Mineral Soil Horizons Research Articles

Phosphorus retention in forest soils and the functioning of buffer zones used in forestry

Vaananen, R. 2008. Phosphorus retention in forest soils and the functioning of buffer zones used in forestry. Dissertationes Forestales 60. 42 pp. Available at http://www.metla.fi/ dissertationes/df60.htm Phosphorus (P) retention properties of soils typical for boreal forest, i.e. podzolic soil and peat soils, vary significantly, but the range of this variation has not been sufficiently documented. To assess the usefulness of buffer zones used in forestry in removing P from the discharge by chemical sorption in soil, and to estimate the risk of P leaching after forestry operations, more data is needed on soil P retention properties. P retention properties of soils were studied at clear-cut areas, unharvested buffer zones adjoining the clear-cut and at peatland buffer zone areas. Desorption-sorption isotherms were determined for the humus layer, the mineral soil horizons E, B and C of the Podzol profile and for the surface layer peat (0-15 cm) and the subsurface layer peat (15-30 cm). The efficiency of buffer zones in retaining P was studied at six peatland buffer zone areas by adding Pcontaining solute in the inflow. A tracer study was conducted at one of the buffer zone areas to determine the allocation of the added P in soil and vegetation. Measured sorption or desorption rather than parameter values of fitted sorption equations described P desorption and sorption behaviour in soil. The highest P retention efficiency was in the B horizon and consequently, if contact occurred or was established between the soluble P in the water and the soil B horizon, the risk of P leaching was low. Humus layer was completely incapable of retaining P after clear-cutting. In the buffer zones, the decrease in P retention properties in the humus layer and the low amount of P sorbed by it indicated that the importance of the layer in the functioning of buffer zones is low. The peatland buffer zone areas were efficient in retaining soluble P from inflow. P sorption properties of the peat soil at the buffer zone areas varied largely but the contribution of P sorption in the peat was particularly important during high flow in spring, when the vegetation was not fully developed. Factors contributing to efficient P retention were large buffer size and low hydrological load whereas high hydrological load combined with the formation of preferential flow paths, especially during early spring or late autumn was disadvantageous. However, small buffer zone areas, too, may be efficient in reducing P load.

Calcium biominerals in typical Argiudolls from the Pampean Plain, Argentina: An approach to the understanding of their role within the calcium biogeochemical cycle

The aims of this work are: (a) to describe the presence of calcium oxalate crystals from fungus and vegetal origin; (b) to determine the contribution from leaves; and (c) to assess the role they could play within the calcium biogeochemical cycle, in typical Argiudolls with different vegetal cover in the Pampean Plain, Argentina. Two plots with different vegetation were investigated: Acacia melanoxylon– Celtis tala and Eucalyptus globulus– Celtis tala. Leaves of the vegetation species were diaphanized and cleared with sodium hypochlorite (50%). Leaves and mycelial mats of the organic horizons were analyzed by optical, petrographic and scanning electronic microscopy. Soil samples were taken to determine particle size distribution and mineralogy, and to test calcium concentration by UV–vis spectrophotometry both in the soils’ saturated paste extract and in leached soil. Different morphologies of weddellite (i.e., primary nuclei, rosettes and druses) in the fungus hyphae were observed. Calcium oxalate crystal production was highest in A. melanoxylon and C. tala. Ca–Na feldspars are the only minerals that could release calcium to the system, but show no features of weathering. Calcium concentration in soil solution was higher in the Eucalyptus plot than in the Acacia, and it decreased from the organic to the mineral soil horizons. Fungus and vegetal calcium biomineral production, in addition to their higher susceptibility to weathering than minerals of inorganic origin, represents an important contribution to the calcium biogeochemical cycle.

Sensitivity to Acidification of Forest Soils in Two Watersheds with Contrasting Hydrological Regimes in the Oil Sands Region of Alberta

Input of large amounts of N and S compounds into forest ecosystems through atmospheric deposition is a significant risk for soil acidification in the oil sands region of Alberta. We evaluated the sensitivity of forest soils to acidification in two watersheds (Lake 287 and Lake 185) with contrasting hydrological regimes as a part of a larger project assessing the role of N and S cycling in soil acidification in forest ecosystems. Fifty six forest soil samples were collected from the two watersheds by horizon from 10 monitoring plots dominated by either jack pine ( Pinus banksiana) or aspen ( Populus tremuloides). Soils in the two watersheds were extremely to moderately acidic with pH (CaCl 2) ranging from 2.83 to 4.91. Soil acid-base chemistry variables such as pH, base saturation, Al saturation, and acid-buffering capacity measured using the acetic acid equilibrium procedure indicated that soils in Lake 287 were more acidified than those in Lake 185. Acid-buffering capacity decreased in the order of forest floor > subsurface mineral soil > surface mineral soil. The most dramatic differences in percent Ca and Al saturations between the two watersheds were found in the surface mineral soil horizon. Percent Ca and Al saturation in the surface mineral soil in Lake 287 were 15% and 70%, respectively; the percent Ca saturation value fell within a critical range proposed in the literature that indicates soil acidification. Our results suggest that the soils in the two watersheds have low acid buffering capacity and would be sensitive to increased acidic deposition in the region.

Response of dissolved organic matter in the forest floor to long-term manipulation of litter and throughfall inputs

Dissolved organic matter (DOM) contributes to organic carbon either stored in mineral soil horizons or exported to the hydrosphere. However, the main controls of DOM dynamics are still under debate. We studied fresh leaf litter and more decomposed organic material as the main sources of DOM exported from the forest floor of a mixed beech/oak forest in Germany. In the field we doubled and excluded aboveground litter input and doubled the input of throughfall. From 1999 to 2005 we measured concentrations and fluxes of dissolved organic C and N (DOC, DON) beneath the Oi and Oe/Oa horizon. DOM composition was traced by UV and fluorescence spectroscopy. In selected DOM samples we analyzed the concentrations of phenols, pentoses and hexoses, and lignin-derived phenols by CuO oxidation. DOC and DON concentrations and fluxes almost doubled instantaneously in both horizons of the forest floor by doubling the litter input and DOC concentrations averaged 82 mg C l−1 in the Oe/Oa horizon. Properties of DOM did not suggest a change of the main DOM source towards fresh litter. In turn, increasing ratios of hexoses to pentoses and a larger content of lignin-derived phenols in the Oe/Oa horizon of the Double litter plots in comparison to the Control plots indicated a priming effect: Addition of fresh litter stimulated microbial activity resulting in increased microbial production of DOM from organic material already stored in Oe/Oa horizons. Exclusion of litter input resulted in an immediate decrease in DOC concentrations and fluxes in the thin Oi horizon. In the Oe/Oa horizon DOC concentrations started to decline in the third year and were significantly smaller than those in the Control after 5 years. Properties of DOM indicated an increased proportion of microbially and throughfall derived compounds after exclusion of litter inputs. Dissolved organic N did not decrease upon litter exclusion. We assume a microbial transformation of mineral N from throughfall and N mineralization to DON. Increased amounts of throughfall resulted in almost equivalently increased DOC fluxes in the Oe/Oa horizon. However, long-term additional throughfall inputs resulted in significantly declining DOC concentrations over time. We conclude that DOM leaving the forest floor derives mainly from decomposed organic material stored in Oe/Oa horizons. Leaching of organic matter from fresh litter is of less importance. Observed effects of litter manipulations strongly depend on time and the stocks of organic matter in forest floor horizons. Long-term experiments are particularly necessary in soils/horizons with large stocks of organic matter and in studies focusing on effects of declined substrate availability. The expected increased primary production upon climate change with subsequently enhanced litter input may result in an increased production of DOM from organic soil horizons.

Impacts of burning and increased nitrogen deposition on nitrogen pools and leaching in an upland moor

1. Upland moorlands are an extensive semi-natural resource, frequently burned either through management or uncontrolled outbreaks of fire. These systems are often situated in areas receiving high levels of atmospheric nitrogen (N) deposition, yet the effects of burning combined with high N deposition on ecosystem N pools and N leaching to surface waters are unknown. 2. A management burn was applied to an upland Calluna vulgaris moor which contained a set of long-term experimental plots treated with simulated increased N deposition at rates of +0, +40, +80 and +120 kg ha−1 year−1. Leaching losses of total dissolved inorganic N (TDNin) and dissolved organic N (DON) from organic and mineral soil horizons and the N pools in these horizons, as well as in litter and vegetation, were compared before and after the burn. 3. The results showed that leaching of TDNin and DON from both soil horizons increased in a 6-month period after the burn, with leaching of TDNin remaining elevated 2–3 years later. N pools in the deeper mineral layer of the soil also increased after the burn. Increasing long-term N additions magnified the burn effect on leaching losses but lessened the burn effect on the N pools in the mineral layer. In the +40 N addition plots, the amount of N removed in burning vegetation was of an equivalent size to the amount of additional N retained within the system. 4. Synthesis: These results suggest that burning approximately every 10 years may be effective in removing N retained in the system at N deposition rates up to 56 kg N ha−1 year−1. However, extensive burning of moorland or uncontrolled outbreaks of fire over wide areas may considerably exacerbate the threat of N loading to groundwater in areas where moors are more heavily N polluted, increasing the potential for acidification, eutrophication and brown water colouration. The data suggest that this is because the mineral horizon of upland moors receiving high N inputs has already been saturated with N such that increased downward percolation rates of N caused by the burn have risen above a threshold for immobilization (hence leading to more substantial post-burn increases in leaching of N).

Tree Species Effects on Soil Organic Matter Dynamics: The Role of Soil Cation Composition

We studied the influence of tree species on soil carbon and nitrogen (N) dynamics in a common garden of replicated monocultures of fourteen angiosperm and gymnosperm, broadleaf and needleleaf species in southwestern Poland. We hypothesized that species would influence soil organic matter (SOM) decomposition primarily via effects on biogeochemical recalcitrance, with species having tissues with high lignin concentrations retarding rates of decomposition in the O and A horizons. Additionally, because prior work demonstrated substantial divergence in foliar and soil base cation concentrations and soil pH among species, we hypothesized that species would influence chemical stabilization of SOM via cation bridging to mineral surfaces in the A-horizon. Our hypotheses were only partially supported: SOM decomposition and microbial biomass were unrelated to plant tissue lignin concentrations, but in the mineral horizon, were significantly negatively related to the percentage of the cation exchange complex (CEC) occupied by polyvalent acidic (hydrolyzing) cations (Al and Fe), likely because these cations stabilize SOM via cation bridging and flocculation and/or because of inhibitory effects of Al or low pH on decomposers. Percent CEC occupied by exchangeable Al and Fe was in turn related to both soil clay content (a parent material characteristic) and root Ca concentrations (a species characteristic). In contrast, species influenced soil N dynamics largely via variation in tissue N concentration. In both laboratory and in situ assays, species having high-N roots exhibited faster rates of net N mineralization and nitrification. Nitrification:mineralization ratios were greater, though, under species with high exchangeable soil Ca 2+ . Our results indicate that tree species contribute to variation in SOM dynamics, even in the mineral soil horizons. To our knowledge the influence of tree species on SOM decomposition via cation biogeochemistry has not been demonstrated previously, but could be important in other poorly buffered systems dominated by tree species that differ in cation nutrition or that are influenced by acidic deposition.

Extraction of water‐soluble organic matter from mineral horizons of forest soils

AbstractDissolved organic matter (DOM) is involved in many important biogeochemical processes in soil. As its collection is laborious, very often water‐soluble organic matter (WSOM) obtained by extracting organic or mineral soil horizons with a dilute salt solution has been used as a substitute of DOM. We extracted WSOM (measured as water‐soluble organic C, WSOC) from seven mineral horizons of three forest soils from North‐Rhine Westphalia, Germany, with demineralized H2O, 0.01 M CaCl2, and 0.5 M K2SO4. We investigated the quantitative and qualitative effects of the extractants on WSOM and compared it with DOM collected with ceramic suction cups from the same horizons. The amounts of WSOC extracted differed significantly between both the extractants and the horizons. With two exceptions, K2SO4 extracted the largest amounts of WSOC (up to 126 mg C kg–1) followed by H2O followed by CaCl2. The H2O extracts revealed by far the highest molar UV absorptivities at 254 nm (up to 5834 L mol–1 cm–1) compared to the salt solutions which is attributed to solubilization of highly aromatic compounds. The amounts of WSOC extracted did not depend on the amounts of Fe and Al oxides as well as on soil organic C and pH. Water‐soluble organic matter extracted by K2SO4 bore the largest similarity to DOM due to relatively analogue molar absorptivities. Therefore, we recommend to use this extractant when trying to obtain a substitute for DOM, but as WSOM extraction is a rate‐limited process, the suitability of extraction procedures to obtain a surrogate of DOM remains ambiguous.

Topographical influences on soil properties in boreal forests

Topography is a major factor controlling both hydrological and soil processes at the landscape scale. This is well-known qualitatively in that topography, along with parent material, climate, biota, and time, is one of the fundamental soil forming factors. The topographic influence is also apparent in the soil catena concept. Digital elevation models (DEMs) and topographic indices calculated from these DEMs allow the relationship between topography and soil characteristics to be measured quantitatively as well. In this study we use data from the Swedish National Forest Soil Inventory, which is a long-term inventory of permanent sample plots from the Swedish National Forest Inventory. It includes a description of soil types and soil horizons as well as sampling of organic and mineral soil horizons for subsequent chemical analyses. We focused on Podzols and Histosols, which provided 4000 sample plots distributed over almost all of Sweden. Plot locations were determined accurately by GPS, which allowed the overlaying of plot data and the DEM. Topographic indices such as the topographic wetness index, TWI (ln(a/tan β)), were computed from gridded digital elevation data for all sample plots. We found several significant correlations between topographic indices and soil properties. The thickness of the organic layer increased with TWI and the thickness of the leached E-horizon increased with upslope area. Soil pH in the organic layer increased with TWI, while the C–N ratio decreased. Soil pH in the organic layer was also found to be higher for south facing slopes than for north facing slopes. The ratio between the divalent base cation (Ca and Mg) and the monovalent base cation (K and Na) concentrations in the O-horizon increased with TWI. These correlations confirmed the importance of topography on soil properties, although there was considerable scatter, which could be attributed to heterogeneity in the large data set.

Organic Matter in Volcanic Ash Soils under Forest and Páramo along an Ecuadorian Altitudinal Transect

The volcanic ash soils along an altitudinal transect in Guandera Biological Station in northern Ecuador have been developed under varying vegetation around the upper forest line. Generally, the soils currently covered by forest are composed of Fulvic Andosols (melanic index >1.7) while those under páramo (tropical alpine grasslands) have developed into Melanic Andosols. This vegetation effect on soil formation is believed to be associated with differences in organic matter composition. In this study, we examined whether Fulvic Andosols differed from Melanic Andosols in organic matter composition. Using analytical pyrolysis techniques, we found hardly any differences in the organic matter characteristics related to vegetation cover, not even between soils that supposedly have been covered by forest and páramo for millennia. Small differences were found within the lipid compounds, while the polysaccharides and lignin were virtually absent from the (deeper) mineral soil horizons. The low abundance of polysaccharides in soils that have undergone severe organic matter decomposition is not unusual for most soils, but is uncommon in other Andosols studied with the same pyrolysis techniques.

Ecosystem carbon accumulation following fallow farmland afforestation with red pine in southern Quebec

We assessed the organic C stocks and inferred their changes in vegetation biomass, forest floor, and soil using a 50 year chronosequence of red pine ( Pinus resinosa Ait.) plantations established on postagricultural fields in southern Quebec, Canada. The data come from soil and tree field surveys carried out in the 1970s in 348 sites. Organic C concentrations were usually measured in three major mineral soil horizons; for the remaining soil horizons, they were estimated using pedotransfer functions. The effect of soil order, drainage, and texture was analysed. Over 22 years, organic C accumulation rates (Mg C·ha–1·year–1) were 1.66 ± 0.03 in vegetation biomass, 0.56 ± 0.07 in forest floor, 0.86 ± 0.47 in loamy soils (0–100 cm), and –0.18 ± 0.24 in sandy soils (0–100 cm). The greater rate of C accumulation in loamy soils was due to the contribution of the 30–100 cm subsoil layer. The overall net accumulation of organic C in these plantation ecosystems was estimated to 51.4 ± 4.8 Mg C·ha–1at 22 years. Soils of these plantations acted as a C sink in the first two decades, particularly in loamy soils compared with sandy soils, with no major differences among soil order or drainage.

Buffer capacities of podzolic and peat gleyic podzolic soils to sulfuric and nitric acids

Soil samples from the main genetic horizons of pale podzolic and peat gleyic podzolic soils from the Central Forest Reserve were subjected to a continuous potentiometric titration by sulfuric and nitric acids. The sulfate sorption capacity was determined in soil mineral horizons. The buffer capacity of mineral horizons of both soils to sulfuric acid was found to be higher than that to the nitric acid. This is explained by the sorption of sulfates via the mechanism of ligand exchange with the release of hydroxyl groups from the surfaces of Fe and Al hydroxide particles and edge faces of clay crystallites. The buffer capacity of organic horizons of the pale podzolic soil to sulfuric acid proved to be higher than that to nitric acid; in organic horizons of the peat gleyic podzolic soil, the buffer capacity to sulfuric acid was lower than that to nitric acid. The reasons for this phenomenon have yet to be investigated.

Mercury Distribution in Soil Profiles Polluted by Lead Smelting

The smelting industry is one of the most important sources of anthropogenic contamination of the environment today. In the vicinity of nonferrous metal smelters, high concentrations of toxic compounds (especially metals and metalloids) have been detected in soils and vegetation (e.g., Ettler et al., 2005a; Suchara and Sucharova, 2002; Svoboda et al., 2000). In these instances, smelter emissions are assumed to be the dominant source of soil contamination (Ettler et al., 2005a,b). In the vicinity of a Pb smelter, Ettler et al. (2004) found that metals such as Pb strongly migrate downwards in soils and accumulate in mineral soil horizons. The form of metal in smelter emissions varies significantly. The smelter emissions in traditional Hg-mining areas are mainly composed of elemental Hg, coming from the vapor produced and emitted by roasting furnaces (Fernandez-Martinez et al., 2006). In contrast, the emissions from Pb smelters are mainly composed of Pb-sulfates and Pb-chlorides, and no specific Hg-bearing phases were detected in fly ash by the mineralogical methods (Ettler et al., 2005b). Nevertheless, soil Hg concentrations can be high enough to be considered a severe contaminant even in areas polluted by Pb smelting (Rieuwerts and Farago, 1996). Interestingly, little attention has been given to Hg concentrations in soils and vegetation in the vicinity of primary and secondary Pb smelters. This article describes the differences in total Hg concentrations between undisturbed forest and tilled soil profiles affected by a Pb smelter at Přibram, Czech Republic. Mercury sources and the vertical migration of mercury through soils are discussed.

Scots pine ectomycorrhizal fungal inoculum potential and dynamics in podzol-specific humus, eluvial and illuvial horizons one and four growth seasons after forest clear-cut logging

The aims of this microcosm-based study were to characterize Scots pine ectomycorrhizal (EcM) inoculum potential in humus (O) and underlying eluvial (E) and illuvial (B) mineral podzol soil horizons and to compare the inoculum potential 1 and 4 years following clear-cut logging. The specific horizons were collected from a Scots pine control uncut stand, the adjacent interface zone (3–10 m from the forest edge), and the adjoining clear-cut area. The highest Simpson's reciprocal diversity indices (SRDI) of ectomycorrhizal morphotypes and polymerase chain reaction – internal transcribed spacer – restriction fragment length polymorphism (PCR-(ITS)-RFLP) taxa were detected in the humus and E horizon. The B horizon supported the lowest SRDI, but the community consisted of mycorrhizas representing active rhizomorph-forming species. Identified RFLP taxa, confirmed via ITS sequence analysis, highlighted horizon specificity for some genera and species. With respect to clear-cutting impacts, the most dominant ectomycorrhizal morphotypes detected and diversity indices were the same irrespective of the sampling time, which strongly indicates that inoculum potential is maintained up to four growth seasons after the clearcut. No forest treatment dependent differences in Scots pine seedling biomass were detected, but, compared with humus, significantly reduced biomass was recorded in deeper mineral soil horizons. The data are discussed in relation with recent vertical profile studies and forest silvicultural practices.

Spatial distribution of fine roots at ploughed Norway spruce forest sites

We examined the spatial distribution of fine roots at two forest sites that were ploughed 20 (site K1) and 33 years (site K2) before sampling and planted with Norway spruce (Picea abies (L.) Karst.) seedlings. Soil core samples were taken from the tilt and beneath the tilt, the furrow and the intermediate undisturbed soil to a depth of 0.4 m for fine root biomass, length and necromass determinations. Norway spruce fine roots were found throughout the ploughed forest sites. The fine roots were, however, unevenly distributed: the fine root biomass was highest in the tilt (624 and 452 g m at sites K1 and K2, respectively) and lowest in the undisturbed soil at site K1 (79 g m) and in the furrow at site K2 (145 g m). The estimated average fine root biomass at the ploughed forest sites (268 and 248 g m at sites K1 and K2, respectively) was, however, similar to those presented in other studies concerning sites that had not been ploughed. In the tilt, a substantial proportion of the fine roots was in the inverted mineral soil horizons and in the new organic horizon above the tilt. Consistent with the fine root biomass findings, the Norway spruce necromass was highest in the tilt but the vertical distribution of the dead roots was different: the necromass was highest in the buried O horizon. The results of this study suggest that at the ploughed forest sites, a substantial part of Norway spruce nutrient and water uptake occured in the tilt during the first 20 or 33 years after plantation.–2–2–2–2BT

A mineral support and biotic catalyst are essential in the formation of highly polymeric soil humic substances

The hypothesis was proposed that highly polymeric humic substances in the mineral horizons of soils in a temperate humid climate originate from polymerization of water-soluble structural precursors directly on mineral surfaces under the catalytic effect of immobilized phenoloxidases (heterophasic biocatalysis). This hypothesis was confirmed by a laboratory experiment using a mixture of monomeric phenols and nitrogenous compounds as structural precursors, fungal laccase as a biotic catalyst, and a hydroxyaluminum-kaolinite complex as a mineral support. Enzymic oxidation of phenolic precursors on the mineral surface was substantially more rapid than abiotic oxidation and led to synthesis of a highly polymeric fraction with a molecular weight over 75 kDa. These products were not produced on the mineral with an absence of laccase (abiotic catalysis) or in solution without the mineral matrix (homogeneous catalysis).

Post-harvest nitrogen cycling in clearcut and alternative silvicultural systems in a montane forest in coastal British Columbia

The MASS (Montane Alternative Silvicultural Systems) trial was established in the coastal mountains of British Columbia to compare clearcut, patch cut, green tree and shelterwood systems. A number of studies were carried out at the MASS trial to determine the extent to which these variable levels of stand retention retained old-growth attributes of N cycling and associated ecological processes. Harvesting led to increases in N mineralization in the forest floor (2×) and mineral soil (10×), and fluxes of N through the upper 25 cm of mineral soil (2× to 3×). However, fluxes of N were not large (< 0.35 kg ha-1per growing season). Nitrogen mineralized was predominantly ammonium and not nitrate in the forest floor (> 95% in all but clearcut, > 75% in clearcut) and upper mineral soil horizon (42–86%). The nitrate component came from heterotrophic decomposition of organic matter, not conversion of ammonium to nitrate by autotrophs, and nitrate increases resulted from decreased gross nitrate consumption with harvesting, rather than increased nitrate production. The increases in soil N availability resulting from harvesting were reflected in only slight increases in seedling foliar N concentrations for two to four years after logging (peak of ~ 2% for western hemlock and ~ 1.6% for amabilis fir) before decreasing to below deficiency thresholds for both species. Overall, estimated losses of N from the rooting zone after harvesting (1 kg ha-1 yr-1) were minimal in comparison to estimated N inputs (4 kg ha-1 yr-1), N exports in logs at harvesting (250 kg ha-1) and soil reserves (11 400 kg ha-1). Although unlikely to affect future site productivity, losses of N could be reduced somewhat through the use of shelterwood harvesting. Key words: alternative silvicultural systems, variable retention harvesting, nitrogen cycling, litterfall, decomposition, nitrification, N mineralization, microbial ecology, leaching, foliar N, Abies amabilis, Tsuga heterophylla, Thuja plicata

Anthropogenic Pb accumulation in forest soils from Lake Clair watershed: Duchesnay experimental forest (Québec, Canada)

Mineral soil horizons (Ae, Bhf1, Bhf2, Bf, BC and C) were carefully collected from two podzolic soil profiles in the Lake Clair watershed (Québec) in order to assess anthropogenic trace metal accumulation. Petrographic and selective analyses were performed to establish the soil mineralogy and properties. Furthermore, a complete sequential extraction procedure has been applied to help understanding the complex chemical speciation of Pb in forest soils. Chemical speciation of Pb showed a strong vertical gradient: 85% of this metal is mainly partitioned in refractory minerals in the C-horizon whereas in the upper Bhf1 and Ae-horizons, less than 50% of Pb is associated with this fraction. In the Ae-horizon, for example, 35%, 30% and 12% of total Pb, respectively, is associated with the exchangeable, labile organic matter and amorphous Fe-Mn oxides fractions. The distribution of Pb and Cr in the studied forest soils mainly reflects progressive contamination of the watershed by anthropogenic atmospheric sources. The anthropogenic source is indicated by elevated Cr and Pb concentrations in the topsoil (Bhf and Ae) horizons and by strong negative correlation between 206Pb/ 207Pb ratios and total Pb concentrations. According to these isotopic values, penetration of anthropogenic Pb does not exceed 10 cm in both soil profiles. Below this depth, both Pb concentrations and isotopic ratios remain nearly constant and similar to values observed in pre-anthropogenic sediments from Lake Clair. These values are interpreted as the natural geochemical backgrounds of the watershed. Based on that behaviour, calculated anthropogenic Pb net inputs amounted to between 1.24 and 1.8 g/m 2.

Dendrogeochemical distinction between geogenic and anthropogenic emissions of metals and gases near a copper smelter

For countries where metal resources represent an important economic sector, one of the main challenges of environmental research is to distinguish between natural and anthropogenic accumulations of potentially toxic metals in mining districts. The present work aims to evaluate a new environmental monitoring tool combining dendrochronology with natural (Ca, Ca/Mn, δ 13 C) and anthropogenic (Cd, Pb, 206 Pb/ 207 Pb, 208 Pb/ 206 Pb) geochemical tracers in tree rings in such a region. We compare spruce trees sampled at a control site near Hudson Bay, with those sampled near the Horne smelter active since 1928 in Rouyn-Noranda. The first effect of smelter emissions is detected by the tree-ring carbon isotope records. The δ 13 C values obtained on trees near the smelter show major changes immediately after 1928. This is due to the presence of atmospheric SO 2 which generates a rapid response of the foliar system. The Ca/Mn ratios in tree-ring pairs of 1936–1937 and younger suggest a SO 2 -related soil acidification. The concentrations in Cd and Pb show a major increase starting in 1944 which coincides with a decrease of the 206 Pb/ 207 Pb ratios. The smelter activities likely generated this increase and the apparent delay of 14 years may have been generated mainly by the residence time of metals in airborne particulates, the buffering effect of the soils and, to a lesser extent, perhaps by mobility of heavy metals in tree stems. The 206 Pb/ 207 Pb and 208 Pb/ 206 Pb ratios indicate that the growth rings contain at least three types of Pb: natural, derived from the mineral soil horizons; industrial, from coal burning urban pollution; and mining, typical of the volcanogenic massive sulphides treated at the Horne smelter. This new combination of natural and anthropogenic tracers allows recognition of the succession of atmospheric and pedogeochemical changes related to industrial activities in the Rouyn-Noranda mining area.

The Complementarity of Extractable and Ester-Bound Lipids in a Soil Profile Under Pine

Extractable and solvent insoluble, ester-bound lipids were analysed in an acid, sandy soil profile under Corsican pine. The n-alkanes and alkanoic acids from the soil profile showed rather poor correlations with those from the pine needles and roots, while the n-alkanol composition in the mineral horizons strongly indicated the presence of lipids derived from a previous grass vegetation. Although the ester-bound lipids (ω-hydroxyalkanoic acids and α,ω-alkanedioic acids (>C24)) suggested that plant sources other than pines were present in the mineral soil horizons their composition was less contaminated and a clear distinction between needle and root input could be discerned. The divergent clustering of soil horizons and plant materials by individual and combined compound classes emphasized the usefulness of both extractable lipids and cutin/suberin in unravelling (past) vegetation and tissue history and contributions to soil organic matter.

Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario

The potential impact of timber harvesting in the boreal forest on aquatic ecosystem water quality and productivity depends in part on the production of nutrients within the soil of the harvested catchment. Nitrogen supplied by organic matter decomposition is of particular interest because of the important role that N plays in biotic processes in surface waters, and in forest nutrition in general. Logging slash quality and input to the forest floor has the potential to influence N availability after harvest on clearcut sites. Net production of organic and inorganic-N and microbial biomass C and N concentrations were determined during a 90-day laboratory incubation at constant temperature and moisture. Incubated soils included F horizon and shallow mineral soil horizons (0–5 cm) from unharvested and full-tree harvested (2 and 12 growing seasons since harvest) boreal forest sites at the Esker Lakes Research Area (ELRA), in northeastern Ontario, Canada. In an ancillary experiment, black spruce foliage was added to unharvested forest floor material after 30 days during a 90-day laboratory incubation to simulate the influence of logging slash from full-tree harvesting on C and N dynamics. Twelve-year old clearcut F horizon material released on average 75 and 5 times more NO 3 - -N and 3 and 2 times as much inorganic-N than soil collected from unharvested and 2-year-old clearcuts, respectively. This increase in NO 3 - -N accumulation during the incubation was accompanied by decreases in both exchangeable NH 4 + -N and microbial biomass C and N levels. Net daily changes in microbial biomass N were significantly related to organic and inorganic-N accumulation or loss within the F horizon. Mineral soil release of inorganic-N was lower than release from the forest floor. Nitrate-nitrogen accumulation was lower, and NH 4 + -N accumulation was higher in mineral soil from unharvested sites when compared to 12-year-old clearcuts. Calculated harvest response ratios indicated that incubated mineral soil from the 12-year-old clearcut sites released significantly greater amounts of NO 3 - -N than 2-year-old clearcuts. Incorporation of black spruce needles into F horizon material reduced the production of organic and inorganic-N and increased microbial biomass N. Laboratory incubations of F horizon and shallow mineral soil from 12-year-old clearcuts suggested that these boreal soils have the capacity for increased inorganic-N production compared to uncut stands several years after harvesting. This has the potential to increase N availability to growing boreal forest plantations and increase N leaching due to greater NO 3 - -N levels in the forest soil.