an ion equivalent basis, NO _inf3 ^sup- contributes as much as SO _inf4 ^sup= to the acidity of winter precipitation, but only one-third as much in the summer months. Although 8.7 yr is too short a time-scale to establish long term variations with any certainty, there does appear to be an overall downward trend in S concentrations and deposition, but not for N. This is not inconsistent with the trends in the emissions of SO₂ and NO_X in the regions upwind of Nova Scotia. The fraction of the S input to the watershed as dry deposition is estimated to average 22% of the total.     

Simultaneous Removal of H2S, NH3, and Ethyl Mercaptan in Biotrickling Filters Packed with Poplar Wood and Polyurethane Foam: Impact of pH During Startup and Crossed Effects Evaluation

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 S^2?) 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.     

Bulk Atmospheric Deposition in the Southern Po Valley (Northern Italy)

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.