Atmospheric deposition to the edge of a spruce forest in Denmark

Atmospheric deposition was measured during 1 year at the forest edge of a Norway spruce stand in Denmark. Inside the forest the deposition of H(+), Ca(2+), Mg(2+), Na(+), K(+), Cl(-), NO(3)(-), NH(4)(2) and SO(4)(2-) with canopy throughfall varies with the distance from the forest edge. The deposition at the edge is found to be 10-20 times as high as deposition to an open field and 2-8 times as high as deposition inside the stand. An exponential decrease in deposition as a function of the distance from the forest edge is found. Increased deposition of K(+) and non-sea salt Mg(2+), which mainly originates as a result of leaching from the needles may be explained by a larger leaf area index (LAI) at the forest edge. Deposition of particulate substances, especially Na(+), Cl(-), Mg(2+) and to some extent SO(4)(2-), NH(4)(+) and NO(3)(-) is increased much more than the LAI, which we believe to be caused by changes in wind movements at the forest edge.     

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+)).     

Spatial variability of throughfall fluxes in a spruce forest

The spatial variability of throughfall deposition of H(+), Ca(2+), Mg(2+), Na(+), K(+), Cl(-), NO(3)(-), NH(4)(+), O(4)(2-) to a Norway spruce (Picea abies (L.) Karst.) forest was intensively examined during the period October 1986 to October 1987. Large systematic spatial variability of the atmospheric deposition within the forest was observed. The flux of throughfall water was higher away from the trunk compared to the flux close to the trunk. In contrast to this, the deposition of all substances was considerably higher close to the trunk compared to the deposition at the periphery of the canopy. A linear decrease in deposition as a function of the distance from the nearest tree trunk was found. Further, the deposition varied quite dramatically between trees according to their size. The observed spatial variability in throughfall may be due to variabilities in the processes taking part in altering the distribution and composition of the precipitated water as it moves through the canopy. The influence of these processes of precipitation, wash-off, dry deposition and canopy exchange is discussed, and it is found that both increased dry deposition and canopy exchange in the tree tops contribute to the higher solute fluxes found close to the tree trunk.     

Fluxes of ions in precipitation, throughfall and stemflow in an urban forest in Kuala Lumpur, Malaysia

A study was carried out to determine the chemical composition of bulk precipitation, throughfall and stemflow in an urban forest in Kuala Lumpur, Malaysia. The mean weekly rainfall recorded during the period of study was 63.2 mm. Throughfall, stemflow and canopy interception of incident precipitation were 77.1%, 1.2% and 21.7% respectively. Bulk precipitation, througfall and stemflow were acidic, the pH recorded being 4.37, 4.71 and 4.15 respectively. In all cases the dominant ions were NO3, SO4, Cl, NH4, K, Ca and Na. Of the ions studied Ca, K, Cl, SO4, Mg and Mn showed net increases in passing through the forest canopy, while NH4, Na, NO3, Zn, H and Fe showed net retention. This study shows that the urban environment of Kuala Lumpur contributes considerable amounts of materials to the atmosphere, as reflected by the high ionic contents in bulk precipitation, throughfall and stemflow.     

Atmospheric input of elements to forest ecosystems: a method of estimation using artificial foliage placed above rain collectors

Usefulness of a method of artificial foliage was tested for estimation of total ionic inputs from the atmosphere to forest ecosystems, as well as of processes relevant to ionic fluxes through tree canopies: uptake, leaching, passive flow. The studies were performed in Norway spruce and European beech stands in Karkonosze Mountains (Poland), in 1995-97. Artificial leaves of increasing leaf area index: 0, 2, 6 and 12 m(2) m(-2 )were placed above standard rain collectors. It has been found that total atmospheric fluxes of H(+), NH(4)(+), Ca(2+), Mg(2+), Pb(2+), NO(3)(-) and SO(4)(2-) rose as surface area of the foliage increased. This was especially true for nitrate, sulphate and ammonium. No such relationship was found for K(+), Na(+), Zn(2+), Cd(2+), Cu(2+) and PO(4)(3-). The increase in anion fluxes exceeded that in neutralising cations (NH(4)(+), Na(+), K(+), Mg(2+), Ca(2+)) and led to progressive rainwater acidification with the increase in the foliage area. An analysis of net canopy exchange (atmospheric input-throughfall flux) has shown that SO(4)(2-), PO(4)(3-), Na(+), Ca(2+) and Cu(2+) flowed passively through the tree crowns; NH(4)(+), NO(3)(-), Zn(2+), Cd(2+) and occasionally Pb(2+) were efficiently absorbed, whereas K(+) was leached from the canopies. Beech was more effective in modifying ionic pool from the atmosphere than spruce. This related to H(+) (greater absorption) and Mg(2+) (greater leaching). It has been demonstrated that the results concerning trends in net canopy exchange and produced by the simple method of artificial foliage are comparable to more sophisticated techniques of the measurements. This proves the method to be useful.     

Rain and throughfall chemistry in a Norway spruce forest in the Western Prealps

From January 1987 to December 1989 precipitation was collected in an open field in a forested area of the Western Prealps. The site faces the intensely industrialized area of the Po Valley. In a Norway spruce plantation, next to the open field sampler, throughfall was collected from January 1987 to August 1989 for a period of 32 months. In the common sampling period median pH values of the open field precipitation and throughfall were 4.28 and 4.19 respectively. Open field precipitation has yearly deposition rates of acidity, Ca, S, and N of 0.81, 9.82, 24.83 and 32.81 kg/ha(-1) respectively. The throughfall showed significant increases in the deposition rates for Ca, Mg, K, N and S, due to abundant dry deposition and, probably, to nutrient leaching contributed by the canopies of the spruce. On the basis of available data, an initial approach to atmosphere-canopy interaction was made.     

Development and validation of a terrestrial biotic ligand model predicting the effect of cobalt on root growth of barley (Hordeum vulgare)

A Biotic Ligand Model was developed predicting the effect of cobalt on root growth of barley (Hordeum vulgare) in nutrient solutions. The extent to which Ca(2+), Mg(2+), Na(+), K(+) ions and pH independently affect cobalt toxicity to barley was studied. With increasing activities of Mg(2+), and to a lesser extent also K(+), the 4-d EC50(Co2+) increased linearly, while Ca(2+), Na(+) and H(+) activities did not affect Co(2+) toxicity. Stability constants for the binding of Co(2+), Mg(2+) and K(+) to the biotic ligand were obtained: logK(CoBL)=5.14, logK(MgBL)=3.86 and logK(KBL)=2.50. Limited validation of the model with one standard artificial soil and one standard field soil showed that the 4-d EC50(Co2+) could only be predicted within a factor of four from the observed values, indicating further refinement of the BLM is needed.     

Stemflow chemistry of urban street trees

pH and ion concentrations (Na(+), K(+), Mg(2+), Ca(2+), NO(-)(3)) in the stemflow of the evergreen broad-leaved tree, Ilex rotunda, planted in the median strip of a highway and nitrogen oxides concentration in the air in an urban site were compared with a suburban site in Fukuoka city, Japan. The annual average of the nitrogen oxides concentration in the air was higher and NO(-)(3) concentration in the stemflow at the urban site was higher or similar compared with the suburban site. However, the annual average of pH in the stemflow at the urban site was higher than at the suburban. The annual average cation concentrations in the stemflow at the urban site were higher than at the suburban except Na(+). In particular, K(+) and Ca(2+) were higher throughout the measurement period. Therefore, higher pH in the urban stemflow was probably due to neutralization by higher concentrations of K(+), Mg(2+) and Ca(2+).     

Development of a biotic ligand model (BLM) predicting nickel toxicity to barley (Hordeum vulgare)

A biotic ligand model (BLM) was developed to predict nickel toxicity, affecting root growth of barley (Hordeum vulgare), in nutrient solutions. The extent to which Ca(2+), Mg(2+), Na(+), K(+) ions and pH each influenced nickel toxicity was determined. Higher activities of Mg(2+) linearly increased the 4d EC50 Ni (2+) , while Ca(2+), Na(+), K(+) and H(+) activities did not significantly influence Ni(2+) toxicity. Stability constants for the binding of Ni(2+) and Mg(2+) to the biotic ligand were obtained: logK(NiBL)=5.27 and logK(MgBL)=3.47. Further, it was calculated that on average 57% of the biotic ligand sites needed to be occupied by nickel to induce 50% root growth inhibition. Auto-validation of the BLM indicated that predicted EC50s differed from the observed EC50s by a factor of less than 2, indicating that the BLM concept may also be used to predict metal toxicity to terrestrial plants.     

Comparison of throughfall and soil solution chemistry between a high-density Corsican pine stand and a naturally regenerated silver birch stand

In Flanders, critical loads for acidification and eutrophication are exceeded in the majority of the forest stands, and many previously nitrogen limited forest ecosystems have become nitrogen saturated. The present study investigates whether a naturally regenerated stand of silver birch (Betula pendula Roth) contributes less to the acidification and eutrophication of the forest soil than a high-density plantation of Corsican pine (Pinus nigra ssp. laricio Maire). Throughfall deposition of inorganic nitrogen was about 3.5 times higher in the Corsican pine stand than in the birch stand. Potassium throughfall deposition was significantly higher under birch due to higher canopy leaching. Magnesium throughfall deposition was significantly higher under the pine canopy due to higher dry deposition. The lower nitrogen throughfall deposition in the birch stand was reflected in a 60% lower nitrate percolation at 1m depth compared with pine. Nitrate soil percolation is linked to losses of aluminium and base cations.     

Effect of vegetation type on throughfall deposition and seepage flux

This paper compares different vegetation types (coniferous and deciduous forest, grassed and pure heathland) in terms of input (throughfall deposition) and output (seepage flux) in a region with intermediate nitrogen load (+/-20kg Nha(-1)y(-1) via bulk precipitation) in comparable conditions in north Belgium. Coniferous forest (two plots Pinus sylvestris and two plots Pinus nigra) received significantly higher nitrogen and sulphur throughfall deposition than deciduous forest and heathland. Grassed and pure heathland had significantly highest throughfall quantities of Ca(2+) and Mg(2+), respectively. The observed differences in throughfall deposition between the different vegetation types were not univocally reflected in the ion seepage flux. Considerable seepage fluxes of NO(3)(-), SO(4)(2-), Ca(2+) and Al(III) were only found under the P. nigra plots. We discuss our hypothesis that the P. nigra forests already evolved to a situation of N saturation, while the other vegetation types did not.     

Effect of cations on copper toxicity to wheat root: implications for the biotic ligand model

The extent to which calcium, magnesium, sodium, potassium and hydrogen ions independently mitigate Cu rhizotoxicity to wheat (Triticumaestivum) in nutrient solutions was examined. Increasing activities of Ca(2+) and Mg(2+) but not Na(+), K(+) and H(+) linearly increased the 2 d EC50 (as Cu(2+) activity), supporting the concept that some cations can compete with Cu(2+) for binding the active sites at the terrestrial organism-solution interface (i.e., the biotic ligand, BL). According to the biotic ligand model (BLM) concept, the conditional stability constants for the binding of Cu(2+), Ca(2+) and Mg(2+) to the BL were derived from the toxicity data. They were 6.28, 2.43 and 3.34 for logK(CuBL), logK(CaBL) and logK(MgBL), respectively. It was calculated that on average 43.6% of BL sites need to be occupied by Cu(2+) to induce 50% root growth inhibition. Using the estimated parameters, a BLM was successfully developed to predict Cu toxicity for wheat as a function of solution characteristics.     

Assessment of the potential for soil acidification in North India using the critical load approach and locally derived data for acidic and basic inputs

Major ions (Cl-, NO3(-), SO4(2-), Ca2+, Mg2+, Na+, K+ and NH4(+)) were analysed in wet and dry deposition samples collected for 2 years using a polyethylene bottle and funnel collector at Agra in India. The deposition of ionic components (Ca2+ and Mg2+) derived from natural sources i.e. soil were higher than those of anthropogenic origin. In rainwater samples, non-sea-salt fraction was found to be 60-90%. In both wet and dry deposition Ca2+ was found to be the dominant ion which may be due to its large particle diameter. Results suggest that most of the acidity, which occurs due to NO3(-), SO4(2-) and Cl- is neutralized by alkaline constituents, which originate from airborne local soil and dust transported from the Thar desert. Acid neutralizing capacity of soil has also been quantified and found to be 33 x 10(3) neqg(-1). Using deposition data, the critical load for acidity of soil with respect to Ashoka and Eucalyptus was evaluated. The present level of deposition of S and N was found to be much lower than critical loads calculated for S and N. Critical load of exceedance in terms of deposition acidity was also calculated and found to be negative. This indicates that with respect to these species, the ecosystem is protected at the current level of deposition.     

Effects of ozone on foliar leaching in Norway spruce (Picea abies L. Karst): confounding factors due to NOx production during ozone generation

Previous experiments with conifers fumigated with O(3), produced by air-operated electric discharge ozonators, have provided evidence that O(3) increases the leaching of NO(3)(-), NH(4)(+), K(+), Ca(2+), Mg(2+) and some other cations from needles, when the trees are treated with acid mist. This evidence has provided the foundation of the ozone-acid mist hypothesis of spruce decline. We report experiments with Norway spruce saplings fumigated with purified and unpurified O(3). The results show that the accumulation of NO(3)(-) in the needles arises from the rapid deposition of N(2)O(5) and HNO(3) formed from N(2) in the ozonator. An increase in removal of NH(4)(+), Na(+), Ca(2+), Mg(2+), Zn(2+) and Mn(2+) from the needles during soaking in H(2)SO(4), pH3, was also observed, which was related to the increase in NO(3)(-) but was independent of O(3) concentration. It is concluded that results of previous experiments cited in support of the ozone-acid mist hypothesis arose from effects which were at least partly caused by N(2)O(5) produced as a contaminant, and were incorrectly attributed to ozone. Other effects, such as growth stimulations, visible symptons, enhanced frost sensitivity, and infestation by pests or pathogens, which have been attributed to O(3) generated by electric discharge in air, should be interpreted with caution. Future experiments with ozone must eliminate this problem by either using O(2)-driven ozonators, or by purifying the output from air-driven ozonators using cold and/or water traps.     

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.     

Atmospheric deposition and ionic interactions within a beech canopy in the Karkonosze Mountains

A method, of artificial foliage placed above rain collectors, which enables to estimate total atmospheric inputs of elements, was employed to study processes related to ionic flow through a tree canopy. The investigations were conducted within a beech forest in the Karkonosze Mountains, in 1996-1997. An analysis of net canopy exchange (throughfall flux-atmospheric input) revealed that NH4+, NO3-, H+ had been retained in the canopy, Ca2+, Na+, Cl-, SO(2-)4, PO(3-)4 flowed passively, whereas K+ and Mg2- had been removed from the tree foliage. Ammonium absorption was more efficient than that of NO3- ions, because NH4+ was taken up from rain-waters and aerosol-gaseous fraction of the atmospheric input, whereas NO3- ions were captured primarily from the latter source. Retention of H+ was also related exclusively to the aerosol-gaseous input. Leaching losses of K+ and Mg2+ did not result from exchange reactions of these ions with retained H+, but from ionic exchange between NH4+ and K+ + Mg2+. At the same time, neutralisation of H+ in the canopy has been attributed to NO3- absorption, resulting most likely from HNO3 vapour penetration into the plants.     

Fluxes of trichloroacetic acid through a conifer forest canopy

Controlled-dosing experiments with conifer seedlings have demonstrated an above-ground route of uptake for trichloroacetic acid (TCA) from aqueous solution into the canopy, in addition to uptake from the soil. The aim of this work was to investigate the loss of TCA to the canopy in a mature conifer forest exposed only to environmental concentrations of TCA by analysing above- and below-canopy fluxes of TCA and within-canopy instantaneous reservoir of TCA. Concentrations and fluxes of TCA were quantified for one year in dry deposition, rainwater, cloudwater, throughfall, stemflow and litterfall in a 37-year-old Sitka spruce and larch plantation in SW Scotland. Above-canopy TCA deposition was dominated by rainfall (86%), compared with cloudwater (13%) and dry deposition (1%). On average only 66% of the TCA deposition passed through the canopy in throughfall and stemflow (95% and 5%, respectively), compared with 47% of the wet precipitation depth. Consequently, throughfall concentration of TCA was, on average, approximately 1.4 x rainwater concentration. There was no significant difference in below-canopy fluxes between Sitka spruce and larch, or at a forest-edge site. Annual TCA deposited from the canopy in litterfall was only approximately 1-2% of above-canopy deposition. On average, approximately 800 microg m(-2) of deposited TCA was lost to the canopy per year, compared with estimates of above-ground TCA storage of approximately 400 and approximately 300 microg m(-2) for Sitka spruce and larch, respectively. Taking into account likely uncertainties in these values ( approximately +/- 50%), these data yield an estimate for the half-life of within-canopy elimination of TCA in the range 50-200 days, assuming steady-state conditions and that all TCA lost to the canopy is transferred into the canopy material, rather than degraded externally. The observations provide strong indication that an above-ground route is important for uptake of TCA specifically of atmospheric origin into mature forest canopies, as has been shown for seedlings (in addition to uptake from soil via transpiration), and that annualized within-canopy elimination is similar to that in controlled-dosing experiments.     

Field intercomparison of throughfall measurements performed within the framework of the Pan European intensive monitoring program of EU/ICP Forest

A 6-month field intercomparison study on throughfall measurements was performed at Speulder forest near the west coast in The Netherlands. Twenty throughfall sampling systems were evaluated on accuracy, sampling strategy and performance under field conditions. Throughfall fluxes of NO3-, K+ and Kjeldahl-N generally could be determined with a larger accuracy than fluxes of SO4(2-), NH4+, Na+, Cl-, Mg2+, Ca2+, and alkalinity. Throughfall fluxes of H+ generally had the lowest accuracy. Only 20% of the sampling systems differed more than 20% from the best estimate, whereas 45% of the systems stayed within a 10% range from the best estimate. The difference from the best estimate was mainly caused by aspects related to sampling strategy, like, for example, collecting area, sampler placement. The inaccuracy induced by the sampling system appeared to be much larger than that resulting from the analysis of the samples by different laboratory as determined by ring-tests. The field intercomparison described in this article gave a good insight in the different aspects contributing to the overall accuracy of the measurements. However, performing a future field intercomparison is recommended for throughfall and stemflow in order to also take in account other aspects that might influence the performance of the different measurement systems (e.g. tree species, climate zone, summer/winter period).     

Dry deposition of particles and canopy exchange: Comparison of wet,bulk and throughfall deposition at five forest sites in Italy

The contribution of dry deposition to the total atmospheric input of acidifying compounds and base cations is of overwhelming importance. Throughfall measurements provide an estimate of the total deposition to forest soils, including dry deposition, but some uncertainties, related to the canopy interaction processes, affect this approach. We compared the concentrations and the fluxes of the main ions determined in wet-only, bulk and throughfall samples collected at five forest sites in Italy. The contribution of coarse particles deposited onto the bulk samplers was of prime importance for base cations, representing on average from 16% to 46% of the bulk deposition. The extent of this dry deposition depended on some geographical features of the sites, such as the distance from the sea and the annual rainfall. The possibility of applying specific bulk/wet ratios to estimate the wet deposition proved to be limited by the temporal variability of these ratios, which must be considered together with the spatial variability. A direct comparison of the dry contribution deriving from the bulk–wet and the throughfall–wet demonstrated that an extensive natural surface (forest canopy) performs better than a small synthetic surface (funnel of the bulk sampler) in collecting dry deposition of SO₄²⁻, NO₃⁻ and Na⁺. The canopy exchange model was applied to both bulk and wet data to estimate the contribution of dry deposition to the total input of base cations, and the uncertainty associated to the model discussed. The exclusive use of bulk data led to a considerable underestimation of base cation dry deposition, which varies among the study sites.