Loss Of Base Cations Research Articles

Landscape variation in microarthropod response to calcium addition in a northern hardwood forest ecosystem

Loss of base cations from soils of the northeastern US may adversely influence forest health. A watershed-level calcium (as wollastonite, CaSiO 3 ) addition experiment was initiated at the Hubbard Brook Experimental Forest, NH, USA, in fall 1999 to examine responses of forest ecosystem structure and function to restoration of exchangeable Ca that was lost over previous decades. We quantified the response of soil microarthropods to Ca addition as part of this larger study, and we also quantified microarthropod response to smaller scale (1×2 m plots) wollastonite additions within one site in an untreated reference watershed. We observed a small increase in pH in the surface organic horizon, accompanied by a decline in microarthropod abundance per gram organic matter three years following wollastonite application. However, responses varied among microarthropod groups, across years, and among study plots that were distributed along an elevation gradient in treatment and reference watersheds. Collembola declined in the treatment relative to the reference watershed in the second year but recovered in the third year following wollastonite application, whereas oribatid, prostigmatid, and mesostigmatid mites all declined in the treatment relative to the reference watershed by the third year following treatment. The largest treatment responses were observed in two base-poor hardwood stands, whereas at a slightly less poor hardwood site we found the least abundant and least variable microarthropod populations, and no response was observed to either the watershed or the plot-level treatments. Our results demonstrate that soil microarthropods are sensitive to relatively small changes in soil Ca, but that landscape position must be considered in testing responses of these soil biota to soil base status.

REGIONAL APPLICATION OF AN INTEGRATED BIOGEOCHEMICAL MODEL TO NORTHERN NEW ENGLAND AND MAINE

An integrated biogeochemical model (PnET-BGC) was applied to 60 Direct/ Delayed Response Program (DDRP) lake watersheds in northern New England and Maine to investigate processes regulating spatial and temporal patterns in lake SO42− concentrations, past changes in the acid–base status of soil and surface waters, and their response to future emission control scenarios. Model simulations indicate that watershed elevation is an important factor influencing inputs of atmospheric S deposition to the watersheds and thus spatial patterns in lake SO42− concentrations. Wetland S retention, vegetation composition, and thickness of surficial deposits were also found to influence lake SO42− concentrations. Model simulations also suggest that decreases in lake SO42− concentrations observed during 1984–2001 were mostly a result of decreases in atmospheric S deposition. Decreases in lake SO42− concentrations were coupled with a near-stoichiometric decline in base cation concentrations. Comparison of atmospheric deposition of base cations and simulated drainage loss during this period indicates that decreases in atmospheric base cation deposition were partially responsible for decreases in lake base cation concentrations. Decreases in drainage loss of base cations were mainly a result of declines in net loss from soil exchange sites associated with decreases in SO42− leaching. Model forecasts generally suggest further decreases in SO42− concentrations and increases in acid neutralizing capacity (ANC) in lake water and soil percent base saturation (BS) at most of the DDRP lake watersheds under three future emission control scenarios, with the more aggressive control scenarios resulting in faster recovery from acidic deposition. Under an aggressive control scenario, surface water ANC is simulated to increase at a median rate of 0.30 μ=·L−1·yr−1 in northern New England and 0.22 μ=·L−1·yr−1 in Maine. However, although marked improvement is expected, recovery to background conditions will probably not occur before 2050.

Comparative Study of Selected Soil Properties Following Introduction of Broad‐Leaf Trees into Clear‐Felled Chinese Fir Forest

After clear‐cutting of the first generation Chinese fir (Cunninghamia lanceolata) planted forest, five management models, viz. mixture of Chinese fir and Kalopanax septemlobus (MCK), mixture of Chinese fir and Alnus cremastogyne (MCA), pure Kalopanax septemlobus stand (PKS), pure Alnus cremastogyne stand (PAS), and pure Chinese fir stand (PCS), were established in 1983. The effects of these management models on soil were evaluated by measuring physico‐chemical parameters and soil solution chemistry 20 years after planting. Both broadleaf monocultures and mixtures of broadleaf and conifer exerted a favorable effect on soil fertility. The concentrations of the mainly atmospherically derived ions, including SO4 2−, Cl−, Na+, and Mg2+, were significantly higher under conifer than under broadleafs and under mixtures of broadleaf and conifer. Whereas the concentrations of ions that were mainly controlled within system processes such as K+ and NH4 + varied little among various management models, with the exception of NO3 −, which was significantly higher below PAS than below the others. The concentrations of H+ and Al3+ were also highest under the conifer. In addition, the aerosol sulfate and SO2 deposition did not result in a net loss of base cations (on an area basis) from the broadleaf monocultures and mixtures of broadleaf and conifer. However, slight decreases in forest floor bases were observed under the conifer. The observed evidence from this study also suggests that the principal factor for forest soil acidification may be the N deposition and nitrification of NH4 +, but not S deposition in this region.

The role of Calamagrostis communities in preventing soil acidification and base cation losses in a deforested mountain area affected by acid deposition

The effects of grass growth and N deposition on the leaching of nutrients from forest soil were studied in a lysimeter experiment performed in the Moravian-Silesian Beskydy Mts. (the Czech Republic). It was assumed that the grass sward formed on sites deforested due to forest decline would improve the soil environment. Lysimeters with growing acidophilous grasses (Calamagrostis arundinacea and C. villosa), common on clear-cut areas, and with unplanted bare forest soil were installed in the deforested area affected by air pollution. Wet bulk deposition of sulphur in SO 4 2− corresponded to 21.6–40.1 kg ha−1 and nitrogen in NH 4 + and NO 3 − to 8.9–17.4 kg N ha−1, with a rain water pH of 4.39–4.59 and conductivity of 18.6–36.4 μS cm−1 during the growing seasons 1997–1999. In addition, the lysimeters were treated with 50 kg N ha−1 yr−1 as ammonium nitrate during the 3 years of the experiment. Rapid growth of planted grasses resulted in a very fast formation of both above- and below-ground biomass and a large accumulation of nitrogen in the tissue of growing grasses. The greatest differences in N accumulation in aboveground biomass were observed at the end of the third growing season; in C. villosa and C. arundinacea, respectively, 2.66 and 3.44 g N m−2 after addition of nitrogen and 1.34 and 2.39 g N m−2 in control. Greater amounts of nitrogen were assessed in below-ground plant parts (9.93–12.97 g N m−2 in C. villosa and 4.29–4.39 g N m−2 in C. arundinacea). During the second and third year of experiment, the following effects were the most pronounced: the presence of growing grasses resulted in a decrease of both the acidity and conductivity of lysimetric water and in a lower amount of leached nitrogen, especially of nitrates. Leaching of base cations (Ca2+ and Mg2+) was two to three times lower than from bare soil without grasses. An excess of labile Al3+ was substantially eliminated in treatments with grasses. Enhanced N input increased significantly the acidity and losses of nutrients only in unplanted lysimeters. The leaching of N from treatments with grasses (3.9–5.6 kg N ha−1) was 31–46% of the amount of N in wet deposition. However, the amount of leached N (4.2–6.0 kg N ha−1) after N application was only 7.1–8.9% of total N input. After a short three year period, the features of soil with planted grasses indicated a slight improvement: higher pH values and Ca2+ and Mg2+ contents. The ability of these grass stands to reduce the excess nitrogen in soil is the principal mechanism modifying the negative impact on sites deforested by acid depositions. Thus it is suggested that grass sward formation partly eliminates negative processes associated with soil acidification and has a positive effect on the reduction of nutrient losses from the soil.

Spatial and Temporal Variation in Calcium and Aluminum in Northern Hardwood Forest Floors

Acid rain results in losses of exchangeable base cations from soils, but the mechanism of base cation displacement from the forest floor is not clear, and has been hypothesized to involve mobilization of aluminum from the mineral soil. We attempted to test the hypothesis that losses of calcium from the forest floor were balanced by increases in Al in NewHampshire northern hardwoods. We measured exchangeable (six stands) and acid extractable (13 stands) Ca and Al in horizons of the forest floor over an interval of 15 years. Our sampling scheme was quite intensive, involving 50 or 60 blocks per stand, composited in groups of 10 for chemical analysis. Even at this level of effort, few stands exhibited changes large enough to be significant. Because of high spatial variability, differences would have had to be greater than about 50% to be statistically detectable. Differences in Ca and Al concentrations between Oi, Oe, Oa, and A horizons, however, were readily detected. Acid-extractable Al increased with depth, while Ca concentrations decreased; Ca-to-Al ratios decreased from 8.3 (charge basis) in the Oi to 0.2 in the A horizon. Therefore, a small change in sampling depth, or the inclusion of more or less A horizon material in the forest floor, could cause large differences in measured Ca and Al concentrations. To detect small changes in exchangeable cations over time would require sampling very intensively with careful control for comparability of horizons.

Elemental translocation and loss from three highly weathered soil–bedrock profiles in the southeastern United States

Chemical weathering of soils and rocks during pedogenesis is significant because it provides many essential elements for life and because it is coupled with the rise and fall of atmospheric CO 2. We used geochemical mass-balance equations to quantify the net result of pedogenic weathering, i.e. elemental loss and gain, in three residual soil–bedrock profiles on the Piedmont of North Carolina. Soils are located on interfluves and derived directly from the bedrock below: a Kanhapludult (Tarrus series) from phyllite, a Kanhapludult (Cecil series) from granitic gneiss, and a Hapludalf (Enon series) from diabase. Bulk density ratios of soils and bedrock as well as elemental concentrations referenced to Zr, Ti, Y, and V were used to estimate strain and open-system mass-transport functions through the soil profiles. Estimated strains of the three soils indicated substantial volumetric changes during C horizon and saprolite formation. Overall, desilication was the most predominant pedogenic process removing chemical elements from the three soils. Losses of Si were about 50% of total elemental molar losses in the 8.5-m deep Tarrus profile, 75% of total losses in the 3.8-m deep Cecil profile, and 39% of total losses in the 4-m deep Enon profile. Base cations were also lost in great amounts following desilication. Losses of base cations accounted for about 50% of the total elemental losses in the Tarrus, 20% of the total losses in the Cecil, and 37% of the total losses in the Enon profiles. The specific base cations lost in greatest amounts differed among the three soils and depended on bedrock mineralogy. Sodium and Mg accounted for 24% and 16% of total elemental loss from Tarrus profiles, Na and K accounted for 14% and 4% of total elemental loss from Cecil profiles, and Ca and Mg accounted for 19% and 12% of total elemental loss from Enon profiles. The vertical pattern of loss of base cations was not always gradual from surface soil horizons to saprolite to bedrock. For example, almost 100% of Ca in the bedrock had been lost from throughout the upper 4.5-m deep Cecil and 8-m deep Tarrus profiles. Aluminum and iron were lost from A and E horizons but were accumulated in B and C horizons due to translocation as well as secondary clay and sesquioxide formation at depth. Physical and chemical data from all three soils and geologic substrata indicate that the entire regolith profile (A through C horizons or solum plus saprolite) is formed by pedogenic processes of elemental inputs, transformations, translocations, and removals.

Patterns of early lake evolution in boreal landscapes: a comparison of stratigraphic inferences with a modern chronosequence in Glacier Bay, Alaska

The chronosequence approach, which infers temporal patterns of environmental change from a spatial array of modem sites, has been a major tool for studying successional processes. A model of early lake ontogeny in boreal landscapes, developed from a chronosequence of lakes in Alaska, suggests that long-term soil development and related hydrological change produce a loss of alkalinity and base cations, a decrease in pH, an increase in DOC and a transient increase followed by a decrease in lakewater nitrogen concentrations over time. We compare this model of lake ontogeny with patterns of change reconstructed from diatom assemblages in 10 sediment cores from the same region. Lakewater pH declined in the majority of lakes, but the pattern, rate and magnitude of decline varied considerably among sites, apparently related to local differences in hydrologic setting. Inferred trends in nitrogen concentration over time are not spatially uniform and appear to vary because of local differences in vegetation history. Thus, patterns of early lake ontogeny may be spatially heterogeneous over timescales of many hundreds of years, even within relatively small geographic areas.

Influence of landscape position and vegetation on long-term weathering rates at the Hubbard Brook Experimental Forest, New Hampshire, USA

The spatial variability of long-term chemical weathering in a small watershed was examined to determine the effect of landscape position and vegetation. We sampled soils from forty-five soil pits within an 11.8-hectare watershed at the Hubbard Brook Experimental Forest, New Hampshire. The soil parent material is a relatively homogeneous glacial till deposited ∼14,000 years ago and is derived predominantly from granodiorite and pelitic schist. Conifers are abundant in the upper third of the watershed while the remaining portion is dominated by hardwoods. The average long-term chemical weathering rate in the watershed, calculated by the loss of base cations integrated over the soil profile, is 35 meq m −2 yr −1—similar to rates in other ∼10 to 15 ka old soils developed on granitic till in temperate climates. The present-day loss of base cations from the watershed, calculated by watershed mass balance, exceeds the long-term weathering rate, suggesting that the pool of exchangeable base cations in the soil is being diminished. Despite the homogeneity of the soil parent material in the watershed, long-term weathering rates decrease by a factor of two over a 260 m decrease in elevation. Estimated weathering rates of plagioclase, potassium feldspar and apatite are greater in the upper part of the watershed where conifers are abundant and glacial till is thin. The intra-watershed variability across this small area demonstrates the need for extensive sampling to obtain accurate watershed-wide estimates of long-term weathering rates.

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

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

Calcium accumulation alleviates soil acidification in Japanese cedar (Cryptomeria japonica) stands

Larger amounts of exchangeable calcium (Ca2+) accumulated in the surface soil in an older Japanese cedar (Cryptomeria japonica) stand, compared with the younger stand. We estimated the Ca2+ accumulation rate and examined the difference in the amounts of exchangeable Ca2+ based on the Ca2+ fluxes. Samples of soil percolated water were taken using stainless tension-free lysimeters at different depths (under 0 horizon, 10,40, and 80 cm). Mobilization of base cations was controlled by total acid production. Proton load associated with N transformation was an important factor for the mobilization of base cations, especially for bivalent cations. Base cations tended to be mobilized in the 0 horizon and immobilized in soil horizons. The amount of Ca2+ supplied from the 0 horizon exceeded the amount recorded at the depth of 0–10 cm in the older Japanese cedar stand, resulting in the immobilization of 120 mmolc m−2 yr−1 of Ca2+ from October 2000 to September 2001. The amount of immobilized Ca2+ in the soil horizons in each period depended on the mobilized amounts in the 0 horizon. Lower amount of supplied Ca2+ in the 0 horizon and mobilization at the depth of 0–10 cm in the younger stand contributed to the difference in the amount of exchangeable Ca2+. Mobilization of base cations in the 0 horizon alleviated the loss of base cations in soil under Japanese cedar stands and contributed to the suppression of soil acidification.

ENHANCING NUTRIENT RETENTION IN TROPICAL TREE PLANTATIONS: NO SHORT CUTS

In the humid tropics large quantities of nutrients can be rapidly leached when the soil is unprotected by actively growing vegetation. We established experimental plan- tations of three indigenous tree species on a fertile Andisol in Costa Rica and managed them under 1- or 4-year cutting cycles with uncut stands as controls. Our goals were to test whether nutrient leaching was greatest under a regime of frequent disturbances that returned modest amounts of biomass to the soil surface (cutting and replanting on a 1-yr cycle) or less frequent disturbances that returned significantly greater amounts of plant tissues to the soil (cutting and replanting on a 4-yr cycle), and to compare those cutting cycles with nutrient leaching from uncut stands. Leaching of NO3 (over 9 yr), Ca2+, Mg2+, and K+ (over 4 yr) from upper soil horizons was monitored. Water balance was determined by linking Penman-Monteith evaporation with changes in soil water storage modeled from soil physical parameters. Drainage water for solute measurement was sampled from porous ceramic cups at 1.1 m depth in the soil. Disturbance frequency proved to be an important determinant of NO3- leaching. Average long-term NO3- leaching losses from stands on a 1-yr cutting cycle were extraordinarily large: 442 mmol_-m-2.yr-1 (62 kg-ha-1.yr-1 of N), compared to 187 mmolc.m-2.yr-1 under a 4-yr cutting cycle and 71 mmolc.m-2.yr-1 from uncut stands. Elevated NO3- leaching was primarily due to increased concentration in the soil solution (rather than increased water drainage), because cutting usually resulted in a reduction of <10% in evapotranspiration. Resilience of stands decreased with continued disturbance; under a 4-yr cutting cycle, stands tended to take longer to return to the low levels of NO3- leaching characteristic of undis- turbed stands with each episode of cutting and replanting, while NO3- losses from annually cut stands became increasingly variable over time. Due to high concentrations of soil Ca at the site, the stands proved resistant to treatment-induced losses of base cations: no increases in Ca2+ or Mg2+ leaching accompanied elevated NO3- leaching, although K+ leaching did increase under the 1-yr cutting cycle. Because of the potential for massive, sustained NO3- losses, development of land use systems for these soils should focus on minimizing frequency of disturbance.

The impact of climate on the biogeochemical functioning of volcanic soils

Rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering, secondary mineral synthesis and soil chemical properties. Along an arid to humid climosequence on Kohala Mountain, Hawaii, we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall. The lavas are influenced by a strong rain shadow with mean annual precipitation (MAP) averaging 160 mm near the coast and rising to >3000 mm near the summit. A temperature decline from 24 to 15 °C with increasing elevation is matched by lower potential evapotranspiration (ET). A water balance model (monthly precipitation minus monthly ET) defines three broad climate zones along the sampling transect: an arid zone with moisture deficit in every month, an intermediate zone with moisture deficit during low-rainfall summer months and moisture surplus during high-rainfall winter months, and a humid zone with moisture surplus during every month. The annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index. The index reaches 1 (total filling of the pore space on an annual basis) at about 1400 mm MAP. Index values >1 imply intense leaching conditions because of pore water replacement. In these 170 ka soils, leaching losses of soluble base cations and Si are nearly complete at index values >1, whereas only 60% of Al has been lost. At index values <1 leaching losses are progressively lower with the lowest rainfall sites having lost 10–20% of the original base cations and Si and none of the Al. At all sites, the secondary clay mineral assemblage is dominated by metastable noncrystalline weathering products; humid soil profiles contain very few crystalline minerals whereas the arid profiles contain halloysite, hematite, gibbsite and small amounts of carbonates. Soil surface exchange properties are influenced strongly by climatic conditions and show a dramatic threshold in base cation saturation, pH and effective cation exchange capacity (ECEC) at leaching index of 1 (1400 mm MAP). Soils with leaching index of <1 have high base cation saturation, near-neutral pH and high ECEC. At MAP >1400 mm, soil buffering capacity has been totally exhausted leading to low pH and low ECEC. The nonlinear decline in ECEC is irreversible under natural conditions; base cation depleted soils will remain so even if the climate shifts to drier conditions. In contrast, a climate shift to wetter conditions can drastically modify surface chemical properties existing in the drier soils as weathering depletes primary minerals, elements are lost to leaching, and surface chemistry is modified. There is a time-dimension implied in climate gradient studies; soils forming in recently rejuvenated landscapes contain more primary minerals and should experience loss of buffering capacity at higher rainfall. Loss of buffering capacity means that biological acidity will move more deeply into the vadose zone or into the aquatic system. The details of this transfer depend on present and past climate, and the age and erosional stability of landscapes.

NUTRIENT LOSSES OVER FOUR MILLION YEARS OF TROPICAL FOREST DEVELOPMENT

Biological, atmospheric, and geochemical processes interact to shape how element cycles and nutrient losses develop within newly formed landscapes. We examined losses of nitrogen (N), phosphorus (P), and base cations across a four-million-year substrate age gradient of Hawaiian montane tropical forests, with the goal of understanding how losses depend on changes in biotic demand, weathering, and atmospheric sources. We were particularly interested in whether losses of nutrients that are not subject to traditional mechanisms of biotic availability could influence ecosystem fertility and nutrient limitation over time. Over a three-year period we sampled nutrient outputs in soil solutions below the active plant–soil system and small streams, gaseous N losses (NO, N2O, and N2), and pools and transformations of N in soils. Weathering was the major determinant of ecosystem losses of P, of base cations and Si, and of ecosystem acid–base status. Sharp reductions in weathering inputs after 20 000 years of forest development caused dramatically lower outputs of P (∼65% reduction), Ca2+ (∼99%), and Si (∼94%), to rates that matched inputs from dilute sea-salt and dust aerosols. Internal production of organic acids, in combination with low weathering, caused highly acidic soil waters (pH < 5.0) with elevated Al (up to 300 μg/L) and Ca:Al ratios (<0.3) below values considered critical thresholds for many plant species. Long-term N and P interactions were more complex than predicted by the Walker and Syers model, with important influences of N and P loss pathways that were not subject to direct biotic availability. While losses of available forms of dissolved N and P, and N gases followed (as predicted) ecosystem nutrient availability, significant dissolved organic N (DON) and dissolved organic P (DOP) losses occurred independent of ecosystem N or P status. DON losses were not sufficient (relative to external inputs) to sustain N limitation beyond 20 000 years, while dissolved P losses remained large enough to maintain P limitation in older forests. Forests developed high N:P loss ratios over time (>300 on mass weight basis) due to efficient P recycling and unexpectedly high N throughputs (4–9 kg N·ha−1·yr−1) by either N fixation and/or N deposition.

Acidification and recovery of aquatic ecosystems in south central Ontario, Canada: regional application of the MAGIC model

Abstract. The dynamic model MAGIC was applied to 25 lakes in south-central Ontario, Canada using a regional modelling methodology. Soil and lake water chemistry for each lake catchment was simulated for the period 1850–2050. Sulphate (SO42–) deposition forecasts were derived from recently proposed emission reductions, which correspond roughly to a 50% reduction in SO42– deposition by 2010 from the 2000 baseline. Changes in SO42– deposition had a significant impact on lake chemistry. Simulated lake water chemistry showed a recovery potential under the current deposition scenario; by 2050 concentration levels recovered to values predicted for the early 1900s. Moreover, simulated future lake water chemistry showed significant recovery compared to 1975 levels. However, although regional simulations predict that base cation losses have decreased in recent years, soils in the region will continue to acidify with Ca2+ losses dominating depletion of the exchangeable pool. Base cation losses from the exchangeable pool are currently buffering lakes against the impacts of acid deposition; ultimately base cation inputs into the lakes will decrease as exchangeable base cation pools become depleted. Further emission reductions are necessary to ensure continued recovery from acidification. Keywords: regional dynamic model, sulphate, acid neutralising capacity, critical loads, lake chemistry, soil base saturation

Weathering rates as a function of climate: results from a climosequence of the Val Genova (Trentino, Italian Alps)

A soil sequence in northern Italy along an elevational gradient ranging from moderate (950 m a.s.l.) to high alpine (2440 m a.s.l.) climate zones was investigated with respect to element losses (Ca, Mg, K, Na, Fe, Al, Si, Mn) and the development of clay minerals. Element losses were derived from mass balance calculations that are based on enrichment/depletion factors using immobile element contents (Ti). Mass balance calculations indicated that extensive mineral weathering resulted in significant leaching losses of major base cations (with losses up to >80% of the initial content in the parent material), Al (particularly, from upper horizons) and Si. Element denudation was greatest in subalpine forests near the timberline. Weathering rates decreased with both higher and lower altitudes. The pattern of smectite distribution along the climosequence has strong similarities to the Al, Si, Na and K losses, while an inverse trend could be detected for clay minerals with a high amount of interlayered Al. Highest smectite contents with up to 30% of the clay fraction and also highest weathering rates were found at sites in subalpine forest near the timberline. Higher precipitation rates and the production of chelating compounds in the soil are believed to promote the appearance of smectites. Weathering rates of Na and K were additionally modelled as a function of precipitation and temperature. The relationship between climate and element weathering is strongly nonlinear and is thought to be overshadowed by the pronounced podzolisation effect near the timberline.

Ion cycling in hemlock-northern hardwood forests of the southern Lake Superior region: a preliminary study.

Upland forests of the southern Lake Superior region are diverse and contain a shifting mosaic of eastern hemlock [Tsuga canadensis (L.) Carr.] and northern hardwood forests dominated by sugar maple (Acer saccharum Marsh.). In this study, we survey the relative effects of management practice (old growth vs. managed), forest cover type (hemlock vs. northern hardwood), and soil great group (Entic Haplorthod vs. Alfic Oxyaquic Fragiorthod) on ion cycling as a precursor to a longer-term, more detailed study. Bulk precipitation, throughfall, and soil leachates at three depths were collected for two growing seasons in eight stands on the Ottawa National Forest in the Upper Peninsula of Michigan. A total of 1210 solutions were analyzed for pH, Na, K, Mg, Ca, Cl, NO3, and SO4. Losses of base cations (Ca, Mg, K) and SO4 from the bottom of the rooting zone generally were greater in old-growth than in managed northern hardwoods on both fragic and nonfragic soils. Leaching losses of base cations and NO3 usually were greater beneath old-growth northern hardwoods than beneath old-growth hemlock on both soil types and for both forest cover types and management practices on fragic than nonfragic soils. Management practice, forest cover type, and soil type all appear to affect ion cycling within these forests. All of the stands featured striking losses of base cations that probably are influenced strongly by NO3 and SO4 in atmospheric deposition.

Patterns of streamwater acidity in Lye Brook Wilderness, Vermont, USA.

Under the United States Clean Air Act Amendments of 1977, a class I designation safeguards wilderness areas from the negative effects of new sources of air pollution. We monitored streamwater chemistry in the class I Lye Brook Wilderness in southwestern Vermont from May 1994 through August 1995. Stream samples were collected biweekly at nine sampling locations throughout the wilderness and were analyzed for major cations and anions, dissolved organic carbon, pH, and acid-neutralizing capacity. Eight of nine sites sampled had mean annual acid neutralizing capacity values below zero. During the study period, decreases in streamwater acid neutralizing capacity values were caused primarily by SO(4)(2-). At some sites, however, NO(3) (-) and naturally occurring, weak organic acids were seasonally important. During high discharge, the low pH and high concentrations of inorganic monomeric Al were at levels that are toxic to acid-sensitive aquatic species. Watershed mass balances were calculated to determine annual gains or losses for measured ions. These budgets indicate that S inputs and outputs were nearly equal, there was a net loss of base cations, and a net gain in N. How long these watersheds can continue to assimilate additional N inputs is unknown.

Recovery from acidification in central Europe—observed and predicted changes of soil and streamwater chemistry in the Lysina catchment, Czech Republic

The geochemical model MAGIC was applied to estimate streamwater and soil chemistry between 1851 and 2030 at the Lysina catchment, an acid-sensitive granitic catchment covered by planted Norway spruce monoculture in the western Czech Republic. The total deposition of sulfur to the catchment was 164 meq m−2 in 1991, but had declined to 52 meq m−2 by 2000. Although SO2 emissions in the region declined by 90% compared to the 1980s, acidification recovery was small within the period 1990–2000. Stream pH increased only slightly (from 3.92 to 4.07), although SO4 concentration declined sharply from 568 μeq l−1 (1990) to 232 μeq l−1 (2000). Organic acids played an important role in streamwater buffering. According to the MAGIC prediction using deposition measured in 1999–2000, streamwater pH will increase to 4.3 and soil base saturation will increase to 6.2% by 2030 (from 5.7% in 2002). Pre-industrial pH was estimated to be 5.5 and soil base saturation 24.7%. The loss of base cations (Ca, Mg, Na, K) was caused predominantly by atmospheric acidity, but intensive forestry was responsible for approximately one third of the net base cation loss via accumulation in harvested biomass. Severely damaged sites, under continued pressure from forestry, will not return to a good environmental status in the near future (if ever) when the acid deposition input is only partially reduced.

Influence of acidic atmospheric deposition on soil solution composition in the Daniel Boone National Forest, Kentucky, USA

Acid atmospheric deposition may enter an environmental ecosystem in a variety of forms and pathways, but the most common components include sulfuric and nitric acids formed when rain water interacts with sulfur (SO x ) and nitrogen (NO x ) emissions. For many soils and watersheds sensitive to acid deposition, the predominant chronic effect appears to be a low pH, loss of base cations, and a shift in the mineral phase controlling the activity of Al3+ and/or SO4 2– in solution. Soil solutions from lysimeters at various depths were taken at two sites in the Daniel Boone National Forest, Kentucky, USA, to evaluate potential impacts caused by acid deposition. The sites chosen were in close proximity to coal-burning power plants near Wolfe and McCreary counties and contained soils from the Rayne and Wernock series, respectively. Physicochemical characteristics of the soils revealed that both sites contained appreciable amounts of exchangeable acidity in the surface horizons, and that their base saturation levels were sufficiently low to be impacted adversely by acidic inputs. Soil solution data indicated that the sites were periodically subjected to relatively high NO3 – and SO4 2– inputs, which may have influenced spatial and temporal variation in Al and pH. As a consequence, the formation of Al-hydroxy-sulfate minerals such as jurbanite, alunite and basaluminite were thermodynamically favored over gibbsite. Given these conditions, long-term changes in soil solution chemistry from acid deposition are acknowledged.

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