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Mean annual (1994-1996) budgets for Cd, Cu, Ni, Pb and Zn at two background, forested catchments, VK and HJ, in Finland are presented. Budgets for plots (VK3, HJ1 and HJ4) included throughfall (TF), litterfall (LF) and soil leaching fluxes, and for catchments terrestrial retention and leaching and lake sedimentation fluxes. Total deposition (TD) loads were relatively tow (Cd < 0.1, Cu < 2, Ni < 1, Pb < 3 and Zn < 5 mg m[sup -2] year[sup -1]) and that even in these areas almost half of the TD was in the form of dry deposition. Retention of TD within catchments was ≥77% for all metals, except for Ni at VK (54%). For Cu and Pb, the retention was 94-97%. Most of the retention (74-97%) took place in the terrestrial part of the catchment, lake sedimentation accounting for the remainder. Plot-scale soil leaching fluxes at 40 cm of Cd, Cu (VK3) and Ni (VK3) were greater (≥ 100%) than TD inputs. Most of the catchment retention must therefore have taken place either deeper in the soil or in the lowland peatland areas. The humus layer was particularly effective in retaining Cu and Cd (65-81% and 51-78% of total inputs to the forest floor (TF + LF)). The retention of Pb by the humus layer was less than expected (26-54% of TF + LF). Litterfall was a particularly important internal flux for Zn. [ABSTRACT FROM AUTHOR]

Temporal trends in sulfate, base cation (Ca2+ + Mg2+ + K+), and H+ ion concentrations in bulk precipitation and throughfall samples collected over a seven year period (1989-95) in four forested catchments in Finland are presented. The catchments are in remote locations and span the boreal zone (61-69 degrees N). The stands represent old, undisturbed forests, and are composed of varying proportions of Scots pine, Norway spruce and deciduous species (mainly Betula spp.). Monthly SO42--S and H+ ion concentrations in bulk precipitation averaged overthe study period and catchments were: 18.7 mu mol L-1 and 32.3 mu mol L-1. The corresponding values for throughfall were: 37.4 mu mol L-1and 32.4 mu mol L-1. Sulfate and H+ ion concentrations in bulk precipitation and throughfall both showed negative linear trends, which were significant (p < 0.05) for the three southernmost catchments. Concentrations and trend slope decreased northwards (e.g., bulk precipitation SO42--S slope estimates: -1.6 to -1.0 mu mol L-1 yr-1). The decline was greater for throughfall than for bulk precipitation, indicating a proportionally greater reduction in dry deposition than wet. The sum of base cation concentrations averaged 12.1 mu mol((+)) L-1 in bulk precipitation and 83.1 mu mol((+)) L-1 in throughfall.There were no significant trends in the sum of base cations (p > 0.05). It is concluded that the reported reduction in S emissions over the study period has resulted in a significant reduction in the acidity and SO42- concentration of bulk precipitation, and this reduction has has been reflected in throughfall concentrations. The greatest reduction has taken place in the southern part of the country. [ABSTRACT FROM AUTHOR]

Food production has a profound eutrophication impact on waterbodies via nutrient leaching. To provide reliable life cycle assessments of the eutrophication potential of agricultural products, accurate nitrogen leaching models are needed. Although many dynamic nitrogen leaching models are in use, their suitability for farm-level assessments remains limited when their requirements for site specific data or numerous parameters are not met. In Finland, less data intensive leaching models for life cycle assessments have been developed using data from conventional farming, however, the suitability of these models for organic farming remains unknown. In this work, we developed new nitrogen leaching models that are applicable to both conventional and organic production. While this paper does not aim to argue in favor of organic or conventional farming it provides tools that can be used to inform decisions about management practices from the environmental perspective. We utilized up to 16 years of field measurements from two leaching fields in Finland. We developed prediction equations for nitrogen leaching for two soil types: sand soil and clay soil. According to our statistical analysis based on the data, the relevant factors for explaining nitrogen leaching included soil type, rainfall, whether the farming is done organically, and the availability of nitrogen for leaching. Computed nitrogen balance as such was found to be a poor proxy for nitrogen available for leaching, while nitrate nitrogen concentration measurement of the soil carried out in the fall was found to be a valuable predictor. Organic farming, with a crop rotation resembling that of conventional farming, resulted on average in 20% less nitrogen leached per hectare as compared to conventional farming with 95% C.I. [-34%, -3%]. The developed models are suitable for integration into a life cycle assessment framework, and especially the models utilizing nitrate nitrogen were shown to be applicable to a wide range of different crop types, making the model well-suited for plots with diverse crop rotations., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: financial support was provided by Business Finland., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Nature-based solutions (NbS) can be beneficial to help human communities build resilience to climate change by managing and mitigating related hydro-meteorological hazards (HMHs). Substantial research has been carried out in the past on the detection and assessment of HMHs and their derived risks. Yet, knowledge on the performance and functioning of NbS to address these hazards is severely lacking. The latter is exacerbated by the lack of practical and viable approaches that would help identify and select NbS for specific problems. The EU-funded OPERANDUM project established seven Open-Air Laboratories (OALs) across Europe to co-develop, test, and generate an evidence base from innovative NbS deployed to address HMHs such as flooding, droughts, landslides, erosion, and eutrophication. Herein, we detail the original approaches that each OAL followed in the process of identifying and selecting NbS for specific hazards with the aim of proposing a novel, generic framework for selecting NbS. We found that the process of selecting NBS was overall complex and context-specific in all the OALs, and it comprised 26 steps distributed across three stages: (i) Problem recognition, (ii) NbS identification, and (iii) NbS selection. We also identified over 20 selection criteria which, in most cases, were shared across OALs and were chiefly related to sustainability aspects. All the identified NbS were related to the regulation of the water cycle, and they were mostly chosen according to three main factors: (i) hazard type, (ii) hazard scale, and (iii) OAL size. We noticed that OALs exposed to landslides and erosion selected NbS capable to manage water budgets within the soil compartment at the local or landscape scale, while OALs exposed to floods, droughts, and eutrophication selected approaches to managing water transport and storage at the catchment scale. We successfully portrayed a synthesis of the stages and steps followed in the OALs' NbS selection process in a framework. The framework, which reflects the experiences of the stakeholders involved, is inclusive and integrated, and it can serve as a basis to inform NbS selection processes whilst facilitating the organisation of diverse stakeholders working towards finding solutions to natural hazards. We animate the future development of the proposed framework by integrating financial viability steps. We also encourage studies looking into the implementation of the proposed framework through quantitative approaches integrating multi-criteria analyses., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Alejandro Gonzalez Ollauri reports financial support was provided by European Commission., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Anthropogenic mercury (Hg) undergoes long-range transport to the Arctic where some of it is transformed into methylmercury (MeHg), potentially leading to high exposure in some Arctic inhabitants and wildlife. The environmental exposure of Hg is determined not just by the amount of Hg entering the Arctic, but also by biogeochemical and ecological processes occurring in the Arctic. These processes affect MeHg uptake in biota by regulating the bioavailability, methylation and demethylation, bioaccumulation and biomagnification of MeHg in Arctic ecosystems. Here, we present a new budget for pools and fluxes of MeHg in the Arctic and review the scientific advances made in the last decade on processes leading to environmental exposure to Hg. Methylation and demethylation are key processes controlling the pool of MeHg available for bioaccumulation. Methylation of Hg occurs in diverse Arctic environments including permafrost, sediments and the ocean water column, and is primarily a process carried out by microorganisms. While microorganisms carrying the hgcAB gene pair (responsible for Hg methylation) have been identified in Arctic soils and thawing permafrost, the formation pathway of MeHg in oxic marine waters remains less clear. Hotspots for methylation of Hg in terrestrial environments include thermokarst wetlands, ponds and lakes. The shallow sub-surface enrichment of MeHg in the Arctic Ocean, in comparison to other marine systems, is a possible explanation for high MeHg concentrations in some Arctic biota. Bioconcentration of aqueous MeHg in bacteria and algae is a critical step in the transfer of Hg to top predators, which may be dampened or enhanced by the presence of organic matter. Variable trophic position has an important influence on MeHg concentrations among populations of top predator species such as ringed seal and polar bears distributed across the circumpolar Arctic. These scientific advances highlight key processes that affect the fate of anthropogenic Hg deposited to Arctic environments., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Sofi Jonsson reports financial support was provided by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (2020-01868). Sofi Jonsson reports financial support was provided by the Swedish Research Council (2017-05275). John Chetelat reports was provided by Environment and Climate Change Canada. Lars-Eric Heimburger-Boavida reports was provided by the AXA Research Fund. Lars-Eric Heimburger-Boavida reports was provided by Chantier Arctique Francais (Pollution in the Arctic System)., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Many recent studies have indicated upward trends in carbon and nutrient concentrations from drained peatland forests over time since their initial drainage, but the mechanisms behind these trends are still poorly understood. We gathered data on nitrogen and phosphorus concentrations discharged from 37 drained boreal peatland forests where we also had data on peat and tree stand characteristics. We found that tree stand volume and peat bulk density were positively correlated with the nitrogen and phosphorus concentrations discharged from particularly the deep-peated sites. We interpret these results to indicate that a plausible reason for the reported upward trends in nutrient concentrations is the maturing and growing of the tree stands over time since initial drainage and the consequent increasing evapotranspiration capacity, which results in lowered soil water levels and enhanced aerobic peat mineralization. We discuss how our results should be considered in the management of drained peatland forests., (© 2022 The Authors. Journal of Environmental Quality © 2022 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

More reliable assessments of nutrient export to surface waters and the Baltic Sea are required to achieve good ecological status of all water bodies. Previous nutrient export estimates have recently been questioned since they did not include the long-term impacts of drainage for forestry. We made new estimates of the total nitrogen (N), total phosphorus (P) and total organic carbon (TOC) export from forests to surface waters at different spatial scales in Finland. This was done by formulating statistical equations between streamwater concentrations and climate, soil, forest management and runoff variables and spatial data on catchment characteristics. The equations were based on a large, long-term runoff and streamwater quality dataset, which was collected from 28 pristine and 61 managed boreal forest catchments located around Finland. We found that the concentrations increased with temperature sum (TS), i.e. from north to south. Nitrogen, P and TOC concentrations increased with the proportion of drained areas in the catchment; those of N and TOC also increased with the proportion of peatlands. In contrast, with the increasing concentrations of N and TOC with time, P concentrations showed a decreasing trend over the last few decades. According to our estimates, altogether 47,300 Mg of N, 1780 Mg of P and 1814 Gg of TOC is transported from forest areas to surface waters in Finland. Forest management contributes 17% of the N export, 35% of the P export and 12% of the TOC export. Our new forest management export estimates for N and P are more than two times higher than the old estimates used by the environment authorities. The differences may be explained by the long-term impact of forest drainage. The spatial results indicate that peatland forests are hotspots for N, P and TOC export, especially in the river basins draining to the Gulf of Bothnia., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Anthropogenic emissions of nitrogen (N) and sulphur (S) compounds and their long-range transport have caused widespread negative impacts on different ecosystems. Critical loads (CLs) are deposition thresholds used to describe the sensitivity of ecosystems to atmospheric deposition. The CL methodology has been a key science-based tool for assessing the environmental consequences of air pollution. We computed CLs for eutrophication and acidification using a European long-term dataset of intensively studied forested ecosystem sites (n = 17) in northern and central Europe. The sites belong to the ICP IM and eLTER networks. The link between the site-specific calculations and time-series of CL exceedances and measured site data was evaluated using long-term measurements (1990-2017) for bulk deposition, throughfall and runoff water chemistry. Novel techniques for presenting exceedances of CLs and their temporal development were also developed. Concentrations and fluxes of sulphate, total inorganic nitrogen (TIN) and acidity in deposition substantially decreased at the sites. Decreases in S deposition resulted in statistically significant decreased concentrations and fluxes of sulphate in runoff and decreasing trends of TIN in runoff were more common than increasing trends. The temporal developments of the exceedance of the CLs indicated the more effective reductions of S deposition compared to N at the sites. There was a relation between calculated exceedance of the CLs and measured runoff water concentrations and fluxes, and most sites with higher CL exceedances showed larger decreases in both TIN and H + concentrations and fluxes. Sites with higher cumulative exceedance of eutrophication CLs (averaged over 3 and 30 years) generally showed higher TIN concentrations in runoff. The results provided evidence on the link between CL exceedances and empirical impacts, increasing confidence in the methodology used for the European-scale CL calculations. The results also confirm that emission abatement actions are having their intended effects on CL exceedances and ecosystem impacts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 The Author(s). Published by Elsevier B.V. All rights reserved.)

The international Long-Term Ecological Research Network (ILTER) encompasses hundreds of long-term research/monitoring sites located in a wide array of ecosystems that can help us understand environmental change across the globe. We evaluated long-term trends (1990-2015) for bulk deposition, throughfall and runoff water chemistry and fluxes, and climatic variables in 25 forested catchments in Europe belonging to the UNECE International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems (ICP IM). Many of the IM sites form part of the monitoring infrastructures of this larger ILTER network. Trends were evaluated for monthly concentrations of non-marine (anthropogenic fraction, denoted as x) sulphate (xSO 4 ) and base cations x(Ca+Mg), hydrogen ion (H + ), inorganic N (NO 3 and NH 4 ) and ANC (Acid Neutralising Capacity) and their respective fluxes into and out of the catchments and for monthly precipitation, runoff and air temperature. A significant decrease of xSO 4 deposition resulted in decreases in concentrations and fluxes of xSO 4 in runoff, being significant at 90% and 60% of the sites, respectively. Bulk deposition of NO 3 and NH 4 decreased significantly at 60-80% (concentrations) and 40-60% (fluxes) of the sites. Concentrations and fluxes of NO 3 in runoff decreased at 73% and 63% of the sites, respectively, and NO 3 concentrations decreased significantly at 50% of the sites. Thus, the LTER/ICP IM network confirms the positive effects of the emission reductions in Europe. Air temperature increased significantly at 61% of the sites, while trends for precipitation and runoff were rarely significant. The site-specific variation of xSO 4 concentrations in runoff was most strongly explained by deposition. Climatic variables and deposition explained the variation of inorganic N concentrations in runoff at single sites poorly, and as yet there are no clear signs of a consistent deposition-driven or climate-driven increase in inorganic N exports in the catchments., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The current understanding, based on previous studies, is that increased discharge nutrient concentrations from boreal peatlands drained for forestry return to similar levels as those of pristine peatlands within about 20years after their drainage. As an implicit consequence of this finding, it has been assumed that there are no long-term increasing trends in nutrient exports from these peatlands after the establishment of forestry. We analysed discharge total nitrogen (TN) and phosphorus (TP) concentration data from 54 catchments with undrained pristine peatlands and 34 catchments with drained peatlands using data with considerably longer drainage history than in previous studies. Our results agree with previous studies in that discharge TN and TP concentrations in areas drained 20-30years ago did not differ much from those in pristine sites. However, we also observed that the TN and TP concentrations were increasing with years since drainage of these catchments. Discharge TN and TP concentrations were over two times higher in areas drained 60years ago when compared with more recently drained areas. Our results challenge the current perceptions by showing that forestry-drained peatlands may contribute to water eutrophication considerably more than previously estimated., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The isotopic composition of Pb was determined in Finnish peat bogs and their porewaters from Harjavalta (HAR, near a Cu-Ni smelter), Outokumpu (OUT, near a Cu-Ni mine), and Hietajärvi (HIJ, a background site). At HIJ and OUT, the porewaters yielded similar concentrations (0.1-0.7 μg/L) and isotopic composition ((206)Pb/(207)Pb = 1.154-1.164). In contrast, the peat profile from HAR yielded greater concentrations of Pb in the porewaters (average 2.4 μg/L), and the Pb is less radiogenic ((206)Pb/(207)Pb = 1.121-1.149). Acidification of the bog surface waters to pH 3.5 by SO2 emitted from smelting (compared to pH 4.0 at the control site) apparently promotes the dissolution of Pb-bearing aerosols, as well as desorption of metals from the surfaces of these particles and from the peat matrix. Despite this, the chronology of anthropogenic, atmospheric deposition for the past millenium recorded by the isotopic composition of Pb in all three peat bogs is remarkably similar. While the immobility of Pb in the peat cores may appear inconsistent with the elevated porewater Pb concentrations, Pb concentrations in the aqueous phase never amount to more than 0.01% of the total Pb at any given depth so that the potential for migration remains small. The low rates of vertical water movement in bogs generally combined with the size of the metal-containing particles in solution may be additional factors limiting Pb mobilization.

Forest harvesting, especially when intensified harvesting method as whole-tree harvesting with stump lifting (WTHs) are used, may increase mercury (Hg) and methylmercury (MeHg) leaching to recipient water courses. The effect can be enhanced if the underlying bedrock and overburden soil contain Hg. The impact of stem-only harvesting (SOH) and WTHs on the concentrations of Hg and MeHg as well as several other variables in the ditch water was studied using a paired catchment approach in eight drained peatland-dominated catchments in Finland (2008-2012). Four of the catchments were on felsic bedrock and four on black schist bedrock containing heavy metals. Although both Hg and MeHg concentrations increased after harvesting in all treated sites according to the randomized intervention analyses (RIAs), there was only a weak indication of a harvest-induced mobilization of Hg and MeHg into the ditches. Furthermore, no clear differences between WTHs and SOH were found, although MeHg showed a nearly significant difference (p = 0.06) between the harvesting regimes. However, there was a clear bedrock effect, since the MeHg concentrations in the ditch water were higher at catchments on black schist than at those on felsic bedrock. The pH, suspended solid matter (SSM), dissolved organic carbon (DOC), and iron (Fe) concentrations increased after harvest while the sulfate (SO4-S) concentration decreased. The highest abundances of sulfate-reducing bacteria (SRB) were found on the sites with high MeHg concentrations. The biggest changes in ditch water concentrations occurred first 2 years after harvesting.

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., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The main objective of this study was to examine if any detectable trends in dissolved organic carbon (DOC), sulphate (SO4-S) concentrations and acid neutralizing capacity (ANC) in throughfall (TF) and soil water (SW) could be found during 1990-2010 and to relate them to recent changes in decreased acid deposition. The study was conducted in seven boreal coniferous forest sites: four of which are managed and three unmanaged forests sites. Generally, temporal trend showed a significant decrease in SO4-S concentrations in bulk precipitation (BP), TF and SW. At some of the sites, there was an increasing tendency in BP and TF in the DOC concentrations. This feature coincides with decreasing SO4-S concentration, indicating that SO4-S may be an important driver of DOC release from the canopy. However, a slightly increased temperature, larger senescing needle mass and consequently increased decaying activity in the canopy may partly explain the increasing trend in DOC. In SW, no consistent DOC trend was seen. At some sites, the decreased base cation concentrations mostly account for the decrease in the ANC values in SW and TF.

Porewaters were collected from three Finnish peat bogs subjected to varying inputs of atmospheric trace metals: Hietajärvi (HIJ), a low-background site, Outokumpu (OUT), near a Cu-Ni mine, and Harjavalta (HAR), near a Cu-Ni smelter. Samples for metal analyses were collected at depths ranging from 10 to 70 cm using a purpose-built syringe-type sampler. Metal concentrations were determined using inductively coupled plasma-sector field-mass spectrometry (ICP-SF-MS). Porewater concentrations at HIJ and OUT (Cd <0.3 nM, Co <1.4 nM, Cu, Ni <8 nM, Zn <250 nM) are independent of metal concentrations in the solid phase (peat). At OUT there is a limited release of Ni to the porewaters, but concentrations in the aqueous phase are generally below 0.3% of the total concentration in any given peat sample. These data are consistent with the immobility of these metals after deposition from the air. In contrast, porewaters at HAR are enriched in trace metals compared to the other sites by a factor of 2 (Zn), 10 (Cd), 20 (Co), and 100 (Cu and Ni) with dissolved fractions of Cu and Ni accounting for ca. 20% of the metal inventories in the cores. The elevated release of metals from solid phases at HAR is consistent with the postdepositional migration of metals at this site and reflects the predominance of oxide phases supplied to the bog surface and the much lower pH values (<3.4). The elevated proton concentrations not only promote mineral dissolution but also compete with cation exchange processes and hinder the formation of metal complexes with organic ligands.

This study aims to determine the extent to which the accumulation rates of Cu, Ni, Co, Zn, and Cd in peat cores agree with established histories of atmospheric emission from local pointsources. Metals accumulating in three Finnish peat cores with known metal deposition histories have been measured using inductively coupled plasma-sector field mass spectrometry. Samples were age-dated using both 210Pb and 14C (bomb pulse curve). At the Outokumpu (OUT) site as well as the low-background site Hietajärvi (HIJ), 210Pb age dates are in excellent agreement with the 14C bomb pulse curve method results, and the precision is between 1 and 10 years for most of the samples; at the Harjavalta (HAR) site, precision is > 6 years. Mean regional "background" concentrations have been calculated from deeper peat layers of the HIJ site (microg g(-1)): Cu, 1.3 +/- 0.2 (n = 62); Co, 0.25 +/- 0.04 (n = 71); Cd, 0.08 +/- 0.01 (n = 23); and Zn, 4 +/- 2 (n = 40). For layers accumulated within the past 100 years, accumulation rates (ARs) have been calculated. At sites with < 0.06 g m(-2) cumulative Ni inventory (HIJ and OUT), ARs of Cu and Co trace the known metal deposition histories very well. At HAR, where metal inventories are much greater, Cu and Co are mobile. ARs of Zn were between 3 and 30 mg m(-2) year(-1) and those of Cd between 24 and 140 microg m(-2) year(-1) at all sites and are independent of the chronology of their inputs from the atmosphere.

Major nutrients and acidity were studied at six plots in four Integrated Monitoring catchments in Finland, located along a south-north deposition gradient. The quality and quantity of bulk precipitation, throughfall, soil water, and litterfall were monitored during the period 1989-1997. The results showed a marked decline in SO4 and H+ concentrations overall. Trends in throughfall ANC values were positive, while those in soil water were mostly negative. The increase in throughfall ANC values indicates recovery from acid deposition. The adsorption of base cations and release of organic acids was implicated in the decrease in soil water ANC trends. For all variables, the changes tended to be the greatest in the most southerly catchment, which received the most deposition loads. Mass balance budgets showed that total deposition inputs were greater than soil leaching outputs (at 40 cm) for NO3, NH4 and SO4, and were attributed to nutrient uptake and cycling processes. In contrast, for Ca, Mg, K and Na, and S (Valkea-Kotinen3 and Vuoskojärvi2 plots only), inputs were less than outputs, indicating net leaching. Throughfall + litterfall inputs to the forest floor showed that the organic layer is particularly important in the retention of Ca, Mg and N. Sulfur was retained in the lower soil layers, and attributed to Al and Fe hydroxide adsorption in the B horizon.

Litterfall (LF) is usually collected by means of open traps. However, this litter will be subject to leaching by the throughfall which passes through the accumulated litter in the traps. The nutrients lost during this leaching are not taken into account in the calculation of LF nutrient fluxes. We report the results from a 2-month (August-September) study carried out in 8 northern coniferous forest stands to assess the possible importance of leaching from litter in LF traps. Compared to throughfall (TF), the litterfall leachate (LFLgross), which includes a throughfall component, had significantly (p < 0.05) higher concentrations and fluxes of Ca, Mg, Na and S. The average net LFL (i.e., LFLnet = LFLgross - TF) fluxes were 21 (Ca), 7 (Mg), 57 (K), 10 (Na), 10 (N), and 19 (S) mg m-2 mo-1. LFLnet accounted for 42%, 37% and 50% of the LFLgross flux, and for 91%, 51% and 49% of the total litterfall flux (i.e., LF + LFLnet) of Na, S and K, respectively. For Ca, Mg and N, the LFLnet flux accounted for 64%, 58% and 29% of the LFLgross flux, and for < 14% of the total litterfall flux. Compared to TF, LF was the dominant return pathway for Ca, Mg and N to the forest floor regardless of whether LFLnet was included or not. However, for K and S, taking LFLnet into account determined whether TF or LF was the dominant pathway. TF remained the dominant pathway for Na even when LFLnet was included.