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Surface waters across much of New York's Adirondack Mountains were acidified in the late 20th century but began to recover following the 1990 amendments to the Clean Air Act. Little data, however, are available to characterize biological impacts and predict recovery of fish assemblages in streams of the region. Quantitative fish and chemistry surveys were completed in 47 headwater streams during summer 2014-2016 to develop logistic (probabilistic) models that characterize the status of contemporary fish assemblages and predict how different nitrogen (N) and sulfur (S) deposition loads may affect future fish assemblages. Models for inorganic monomeric aluminum ([Al.sub.i]) and richness [greater than or equal to] 1 species and for acid neutralizing capacity (ANC) and total density >400 fish/0.1 ha, total biomass >1500 g/0.1 ha, brook trout (Salvelinus fontinalis) density >0 or >200 fish/0.1 ha, and brook trout biomass >1000 g/0.1 ha were suitable for evaluating community and population responses to changes in acid-base chemistry. Anticipated changes in national (US) secondary standards for atmospheric emissions of nitrogen oxides (N[O.sub.x]) and sulfur oxides (S[O.sub.x]) to achieve target N and S deposition loads will alter acid-base chemistry and the probabilities for observing various levels of fish metrics in streams across the region and elsewhere. Les eaux de surface dans une bonne partie des monts Adirondack de l'Etat de New York se sont acidifiees vers la fin du 20e siecle, mais ont commence a se retablir dans la foulee des amendements de 1990 a la Clean Air Act. Peu de donnees etaient toutefois disponibles pour caracteriser les impacts biologiques et predire le retablissement des assemblages de poissons dans les cours d'eau de la region. Des recensements quantitatifs de poissons et des leves chimiques ont ete realises dans 47 cours d'eau d'amont durant les etes de 2014 a 2016, afin d'elaborer des modeles logistiques (probabilistes) qui caracterisent l'etat des assemblages de poissons actuels et de predire l'incidence possible de differentes charges de depot d'azote (N) et de soufre (S) sur les assemblages de poissons futurs. Des modeles pour l'aluminium inorganique monomere (Ali) et une richesse [greater than or equal to] 1 espece, ainsi que pour le potentiel de neutralisation de l'acide (PNA) et une densite totale >400 poissons/0,1 ha, une biomasse totale >1500 g/0,1 ha, une densite d'ombles de fontaine (Salvelinus fontinalis) >0 ou >200 poissons/0,1 ha, et une biomasse d'ombles de fontaine >1000 g/0,1 ha se pretent a l'evaluation des reactions des communautes et des populations a des changements des conditions acidobasiques. Des modifications prevues a des normes secondaires nationales (Etats-Unis) concernant les emissions atmospheriques d'oxydes d'azote (N[O.sub.x]) et d'oxydes de soufre (S[O.sub.x]) pour atteindre des cibles de charges de depot de N et S modifieront les conditions acidobasiques et les probabilites d'observer des valeurs variees de parametres associes aux poissons dans les cours de la region et ailleurs. [Traduit par la Redaction], Introduction Although acid deposition has declined precipitously across eastern North America (McHale et al. 2017), subsequent improvements in water chemistry and biology of streams appear to be lagging considerably (Baldigo [...]

Summary: Soil microbial community composition routinely correlates with pH, reflecting both direct pH effects on microbial physiology and long‐term biogeochemical feedbacks. We used two watershed‐scale liming experiments to identify short‐ (2 years) and long‐term (25 years) changes in the structure and function of bacterial and fungal communities in organic horizons (Oe and Oa) of acid forest soils. Liming increased soil pH, extractable calcium, and soil carbon stocks, reduced biomass‐specific respiration, and caused major changes in the soil microbiome in the short and long term. More taxa responded to liming in the short term (70%) than in the long term (30%), with most showing consistent directional responses at both sites. The ratio of change in relative abundance between limed and reference sites was twofold higher at the long than the short‐term site, indicating that the effects of liming grew over time. Liming impacts were most pronounced in fungi, as steep declines of dominant ectomycorrhizal fungi (Cenococcum and Russula) occurred at both sites. Liming favoured neutrophilic bacteria over acidophilic populations according to estimated environmental pH optima. Collectively, these results demonstrate that a liming‐induced change of one pH unit has an immediate and persistent effect on the structure and function of microbial communities in acid forest soils. The corresponding suppression of respiration indicates that anthropogenic alterations of soil pH, as driven by acid deposition or liming, can affect forest floor C stocks due to pH‐driven shifts in community structure. [ABSTRACT FROM AUTHOR]

Depletion of Ca from forest soils due to acidic deposition has had potentially pervasive effects on forest communities, but these impacts remain largely unknown. Because snails, salamanders, and plants play essential roles in the Ca cycle of northern hardwood forests, we hypothesized that their community diversity, abundance, and structure would vary with differences in biotic Ca availability. To test this hypothesis, we sampled 12 upland hardwood forests representing a soil Ca gradient in the Adirondack Mountains, New York (USA), where chronic deposition has resulted in acidified soils but where areas of well-buffered soils remain Ca rich due to parent materials. Along the gradient of increasing soil [[Ca.sup.2+]], we observed increasing trends in snail community richness and abundance, live biomass of redback salamanders (Plethodon cinereus (Green, 1818)), and canopy tree basal area. Salamander communities were dominated by mountain dusky salamanders (Desmognathus ochrophaeus Cope, 1859) at Ca-poor sites and changed continuously along the Ca gradient to become dominated by redback salamanders at the Ca-rich sites. Several known calciphilic species of snails and plants were found only at the highest-Ca sites. Our results indicated that Ca availability, which is shaped by geology and acidic deposition inputs, influences northern hardwood forest ecosystems at multiple trophic levels, although the underlying mechanisms require further study. Resume: L'epuisement du Ca dans les sols forestiers a cause des depots acides a eu des repercussions potentiellement generalisees sur les communautes forestieres mais ces impacts demeurent largement inconnus. Etant donne que les escargots, les salamandres et les plantes jouent un role essentiel dans le cycle du Ca des forets feuillues nordiques, nous avons emis l'hypothese que la diversite, l'abondance et la structure de leurs communautes varieraient en fonction de la disponibilite du Ca. Pour tester cette hypothese, nous avons echantillonne 12 forets feuillues en milieu sec dans les monts Adirondacks, dans l'Etat de New York aux Etats-Unis d'Amerique, ou des depots chroniques ont acidifie les sols mais ou il y a encore des en-droits ou les sols ont un pouvoir tampon eleve et demeurent riches en Ca a cause du materiau originel. A mesure que la concentration de [Ca.sup.2+] augmentait le long du gradient, nous avons observe des tendances a la hausse de l'abondance et de la richesse des communautes d'escargots, de la biomasse vivante de salamandres rayees (Plethodon cinereus (Green, 1818)) et de la surface terriere des arbres qui forment la canopee. Les communautes de salamandres etaient dominees par la salaman-dre sombre des montagnes (Desmognathus ochrophaeus Cope, 1859) dans les stations pauvres en Ca et changeaient progressivement le long du gradient de Ca pour devenir dominees par la salamandre rayee dans les stations riches en Ca. Plusieurs especes calcicoles connues d'escargots et de plantes ont ete observees seulement dans les stations les plus riches en Ca. Nos resultats indiquent que la disponibilite du Ca, qui est determinee par les conditions geologiques et les apports de depots acides, influence les ecosystemes de feuillus nordiques a de multiples niveaux trophiques bien que les mecanismes sous-jacents necessitent plus de recherche. [Traduit par la Redaction], Introduction Research on forest ecosystem processes has suggested that Ca availability plays a critical role in shaping ecosystem structure, function, and responses to change (McLaughlin and Wimmer 1999). In the [...]

The biogeochemical processes that control NO3- movement through forested watersheds in the Catskill Mountains of New York have been investigated. The correlation of stream NO3-concentrations with the mean annual air temperature indicate that the rates of nitrogen mineralization and nitrificatin and not deposition or vegetation uptake control nitrogen leaching from forests where nitrogen in excess of the biological demand is available.

The chemistry of extremely acid Oa horizons does not conform to traditional pH, Al, and base saturation relationships. Results from two separate studies of northeastern U.S. forested soils were used to investigate relationships between pH in water or dilute salt solutions and other soil characteristics. In Oa horizons with pH below 4, soil pH in dilute Ca[Cl.sub.2] solution was correlated with exchangeable [H.sup.+] measured either by titration (r = -0.88, P = 0.0001, n = 142) or by electrode (r = -0.89, P = 0.0001, n = 45). Exchangeable [H.sup.+] expressed as a percentage of the cation-exchange capacity (CEC) was linear with pH and showed similar slopes for data from both studies. For all samples, pHw = 4.21 - 1.80 x [H.sup.+]/CEC ([R.sup.2] = 0.69, n = 194). The reciprocal of the [H.sup.+]/CEC ratio is base saturation with Al added to the bases. Because of the low pH, exchangeable Al does not appear to behave as an acid. Exchangeable [H.sup.+] remains an operationally defined quantity because of the difficulty in separating exchange and hydrolysis reactions. In a variety of neutral-salt extractants, concentrations of [H.sup.+] were correlated with 0.1 M Ba[Cl.sub.2]-exchangeable [H.sup.+] (r > 0.91, P = 0.0001, n = 26) regardless of the strength of the extract. Nine successive extractions with 0.33 mM Ca[Cl.sub.2] removed more [H.sup.+] than was removed by single batch extractions with either 1 M KCl or 0.1 M Ba[Cl.sub.2] (average [H.sup.+] of 70, 43, and 49 mmol [kg.sup.-1], respectively for 26 samples). The data showed little difference in the chemical behavior of Oa horizons from a variety of geographical sites and vegetation types.

The reactive form of Aluminum (Al) is mobilized from the mineral soil to the forest-floor soil due to acid deposition. This reactive Al reduces the availability of Calcium (Ca) present in the forest-floor soil to the plants. The Ca uptake by plants decrease as a consequence. The decrease of exchangeable Ca in the upper soil horizon is not accompanied by a change in exchangeable H or soil pH. Dissolution of mineral Al or decomplexation of organic Al are not responsible for the loss of Ca since these does not occur from acid deposition.

Acidic atmospheric deposition has adversely affected aquatic ecosystems globally. As emissions and deposition of sulfur (S) and nitrogen (N) have declined in recent decades across North America and Europe, ecosystem recovery is evident in many surface waters. However, persistent chronic and episodic acidification remain important concerns in vulnerable regions. We evaluated acidification in 269 headwater streams during 2010–2012 along the Appalachian Trail (AT) that transits several ecoregions and is located downwind of high levels of S and N emission sources. Discharge was estimated by matching sampled streams to those of a nearby gaged stream and assuming equivalent daily mean flow percentiles. Charge balance acid‐neutralizing capacity (ANC) values were adjusted to the 15th (Q15) and 85th flow percentiles (Q85) by applying the ANC/discharge slope among sample pairs collected at each stream. A site‐based approach was applied to streams sampled twice or more and a second regression‐based approach to streams sampled once to estimate episodic acidification magnitudes as the ANC difference from Q15 to Q85. Streams with ANC <0 μeq/L doubled from 16% to 32% as discharge increased from Q15 to Q85 according to the site‐based approach. The proportion of streams with ANC <0 μeq/L at low flow and high flow decreased from north to south. Base cation dilution explained the greatest amount of episodic acidification among streams and variation in sulfate (SO42−) concentrations was a secondary explanatory variable. Episodic SO42− patterns varied geographically with dilution dominant in northern streams underlain by soils developed in glacial sediment and increased concentrations dominant in southern streams with older, highly weathered soils. Episodic acidification increased as low‐flow ANC increased, exceeding 90 μeq/L in 25% of streams. Episodic increases in ANC were the dominant pattern in streams with low‐flow ANC values <30 μeq/L. Chronic and episodic acidification remain an ecological concern among AT streams. The approach developed here could be applied to estimate the magnitude and extent of chronic and episodic acidification in other regions recovering from decreasing levels of atmospheric S and N deposition. [ABSTRACT FROM AUTHOR]