Tiina M. Nieminen

Metal and macronutrient fluxes in heavy-metal polluted Scots pine ecosystems in SW Finland

Abstract Cu, Ni, Zn, SO 4 –S and macronutrient fluxes in Scots pine ecosystems were investigated during 1992–1996 at distances of 0.5, 4 and 8 km from the Harjavalta Cu–Ni smelter, SW Finland. The flux of water percolating down to a soil depth of 5 cm at 0.5 km was more than double that at 4 and 8 km. There was a net loss of Zn from the 40-cm thick soil layer, but a net gain for Cu, Ni and SO 4 –S. Copper was more strongly retained in the organic layer than Ni. Cu, Ni and Zn fluxes at 0.5 km were extremely large compared to those at 4 and 8 km. The fluxes of Ca, Mg, K and PO 4 –P to a depth of 5 cm at 0.5 km distance were much higher than the input via bulk precipitation, and the flux of Mg higher than the input in throughfall. There was a net loss of Mg and K at a depth of 40 cm compared to the input via bulk precipitation.

Enrichment of Cu, Ni, Zn, Pb and As in an ombrotrophic peat bog near a Cu-Ni smelter in southwest Finland.

The accumulation of selected trace elements (Cu, Ni, Zn, Pb, As) in the surface peat layer of an ombrotrophic bog 2.4 km from a Cu-Ni smelter at Harjavalta, Finland was studied using a peat core. A reference core was taken from an ombrotrophic bog at a background site, Hietajärvi, in eastern Finland. Element concentrations were analysed from 1-cm slices and enrichment factors (EF) were calculated. The enrichment factors of both Cu and Ni in the Harjavalta peat bog are extremely high compared to the Hietajärvi site. However, only the 6-cm surface peat Pb values are higher in Harjavalta compared to Hietajärvi. Precipitation was collected during 1992-1996, in the vicinity of the Harjavalta smelter, in order to estimate the current atmospheric deposition load. Comparison between the precipitation and peat data reveals that at Harjavalta the surface peat is relatively much more polluted than the current precipitation. The variation in EF of the Harjavalta peat core with respect to depth shows two patterns: Cu and Pb are similar, as are Ni, Zn and As. The vertical gradient in Harjavalta Cu EF suggests that Cu supplied to the peat by atmospheric deposition is very well preserved by the bog.

Heavy Metal and Arsenic Profiles in Ombrogenous Peat Cores from Four Differently Loaded Areas in Finland

The concentrations and vertical distribution of Cu, Ni, Zn, Pb and As were studied in four different ombrotrophic peat bogs with varying heavy metal loads at Hietajärvi, Outokumpu, Harjavalta and Alkkia in Finland. At each site a peat sample (15 cm × 15 cm × 100 cm) was taken using a Titanium Wardenaar corer, and the samples were cut into 5 cm slices. Dried and milled samples were determined by X-ray fluorescence (XRF). The mean concentrations of the elements were at their highest at Harjavalta (the most polluted area), apart from Cu which had the highest value at the Cu-treated site at Alkkia. Cu concentrations were above ‘the lowest effective limit’ (LOEL) on all the plots except for the background plot at Hietajärvi. The maximum Cu values were reached in the topmost 20 cm layer, indicating the effects of mining and smelting activities. The highest Zn and Ni concentrations occurred in the 0–40 cm layer. At all sites, the maximum Pb concentrations were located between 10 and 50 cm. However, the Pb concentrations were higher at Alkkia and Harjavalta than at Outokumpu and Hietajärvi, indicating anthropogenic sources of Pb at the former sites. The As concentration was also the highest in the uppermost peat layers. The mean concentrations were markedly lower in the deeper layers (40–80 cm) than in the upper layers.

Linking variability in soil solution dissolved organic carbon to climate, soil type, and vegetation type

Lateral transport of carbon plays an important role in linking the carbon cycles of terrestrial and aquatic ecosystems. There is, however, a lack of information on the factors controlling one of the main C sources of this lateral flux, i.e., the concentration of dissolved organic carbon (DOC) in soil solution across large spatial scales and under different soil, vegetation, and climate conditions. We compiled a database on DOC in soil solution down to 80 cm and analyzed it with the aim, first, to quantify the differences in DOC concentrations among terrestrial ecosystems, climate zones, soil, and vegetation types at global scale and second, to identify potential determinants of the site-to-site variability of DOC concentration in soil solution across European broadleaved and coniferous forests. We found that DOC concentrations were 75% lower in mineral than in organic soil, and temperate sites showed higher DOC concentrations than boreal and tropical sites. The majority of the variation (R2 = 0.67–0.99) in DOC concentrations in mineral European forest soils correlates with NH4+, C/N, Al, and Fe as the most important predictors. Overall, our results show that the magnitude (23% lower in broadleaved than in coniferous forests) and the controlling factors of DOC in soil solution differ between forest types, with site productivity being more important in broadleaved forests and water balance in coniferous stands.

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.

Determination of low methylmercury concentrations in peat soil samples by isotope dilution GC-ICP-MS using distillation and solvent extraction methods

Most often, only total mercury concentrations in soil samples are determined in environmental studies. However, the determination of extremely toxic methylmercury (MeHg) in addition to the total mercury is critical to understand the biogeochemistry of mercury in the environment. In this study, N2-assisted distillation and acidic KBr/CuSO4 solvent extraction methods were applied to isolate MeHg from wet peat soil samples collected from boreal forest catchments. Determination of MeHg was performed using a purge and trap GC-ICP-MS technique with a species-specific isotope dilution quantification. Distillation is known to be more prone to artificial MeHg formation compared to solvent extraction which may result in the erroneous MeHg results, especially with samples containing high amounts of inorganic mercury. However, methylation of inorganic mercury during the distillation step had no effect on the reliability of the final MeHg results when natural peat soil samples were distilled. MeHg concentrations determined in peat soil samples after distillation were compared to those determined after the solvent extraction method. MeHg concentrations in peat soil samples varied from 0.8 to 18 μg kg(-1) (dry weight) and the results obtained with the two different methods did not differ significantly (p=0.05). The distillation method with an isotope dilution GC-ICP-MS was shown to be a reliable method for the determination of low MeHg concentrations in unpolluted soil samples. Furthermore, the distillation method is solvent-free and less time-consuming and labor-intensive when compared to the solvent extraction method.

Effects of soil copper and nickel on survival and growth of Scots pine.

The contribution of soil Cu and Ni pollution to the poor vitality and growth rate of Scots pine growing in the vicinity of a Cu-Ni smelter was investigated in two manipulation experiments. In the first manipulation, Cu-Ni smelter-polluted soil cores were transported from a smelter-pollution gradient to unpolluted greenhouse conditions. A 4-year-old pine seedling was planted in each core and cultivated for a 17-month period. In the second manipulation, pine seedlings from the same lot were cultivated for the same 17-month period in a quartz sand medium containing increasing doses of copper sulfate, nickel sulfate, and a combination of both. The variation in the biomass growth of the seedlings grown in the smelter-polluted soil cores was very similar to that of mature pine stands growing along the same smelter-pollution gradient in the field. In addition, the rate of Cu and Ni exposure explained a high proportion of the biomass growth variation, and had an effect on the Ca, K, and Mg status of the seedlings. According to the lethal threshold values determined on the basis of the metal sulfate exposure experiments, both the Cu and Ni content of the 0.5 km smelter-polluted soil cores were high enough to cause the death of most of the seedlings. The presence of Cu seemed to increase Ni toxicity.

Exceedance of critical loads and of critical limits impacts tree nutrition across Europe

Key messageExceedance of critical limits in soil solution samples was more frequent in intensively monitored forest plots across Europe with critical loads for acidity and eutrophication exceeded compared to other plots from the same network. Elevated inorganic nitrogen concentrations in soil solution tended to be related to less favourable nutritional status.ContextForests have been exposed to elevated atmospheric deposition of acidifying and eutrophying sulphur and nitrogen compounds for decades. Critical loads have been identified, below which damage due to acidification and eutrophication are not expected to occur.AimsWe explored the relationship between the exceedance of critical loads and inorganic nitrogen concentration, the base cation to aluminium ratio in soil solutions, as well as the nutritional status of trees.MethodsWe used recent data describing deposition, elemental concentrations in soil solution and foliage, as well as the level of damage to foliage recorded at forest plots of the ICP Forests intensive monitoring network across Europe.ResultsCritical loads for inorganic nitrogen deposition were exceeded on about a third to half of the forest plots. Elevated inorganic nitrogen concentrations in soil solution occurred more frequently among these plots. Indications of nutrient imbalances, such as low magnesium concentration in foliage or discolouration of needles and leaves, were seldom but appeared more frequently on plots where the critical limits for soil solution were exceeded.ConclusionThe findings support the hypothesis that elevated nitrogen and sulphur deposition can lead to imbalances in tree nutrition.

The Applicability of Needle Chemistry for Diagnosing Heavy Metal Toxicity to Trees

To estimate the validity of needle chemistry as a tool for diagnosing heavy metal toxicity, we collected needle samples from mature pines and young seedlings and monitored metal deposition in the vicinity of a Cu-Ni smelter in SW Finland. Needle Cu, Ni, Zn and Fe concentrations in a pine stand growing next to the smelter were determined in 1992 and in 1998. Deposition was collected as bulk precipitation (open area) and as stand throughfall (below the canopy) during 1992-1998. Copper deposition in stand throughfall (TF) was relatively constant during 1992-1998, but for Ni in stand TF there was a strong increase from 100 mg m−2 in 1997 to 600 mg m−2 in 1998. There was a decreasing trend during the study period for both Zn and Fe deposition in TF, indicating a decrease in the emissions of these metals from the smelter. Washing the needles with chloroform removed a part of the Fe and Ni, but there was no clear difference for Cu or Zn between the washed and unwashed samples. However, needle Ni, Fe and Cu concentrations in pine seedlings grown in unpolluted soil close to the Cu-Ni smelter were considerably higher than in seedlings grown in a greenhouse in polluted soil taken from close to the smelter. Hence, our results suggest that not all the needle Ni, Fe and Cu derived from aerial deposition is washed-off from the canopy by rainfall (or by the washing of needle samples with e.g. chloroform).

Leaching of Dissolved Organic Carbon and Trace Elements After Stem-Only and Whole-Tree Clear-cut on Boreal Peatland

The aim of this work was to study the short-term effect of clear-cut harvest on concentrations of dissolved organic carbon (DOC), B, Al, Zn, Cu, Ni, Cr, Cd and Pb in drainage water from northern peatland catchments in Finland underlain by granitic or black shale bedrock, the latter having higher concentrations of several trace elements, such as Ni and Zn. Stem-only harvest (SOH) or whole-tree harvest (WTH) with stump removal were carried out at coniferous sites. Controls were left unharvested. DOC and trace element concentrations were monitored during one pre-treatment and two post-treatment years. There was no constant increase in the element concentrations. However, there were signs that both SOH and WTH clear-cut harvest on northern peatland catchments increases the concentrations of DOC, B, Al, Zn and Ni in ditchwater in some sites irrespective of the bedrock type. The greatest increases were observed in WTH sites but the study does not allow us to assess the statistical significance of the magnitude of the difference between SOH and WTH. We conclude that the element concentrations in ditchwater depend largely on site characteristics masking the possible effect of harvest.