Response of a grassland ecosystem to air pollutants: II--The chemical climate: Fluxes of sedimenting airborne matter

Measurement of the deposition of sedimenting particles requires a sampling device, which avoids simultaneous deposition of gases and aerosols to the collection surface. A sampler constructed for the purpose of collecting rain and sedimenting particles is described and characterized in detail, in particular with regard to its collection efficiency for rain. Its collection properties for gases and aerosols are shown to be negligible. From two years of sampling at different heights it was found that resuspension of particles and co-condensation of gases near the plant canopy may lead to a major overestimation of bulk deposition. As a consequence, the extension towards the canopy of the constant flux layer for sedimenting particles has to be determined experimentally. Bulk deposition of sodium, potassium, magnesium, calcium, lead, copper, cadmium, manganese, iron, ammonium, nitrate, phosphate, sulfate, total sulfur and chloride at Braunschweig-V?lkenrode, Southeast Lower Saxony, Germany, were recorded for six years. During this period a considerable decrease was observed in the deposition of lead, cadmium, nitrate, sulfate and total sulfur.     

Contribution of canopy leaching to sulphate deposition in a Scots pine forest

Radioactive sulphate (35SO4) was applied to the soil below a Scots pine forest on 23 June 1989, and its movement into the canopy and into throughfall and stemflow was measured over 4 months. The specific activity, Bq (mg S)(-1), of the canopy increased monotonically; uptake by current-year (1989) expanding needles was initially twice as fast as by older needles or live twigs. By 10 October the canopy average specific activity was 62 Bq (mg S)(-1). The specific activity of net throughfall (throughfall + stemflow - rain), deduced from measurements from six throughfall collectors, six stemflow collectors and two rain collectors, fell rapidly from 12.6 Bq (mg S)(-1) in late July to <1 Bq (mg S)(-1) in mid-August. The results suggest (assuming rapid equilibration of 35S with sulphate in soil) that root-derived sulphate contributed c. 3% of sulphate in net throughfall and that dry deposition of SO2 and sulphate particles contributed c. 97% of the 0.56 g S m(-2) measured in net throughfall over the period. Simultaneous measurements of SO2 at canopy height and of NH3 above and within the canopy gave mean concentrations of 5.9 and 0.86 microg m(-3), respectively, sufficient to account for the sulphate measured in net throughfall only if codeposition of NH3 and SO2 occurred to canopy surfaces. The large values of specific activity observed in July, however, indicate that throughfall composition may be closely related to recent soil input of sulphate, and that equilibrium cannot be safely assumed. The possibility of a significant contribution of soil-derived sulphate to sulphate deposition in net throughfall cannot be ruled out on the basis of this experiment.     

Chloride imbalances in soil lysimeters

The assumption that soil neither acts as a source or a sink of chloride is evaluated by incubating soil cores in lysimeters in a climate chamber under controlled conditions. Some of the lysimeters acted as a sink while others acted as a source of chloride. Considerable amounts of organic chlorine were lost by leaching. The loss by leaching of organic chlorine could only explain part of the discrepancy in the lysimeters where the soil acted as a sink and it could certainly not explain the cases where the soil acted as a source.The storage of organic chlorine was four times larger than the storage of chloride and comparably small changes in the organic chlorine storage will thus have a considerable influence on the chloride budget. However, the soil was too heterogeneous to determine whether a change in the storage had taken place or not. It is concluded that the observed chloride surplus and also, at least to some extent, the observed chloride deficit, most likely was caused by net-changes in the storage of organic chlorine in soil. An inverse correlation was found between the initial chloride content of the soil and the imbalance in the chloride budget.Dry deposition of chloride is generally assumed to equal the run-off minus the wet deposition. Extrapolation to the field situation suggests that the output of organic chlorine by soil leachate is at risk to cause an underestimation of the dry deposition by about 25%.     

Sulphur dioxide adsorption in Scots pine canopies exposed to high ammonia emissions near a Cu-Ni smelter in SW Finland

Since 1994 the nickel-processing plant at the Cu-Ni smelter at Harjavalta, south-west Finland, has emitted considerable amounts of NH(3) into the atmosphere. The effects of NH(3) emissions on nitrogen and sulphur deposition in throughfall and the foliar nutrient status were investigated in a Scots pine stand at 0.5 km distance. Bulk deposition, stand throughfall and percolation water (20 cm depth) samples were collected at 4-week intervals during 1992-1998. pH and the Ca, Mg, K, NH(4) and SO(4) concentrations were determined on the samples. NH(3) emissions have strongly increased the scavenging of SO(2) from the air in the pine stand, and the increased levels of N and S deposition were clearly evident as increased foliar N and S concentrations and larger needle size. The increased input of SO(4) into the forest floor was not associated with an increase in the leaching of Ca and Mg from the surface soil layers.     

Composition of wet and bulk deposition in Erzurum, Turkey

Seasonal variations in the chemical characteristics of wet and bulk deposition samples collected in Erzurum were investigated for the period March 2002-January 2003. Major cations (Ca2+, K+, Mg2+) and major anions (SO4(2-),NO3-) were determined in bulk and wet deposition samples; pH was also measured in wet deposition. The average pH of the wet deposition at Erzurum was 6.6 due to extensive neutralization of the acidity. A strong relationship between pH and SO4(2-) concentrations was observed in all seasons; however, only a weak relationship was found between pH and NO3-. On a seasonal basis, the correlation between Ca2+ and SO4(2-) concentrations was stronger in winter than in summer. Seasonal variations of ions were examined in both wet and bulk deposition samples. Although maximum concentrations of anions generally occurred during winter and spring, cation concentrations peaked in summer for both wet and bulk deposition. Results indicated that Ca2+ was the dominant cation and SO4(2-) the dominant anion in all deposition samples at Erzurum. Even though correlations among the crustal ions (calcium, magnesium and potassium) were high, the relationship between anthropogenic ions (sulfate and nitrate) was less clear in bulk deposition.     

Element fluxes through European forest ecosystems and their relationships with stand and site characteristics

This paper describes a European wide assessment of element budgets, using available data on deposition, meteorology and soil solution chemistry at 121 Intensive Monitoring plots. Input fluxes from the atmosphere were derived from fortnightly or monthly measurements of bulk deposition and throughfall, corrected for canopy uptake. Element outputs from the forest ecosystem were derived by multiplying fortnightly or monthly measurements of the soil solution composition at the bottom of the root zone with simulated unsaturated soil water fluxes. Despite the uncertainties in the calculated budgets, the results indicate that: (i) SO4 is still the dominant source of actual soil acidification despite the generally lower input of S than N, due to the different behaviour of S (near tracer) and N (strong retention); (ii) base cation removal due to man-induced soil acidification is limited; and (iii) Al release is high in areas with high S inputs and low base status.     

Trace Metals in Upland Headwater Lakes in Ireland

Trace elements (n = 23) in Irish headwater lakes (n = 126) were investigated to determine their ambient concentrations, fractionation (total, dissolved, and non-labile), and geochemical controls. Lakes were generally located in remote upland, acid-sensitive regions along the coastal margins of the country. Total trace metal concentrations were low, within the range of natural pristine surface waters; however, some lakes (~20 %) had inorganic labile aluminum and manganese at levels potentially harmful to aquatic organisms. Redundancy analysis indicated that geochemical weathering was the dominant controlling factor for total metals, compared with acidity for dissolved metals. In addition, many metals were positively correlated with dissolved organic carbon indicating their affinity (or complexation) with humic substances (e.g., aluminum, iron, mercury, lead). However, a number of trace metals (e.g., aluminum, mercury, zinc) were correlated with anthropogenic acidic deposition (i.e., non-marine sulfate), suggesting atmospheric sources or elevated leaching owing to acidic deposition. As transboundary air pollution continues to decline, significant changes in the cycling of trace metals is anticipated.     

Acid deposition and the element composition of pine tree rings

The element contents of pine tree rings (Pinus sylvestris L.) were analyzed in five areas differing in the level of sulphur deposition. The elements studied and their average content in xylem were as follows:

aluminium 4.2, manganese 65, zinc 8.4, potassium 390, rubidium 2.2, calcium 930, magnesium 131, phosphorus 38, sulphur 56, nitrogen 0.65, boron 4.3 and molybdenum 0.03 mg/kg.

The contents of aluminium, potassium and rubidium were higher in tree rings from the 1950's on, particularly in southern Finland. The increase is probably due to acid deposition in the soil.     

Soil solution nitrogen and cations influenced by (NH4)2SO4 deposition in a coniferous forest

The effects of chronically enhanced (NH(4))(2)SO(4) deposition on ion concentrations in soil solution and ionic fluxes were investigated in a Picea abies plot at Grizedale forest, NW England. Soil cores closed at the base and containing a ceramic suction cup sampler were 'roofed' and watered every 2 weeks with bulk throughfall collected in the field. Treatments consisted of the inclusion of living roots from mature trees in the lysimeters and increasing (NH(4))(2)SO(4) deposition (NS treatment) to ambient + 75 kg N ha(-1) a(-1). Rainfall, throughfall and soil solutions were collected every 2 weeks during 18 months, and analysed for major cations and anions. NO(3)(-) fluxes significantly increased following NS treatment, and were balanced by increased Al(3+) losses. Increased SO(4)(2-) concentrations played a minor role in controlling soil solution cation concentrations. The soil exchange complex was dominated by Al and, during the experimental period, cores of all treatments 'switched' from Ca(2+) to Al(3+) leaching, leading to mean [Formula: see text] molar ratios in soil solution of NS treated cores of 0.24. The experiment confirmed that the most sensitive soils to acidification (through deposition or changing environmental conditions) are those with low base saturation, and with a pH in the lower Ca, or Al buffer ranges.     

Stabilization of Pb- and Cu-contaminated soil using coal fly ash and peat

The stabilization of metal contaminated soil is being tested as an alternative remediation method to landfilling. An evaluation of the changes in Cu and Pb mobility and bioavailability in soil induced by the addition of coal fly ash and natural organic matter (peat) revealed that the amount of leached Cu decreased by 98.2% and Pb by 99.9%, as assessed by a batch test. Metal leaching from the treated soil was lower by two orders of magnitude compared to the untreated soil in the field lysimeters. A possible formation of mineral Cu- and Pb-bearing phases and active surface with oxides were identified by chemical equilibrium calculations. Low metal leaching during a two-year observation period, increased seed germination rate, reduced metal accumulation in plant shoots, and decreased toxicity to plants and bacteria, thereby demonstrating this stabilization method to be a promising technique for in situ remediation of Cu and Pb contaminated soil.     

Throughfall chemistry in a spruce chronosequence in southern Poland

The chemical composition of throughfall and canopy leaching, as well as the acid neutralizing capacity and alkalinity depended on the age of Norway spruce (Picea abies Karst) stands and season of the year. A higher amount of sulphur and strong acids was deposited to the soil in the older age classes. Concentrations of SO(4)(2)(-), K(+), H(+), Mn(2+), Fe(2+) and Zn(2+) in throughfall were higher than in bulk precipitation in any season. This suggests that these ions were washed out or washed from the surface of needles and/or barks. The other ions NO(3)(-), NH(4)(+), Ca(2+) and Mg(2+) were retained by the canopy, in particular Ca(2+) and Mg(2+) during the growing season in young stands. Principal component analysis identified five factors responsible for the data structure and suggested the major anthropogenic emission sources were acidic emission (SO(4)(2)(-)+NO(3)(-)), heavy metals-dust particles (Fe(2+)+Mn(2+)+Zn(2+)), ammonium (NH(4)(+)) and H(+), while the natural-origin emission was mineral dust (Na(+)+K(+)+Ca(2+)+Mg(2+)).     

Atmospheric Deposition and Ionic Input in Adirondack Forests

Major mechanisms for input of ions to forest ecosystems in the central Adirondack Mountains of New York State were studied. Precipitation and throughfall in adjacent northern hardwood and lake margin coniferous forests were continuously sampled from May 2, 1979 to May 7, 1980. Important mechanisms for transport of ions from atmosphere to forest floor were identified using regression analyses and the assumption that deciduous and coniferous forests capture particulates and aerosols with differing efficiencies. Sodium was delivered in precipitation and dry-fall and interacted little with the forest canopies. Hydrogen, potassium, and magnesium were also deposited primarily by bulk precipitation but hydrogen was retained by foliage while additional quantities of potassium and magnesium were leached from tree canopies. Impaction of suspended particulates and/or aerosols on forest vegetation was an important source of additional sulfate and nitrate, and these ions contributed to the leaching of calcium from foliage.     

Relation between estimated dry deposition and throughfall in a coniferous forest exposed to controlled levels of SO2 and NO2

Throughfall was collected in a Scots pine forest exposed to about 14 microg m(-3) of both SO2 and NO2, and in a control forest with 1 microg m(-3) SO2 and < 1 microg m(-3) NO2. Precipitation was collected in a nearby open field. Collection was performed on an event basis during the whole vegetation period. Exposure was made by an open-air release system during the vegetation period, except during rain and at night. Additional sulfate deposition in the exposed forest (compared to control forest) was nearly equal to dry deposition of sulfur dioxide, as estimated with a stomatal conductance model adapted for the particular forest. It is thus concluded that essentially all of the dry deposited sulfur dioxide is eventually extracted and appears in throughfall-including the fraction that has been deposited through stomata. Attempts to relate net throughfall deposition to dry deposition of sulfate in the control forest were inconclusive, since a minor (10%) uncertainty in the water balance had a major influence on calculated deposition velocity for particulate sulfate. Nitrate throughfall deposition is about half of the open field wet deposition, both for the exposed and control forest. Thus, a long-term exposure with about 14 microg m(-3) NO2 decreased nitrate throughfall deposition.     

Atmospheric deposition and canopy exchange processes in heathland ecosystems

The aims of the present study were to determine canopy exchange processes and to quantify total atmospheric deposition of sulphur and nitrogen in heathland. The study was carried out in dry inland heath vegetation, dominated by Calluna vulgaris, in two nature reserves in the eastern part of the Netherlands. Atmospheric deposition was determined with throughfall-stemflow measurements, adapted for low vegetation. Throughflow measurements (sum of throughfall and stemflow) in artificial Calluna canopies showed co-deposition of SOx and NHy upon heathland vegetation. In the real Calluna canopy, a significant part of the deposited ammonia/ammonium was directly assimilated by the Calluna shoots, especially in wet periods. The concentrations of potassium, calcium and magnesium in throughflow, after passage through the Calluna canopy, increased significantly compared with bulk precipitation. The amount of cations lost from the canopy were in good agreement with the observed ammonium uptake by the Calluna. A field experiment demonstrated that losses of the above-mentioned cations can be doubled by application of ammonium sulphate. It was shown that interception deposition is an important component of the atmospheric deposition of sulphur and nitrogen upon Calluna heathland; bulk precipitation amounted to only c. 35-40% of total atmospheric input. Total atmospheric deposition of sulphur and nitrogen in the investigated heathlands was 1.5-2.1 (27-33 kg S ha(-1) yr(-1)) and 2.1-3.1 kmolc ha(-1) yr(-1) (30-45 kg N ha(-1) yr(-1)), respectively. It is concluded that the present atmospheric nitrogen deposition is a continuous threat for the existence of heathlands in Western Europe.     

Metal mobility at an old, heavily loaded sludge application site

This study was undertaken to determine the present distribution and mobility of sludge-applied metals at an old land application site. Trace metals concentrations were determined for soils (using 4 M HNO3 extracts), soil leachates (collected with passive wick lysimeters over a 2.5-year period), and plant tissue from a field site which received a heavy loading of wastewater sludge in 1978 and an adjacent control plot. Blue dye was used to indicate preferential percolate flowpaths in the sludge plot soil for sampling and comparison with bulk soil metals concentrations. After nearly 20 years, metals in the sludge plot leachate were found at significantly greater concentrations than in the control plot, exceeding drinking water standards for Cd, Ni, Zn, and B. Annual metals fluxes were only a fraction of the current soil metal contents, and do not account for the apparent substantial past metals losses determined in a related study. Elevated Cd, Cu, and Ni levels were found in grass growing on the sludge plot. Despite heavy loadings, fine soil texture (silty clay loam) and evidence of past and ongoing metals leaching, examination of the bulk subsoil indicated no statistically significant increases in metals concentrations (even in a calcareous subsoil horizon with elevated pH) when comparing pooled sludge plot soil profiles with controls. Sampling of dyed preferential flow paths in the sludge plot detected only slight increases in several metals. Preferential flow and metal complexation with soluble organics apparently allow leaching without easily detectable readsorption in the subsoil. The lack of significant metal deposition in subsoil may not be reliable evidence for immobility of sludge-applied metals.     

Chernoff-Flury faces: a statistical means for representing multivariate response parameters of air pollution induced injury on plants

To evaluate the effects of dry and wet deposition on forest trees (Picea abies [L.] Karst.), the LIS-Essen is operating an Open-Top Chamber Field Station within an area where novel forest decline has been prevalent since 1982. Chambers are ventilated with either ambient or charcoal-filtered air and receive either natural or artificial rain, the latter being prepared by natural rain and distilled water in ratio 1:10. Besides deposition data, acquired above and below the tree crowns as well as via lysimeters of soil percolates, various parameters describing vitality of trees are measured. To obtain a persuading representation of total parameters and their interdependencies, a multivariate graphical cluster analysis has been performed by use of Chernoff-Flury faces. Interdependencies of vitality parameters are more easily recognizable in this multivariate picture than in usually applied binary correlation diagrams.     

Interactions between precipitation and Scots pine canopies along a heavy-metal pollution gradient

Bulk precipitation and stand throughfall were collected during 1992-96 at distances of 0.5, 4 and 8 km from the Harjavalta Cu-Ni smelter, southwestern Finland. The amounts of heavy metals (Cu, Ni, Zn, Fe) and mineral nutrients in bulk precipitation and throughfall were highest at 0.5 km. Although the canopy coverage was low at 0.5 km, the amounts of heavy metals intercepted by the canopy were extremely high. The proportion of foliar leaching relative to the wash-off of dry deposition from the needle surfaces decreased on moving towards the smelter for all elements, except for K. The high rate of K leaching from the needle tissues close to the smelter demonstrated that the K throughfall flux has been greatly altered by the heavy pollution load.     

A strategy for controlling deposition of struvite in municipal wastewater treatment plants.

This paper presents strategies to reduce the risk of struvite deposition by controlling its location of formation. Two technical routes were investigated: (1) to fix the phosphate into the dewatered sludge cake, and (2) to remove phosphate from centrate or filtrate. Chemicals used include magnesium hydroxide [Mg(OH)2], both of reagent grade and reclaimed from a flue gas desulfurization system, magnesium chloride (MgCl2), calcium hydroxide [Ca(OH)2], ferric chloride (FeCl3) and aluminum sulfate [Al2(SO4)3]. Research results indicate that (1) for anaerobically well-digested sludge, Mg(OH)2 is effective in fixing phosphate into sludge cake and improving sludge dewaterability, and (2) adding Mg(OH)2 into a reactor, located between the sludge dewatering facilities and the centrate or filtrate discharge line, and using air for mixing and carbon dioxide stripping, proves feasible in reducing struvite deposition in centrate or filtrate discharge lines and can generate a potentially valuable plant fertilizer--struvite.     

Effects of rhizobium, arbuscular mycorrhizal fungi and anion content of simulated rain on subterranean clover

An experiment was conducted to determine the extent to which rhizobia, mycorrhizal fungi, and anions in simulated rain affect plant growth response to acid deposition. Germinating subterranean clover seeds were planted in steam-pasteurized soil in pots and inoculated with Rhizobium leguminosarum, Glomus intraradices, Glomus etunicatum, R. leguminosarum + G. intraradices, R. leguminosarum + G. etunicatum, or no microbial symbionts. Beginning 3 weeks later, plants and the soil surface were exposed to simulated rain in a greenhouse on 3 days week(-1) for 12 weeks. Rain solutions were deionized water amended with background ions only (pH 5.0) or also adjusted to pH 3.0 with HNO3 only, H2SO4 only, or a 50/50 mixture of the two acids. Glomus intraradices colonized plant roots poorly, and G. intraradices-inoculated plants responded like nonmycorrhizal plants to rhizobia and rain treatments. Variation in plant biomass attributable to different rain formulations was strongest for G. etunicatum-inoculated plants, and the effect of rain formulation differed with respect to nodulation by rhizobia. The smallest plants at the end of the experiment were noninoculated plants exposed to rains (0.38 g mean dry weight total for 3 plants pot(-1)). Among nonnodulated plants infected by G. etunicatum, those exposed to HNO3 rain were largest, followed by plants exposed to HNO3 + H2SO4, pH 5.0, and H2SO4 rain, in that order. Among plants inoculated with both R. leguminosarum + G. etunicatum, however, the greatest biomass occurred with pH 5.0 rains, resulting in the largest plants in the study (1.00 g/3 plants). Treatment-related variation among root and shoot biomass data reflected those for whole-plant biomass. Based on quantification of biomass and N concentrations in shoot and root tissues, total N content of plants inoculated with G. etunicatum alone and exposed to the HNO3 + H2SO4 rains was approximately the same as plants inoculated with R. leguminosarum + G. entunicatum and exposed to pH 5 rains. Thus, the acid-mixture rains and rhizobia under no acid deposition provided approximately equal amounts of N in biomass. The significant interactions among rain formulation and the symbiotic status of the plants suggest that conclusions concerning the impact of acid deposition on plants in the environment cannot be considered reliable because most experiments on which such assessments are based have not tested confounding influences of microorganisms and precipitation characteristics.