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At least 55 records · Page 3Linked to original sources
USGS2016

Response of fish assemblages to declining acidic deposition in Adirondack Mountain lakes, 1984–2012

Adverse effects of acidic deposition on the chemistry and fish communities were evident in Adirondack Mountain lakes during the 1980s and 1990s. Fish assemblages and water chemistry in 43 Adirondack Long-Term Monitoring (ALTM) lakes were sampled by the Adirondack Lakes Survey Corporation and the New York State Department of Environmental Conservation during three periods (1984–87, 1994–2005, and 2008–12) to document regional impacts and potential biological recovery associated with the 1990 amendments to the 1963 Clean Air Act (CAA). We assessed standardized data from 43 lakes sampled during the three periods to quantify the response of fish-community richness, total fish abundance, and brook trout ( Salvelinus fontinalis) abundance to declining acidity that resulted from changes in U.S. air-quality management between 1984 and 2012. During the 28-year period, mean acid neutralizing capacity (ANC) increased significantly from 3 to 30 μeq/L and mean inorganic monomeric Al concentrations decreased significantly from 2.22 to 0.66 μmol/L, yet mean species richness, all species or total catch per net night (CPNN), and brook trout CPNN did not change significantly in the 43 lakes. Regression analyses indicate that fishery metrics were not directly related to the degree of chemical recovery and that brook trout CPNN may actually have declined with increasing ANC. While the richness of fish communities increased with increasing ANC as anticipated in several Adirondack lakes, observed improvements in water quality associated with the CAA have generally failed to produce detectable shifts in fish assemblages within a large number of ALTM lakes. Additional time may simply be needed for biological recovery to progress, or else more proactive efforts may be necessary to restore natural fish assemblages in Adirondack lakes in which water chemistry is steadily recovering from acidification.

New York↗
USGS2016

Increasing aeolian dust deposition to snowpacks in the Rocky Mountains inferred from snowpack, wet deposition, and aerosol chemistry

Mountain snowpacks are a vital natural resource for ∼1.5 billion people in the northern Hemisphere, helping to meet human and ecological demand for water in excess of that provided by summer rain. Springtime warming and aeolian dust deposition accelerate snowmelt, increasing the risk of water shortages during late summer, when demand is greatest. While climate networks provide data that can be used to evaluate the effect of warming on snowpack resources, there are no established regional networks for monitoring aeolian dust deposition to snow. In this study, we test the hypothesis that chemistry of snow, wet deposition, and aerosols can be used as a surrogate for dust deposition to snow. We then analyze spatial patterns and temporal trends in inferred springtime dust deposition to snow across the Rocky Mountains, USA, for 1993–2014. Geochemical evidence, including strong correlations (r 2 ≥ 0.94) between Ca 2+ , alkalinity, and dust concentrations in snow deposited during dust events, indicate that carbonate minerals in dust impart a strong chemical signature that can be used to track dust deposition to snow. Spatial patterns in chemistry of snow, wet deposition, and aerosols indicate that dust deposition increases from north to south in the Rocky Mountains, and temporal trends indicate that winter/spring dust deposition increased by 81% in the southern Rockies during 1993–2014. Using a multivariate modeling approach, we determined that increases in dust deposition and decreases in springtime snowfall combined to accelerate snowmelt timing in the southern Rockies by approximately 7–18 days between 1993 and 2014. Previous studies have shown that aeolian dust emissions may have doubled globally during the 20th century, possibly due to drought and land-use change. Climate projections for increased aridity in the southwestern U.S., northern Africa, and other mid-latitude regions of the northern Hemisphere suggest that aeolian dust emissions may continue to increase, compounding the risk that climate warming poses to snowpack water resources in arid/semi-arid regions of the world.

Atmospheric Environment↗
USGS2016

Atmospheric inputs of organic matter to a forested watershed: Variations from storm to storm over the seasons

The objectives of this study were to determine the quantity and chemical composition of precipitation inputs of dissolved organic carbon (DOC) to a forested watershed; and to characterize the associated temporal variability. We sampled most precipitation that occurred from May 2012 through August 2013 at the Susquehanna Shale Hills Critical Zone Observatory (Pennsylvania, USA). Sub-event precipitation samples (159) were collected sequentially during 90 events; covering various types of synoptic meteorological conditions in all climatic seasons. Precipitation DOC concentrations and rates of wet atmospheric DOC deposition were highly variable from storm to storm, ranging from 0.3 to 5.6 mg C L −1 and from 0.5 to 32.8 mg C m −2 h −1 , respectively. Seasonally, storms in spring and summer had higher concentrations of DOC and more optically active organic matter than in winter. Higher DOC concentrations resulted from weather types that favor air advection, where cold frontal systems, on average, delivered more than warm/stationary fronts and northeasters. A mixed modeling statistical approach revealed that factors related to storm properties, emission sources, and to the chemical composition of the atmosphere could explain more than 60% of the storm to storm variability in DOC concentrations. This study provided observations on changes in dissolved organic matter that can be useful in modeling of atmospheric oxidative chemistry, exploring relationships between organics and other elements of precipitation chemistry, and in considering temporal changes in ecosystem nutrient balances and microbial activity.

Atmospheric Environment↗
USGS2016

Acid rain and its environmental effects: Recent scientific advances

The term ‘acid rain’ refers to atmospheric deposition of acidic constituents that impact the earth as rain, snow, particulates, gases, and vapor. Acid rain was first recognized by Ducros (1845) and subsequently described by the English chemist Robert Angus Smith (Smith, 1852) whose pioneering studies linked the sources to industrial emissions and included early observations of deleterious environmental effects (Smith, 1872). Smith's work was largely forgotten until the mid-20th century when observations began to link air pollution to the deposition of atmospheric sulfate (SO 4 2− ) and other chemical constituents, first near the metal smelter at Sudbury, Ontario, Canada, and later at locations in Europe, North America, and Australia (Gorham, 1961). Our modern understanding of acid rain as an environmental problem caused largely by regional emissions of sulfur dioxide (SO 2 ) and nitrogen oxides (NO x ) stems from observations in the 1960s and early 1970s in Sweden by Svante Odén (Odén, 1976), and in North America by Gene Likens and colleagues (Likens and Bormann, 1974). These scientists and many who followed showed the link to emissions from coal-fired power plants and other industrial sources, and documented the environmental effects of acid rain such as the acidification of surface waters and toxic effects on vegetation, fish, and other biota.

Atmospheric Environment↗
USGS2018

Spatial and temporal variation in sources of atmospheric nitrogen deposition in the Rocky Mountains using nitrogen isotopes

Variation in source areas and source types of atmospheric nitrogen (N) deposition to high-elevation ecosystems in the Rocky Mountains were evaluated using spatially and temporally distributed N isotope data from atmospheric deposition networks for 1995-2016. This unique dataset links N in wet deposition and snowpack to mobile and stationary emissions sources, and enhances understanding of the impacts of anthropogenic activities and environmental policies that mitigate effects of accelerated N cycling across the Rocky Mountain region. δ 15 N−NO 3 − at 50 U.S. Geological Survey Rocky Mountain Snowpack (Snowpack) sites ranged from −3.3‰ to +6.5‰, with a mean value of +1.4‰. At 15 National Atmospheric Deposition Program (NADP)/National Trends Network wet deposition (NADP Wetfall) sites, summer δ 15 N−NO 3 − is significantly lower ranging from −7.6‰ to −1.3‰ while winter δ 15 N−NO 3 − ranges from −2.6‰ to +5.5‰, with a mean value of +0.7‰ during the cool season. The strong seasonal difference in NADP Wetfall δ 15 N−NO 3 − is due in part to variation in the proportion of N originating from source regions at different times of the year due to seasonal changes in weather patterns. Snowpack NO 3 − and δ 15 N−NO 3 − are significantly related to NADP Wetfall (fall and winter) suggesting that bulk snowpack samples provide a reliable estimate at high elevations. Spatial trends show higher NO 3 − concentrations and δ 15 N−NO 3 − in the Southern Rocky Mountains located near larger anthropogenic N emission sources compared to the Northern Rocky Mountains. NADP Wetfall δ 15 N−NH 4 + ranged from −10‰ to 0‰, with no observed spatial pattern. However, the lowest δ 15 N−NH 4 + (−9‰), and the highest NH 4 + concentration (35 μeq/L) were observed at a Utah site dominated by local agricultural activities, whereas the higher δ 15 N−NH 4 + observed in Colorado and Wyoming are likely due to mixed sources, including fossil fuel combustion and agricultural sources. These findings show spatial and seasonal variation in N isotope data that reflect differences in sources of anthropogenic N deposition to high-elevation ecosystems and have important implications for environmental policy across the Rocky Mountain region.

Rocky Mountains↗
USGS2018

Iron dissolution and speciation in atmospheric mineral dust: Metal-metal synergistic and antagonistic effects

Under acidic atmospheric conditions, iron leached from atmospheric mineral dust may influence the distribution of bioavailable iron at a global scale. However, the effects of non-Fe-containing minerals on iron dissolution remain unknown. This work describes metal-metal synergistic and antagonistic effects on iron dissolution that go beyond aggregation and ionic strength effects in mineral dust mixtures. In this study, we investigated iron mobilization by proton-promoted dissolution in natural mineral dust samples from the Kalahari Desert (SZ1) and Australian Red Dawn event (RO), along with one iron oxide proxy, hematite. The total iron dissolution in natural dust samples highly corresponds with the respective amount of Ti, rather than their particle sizes or Fe contents. The dust sample with high Ti content, SZ1, also showed a higher fraction of dissolved Fe(II), under dark conditions. These observations are in good agreement with the dissolution data for hematite artificially mixed with metal oxides. Total iron dissolution in hematite, mixed with TiO 2 , is 1.5- and 2-fold higher compared to that of just hematite under dark and light conditions, respectively. However, dissolution of hematite is suppressed when mixed with Al 2 O 3 and CaO. Under dark conditions, furthermore, dissolved Fe(II) fraction is enhanced for hematite when mixed with TiO 2 compared to that of other mixtures or hematite alone. Yet, dissolved Fe(II) is lower in hematite mixed with TiO 2 under light conditions compared to that of hematite alone, suggesting photo-oxidation of Fe(II) by reactive oxygen species, such as OH radicals.

Atmospheric Environment↗
USGS2019

Bioavailable iron production in airborne mineral dust: Controls by chemical composition and solar flux

A large part of oceanic biological production is limited by the scarcity of dissolved iron. Mineral dust aerosol , processed under acidic atmospheric conditions , is the primary natural source of bioavailable iron to oceanic life. However, synergistic and antagonistic effects of non-Fe-containing minerals on atmospheric processing of Fe-containing minerals and Fe solubilization are poorly understood. The current study focuses on mineralogical influences of non-Fe-bearing semiconductor minerals, such as titanium dioxide (TiO 2 ), on the dissolution of iron in selected natural mineral dust aerosols under atmospherically relevant conditions. Further, the role of elevated Ti concentrations in dust is evaluated using magnetite , a proxy for Fe(II) containing minerals, under both dark and light conditions. Our results highlight that relatively higher Ti:Fe ratios, regardless of their total Fe content, enhances the total iron dissolution in mineral dust aerosols as well as in magnetite. Moreover, elevated Ti percentages also yield high Fe(II) fractions in mineral dust systems under dark conditions. Upon irradiation however, dissolved Fe(II) is suppressed by high Ti levels due to the involvement of photochemical redox cycling reactions with hydroxyl radicals ( • OH). These synergistic and antagonistic effects of Ti are further evaluated by altering the chemical composition of natural dusts with artificially added anatase (TiO 2 ) and synthetic amorphous titania . The current study reveals important mineralogical controls by non-Fe-bearing minerals on dust iron dissolution to better understand global iron mobilization.

Atmospheric Environment↗
USGS2019

Air pollution and respiratory hospital admissions in Shiraz, Iran, 2009 to 2015

Air pollution has been identified as one of the most challenging health issues in urban areas worldwide. The aim of this study was to investigate the association between short-term exposure to ambient air pollution and respiratory disease over a long-term period in Shiraz, one of the largest cities in Iran. Methods: hospital admissions due to respiratory diseases (asthma, pneumonia, chronic obstructive pulmonary disease(COPD) and pleural effusion) in residents of Shiraz between March 21, 2009 and March 20, 2015 were included. Demographics for each patient and meta data to include principal meteorological variables (temperature and relative humidity) and five ambient pollutants (CO, O 3 , SO 2 , NO 2 , and PM 10 ) were also included. Statistical analysis was performed by Poisson regression in single-pollutant generalized linear model with principal component analysis (GLPCA) to analyze the relationship between pollutants and hospital admissions at the 0–9 cumulative lag day period. Pearson correlation test was used to determine the relationship between different pollutants, temperature and humidity. Results It was found that the highest increase in asthma admission was related to PM 10 (relative risk (RR) = 1.31, 95% CI = 1.17, 1.47). For COPD, the rate of hospital visits significantly increased with the increase in NO 2 concentration (RR = 1.17, 95% CI = 1.09.1.27). In the children's hospital, O 3 (RR = 1.25, 95% CI = 1.06, 1.47) and SO 2 (RR = 1.17, 95% CI = 1.07, 1.28) affected the asthma admissions and all contaminants (highest RR observed was for NO 2 (RR = 1.28 95% CI = 1.18, 1.40) affected pneumonia admissions on cumulative lag days of 0–9. Conclusions: These data confirm an association between ambient air pollutants and hospital admissions due to respiratory disease.

Shiraz↗
USGS2021

Trends in precipitation chemistry across the U.S. 1985–2017: Quantifying the benefits from 30 years of Clean Air Act amendment regulation

Acid rain was first recognized in the 1970s in North America and Europe as an atmospheric pollutant that was causing harm to ecosystems. In response, the U.S. Congress enacted Title IV of the Clean Air Act Amendments (CAA) in 1990 to reduce sulfur and nitrogen emissions from fossil fuel burning power plants. This study reports trends in wet-precipitation chemistry in response to emissions reductions implemented as part of the CAA. Trends were calculated for sulfate (SO 4 ), nitrate (NO 3 ) and ammonium (NH 4 ) from 1985 to 2017 at 168 stations operated by the National Atmospheric Deposition Program (NADP); stations were divided into 9 regions across the United States. Trend analyses were conducted for three time periods: Period 1 (1985–1999), Period 2 (2000–2017), and the entire study period (1985–2017). Seasonal and regional Kendall trend analyses reveal significant decreasing trends in mean wet-precipitation SO 4 concentrations in all 9 regions during the entire study period. The largest decreasing trends in monthly mean SO 4 precipitation-weighted concentrations were measured in the Mid-Atlantic (−1.29 μeq/l/yr), Midwest (−1.15 μeq/l/yr), and Northeast regions (−1.10 μeq/l/yr). The trends in monthly mean NO 3 concentrations were not as strong as those for SO 4 , but all of the regions had significant decreasing trends in NO 3 and again the Mid-Atlantic (−0.53 μeq/l/yr), Midwest (−0.44 μeq/l/yr), and Northeast regions (−0.50 μeq/l/yr) had the strongest trends. Trends were steepest during Period 2 for SO 4 and NO 3 , in fact for NO 3 86% of the stations had significant decreasing trends during Period 2 while only 8% of the stations had significant decreasing trends during Period 1. The stations with the highest concentrations of SO 4 and NO 3 at the beginning of the study had the strongest decreasing trends and the relations were stronger during Period 2 than Period 1. For NH 4 , 22% of the stations had statistically significant increasing trends in concentration during Period 1. The largest increasing trends in wet-precipitation NH 4 concentration occurred in the North-Central region during Period 1, Period 2 and throughout the entire study. By comparison, NH 4 trends in the Rocky-North and Rocky-South regions were about half as steep and trends in the South-Central and Midwest regions were about one-third as steep. We compared trends in SO 4 and NO 3 concentrations from NADP stations to emissions of sulfur dioxide and nitrogen oxides, respectively to determine whether there was a relation between emissions and wet-precipitation concentration trends within proximity to NADP stations. There was a statistically significant relation (r 2 = 0.62–0.69, p < 0.01) between the trend in SO 4 concentrations at individual NADP stations and total and mean sulfur dioxide (SO 2 ) emissions from power plants within a range of 750 km and 1000 km from each station. There were also significant relations between NO 3 concentration trends at NADP stations and power plant emissions of nitrogen oxides, but they were not nearly as strong (r 2 = 0.18–0.36, p < 0.01) as those for SO 4 and were strongest for emissions within a range of 1000 km and 1500 km from each NADP station. Decreases in wet-precipitation SO 4 concentrations were more consistent across regions and through time than decreases in NO 3 and SO 4 trends were more closely linked to stationary emissions sources than NO 3 trends. There were statistically significant increases in NH 4 wet-precipitation concentrations, as have been reported in previous studies, but this study found that those increases were strongest during Period 1 and were not consistent across the United States. During the first 3 years of the study period, wet-precipitation acidity was dominated by SO 4 in 8 of the 9 regions; by 2017 NO 3 dominated the acidity of wet-precipitation in 7 of the 9 regions. There has also been a downward shift in the NO 3 :NH 4 ratio of wet-precipitation as the emissions of nitrogen oxides have declined while ammonia emissions have remained essentially constant. This shift has resulted in an increase in wet-precipitation total nitrogen concentrations in 7 of the 9 regions and indicate that efforts to control NH 3 emissions will become increasingly important as emissions of nitrogen oxides continue to decline.

Atmospheric Environment↗
USGS2021

Biological and chemical recovery of acidified Catskill Mountain streams in response to the Clean Air Act Amendments of 1990

Decades of acidic deposition have adversely affected aquatic and terrestrial ecosystems in acid-sensitive watersheds in parts of the eastern United States. The national Acid Rain Program (Title IV of the 1990 Clean Air Act Amendments - CAAA) helped reduce emissions of sulfur dioxide (SO 2 ) and nitrogen oxides (NO x ) and resulted in sharp decreases in the acidity of atmospheric deposition. The decrease in acidic deposition produced a steady decline in the acidity of streams in many poorly buffered waters across the western Adirondacks and parts of the Catskill Mountains of New York. Until recently, however, there has been little evidence of biological recovery in most acid-sensitive streams in both regions. Long-term deposition and stream-chemistry records and fish-community data from quantitative surveys done during 1991–93 and again during 2012–19 at 13 sites in the upper Neversink River and its tributaries were evaluated to determine if chemical and biological recovery were evident in this Catskill Mountain watershed and if they could be linked to regional declines in acidic deposition. Between 1991 and 2019, large decreases in sulfate and nitrate deposition in the basin mirrored declines in total nationwide SO 2 and NO x emissions. There were corresponding decreases in sulfate and nitrate concentrations in deposition at a National Trends Network station at Frost Valley (NY68) and coincident declines in sulfate concentrations at four long-term monitoring sites in the Neversink River watershed. Mean acid neutralizing capacity and pH increased and inorganic aluminum (Al i ) concentrations from routine summertime samples decreased significantly at most moderately to severely acidified sites between the two study periods. Richness, density, and biomass of fish communities increased at most sites, while the density and biomass of brook trout Salvelinus fontinalis populations increased at fewer sites that were undergoing chemical recovery. Although recovery is far from complete, trends in deposition chemistry, water quality, and fish assemblages in streams of the upper Neversink watershed indicate that the 1990 CAAA is having positive impacts on aquatic ecosystems in the Catskill Mountain region, New York.

New York↗
USGS2021

Atmospheric nitrogen deposition in the Chesapeake Bay watershed: A history of change

The Chesapeake Bay watershed has been the focus of pioneering studies of the role of atmospheric nitrogen (N) deposition as a nutrient source and driver of estuarine trophic status. Here, we review the history and evolution of scientific investigations of the role of atmospheric N deposition, examine trends from wet and dry deposition networks, and present century-long (1950–2050) atmospheric N deposition estimates. Early investigations demonstrated the importance of atmospheric deposition as an N source to the Bay, providing 25%–40% among all major N sources. These early studies led to the unprecedented inclusion of targeted decreases in atmospheric N deposition as part of the multi-stakeholder effort to reduce N loads to the Bay. Emissions of nitrogen oxides (NO x ) and deposition of wet nitrate, oxidized dry N, and dry ammonium (NH 4 + ) sharply and synchronously declined by 60%–73% during 1995–2019. These decreases largely resulted from implementation of Title IV of the 1990 Clean Air Act Amendments, which began in 1995. Wet NH 4 + deposition shows no significant trend during this period. The century-long atmospheric N deposition estimates indicate an increase in total atmospheric N deposition in the Chesapeake watershed from 1950 to a peak of ~15 kg N/ha/yr in 1979, trailed by a slight decline of <10% through the mid-1990s, and followed by a sharp decline of about 40% thereafter through 2019. An additional 21% decline in atmospheric N deposition is projected from 2015 to 2050. A comparison of the Potomac River and James River watersheds indicates higher atmospheric N deposition in the Potomac, likely resulting from greater emissions from higher proportions of agricultural and urban land in this basin. Atmospheric N deposition rose from 30% among all N sources to the Chesapeake Bay watershed in 1950 to a peak of 40% in 1973, and a decline to 28% by 2015. These data highlight the important role of atmospheric N deposition in the Chesapeake Bay watershed and present a potential opportunity for decreases in deposition to contribute to further reducing N loads and improving the trophic status of tidal waters.

New York, New Jersey, Delaware, Maryland, Pennsylv↗
USGS2020

Recognition of typical antibiotic residues in environmental media related to groundwater in China (2009−2019)

The potential adverse environmental and health-related impacts of antibiotics are becoming more and more concerning. China is globally the largest antibiotic producer and consumer, possibly resulting in the ubiquity and high detection levels of antibiotics in environmental compartments. Clear status on the concentration levels and spatial distribution of antibiotic contamination in China's environment is necessary to gain insight into the establishment of legal and regulatory frameworks. This study collects information from over 170 papers reporting the occurrence and distribution of antibiotics in China's environment. A total of 110 antibiotics were detected, and 28 priority antibiotics were ubiquitous in China in almost all compartments of the environment, excluding the atmosphere. Seven dominant antibiotics in all environment compartments were identified by cluster analysis, including tetracycline, oxytetracycline, chlortetracycline, ofloxacin, enrofloxacin, norfloxacin, and ciprofloxacin. Meanwhile, sulfamethoxazole, sulfadiazine, and sulfamethazine were also frequently found in aqueous phases. Among the main basins where antibiotics were detected, the Haihe River Basin had higher median antibiotic concentrations in surface water compared to other basins, while the Huaihe River Basin had higher median concentrations in sediment. The median values of antibiotic concentrations in the sources were as follows: animal manure, 39 μg/kg (microgram per kilogram); WWTP (wastewater treatment plant) sludge, 39 μg/kg; animal wastewater, 156 ng/L (nanogram per liter); WWTP effluent: 15 ng/L. These concentrations are 1 − 2 orders of magnitude higher than that of the receptors (soil, 2.1 μg/kg; sediment, 4.7 μg/kg; surface water, 8.1 ng/L; groundwater, 2.9 ng/L), whether in solid or aqueous phases. Based on the number of detected antibiotics in various environmental compartments, animal farms and WWTPs are the main sources of antibiotics, and surface water and sediment are the main receptors of antibiotics. Hierarchical clustering identified the two main pathways of antibiotic transfer in various environmental compartments, which are from animal wastewater/WWTP effluent to surface water/sediment and from animal manure/WWTP sludge to soil/groundwater.

Journal of Hazardous Materials↗
USGS2001

Dry deposition of ammonia, nitric acid, ammonium, and nitrate to alpine tundra at Niwot Ridge, Colorado

Micrometeorological measurements and ambient air samples, analyzed for concentrations of NH3, HNO3, NH4+, and NO3-, were collected at an alpine tundra site on Niwot Ridge, Colorado. The measured concentrations were extremely low and ranged between 5 and 70ngNm-3. Dry deposition fluxes of these atmospheric species were calculated using the micrometeorological gradient method. The calculated mean flux for NH3 indicates a net deposition to the surface and indicates that NH3 contributed significantly to the total N deposition to the tundra during the August-September measurement period. Our pre-measurement estimate of the compensation point for NH3 in air above the tundra was 100-200ngNm-3; thus, a net emission of NH3 was expected given the low ambient concentrations of NH3 observed. Based on our results, however, the NH3 compensation point at this alpine tundra site appears to have been at or below about 20ngNm-3. Large deposition velocities (>2cms-1) were determined for nitrate and ammonium and may result from reactions with surface-derived aerosols. Copyright (C) 2001 Elsevier Science B.V.Micrometeorological measurements and ambient air samples, analyzed for concentrations of NH3, HNO3, NH4+, and NO3-, were collected at an alpine tundra site on Niwot Ridge, Colorado. The measured concentrations were extremely low and ranged between 5 and 70 ng N m-3. Dry deposition fluxes of these atmospheric species were calculated using the micrometeorological gradient method. The calculated mean flux for NH3 indicates a net deposition to the surface and indicates that NH3 contributed significantly to the total N deposition to the tundra during the August-September measurement period. Our pre-measurement estimate of the compensation point for NH3 in air above the tundra was 100-200 ng N m-3; thus, a net emission of NH3 was expected given the low ambient concentrations of NH3 observed. Based on our results, however, the NH3 compensation point at this alpine tundra site appears to have been at or below about 20 ng N m-3. Large deposition velocities (>2 cm s-1) were determined for nitrate and ammonium and may result from reactions with surface-derived aerosols.

Atmospheric Environment↗
USGS2001

Use of stable sulfur isotopes to identify sources of sulfate in Rocky Mountain snowpacks

Stable sulfur isotope ratios and major ions in bulk snowpack samples were monitored at a network of 52 high-elevation sites along and near the Continental Divide from 1993 to 1999. This information was collected to better define atmospheric deposition to remote areas of the Rocky Mountains and to help identify the major source regions of sulfate in winter deposition. Average annual ??34S values at individual sites ranged from + 4.0 to + 8.2??? and standard deviations ranged from 0.4 to 1.6???. The chemical composition of all samples was extremely dilute and slightly acidic; average sulfate concentrations ranged from 2.4 to 12.2 ??eql-1 and pH ranged from 4.82 to 5.70. The range of ??34S values measured in this study indicated that snowpack sulfur in the Rocky Mountains is primarily derived from anthropogenic sources. A nearly linear relation between ??34S and latitude was observed for sites in New Mexico, Colorado, and southern Wyoming, which indicates that snowpack sulfate in the southern part of the network was derived from two isotopically distinct source regions. Because the major point sources of SO2 in the region are coal-fired powerplants, this pattern may reflect variations in the isotopic composition of coals burned by the plants. The geographic pattern in ??34S for sites farther to the north in Wyoming and Montana was much less distinct, perhaps rflecting the paucity of major point sources of SO2 in the northern part of the network.

Atmospheric Environment↗
USGS2001

Nitric acid dry deposition to conifer forests: Niwot Ridge spruce-fir-pine study

The dry deposition velocity of nitric acid, Vd(HNO3), over a 12-m (mean height) spruce-fir forest at Niwot Ridge, Colorado was estimated during 13 daytime periods using the flux-gradient approach. Turbulence intensity at this site is high (mean u* of 0.65ms-1 with u of 2.9ms-1) and contributed to the large observed Vd(HNO3). The overriding contributor is identified to be the small aerodynamic needle width of the conifer trees. Two cases had inflated Vd(HNO3) due to height-differentiated nitric acid loss to soil-derived particle surfaces. Not considering these cases, the mean Vd(HNO3) was 7.6cms-1. The mean laminar boundary layer resistance (Rb) was found to be 7.8sm-1 (of similar magnitude to that of the aerodynamic resistance, 8.5sm-1). The data-determined Rb is bracketed by two theoretical estimates of the mean Rb, 5.9 and 8.6sm-1, that include consideration of the small canopy length scale (aerodynamic needle width), 1mm or less, at this conifer forest. However, the poor correlation of data-determined Rb values with both sets of theoretical estimates indicates that measurement error needs to be reduced and/or improved formulations of theoretical Rb values are in order. The large observed Vd(HNO3) at this conifer forest site is attributed to high turbulence intensity, and, especially, to small aerodynamic needle width. Copyright ?? 2001 Elsevier Science Ltd.

Atmospheric Environment↗
USGS2001

Major-ion chemistry of the Rocky Mountain snowpack, USA

During 1993-97, samples of the full depth of the Rocky Mountain snowpack were collected at 52 sites from northern New Mexico to Montana and analyzed for major-ion concentrations. Concentrations of acidity, sulfate, nitrate, and calcium increased from north to south along the mountain range. In the northern part of the study area, acidity was most correlated (negatively) with calcium. Acidity was strongly correlated (positively) with nitrate and sulfate in the southern part and for the entire network. Acidity in the south exceeded the maximum acidity measured in snowpack of the Sierra Nevada and Cascade Mountains. Principal component analysis indicates three solute associations we characterize as: (1) acid (acidity, sulfate, and nitrate), (2) soil (calcium, magnesium, and potassium), and (3) salt (sodium, chloride, and ammonium). Concentrations of acid solutes in the snowpack are similar to concentrations in nearby wetfall collectors, whereas, concentrations of soil solutes are much higher in the snowpack than in wetfall. Thus, dryfall of acid solutes during the snow season is negligible, as is gypsum from soils. Snowpack sampling offers a cost-effective complement to sampling of wetfall in areas where wetfall is difficult to sample and where the snowpack accumulates throughout the winter. Copyright ?? 2001 .

Atmospheric Environment↗
USGS2002

Comparison of snowpack and winter wet-deposition chemistry in the Rocky Mountains, USA: Implications for winter dry deposition

Depth-integrated snowpack chemistry was measured just prior to maximum snowpack depth during the winters of 1992-1999 at 12 sites co-located with National Atmospheric Deposition Program/National Trend Network (NADP/NTN) sites in the central and southern Rocky Mountains, USA. Winter volume-weighted mean wet-deposition concentrations were calculated for the NADP/NTN sites, and the data were compared to snowpack concentrations using the paired t-test and the Wilcoxon signed-rank test. No statistically significant differences were indicated in concentrations of SO42- or NO3- (p>0.1). Small, but statistically significant differences (p???0.03) were indicated for all other solutes analyzed. Differences were largest for Ca2+ concentrations, which on average were 2.3??eql-1 (43%) higher in the snowpack than in winter NADP/NTN samples. Eolian carbonate dust appeared to influence snowpack chemistry through both wet and dry deposition, and the effect increased from north to south. Dry deposition of eolian carbonates was estimated to have neutralized an average of 6.9??eql-1 and a maximum of 12??eql-1 of snowpack acidity at the southernmost sites. The good agreement between snowpack and winter NADP/NTN SO42- and NO3- concentrations indicates that for those solutes the two data sets can be combined to increase data density in high-elevation areas, where few NADP/NTN sites exist. This combination of data sets will allow for better estimates of atmospheric deposition of SO42- and NO3- across the Rocky Mountain region.

Atmospheric Environment↗
USGS2003

Atmospheric nitrogen deposition in the Rocky Mountains of Colorado and southern Wyoming - A review and new analysis of past study results

The Rocky Mountain region of Colorado and southern Wyoming receives as much as 7kgha-1yr-1 of atmospheric nitrogen (N) deposition, an amount that may have caused changes in aquatic and terrestrial life in otherwise pristine ecosystems. Results from published studies indicate a long-term increase in the rate of atmospheric N deposition during the 20th century, but data from the National Atmospheric Deposition Program and Clean Air Status and Trends Network show no region-wide increase during the past 2 decades. Nitrogen loads in atmospheric wet deposition have increased since the mid-1980s, however, at three high elevation (>3000m) sites east of the Continental Divide in the Front Range. Much of this increase is the result of increased ammonium (NH4+) concentrations in wet deposition. This suggests an increase in contributions from agricultural areas or from vehicles east of the Rocky Mountains and is consistent with the results of previous studies that have suggested a significant eastern source for atmospheric N deposition to the Front Range. The four sites with the highest NH4+ concentrations in wet deposition were among the six easternmost NADP sites, which is also consistent with a source to the east of the Rockies. This analysis found an increase in N loads in wet deposition at Niwot Ridge of only 0.013kgha-1yr-1, more than an order of magnitude less than previously reported for this site. This lower rate of increase results from application of the non-parametric Seasonal Kendall trend test to mean monthly data, which failed a test for normality, in contrast to linear regression, which was applied to mean annual data in a previous study. Current upward trends in population growth and energy use in Colorado and throughout the west suggest a need for continued monitoring of atmospheric deposition of N, and may reveal more widespread trends in N deposition in the future.

Atmospheric Environment↗