Soil, climate, and landscape drivers of base cation concentrations in green stormwater infrastructure soils

Deicing practices and infrastructure weathering can impact plants, soil, and water quality through the input and transport of base cations. Base cation accumulation in green stormwater infrastructure (GSI) soils has the potential to decrease soil infiltration rates and plant water uptake or to promote leaching of metals and nutrients. To understand base cation retention in GSI soils and its drivers, we sampled 14 GSI soils of different age, contributing areas, and infiltration areas, across 3 years. We hypothesized that soil, climate, and landscape drivers explain the spatial and temporal variability of GSI soil base cation concentrations. Sodium (Na), Calcium (Ca), and Magnesium (Mg) concentrations in GSI soils were higher than in reference soils, while Ca and Mg were similar to an urban floodplain soil. Neither the contributing area, contributing impervious area, nor their ratios to infiltration area predicted base cation concentrations. Age predicted the spatial variability of Potassium (K) concentrations. Ca and Mg were moderately predicted by sand and silt, while clay predicted Mg, and sand predicted K. However, no soil characteristics predicted Na concentrations. A subset of sites had elevated Na in Fall 2019, which followed a winter with many freezing events and higher-than-average deicer salt application. K in sites with elevated Na was lower than in non-elevated sites, suggesting that transient spikes of Na driven by deicer salt decreased the ability of GSI soils to accumulate K. These findings demonstrate the large variability of GSI soil base cation concentrations and the relative importance of soil, climate, and landscape drivers of base cation dynamics. High variability in GSI soil data is commonly observed and further research is needed to reduce uncertainties for modeling studies and design. Improved understanding of how GSI soil properties evolve over time, and their relation to GSI performance, will benefit GSI design and maintenance practices.

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.

Carbon and nutrient pools and fluxes in unmanaged mountain Norway spruce forests, and losses after natural tree dieback

Forest areas infected by insects are increasing in Europe and North America due to accelerating climate change. A 2000-2020 mass budget study on major elements (C, N, P, Ca, Mg, K) in the atmosphere-plant-soil-water systems of two unmanaged catchments enabled us to evaluate changes in pools and fluxes related to tree dieback and long-term accumulation/losses during the post-glacial period. A bark-beetle outbreak killed >75 % of all trees in a mature mountain spruce forest in one catchment and all dead biomass was left on site. A similar forest in a nearby catchment was only marginally affected. We observed that: (1) the long-term (millennial) C and N accumulation in soils averaged 10-22 and 0.5-1.1 kg ha-1 yr-1, respectively, while losses of Ca, Mg, and K from soils ranged from 0.1 to 2.6 kg ha-1 yr-1. (2) Only <0.8 % and <1.5 % of the respective total C and N fluxes entering the soil annually from vegetation were permanently stored in soils. (3) The post-disturbance decomposition of dead tree biomass reduced vegetation element pools from 27 % (C) to 73 % (P) between 2004 and 2019. (4) Tree dieback decreased net atmospheric element inputs to the impacted catchment, and increased the leaching of all elements and gaseous losses of C (∼2.3 t ha-1 yr-1) and N (∼14 kg ha-1 yr-1). The disturbed catchment became a net C source, but ∼50 % of the N released from dead biomass accumulated in soils. (5) Despite the severe forest disturbance, the dissolved losses of Ca and Mg represented 52-58 % of their leaching from intact stands during the peaking atmospheric acidification from 1970 to 1990. (6) Disturbance-related net leaching of P, Ca, Mg, and K were 4, 69, 16, and 114 kg ha-1, respectively, which represented 7-38 % of the losses potentially related to sanitary logging and subsequent removal of the aboveground tree biomass.

Characteristics and acidic soil amelioration effects of biochar derived from a typical halophyte Salicornia europaea L. (common glasswort)

Glycophyte biomass - derived biochars have proven to be effective in the amelioration of acidic soil. However, there is scarce information on the characteristics and soil amelioration effects of halophyte-derived biochars. In this study, a typical halophyte Salicornia europaea, which is mainly distributed in the saline soils and salt-lake shores of China, and a glycophyte Zea mays, which is widely planted in the north of China, were selected to produce biochars with a pyrolysis process at 500 °C for 2 h. S. europaea-derived and Z. mays-derived biochars were characterized in elemental content, pores, surface area, and surface functional groups, and then by using a pot experiment their potential utilizable value as acidic soil conditioner was evaluated. The results showed that compared with Z. mays-derived biochar, S. europaea-derived biochar displayed higher pH, ash contents, base cations (K⁺, Ca²⁺, Na⁺, and Mg²⁺) contents and exhibited more larger surface area and pore volume than Z. mays-derived biochar. Both biochars had abundant oxygen-containing functional groups. Upon treating the acidic soil, the pH of acidic soil was increased by 0.98, 2.76, and 3.36 units after the addition of 1%, 2%, and 4% S. europaea-derived biochar, while it was increased only by 0.10, 0.22, and 0.56 units at 1%, 2%, and 4% Z. mays-derived biochar. High alkalinity in S. europaea-derived biochar was the main reason for the increase of pH value and base cations in acidic soil. Thus, application of halophyte biochar such as S. europaea-derived biochar is an alternative method for the amelioration of acidic soils.

Four decades of regional wet deposition, local bulk deposition, and stream-water chemistry show the influence of nearby land use on forested streams in Central Appalachia

Hydrologic monitoring began on two headwater streams (<1 km²) on the University of Kentucky's Robinson Forest in 1971. We evaluated stream-water (1974-2013) and bulk-deposition (wet + dust) (1984-2013) chemistry in the context of regional wet-deposition patterns that showed decreases in both sulfate and nitrate concentrations as well as proximal surface-mine expansion. Decadal time steps (1974-83, 1984-93, 1994-2003, 2004-2013) were used to quantify change. Comparison of the first two decades showed similarly decreased sulfate (minimum flow-adjusted annual-mean concentration of ≈13.5 mg/L in 1982 to 8.8 mg/L in 1992) and increased pH (6.6-6.8) in both streams, reflecting contemporaneous changes in both bulk and wet deposition. In contrast, concentrations of nitrate (0.14 to >0.25 mg/L) and base cations increased between these two decades, coinciding with expansion of surface mining between 1985 and 1995. In 2004, stream-water pH (6.7 in 2004), sulfate (9.2 mg/L), and nitrate (>0.11 mg/L) were similar to 1982, despite wet-deposition concentrations being lower. Base-cation concentrations were higher in the stream adjacent to ongoing surface mining relative to the stream situated near the middle of the experimental forest. However, pH decreased to approximately 5.7 by 2013 for both streams, which, combined with a shift in dominant cations from calcium to magnesium and potassium, indicates that the soil-buffering capacity of this landscape has been exceeded. Ratios of bulk deposition and stream-water concentrations indicate enrichment of sulfate (1.7-25.2) and cations (0.5-64.8), but not nitrogen (0.1-5.6), indicating that the Forest is not nitrogen saturated and that ongoing changes in water-quality are sulfate driven. When concentrations were adjusted to account for changes in streamflow (climate) over the 4 decades, external influences (land management/regulation) explained most change. The amount and direction of change differed among constituents, both between consecutive decades and between the first and last decades, reflecting the influence of localized surface mining even as regional wet deposition continued to improve due to the Clean Air Act. The implication is that localized stressors have the potential to out-pace the benefits of national environmental policies for communities that depend on local water-resources in similar environments.

Are bog plant/lichen tissue concentrations of Ca, Mg, K, and P affected by fugitive dust released from oil sands development in the Fort McMurray region of Alberta?

Bogs are ombrotrophic, relying solely on atmospheric deposition for new inputs of elements. Increased element deposition through anthropogenic activities has the potential to alter nutrient availability, and hence ecosystem function, in bogs. Further, because of efficient element retention, bogs may function as effective monitors of element deposition. To assess the potential effects of particulate fugitive dust from oil sands development in Alberta, Canada, we quantified plant/lichen tissue Ca, Mg, K, and P concentrations in 6 bogs ranging from 12 to 77 km from the oil sands industrial center. Deposition of Ca and Mg, but not K or P, quantified using ion exchange resin collectors, to bogs decreased with distance from the oil sands industrial center. Concentrations of Ca and Mg, but not K or P, in tissues of lichens (Cladonia mitis, Evernia mesomorpha) and Sphagnum (S. capillifolium, S. fuscum) decreased with distance from the oil sands industrial center. Tissue Ca concentrations were positively correlated with growing season Ca and Mg deposition in all species except Vaccinium oxycoccos, Rhododendron groenlandicum, and Picea mariana; leaf Mg concentrations were positively correlated with growing season Mg deposition for all species except P. mariana. Tissue concentrations of K and P were not correlated with growing season K and P deposition. For each species, receptor modeling identified two distinct sources, one dominated by Ca and Mg, presumed to represent particulate fugitive dust from oil sands activities, and a second dominated by K and P, which may reflect tight internal cycling and upward translocation of K and P in peat and/or K and P deposition as particulates generated in wildfires. Increasing Ca²⁺ and Mg²⁺ deposition may acidify bog porewaters through cation exchange in peat.

Impact of tree species diversity on throughfall deposition in a young temperate forest plantation

Throughfall deposition is an important pathway via which particles, aerosols and gases can move from the atmosphere to the forest floor, which can greatly impact forest biodiversity and functioning. Although throughfall deposition biochemistry has been well studied in forest ecosystems, less is known about how throughfall deposition is modified by tree species diversity. To disentangle the effects of tree species identity and diversity on throughfall deposition, we installed rain gauges in a 10-year-old tree diversity experiment. With these rain gauges, we monitored throughfall biweekly, and performed chemical analyses monthly for all the major ions (Na⁺, Cl^-, SO₄^2--S, K⁺, Ca²⁺, Mg²⁺, PO₄^3--P, NO₃^--N and NH₄⁺-N), for a period of one year. Based on these data, we analysed species identity (i.e. whether throughfall deposition depended on the tree species present in the overstorey), and diversity effects (i.e. whether throughfall deposition depended on tree species richness). We confirmed species identity effects on throughfall deposition. Presence of pine led to higher throughfall deposition of inorganic nitrogen, and lower amounts of phosphorus, calcium and magnesium reaching the forest floor. Additionally, species characteristics and stand structural characteristics, i.e. basal area and canopy cover, emerged as key factors driving throughfall deposition of sodium, chloride, nitrate, sulphate and potassium. Tree species diversity effects on throughfall deposition were also present, mostly via increased basal area and canopy cover, leading to increased throughfall deposition of inorganic nitrogen, sulphate, chloride, sodium and potassium. Our findings thus suggest that tree species diversity enhances throughfall deposition of most ions that we analysed, potentially increasing nutrient availability for below-canopy plant communities. Given that inorganic nitrogen and sulphur are major atmospheric pollutants, increased deposition in mixed plots might affect ecosystem functioning. Further research will be needed to determine the extent of this impact.

Stream bacterial diversity peaks at intermediate freshwater salinity and varies by salt type

Anthropogenic freshwater salinization is an emerging and widespread water quality stressor that increases salt concentrations of freshwater, where specific upland land-uses produce distinct ionic profiles. In-situ studies find salinization in disturbed landscapes is correlated with declines in stream bacterial diversity, but cannot isolate the effects of salinization from multiple co-occurring stressors. By manipulating salt concentration and type in controlled microcosm studies, we identified direct and complex effects of freshwater salinization on bacterial diversity in the absence of other stressors common in field studies using chloride salts. Changes in both salt concentration and cation produced distinct bacterial communities. Bacterial richness, or the total number of amplicon sequence variants (ASVs) detected, increased at conductivities as low as 350 μS cm^-1, which is opposite the observations from field studies. Richness remained elevated at conductivities as high as 1500 μS cm^-1 in communities exposed to a mixture of Ca, Mg, and K chloride salts, but decreased in communities exposed to NaCl, revealing a classic subsidy-stress response. Exposure to different chloride salts at the same conductivity resulted in distinct bacterial community structure, further supporting that salt type modulates responses of bacterial communities to freshwater salinization. Community variability peaked at 125-350 μS cm^-1 and was more similar at lower and upper conductivities suggesting possible shifts in deterministic vs. stochastic assembly mechanisms across freshwater salinity gradients. Based on these results, we hypothesize that modest freshwater salinization (125-350 μS cm^-1) lessens hypo-osmotic stress, reducing the importance of salinity as an environmental filter at intermediate freshwater ranges but effects of higher salinities at the upper freshwater range differ based on salt type. Our results also support previous findings that ~300 μS cm^-1 is a biological effect concentration and effective salt management strategies may need to consider variable effects of different salt types associated with land-use.

Freshwater salinization increases survival of Escherichia coli and risk of bacterial impairment

Elevated levels of Escherichia coli (E. coli) are responsible for more designated freshwater stream impairments than any other contaminant in the United States. E. coli are intentionally used as a sentinel of fecal contamination for freshwaters because previous research indicates that salt concentrations in brackish or marine waters reduce E. coli survival, rendering it a less effective indicator of public health risks. Given increasing evidence of freshwater salinization associated with upland anthropogenic land-use, understanding the effects on fecal indicators is critical; however, changes in E. coli survival along the freshwater salinity range (≤ 1500 µS cm^-1) have not been previously examined. Through a series of controlled mesocosm experiments, we provide direct evidence that salinization causes E. coli survival rates in freshwater to increase at conductivities as low as 350 µS cm^-1 and peak at 1500 µS cm^-1, revealing a subsidy-stress response across the freshwater-marine continuum. Furthermore, specific base cations affect E. coli survival differently, with Mg²⁺ increasing E. coli survival rates relative to other chloride salts. Further investigation of the mechanisms by which freshwater salinization increases susceptibility to or exacerbates bacterial water quality impairments is recommended. Addressing salinization with nuanced approaches that consider salt sources and chemistry could assist in prioritizing and addressing bacterial water quality management.

Striking a balance between N sources: Mitigating soil acidification and accumulation of phosphorous and heavy metals from manure

Manure amendment has been shown to effectively prevent red soil (Ferralic Cambisol) acidification from chemical nitrogen (N) fertilization. However, information is lacking on how much manure is needed to mitigate acidification and maintain soil productivity while preventing accumulation of other nutrients and heavy metals from long-term inputs. This study determined the effects of various combinations of manure with urea-N on acidification and changes in soil P, K, and heavy metals in a 9-year maize field experiment in southern China. Treatments included chemical N, P and K fertilization only (NPKM0), and NPK plus swine manure, which supplied 20% (NPKM20), 40% (NPKM40), and 60% (NPKM60) of total N at 225 kg N ha^-1 year^-1. Soil pH, exchangeable acidity, available P and K, and maize yield were determined annually from 2009 to 2018. Soil exchangeable base cations, total and phytoavailable Cr, Pb, As, Ni, Cd, Cu, and Zn were measured in 2018. A significant decrease in soil pH occurred under NPKM0 and NPKM20 from initial 4.93 to 4.46 and 4.71, respectively. Whereas, under NPKM40 and NPKM60 no change or a significant increase in soil pH (to 5.47) occurred, as well as increased exchangeable base cations, and increased yields. Manure application markedly increased soil available P (but not K) to 67.6-182.6 mg kg^-1 and significantly increased total Pb, Cu, and Zn and available Cu and Zn in soil. The results indicate sourcing 40% or greater of total N from manure can prevent or reverse acidification of red soil, and provide all P required, however, additional K inputs are required for balanced plant nutrient supply. An integrated approach of increasing N use efficiency, reducing chemical input, and reducing heavy metal concentrations in animal feed are all necessary for sustainable use of manure in soil acidity and nutrient management as well as minimizing environmental risks.

Ambient concentrations and total deposition of inorganic sulfur, inorganic nitrogen and base cations in the Athabasca Oil Sands Region

Trace gas, particulate matter and deposition data collected in the Athabasca Oil Sands Region (AOSR) from 2000 to 2017 were evaluated as part of a broad scientific programmatic review. Results showed significant spatial patterns and temporal trends across the region. Concentrations of reactive gases were highest near the center of surface oil sands production operations and decreased towards the edges of the monitoring domain by factors of 8, 20, 4 and 3 for SO₂, NO₂, HNO₃ and NH₃, respectively. 18 of 30 sites showed statistically significant (p < 0.05) negative trends in SO₂ concentrations suggesting an ~40% decrease since 2000. In contrast, only 2 of 30 sites showed statistically significant temporal trends (1 positive, 1 negative) for NO₂. NH₃ data showed (i) intermittent wildfire impacts, and (ii) high seasonality, with low concentrations during winter and significantly higher values during the summer. PM₁₀ measurements were more limited, but also showed significant spatio-temporal variability. Comparison of PM₁₀ and PM_2.5 data showed that >80% of SO₄^2- was in the PM_2.5 fraction, while > 60% of Ca²⁺, Mg²⁺, Na⁺ and Cl^- were in the PM_10-2.5 fraction. Ion balances of both PM₁₀ and PM_2.5 contained cation excesses at near-field oil sand sites, but PM_2.5 samples at forest health sites >20 km from surface production locations contained anion excesses. Monthly average concentrations of PM₁₀ ions showed peak Ca²⁺ during March-April to November, but peak SO₄^2-, NH₄⁺ and NO₃^- from November-March. Deposition estimates showed rapid declines as a function of distance to oil sand operations. Estimated total N and total S deposition to forest health monitoring sites ranged from 2.0 to 5.7 kg ha^-1 a^-1 and 2.1-14.0 kg ha^-1 a^-1, respectively. Potential acid input (PAI) ranged from -0.46 to 0.79 keq ha^-1 a^-1 and was mostly 0.1-0.2 keq ha^-1 a^-1 throughout the domain, except for two clusters of sites near oil sand operations.

Litter quality and the law of the most limiting: Opportunities for restoring nutrient cycles in acidified forest soils

The adverse effects of soil acidification are extensive and may result in hampered ecosystem functioning. Admixture of tree species with nutrient rich litter has been proposed to restore acidified forest soils and improve forest vitality, productivity and resilience. However, it is common belief that litter effects are insufficiently functional for restoration of poorly buffered sandy soils. Therefore we examined the effect of leaf litter on the forest floor, soil chemistry and soil biota in temperate forest stands along a range of sandy soil types in Belgium, the Netherlands and Germany. Specifically, we address: i) Which tree litter properties contribute most to the mitigation of soil acidification effects and ii) Do rich litter species have the potential to improve the belowground nutrient status of poorly buffered, sandy soils? Our analysis using structural equation modelling shows that litter base cation concentration is the decisive trait for the dominating soil buffering mechanism in forests that are heavily influenced by atmospheric nitrogen (N) deposition. This is in contrast with studies in which leaf litter quality is summarized by C/N ratio. We suggest that the concept of rich litter is context dependent and should consider Liebig's law of the most limiting: if N is not limiting in the ecosystem, litter C/N becomes of low importance, while base cations (calcium, magnesium, potassium) become determining. We further find that on poorly buffered soils, tree species with rich litter induce fast nutrient cycling, sustain higher earthworm biomass and keep topsoil base saturation above a threshold of 30%. Hence, rich litter can trigger a regime shift to the exchange buffer domain in sandy soils. This highlights that admixing tree species with litter rich in base cations is a promising measure to remediate soil properties on acidified sandy soils that receive, or have received, high inputs of N via deposition.

Fecal indicator dynamics at the watershed scale: Variable relationships with land use, season, and water chemistry

Tracking fecal contamination in surface waters is critical to remediating water quality; however, general and source-specific fecal indicators often provide conflicting results. To understand the spatial and temporal dynamics of multiple fecal indicators and the sources they represent, we measured weekly concentrations of two general fecal indicator bacteria (FIB), a genetic indicator of human-associated Bacteroides (HF183), and surface water chemistry in nine mixed land-use watersheds in southwest Virginia, USA. At the watershed scale, general and source-specific indicators were decoupled, with distinct spatial, temporal, and chemical patterns. Random Forest analysis of individual sample variability identified temperature, watershed, nutrients, and cations as top predictors of indicator concentrations. However, these patterns - and the specific nutrients and cations identified - varied by indicator type. Among watersheds, FIB increased with developed land cover and during the summer months, while HF183 increased during the winter and only in urban watersheds. Nutrients generally related poorly to FIB and HF183, except E. coli, which correlated with total nitrogen. In contrast, all fecal indicators showed strong correlations with cations. FIB were more strongly related to calcium, magnesium, and potassium concentrations, while HF183 was related to sodium. These results suggest that, even at the watershed scale, 1) HF183 detects mainly human fecal contamination, while FIB detect broader ecosystem fecal inputs, and 2) poor correlation between specific and generalist fecal indicators is caused by unique spatial, temporal, and transport dynamics of different fecal sources in watersheds.

Alleviation of aluminum phytotoxicity by canola straw biochars varied with their cultivating soils through an investigation of wheat seedling root elongation

The types and amounts of cations and their uptake by plants vary with cultivating soils, which correlates with the carbonates and subsequent alkalis contents in the derived biochars. However, regional differences in the alkaline properties of crop straw biochars are unclear. In the present study, biochars pyrolyzed from canola straws collected from four different regions were used to assess the differences in the alkaline properties among them. The biochars were referred to as YTBC, XCBC, NJBC, and HYBC, respectively, and their feedstocks were collected from four different regions from south to north of China. The NH₄OAC exchangeable base cations (K⁺, Na⁺, Ca²⁺, Mg²⁺) in the biochars were 270.74, 1427.05, 2089.23, and 1516.48 mmol kg^-1 for YTBC, XCBC, NJBC, and HYBC, respectively, which were roughly consistent with the exchangeable base cations in the corresponding planting soils (17.57, 28.20, 151.26 and 444.65 mmol kg^-1, respectively). The pH, carbonates content, and alkalinity of biochars considerably increased as follows: YTBC < XCBC < NJBC < HYBC. Wheat seedling root elongation experiment indicated that the Al(III) phytotoxicity alleviation effect of the biochars was as follows: HYBC > NJBC > XCBC > YTBC, which was corroborated by the subsequent findings of Evans blue staining, the remnant aluminum (Al(III)) in the reaction solution and Al(III) distribution in the wheat seedling roots. Thus, planting soil had a dominant influence in alleviating Al(III) phytotoxicity, and studies on crop straw biochar properties concerning alkalinities or liming potentials should not only consider crop genera and pyrolysis conditions, but also cultivating conditions.

Migration and leaching characteristics of base cation: indicating environmental effects on soil alkalinity in a karst area

In karst areas, rock dissolution often results in the development of underground networks, which act as subterranean pathways for rapid water and nutrient (and possibly soil) loss during precipitation events. Loss of soluble nutrients degrades surface soils and decreases net primary productivity, so it is important to establish flow pathways and quantify nutrient loss during rainfall events of different magnitudes. We conducted a simulated rainfall experiment in karst and nonkarst areas to compare the concentration of nutrients in surface and subsurface flow water and effects on soil alkalinity in three lithologic soil formations under five different rainfall intensity treatments. Compared with the nonkarst area, the runoff in subsurface flows and the proportion of nutrient loss in the subsurface flow are larger in the karst area and less affected by rain intensity. The maximum loss loads of calcium (Ca²⁺) and magnesium (Mg²⁺) ions were 32.9 and 19.8 kg ha^-1, respectively. With the estimate of base cation loss loads in the China southern karst area under the rainfall intensity of 45 mm h^-1, more than 80% of the base cation loss load occurred in the limestone karst area. Although the alkalinity leaching value in nonkarst was similar to that in the karst area under simulated rainfall conditions, its impact on the ecological environment was quite different.

Changes in surface water chemistry caused by natural forest dieback in an unmanaged mountain catchment

Ionic and nutrient compositions of throughfall, tributaries and lake outlet were analysed in the Plešné catchment-lake system (an unmanaged mountain forest in Central Europe) from 1997 to 2016. The aim was to evaluate changes in surface water chemistry after natural forest dieback. In the 2004-2008, 93% of the Norway spruce trees were killed by bark beetle outbreak, and all dead biomass remained in the catchment. Forest dieback changed the chemistry of all water fluxes, and the magnitude, timing, and duration of these changes differed for individual water constituents. The most pronounced decreases in throughfall concentrations occurred for K⁺, dissolved organic carbon (DOC), Ca²⁺ and Mg²⁺, i.e. elements mostly originating from canopy leaching, while concentrations of NH₄⁺ and soluble reactive phosphorus (SRP) remained almost unaffected. In tributaries, the most rapid changes were increases in NO₃^-, K⁺, H⁺ and ionic aluminium (Al_i) concentrations, while terrestrial export of DOC and P forms started more slowly. Immediately after the forest dieback, increase in NO₃^- concentrations was delayed by elevated DOC availability in soils. NO₃^- became the dominant anion, with maximum concentrations up to 346μeqL^-1 within 5-7years after the bark beetle outbreak, and then started to decrease. Terrestrial exports of Al_i, K⁺, H⁺, Mg²⁺, and Ca²⁺ accompanied NO₃^- leaching, but their trends differed due to their different sources. Elevated losses of SRP, DOC, and dissolved organic nitrogen continued until the end of the study. In the lake, microbial processes significantly decreased concentrations of NO₃^-, organic acid anions, H⁺ and Al_i, and confounded the chemical trends observed in tributaries. Our results suggest that terrestrial losses of elements and the deterioration of waters after forest dieback are less pronounced in unmanaged than managed (clear-cut) catchments.

Effect of industrial dust on precipitation chemistry in the Czech Republic (Central Europe) from 1850 to 2013

Using statistical relationships between the composition of precipitation at eight long-term monitoring stations and emission rates of sulphur (S) and nitrogen (N) compounds, as well as industrial dust in the Czech Republic and Slovakia (Central Europe), we modelled historic pH and concentrations of sulphate (SO4(2-)), nitrate (NO3(-)), ammonium (NH4(+)), chloride (Cl(-)), base cations (BC), and bicarbonate (HCO3(-)) in bulk precipitation from 1850 to 2013. Our model suggests that concentrations of SO4(2-), NO3(-), and HCO3(-) were similar (11-16 μeq l(-1)) in 1850. Cations were dominated by NH4(+) and BC (24-27 μeq l(-1)) and precipitation pH was >5.6. The carbonate buffering system was depleted around 1920 and precipitation further acidified at an exponential rate until the 1980s, when concentrations of SO4(2-), NO3(-), Cl(-), NH4(+) and BC reached maxima of 126, 55, 16, 76, and 57 μeq l(-1), respectively, and pH decreased to 4.2. Dust emissions from industrial sources were an important source of BC. Without their contribution, pH would have decreased to 4.0 in the 1980s, and the carbonate buffering system would have been depleted already in the 1870s. Since the late 1980s, concentrations of strong acid anions and BC have decreased by 46-81% (i.e. more than in Europe on average) due to a 53-93% reduction in regional emissions of S and N compounds and dust from industrial and agricultural sources. The present composition of precipitation is similar to the late 19th century, except for NO3(-) concentrations, which are similar to those during 1926-1950. Precipitation pH now exceeds 5.0, the carbonate buffering system has been re-established, and HCO3(-) has again become (after almost a century) a significant component of precipitation chemistry.

Sphagnum can 'filter' N deposition, but effects on the plant and pore water depend on the N form

The ability of Sphagnum moss to efficiently intercept atmospheric nitrogen (N) has been assumed to be vulnerable to increased N deposition. However, the proposed critical load (20kgNha(-1)yr(-1)) to exceed the capacity of the Sphagnum N filter has not been confirmed. A long-term (11years) and realistic N manipulation on Whim bog was used to study the N filter function of Sphagnum (Sphagnum capillifolium) in response to increased wet N deposition. On this ombrotrophic peatland where ambient deposition was 8kgNha(-1)yr(-1), an additional 8, 24, and 56kgNha(-1)yr(-1) of either ammonium (NH4(+)) or nitrate (NO3(-)) has been applied for 11years. Nutrient status of Sphagnum and pore water quality from the Sphagnum layer were assessed. The N filter function of Sphagnum was still active up to 32kgNha(-1)yr(-1) even after 11years. N saturation of Sphagnum and subsequent increases in dissolved inorganic N (DIN) concentration in pore water occurred only for 56kgNha(-1)yr(-1) of NH4(+) addition. These results indicate that the Sphagnum N filter is more resilient to wet N deposition than previously inferred. However, functionality will be more compromised when NH4(+) dominates wet deposition for high inputs (56kgNha(-1)yr(-1)). The N filter function in response to NO3(-) uptake increased the concentration of dissolved organic N (DON) and associated organic anions in pore water. NH4(+) uptake increased the concentration of base cations and hydrogen ions in pore water though ion exchange. The resilience of the Sphagnum N filter can explain the reported small magnitude of species change in the Whim bog ecosystem exposed to wet N deposition. However, changes in the leaching substances, arising from the assimilation of NO3(-) and NH4(+), may lead to species change.

Acid deposition in the Athabasca Oil Sands Region: a policy perspective

Industrial emissions of sulphur (S) and nitrogen (N) to the atmosphere associated with the oil sands industry in north-eastern Alberta are of interest as they represent the largest localized source in Canada (with potential for future growth) and the region features acid-sensitive upland terrain. Existing emission management policy for the Regional Municipality of Wood Buffalo, where the industry is located, is based on a time-to-effect approach that relies on dynamic model simulations of temporal changes in chemistry and features highly protective chemical criteria. In practice, the policy is difficult to implement and it is unlikely that a scientifically defensible estimate of acidification risk can be put forward due to the limitations primarily associated with issues of scale, chemical endpoint designation (selection of chemical limit for ecosystem protection from acidification) and data availability. A more implementable approach would use a steady-state critical load (CL) assessment approach to identify at-risk areas. The CL assessment would consider areas of elevated acid deposition associated with oil sands emissions rather than targeted political jurisdictions. Dynamic models should only be (strategically) used where acidification risk is identified via CL analysis, in order to characterize the potential for acidification-induced changes that can be detrimental to sensitive biota within the lifespan of the industry.

Cation export by overland flow in a recently burnt forest area in north-central Portugal

The current fire regime in the Mediterranean Basin constitutes a serious threat to natural ecosystems because it drastically enhances surface runoff and soil erosion in the affected areas. Besides soil particles themselves, soil cations can be lost by fire-enhanced overland flow, increasing the risk of fertility loss of the typically shallow and nutrient poor Mediterranean soils. Although the importance of cations for land-use sustainability is widely recognized, cation losses by post-fire runoff have received little research attention. The present study aimed to address this research gap by assessing total exports of Na(+), K(+), Ca(2+) and Mg(2+) in a recently burnt forest area in north-central Portugal. These exports were compared for two types of planted forest (eucalypt vs. maritime pine plantations), two types of parent materials (schist vs. granite) and for two spatial scales (micro-plot vs. hill slope). The study sites were a eucalypt plantation on granite (BEG), a eucalypt plantation on schist (BES) and a maritime pine plantation on schist (BPS). Overland flow samples were collected during the first six months after the wildfire. Cation losses differed strikingly between the two forest types on schist, being higher at the eucalypt than pine site. This difference was evident at both spatial scales, and probably due to the extensive cover of a needle cast from the scorched pine crowns. The role of parent material in cation export was less straightforward as it varied with spatial scale. Cation losses were higher for the eucalypt plantation on schist than for that on granite at the micro-plot scale, whereas the reverse was observed at the hill slope scale. Finally, cation yields were higher at the micro-plot than slope scale, in agreement with the general notion of scaling-effect in runoff generation.

The importance of atmospheric base cation deposition for preventing soil acidification in the Athabasca Oil Sands Region of Canada

Industrial activities in the oil sands region of Alberta, Canada have resulted in greatly elevated emissions of SO2 and N (NO(x) and NH3) and there are concerns over possible widespread ecosystem acidification. Acid sensitive soils in the region are common and have very low base cation weathering rates: the median base cation weathering rate estimated for 63 sites using PROFILE was just 17 mmol cm(-2) yr(-1). Deposition of S and N in throughfall was approximately twice as high as deposition measured with open collectors and could be as high as 360 mmol cm(-2) yr(-1) within 20 km of the main industrial center, although deposition declined logarithmically with distance from the industrial activities. Base cation deposition however, mostly exceeded the combined inputs of S and N in bulk deposition and throughfall, particularly during the summer months. The potential for soil acidification at a site close (<3 km) to the largest mine was assessed using the dynamic ecosystem acidification model, MAGIC (Model of Acidification of Groundwater in Catchments). Despite very low base cation weathering rates (~6 mmol cm(-2) yr(-1)) and high (~250 mmol cm(-2) yr(-1)) acid (S+N) deposition at the site, soil base saturation and soil solution pH and molar Ca:Al ratio were predicted to increase in the future assuming acid and base cation deposition constant at current rates. This work shows that despite extremely low soil base cation weathering rates in the region, the risk of soil acidification is mitigated to a large extent by high base cation deposition, which in contrast to S emissions is derived from fugitive dust sources in the mines, and is poorly quantified for regional modeling studies.

Metal and nutrient dynamics in decomposing tree litter on a metal contaminated site

In a forest on sandy, metal polluted soil, we examined effects of six tree species on litter decomposition rates and accompanied changes in metal (Cd, Zn) and nutrient (base cations, N, C) amounts. Decomposition dynamics were studied by means of a litterbag experiment lasting for 30 months. The decomposition peak occurred within the first year for all tree species, except for aspen. During litter decomposition, high metal litter types released part of their accumulated metals, whereas low metal litter types were characterized by a metal enrichment. Base cations, N and C were released from all litter types. Metal release from contaminated litter might involve risks for metal dispersion towards the soil. On the other hand, metal enrichment of uncontaminated litter may be ecologically relevant as it can be easily transported or serve as food source.