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This data note describes the Biscuit Brook and Neversink Reservoir watershed long‐term monitoring data that includes: 1) stream discharge, (1983–2020 for Biscuit Brook and 1937–2020 for the Neversink Reservoir watershed), 2) stream water chemistry, 1983–2020, at 4 stations, 3) fish survey data from 16 locations in the watershed 1990–2019, 4) soil chemistry data from 2 headwater sub‐watersheds, 1993–2012 and 5) periodic stream water chemistry sampling data from 364 locations throughout the watershed, 1983–2020. The Neversink Reservoir watershed in the Catskill Mountains of New York, USA drains an area of 172.5 km2. The watershed feeds one of six reservoirs in New York City's West of Hudson water supply, which accounts for about 90% of the city's water supply. Biscuit Brook is a 9.63 km2 tributary sub‐watershed within the Neversink Reservoir watershed. [ABSTRACT FROM AUTHOR]

The Buck Creek‐Boreas River Adirondack Watershed Monitoring Program, located in the Adirondack region of New York State, United States, combines the monitoring of headwater streams, soils, and vegetation based on a watershed design. Continuous monitoring of six watersheds is linked to the sampling of more than 400 additional Adirondack streams between 2003 and 2019 for chemical analysis of 14 constituents throughout the highly valued Adirondack ecoregion that covers an area of more than 24 000 km2. Much of this landscape has a low capacity for acid buffering, but due to spatial variation in geologic features, some areas are moderately to well acid buffered. This program includes data that extends back to the early 1980s and is ongoing. The focus of the program is on the watersheds of headwater Adirondack streams. Soil, vegetation and stream data are used to better understand environmental effects on the linkages of these ecosystem components. Documentation of the long‐term responses of Adirondack ecosystems to environmental disturbances such as acid rain, climate change and other unforeseen factors is the primary objective of the program. [ABSTRACT FROM AUTHOR]

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 SO 4 2− 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 SO 4 2−. Nevertheless, Ca2+ continued to be leached from soils by SO 4 2−, organic acids and NO 3 −, limiting the replenishment of available soil Ca2+, a prerequisite to stem further dilution of stream water. As recovery from acidic deposition proceeds slowly, chemical dilution of surface waters emerges as a key factor in the recovery process.Chemical records from 130 streams in the Adirondack region of New York show widespread decreases in conductance that are ongoing even as acidic deposition levels approach those estimated for the early 1900s.Further dilution is likely as release of SO 4 2− from soils at a gradually decreasing rate continues into the future. [Display omitted] • Chemical recovery from acidic deposition in Adirondack streams is widespread but incomplete. • Recovery remains slow despite atmospheric deposition nearing pre-industrial levels. • Dilution of stream chemistry is emerging as a key factor in recovery. • Accumulated effects of acidic deposition on soils are now driving dilution. • Dilution is slowing recovery by increasing dissolved organic carbon mobilization. [ABSTRACT FROM AUTHOR]

Mortality of brook trout Salvelinus fontinalis and water chemistry were characterized in 6 headwater streams in the western Adirondacks of New York during spring 2015, 2016, and 2017 and compared with results from analogous tests done between 1980 and 2003 in many of the same streams, to assess temporal changes in toxicity and inorganic monomeric aluminum (Ali) concentrations, and the role of Ali exposure duration on brook trout survival. The Ali concentrations of 2 and 4 µmol L–1 corresponded to low‐to‐moderate and high mortality thresholds, but prolonged exposure to ≥1 µmol Ali L–1 also produced mortality. The variability, mean, and highest Ali concentrations in Buck Creek year round, and in several other streams during spring, have decreased significantly over the past 3 decades. Logistic models indicate that Ali surpassed highly toxic concentrations in Buck Creek for 3 to 4 mo annually during 2001 to 2003 and for 2 to 3 wk annually during 2015 to 2017. The loss of extremely high Ali episodes indicates that toxicity has declined markedly between the 1989 to 1990, 2001 to 2003, and 2015 to 2017 test periods, yet Ali concentrations can still cause moderate‐to‐high and complete (100%) mortality. The logistic models illustrate how mortality of brook trout in several Adirondack streams likely decreased in response to the 1990 Amendments to the United States' Clean Air Act (which decreased acidity, Ali concentrations, and duration of toxic episodes) and offer a means to predict how changes in US regulations that limit emissions of NOx and SOx (and N and S deposition loads) could affect fish survival and stream ecosystems in this region and across the Northeast. Environ Toxicol Chem 2020;39:623–636. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Increasing pH and decreasing Al in surface waters recovering from acidification have been accompanied by increasing concentrations of dissolved organic carbon (DOC) and associated organic acids that partially offset pH increases and complicate assessments of recovery from acidification. To better understand the processes of recovery, monthly chemistry from 42 lakes in the Adirondack region, NY, collected from 1994 to 2011, were used to (1) evaluate long-term changes in DOC and associated strongly acidic organic acids and (2) use the base-cation surplus (BCS) as a chemical index to assess the effects of increasing DOC concentrations on the Al chemistry of these lakes. Over the study period, the BCS increased (p < 0.01) and concentrations of toxic inorganic monomeric Al (IMAl) decreased (p < 0.01). The decreases in IMAl were greater than expected from the increases in the BCS. Higher DOC concentrations that increased organic complexation of Al resulted in a decrease in the IMAl fraction of total monomeric Al from 57% in 1994 to 23% in 2011. Increasing DOC concentrations have accelerated recovery in terms of decreasing toxic Al beyond that directly accomplished by reducing atmospheric deposition of strong mineral acids. [ABSTRACT FROM AUTHOR]

Abstract: Limited stream chemistry and macroinvertebrate data indicate that acidic deposition has adversely affected benthic macroinvertebrate assemblages in numerous headwater streams of the western Adirondack Mountains of New York. No studies, however, have quantified the effects that acidic deposition and acidification may have had on resident fish and macroinvertebrate communities in streams of the region. As part of the Western Adirondack Stream Survey, water chemistry from 200 streams was sampled five times and macroinvertebrate communities were surveyed once from a subset of 36 streams in the Oswegatchie and Black River Basins during 2003–2005 and evaluated to: (a) document the effects that chronic and episodic acidification have on macroinvertebrate communities across the region, (b) define the relations between acidification and the health of affected species assemblages, and (c) assess indicators and thresholds of biological effects. Concentrations of inorganic Al in 66% of the 200 streams periodically reached concentrations toxic to acid-tolerant biota. A new acid biological assessment profile (acidBAP) index for macroinvertebrates, derived from percent mayfly richness and percent acid-tolerant taxa, was strongly correlated (R 2 values range from 0.58 to 0.76) with concentrations of inorganic Al, pH, ANC, and base cation surplus (BCS). The BCS and acidBAP index helped remove confounding influences of natural organic acidity and to redefine acidification-effect thresholds and biological-impact categories. AcidBAP scores indicated that macroinvertebrate communities were moderately or severely impacted by acidification in 44–56% of 36 study streams, however, additional data from randomly selected streams is needed to accurately estimate the true percentage of streams in which macroinvertebrate communities are adversely affected in this, or other, regions. As biologically relevant measures of impacts caused by acidification, both BCS and acidBAP may be useful indicators of ecosystem effects and potential recovery at the local and regional scale. [Copyright &y& Elsevier]

The article discusses a stream assessment in the Oswegatchie and Black River drainages. Acidification was investigated with the base-cation surplus (BCS) and the conventional acid-neutralizing capacity by Gran titration. Results showed that the contribution of acidic deposition to stream acidification was greater than that of strongly acidic organic acids in each of the surveys. The percentage attributed to acidic deposition during snowmelt was 81%, whereas the percentage was 66% during the October 2003 survey, when dissolved organic carbon concentrations were highest.

Presents a study on the use of stream chemistry for monitoring acidic deposition effects in the Adirondack Region of New York. Measurement of acid-neutralizing capacity (ANC) and hydrogen-ion concentration (pH) in several streams; Determination of the inverse correlation of ANC and pH with flow stream; Examination of residuals of the concentration-discharge relations.

A method for estimation of mean baseflow residence time in watersheds from hydrograph runoff recession characteristics was developed. Runoff recession characteristics were computed for the period 1993-96 in the 2 km² Winnisook watershed, Catskill Mountains, southeastern New York, and were used to derive mean values of subsurface hydraulic conductivity and the storage coefficient. These values were then used to estimate the mean baseflow residence time from an expression of the soil contact time, based on watershed soil and topographic characteristics. For comparison, mean baseflow residence times were calculated for the same period of time through the traditional convolution integral approach, which relates rainfall i[sup18]O to i[sup18]O values in streamflow. Our computed mean baseflow residence time was 9 months by both methods. These results indicate that baseflow residence time can be calculated accurately using recession analysis, and the method is less expensive than using environmental and/or artificial tracers. [ABSTRACT FROM AUTHOR]

Mobilization of toxic forms of aluminum (Al i) 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 Al i concentrations in surface waters starting in the 1990s. However, recent studies indicate that fish communities are still being impaired by elevated Al i 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 Al i 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 Al i (>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 Al i concentrations in 2018. Temporal decreases in Al i concentrations were due in part to a shift in speciation from Al i 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 Al i 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. • Toxic aluminum concentrations have continued to decline in Adirondack streams. • Toxic aluminum still occurs in 35% of western Adirondack streams during snowmelt. • Increases in dissolved organic carbon are reducing aluminum toxicity. • Recent rise in calcium availability is lowering toxic aluminum concentrations. • Rise in calcium availability is coincident with recent acid rain reductions. [ABSTRACT FROM AUTHOR]