Chronic Acid Deposition Research Articles

Long‐term treatments alter acidification, fertility and carbon in soils of the Fork Mountain long‐term soil productivity experiment

AbstractHistoric atmospheric acidic deposition resulting from the combustion of fossil fuels may alter the pools of important nutrients and base cations in sensitive forest soils. This raises concern that chronic acidic deposition, particularly when coupled with intensive forest biomass harvesting, may diminish long‐term soil fertility, forest productivity, and carbon storage potential. To address these concerns, the Fork Mountain long‐term soil productivity experiment was initiated in 1996 at the Fernow Experimental Forest, West Virginia. The replicated experimental design consists of 16 plots (0.2 ha) that receive one of four treatments: (1) whole‐tree harvesting (removal of all aboveground biomass, WT plots); (2) whole‐tree harvesting + ammonium‐sulfate fertilization (WT + NS plots); (3) whole‐tree harvesting + ammonium‐sulfate fertilization + dolomitic lime (WT + NS + Lime plots); and (4) untreated reference plots. We present forest floor and soil chemistry responses after ∼25 years of treatment and evaluate the temporal changes to illuminate these results. Soil acidification has occurred, and base cation movement through the soil profile was observed, with effective cation exchange capacity increasing slightly in the deepest soil horizon by the end of the 25 years. However, some of our hypotheses were not supported. In particular, soil C did not increase over time with fertilization/soil acidification but was mainly altered by WT harvesting, as were other nutrients. Dolomitic lime provided some amelioration of acidification, but surprisingly, most of the changes in base cations appeared to be the results of Mg, not Ca, likely due to greater tree requirements and uptake of Ca.

The Bear Brook Watershed in Maine: Multi‐decadal whole‐watershed experimental acidification

AbstractThe Bear Brook Watershed in Maine (BBWM) is a long‐term research site established to study the response of forest ecosystem function to environmental disturbances of chronic acidic deposition and ecosystem nitrogen enrichment. Starting in 1989, the West Bear (treated) watershed received bimonthly applications of ammonium sulfate [(NH4)2SO4] fertilizer from above the canopy, whereas East Bear (reference) received ambient deposition. The treatments were stopped in 2016, marking the beginning of the recovery phase. Research at the site has focused on soils, streams, and vegetation. Here, we describe data collected over three decades at the BBWM—input and stream output nutrient fluxes, quantitative soil pits and soil chemistry, and soil temperature and moisture.

Assessing Temperate Forest Growth and Climate Sensitivity in Response to a Long‐Term Whole‐Watershed Acidification Experiment

AbstractAcid deposition is a major biogeochemical driver in forest ecosystems, but the impacts of long‐term changes in deposition on forest productivity remain unclear. Using a combination of tree ring and forest inventory data, we examined tree growth and climate sensitivity in response to 26 years of whole‐watershed ammonium sulfate ((NH4)2SO4) additions at the Fernow Experimental Forest (West Virginia, USA). Linear mixed effects models revealed species‐specific responses to both treatment and hydroclimate variables. When controlling for environmental covariates, growth of northern red oak (Quercus rubra), red maple (Acer rubrum), and tulip poplar (Liriodendron tulipifera) was greater (40%, 52%, and 42%, respectively) in the control watershed compared to the treated watershed, but there was no difference in black cherry (Prunus serotina). Stem growth was generally positively associated with growing season water availability and spring temperature and negatively associated with vapor pressure deficit. Sensitivity of northern red oak, red maple, and tulip poplar growth to water availability was greater in the control watershed, suggesting that acidification treatment has altered tree response to climate. Results indicate that chronic acid deposition may reduce both forest growth and climate sensitivity, with potentially significant implications for forest carbon and water cycling in deposition‐affected regions.

Fungal and Bacterial Communities Exhibit Consistent Responses to Reversal of Soil Acidification and Phosphorus Limitation over Time.

Chronic acid deposition affects many temperate hardwood forests of the northeastern United States, reduces soil pH and phosphorus (P) availability, and can alter the structure and function of soil microbial communities. The strategies that microorganisms possess for survival in acidic, low P soil come at a carbon (C) cost. Thus, how microbial communities respond to soil acidification in forests may be influenced by plant phenological stage as C allocation belowground varies; however, this remains largely unexplored. In this study, we examined microbial communities in an ecosystem level manipulative experiment where pH and/or P availability were elevated in three separate forests in Northeastern Ohio. Tag-encoded pyrosequencing was used to examine bacterial and fungal community structure at five time points across one year corresponding to plant phenological stages. We found significant effects of pH treatment and time on fungal and bacterial communities in soil. However, we found no interaction between pH treatment and time of sampling for fungal communities and only a weak interaction between pH elevation and time for bacterial communities, suggesting that microbial community responses to soil pH are largely independent of plant phenological stage. In addition, fungal communities were structured largely by site, suggesting that fungi were responding to differences between the forests, such as plant community differences.

Fifteen\u2013year record of soil temperature at the Bear Brook Watershed in Maine

This paper describes a record of air and soil temperature collected from 2001 to 2016 in temperate forests at the Bear Brook Watershed in Maine (BBWM). BBWM is a long-term research site established to study the response of forest ecosystem function to various environmental disturbances, including chronic acidic deposition. Replicate HOBO data loggers were deployed in BBWM’s two forest types (coniferous and deciduous), to record temperatures at four positions: (1) air temperature, 100 cm above the forest floor; (2) surface organic soil, 2 cm below the forest floor surface; (3) mineral soil, 10 cm below the organic–mineral horizon interface; and (4) mineral soil, 25 cm below the organic–mineral horizon interface. Data were recorded every three hours, and these raw data were used to compute daily maximum, daily minimum, daily average, and monthly average values. This fifteen–year record represents one of the few readily–available soil temperature datasets in the region, and provides information on long-term changes in climatology, and seasonal and episodic weather patterns.

Mycorrhizal fungal communities respond to experimental elevation of soil pH and P availability in temperate hardwood forests.

Many forests are affected by chronic acid deposition, which can lower soil pH and limit the availability of nutrients such as phosphorus (P), but the response of mycorrhizal fungi to changes in soil pH and P availability and how this affects tree acquisition of nutrients is not well understood. Here, we describe an ecosystem-level manipulation in 72 plots, which increased pH and/or P availability across six forests in Ohio, USA. Two years after treatment initiation, mycorrhizal fungi on roots were examined with molecular techniques, including 454-pyrosequencing. Elevating pH significantly increased arbuscular mycorrhizal (AM) fungal colonization and total fungal biomass, and affected community structure of AM and ectomycorrhizal (EcM) fungi, suggesting that raising soil pH altered both mycorrhizal fungal communities and fungal growth. AM fungal taxa were generally negatively correlated with recalcitrant P pools and soil enzyme activity, whereas EcM fungal taxa displayed variable responses, suggesting that these groups respond differently to P availability. Additionally, the production of extracellular phosphatase enzymes in soil decreased under elevated pH, suggesting a shift in functional activity of soil microbes with pH alteration. Thus, our findings suggest that elevating pH increased soil P availability, which may partly underlie the mycorrhizal fungal responses we observed.

Effects of calcium silicate treatment on the composition of forest floor organic matter in a northern hardwood forest stand

Calcium amendment can help improve forest sustainability in stands that have been impacted by chronic acid deposition. An important component of this improvement is the stimulation of the microbial activity that supports ecosystem nutrient cycling processes. To test the hypothesis that Ca treatment alters the structure and solubility of organic matter substrates, an important driver of microbial activity, we investigated the effect of wollastonite (CaSiO3) treatment on soil organic matter (SOM) and hot-water-extractable organic matter (HWEOM). We found a decrease in the HWEOM content of forest floor soils within 2 years of treatment with a high dosage of wollastonite (4,250 kg Ca/ha), but not at a low dosage (850 kg Ca/ha). High-dosage treatment did not reduce the biodegradability of HWEOM. Hence, a high dose of CaSiO3 appears to reduce the solubility of organic matter in the forest floor but not the bioavailability of the extracted SOM. Nuclear magnetic resonance spectroscopy revealed no significant changes in the O-alkyl C content of SOM in response to wollastonite addition, but a reduction in the O-alkyl C content of HWEOM suggests that the extractability of carbohydrate structures was reduced by added CaSiO3. Phosphorous treatment, when performed in combination with Ca, also decreased the O-alkyl C content of HWEOM, but had no effect when performed without Ca. The reduced solubility of SOM after Ca treatment may have been the result of bridging between Ca2+ and negatively charged sites on SOM, as suggested in other studies. Also, high concentrations of Si in soil solution, due to dissolution of the wollastonite, likely resulted in oversaturated conditions with respect to SiO2 or kaolinite, perhaps leading to co-precipitation of soluble organic matter. Overall, our results suggest that added Ca and/or Si may react with SOM to reduce the accessibility of labile C forms to soil microbes.

Rate of litter decay and litter macroinvertebrates in limed and unlimed forests of the Adirondack Mountains, USA

Acid deposition can reduce the rate of litter decay in forests by changing environmental and substrate quality for macroinvertebrates and microbes. Terrestrial application of lime can ameliorate many of the negative effects of acid deposition, but the effects of liming on forest litter decay and fauna are poorly understood. We used reciprocal transplants of litter bags to better understand the effects of substrate calcium content and incubation context (limed plots versus unlimed plots) on rate of litter decay and abundance of litter-dwelling macroinvertebrates. Our study took place in the Adirondack Mountains (Adirondacks) of New York State, USA, a region affected by chronic acid deposition. Lime was added to randomly-selected plots at a rate of 10Mgha−1; control plots were not limed. Leaves for high-calcium litter bags were collected under trees grown in limed plots, and leaves for low-calcium litter bags were collected in unlimed plots. High-calcium and low-calcium leaves differed in %Ca but not in %N or C:N at the beginning of our study. Leaf litter decay was faster for bags containing high-calcium leaves than for those litter bags containing low-calcium leaves, and decay was slower in limed than unlimed plots. Assemblages of litter-dwelling macroinvertebrates were markedly different between litter bags collected from limed and those collected from unlimed plots. Snails increased in abundance; whereas, millipedes and spiders decreased in abundance at limed plots following liming. Millipedes likely were important litter-eating macroinvertebrates at these sites, and the decline in millipedes may have contributed to the reduction in rate of litter decay. The liming of areas negatively affected by acid deposition may decrease rate of litter decay immediately following lime application. This was a short-term study. Understanding the long-term, as well as immediate, effects of liming is necessary to determine the advisability of lime application in regions affected by acid deposition.

Regeneration responses to exogenous disturbance gradients in southern Appalachian Picea-Abies forests

Because of the devastation caused by the combined impacts of the balsam woolly adelgid (Adelges piceae; BWA, a non-native insect) and chronic acid deposition, Picea-Abies (spruce-fir) forests are one of the most threatened vegetation communities in North America. Endemic Abies fraseri (Fraser fir), the dominant overstory species in these forests, has experienced near complete overstory mortality as result of the adelgid. Observed forest regeneration patterns suggest high spatial variability, with dense patches of Rubus spp. (blackberry), A. fraseri, and deciduous regeneration repeating across the landscape. To quantify the spatial variability and density of A. fraseri, Picea rubens (red spruce), and deciduous regeneration in these forests, we sampled 60 randomly selected plots within Picea-Abies forests of Great Smoky Mountains National Park (GSMNP). As a measure of local variability in regeneration, we used regeneration density within 30 1×1m subplots per plot to calculate a coefficient of within-plot variation for each species. Despite the impacts of the BWA and chronic acid deposition, A. fraseri remained an important component of southern Appalachian Picea-Abies forests at elevations above 1750m. Density of A. fraseri in all size classes was associated with time since disturbance by BWA infestation. On plots where A. fraseri regeneration occurred, its local variability (among 30 subplots) was significantly greater than that of P. rubens or deciduous species. Regression models attributed this local-scale variability in A. fraseri regeneration to the influence of elevation, Rubus spp. cover, B-horizon nitrogen concentration, and O-horizon calcium to aluminum ratio. We propose that co-occurring gradients of BWA-induced mortality and acid deposition have created patches of increased light and nitrogen availability, which have increased competition from ruderal species such as Rubus spp. Additionally, our results suggest that high soil aluminum content relative to calcium may exclude A. fraseri from certain locations, further contributing to the local variability of A. fraseri regeneration.

Soil and tree chemistry reflected the cumulative impact of acid deposition in Pinus banksiana and Populus tremuloides stands in the Athabasca oil sands region in western Canada

The spatial variability of soil chemistry and Ca/Al ratios of soil solution and fine roots were investigated in jack pine (Pinus banksiana) and trembling aspen (Populus tremuloides, aspen) stands to assess the impact of chronic acid deposition on boreal forest ecosystems in the Athabasca oil sands region (AOSR) in Alberta, Canada. Available SO42− (as the sum of soluble and adsorbed SO42−) accumulated in the soil near tree boles of both species, reflecting the influence of canopy intercepted SO42−. In jack pine stands, pH and soluble base cation concentrations decreased towards tree boles due to increased SO42− leaching; the reverse was found in aspen stands due to deposition of base cations leached from the canopy. As a result, Ca/Al ratios in the soluble fraction in soils near jack pine boles were 5–20 times lower than that near aspen boles. The Ca/Al ratio did not reach the critical limits of 1.0 for soil solution (ranged from 1.0 to 4.1) or 0.5 for fine roots (0.7–7.9) in the studied watersheds. However, Aln+ concentrations in the soil solution ranged from 0.2 to 4.1mgL−1 in NE7 and from 0.1 to 8.5mgL−1 in SM8 that can inhibit the growth of white spruce (Picea glauca) seedlings that commonly succeed aspen in upland sites in the AOSR. We suggest that the spatial variation caused by tree canopies/stems will affect forest regeneration and the effect of acid deposition on forest succession in the AOSR should be further studied.

Interacting effects of wildfire severity and liming on nutrient cycling in a southern Appalachian wilderness area

Aims Wilderness and other natural areas are threatened by large-scale disturbances (e.g., wildfire), air pollution, climate change, exotic diseases or pests, and a combination of these stress factors (i.e., stress complexes). Linville Gorge Wilderness (LGW) is one example of a high elevation wilderness in the southern Appalachian region that has been subject to stress complexes including chronic acidic deposition and several wildfires, varying in intensity and extent. Soils in LGW are inherently acidic with low base cation concentrations and decades of acidic deposition have contributed to low pH, based saturation, and Ca:Al ratio. We hypothesized that wildfires that occurred in LGW followed by liming burned areas would accelerate the restoration of acidic, nutrient depleted soils. Because soils at LGW had extremely low concentrations of exchangeable Ca 2+ and Mg 2+ dolomitic lime was applied to further boost these cations. We evaluated the effectiveness of dolomitic lime application in restoring exchangeable Ca 2+ and Mg 2+ and subsequently increasing pH and Ca:Al ratio of soils and making Ca and Mg available to recovering vegetation. Methods Five treatment areas were established: severely burned twice (2000 & 2007) with dolomitic lime application (2xSBL); moderately burned twice with lime application (2xMBL); severely burned twice, unlimed (2xSB); moderately burned once (2000), unlimed (1xMB); and a reference area (REF; unburned, unlimed). In 2008 and 2009, we measured overstory, understory, and ground-layer vegetation; forest floor mass and nutrients; and soil and soil solution chemistry within each treatment area. Results All wildfire burned sites experienced substantial overstory mortality. However, understory biomass doubled between sample years on the most recently burned sites due to the rapid regrowth of ericaceous shrubs and prolific sprouting of deciduous trees. Burning followed by lime application (2xSBL and 2xMBL) significantly increased shallow soil solution NO3-N, but we found no soil solution NO3-N response to burning alone (2xSB and 1xMB). Surface soil base saturation and exchangeable Ca 2+ were significantly affected by liming; Ca 2+ concentrations were greater on 2xMBL and 2xSBL than 2xSB, 1xMB and REF.

High‐elevation ground‐layer plant community composition across environmental gradients in spruce‐fir forests

AbstractWe examined the influence of vegetation structure and soil chemistry on post‐adelgid, ground‐layer plant communities in high‐elevation forests of the southern Appalachian Mountains. Specifically, we hypothesized that post‐disturbance community composition and diversity would vary along a gradient of soil acidity and other soil characteristics influenced by acid deposition. Ground‐layer vegetation and soils were sampled on 60 randomly located nested vegetation plots in the spruce‐fir (Picea abies) zone of Great Smoky Mountains National Park, TN and NC, USA. To capture a range of deposition levels, plot placement was stratified based on modeled acid deposition classes. Ordination and multiple regression results showed that ground‐layer composition and diversity were negatively associated with acidity of the A horizon and the presence of ericaceous shrubs (i.e., Rhododendron spp.). A strong correspondence between soil acidity and ericaceous shrub cover was also observed, suggesting that soil acidity may be, in conjunction with overstory disturbance resulting from chronic acid deposition and adelgid induced mortality, an important driver of ericaceous shrub thicket expansion. Slow‐decaying, acidic ericaceous litter may also induce a positive feedback resulting in enhanced acidification.

Diminished Soil Quality in an Old-Growth, Mixed Mesophytic Forest Following Chronic Acid Deposition

Human activities have increased acid deposition throughout the Ohio River Valley due to the large number of coal-fired power-generating facilities. The long-term effects of chronic acid deposition can include a decrease in soil pH, loss of soil fertility, and a decrease in base saturation—all of which can reduce forest productivity. Dysart Woods, a remnant old-growth, mixed mesophytic forest in eastern Ohio, has experienced a decrease in soil pH from 5.0 in 1971 to 4.6 in 1997, which may be due to chronic acid deposition. The objective of this study was to utilize a long-term study to evaluate how soil quality has changed due to chronic acid deposition. To meet the study objectives, a variety of soil chemical properties (pH, base saturation, C, N, P, etc.) were measured from surface soil within two stands of opposing aspect at Dysart Woods within the unglaciated Allegheny Plateau. Because soil pH correlates strongly with other soil chemical properties, we used pH data from 1971 to estimate how soil quality has changed over time. Mean soil pH from the south-facing stand was 5.0 in 1971, 4.6 in 1997, and 4.3 in 2007. While soil pH was not measured in the north-facing stand in 1971, pH was 4.6 in 1997 and 4.7 in 2007. Using changes in pH to estimate past soil properties, our results suggest that available base cations in the south-facing stand have been reduced from ≈12 to 6 (cmolc kg-1), with a 50% reduction in base saturation since 1971. Considering that both stands receive the same amount of acid deposition due to their close proximity to each other, results raise an interesting question: Are unglaciated Allegheny Plateau south-facing soils more susceptible to the effects of acid deposition than north-facing soils?

Factors controlling the acid‐neutralizing capacity of Japanese cedar forest watersheds in stands of various ages and topographic characteristics

AbstractAcid‐neutralizing capacity (ANC) is an important index for streamwater acidification caused by external factors (i.e. chronic acid deposition) and internal factors such as soil acidification due to nitrification. In this study, the influence of forest clear‐cutting and subsequent regrowth on internal acidification was investigated in central Japan, where stream pH (near 7·0) and ANC (above 0·1 meq L−1) are high. pH, the concentrations of major cations (Na+, K+, Mg2+ and Ca2+), major anions (NO3−, Cl− and SO42−) and dissolved silica (Si), and ANC were measured in 33 watersheds of various stand ages, during 2002 to 2004. Only NO3− concentration decreased with stand age, whereas pH, ANC, and concentrations of the sum of base cations (BC) and Si were negatively correlated with the minimum elevation of the watershed. The correlation between the BC/Si ratio and minimum elevation suggested that factors contributing to acid neutralization changed at 1100 m above sea level. In watersheds at lower elevations (⩽1100 m), the relatively high contribution of soil water with longer soil contact times should result in higher ANC, and cation exchange reactions should be the dominant process for acid neutralization due to deposition of colluvial soils on the lower slope. In contrast, in higher‐elevation watersheds (≥1100 m), weathered residual soils are thin and the small contribution of deeper groundwater results in lower ANC. These results suggest that the local acid sensitivity is determined by the hydrological and geomorphologic factors generated by steep topography. Copyright © 2008 John Wiley & Sons, Ltd.

Primary mineral weathering in the central Appalachians: a mass balance approach

We use a mass balance approach to calculate long-term weathering rates for three forested watersheds in the southeastern USA. One watershed (Shaver Hollow) is underlain by Precambrian granodiorite, and two (White Oak Run, Deep Run) are underlain by Cambrian metasedimentary units. Each of the study areas receives high levels of acidic precipitation, and each watershed was almost completely defoliated by gypsy moth larvae for at least two consecutive years during the study period. Our analysis uses stream and precipitation chemistry obtained weekly from 1987 to 1993 for Shaver Hollow and from 1980 to 1993 for White Oak Run and Deep Run. Mass balance calculations for the granodiorite watershed indicate that plagioclase feldspar is the dominant reactant and that basalt dikes which comprise a small fraction of the catchment make a significant contribution to the base cation budget. Corresponding calculations for the metasedimentary bedrock watersheds indicate contributions from plagioclase feldspar, muscovite, and biotite. At best, the mass balance models provide an approximation of weathering processes because the soils are immature and contain few stoichiometric clay minerals such as kaolinite. Annual cation release rates from Shaver Hollow suggest soil profile ages of ∼4 ka, consistent with the observed surficial geology and the geological history of the area. Base cation efflux patterns during the period of severe defoliation differ markedly between the three watersheds and reflect a continuum of ecosystem sensitivities. The Pedlar granodiorite system is relatively robust to the effects of disturbance: calculated weathering rates and proportions change by <10% during defoliation. The Chilhowee Formation watershed White Oak Run is moderately acid-sensitive and is unstable with respect to defoliation: annual base cation export by roughly 30% during each year of larval infestation. The Deep Run watershed is superficially robust to defoliation, as base cation efflux increased by only 5% during the disturbance. However, seasonal patterns of base cation uptake and release both prior to and during defoliation indicate this system is severely stressed, presumably as a result of chronic acid deposition. Mass balance calculations suggest that base cation availability in this watershed is low enough to inhibit normal biomass aggradation even in the absence of extreme defoliation.

Predicting watershed acidification under alternate rainfall conditions

The effect of alternate rainfall scenarios on acidification of a forested watershed subjected to chronic acidic deposition was assessed using the model of acidification of groundwater in catchments (MAGIC). The model was calibrated at the Panola Mountain Research Watershed, near Atlanta, Georgia, U.S.A. using measured soil properties, wet and dry deposition, and modeled hydrologic routing. Model forecast simulations were evaluated to compare alternate temporal averaging of rainfall inputs and variations in rainfall amount and seasonal distribution. Soil water alkalinity was predicted to decrease to substantially lower concentrations under lower rainfall compared with current or higher rainfall conditions. Soil water alkalinity was also predicted to decrease to lower levels when the majority of rainfall occurred during the growing season compared with other rainfall distributions. Changes in rainfall distribution that result in decreases in net soil water flux will temporarily delay acidification. Ultimately, however, decreased soil water flux will result in larger increases in soil-adsorbed sulfur and soil-water sulfate concentrations and decreases in alkalinity when compared to higher water flux conditions. Potential climate change resulting in significant changes in rainfall amounts, seasonal distribution of rainfall, or evapotranspiration will change net soil water flux and, consequently, will affect the dynamics of the acidification response to continued sulfate loading.

Smelting iron ores by electricity in New York State

Acid deposition can reduce the rate of litter decay in forests by changing environmental and substrate quality for macroinvertebrates and microbes. Terrestrial application of lime can ameliorate many of the negative effects of acid deposition, but the effects of liming on forest litter decay and fauna are poorly understood. We used reciprocal transplants of litter bags to better understand the effects of substrate calcium content and incubation context (limed plots versus unlimed plots) on rate of litter decay and abundance of litter-dwelling macroinvertebrates. Our study took place in the Adirondack Mountains (Adirondacks) of New York State, USA, a region affected by chronic acid deposition. Lime was added to randomly-selected plots at a rate of 10 Mg ha−1; control plots were not limed. Leaves for high-calcium litter bags were collected under trees grown in limed plots, and leaves for low-calcium litter bags were collected in unlimed plots. High-calcium and low-calcium leaves differed in %Ca but not in %N or C:N at the beginning of our study. Leaf litter decay was faster for bags containing high-calcium leaves than for those litter bags containing low-calcium leaves, and decay was slower in limed than unlimed plots. Assemblages of litter-dwelling macroinvertebrates were markedly different between litter bags collected from limed and those collected from unlimed plots. Snails increased in abundance; whereas, millipedes and spiders decreased in abundance at limed plots following liming. Millipedes likely were important litter-eating macroinvertebrates at these sites, and the decline in millipedes may have contributed to the reduction in rate of litter decay. The liming of areas negatively affected by acid deposition may decrease rate of litter decay immediately following lime application. This was a short-term study. Understanding the long-term, as well as immediate, effects of liming is necessary to determine the advisability of lime application in regions affected by acid deposition.