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At least 19 recordsLinked to original sources
USGS2005

Laboratory determination of the carbon kinetic isotope effects (KIEs) for reactions of methyl halides with various nucleophiles in solution

Large carbon kinetic isotope effects (KIEs) were measured for reactions of methyl bromide (MeBr), methyl chloride (MeCl), and methyl iodide (MeI) with various nucleophiles at 287 and 306 K in aqueous solutions. Rates of reaction of MeBr and MeI with H 2 O (neutral hydrolysis) or Cl − (halide substitution) were consistent with previous measurements. Hydrolysis rates increased with increasing temperature or pH (base hydrolysis). KIEs for hydrolysis were 51 ± 6% 0 for MeBr and 38 ± 8% 0 for MeI. Rates of halide substitution increased with increasing temperature and greater reactivity of the attacking nucleophile, with the fastest reaction being that of MeI with Br − . KIEs for halide substitution were independent of temperature but varied with the reactant methyl halide and the attacking nucleophile. KIEs were similar for MeBr substitution with Cl − and MeCl substitution with Br − (57 ± 5 and 60 ± 9% 0 , respectively). The KIE for halide exchange of MeI was lower overall (33 ± 8% 0 ) and was greater for substitution with Br − (46 ± 6% 0 ) than with Cl − (29 ± 6% 0 ).

Journal of Atmospheric Chemistry↗
USGS1994

Vapor saturation and accumulation in magmas of the 1989-1990 eruption of Redoubt Volcano, Alaska

The 1989–1990 eruption of Redoubt Volcano, Alaska, provided an opportunity to compare petrologic estimates of SO 2 and Cl emissions with estimates of SO 2 emissions based on remote sensing data and estimates of Cl emissions based on plume sampling. In this study, we measure the sulfur and chlorine contents of melt inclusions and matrix glasses in the eruption products to determine petrologic estimates of SO 2 and Cl emissions. We compare the results with emission estimates based on COSPEC and TOMS data for SO 2 and data for Cl/SO 2 in plume samples. For the explosive vent clearing period (December 14–22, 1989), the petrologic estimate for SO 2 emission is 21,000 tons, or ~12% of a TOMS estimate of 175,000 tons. For the dome growth period (December 22, 1989 to mid-June 1990), the petrologic estimate for SO 2 emission is 18,000 tons, or ~3% of COSPEC-based estimates of 572,000–680,000 tons. The petrologic estimates give a total SO 2 emission of only 39,000 tons compared to an integrated TOMS/COSPEC emission estimate of ~1,000,000 tons for the whole eruption, including quiescent degassing after mid-June 1990. Petrologic estimates also appear to underestimate Cl emissions, but apparent HCl scavenging in the plume complicates Cl emission comparisons. Several potential sources of ‘excess sulfur’ often invoked to explain petrologic SO 2 deficits are concluded to be unlikely for the 1989–1990 Redoubt eruption — e.g., breakdown of sulfides, breakdown of anhydrite, release of SO 2 from a hydrothermal system, degassing of commingled infusions of basalt in the magma chamber, and syn-eruptive degassing of sulfur from melt present in non-erupted magma. Leakage and/or diffusion of sulfur from melt inclusions do not provide convincing explanations for the petrologic SO 2 deficits either. The main cause of low petrologic estimates for SO 2 is that melt inclusions do not represent the total sulfur content of the Redoubt magmas, which were vapor-saturated magmas carrying most of their sulfur in an accumulated vapor phase. Almost all the sulfur of the SO 2 emissions was present prior to emission as accumulated magmatic vapor at 6–10 km depth in the magma that supplied the eruption; whole-rock normalized concentrations of gaseous excess S in these magmas remained at ~0.2 wt.% throughout the eruption, equivalent to ~0.7 vol.% at depth. Data for CO 2 emissions during the eruption indicate that CO 2 at whole-rock concentrations of ~0.6 wt.% in the erupted magma was a key factor in creating the vapor saturation and accumulation condition making a vapor phase source of excess sulfur possible at depth. When explosive volcanism involves magma with accumulated vapor, melt inclusions do not provide a sufficient basis for predicting SO 2 emissions. Thus, petrologic estimates made for SO 2 emissions during explosive eruptions of the past may be too low and may significantly underestimate impacts on climate and the chemistry of the atmosphere.

Journal of Volcanology and Geothermal Research↗
USGS2001

Effect of canopy removal on snowpack quantity and quality, fraser experimental forest, Colorado

Snowpack peak water equivalent (PWE), ion concentration, content, and spatial distribution of ion load data from spring 1987-1996 in a 1 ha clearcut and adjacent forested plots vegetated by mature Picea engelmannii and Abies lasiocarpa in the Fraser experimental forest (FEF), Colorado are presented. Our objectives were: (1) to see if a forest opening might redistribute snowfall, snowpack moisture, and snowpack chemical content, and (2) to examine the importance of canopy interception on snowpack quantity and chemistry. On an average, the canopy intercepted 36% of snowfall. Interception was correlated with snowfall amount, snowpack PWE beneath the canopy, and air temperature. Canopy removal increased snowpack PWE to >90% cumulative snowfall inputs. Snowpack K-, H-, and NH4+ concentrations on the clearcut were lower and NO3- higher than in the snowpack beneath the forested plots. Cu mulative snowfall K+ input was less than in the clearcut snowpack; H+ inputs were greater in snowfall than in the snowpack of any plot; and inorganic N (NO3- and NH4+) inputs from snowfall to the clearcut were greater than to the forested plots. Processes accounting for the differences between snowfall inputs and snowpack ion content were leaching of organic debris in the snowpack, differential elution of the snowpack, and canopy retention. There were significant trends by year in snowpack ion content at PWE without similar trends in snowfall inputs. This finding coupled with snowpack ion elution bring into question the use of snowpack chemistry as an indicator of winter atmospheric inputs in short-term studies. ?? 2001 Elsevier Science B.V.

Journal of Hydrology↗
USGS2013

Accumulation of atmospheric sulfur in some Costa Rican soils

Sulfur is one of the macronutrient elements whose sources to terrestrial ecosystems should shift from dominance by rock-weathering to atmospheric deposition as soils and underlying substrate undergo progressive weathering and leaching. However, the nature and timing of this transition is not well known. We investigated sources of sulfur to tropical rain forests growing on basalt-derived soils in the Osa Peninsula region of Costa Rica. Sulfur sources were examined using stable isotope ratios (δ 34 S) and compared to chemical indices of soil development. The most weathered soils, and the forests they supported, are dominated by atmospheric sulfur, while a less weathered soil type contains both rock-derived and atmospheric sulfur. Patterns of increasing δ 34 S with increasing soil sulfur concentration across the landscape suggest atmospheric sulfur is accumulating, and little rock-derived sulfur has been retained. Soil sulfur, minus adsorbed sulfate, is correlated with carbon and nitrogen, implying that sulfur accumulation occurs as plants and microbes incorporate sulfur into organic matter. Only the lower depth increments of the more weathered soils contained significant adsorbed sulfate. The evidence suggests a pattern of soil development in which sulfur-bearing minerals in rock, such as sulfides, weather early relative to other minerals, and the released sulfate is leached away. Sulfur added via atmospheric deposition is retained as organic matter accumulates in the soil profile. Adsorbed sulfate accumulates later, driven by changes in soil chemistry and mineralogy. These aspects of sulfur behavior during pedogenesis in this environment may hasten the transition to dominance by atmospheric sources.

Journal of Geophysical Research: Biogeosciences↗
USGS2019

Assessing the seasonal dynamics of nitrate and sulfate aerosols at the South Pole utilizing stable isotopes

Atmospheric nitrate (NO 3 − = particulate NO 3 − + gas‐phase nitric acid [HNO 3 ]) and sulfate (SO 4 2− ) are key molecules that play important roles in numerous atmospheric processes. Here, the seasonal cycles of NO 3 − and total suspended particulate sulfate (SO 4 2− (TSP) ) were evaluated at the South Pole from aerosol samples collected weekly for approximately 10 months (26 January to 25 October) in 2002 and analyzed for their concentration and isotopic compositions. Aerosol NO 3 − was largely affected by snowpack emissions in which [NO 3 − ] and δ 15 N(NO 3 − ) were highest (49.3 ± 21.4 ng/m 3 , n = 8) and lowest (−47.0 ± 11.7‰, n = 5), respectively, during periods of sunlight in the interior of Antarctica. The seasonal cycle of Δ 17 O(NO 3 − ) reflected tropospheric chemistry year‐round with lower values observed during sunlight periods and higher values observed during dark periods, reflecting shifts from HO x ‐ to O 3 ‐dominated oxidation chemistry. SO 4 2− (TSP) concentrations were highest during austral summer and fall (86.7 ± 73.7 ng/m 3 , n = 18) and are indicated to be derived from dimethyl sulfide (DMS) emissions, as δ 34 S(SO 4 2− ) (TSP) values (18.5 ± 1.0‰, n = 10) were similar to literature δ 34 S(DMS) values. The seasonal cycle of Δ 17 O(SO 4 2− ) (TSP) exhibited minima during austral summer (0.9 ± 0.1‰, n = 5) and maxima during austral fall (1.3 ± 0.3‰, n = 6) and austral spring (1.6 ± 0.1‰, n = 5), indicating a shift from HO x ‐ to O 3 ‐dominated chemistry in the atmospheric derived SO 4 2− component. Overall, the budgets of NO 3 − and SO 4 2− (TSP) at the South Pole were complex functions of transport, localized chemistry, biological activity, and meteorological conditions, and these results will be important for interpretations of oxyanions in ice core records in the interior of Antarctica.

Journal of Geophysical Research D: Atmospheres↗
USGS2019

Probabilistic relationships between acid-base chemistry and fish assemblages in streams of the western Adirondack Mountains, New York, USA

Surface waters across much of the Adirondacks of New York were acidified in the late 20th century but began to recover after the 1990 amendments to the Clean Air Act. Little data, however, were available to characterize biological impacts and predict recovery of fish assemblages in regional streams. Quantitative fish and chemistry surveys were completed in 47 headwater streams during summer 2014-16 to develop logistic (probabilistic) models that characterize the status of contemporary fish assemblages and predict how different N and S deposition loads may affect future fish assemblages. Models for Ali and richness ≥1 species, ANC and total density >400 fish/0.1 ha, ANC and total biomass >1500 g/0.1, presence of Brook Trout, trout density >200 fish/0.1 ha, and 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 NOx and SOx 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.

New York↗
USGS2010

Using multiple chemical indicators to characterize and determine the age of groundwater from selected vents of the silver springs group, Central Florida, USA

The Silver Springs Group, Florida (USA), forms the headwaters of the Silver River and supports a diverse ecosystem. The 30 headwater springs divide into five subgroups based on chemistry. Five selected spring vents were sampled in 2007 to better understand the contaminant sources and groundwater flow system. Elevated nitrate-N concentrations (>0.8mg/L) in the five spring vents likely originate from inorganic (fertilizers) and organic sources, based on nitrogen and oxygen isotope ratios of nitrate. Evidence for denitrification in the Lost River Boil spring includes enriched ??15N and ??18O, excess N2 gas, and low dissolved O2 concentrations (<0.5mg/L). Multiple age-tracer data (SF6, 3H, tritiogenic 3He) for the two uppermost springs (Mammoth East and Mammoth West) indicate a binary mixture dominated by recent recharge water (mean age 6-7 years, and 87-97% young water). Tracer data for the three downstream spring vents (Lost River Boil, Catfish Hotel-1, and Catfish Conventional Hall-1) indicate exponential mixtures with mean ages of 26-35 years. Contamination from non-atmospheric sources of CFCs and SF5CF3 precluded their use as age tracers here. Variations in chemistry were consistent with mean groundwater age, as nitrate-N and dissolved O2 concentrations were higher in younger waters, and the Ca/Mg ratio decreased with increasing mean age. ?? 2010 Springer-Verlag (outside the USA).

Hydrogeology Journal↗
USGS1984

Causes of acidification of four streams on Laurel Hilld in southwestern Pennsylvania

Atmospheric deposition, soils developed from bedrock, a natural bog, gas wells, and a ski area were all investigated as possible sources of water quality degradation for four streams on Laurel Hill in southwestern Pennsylvania where fish kills have been reported since 1960. An intensive study of the chemistry of atmospheric deposition, soil leachate, and stream water and fish populations was conducted on these basins during 1980&ndash;1981 with emphasis on dormant season periods with runoff from snowmelt and rain. Although bedrock geology was found to control the natural buffering capacity of these streams, only acid precipitation could be linked to sharp drops in pH and increases in total Al concentrations observed during stormflows in the poorly buffered streams. Three poorly buffered streams exhibited drops to pH 4.4 to 4.5 and increases in total Al concentrations up to 1.5 mg/L during observed peak flows. Mineral soil leachate from the three major soil series on the basins during this time exhibited a low pH of 4.3 and mean total Al concentrations of 3.6 mg/L, indicating stream response during storms was closely linked to chemistry of soil leachate. Poorly buffered streams did not support reproducing populations of trout ( Salmonidae sp.) or other fishes. In contrast, one well-buffered stream (20 mg/L CaCO 3 ) exhibited drops to pH 5.5 during peak flow and supported reproducing trout and sculpin ( Cottus bairdi ) populations. The acidification of the four streams studied was attributed to atmospheric deposition.

Journal of Environmental Quality↗
USGS1990

Denitrification in sediments from the hyporheic zone adjacent to a small forested stream

Denitrifying potentials increased with increasing distance from the stream channel. Dissolved oxygen was 100% of the concentration expected in equilibrium with the atmosphere in water obtained from monitoring wells immediately adjacent to the stream but was as low as 7% of the expected value in water 11.4 m inland. Both nitrate and dissolved organic carbon decreased over summer in wells at the base of the alder-forested slope. A 48-h injection of nitrate-amended stream water into hyporheic water 8.4 m inland stimulated nitrous oxide production in the presence of acetylene. Nitrous oxide was generated as nitrate and acetylene were co-transported to a well 13 m down-gradient. Acetylene-block experiments coupled with the chemistry data suggest that denitrification can modify the chemistry of water during passage through the hyporheic zone. -from Authors

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1995

Seasonal cycles of dissolved constituents in streamwater in two forested catchments in the mid-Atlantic region of the eastern U.S.A.

Streamwater discharge and chemistry of two small catchments on Catoctin Mountain in north-central Maryland have been monitored since 1982. Repetitive seasonal cycles in stream-water chemistry have been observed each year, along with seasonal cycles in the volume of stream discharge and in groundwater levels. The hypothesis that the observed streamwater chemical cycles are related to seasonal changes in the hydrological flow paths that contribute to streamflow is examined using a combination of data on groundwater levels, shallow and deep groundwater chemistry, streamwater discharge, streamwater chemistry, soil-water chemistry, and estimates of water residence times. The concentrations of constituents derived from rock weathering, particularly bicarbonate and silica, increase in streamwater during the summer when the water table is below the regolith-bedrock interface and stream discharge consists primarily of deep groundwater from the fractured-bedrock aquifer. Conversely, the concentrations in streamwater of atmospherically derived components, particularly sulfate, increase in winter when the water table is above the regolith-bedrock interface and stream discharge consists primarily of shallow groundwater from the regolith. Tritium and chlorofluorocarbon (CFC) measurements suggest that the groundwater in these systems is young, with a residence time of less than several years. The results of this study have implications for the design of large-scale water-quality monitoring programs.

Maryland↗
USGS1991

Assessment of the sensitivity of Missouri reservoirs to acidification

We used water quality information from 103 Missouri reservoirs to assess their sensitivity to acidification from acidic atmospheric deposition. Total alkalinity less than 20 mg/L or a Calcite Saturation Index (CSI) of 1.0 or greater were the criteria to classify reservoirs as sensitive to acidification. Most of the reservoirs (83 of 103) would be considered circumneutral, hard water systems with high acid neutralizing capacity. Thirteen reservoirs were sensitive to acidification based on alkalinity or CSI. Four reservoirs with both low alkalinity and high CSI are located in southeast Missouri in areas of igneous rock outcroppings or chert deposits in limestone formations. These reservoirs are small (<40 ha) and have limited watersheds (<600 ha) and site-specific edaphic factors that likely determined their water chemistry. Site-specific factors also influenced water chemistry of acid-sensitive reservoirs that were located in regions expected to yield highly buffered water. No reservoir classified as acid-sensitive presently seems affected by acidification.

Journal of Freshwater Ecology↗
USGS2006

Investigating the role of gas bubble formation and entrapment in contaminated aquifers: Reactive transport modelling

In many natural and contaminated aquifers, geochemical processes result in the production or consumption of dissolved gases. In cases where methanogenesis or denitrification occurs, the production of gases may result in the formation and growth of gas bubbles below the water table. Near the water table, entrapment of atmospheric gases during water table rise may provide a significant source of O 2 to waters otherwise depleted in O 2 . Furthermore, the presence of bubbles will affect the hydraulic conductivity of an aquifer, resulting in changes to the groundwater flow regime. The interactions between physical transport, biogeochemical processes, and gas bubble formation, entrapment and release is complex and requires suitable analysis tools. The objective of the present work is the development of a numerical model capable of quantitatively assessing these processes. The multicomponent reactive transport code MIN3P has been enhanced to simulate bubble growth and contraction due to in-situ gas production or consumption, bubble entrapment due to water table rise and subsequent re-equilibration of the bubble with ambient groundwater, and permeability changes due to trapped gas phase saturation. The resulting formulation allows for the investigation of complex geochemical systems where microbially mediated redox reactions both produce and consume gases as well as affect solution chemistry, alkalinity, and pH. The enhanced model has been used to simulate processes in a petroleum hydrocarbon contaminated aquifer where methanogenesis is an important redox process. The simulations are constrained by data from a crude oil spill site near Bemidji, MN. Our results suggest that permeability reduction in the methanogenic zone due to in-situ formation of gas bubbles, and dissolution of entrapped atmospheric bubbles near the water table, both work to attenuate the dissolved gas plume emanating from the source zone. Furthermore, the simulations demonstrate that under the given conditions more than 50% of all produced CH 4 partitions to the gas phase or is aerobically oxidised near the water table, suggesting that these processes should be accounted for when assessing the rate and extent of methanogenic degradation of hydrocarbons.

Journal of Contaminant Hydrology↗
USGS2007

The concept of hydrologic landscapes

Hydrologic landscapes are multiples or variations of fundamental hydrologic landscape units. A fundamental hydrologic landscape unit is defined on the basis of land-surface form, geology, and climate. The basic land-surface form of a fundamental hydrologic landscape unit is an upland separated from a lowland by an intervening steeper slope. Fundamental hydrologic landscape units have a complete hydrologic system consisting of surface runoff, ground-water flow, and interaction with atmospheric water. By describing actual landscapes in terms of land-surface slope, hydraulic properties of soils and geologic framework, and the difference between precipitation and evapotranspiration, the hydrologic system of actual landscapes can be conceptualized in a uniform way. This conceptual framework can then be the foundation for design of studies and data networks, syntheses of information on local to national scales, and comparison of process research across small study units in a variety of settings. The Crow Wing River watershed in central Minnesota is used as an example of evaluating stream discharge in the context of hydrologic landscapes. Lake-research watersheds in Wisconsin, Minnesota, North Dakota, and Nebraska are used as an example of using the hydrologic-landscapes concept to evaluate the effect of ground water on the degree of mineralization and major-ion chemistry of lakes that lie within ground-water flow systems.

Minnesota, Nebraska, North Dakota, Wisconsin↗
USGS1986

Determination of the components of stormflow using water chemistry and environmental isotopes, Mattole River basin, California

The chemical and isotopic composition of rainfall and stream water was monitored during a storm in the Mattole River basin of northwestern California. About 250 mm of rain fell during 6 days (∼80% within a 42 h period) in late January, 1972, following 24 days of little or no precipitation. River discharge near Petrolia increased from 22 m 3 s −1 to a maximum of 1300 m 3 s −1 while chloride and silica concentrations decreased only from 3.2 to 2.1 and 11.5 to 8.6 mgl −1 , respectively. Meanwhile, the isotopic composition of the river changed from δD = -42%, δ 18 O = -6.8% and 40 tritium units (T.U.) to extreme values at highest flow of δD = -35%, δ 18 O = -5.9% and 25 T.U. in response to volume-weighted rainfall averaging δD = -19.5%, δ 18 O = -3.1% and 18 T.U. Despite much rainfall of a composition quite different from that of the prestorm river water, “buffering” processes in the watershed greatly restricted changes in the chemical and isotopic content of the river during storm runoff. Because of the physical and hydrologic characteristics of the watershed, major contributions of groundwater to stormflow are very unlikely. The large increase in dissolved chemical load observed at maximum river discharge required that extensive interaction with, and presumably penetration of, soils occurred within a few hours time. Such a large increase in chemical load also required subsurface stormflow throughout a high proportion of the watershed. Chemical and isotopic stabilization of stormflow is believed to be due mainly to displacement of prestorm soil water, with some effects on river chemistry due to rapid rain-soil interactions. The isotopic and chemical composition of prestorm soil moisture cannot readily be predicted a priori because of possible variability in rainfall composition, evaporation, and exchange with atmospheric moisture, nor can it be assumed that baseflow has a predictable relation to the chemical or isotopic composition of water displaced from soils during storms. Therefore, it seems inappropriate to draw conclusions as to the relative proportions of groundwater and rainfall in runoff from a particular storm based only on the average compositions of rainfall, stormflow, and prestorm river water, as has been done in most previous isotope hydrograph studies. Given the great variation in hydrology, topography, soil characteristics, rainfall intensity and quantity, etc. from place to place, the relative amount of overland flow, subsurface flow from the unsaturated zone and of groundwater in stormflow can vary greatly in time and space.

California↗
USGS2020

Timescales and processes of methane hydrate formation and breakdown, with application to geologic systems

Gas hydrate is an ice-like form of water and low molecular weight gas stable at temperatures of roughly -10ºC to 25ºC and pressures of ~3 to 30 MPa in geologic systems. Natural gas hydrates sequester an estimated one-sixth of Earth’s methane and are found primarily in deepwater marine sediments on continental margins, but also in permafrost areas and under continental ice sheets. When gas hydrate is removed from its stability field, its breakdown has implications for the global carbon cycle, ocean chemistry, marine geohazards, and interactions between the geosphere and the ocean-atmosphere system. Gas hydrate breakdown can also be artificially driven as a component of studies assessing the resource potential of these deposits. Furthermore, geologic processes and perturbations to the ocean-atmosphere system (e.g., warming temperatures) can cause not only dissociation, but also more widespread dissolution of hydrate or even formation of new hydrate in reservoirs. Linkages between gas hydrate and disparate aspects of Earth’s near-surface physical, chemical, and biological systems render an assessment of the rates and processes affecting the persistence of gas hydrate an appropriate Centennial Grand Challenge. This paper reviews the thermodynamic controls on methane hydrate stability and then describes the relative importance of kinetic, mass transfer, and heat transfer processes in the formation and breakdown (dissociation and dissolution) of gas hydrate. Results from numerical modeling, laboratory, and some fields studies are used to summarize the rates of hydrate formation and breakdown, followed by an extensive treatment of hydrate dynamics in marine and cryospheric gas hydrate systems.

Journal of Geophysical Research-Solid Earth↗
USGS2006

Globally synchronous ice core volcanic tracers and abrupt cooling during the last glacial period

We perform a Monte Carlo pattern recognition analysis of the coincidence between three regional volcanic histories from ice coring of Greenland and Antarctica over the period 2 to 45 ka, using SO4 anomalies in Greenland and East Antarctica determined by continuous core chemistry, together with West Antarctic volcanic ash layers determined by remote optical borehole logging and core assays. We find that the Antarctic record of volcanism correlates with Glacial abrupt climate change at a 95% to >99.8% (???3??) significance level and that volcanic depositions at the three locations match at levels exceeding 3??, likely indicating that many common horizons represent single eruptive events which dispersed material world wide. These globally coincident volcanics were associated with abrupt cooling, often simultaneous with onsets or sudden intensifications of millennial cold periods. The striking agreement between sites implies that the consistency of current timescales obtained by isotopic and glaciological dating methods is better than estimated. Copyright 2006 by the American Geogphysical Union.

Journal of Geophysical Research D: Atmospheres↗
USGS2022

Biogeochemical and ecosystem properties in three adjacent semiarid grasslands are resistant to nitrogen deposition but sensitive to edaphic variability

Drylands have low nitrogen stocks and are predicted to be sensitive to modest increases in reactive nitrogen availability, but direct evidence that atmospheric nitrogen deposition will have sustained effects on dryland ecosystems is sparse and conflicting. We used three long-running in situ nitrogen deposition simulation experiments and a complementary laboratory incubation experiment to address fundamental questions about how nitrogen inputs affect drylands: 1) What are the long- and short-term consequences of nitrogen inputs for biogeochemical and ecosystem properties?; 2) Do these consequences depend on soil moisture availability?; and 3) Does soil texture modify the effects of nitrogen inputs and/or soil moisture availability? In 2011, we established three study sites along a soil texture gradient in Arches National Park with plots receiving 0, 2, 5, or 8 kg N ha -1 annually ( n = 5 per treatment per site). We assessed a suite of biogeochemical metrics over the long- and short-term. To assess longer-term effects, we sampled annually (2013-2019), just prior to spring nitrogen fertilization. To assess short-term effects, we sampled immediately before and after spring nitrogen fertilization in 2013. Additionally, we compared foliar chemistry, soil extracellular enzyme activities, heterotrophic respiration rates, and nitrogen trace gas fluxes at select intervals during the study period (2011-2019). Finally, we conducted a laboratory incubation to measure the individual and interacting effects of soil moisture and nitrogen additions on soil microbial activity. We identified some short-term effects in situ , but no lasting consequences of added nitrogen for any of the metrics measured. In the incubation, soil moisture treatments independently increased heterotrophic respiration rates but did not modify the effects of added nitrogen. In contrast to nitrogen treatments, soil texture was associated with large differences in biogeochemical cycling. Our results oppose the common prediction that coupled dryland biogeochemical cycles are sensitive to nitrogen inputs and suggest that fine scale edaphic heterogeneity is a key driver of dryland ecosystem properties. Synthesis . This study synthesizes a rare, long-term dataset, which provides robust evidence that carbon and nutrient cycling and availability are resistant to realistic levels of atmospheric nitrogen deposition in remote dryland ecosystems.

Utah↗