Base Cation Fluxes Research Articles

Base Cation Fluxes in Mountain Landscapes of Lake Baikal Southern Shore

Assessing base cation [calcium (Ca2+), magnesium (Mg2+), potassium (K+)] fluxes is necessary for determining ecosystem stability. This study was conducted in the Osinovka River catchment located on the Khamar‐Daban Ridge, South Baikal, which is characterized by high precipitation (more than 1700 mm per annum). The contributions of different ecosystem components such as atmospheric deposition, soil exchange pool, minerals, vegetation, surface water, and groundwater into the total base cations flux were evaluated, combining the strontium isotope approach and budget study. Results show the leading role of atmosphere in ecosystem supply with base cations. The atmosphere contributes 48% of total base cations flux, and its contributions to plant‐available nutrition pools of both organic and mineral horizons are equal to 50%. This makes the vitality of vegetation, to a great extent, dependent on the stability of atmospheric chemistry.

Investigating the soil acid–base status in managed boreal forests using the SAFE model

A dynamic soil chemistry model, SAFE, was applied to boreal stands located in three regions of Quebec (Canada) to investigate the relative contributions of forest harvesting methods (whole-tree and stem-only harvesting), natural disturbances (wildfire and spruce budworm outbreak) and atmospheric deposition on base cation fluxes and the soil acid–base status. Model parameterization was done using measured and published soil and vegetation data, published trends of nutrient dynamics, governmental databases on atmospheric deposition and climate, the reconstruction method MAKEDEP and throughfall equations that we developed for coniferous stands. The model suggested that forest disturbances, both anthropogenic and natural, increased base saturation, and thus base cation availability, to different degrees for periods of one to five decades. However, such disturbances, no matter their interval of return and their intensity, did not appear to be the main driving force of soil chemistry in the long term. On the other hand, simulation results showed that the B horizon at all sites has undergone acidification due to acid atmospheric deposition during the 20th century. Results suggest that atmospheric deposition is the main driver of long-term trends of soil chemistry for the study sites and that the issue of sustainability of soil productivity depends more on air pollution abatement policies than on forest management strategies.

Climatically driven pH changes in two Norwegian alpine lakes

Two alpine lakes in the south-central part of Norway have been studied for recent changes in diatom assemblages preserved in their sediments. Both lakes experience a post 1980 AD increase in diatom valve accumulation rates possibly reflecting an increase in lake productivity. In addition there is an overall increase in diatom-inferred pH at both sites. Recovery from lake acidification can be disregarded as a possible cause of increased pH as the lakes are situated in catchments with high buffering capacities in areas that have received low amounts of acid deposition. We suggest that recent climate warming has influenced both sites with the important effect of increasing mineralization in the catchments, resulting in greater fluxes of nutrients and base cations to the lakes, leading to an increase in diatom-inferred pH. Taxa that have increased in abundance include Achnanthes minutissima, Achnanthes nodosa, Cyclotella spp., Navicula schmassmannii, Staurosirella lapponica, and S. pinnata. In one of the lakes, the maximum diatom-inferred pH values reached at the top of the core are as high as pH values reconstructed from the diatom assemblages deposited at the end of the Mid-Holocene thermal maximum c. 4000 cal. BP.

Seasonal dry deposition and canopy leaching of base cations in a subtropical evergreen mixed forest, China

We evaluated the dry deposition and canopy leaching fluxes of base cations in the growing and the dormant seasons using the Na-ratio method based on the 4-year (2000–2003) monitoring data in Shaoshan subtropical evergreen mixed forest, China. The dry deposition of base cations in the growing seasons was lower than that in the dormant seasons, while the canopy leaching of base cations was higher in the growing seasons than that in the dormant seasons. The precipitation quantity and H significantly impacted the canopy leaching processes. The annual canopy leaching of K, Ca and Mg accounted for 88, 46 and 38% of net throughfall flux, respectively. The canopy retention of proton (H and NH) is close to the canopy leaching of base cations calibrated by weak acids, indicating that the canopy cations leaching is neutralizing acid precipitation.++2+2++4+

Base-cation Cycling by Individual Tree Species in Old-growth Forests of Upper Michigan, USA

The influence of individual tree species on base-cation (Ca, Mg, K, Na) distribution and cycling was examined in sugar maple (Acer saccharum Marsh.), basswood (Tilia americana L.), and hemlock (Tsuga canadensis L.) in old-growth northern hardwood – hemlock forests on a sandy, mixed, frigid, Typic Haplorthod over two growing seasons in northwestern Michigan. Base cations in biomass, forest floor, and mineral soil (0–15 cm and 15–40 cm) pools were estimated for five replicated trees of each species; measured fluxes included bulk precipitation, throughfall, stemflow, litterfall, forest-floor leachate, mineralization + weathering, shallow-soil leachate, and deep-soil leachate. The three species differed in where base cations had accumulated within the single-tree ecosystems. Within these three single-tree ecosystems, the greatest quantity of base cations in woody biomass was found in sugar maple, whereas hemlock and basswood displayed the greatest amount in the upper 40 cm of mineral soil. Base-cation pools were ranked: sugar maple > basswood, hemlock in woody biomass; sugar maple, basswood > hemlock in foliage; hemlock > sugar maple, basswood in the forest floor, and basswood > sugar maple, hemlock in the mineral soil. Base-cation fluxes in throughfall, stemflow, the forest-floor leachate, and the deep-soil leachate (2000 only) were ranked: basswood > sugar maple > hemlock. Our measurements suggest that species-related differences in nutrient cycling are sufficient to produce significant differences in base-cation contents of the soil over short time intervals (<65 years). Moreover, these species-mediated differences may be important controls over the spatial pattern and edaphic processes of northern hardwood-hemlock ecosystems in the upper Great Lakes region.

Proton budgets for a monitoring network of European forested catchments: impacts of nitrogen and sulphur deposition

Abstract Proton (H+ ion) budgets were calculated for 17 forested sites in Europe using open field (bulk) and throughfall deposition and runoff or soil leachate data. Proton budgets integrate information about the complex chemical and biological processes that govern the generation or consumption of acidity in the ecosystem into a single parameter. The sites belong to the multidisciplinary ICP integrated monitoring network, set up to assess the environmental impacts of transboundary air pollution. Mean annual H+ budgets were estimated to quantify the relative importance of different biogeochemical processes, with special emphasis on the N deposition. N deposition exceeded S deposition on an equivalent basis at the studied sites. Model based estimates for quantifying the impact of agreed international emission reduction measures showed that the relative importance of N deposition still is likely to increase in the future. Base cation weathering and ion exchange were the main processes for proton consumption. Sites on base poor soil material showed low base cation fluxes, export of acidity and high external/internal H+ source ratios. At these sites the dissociation of organic acids was commonly a significant internal H+ source. Depending on deposition inputs, the importance of N processes on the H+ budget varied between −4.5 mequiv. m−2 a−1 (small H+ consumption) and 46.2 mequiv. m−2 a−1 (H+ production). A relationship between the deposition inputs and the H+ production from N transformations was also observed, with higher H+ production at higher deposition levels. Net release of sulphate (and associated H+ production) was observed at many sites, being consistent with observations from other recent European budget studies.

Base cation and silicon biogeochemistry under pine and scrub oak monocultures: implications for weathering rates

Vegetation type has a profound influence over biogeochemical processes, including canopy leaching, stemflow, litterfall, and nutrient uptake. Understanding the relationship between plants and soil processes, such as mineral weathering, is a difficult task considering the interactions among biotic and abiotic soil-forming factors. In this study, soils planted with pure stands of scrub oak ( Quercus dumosa Nutt.) and Coulter pine ( Pinus coulteri B. Don) were used to identify key biogeochemical processes in each soil–plant system. The experimental design, a true biosequence, allowed an opportunity to link biogeochemical processes to mineral weathering. Precipitation, throughfall, litter leachate, and soil solutions were collected following rain events from November of 1996 to April of 1998. Relatively high Na and Ca concentrations in pine throughfall suggest that atmospheric deposition is a more important process within the pine canopy than is canopy leaching. In contrast to pine throughfall, mean K concentrations were higher than Ca in oak throughfall, reflecting the importance of canopy leaching. Nutrient cycling was more rapid within the scrub oak soil–plant system as evidenced by significantly reduced levels of cations in soil solution at the 7.5 cm depth compared to litter leachate. Mean Si concentrations at the 65 cm depth were 334 μmol L −1 under oak and 431 μmol L −1 under pine. Silicon and base cation fluxes indicate higher weathering rates under pine. Solution chemistry shows that canopy and nutrient cycling processes are different between the two species and are impacting the cation loss rates.

Effects of forest clear-cutting on the sulphur, phosphorus and base cations fluxes through podzolic soil horizons

Clear-cutting considerably alters the flow of nutrients through the forest ecosystem. These changes are reflected in soil solution concentrations and fluxes. The effects of clear-cutting (stems only) on the fluxes of water soluble phosphorus (P), sulphur (S) and base cations (Ca, Mg and K) through a podzolic soil were studied in a Norway spruce dominated mixed boreal forest in eastern Finland. Bulk deposition, total throughfall (throughfall + stemflow) and soil percolate from below the organic (O), eluvial (E) and illuvial (B) horizons were collected for 4 years before and for 3 years after cutting. Annual deposition loads (kg ha−1) to the forest floor were less after clear-cutting, averaging 1.7 S, 0.84 Ca, 0.14 Mg, 0.64 K and 0.10 P. Before cutting, the loads were 4.6 S, 2.7 Ca, 0.70 Mg, 6.2 K and 0.20 P. Annual fluxes of total S and sulphate (SO 4 2− ) from below the O-horizon were also lower (33%) after clear-cutting, total S averaging 2.0 kg ha−1, the flux from below the B-horizon also diminished after clear-cutting. The flux of total P (mainly inorganic) from below the O-horizon increased threefold (6.9 kg ha−1; sum over the 3-year period) compared to period before cutting. The fluxes of base cations from below the O-horizon increased twofold. The flux of K+ from below the O- and E-horizons was most strongly correlated with that of phosphate (PO 4 3− ) and those of Ca2+ and Mg2+ with the DOC flux. Increased fluxes of P and base cations to the mineral soil generated only slightly increased fluxes from below the B-horizon. The retention of base cations and P in the mineral soil indicates there was little change in leaching to ground and surface waters after clear-cutting.

Direct effect of ice sheets on terrestrial bicarbonate, sulphate and base cation fluxes during the last glacial cycle: minimal impact on atmospheric CO 2 concentrations

Chemical erosion in glacial environments is normally a consequence of chemical weathering reactions dominated by sulphide oxidation linked to carbonate dissolution and the carbonation of carbonates and silicates. Solute fluxes from small valley glaciers are usually a linear function of discharge. Representative glacial solute concentrations can be derived from the linear association of solute flux with discharge. These representative glacial concentrations of the major ions are ∼25% of those in global river water. A 3-D thermomechanically coupled model of the growth and decay of the Northern Hemisphere ice sheets was used to simulate glacial runoff at 100-year time steps during the last glacial cycle (130 ka to the present). The glacially derived fluxes of major cations, anions and Si over the glaciation were estimated from the product of the glacial runoff and the representative glacial concentration. A second estimate was obtained from the product of the glacial runoff and a realistic upper limit for glacial solute concentrations derived from theoretical considerations. The fluxes over the last glacial cycle are usually less than a few percent of current riverine solute fluxes to the oceans. The glacial fluxes were used to provide input to an oceanic carbon cycling model that also calculates changes in atmospheric CO 2. The potential change in atmospheric CO 2 concentrations over the last glacial cycle that arise from perturbations in glacial solute fluxes are insignificant, being <1 ppm.

DEPOSITION AND LEACHING OF SULPHATE AND BASE CATIONS IN A MIXED BOREAL FOREST IN EASTERN FINLAND

Monthly fluxes of sulphate (SO4 2-) and base cations(Ca2+, Mg2+, K+) were studied from 1993 to 1996 as precipitation passed through forest vegetation and surfacesoil layers in an area receiving low and declining levels of atmospheric sulphate pollution. The canopy was dominated by mature Norway spruce (Picea abies Karsten) and the soilwas a podzol developed on glacial till material. The mean annual bulk deposition of SO4 2- collected in the open was 136 molc ha-1 and that of Ca2+, Mg2+ and K+ was 44, 11 and 25 molc ha-1, respectively. The annual total throughfall deposition of SO4 2- was 318 molc ha-1 and that of Ca2+, Mg2+ and K+ was 151, 64 and 181 molcha-1, respectively. Sulphate was the dominant anion accompanying the base cations leached from the canopy. More than half (58%) of the annual total throughfall deposition ofSO4 2- was retained by the O-horizon and only 15% leached from below the B-horizon. The annual leaching of Ca2+, Mg2+ and K+ from below the B-horizon was14, 25 and 9% of the annual total throughfall deposition, respectively. The transport of base cations through the soil was predominantely countered by SO4 2- anions.

Pathways of nutrient loading and impacts on plant diversity in a New York peatland

Nutrient loading is a subtle, yet serious threat to the preservation of high diversity wetlands such as peatlands. Pathways of nutrient loading and impacts on plant diversity in a small peatland in New York State, USA were determined by collecting and analyzing a suite of hydrogeological, hydro-chemical, soil, and vegetation data. Piezometer clusters within an intensive network constituted hydro-chemical sampling points and focal points for randomly selected vegetation quadrats and soil-coring locations. Hydrogeological data and nutrient analyses showed that P and K loading occurred chiefly by means of overland flow from an adjacent farm field, whereas N loading occurred predominantly through ground-water flow from the farm field. Redundancy analysis and polynomial regression showed that nutrients, particularly total P in peat, total K in peat, extractable NH4-N, and NO3-N flux in ground water, were strongly negatively correlated with plant diversity measures at the site. No other environmental variables except vegetation measures associated with eutrophication demonstrated such a strong relationship with plant diversity. Nitrate loading over 4 mg m−2 day−1 was associated with low plant diversity, and Ca fluxes between 80 and 130 mg m−2 day−1 were associated with high plant diversity. Areas in the site with particularly low vascular plant and bryophyte species richness and Shannon-Wiener diversity (H′) occurred adjacent to the farm field and near a hillside spring. High H′ and species richness of vascular plants and bryophytes occurred in areas that were further removed from agriculture, contained no highly dominant vegetation, and were situated directly along the ground-water flow paths of springs. These areas were characterized by relatively constant water levels and consistent, yet moderate fluxes of base cations and nutrients. Overall, this study demonstrates that knowledge of site hydrogeology is crucial for determining potential pathways of nutrient loading and for developing relationships between nutrient inflows and wetland plant diversity.

Calibration of the sodium base cation dominance index of weathering for the River Dee catchment in north-east Scotland

Previously the dominance of base cations by Na + in river water in upland catchments with low weathering rates and influenced by marine-derived aerosols has been suggested as a quantitative index of weathering rate upstream of the sampling point. Using data for 59 sites from a study of the River Dee catchment in NE Scotland, the index has been fully calibrated against catchment weathering rates and net alkalinity production, derived through input output budget methods, for both upland and agricultural catchments and over a wide range of parent materials. It is shown that the relationship between Na + dominance and weathering rate is logarithmic, rather than linear as initially suggested. The excellent correlations highlight the potential use of this Na + dominance index for the direct quantification of catchment susceptibility to acidification at fine spatial resolution, using a few simple and inexpensive measurements. Stronger correlations were observed between the % Na + dominance and net annual flux of alkalinity than between % Na + dominance and weathering rate derived from summation of base cation fluxes. This demonstrates the importance of mechanisms controlling the transport of base cations out of catchments, namely in association with organic matter and with anthropogenically derived SO 4 2−. These processes are shown to reduce the residual alkalinity derived through weathering. The partial neutralization of organic acidity by internally generated alkalinity has implications in the context of using the mass balance approach for setting critical loads for catchments.

Are there signs of acidification reversal in freshwaters of the low mountain ranges in Germany?

Abstract. The reversal of freshwater acidification in the low mountain ranges of Germany is of public, political and scientific concern, because these regions are near natural ecosystems and function as an important drinking water supply. The aim of this study was to evaluate the status and trends of acidification reversal after two decades of reduced anthropogenic deposition in selected freshwaters of the low mountain ranges in the Harz, the Fichtelgebirge, the Bavarian Forest, the Spessart and the Black Forest. In response to decreased sulphate deposition, seven out of nine streams investigated had significantly decreasing sulphate concentrations (all trends were calculated with the Seasonal Kendall Test). The decrease in sulphate concentration was only minor, however, due to the release of previously stored soil sulphur. No increase was found in pH and acid neutralising capacity (defined by Reuss and Johnson, 1986). Aluminum concentrations in the streams did not decrease. Thus, no major acidification reversal can currently be noted in spite of two decades of decreased acid deposition. Nevertheless, the first signs of improvement in water quality were detected as there was a decrease in the level and frequency of extreme values of pH, acid neutralising capacity and aluminium concentrations in streams. With respect to nitrogen, no change was determined for either nitrate or ammonium concentrations in precipitation or stream water. Base cation fluxes indicate increasing net loss of base cations from all ecosystems investigated, which could be interpreted as an increase in soil acidification. The latter was due to a combination of continued high anion leaching and significant reduction of base cation deposition. No major improvement was noted in biological recovery, however, initial signs of recovery were detectable as there was re-occurrence of some single macroinvertebrate species which were formerly extinct. The results of this study have important implications for water authorities, forest managers and policy makers: the delay in acidification reversal suggests a need for ongoing intensive amelioration of waters, a careful selection of management tools to guarantee sustainable management of forests and the reduction of nitrogen deposition to prevent further acidification of soils and waters. Keywords: freshwater, acidification reversal, drinking water supply, forested catchments, Germany

Trends in the Output of First-order Basins at Turkey Lakes Watershed, 1982-96

In 1981, we began to monitor the stream flow and chemistry of 13 first-order basins at the Turkey Lakes Watershed, with the objective of measuring the response of an undisturbed forested ecosystem to acid deposition. There was no trend in total annual precipitation received by the watershed, but the average annual water yield (percentage of annual precipitation) declined over the observation period. The proportion of runoff occurring in different seasons also changed, decreasing in the winter and increasing in the spring. In most streams the concentration of SO4 2− has decreased coincident with the decline in precipitation inputs. Recovery of the basins from acid deposition (as evidenced by increased pH, increased alkalinity, and decreasing base cation fluxes) has not been uniform. Basins that do not show signs of recovery are characterized by deeper flowpaths and greater potential neutralizing capacity, which minimizes the impacts of acid deposition. Basins that are dominated by shallow flowpaths and lower levels of potential neutralizing capacity are showing some signs of recovery, but their recovery is not complete and it is possible that cation depletion may prevent or retard it.

Seasonal Dynamics of Biogeochemical Proton and Base Cation Fluxes in a White Birch Forest in Hokkaido, Japan

Biogeochemical proton and base cation fluxes in a 30-year old white birch forest composed of Dystric Cambisols in northern Hokkaido, Japan were estimated using data on atmospheric deposition (AD), throughfall (TF), stemflow (SF), and discharge from soils (DS) and plant uptake (UP) from early June to November 1999. In the monitoring period, proton flux was 0.20kmolcha−1 for AD, 0.07 for TF+SF, and 0.03 for DS, indicating that atmospheric acid input was neutralized through plant and soil. Base cation flux was 1.29 for AD, 1.23 for TF+SF, and 0.99 for DS and plant base cation uptake was 2.14, indicating that the soil was the major source of base cation for plant. However, these seasonal fluxes showed various trends. Cumulative base cation flux in TF+SF showed constant increase trend during the whole period, which was similar to AD. Proton flux in AD jumped once just after a heavy rain of 255mm for 8 days at the end of July. Trends for the proton and base cation fluxes in TF plus SF were similar to that of AD. Although proton and base cation fluxes of DS were not found until middle July because of vegetation uptake and no flow, both fluxes increased suddenly after the heavy rain in July. After August, the base cation and proton fluxes in the DS increased continuously, due to the lack of plant uptake and intermittent rainfall. In this study, it is clear that plant activity and water flow are very important driving force for seasonal dynamics of biogeochemical cycling.

Nutrient fluxes in a snow-dominated, semi-arid forest : Spatial and temporal patterns

We tested five hypotheses regarding the potential effects of precipitation change on spatial and temporal patterns of water flux, ion flux, and ion concentration in a semiarid, snowmelt-dominated forest in Little Valley, Nevada. Variations in data collected from 1995 to 1999 were used to examine the potential effects of snowpack amount and duration on ion concentrations and fluxes. Soil solution NO3−, NH4+, and ortho-phosphate concentrations and fluxes were uniformly low, and the variations in concentration bore no relationship to snowmelt water flux inputs of these ions. Weathering and cation exchange largely controlled the concentrations and fluxes of base cations from soils in these systems; however, soil solution base cation concentrations were affected by cation concentrations during snowmelt episodes. Soil solution Cl− and SO42− concentrations closely followed the patterns in snowmelt water, suggesting minimal buffering of either ion by soils. In contrast to other studies, the highest concentration and the majority of ion flux from the snowpack in Little Valley occurred in the later phases of snowmelt. Possible reasons for this include sublimation of the snowpack and dry deposition of organic matter during the later stages of snowmelt. Our comparison of interannual and spatial patterns revealed that variation in ion concentration rather than water flux is the most important driver of variation in ion flux. Thus, it is not safe to assume that changes in total precipitation amount will cause concomitant changes in ion inputs to this system.

Importance of Internal Proton Production for the Proton Budget in Japanese Forested Ecosystems

Annual biogeochemical fluxes (bulk precipitation, throughfall, stem flow, soil solution and vegetation uptake) of inorganic elements were observed in eight cool temperature forested ecosystems in Hokkaido, northern Japan, in order to determine the mechanisms of acid neutralization in Japanese forest ecosystems. We compared our results with the other biogeochemical studies in Japan, north Europe and US from the literature. In many Japanese forests, the internal proton production (IPS) by base cation accumulation into the vegetation was a major proton source, rather than external acidic deposition, and the IPS also affected the base cation fluxes from the mineral. IPS in Japanese forest tended to be larger than that in north Europe and US. Our results suggested that the high acid neutralizing ability of Japanese forests could be attributed to the strong relationship between the base cation buffering of the soil and the larger contribution of IPS as a proton source. acidic deposition|biogeochemical cycling|forest ecosystem|Japan|proton budget

Sensitivity of soil acidification model to deposition and forest growth

We report an investigation concerning the impacts of acid deposition and forest growth scenarios on simulated soil effective base saturation for a forested catchment in eastern Finland. These forests have not been managed during the last 150 yr and the area receives low levels of acidifying deposition. The fluxes of sulphur, nitrogen and base cations were assessed with models simulating historic and future deposition, stand uptake and leaching. We tested the effects of calibrating the modelled deposition time series to high and low estimates of current levels of deposition. The highest future soil base saturation was predicted when using the year with the lowest observed sulphur and nitrogen deposition (1993) as representative of the present deposition. The lowest historical and future soil base saturation resulted for using the year with the highest observed deposition of sulphur and nitrogen (1988). All scenarios concerning nutrient uptake, emission reduction levels and timing of the reductions resulted in simulated future soil base saturation values located between those predicted with the high and low observed present deposition. The standard deviation in the soil base saturation introduced by varying the present forest biomass and growth was smaller than that produced by varying the present deposition values.

Modelling water chemistry for a major Scottish river from catchment attributes

1. The prediction of water quality is increasingly required in river catchment management, but methods are still developmental. We therefore derived empirical models to predict the concentrations of base cations, H+ and alkalinity at any point in a complex Scottish river system, and under diverse discharge conditions. Input data were readily available from geological and topographic maps, whole rock composition data and catchment land use inventories in geographical information systems (GIS). 2. A key and novel feature of the model was prediction using geological data for the riparian zone within 50 m of the river. The discharge contributions that passed through soil derived from each parent rock were estimated and used as weightings in predicting final run‐off quality. 3. Typical equations for upland catchments for mean, maximum or minimum river water Ca concentration, [Ca], were of the form [Ca] = a + b √{Carz}, where {Carz} denotes flow routing‐weighted rock CaO concentration of the riparian zone rock types present. These equations were significant at P &lt; 0·0001. Similar approaches were applicable to alkalinity and to other base cations. 4. Predictions of [Ca] in catchments with mixed land use were improved by including model terms for catchment riparian zone cover of agriculturally improved (intensified) grassland and arable land. These results indicated anthropogenic effects on base cation flux that would not be represented by geological data alone. 5. Similarly, concentrations of Na, Mg and K were correlated with Cl concentration in the river water, primarily as a consequence of marine‐derived Cl. Including distance from the east coast as a predictive variable in place of [Cl] obviated the need for direct [Cl] measurement in model operation. 6. We advocate further work to assess whether similar models can be developed and applied in other geographical locations, where features such as land use, geology and sea salt inputs will all vary.

Cycling of nutrient base cations in a twelve year old Sitka spruce plantation in upland mid-Wales

Abstract. The effects of the early growth of plantation forestry on the biogeochemical cycling of potassium, calcium and magnesium have been investigated in a stand of 12 year old Sitka spruce and adjacent moorland growing on acid peaty podzol soils in mid Wales. Element budgets have been calculated for both systems using measurements of soil and vegetation base cation pools and fluxes. In the moorland, the magnesium budget is approximately at steady-state with no net change to the soil store whilst the soil is accumulating potassium. The calcium budget is approximately balanced but contains significant uncertainties due to between plot variability in calcium leaching losses. Afforestation has greatly increased the above-ground living biomass which holds 7 to 15 times more nutrients compared to the living aerial biomass in the moorland. With the exception of magnesium, the base cation stores within the forest soil are being depleted as the increase in atmospheric deposition due to the forest canopy provides only a small offset to the much larger accumulation of base cations within the trees. The current net rate of change in the soil store of calcium is sustainable for only 65 years. However, as the trees mature, their demand for calcium will be reduced and they should be able to ‘tap' deeper sources of calcium in the soil profile as well as in the drift and regolith material. Keywords: Forestry, base cations, element cycling, calcium, magnesium, potassium