The use of calibrated lakes and watersheds for estimating atmospheric deposition near a large point source

We have measured the input and output rates of substances to and from both lakes and watersheds in the Sudbury and Muskoka-Haliburton areas of Ontario. At the former location, we have conducted mass balance studies on 5 lakes and their watersheds for 2½ yrs. At the latter site, we have measured mass balances for 6 lakes and about 30 individual watersheds for the past 5 yrs. Substances studied included SO₄ ^2?, NO₃ ^?, NH₄ ⁺, H⁺, major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) and HCO₃ ^?. During the course of the investigation at Sudbury we have made several observations that indicate that the inputs of some substances, specifically SO₄ ^2? or SO₄ ^2?-precursors and strong acids, to lakes and watersheds are underestimated when measured as bulk deposition (i.e. by collection in a continuously open container): (a) The output of SO₄ ^2? from the calibrated watersheds was substantially greater than the input measured as bulk deposition. (b) The SO₄ ^2? concentrations of the lakes could not be explained on the basis of the measured inputs. An additional input directly to the lake surface was needed to obtain a mass balance. (c) The net input of acids measured as bulk deposition to the watersheds was much less than the acid consumed, which was estimated by the net output of Ca²⁺, Mg²⁺, Na⁺, K⁺, Al³⁺, and the net retention of NO₃ ^?. (d) The major cation content of the study lakes could be explained on the basis of weathering reactions in the lakes' watersheds only if the input of strong acid had been underestimated. When these observations were quantified, they indicated a major portion of the total input of SO₄ ^2?-precursors and of strong acid was not included in our bulk deposition measurements. Deposition of SO₂ is the most likely explanation for these observations.     

Transformation of simulated wet sulfate deposition in forest soils assessed by a core experiment using stable sulfur isotopes

The effects of elevated atmospheric SO ₄ ^2? deposition on S cycling in forest soils were assessed in an irrigation experiment using stable S isotopes. Over a period of 20 months, core lysimeters of five acidic forest soils from Southern Germany with different parent material and pedogenesis were irrigated with solutions chemically similar to canopy throughfall. Sulfate deposition in three experimental variants corresponded to 23, 42 and 87 kg S ha^?1 yr^?1. The SO ₄ ^2? used for irrigation had aδ ³⁴S ratio of +28.0‰ CDT (Canon Diablo Troilite standard), differing by more than +25‰ from natural and anthropogenic S in Southern Germany. A combination of chemical and isotopic analyses of soil and seepage water samples was used to elucidate the fluxes and transformations of simulated wet SO ₄ ^2? deposition in each soil core. Retention of experimentally deposited S ranged from 57±5% in coarse-grained soils low in sesquioxides and clay, to 80±8% in loamy soils with high sesquioxide content. The sesquioxide content proved to be the major factor governing S retention. The ratio of S retained as inorganic SO ₄ ^2? (mainly by adsorption) to that incorporated into organic compounds (presumably by microbial synthesis) ranged from 2 to 4. For the organic S pool, the amount of S retained as C-bonded S exceeded by far that immobilized as ester sulfate in four of the five soils. Application of³⁴S-enriched SO ₄ ^2? appears to be a suitable experimental tool to assess fluxes and transformations of deposited S in forest soils, if aerobic conditions are maintained. In contrast to radioactive S tracers, the concept should be applicable not only in laboratory and lysimeter experiments, but also in long term studies of whole forest ecosystems (e.g., experimental watersheds).     

Recovery of Surface Waters in the Northeastern U.S. from Decreases in Atmospheric Deposition of Sulfur

A simple mass flux model was developed to simulate the response of SO₄ ^2- concentrations in surface waters to past and anticipated future changes in atmospheric deposition of SO₄ ^2-. Values of bulk (or wet) SO₄ ^2- deposition and dry deposition of S determined from measured air concentrations and a deposition velocity were insufficient to balance watershed SO₄ ^2- export at the Hubbard Brook Experimental Forest, NH and for a regional survey of watersheds in the northeastern U.S. We propose two explanations for the unmeasured S source: 1) a significant underestimation of dry S deposition, and/or 2) internal watershed S sources, such as weathering and/or mineralization of soil organic S. Model simulations based on these two mechanisms agreed closely with measured stream SO₄ ^2- concentrations at Hubbard Brook. Close agreement between measured and model predicted results precluded identification of which of the two mechanisms controlled long-term trends in stream SO₄ ^2-. Model simulations indicated that soil adsorption reactions significantly delayed the response of stream water to declines in SO₄ ^2- inputs since 1970, but could not explain the discrepancy in watershed S budgets. Extrapolation of model predictions into the future demonstrates that uncertainty in the source of the S imbalance in watersheds has important implications for assessments of the recovery of surface water acid neutralizing capacity in response to anticipated future reductions in SO2 emissions.     

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.     

Water,NaHCO3−, NaH2PO4− and NaCl-extractable SO42− in acid forest soils

A variety of different methods have been used for the determination of inorganic soil SO₄^2? in the past, which makes it difficult to compare SO₄^2? contents of soils. Sulfate was extracted with the four commonly used extraction solutions 0.5 M NaHCO₃, 0.02 M NaH₂PO₄, 0.1 M NaCl and H₂O from A-, Bw- and Bs-horizons of six acid forest soils. 5 g of field moist soil were percolated with a flow rate of 5 ml/h and percolations were repeated as long as SO₄^2? was detectable in the percolate (> 0.5 mg SO₄·l^?1). NaCl and NaHCO₃ extracted highest amounts of total inorganic SO₄^2? in A-horizons, but NaHCO₃ caused analytical problems. NaHCO₃ and NaH₂PO₄ yielded highest amounts in B-horizons. With the exception of Bs-horizons more than 70% of the total inorganic SO₄^2? was H₂O-soIuble. Thus, if H₂O-soluble SO₄^2? is defined as reversibly bound, the greater part of the inorganic SO₄^2? in the investigated acid forest soils was reversibly bound. This SO₄^2? fraction can potentially be released, if SO₄^2? deposition decreases.     

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.     

Retention and release of S from A freshwater wetland

A freshwater wetland at the Experimental Lakes Area in northwestern Ontario stored most of the SO₄ ^2? received annually from precipitation, runoff and experimental additions. The S budget was determined for a small fen spray irrigated with H₂SO₄ and HNO₃. Annual S retention was greatest during the first year of experimental addition of H₂SO₄ (73% of input in 1983). Retention was lowest (22%) in 1984, a year of lower than average precipitation with a long hot summer. During years with hot, dry summers, SO₄ ^2? was produced from the reoxidation of reduced S compounds in the peat and released to surface waters. The autumn SO₄ ^2? pulse was accompanied by the release of Ca and Mg but was not accompanied by a H⁺ release as has been detected in eastern Ontario and southern Norway, areas which receive more acidic precipitation.     

Extractability and adsorption of sulphate in soils

Virtually all of the indigenous sulphate (SO₄) in a range of UK soils with moderately high pH values (> 6) was found to be present in the soil solution and, as a consequence, was highly susceptible to leaching. For acid soils containing adsorbed SO₄, the extractability of SO₄ in NaCl and CaCl₂ solutions was dependent on both the ionic strength and cation species. Addition of small amounts (<～ 10^?2M) of either NaCl or CaCl₂ actually decreased the amount of SO₄ extracted, but SO₄ extractability increased sharply with concentrations of NaCl or CaCl₂ higher than about 0.1 M. At a similar ionic strength, more SO₄ was extracted by NaCl than CaCl₂. Sequential extraction with 1 M NaCl removed essentially all of the absorbed SO₄. The release characteristics of SO₄ were very different to those of phosphate and this difference in behaviour is not easily reconciled with the view that SO₄ is chemisorbed, as is phosphate. Except for a few acid soils with high oxide contents, the capacity of the soils to adsorb added SO₄ was quite small. None of the soils with pH values higher than 6 adsorbed a significant amount SO₄. The results raise questions regarding the efficiency of SO₄-containing fertilizers in correcting and preventing S deficiency in situations where leaching is important.     

Analysis of 35SO4 = using ion chromatography and liquid scintillation counting

Abstract

A rapid method for determination of ³⁵SO₄ ⁼ activity and SO₄ ⁼ concentration in soil and sediment extracts is described. Sulfate concentrations are determined by non‐suppressed ion chromatography, and an eluent fraction encompassing the sulfate peak is collected for liquid scintillation counting. Inaccuracies due to extraction of non‐sulfate, ³⁵S‐containing species are eliminated, and radioactive samples are more conveniently and safely handled than is the case with other methods.     

Influence of iron nutrition on sulphur uptake and metabolism in maize (Zea mays L.) roots

Abstract

Recent research has evidenced a relationship between Fe nutrition and S nutrition. Aim of the present work was to investigate the effect of Fe deficiency on the capacity of maize roots to take up and metabolize S. Maize (Zea mays L. cv. Cecilia) plants were grown for 10 d in nutrient solution (NS) with (+S) or without (?S) sulphate and Fe was added as Fe^III-EDTA at 80 μm. After removing the extraplasmatic Fe pool, half of the plants of each treatment (+S and ?S) were transferred to a new Fe-free NS. Roots were collected 4 and 24 h from the beginning of Fe deprivation. Fe deprivation slightly increased root thiols content in both nutritive conditions (+S and ?S). ATP sulphurylase activity was enhanced by sulphur deprivation, but greatly depressed when Fe and S were both omitted from the nutrient solution. O-Acetylserine sulphydrylase activity was also enhanced by S deprivation; this activity was increased by Fe starvation in +S plants, while it was unaffected by Fe nutrition in ?S plants. S deprivation greatly increased uptake rates of ³⁵SO₄ ^2? (1.9 ± 0.1 vs. 5.2 ± 0.2 μmol g^?1 root d.w. h^?1); furthermore, Fe deficiency increased ³⁵SO₄ ^2? uptake rates by 11 and 55% in +S and ?S plants, respectively. Data show that Fe-deficiency in maize results in a higher ability to take up sulphate, while limiting the first step of S assimilation in S deprived plants.     

Sulphate uptake from surface water by peat

Time-dependent uptake of ³⁵S]SO₄^2? from surface water overlying cores of peat occurred by passive diffusion along a concentration gradient set up by SO₄^2? metabolism in the peat. The limiting rate constant of SO₄^2? uptake was related to concentration according to Michaelis-Menten kinetics. In peat cores taken from an area of mire submerged by surface water biologically-mediated uptake began immediately. But in cores taken from an adjacent area where the water table was about 5 cm below the peat surface, SO₄^2? metabolism was slower and developed after a lag of about 2.3–4.0 days. Only about 2.2% of [³⁵S]SO₄^2? taken up by peat cores remained in the water-soluble pool, while about 11% was associated with acid-volatile H₂S. Most of the remainder appeared to be incorporated into organic matter. Less than 0.3% was released as H₂S into the gas phase. The experimental results are consistent with a flux into the peat of 3.28–7.71 g S m^?2yr^?1, comparable with 4.76–6.06 g S m^?2yr^?1 indicated by measurements of S content and age of the peat. The results suggest that uptake and metabolism of dissolved SO₄^2? may be the major route of S incorporation into peat.     

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.     

Sulfur Isotope Variations in Atmospheric Sulfur Oxides, Particulate Matter and Deposits Collected at Kyushu Island, Japan

Atmospheric sulfur oxides, particulate matter and deposits (wet and dry deposits) were collected from July 1998 to June 1999 at Kyushu Island, Japan. The isotopic composition of sulfur (δ³⁴S) was measured to identify the source of sulfur in the samples. The monthly δ³⁴S values were always low in the order of the sulfur oxides, sulfate in particulate matter and deposits. The δ³⁴S values of the sulfur oxides ranged from ?2.7 ‰ to ?0.4 ‰ and were close to those of fossil fuels used in Japan. The δ³⁴S values of sulfate in the particulate matter and deposits correlated with seasalt contribution, so that the δ³⁴Snss value was calculated for non-seasalt sulfate. The δ³⁴Snss values of sulfate in the particulate matter and deposits trended higher in winter than summer, suggesting the possibility of isotopic fractionation during chemical transformation (SO₂ to SO₄ ^2?) and of contribution of sulfate derived from sulfur sources with higher δ³⁴S values.     

Variation in the sensitivity of DOC release between different organic soils following H2SO4 and sea‐salt additions

Long‐term monitoring data from eastern North America and Europe indicate a link between increased dissolved organic carbon (DOC) concentrations in surface waters over the last two decades and decreased atmospheric pollutant and marine sulphur (S) deposition. The hypothesis is that decreased acidity and ionic strength associated with declining S deposition has increased the solubility of DOC. However, the sign and magnitude of DOC trends have varied between sites, and in some cases at sites where S deposition has declined, no significant increase in DOC has been observed, creating uncertainty about the causal mechanisms driving the observed trends. In this paper, we demonstrate chemical regulation of DOC release from organic soils in batch experiments caused by changes in acidity and conductivity (measured as a proxy for ionic strength) associated with controlled SO₄^2? additions. DOC release from the top 10 cm of the O‐horizon of organo‐mineral soils and peats decreased by 21–60% in response to additions of 0–437 µeq SO₄^2? l^?1 sulphuric acid (H₂SO₄) and neutral sea‐salt solutions (containing Na⁺, Mg²⁺, Cl^?, SO₄^2?) over a 20‐hour extraction period. A significant decrease in the proportion of the acid‐sensitive coloured aromatic humic acids (measured by specific ultra‐violet absorbance (SUVA) at 254 nm) was also found with increasing acidity (P < 0.05) in most, but not all, soils, confirming that DOC quality, as well as quantity, changed with SO₄^2? additions. DOC release appeared to be more sensitive to increased acidity than to increased conductivity. By comparing the change in DOC release with bulk soil properties, we found that DOC release from the O‐horizon of organo‐mineral soils and semi‐confined peats, which contained greater exchangeable aluminium (Al) and had lower base saturation (BS), were more sensitive to SO₄^2? additions than DOC release from blanket peats with low concentrations of exchangeable Al and greater BS. Therefore, variation in soil type and acid/base status between sites may partly explain the difference in the magnitude of DOC changes seen at different sites where declines in S deposition have been similar.     

Changes in the Chemistry of Precipitation in the United States, 1981–1998

Regulatory measures in the United States, such as Title IV of the Clean Air Act Amendments of 1990, have primarily restricted sulfur dioxide emissions as a way to control acidic deposition. These restrictions, coupled with increasing concentrations of NH₄ ⁺ in wet deposition in some regions of the U.S. and continued high emissions of nitrogen oxides have generated a significant shift in the chemistry of precipitation as measured at National Atmospheric Deposition Program/National Trends Network sites. Trends in precipitation chemistry at NADP/NTN sites were evaluated for statistical significance for the period 1981–1998 using a Seasonal Mann-Kendall Test, a robust non-parametric test for detection of monotonic trends. SO₄ ^2? declines were detected at 100 of the 147 sites examined while no sites exhibited increasing SO₄ ^2? trends. On average, SO₄ ^2? declined 35% over the period 1981–1998 with downward SO₄ ^2? trends being most pronounced in the north-eastern United States. In contrast, no consistent trends in NO₃ ^? concentrations were observed in precipitation in any major region of the United States. Although the majority of sites did not exhibit significant trends in NH₄ ⁺ concentration, 30 sites exhibited upward trends. For Ca²⁺ concentration in precipitation, 64 sites exhibited a significant decreasing trend and no sites exhibited an upward trend.     

Sulphate sorption by variable charge soils

The sorption of sulphate (SO^2?₄) by three variable charge soils from the Canary Islands (Spain) was studied. Sulphate sorption decreased with increasing pH. Only negligible amounts of SO^2?₄ were sorbed above pH 6.5. When the soils were washed with an indifferent electrolyte (0.01 M KCl), more SO^2?₄ was recovered than had been sorbed. This indicated a release of native SO^2?₄ Sulphate replaced hydroxyl ions (OH) and co-ordinated H₂O molecules, as well as very small amounts of silicate (Si). No measurable amount of phosphate (P) was released. On average hydroxyl release accounted for 50% of SO^2?₄ sorbed, the rest being accounted for by the increase in negative charge as measured by K⁺ adsorption. The results presented here are consistent with the sorption of SO^2?₄ through a ligand exchange mechanism, but in a different plane of sorption to that of phosphate.     

Differentiation between adsorbed and precipitated sulphate in soils and at micro-sites of soil aggregates by sulphur K-edge XANES

To investigate the potential of synchrotron‐based X‐ray Absorption Near‐Edge Structure spectroscopy (XANES) at the sulphur (S) K‐edge for a discrimination of adsorbed and precipitated sulphate in soils and soil particles, XANES spectra of ionic sulphate compounds and Al/Fe hydroxy sulphate minerals were compared with spectra of SO₄^2? adsorbed to ferrihydrite, goethite, haematite, gibbsite or allophane. Ionic sulphate and hydroxy sulphate precipitates had broader white‐lines (WL) at 2482.5 eV (full width at half maximum (FWHM) of edge‐normalized spectra, 2.4–4.2 eV; Al hydroxy sulphates, 3.0 eV) than SO₄^2? adsorbed to Al/Fe oxyhydroxides or allophane (FWHM, 1.8–2.4 eV). The ratio of the white‐line (WL) height to the height of the post‐edge feature at 2499 eV (WL/PEF) was larger for SO₄^2? adsorbed to Al/Fe oxyhydroxides or allophane (8.1–11.9) than for Al/Fe hydroxy sulphates and ionic sulphates (3.9–5.7). The WL/PEF ratio of edge‐normalized S K‐edge XANES spectra can be used to distinguish adsorbed from precipitated SO₄^2? in soils and also at microsites of soil particles. The contribution of adsorbed and precipitated SO₄^2? to the total SO₄^2? pool can be roughly quantified. Adsorbed ester sulphate may result in overestimation of precipitated SO₄^2?. The spectra of most soils could be fitted by linear combination fitting (LCF), yielding a similar partitioning between adsorbed and precipitated SO₄^2? as an evaluation of the WL/PEF ratio. The SO₄^2? pool of German forest soils on silicate parent material in most cases was strongly dominated by adsorbed SO₄^2?; however, in three German forest soils subject to elevated atmospheric S deposition, a considerable portion of the SO₄^2? pool was precipitated SO₄^2?, most likely Al hydroxy sulphate. The same is true for Nicaraguan Eutric and Vitric Andosols subject to high volcanogenic S input. In the subsoil of the Vitric Andosol, adsorbed SO₄^2? and Al hydroxy sulphate coexist on a micron scale.     

Effects of glucose and rhizodeposits (with or without cysteine-S) on immobilized-35S, microbial biomass-35S and arylsulphatase activity in a calcareous and an acid brown soil

Our aim was to study the effects of C (as glucose and artificial rhizodeposits) on S immobilization, in relation to microbial biomass‐S and soil arylsulphatase (ARS) activity, in contrasting soils (a calcareous and an acid brown soil). The glucose‐C and artificial rhizodeposit‐C with or without cysteine were added at six rates (0, 100, 200, 400, 600 and 800 mg kg^?1 soil) to the two soils and then incubated with Na₂³⁵SO₄ for 1 week prior to analysis. The percentages of ³⁵S immobilized increased when C as glucose and rhizodeposit (without cysteine) were added to both soils. With cysteine‐containing rhizodeposit, the percentages of ³⁵S immobilized remained relatively stable (23.5% to 29.9%) in the calcareous soil, but decreased in the acid brown soil (52.7% to 31.5%). For both soils, cysteine‐containing rhizodeposit additions showed no significant correlation between immobilized‐³⁵S and microbial biomass‐³⁵S, suggesting that microorganisms immobilized cysteine‐S preferentially instead of ³⁵S from the tracer (Na₂³⁵SO₄). In the calcareous soil, a positive and significant correlation was found between ARS activity and microbial biomass‐³⁵S (r = 0.85, P < 0.05) when glucose was added. We also saw this correlation in the acid brown soil when rhizodeposit‐C without cysteine was added (r = 0.90, P < 0.05). Accordingly, the results showed the presence of extracellular arylsulphatase activity of 48.7 mg p‐nitrophenol kg^?1 soil hour^?1 in the calcareous soil and of 27.0 mg p‐nitrophenol kg^?1 soil hour^?1 in the acid brown soil.     

Chemical fractionation,water solubility and temporal distribution of sheep faecal sulphur fractions in grazed pastures receiving long‐term sulphate fertilization

Abstract

Although over 40% of excretal S is returned to intensively sheep ‐grazed pastures as faecal S, limited information is available on faecal S fractions, their water solubility and temporal distribution. This study reports results obtained from sheep faeces returned to grazed pastures which have received long‐term annual sulphate applications for 15–20 years. Five freshly‐voided sheep faecal samples (<100 g moist faeces per sample) per sampling were randomly collected at approximately one month intervals over a one‐year growing season. Faeces were fractionated into total S, inorganic SO₄ ^2‐, ester SO₄ ^2‐, Hi‐reducible S and C‐bonded S. Results obtained showed that faecal total S, ester SO₄ ^2‐ Hi‐reducible S and C‐bonded S fractions varied significantly throughout the year. Carbon‐bonded S was the dominant (>80%) faecal S fraction, regardless of faecal total S content or the time of year faecal samples were deposited. Faecal ester SO₄ ^2‐ and inorganic _SO₄ ^2‐fractions accounted for 3.3–7.1% and 0.1–14% of faecal total S respectively. Thus approximately 3.4–21.1% of faecal total S was estimated to be potentially leached or readily available to pasture plants. The Hi‐reducible faecal S fraction was significantly‐correlated (r = 0.59***; *** = P ≤ 0.001) with HCl‐extractable faecal inorganic S, which was considered to represent faecal total SO₄ ^2‐ (ester SO₄ ^2‐ and inorganic SO₄ ^2‐ fractions).

The solubility of different faecal S fractions was determined by sequential extraction of ground (< 1 mm) faeces three times (30 minutes per extraction) with water or 0.01 M Ca(H₂PO₄)₂ solution (1: 5 ratio of faecal DM: extractant). Both amounts of water‐extractable and Ca(H₂PO₄)‐extractable faecal S fractions were found to vary significantly throughout the year. Ca(H₂PO₄)₂ tended to extract more inorganic faecal S than water, attributed to the presence of phosphate and the low pH (pH=4) of Ca(H₂PO₄)₂ extractant. A significant proportion (15–25%) of faecal S was extracted by water and most (70%) of this water‐extractable faecal S was in the organic S fraction. Water‐extractable inorganic faecal S probably originated from the faecal total SO₄ ^2‐ fraction as shown by their significant correlation (r = 0.45** ‐0.63***; ** = P≤ 0.01; *** = P≤ 0.001). Some of the faecal S in water extracts may also originate from the faecal C‐bonded S fraction, as a significant correlation was obtained between C‐bonded faecal S and either water‐extractable faecal organic S (r = 0.53–0.57***; *** = P ≤ 0.001) or water‐extractable faecal inorganic S (r = 0.40–0.41*; * = P ≤ 0.05).

Significant amounts of faecal inorganic SO₄ ^2‐ and ester SO₄ ^2‐ fractions were removed by Ca(H₂PO₄)₂ extractant. The Ca(H₂PO₄)₂‐extractable faecal inorganic S was significantly correlated (r = 0.73***^; *** = P ≤ 0.001) with water‐extractable faecal inorganic S.     

Elemental concentrations in fresh snowfall across a regional transect in the northeastern U.S.: Apparent sources and contribution to acidity

Fresh snowfall was collected on the surface of 8 lakes across a 350 km west-east transect from northeastern New York state to the coast of Maine after a single storm. In addition, every snowfall event during the winter of 1993 was collected on a single lake near the center of the transect. Across the transect, midwestern sources appear to dominate Pb and Cd concentrations, while Sb appears to be derived from midwestern sources as well as local and/or industrial East Coast sources. In all samples, the highest Na, Cl and Mg concentrations reflect a marine influence, but at some transect sites roadspray aerosol appears to contribute to Na and Cl concentrations. The regional pattern of Ca, K, Mn and Sr concentrations and Mn/Sr ratios indicate that woodsmoke may be an important winter source of these elements at some sites. In all samples, H⁺ is strongly correlated with NO₃ ^? (R² = 0.97) and mean NO₃ ^?/SO₄ ^2? molar ratios of 6.4 for transect samples, and 4.7 for temporal samples, are higher than mean NO₃ ^?/SO₄ ^2? reported for other precipitation studies in the same region. The contribution of NO₃ ^? to the snowpack greatly exceeds that of SO₄ ^2?, and may be a major source of acidity in aquatic ecosystems during snowmelt.