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USGS2021

The Robinson Forest environmental monitoring network: Long‐term evaluation of streamflow and precipitation quantity and stream‐water and bulk deposition chemistry in eastern Kentucky watersheds

The University of Kentucky (U KY) has owned Robinson Forest (37.460723° N, 83.158598° W) since 1923, conducting experiments crucial to understanding the environmental effects of land management in the region. Part of the management of Robinson Forest has been collection of environmental data, including precipitation quantity, bulk‐deposition chemistry, streamflow, stream‐water chemistry, and air and stream temperature. Over the years, these data have been collected and archived using various technologies and have been mostly inaccessible for research use – unedited and uncompiled, scattered across several spreadsheets and paper records. Through a partnership between the U.S. Geological Survey (USGS) and U KY, daily precipitation data for six stations and stream data from four watersheds in Robinson Forest have been compiled for 1971–2018, checked for transcription errors, and annotated for changes in methodologies. These data are available as a USGS data release at https://doi.org/10.5066/P9FPLG1O . Improved accessibility of this data set provides an important research resource for understanding water quality in minimally effected forests in the region. Preliminary results indicate that these data present a valuable opportunity to evaluate linkages among atmospheric deposition and stream chemistry, the effects of environmental policy, such as the Clean Air Act, and effects from nearby land disturbance in the form of surface mining. Furthermore, these data fill a geographic and physiographic gap in what is available to examine deposition and streamflow patterns over the last 45 years, supplementing those long‐term records of research sites in northern (e.g., Hubbard Brook Experimental Forest), central (e.g., Fernow Experimental Forest) and southern Appalachia (e.g., Coweeta Hydrologic Laboratory). As an oasis in the midst of significant surface mining activity, Robinson Forest presents a unique opportunity to understand environmental conditions characteristic of minimally disturbed forests similar to pre‐mining conditions in the Central Appalachian region.

Kentucky↗

USGS2005

Response of surface water chemistry to reduced levels of acid precipitation: Comparison of trends in two regions of New York, USA

In light of recent reductions in sulphur (S) and nitrogen (N) emissions mandated by Title IV of the Clean Air Act Amendments of 1990, temporal trends and trend coherence in precipitation (1984-2001 and 1992-2001) and surface water chemistry (1992-2001) were determined in two of the most acid-sensitive regions of North America, i.e. the Catskill and Adirondack Mountains of New York. Precipitation chemistry data from six sites located near these regions showed decreasing sulphate (SO42-), nitrate (NO3-), and base cation (CB) concentrations and increasing pH during 1984-2001, but few significant trends during 1992-2001. Data from five Catskill streams and 12 Adirondack lakes showed decreasing trends in SO42- concentrations at all sites, and decreasing trends in NO3-, CB, and H+ concentrations and increasing trends in dissolved organic carbon at most sites. In contrast, acid-neutralizing capacity (ANC increased significantly at only about half the Adirondack lakes and in one of the Catskill streams. Flow correction prior to trend analysis did not change any trend directions and had little effect on SO42- trends, but it caused several significant non-flow-corrected trends in NO3- and ANC to become non-significant, suggesting that trend results for flow-sensitive constituents are affected by flow-related climate variation. SO42- concentrations showed high temporal coherence in precipitation, surface waters, and in precipitation-surface water comparisons, reflecting a strong link between S emissions, precipitation SO42- concentrations, and the processes that affect S cycling within these regions. NO3- and H+ concentrations and ANC generally showed weak coherence, especially in surface waters and in precipitation-surface water comparisons, indicating that variation in local-scale processes driven by factors such as climate are affecting trends in acid-base chemistry in these two regions. Copyright ?? 2005 John Wiley & Sons, Ltd.

Hydrological Processes↗

USGS2021

Efficient genotyping with backwards compatibility: Converting a legacy microsatellite panel for muskellunge (Esox masquinongy) to genotyping-by-sequencing chemistry

Microsatellites have been a staple of population genetics research for over three decades, and many large datasets have been generated with these markers. Microsatellites have been used, for example, to conduct genetic monitoring and construct large multigeneration pedigrees as well as genotype thousands of individuals from a given species to create high-resolution baselines of spatial genetic structure. However, the capillary electrophoresis (CE) approach used to genotype microsatellites is inefficient compared to newer genotyping-by-sequencing (GBS) approaches, and researchers have begun transitioning away from CE. Backward compatibility between GBS and CE would facilitate a seamless transition to a more efficient chemistry, while ensuring that research based on CE panels could continue. Here, we explore the feasibility of converting a legacy panel of 15 microsatellites developed for muskellunge ( Esox masquinongy ) from CE to GBS chemistry. Muskellunge are an important sportfish in the Great Lakes region, and the existing microsatellite panel has been used to genotype thousands of samples to develop a region-wide baseline of genetic structure. We successfully converted all 15 microsatellites to GBS chemistry. GBS produced high genotyping rates (98%) and had high concordance with CE microsatellite genotypes (99%). Conversion to GBS required redesign of some primers and pairs to shorten amplicon length and adjust melting temperatures, optimization of primer concentrations, and comparisons with CE genotypes to optimize GBS genotyping parameters; however, none of these steps were especially onerous. Our results demonstrate that it is highly feasible to convert legacy CE panels to GBS, ensuring seamless continuation of important, often long-term research.

Conservation Genetics Resources↗

USGS1969

Chemical composition of selected Kansas brines as an aid to interpreting change in water chemistry with depth

Chemical analyses of approximately 1,881 samples of water from selected Kansas brines define the variations of water chemistry with depth and aquifer age. The most concentrated brines are found in the Permian rocks which occupy the intermediate section of the geologic column of this area. Salinity decreases below the Permian until the Ordovician (Arbuckle) horizon is reached and then increases until the Precambrian basement rocks are reached. Chemically, the petroleum brines studied in this small area fit the generally accepted pattern of an increase in calcium, sodium and chloride content with increasing salinity. They do not fit the often-predicted trend of increases in the calcium to chloride ratio, calcium content and salinity with depth and geologic age. The calcium to chloride ratio tends to be asymptotic to about 0.2 with increasing chloride content. Sulfate tends to decrease with increasing calcium content. Bicarbonate content is relatively constant with depth. If many of the hypotheses concerning the chemistry of petroleum brines are valid, then the brines studied are anomolous. An alternative lies in accepting the thesis that exceptions to these hypotheses are rapidly becoming the rule and that indeed we still do not have a valid and general hypothesis to explain the origin and chemistry of petroleum brines.

Kansas↗

USGS1991

Fluid inclusion gas chemistry as a potential minerals exploration tool: Case studies from Creede, CO, Jerritt Canyon, NV, Coeur d'Alene district, ID and MT, southern Alaska mesothermal veins, and mid-continent MVT's

Recent advances in instrumentation now permit quantitative analysis of gas species from individual fluid inclusions. Fluid inclusion gas data can be applied to minerals exploration empirically to establish chemical (gas composition) signatures of the ore fluids, and conceptually through the development of genetic models of ore formation from a framework of integrated geologic, geochemical, and isotopic investigations. Case studies of fluid inclusion gas chemistry from ore deposits representing a spectrum of ore-forming processes and environments are presented to illustrate both the empirical and conceptual approaches. We consider epithermal silver-gold deposits of Creede, Colorado, Carlin-type sediment-hosted disseminated gold deposits of Jerritt Canyon, Nevada, metamorphic silver-base-metal veins of the Coeur d'Alene district, Idaho and Montana, gold-quartz veins in accreted terranes of southern Alaska, and the mid-continent base-metal sulfide deposits of Mississippi Valley-Type (MVT's). Variations in gas chemistry determine the redox state of the ore fluids, provide compositional input for gas geothermometers, characterize ore fluid chemistry (e.g., CH 4 CO 2 , H 2 SSO 2 , CO 2 /H 2 S, organic-rich fluids, gas-rich and gas-poor fluids), identify magmatic, meteoric, metamorphic, shallow and deep basin fluids in ore systems, locate upwelling plumes of magmatic-derived volatiles, zones of boiling and volatile separation, interfaces between contrasting fluids, and important zones of fluid mixing. Present techniques are immediately applicable to exploration programsas empirical studies that monitor fluid inclusion gas threshold concentration levels, presence or absence of certain gases, or changes in gas ratios. We suggest that the greater contribution of fluid inclusion gas analysis is in the integrated and comprehensive chemical dimension that gas data impart to genetic models, and in the exploration concepts based on processes and environments of ore formation derived from these genetic models.

Journal of Geochemical Exploration↗

USGS1987

The relation of stream sediment surface area, grain size and composition to trace element chemistry

Intensive studies of 17 geographically and hydrologically diverse stream bed sediments provide information on the relation between grain size, surface area, and operationally defined geochemical phases (e.g. Mn oxides, amorphous Fe oxides) to trace element concentrations. Of the size fractions investigated (<2, <16, <63and<125 μm), the strongest correlation with trace elements occurs with the percent <63 μm or<125 μm fractions. As the proportion of these size fractions increases in the samples, so do the trace element concentrations. When surface area (as defined by nitrogen adsorption and the BET equations) increases, trace element levels also increase. Correlations between bulk sediment chemistry and surface area are as strong as those between sediment chemistry and the proportion of the <63or<125 μm fractions. Surface area appears to serve as a proxy for grain size. The strongest correlations between grain size and surface area are the same as for trace elements and grain size (with the <63or<125 μm fractions). Surface area also is affected by geochemical phase, as are the trace elements associated with sediments. Of the phases considered (carbonates, Mn oxides, reactive Fe, amorphous Fe, organic matter), amorphous Fe oxides appear to exert the greatest control over both surface area and trace element levels. The concentrations of various geochemical phases affect surface area, grain size, and trace element chemistry. However, the effect of phase is grain-size dependent. For material with mean grain sizes in the fine sand range and coarser (> 125 μm), each of the various phases contribute to overall sample surface area. For material having mean grain sizes in the very fine sand range and finer (<125 μm), the same phases act as surface-area inhibitors by cementing fine grains together to form aggregates. This increases the mean grain size of the sample and reduces the surface area. The presence of these aggregates may explain why the <63 μm or<125 μm size fractions are more important to sediment-trace element levels and surface area than other finer fractions.

Applied Geochemistry↗

USGS2015

Stable-isotope and solute-chemistry approaches to flow characterization in a forested tropical watershed, Luquillo Mountains, Puerto Rico

The prospect of changing climate has led to uncertainty about the resilience of forested mountain watersheds in the tropics. In watersheds where frequent, high rainfall provides ample runoff, we often lack understanding of how the system will respond under conditions of decreased rainfall or drought. Factors that govern water supply, such as recharge rates and groundwater storage capacity, may be poorly quantified. This paper describes 8-year data sets of water stable isotope composition ( δ 2 H and δ 18 O) of precipitation (4 sites) and a stream (1 site), and four contemporaneous stream sample sets of solute chemistry and isotopes, used to investigate watershed response to precipitation inputs in the 1780-ha Río Mameyes basin in the Luquillo Mountains of northeastern Puerto Rico. Extreme δ 2 H and δ 18 O values from low-pressure storm systems and the deuterium excess ( d -excess) were useful tracers of watershed response in this tropical system. A hydrograph separation experiment performed in June 2011 yielded different but complementary information from stable isotope and solute chemistry data. The hydrograph separation results indicated that 36% of the storm rain that reached the soil surface left the watershed in a very short time as runoff. Weathering-derived solutes indicated near-stream groundwater was displaced into the stream at the beginning of the event, followed by significant dilution. The more biologically active solutes exhibited a net flushing behavior. The d- excess analysis suggested that streamflow typically has a recent rainfall component (∼25%) with transit time less than the sampling resolution of 7 days, and a more well-mixed groundwater component (∼75%). The contemporaneous stream sample sets showed an overall increase in dissolved solute concentrations with decreasing elevation that may be related to groundwater inputs, different geology, and slope position. A considerable amount of water from rain events runs off as quickflow and bypasses subsurface watershed flowpaths, and better understanding of shallow hillslope and deeper groundwater processes in the watershed will require sub-weekly data and detailed transit time modeling. A combined isotopic and solute chemistry approach can guide further studies to a more comprehensive model of the hydrology, and inform decisions for managing water supply with future changes in climate and land use.

Applied Geochemistry↗

USGS2004

Functional group and individual maceral chemistry of high volatile bituminous coals from southern Indiana: Controls on coking

The individual maceral chemistries of two Pennsylvanian, high volatile bituminous coals, the Danville Coal Member (Dugger Formation, R o=0.55%) and the Lower Block Coal Member (Brazil Formation, R o=0.56%) of Indiana, were investigated using electron microprobe and Fourier Transform Infrared Spectrometry (FTIR) techniques, with the purpose of understanding differences in their coking behavior. Microprobe results reveal that carbon contents are highest in inertinite and sporinite, followed by desmocollinite and telocollinite. Oxygen and organic nitrogen are most abundant in telocollinite and desmocollinite; sporinite and inertinite contain lesser amounts of these two elements. Organic sulfur contents are highest in sporinite, lowest in inertinite, and intermediate in desmocollinite and telocollinite. Vitrinites within the Danville and Lower Block coals are very similar in elemental composition, while Lower Block inertinites and sporinites have higher carbon, lower oxygen, and sulfur contents which, when combined with the inertinite-and sporinite-rich composition of the Lower Block seam, strongly influences its whole coal chemistry. Fourier transform infrared spectrometry revealed greater aromatic hydrogen in the Lower Block coal, along with higher CH2/CH3 ratios, which suggest that liptinites contribute considerable amounts of long-chain, unbranched aliphatics to the overall kerogen composition of the Lower Block coal. Long-chain, unbranched aliphatics crack at higher temperatures, producing tar and oily byproducts during coking; these may help increase Lower Block plasticity. Electron microprobe and FTIR results indicate that individual maceral chemistries, combined with the maceral composition of the seam, are the primary control of better coking properties of the Lower Block coal. ?? 2003 Elsevier B.V. All rights reserved.

International Journal of Coal Geology↗

USGS2007

Application of a coupled ecosystem-chemical equilibrium model, DayCent-Chem, to stream and soil chemistry in a Rocky Mountain watershed

Atmospheric deposition of sulfur and nitrogen species have the potential to acidify terrestrial and aquatic ecosystems, but nitrate and ammonium are also critical nutrients for plant and microbial productivity. Both the ecological response and the hydrochemical response to atmospheric deposition are of interest to regulatory and land management agencies. We developed a non-spatial biogeochemical model to simulate soil and surface water chemistry by linking the daily version of the CENTURY ecosystem model (DayCent) with a low temperature aqueous geochemical model, PHREEQC. The coupled model, DayCent-Chem, simulates the daily dynamics of plant production, soil organic matter, cation exchange, mineral weathering, elution, stream discharge, and solute concentrations in soil water and stream flow. By aerially weighting the contributions of separate bedrock/talus and tundra simulations, the model was able to replicate the measured seasonal and annual stream chemistry for most solutes for Andrews Creek in Loch Vale watershed, Rocky Mountain National Park. Simulated soil chemistry, net primary production, live biomass, and soil organic matter for forest and tundra matched well with measurements. This model is appropriate for accurately describing ecosystem and surface water chemical response to atmospheric deposition and climate change. ?? 2006 Elsevier B.V. All rights reserved.

Ecological Modelling↗

USGS2017

The response of soil and stream chemistry to decreases in acid deposition in the Catskill Mountains, New York, USA

The Catskill Mountains have been adversely impacted by decades of acid deposition, however, since the early 1990s, levels have decreased sharply as a result of decreases in emissions of sulfur dioxide and nitrogen oxides. This study examines trends in acid deposition, stream-water chemistry, and soil chemistry in the southeastern Catskill Mountains. We measured significant reductions in acid deposition and improvement in stream-water quality in 5 streams included in this study from 1992 to 2014. The largest, most significant trends were for sulfate (SO 4 2− ) concentrations (mean trend of −2.5 μeq L −1 yr −1 ); hydrogen ion (H + ) and inorganic monomeric aluminum (Al im ) also decreased significantly (mean trends of −0.3 μeq L −1 yr −1 for H + and −0.1 μeq L −1 yr −1 for Al im for the 3 most acidic sites). Acid neutralizing capacity (ANC) increased by a mean of 0.65 μeq L −1 yr −1 for all 5 sites, which was 4 fold less than the decrease in SO 4 2− concentrations. These upward trends in ANC were limited by coincident decreases in base cations (−1.3 μeq L −1 yr −1 for calcium + magnesium). No significant trends were detected in stream-water nitrate (NO 3 − ) concentrations despite significant decreasing trends in NO 3 − wet deposition. We measured no recovery in soil chemistry which we attributed to an initially low soil buffering capacity that has been further depleted by decades of acid deposition. Tightly coupled decreasing trends in stream-water silicon (Si) (−0.2 μeq L −1 yr −1 ) and base cations suggest a decrease in the soil mineral weathering rate. We hypothesize that a decrease in the ionic strength of soil water and shallow groundwater may be the principal driver of this apparent decrease in the weathering rate. A decreasing weathering rate would help to explain the slow recovery of stream pH and ANC as well as that of soil base cations.

New York↗

USGS2016

The chemistry and isotopic composition of waters in the low-enthalpy geothermal system of Cimino-Vico Volcanic District, Italy

Geothermal energy exploration is based in part on interpretation of the chemistry, temperature, and discharge rate of thermal springs. Here we present the major element chemistry and the δD, δ 18 O, 87 Sr/ 86 Sr and δ 11 B isotopic ratio of groundwater from the low-enthalpy geothermal system near the city of Viterbo in the Cimino-Vico volcanic district of west-Central Italy. The geothermal system hosts many thermal springs and gas vents, but the resource is still unexploited. Water chemistry is controlled by mixing between low salinity,HCO 3 -rich fresh waters (<24.2°C) flowing in shallow volcanic rocks and SO 4 -rich thermal waters (25.3°C to 62.2°C) ascending from deep, high permeability Mesozoic limestones. The (equivalent) SO 4 /Cl (0.01–0.02), Na/Cl (2.82–5.83) and B/Cl ratios (0.02–0.38) of thermal waters differs from the ratios in other geothermal systems from Central Italy, probably implying a lack of hydraulic continuity across the region. The δ 18 O (−6.6‰ to −5.9‰) and δD (−40.60‰ to −36.30‰) isotopic composition of spring water suggest that the recharge area for the geothermal system is the summit region of Mount Cimino. The strontium isotope ratios ( 87 Sr/ 86 Sr) of thermal waters (0.70797–0.70805) are consistent with dissolution of the Mesozoic evaporite-carbonate units that constitute the reservoir, and the ratios of cold fresh waters mainly reflect shallow circulation through the volcanic cover and some minor admixture (<10%) of thermal water as well. The boron isotopic composition (δ 11 B) of fresh waters (−5.00 and 6.12‰) is similar to that of the volcanic cover, but the δ 11 B of thermal waters (−8.37‰ to −4.12‰) is a mismatch for the Mesozoic reservoir rocks and instead reflects dissolution of secondary boron minerals during fluid ascent through flysch units that overlie the reservoir. A slow and tortuous ascent enhances extraction of boron but also promotes conductive cooling, partially masking the heat present in the reservoir. Overall data from this study is consistent with previous studies that concluded that the geothermal system has a large energy potential.

Journal of Volcanology and Geothermal Research↗

USGS2022

Indicator mineral analyses of stream-sediment samples using automated mineralogy and mineral chemistry: Applicability to exploration in covered terranes in eastern Alaska, USA

In the past two decades, significant research efforts have been devoted to porphyry copper indicator mineral (PCIM) identification and mineral chemistry to assist exploration. Such studies are important in the Yukon-Tanana upland region of eastern Alaska because well-established geochemical exploration techniques, such as the geochemistry of stream-sediment samples, are less effective in the search for mineral resources owing to cover materials that subdue geochemical signatures. The unglaciated Yukon-Tanana upland region is well-endowed with mineral resources, including porphyry Cu-Mo-Au deposits at Taurus, Bluff, Dennison, and Oreo. Using automated scanning electron microscope (SEM) techniques, numerous PCIMs have been identified in rocks and stream-sediment samples that would likely not have been observed using visual binocular microscope methods. Sulfide minerals such as chalcopyrite, chalcocite, covellite, bornite, molybdenite, and pyrrhotite were identified in rock samples, and more than half of the stream-sediment samples from drainages containing known porphyry mineral occurrences contain chalcopyrite with or without bornite. Many drainages without known occurrences also contain these minerals, which suggests potential for additional occurrences. Svanbergite, an aluminum phosphate sulfate (APS) mineral [SrAl 3 (PO 4 )(SO 4 )(OH) 6 ], was identified in some of the altered or mineralized rock samples from Taurus, and in stream drainages containing porphyry occurrences and may represent the best indicator mineral for Taurus-like porphyry deposits. Apatite chemistry has great potential as a tool for assessing the presence of porphyry mineralization. Grains from rock and stream-sediment samples that contain high Cl (>∼0.4 wt%), Fe (>0.4 wt%), and Mn (>2000 ppm) clearly distinguish apatite from other sources (metamorphic, unmineralized igneous rocks). This study is one of the first to document new streamlined indicator mineral sample collection and processing methods and to combine automated SEM techniques and chemistry of minerals derived from both bedrock and surficial (stream) sediments as they apply to porphyry exploration.

Alaska↗

USGS2007

Influence of soil chemistry on metal and bioessential element concentrations in nymphal and adult periodical cicadas (Magicicada spp.)

Metal and bioessential element concentrations were measured in three species of 17-year periodical cicadas (Magicicada spp.) to determine how cicada tissue chemistry is affected by soil chemistry, measure the bioavailability of metals from both uncontaminated and lead-arsenate-pesticide contaminated soils, and assess the potential risks of observed metal contamination for wildlife. Periodical cicada nymphs feed on root xylem fluids for 13 or 17??years of underground development. The nymphs then emerge synchronously at high densities, before leaving their nymphal keratin exoskeleton and molting into their adult form. Cicadas are an important food source for birds and animals during emergence events, and influence nutrient cycles in woodland ecosystems. Nymphal exoskeletons and whole adult cicadas were sampled in Clarke and Frederick Counties, Virginia and Berkeley and Jefferson Counties, West Virginia during the Brood X emergence in May and June, 2004. Elements, such as Al, Fe, and Pb, are strongly enriched in the nymphal exoskeleton relative to the adult body; Cu and Zn are enriched in bodies. Concentrations of Fe and Pb, when normalized to relatively inert soil constituents such as Al and Ce, are similar in both the molt exoskeleton and their host soil, implying that passive assimilation through prolonged soil contact (adhesion or adsorption) might control these metal concentrations. Normalized concentrations of bioessential elements, such as S, P, K, Ca, Mn, Cu, Zn, and Mo, and chalcophile (sulfur-loving) elements, such as As, Se, and Au, indicate strong enrichment in cicada tissues relative to soil, implying selective absorption and retention by xylem fluids, the cicada nymphs themselves, or both. Element enrichment patterns in cicada tissues are similar to enrichment patterns observed in xylem fluids from tree roots. Chalcophile elements and heavy metals accumulate in keratin-rich tissues and may bind to sulfhydryl groups. Metal concentrations in the nymphal exoskeleton show a positive correlation with soil metal concentrations, with Au exhibiting particularly strong enrichment in the exoskeleton relative to soil concentrations. Metal concentrations in adult bodies do not correlate with soil chemistry. Bioessential elements S, Ca, Mn, Fe, and Zn differed by sex in adults, whereas Na, Mg, K, Ca, Mn, Fe, Zn, and As differed by species. Body concentrations of Ca differed by site conditions (orchard or reference setting). The high Pb contents of orchard soils contaminated by arsenical pesticide residues might inhibit Ca uptake by cicada nymphs. The adult cicadas contain concentrations of metals similar to, or less than, other invertebrates, such as earthworms. There does not appear to be a dietary threat to birds or other consumers of adult cicadas based on Maximum Tolerable Dietary Level (MTDL) Guidelines developed for agricultural animals.

Science of the Total Environment↗

USGS2008

The effects of land use on fluvial sediment chemistry for the conterminous U.S. - Results from the first cycle of the NAWQA Program: Trace and major elements, phosphorus, carbon, and sulfur

In 1991, the U.S. Geological Survey (USGS) began the first cycle of its National Water Quality Assessment (NAWQA) Program. The Program encompassed 51 river basins that collectively accounted for more than 70% of the total water use (excluding power generation), and 50% of the drinking water supply in the U.S. The basins represented a variety of hydrologic settings, rock types (geology), land-use categories, and population densities. One aspect of the first cycle included bed sediment sampling; sites were chosen to represent baseline and important land-use categories (e.g., agriculture, urban) in each basin. In total, over 1200 bed sediment samples were collected. All samples were size-limited (< 63????m) to facilitate spatial and/or temporal comparisons, and subsequently analyzed for a variety of chemical constituents including major (e.g., Fe, Al,) and trace elements (e.g., Cu, Zn, Cd), nutrients (e.g., P), and carbon. The analyses yielded total (??? 95% of the concentrations present), rather than total-recoverable chemical data. Land-use percentages, upstream underlying geology, and population density were determined for each site and evaluated to asses their relative influence on sediment chemistry. Baseline concentrations for the entire U.S. also were generated from a subset of all the samples, and are based on material collected from low population (??? 27??p km- 2) density, low percent urban (??? 5%), agricultural or undeveloped areas. The NAWQA baseline values are similar to those found in other national and global datasets. Further, it appears that upstream/underlying rock type has only a limited effect (mostly major elements) on sediment chemistry. The only land-use category that appears to substantially affect sediment chemistry is percent urban, and this result is mirrored by population density; in fact, the latter appears more consistent than the former.

Science of the Total Environment↗

USGS2000

Relations between basin characteristics and stream water chemistry in alpine/subalpine basins in Rocky Mountain National Park, Colorado

Relations between stream water chemistry and topographic, vegetative, and geologic characteristics of basins were evaluated for nine alpine/subalpine basins in Rocky Mountain National Park, Colorado, to identify controlling parameters and to better understand processes governing patterns in stream water chemistry. Fractional amounts of steep slopes (≥30°), unvegetated terrain, and young surficial debris within each basin were positively correlated to each other. These terrain features, which commonly occur on steep valley side slopes underlain by talus, were negatively correlated with concentrations of base cations, silica, and alkalinity and were positively correlated with nitrate, acidity, and runoff. These relations might result from the short residence times of water and limited soil development in the talus environment, which limit chemical weathering and nitrogen uptake. Steep, unvegetated terrains also tend to promote high Ca/Na ratios in stream water, probably because physical weathering rates in those areas are high. Physical weathering exposes fresh bedrock that contains interstitial calcite, which weathers relatively quickly. The fractional amounts of subalpine meadow and, to a lesser extent, old surficial debris in the basins were positively correlated to concentrations of weathering products and were negatively correlated to nitrate and acidity. These relations may reflect more opportunities for silicate weathering and nitrogen uptake in the lower‐energy environments of the valley floor, where soils are finer‐grained, older, and better developed and slopes are relatively flat. These results indicate that in alpine/subalpine basins, slope, vegetation (or lack thereof), and distribution and age of surficial materials are interrelated and can have major effects on stream water chemistry.

Colorado↗

USGS2003

Changes in the chemistry of lakes and precipitation in high-elevation national parks in the western United States, 1985–1999

High-elevation lakes in the western United States are sensitive to atmospheric deposition of sulfur and nitrogen due to fast hydrologic flushing rates, short growing seasons, an abundance of exposed bedrock, and a lack of well-developed soils. This sensitivity is reflected in the dilute chemistry of the lakes, which was documented in the U.S. Environmental Protection Agency's Western Lake Survey of 1985. Sixty-nine lakes in seven national parks sampled during the 1985 survey were resampled during fall 1999 to investigate possible decadal-scale changes in lake chemistry. In most lakes, SO 4 concentrations were slightly lower in 1999 than in 1985, consistent with a regional decrease in precipitation SO 4 concentrations and in SO 2 emissions in the western United States. Nitrate concentrations also tended to be slightly lower in 1999 than in 1985, in contrast with generally stable or increasing inorganic N deposition in the west. Differences in alkalinity were variable among parks but were relatively consistent within each park. Possible effects of annual and seasonal-scale variations in precipitation amount on lake chemistry were evaluated based on climate data available for the parks and an analysis of climatic effects at two research watersheds with long-term records. Results suggest that rain prior to sampling in 1985 may have caused elevated NO 3 in some lakes due to direct runoff of precipitation and flushing of NO 3 from alpine soils, which may explain some of the decrease in NO 3 concentrations observed in survey lakes.

Water Resources Research↗

USGS2011

Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions

The magnitude and feedbacks of future methane release from the Arctic region are unknown. Despite limited documentation of potential future releases associated with thawing permafrost and degassing methane hydrates, the large potential for future methane releases calls for improved understanding of the interaction of a changing climate with processes in the Arctic and chemical feedbacks in the atmosphere. Here we apply a “state of the art” atmospheric chemistry transport model to show that large emissions of CH4 would likely have an unexpectedly large impact on the chemical composition of the atmosphere and on radiative forcing (RF). The indirect contribution to RF of additional methane emission is particularly important. It is shown that if global methane emissions were to increase by factors of 2.5 and 5.2 above current emissions, the indirect contributions to RF would be about 250% and 400%, respectively, of the RF that can be attributed to directly emitted methane alone. Assuming several hypothetical scenarios of CH4 release associated with permafrost thaw, shallow marine hydrate degassing, and submarine landslides, we find a strong positive feedback on RF through atmospheric chemistry. In particular, the impact of CH4 is enhanced through increase of its lifetime, and of atmospheric abundances of ozone, stratospheric water vapor, and CO2 as a result of atmospheric chemical processes. Despite uncertainties in emission scenarios, our results provide a better understanding of the feedbacks in the atmospheric chemistry that would amplify climate warming.

Global Biogeochemical Cycles↗

USGS2010

Mineralogy and chemistry of cobbles at Meridiani Planum, Mars, investigated by the Mars Exploration Rover Opportunity

Numerous loose rocks with dimensions of a few centimeters to tens of centimeters and with no obvious physical relationship to outcrop rocks have been observed along the traverse of the Mars Exploration Rover Opportunity. To date, about a dozen of these rocks have been analyzed with Opportunity's contact instruments, providing information about elemental chemistry (Alpha Particle X‐ray Spectrometer), iron mineralogy and oxidation states (Mössbauer Spectrometer) and texture (Microscopic Imager). These “cobbles” appear to be impact related, and three distinct groups can be identified on the basis of chemistry and mineralogy. The first group comprises bright fragments of the sulfate‐rich bedrock that are compositionally and texturally indistinguishable from outcrop rocks. All other cobbles are dark and are divided into two groups, referred to as the “Barberton group” and the “Arkansas group,” after the first specimen of each that was encountered by Opportunity. Barberton group cobbles are interpreted as meteorites with an overall chemistry and mineralogy consistent with a mesosiderite silicate clast composition. Arkansas group cobbles appear to be related to Meridiani outcrop and contain an additional basaltic component. They have brecciated textures, pointing to an impact‐related origin during which local bedrock and basaltic material were mixed.

Journal of Geophysical Research E: Planets↗