Effects Of Acid Deposition Research Articles

Effects of climate and acidic deposition on interannual variations of stream water chemistry in forested watersheds in the Shimanto River Basin, southern Japan

AbstractAlthough the amount of acidic deposition has recently decreased in Japan, it has still deteriorated some forest ecosystems during the past several decades. Moreover, recent climate changes can affect stream water chemistry. We investigated the temporal trend and effects of climate conditions on stream water chemistry for more than 20 years in two areas (Yusuhara and Taisho) in the Shmanto River Basin, southern Japan, where the effects of acidic deposition are considered to be modest. Stream water samples were collected monthly from three forest watersheds selected at each site. The annual means of the stream chemistry were predicted by multiple regression analysis. The ammonium, nitrate, and sulfate concentrations in the bulk precipitation have decreased at Yusuhara, and the sodium, magnesium, calcium, chloride, nitrate, and sulfate concentrations in the stream water have decreased in both areas. The nitrate and sulfate concentrations apparently responded to the decreasing input of acidic deposition. The sunlight hours were positively related with the potassium, magnesium, calcium, nitrate, sulfate, and bicarbonate concentrations in stream water. The results suggest that long sunlight hours boost the photosynthetic activities, thus promoting soil respiration and decomposition of soil organic matter. Moreover, a higher carbonic acid concentration in the soil solution promotes cation weathering and carbonic acid dissociation to bicarbonate. Given the decreasing trends in magnesium and calcium concentration with no change in bicarbonate concentration, we inferred that previousinputs of acidic deposition enhanced the rate of rock weathering.

Pike Mercury Concentration in Small Boreal Headwater Lakes During Four Decades of Regional and Local Changes

We measured the total mercury (THg) concentration in the muscle of northern pike (Esox lucius L.) from 12 boreal headwater lakes once per decade during the 1980s to 2010s. Relations of pike THg to regional environmental changes, such as reduction of acid deposition and increase in water colour (i.e. browning), were examined as well as the effects of local lake-specific changes caused by introduced beavers (Castor canadensis) and intensive fishing of pike. No consistent decrease in pike THg took place during 1983–2013 despite the reductions in mercury emissions from European sources since the 1990s and the associated decreased mercury deposition in Finland. In most of the lakes, individual pike exceeded the recommended limit for human consumption (1 mg kg−1, wet weight). The highest THg levels were recorded in 2002 following intensive browning of the lakes in the 1990s in connection with decreased sulphate deposition. The effects of acid deposition were only seen as the highest pike THg in the two most acidic lakes in the early 1980s. After taking length effects into account, pike THg had a negative relationship with growth (i.e. growth dilution), but a positive relationship with water colour, iron, nutrients and maximum lake depth. Females grew faster and had lower THg than males. Pike THg was elevated in beaver-impacted lakes. Experimental removal of pike from three study lakes during 2005–2013 resulted in a decrease of pike THg. These findings emphasize the significance of local abiotic and biotic drivers when interpreting the regional long-term trends in pike THg.

Widespread chemical dilution of streams continues as long-term effects of acidic deposition slowly reverse

Studies of recovery from acidic deposition have focused on reversal of acidification and its associated effects, but as recovery proceeds slowly, chemical dilution of surface waters is emerging as a key factor in the recovery process that has significant chemical and biological implications. This investigation uses long-term chemical records from 130 streams in the Adirondack region of New York, USA, to evaluate the role of ongoing decreases in conductance, an index of dilution, in the recovery of these streams. Stream chemistry data spanning up to 40 years (1980s–2022) showed that acid-neutralizing capacity has increased in 92% of randomly selected streams, but that harmful levels of acidification still occur in 37% of these streams. Conductance and Ca2+ concentrations decreased in 79% of streams, and SO42− concentrations in streams continued to show strong decreases but remained several times higher than concentrations in precipitation. These changes were ongoing through 2022 even though acidic deposition levels were approaching those estimated for pre-industrialization. Further dilution is continuing through ongoing decreases in stream SO42−. Nevertheless, Ca2+ continued to be leached from soils by SO42−, organic acids and NO3−, limiting the replenishment of available soil Ca2+, a prerequisite to stem further dilution of stream water.

Consequences of elevated CO2 on soil acidification, cation depletion, and inorganic carbon: A column-based experimental investigation

The anthropogenic release of atmospheric CO2 affects soil nutrient cycling through varied biogeochemical processes. Cation depletion from exchange sites, carbonate mineral dissolution, and subsequent changes in organic and inorganic carbon flux are growing concerns for soil health and sustainability. Particularly, the effects of acid deposition on soil pH and soil health under changing global carbon flux is poorly understood. To estimate the magnitude and effects of pH change across different soil profiles, the depth-wise response of soil cations, pH, and soil inorganic carbon (SIC) to varying CO2 levels was investigated using column-leachate experiments. Six soils, representing acidic, neutral, and alkaline pH, were exposed to different CO2 enrichments (100%, 10%, 1%, and Control) of water percolate for 30 days. Analysis of the column leachates revealed that the base cations (Ca, Mg, Na) were higher initially than on day 30, while Si leaching increased with time. The pH in leachates tended to attain an equilibrium state with time under CO2 saturation, indicating the buffering capacity of alkaline and neutral soils. Evaluation of the soil before and after the experiments showed that the solid SIC, such as carbonate minerals and any dissolved SIC components (e.g., carbonate, bicarbonate ions) entrained in the pore space increased, whereas the potential cation exchange capacity (PCEC) decreased in all soils. This trend was especially prominent for alkaline soils at 100% CO2 enrichment. Over the short-term study, the SIC showed minimal response to varying CO2 enrichment conditions in neutral and acidic soils. The altered cation concentrations in the leachates suggest that under long-term exposure to elevated CO2, a deficiency of cationic essential plant nutrients such as Ca2+, Mg2+, and K+ is likely, especially with low buffering capacity and primary mineral content. In contrast, an increase in nutrient solubility and elemental toxicity (e.g., Al3+ Mn) can be observed in the short term. The initial soils with greater ECEC experienced an increased SIC leaching in the shorter term and suggested potential deposition in deeper layers. The resultant SIC loss might be amplified in arid to semi-arid soils with low SIC and affect soil health.

Experimental research on the effect of acid and ash deposition on heat transfer characteristics of PTFE-coated 3-D finned tube

With characteristics of strong flow disturbance and high heat transfer coefficient, 3-D finned tubes have significant advantages in recovering flue gas waste heat. However, fly ash particles and sulfuric acid vapor in power plant flue gases can foul and corrode 3-D finned tubes when deposited on their wall surfaces, resulting in a reduction in the efficiency of the heat exchanger. To protect the heat exchanger from corrosion, corrosion resistance coatings are the most economical solution. However, acid and ash deposition and their effects on heat transfer performance of the 3-D finned tube coated with corrosion resistance coating have not been clear. In this work, firstly, uncoated, ceramic-coated, Teflon lacquer-coated and PTFE-coated 3-D finned tubes were immersed in sulfuric acid solution and the PTFE coating with better corrosion resistance was screened by corrosion weight loss method and SEM characterization. Then, the heat transfer performance of PTFE-coated 3-D finned tubes under acid-ash coupling conditions was investigated using the simulated flue gas method. Impacts of fin structure parameters (fin height, fin width and axial fin spacing) and experimental working conditions (cooling water inlet temperature, fly ash concentration and sulfuric acid volume fraction) on Nu number were investigated. Results demonstrate that PTFE-coated 3-D finned tube have a lower Nu at the initial moment than uncoated tubes. That is because PTFE coating increases the thermal resistance. However, as the experiment progressed to a steady state, Nu were higher and ash deposition weight was smaller in the PTFE-coated 3-D finned tube. In addition, the effects of fin structural parameters and experimental conditions on heat transfer characteristics of PTFE-coated 3-D finned tube were investigated. In the acid-ash coupled condition, the Nu value increases with an increase of fin height or a decrease of fin width and axial fin spacing. Also, decreasing the cooling water inlet temperature, the fly ash concentration, or the sulfuric acid vapor volume fraction increases the Nu value.

Exploring the Effects of Wetting and Free Fatty Acid Deposition on an Atomistic Hair Fiber Surface Model Incorporating Keratin-Associated Protein 5-1.

The complex development of cosmetic and medical formulations relies on an ever-growing accuracy of predictive models of hair surfaces. Hitherto, modeling efforts have focused on the description of 18-methyl eicosanoic acid (18-MEA), the primary fatty acid covalently attached to the hair surface, without explicit modeling of the protein layer. Herein, the molecular details of the outermost surface of the human hair fiber surface, also called the F-layer, were studied using molecular dynamics (MD) simulations. The F-layer is composed primarily of keratin-associated proteins KAP5 and KAP10, which are decorated with 18-MEA on the outer surface of a hair fiber. In our molecular model, we incorporated KAP5-1 and evaluated the surface properties of 18-MEA through MD simulations, resulting in 18-MEA surface density, layer thickness, and tilt angles in agreement with previous experimental and computational studies. Subsequent models with reduced 18-MEA surface density were also generated to mimic damaged hair surfaces. Response to wetting of virgin and damaged hair showed rearrangement of 18-MEA on the surface, allowing for water penetration into the protein layer. To demonstrate a potential use case for these atomistic models, we deposited naturally occurring fatty acids and measured 18-MEA's response in both dry and wet conditions. As fatty acids are often incorporated in shampoo formulations, this work demonstrates the ability to model the adsorption of ingredients on hair surfaces. This study illustrates, for the first time, the complex behavior of a realistic F-layer at the molecular level and opens up the possibility of studying the adsorption behavior of larger, more complex molecules and formulations.

Long term trends of dry and wet deposition of air pollutants at declining forest site of Mt. Oyama in Japan during 1994–2019

Forest decline, which occurs in mountainous regions in many countries, may result from the effects of acid fog, ozone, or deposition of other pollutants. We observed wet deposition of air pollutants at different altitudes on Mt. Oyama, situated southwest of Tokyo, for 1994 until 2019. During this period, the domestic atmospheric environment was improved in Japan. The average concentration of air pollutants around all the sampling sites on Mt. Oyama decreased by 63.01%, 32.08%, 8.80%, and 39.73% for NH3, HCl, HNO3, and SO2, respectively. The volume weighted mean (VWM) pH values showed an increasing trend for bulk deposition (+0.70% y-1), fog water (+2.58% y-1), and throughfall (+2.60% y-1). Stemflow also increased (cedar, +1.17% y-1; fir, +0.82% y-1), although it included organic acids dissolved from the stem and it primarily had a low VWM pH value. The overall pH value of the fog water increased at the site, although acidic fog was still observed. Comparing fog water between winter and summer, a significant increase in pH occurred in summer, whereas no change occurred in winter. In summer, the sources of pollutants at Mt. Oyama are mainly from mainland Japan, and the frequency of low-pH acidic fog decreased annually. In winter, Mt. Oyama was affected by transboundary pollution, and acid fog occasionally occurred. Improvements in the domestic atmospheric environment and control of transboundary pollution will provide better conditions for mountain ecology that are free from acidic pollutants.

Annual-scale assessment of mid-20th century anthropogenic impacts on the algal ecology of Crawford Lake, Ontario, Canada.

Meromictic Crawford Lake, located in SW Ontario, Canada is characterized by varved sediments, making it suitable for high-resolution paleoecological studies. Freeze cores, the only coring method available that reliably preserves the fragile laminations representative of seasonal deposition in the lake, were used to document siliceous diatom and chrysophyte community structure at an annual resolution from 1930-1990CE. Stratigraphically constrained cluster analysis identified major assemblage changes that are believed to have been caused by local, regional and possibly global anthropogenic impacts. The assemblage changes within the siliceous algae are attributed to regional weather and increased industrial emissions and related effects of acid deposition on the lake's catchment associated with the Great Acceleration -the massive economic, industrial, and demographic expansion beginning in the mid-20th century. Observed increases in spheroidal carbonaceous particles (SCPs) in varved lake sediment dating to the early 1950s record rapidly expanding steel production without emission controls around 30 km upwind of the lake. The findings reported here reflect major changes in earth systems that the Anthropocene Working Group recommends for a proposed epoch to be termed the Anthropocene, providing support for the laminated sediments from Crawford Lake as a potential Global boundary Stratotype Section and Point (GSSP).

Landscape acidification has trophic-mediated effects on Ovenbirds (Seiurus aurocapilla)

Acid deposition from fossil fuel combustion caused calcium depletion in eastern North America during the 20th century, and calcium is a critical resource for birds during both the egg laying and nesting periods. The effects of acid deposition on animals have largely acted through trophic relationships, with reduced calcium availability in prey possibly being a limiting factor for forest songbirds. Following 21 years of experimental whole-watershed acidification at the Bear Brook Watershed in Maine, we investigated Ovenbird (Seiurus aurocapilla) territory size and potential prey (leaf litter arthropod) abundance, assemblage, and calcium concentration during one breeding season. We delineated and estimated the area of 8 Ovenbird territories in an acidified and a control watershed, but found that territory size did not differ between watersheds. However, while calcium concentrations of potential prey also did not differ between watersheds, territory size decreased as calcium concentrations of potential prey increased, regardless of watershed. Our results suggest that calcium limitation can be a determinant of territory size in some landscapes, and this provides further support to importance of the role of calcium in the lives of passerines.

Long Term Trends of Base Cation Budgets of Forests in the UK to Inform Sustainable Harvesting Practices

There is growing concern in the UK that available base cation pools in soil are declining due to the combined effects of acid deposition and forest harvesting. To help inform the issue, elemental mass balances for calcium (Ca), magnesium (Mg) and potassium (K) were calculated using more than 10-years (10–24 years) of data from the UK’s ICP Forest Intensive Monitoring Network (Level II) of plots, covering a range of soil types and three tree species—oak, Scots pine and Sitka spruce. Out of the ten sites investigated, small negative Ca balances were observed at three sites and negative K balances on two sites, all on acid geology and nutrient poor soils, which were previously heavily acidified due to acid deposition. There is sufficient Ca and K in the soil exchangeable pool to sustain forest growth on these sites, however, if the present rate of Ca and K loss continues forest health and productivity are likely to be threatened within a few forest rotations. Magnesium showed a positive balance at all but one site, partly sustained by marine deposition. Base cation budgets were significantly (p < 0.01) positively related to soil exchangeable cations and soil base saturation status. Six of the sites showed an increasingly statistically significant positive cation balance with time, attributed to a decline in leaching linked to recovery from acidification. This included the three sites with negative Ca balance, although Ca remained in deficit. One site (Alice Holt) exhibited a decreasing cation balance, driven by a continued significant decline in base cation deposition thought to be related to pollutant emission control. The results were used to simulate the impact of different forest biomass harvesting scenarios involving the removal of brown (extracted after needle drop) or green (extracted before needle drop) brash. Podzols and deep peats were found to be the most vulnerable to brash harvesting causing Ca and K imbalance, but problems also occurred on brown earths. Impacts were greatest for the extraction of green brash from higher productivity stands. Base cation balance calculations remain highly uncertain due to the restricted nature of available measurements and wide variation of some estimates, particularly inputs from mineral weathering. More data are required to check and improve model predictions to better guide forest harvesting practice and ensure sustainable forest management.

Acid Deposition: Anthropogenic Causes, Destructive Effects and Probable Remedies

The harmful effect of acid deposition is considered as one of the most serious environmental problems in the modern world. It has reached alarming proportions mainly in the industrialized countries which affected global ecology vastly. Acid rain creates several health problems to the human body like eye, nose, and throat irritations, lung disorders such as dry coughs, asthma, headaches, and bronchitis. The excessive presence of sulfur dioxide and oxides of nitrogen in rainwater is the main reason behind acid rain. Emissions of these gases have increased in the atmosphere due to human activities, such as combustion of fossil fuels in thermal power plants, burnable wastes, automobiles and airplanes etc. To reduce and protect the world from acid rain it is necessary to identify the causes and find suitable strategies for the eradication of those causes. Probable remedies for the reduction of acid deposition have been discussed here for the welfare of global ecology.

Experimental investigation into the seismic behavior of squat reinforced concrete walls subjected to acid rain erosion

Acid rain erosion will continuously deteriorate the physical and mechanical properties of materials and finally degrade the seismic performance of reinforced concrete (RC) structures. Nevertheless, the effect of acid deposition on squat RC walls, an important part of lateral force-resisting systems, has not been reported in existing research. Thus, in this paper, an artificial climate simulation method was used to accelerate the acidic attack process on four squat RC wall specimens with an aspect ratio of 1.0. Then quasi-static loading tests were conducted to observe their cyclic behavior under different acid rain spraying cycles (ARSCs). The results show that as ARSCs increase, the degree of degradation of concrete strength and the corrosion weight loss of steel bars have a rising trend, and the bearing capacity and deformation capacity of the squat RC walls deteriorate gradually. Simultaneously, the ratio of shear displacement to total lateral displacement increases, indicating a more noticeable shear failure characteristic with the addition of ARSCs. Moreover, the failure mode shifts from the mixed flexure and diagonal compression mode to the diagonal tension mode with a significant decrease in ductility and energy-dissipation capacity. It is also found that the degradation rate of the shear strength of squat walls under acid rain erosion is larger than that of the flexural strength, which may lead to the transition of failure mode.

남해안 주요 도서 곰솔림에 미치는 산성강하물의 영향

본 연구는 남해안의 주요 도서를 중심으로 산림내에 유입되는 산성강하물의 성분을 분석하고 곰솔의 쇠퇴를 조사하여 산성강하물이 수목에 미치는 영향을 파악하여 도서지방연구에 기초자료를 제공하고자 수행하였다. 곰솔림내 수관통과우의 산도는 남해조사구가 봄철이 pH4.98, 가을철이 pH 5.02 로서 가장 낮았다. 도서 지역의 수관통과 강우 중에서 NO₃^- 는 남해조사구가 각각 47.28mg/L, 46.22mg/L 로서 가장 높았다. SO₄^2- 는 남해조사구가 평균 58.47㎎/L로 가장 높았고, 남해조사구는 대조지역보다 농도가 2.0배로 높았으며, 음이온의 지역별 농도는 남해조사구>거제조사구>통영조사구>대조구의 순이었다. 양이온은 Mg²⁺ 는 남해조사구가 각각 16.23mg/L, 16.29mg/L이었고, 지역별로 남해조사구가 가장 농도가 높았으며 대조지역보다 2.1배 높았다. 다음으로 거제, 통영조사구에서 측정치가 유사하였다. Ca²⁺ 의 농도는 남해조사구가 각각 30.27mg/L, 29.45mg/L이었고, 대조지역은 각각 15.92mg/L, 16.02mg/L이었다. 지역별로 남해조사구가 가장 농도가 높았으며 대조지역보다 1.9배 높았다. 다음으로 거제, 통영조사구에서 순이었다. 도서 지역 곰솔림의 엽록소 함량을 분석한 결과는 거제조사구가 가장 높았고, 남해조사구가 0.2987mg/g로 가장 낮았다. 도서 섬지역의 곰솔림 내에서 SO₂ 농도와 NO₂농도는 NO₂ 과 SO₂ 농도는 남해조사구는 봄철에 각각 0.051ppm, 0.063ppm, 가을철은 0.049ppm, 0.062ppm이었고, 남해조사구가 가장 높았는데, NO₂ 농도는 남해조사구는 대조구보다 봄철은 1.7배, 가을철은 1.5배 높은 결과였고, SO₂ 농도는 남해조사구는 대조구보다 봄철은 1.9배, 가을철은 2.1배 높은 결과였다. 도서 섬 조사지 곰솔의 쇠퇴도는 거제조사구는 2.10, 통영조사구는 1.80, 남해조사구는 3.27, 대조구는 1.40이었다. 쇠퇴도가 가장 높은 남해조사구는 대조구보다 2.9배 높게 조사되었고, 다음으로 거제 조사구이었고, 통영조사구는 가장 낮아 대조구와 유사하였다. 곰솔의 쇠퇴에 영향을 주는 인자의 상관분석은 강우산도는 부의상관(r=-0.8773)이었고, 대기 중 SO₂ 농도는 정의상관 (r=0.8946)이었고, NO₂농도는 정의상관(r=0.8832)이었다. 산성강하물 상호간의 상관관계는 pH(r=-0.8773), NO₃^- (r=0.8474), SO₄^2-(r=0.9847)이온, SO₂ (r=0.8946), NO₂ (r=0.8932), 엽록소 함량(r=9628)는 1% 수준에서 상관이었다. 가장 영향력을 미치는 변수는 pH로서 설명력은 78% 이었다. 곰솔의 쇠퇴에 영향을 하는 인자에 대하여 회귀 방정식을 나타내면 Y=4.8578 + 0.7820X2 + 0.8533X5 + 0.8698X11 +0.8788X12 + 0.8901X6 (r2=0.8934)로 추정되었다. 여기에서 X2는 pH, X5는 SO₄^2-, X11은 SO₂, X12은 NO₂, X6는 NO₃^- 이고, 이때의 설명력은 89% 이였다.

Trends and current status of aluminum chemistry in Adirondack headwater streams 30 Years after the Clean Air Act Amendments of 1990

Mobilization of toxic forms of aluminum (Ali) have been one of the most harmful effects of acidic deposition on aquatic ecosystems. Large decreases in acidic deposition levels have resulted in decreases in Ali concentrations in surface waters starting in the 1990s. However, recent studies indicate that fish communities are still being impaired by elevated Ali concentrations in streams, suggesting the need for a present-day assessment of the recovery status of Al chemistry in impacted regions such as the Adirondack region of New York, United States. Therefore, the recovery status of Al was assessed from long-term high-frequency monitoring of three Adirondack streams up through 2019, and multiple resampling of 127 headwater streams throughout the Adirondack region between 2004/2005 and 2018/2019. Results indicated that concentrations of Ali have continued to decrease throughout the Adirondack region, but that harmful conditions still exist in a substantial number of streams during spring snowmelt. In the western Adirondack region, 35 percent of streams during spring snowmelt, (typically the most acidic period), and 10 percent of streams during summer were still experiencing harmful concentrations of Ali (>1.0 μmol L−1) in 2018/2019. In the less-impacted east-central Adirondack region, 10 percent of streams during snowmelt, and 4 percent of streams during summer were experiencing harmful Ali concentrations in 2018. Temporal decreases in Ali concentrations were due in part to a shift in speciation from Ali to non-toxic organically complexed Al as dissolved organic carbon concentrations increased, which was also a response to decreasing acidic deposition. Increased availability of calcium resulting from acid-neutralization processes such as weathering also contributed to the decrease in Ali over the past 5–8 years. The current low levels of acidic deposition may have begun to enhance recovery by increasing the effectiveness of ambient acid-neutralization processes.

From legacy effects of acid deposition in boreal streams to future environmental threats

Few environmental issues have resulted in such a heated policy-science controversy in Sweden as the 1990s acidification debate in the north of the country. The belief that exceptionally high stream acidity levels during hydrological events was caused by anthropogenic deposition resulted in a governmentally funded, multi-million dollar surface-water liming program. This program was heavily criticized by a large part of the scientific community arguing that the acidity of northern streams was primarily caused by naturally occurring organic acids. Here, we revisit the acid deposition legacy in northern Sweden two decades after the culmination of the controversy by examining the long-term water chemistry trends in the Svartberget/Krycklan research catchment that became a nexus for the Swedish debate. In this reference stream, trends in acidic episodes do show a modest recovery that matches declines in acid deposition to pre-industrial levels, although stream acidity continues to be overwhelmingly driven by organic acidity. Yet there are legacies of acid deposition related to calcium losses from soils, which are more pronounced than anticipated. Finally, assessment of these trends are becoming increasingly complicated by new changes and threats to water resources that must be recognized to avoid unnecessary, expensive, and potentially counterproductive measures to adapt and mitigate human influences. Here we make the argument that while the acidification era is ending, climate change, land-use transitions, and long-range transport of other contaminants warrant close monitoring in the decades to come.

Water Chemistry of Arctic Lakes under Airborne Contamination of Watersheds

The data on the metal contents and acidification of small lakes caused by airborne contamination of the watershed in three industrial regions of the Arctic—European Russia (Kola region), Western (Yamal-Nenets region) and Eastern Siberia (Norilsk region)—have been presented for the first time. It has been proven that acidification and enrichment by metals of water connect with sulfur dioxide and metals emissions from copper–nickel smelters, contaminating the catchments, with associated gas burning during raw hydrocarbon production. To assess the effects of acid deposition, critical loads and their exceeds were calculated: exceeded by 56% and 12.5%, respectively, in lakes in the Kola region and in the north of Western Siberia; the catchments of the East Siberian region are resistant to acidification. Water enrichment factors (EF) by elements were calculated to show that the waters of the Norilsk and Kola regions are enriched with Ni, Cd, As, Sb and Se as a result of emissions from copper–nickel smelters. The oil and gas industry in the northern regions of Western Siberia lead to the increase in V, Pb and Mo concentrations in the waters. The high values of EF and excess of acidity critical loads for water are explained by the local and transboundary pollution impacts on the catchment of small lakes.

Occurrence of endogenous hormones in the roots of Masson pine (Pinus massoniana Lamb.) seedlings subjected to aluminum stress under the influence of acid deposition

Aluminum (Al) toxicity is perceived as a potential threat to the integrity of forest ecosystems. The detrimental effects of acidic deposition on trees are caused by mobilization of Al in soils. To better understand how roots adapt to acidic deposition releasing toxic Al including the endogenous hormones {{abscisic acid (ABA), gibberellic acid (GA3), indole-3-acetic acid (IAA) and zeatin riboside (ZR)}}, chemistry {{Ca/Al ratio, and base saturation (BS)}}, and growth rate, with the 100-day-old Masson pine (Pinus massoniana Lamb.) seedlings as research target, we studied the responses of the hormones to rhizospheric Al concentrations and their relationships between pine growth rates and Ca/Al ratios in the simulated soil solutions and forested soils differing in BS. In a hydroponic culture, after the seedlings were exposed to the simulated soil solutions containing 0 (control), 50, 100, 150, 200 µM Al at pH 4.0, ABA formed in the roots increased significantly with the time and intensity of Al exposure. ABA concentrations were positively correlated with rhizospheric Al concentrations (r = 0.92), whereas the opposite trend was seen for GA3 (r = −0.77). Simultaneously, IAA and ZR did not change with the increasing Al concentrations. Increasing of either Al concentration or exposure time caused an inhibition of root elongation and seedling growth. Moreover, in a field soil culture, the seedlings were grown for 60 days (d) in either A horizon soils with a BS above 17% or B horizon soils with a BS below 7%. Evident regional variation of ABA concentrations was observed in the pine roots, which declined in the order: Jin Yun Shan > Nan Shan > Tie Shan Ping, as well as B horizon soil > A horizon soil. Also, ABA concentrations were negatively correlated with soil Ca/Al ratios (r = −0.67). The opposite trends were simultaneously observed for GA3, IAA and ZR (r = 0.45, 0.25 and 0.18, respectively). Based on the laboratory and field results, under the influence of acid deposition, ABA, and GA3 may play an important synergic role in regulating Al resistance of Masson pine as an Al-stress signal.

Effects of One-Year Simulated Nitrogen and Acid Deposition on Soil Respiration in a Subtropical Plantation in China

Atmospheric nitrogen (N) and acid deposition have become global environmental issues and are likely to alter soil respiration (Rs); the largest CO2 source is from soil to the atmosphere. However, to date, much less attention has been focused on the interactive effects and underlying mechanisms of N and acid deposition on Rs, especially for ecosystems that are simultaneously subjected to elevated levels of deposition of both N and acid. Here, to examine the effects of N addition, acid addition, and their interactions with Rs, we conducted a two-way factorial N addition (control, CK; 60 kg N ha−1 a−1, LN; 120 kg N ha−1 a−1, HN) and acid addition (control, CK; pH 4.5, LA; pH 2.5, HA) field experiment in a subtropical plantation in China. Our results showed the following: (1) During the one-year observation period, the seasonal dynamics of Rs presented a single peak curve model, which was closely related to the surface soil temperature. (2) The simulated N deposition and acid deposition significantly decreased the Rs in the subtropical plantation. Compared to the CK plots, the LN and HN treatments reduced the annual mean values of Rs by 41% and 56%, and the annual mean values of Rs were inhibited by 26% and 31% in the LA and HA plots. The inhibition of N application on Rs was stronger than that of the simulated acid deposition. (3) Significant interactions between N addition and acid addition on Rs were detected, and Rs was significantly inhibited under four co-addition treatments. (4) The underlying mechanism and main reason for the responses of Rs to simulated N and acid deposition in this study might be the inhibition of soil microbial biomass and soil enzyme activity due to soil acidification under increased N and acid input.

Plant richness and composition in hardwood forest understories vary along an acidic deposition and soil-chemical gradient in the northeastern United States

AimsA century of atmospheric deposition of sulfur and nitrogen has acidified soils and undermined the health and recruitment of foundational tree species in the northeastern US. However, effects of acidic deposition on the forest understory plant communities of this region are poorly documented. We investigated how forest understory plant species composition and richness varied across gradients of acidic deposition and soil acidity in the Adirondack Mountains of New York State.MethodsWe surveyed understory vegetation and soils in hardwood forests on 20 small watersheds and built models of community composition and richness as functions of soil chemistry, nitrogen and sulfur deposition, and other environmental variables.ResultsCommunity composition varied significantly with gradients of acidic deposition, soil acidity, and base cation availability (63% variance explained). Several species increased with soil acidity while others decreased. Understory plant richness decreased significantly with increasing soil acidity (r = 0.60). The best multivariate regression model to predict richness (p < 0.001, adjusted-R2 = 0.60) reflected positive effects of pH and carbon-to-nitrogen ratio (C:N).ConclusionsThe relationship we found between understory plant communities and a soil-chemical gradient, suggests that soil acidification can reduce diversity and alter the composition of these communities in northern hardwood forests exposed to acidic deposition.

An assessment of long-term soil acidification trends in Alberta, Canada

Long-term soil acidification monitoring was initiated in 1981 to track potential effects of acidic atmospheric deposition on soils in Alberta, Canada. Six of eight long-term sampling sites were located in forest ecosystems on sandy soils in northern and central Alberta, and two were situated in grasslands on sandy and fine-loamy soils in southern Alberta. Sampling was undertaken every four or five years, with 12 replicate samples taken from seven depth increments from 0–60 cm at each site. The statistical analysis of pH, exchangeable base saturation (BS) percentage, and solution base cation (BC) to aluminum (Al) ratio was conducted in the topmost soil layers (0–2, 2–5 and 5–10 cm). Analysis of variance (ANOVA) and linear regression indicated decreasing trends in pH and BS percentage in some of the sites. Comparison of the initial and most recent monitoring data indicated decreases of up to 0.5 pH units in these layers at five of the forested sites. At two forested sites located in the vicinity of oil sands and heavy oil processing plants, decreasing BS was observed early in the monitoring period, but the trend showed more variability since 2000, even though pH has continued to decline since 1981. BC to Al ratio showed statistically significant variations within some sites over time, but except for a downward trend at one central Alberta site, there were no overall patterns evident at the other sites over time. Both grassland sites had much higher BC to Al ratio and exchangeable BS percentages than the forested sites, and acidification trends were not detected at either of these sites. ANOVA and linear modelling approaches showed significant differences even in instances where pH differed by 0.1–0.2 units, or where other parameters showed very small differences. It is therefore necessary to distinguish between statistically important and biologically important differences in this monitoring program, which is intended to continue for several more years.