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At least 631 records · Page 35Linked to original sources
USGS2017

Seventy-five years of vegetation treatments on public rangelands in the Great Basin of North America

On the Ground Land treatments occurring over millions of hectares of public rangelands in the Great Basin over the last 75 years represent one of the largest vegetation manipulation and restoration efforts in the world. The ability to use legacy data from land treatments in adaptive management and ecological research has improved with the creation of the Land Treatment Digital Library (LTDL), a spatially explicit database of land treatments conducted by the U.S. Bureau of Land Management. The LTDL contains information on over 9,000 confirmed land treatments in the Great Basin, composed of seedings (58%), vegetation control treatments (24%), and other types of vegetation or soil manipulations (18%). The potential application of land treatment legacy data for adaptive management or as natural experiments for retrospective analyses of effects of land management actions on physical, hydrologic, and ecologic patterns and processes is considerable and just beginning to be realized.

California, Idaho, Nevada, Oregon, Utah↗
USGS2024

Snow-cover remote sensing of conifer tree recovery in high-severity burn patches

The number of large, high-severity wildfires has been increasing across the western United States over the last several decades. It is not fully understood how changes in the frequency of large, severe wildfires may impact the resilience of conifer forests, due to alterations in regeneration success or failure. Our research investigates 30 years of conifer recovery patterns within 34 high-severity wildfire complexes (1988–1991) of the Northern Rocky Mountains. We evaluate the capability of snow-cover Landsat to characterize conifer tree recolonization of high-severity burn patches. Snow-cover images isolate conifer-specific vegetation signals by diminishing spectral contributions from soil and deciduous vegetation. The presence of conifer regeneration was successfully classified by snow-cover Landsat at >10% canopy cover at 98% accuracy and modeled at 3-year intervals post-fire. Spectral detectability of regenerating conifer vegetation began 11–19 years post-fire, varying across forest types. Thirty years post-fire, 65% of the total high-severity burn area had been recolonized by conifer trees, with differences observed between forest types: 72% of lodgepole pine, 77% of Douglas-fir, and 44% of fir-spruce severely burned areas containing conifer regeneration. Projected recovery timelines to pre-fire conifer vegetation also differed between lodgepole pine (29.5 years), Douglas-fir (36.9 years), and fir-spruce forests (48.7 years), as estimated from snow-cover NDVI trends. Although we generally documented patterns of conifer resilience, we also identified reduced likelihoods of recovery within high-severity burn patches exhibiting greater area-to-perimeter ratios, aridity, south-facing aspects, slopes, and elevation. Snow-cover Landsat imagery was shown to improve the characterization of post-fire forest recovery and may be applied to support forest restoration decision-making following high-severity wildfire.

Remote Sensing of Environment↗
USGS2001

A minimalist probabilistic description of root zone soil water

The probabilistic response of depth‐integrated soil water to given climatic forcing can be described readily using an existing supply‐demand‐storage model. An apparently complex interaction of numerous soil, climate, and plant controls can be reduced to a relatively simple expression for the equilibrium probability density function of soil water as a function of only two dimensionless parameters. These are the index of dryness (ratio of mean potential evaporation to mean precipitation) and a dimensionless storage capacity (active root zone soil water capacity divided by mean storm depth). The first parameter is mainly controlled by climate, with surface albedo playing a subsidiary role in determining net radiation. The second is a composite of soil (through moisture retention characteristics), vegetation (through rooting characteristics), and climate (mean storm depth). This minimalist analysis captures many essential features of a more general probabilistic analysis, but with a considerable reduction in complexity and consequent elucidation of the critical controls on soil water variability. In particular, it is shown that (1) the dependence of mean soil water on the index of dryness approaches a step function in the limit of large soil water capacity; (2) soil water variance is usually maximized when the index of dryness equals 1, and the width of the peak varies inversely with dimensionless storage capacity; (3) soil water has a uniform probability density function when the index of dryness is 1 and the dimensionless storage capacity is large; and (4) the soil water probability density function is bimodal if and only if the index of dryness is <1, but this bimodality is pronounced only for artificially small values of the dimensionless storage capacity.

Water Resources Research↗
USGS2022

Multi-stage soil-hydraulic recovery and limited ravel accumulations following the 2017 Nuns and Tubbs wildfires in Northern California

Wildfire can impact soil-hydraulic properties by reducing saturated hydraulic conductivity and sorptivity, making recently burned landscapes prone to debris flows and flash floods. The post-fire hazard window can range from years to decades. In Northern California, where wildfire frequency is steadily increasing, the impact and soil-hydraulic recovery from wildfires is unknown. Following the October 2017 Nuns and Tubbs fires in the Northern Bay Area of California, we established 41 monitoring sites for repeat tension-disc infiltrometer measurements of field-saturated hydraulic conductivity ( K fs ) over 3.5 years. Our site arrays, which encompass grasslands, chaparral, and oak and conifer forests across a range in lithology, show a marked decrease in K fs following the wildfires and a swift partial recovery following the initial post-fire rainy season. Our time series reveals a complex path to soil-hydraulic recovery marked by distinct seasonal stages. Analysis of changing K fs , sorptivity, and infiltration model residuals collectively suggests that these stages are related to transitions between soil-hydraulic processes like structural soil sealing from rainsplash, thermal cracking of bare soil, and vegetation regrowth. While soil infiltration rates were strongly impacted by the 2017 fires, dry ravel estimates are an order of magnitude less for similar slopes than the 2009 Station fire in the San Gabriel mountains of Southern California, suggesting that limited ravel flux may insufficiently load channels for debris flows that initiate from within-channel failure. Our analysis suggests that burned landscapes in the Northern Bay Area of California may experience rapid soil-hydraulic recovery and limited pathways toward post-fire debris flow initiation.

California↗
USGS2012

Compositional variations on the Moon: Recalibration of Galileo solid‐state imaging data for the Orientale region and farside

Updated radiometric calibration and systematic processing procedures for Galileo solid‐state imaging (SSI) data from the first (1990) Earth‐Moon encounter are presented. These procedures were applied to a whole‐disk imaging sequence of the Moon centered near Mare Orientale, called Lunmap 14 (L14). Processing of L14 data included radiometric calibration, subpixel coregistration, scattered light removal, geometric control and reprojection, photometric normalization, and calibration to Earth‐based spectra. Coregistration and scattered‐light removal procedures are improvements over the initial calibration of the SSI mosaics. The effects of scattered light correction are best seen using a whole‐Moon view such as L14; resolution of the debated amounts of light scattering from within or outside the camera field of view is not necessary. Scattered light removal particularly affects the 1‐μm spectral region and has implications for interpretation of mafic mineral signatures in mare deposits of the lunar limb and farside. Recalibrated spectra indicate that mare ponds of the limb show moderately deep 1‐μm absorptions, and thus mafic mineral contents, comparable to those of other nearside basalts. Mafic mineral contents of Schiller‐Shickard cryptomaria are higher than previously thought and are similar to some low‐Ti nearside basalts. Many of the recalibrated spectra from South Pole/Aitken are similar to those of Schiller‐Schickard cryptomaria, suggesting that many of these soils represent a mixed mare/highland lithology. The hypothesis that there is an olivine enrichment in southern South Pole/Aitken basin is not supported strongly by spectra shown here.

Journal of Geophysical Research: Planets↗
USGS1996

Mineral nitrogen transformations in and under seasonal snow in a high-elevation catchment in the Rocky Mountains, United States

In an effort to understand sources of nitrate (NO 3 − ) in surface waters of high-elevation catchments, nitrogen (N) transformations in and under seasonal snow were investigated from 1993 to 1995 on Niwot Ridge, an alpine ecosystem at 3,500 m located in the Colorado Front Range of the Rocky Mountains. Ammonium (NH 4 + ) and NO 3 − labeled with 15 N applied as nonconservative tracers to the snow showed no evidence of nitrification in the snowpack. Furthermore, NH 4 + movement through the amended snowpack was highly correlated with a conservative chloride tracer ( r 2 = 0.99). In an unamended snowpack NH 4 + concentrations in meltwater before contact with the ground were highly correlated with NO 3 − concentrations ( r 2 = 0.98), which is consistent with no nitrification in the snowpack. The isotopically labeled 15 NH + 4 applied to the snowpack was found in underlying soils, showing that NH 4 + released from snow can be rapidly immobilized. Resin bag (mixed-bed ion-exchange resins) measurements (n = 22) showed that 80% of the mobile inorganic N in unamended subnivial soils was NO 3 − . Measurements of KCl-extractable inorganic N from surface soils showed that highest values were prior to the initiation of snowmelt and lowest values were during the growing season. The natural δ 15 N abundance of unamended soils was negative and ranged from −12 to −2, suggesting that atmospheric deposition of δ 15 N-depleted N is an important component of N cycling in these alpine soils. These results suggest that soil mineralization under seasonal snow, rather than snowmelt release of NO 3 − , may control NO 3 − concentrations in surface waters of high-elevation catchments.

Water Resources Research↗
USGS2010

A compositional multiphase model for groundwater contamination by petroleum products: 1. Theoretical considerations

A mathematical model is developed to describe the fate of hydrocarbon constituents of petroleum products introduced to soils as an immiscible liquid from sources such as leaking underground storage tanks and ruptured pipelines. The problem is one of multiphase transport (oil (immiscible), air, and water phases) of a reactive contaminant with constituents such as benzene, toluene, and xylene found in refined petroleum products like gasoline. In the unsaturated zone, transport of each constituent can occur as a solute in the water phase, vapor in the air phase, and as an unaltered constituent in the oil phase. Additionally, the model allows for adsorption. Molecular transformations, microbially mediated or abiotic, are incorporated as sink terms in the conservation of mass equations. An equilibrium approximation, applicable to any immiscible organic contaminant is applied to partition constituent mass between the air, oil, water, and adsorbed phases for points in the region where the oil phase exists. Outside the oil plume the equilibrium approximation takes on a simpler form to partition constituent mass between the air, water, and adsorbed phases only. Microbial degradation of petroleum products is first discussed in a general model, then the conservation of mass equation for oxygen is incorporated into the analysis which takes advantage of the key role played by oxygen in the metabolism of hydrocarbon utilizing microbes in soil environments. Approximations to two subproblems, oil plume establishment in the unsaturated zone, and solute and vapor transport subsequent to immiscible plume establishment are then developed from the general model.

Water Resources Research↗
USGS2019

FLUXNET-CH4 synthesis activity: Objectives, observations, and future directions

This paper describes the formation of, and initial results for, a new FLUXNET coordination network for ecosystem-scale methane (CH 4 ) measurements at 60 sites globally, organized by the Global Carbon Project in partnership with other initiatives and regional flux tower networks. The objectives of the effort are presented along with an overview of the coverage of eddy covariance (EC) CH 4 flux measurements globally, initial results comparing CH 4 fluxes across the sites, and future research directions and needs. Annual estimates of net CH 4 fluxes across sites ranged from −0.2 ± 0.02 g C m –2 yr –1 for an upland forest site to 114.9 ± 13.4 g C m –2 yr –1 for an estuarine freshwater marsh, with fluxes exceeding 40 g C m –2 yr –1 at multiple sites. Average annual soil and air temperatures were found to be the strongest predictor of annual CH 4 flux across wetland sites globally. Water table position was positively correlated with annual CH 4 emissions, although only for wetland sites that were not consistently inundated throughout the year. The ratio of annual CH 4 fluxes to ecosystem respiration increased significantly with mean site temperature. Uncertainties in annual CH 4 estimates due to gap-filling and random errors were on average ±1.6 g C m –2 yr –1 at 95% confidence, with the relative error decreasing exponentially with increasing flux magnitude across sites. Through the analysis and synthesis of a growing EC CH 4 flux database, the controls on ecosystem CH 4 fluxes can be better understood, used to inform and validate Earth system models, and reconcile differences between land surface model- and atmospheric-based estimates of CH 4 emissions.

Bulletin of the American Meteorological Society↗
USGS2001

Trail resource impacts and an examination of alternative assessment techniques

Trails are a primary recreation resource facility on which recreation activities are performed. They provide safe access to non-roaded areas, support recreational opportunities such as hiking, biking, and wildlife observation, and protect natural resources by concentrating visitor traffic on resistant treads. However, increasing recreational use, coupled with poorly designed and/or maintained trails, has led to a variety of resource impacts. Trail managers require objective information on trails and their conditions to monitor trends, direct trail maintenance efforts, and evaluate the need for visitor management and resource protection actions. This paper reviews trail impacts and different types of trail assessments, including inventory, maintenance, and condition assessment approaches. Two assessment methods, point sampling and problem assessment, are compared empirically from separate assessments of a 15-mile segment of the Appalachian Trail in Great Smoky Mountains National Park. Results indicate that point sampling and problem assessment methods yield distinctly different types of quantitative information. The point sampling method provides more accurate and precise measures of trail characteristics that are continuous or frequent (e.g., tread width or exposed soil). The problem assessment method is a preferred approach for monitoring trail characteristics that can be easily predefined or are infrequent (e.g., excessive width or secondary treads), particularly when information on the location of specific trail impact problems is needed. The advantages and limitations of these two assessment methods are examined in relation to various management and research information needs. The choice and utility of these assessment methods are also discussed.

Journal of Park and Recreation Administration↗
USGS1997

Some comparisons between recent ground-motion relations

We provide an overview of new ground-motion relations for eastern North America (ENA) developed over the last five years. The empirical-stochastic relations of Atkinson and Boore (1995) are compared to relations developed by the Electric Power Research Institute (EPRI, 1993; also Toro et al. , 1994), Frankel et al. (1996), and the consensus ENA ground-motion values as reported by SSHAC (1996). The main difference between our relations and those of EPRI or Frankel is in the low-frequency amplitudes ( f < 2 Hz, all magnitudes). We predict lower amplitudes (by more than a factor of two) at 1 Hz, largely due to our use of an empirical source model rather than a single-corner-frequency Brune source model; the use of the empirical source model is motivated by the desire to match the ENA ground-motion database as closely as possible. We also compare our new ENA relations to empirical relations for California. The comparison is complicated by the need to adjust the ENA hard-rock motions to obtain equivalent motions for typical California soil conditions. Two alternative methods of making this correction lead to somewhat different conclusions. One possible conclusion is that our ENA relations predict similar low-frequency amplitudes to those predicted by Boore et al. (1993, 1994) and Abrahamson and Silva (1996) for California, but our predicted ENA amplitudes are much higher (factor > 2) than California values at high frequencies. The alternative soil correction leads to the conclusion that our ENA relations are moderately lower (factor<2) than the California relations at low frequencies, and moderately higher at high frequencies. Both of these conclusions imply that ground-motion relations or time series for earthquakes in one region cannot be simply modified for use in engineering analyses in another region.

Seismological Research Letters↗
USGS1996

Loess stratigraphy of the Lower Mississippi Valley

Loesses of the Lower Mississippi Valley (LMV) are world-famous. Sir Charles Lyell (1847), Hilgard (1860), Stafford (1869), Call (1891) and Mabry (1898), thought the LMV loess was a single water deposit although "double submergence" was noted by Call (1891) and Salisbury (1891). Shimek (1902) and Emerson (1918) recognized LMV loess as a wind deposit which came from the valley. Although wind-deposited loess gained wide acceptance, Russell (1944a) published his controversial theory of "loessification" which entailed weathering of backswamp deposits, downslope movement and recharge by carbonates to form loess. Wascher et al. (1947) identified three LMV loesses, mapped distributions and strongly supported eolian deposition. Leighton and Willman (1950), identified four loesses and supported eolian deposition as did Krinitzsky and Turnbull (1967) and Snowden and Priddy (1968), but Krinitzsky and Turnbull questioned the deepest loess. Daniels and Young (1968) and Touchet and Daniels (1970) studied the distribution of loesses in south-central Louisiana. West et al. (1980) and Rutledge et al. (1985) studied the source areas and wind directions which deposited the loesses on and adjoining Crowley's Ridge. B.J. Miller and co-workers (Miller et al., 1985, 1986, Miller and Alford, 1985) proposed that the Loveland Silt was Early Wisconsin rather than Illinoian age and advanced the name Sicily Island loess. They proposed the underlying loess was Illinoian and advanced the name Crowley's Ridge. We termed the loesses, from the surface downward, Peoria Loess, Roxana Silt, Loveland/Sicily Island loess, Crowley's Ridge Loess and Marianna loess. Researchers agree that the surfical Peoria Loess is Late Wisconsin and the Roxana Silt is Late to Middle Wisconsin, but little agreement exists on the age of the older loesses. Pye and Johnson (1988) proposed Early Wisconsin for the Loveland/Sicily Island. McKay and Follmer (1985) suggested this loess correlated with a loess under Illinoian till. Clark et al. (1989) agreed on Crowley's Ridge, but suggested the Loveland/Sicily Island loess on Sicily Island was older. Mirecki and Miller (1994) and Millard and Maat (1994) suggested an Illinoian age for the Loveland/Sicily Island loess. Miller and co-workers suggested, as did Pye and Johnson (1988), an Illinoian age for the Crowley's Ridge loess. McKay and Follmer (1985) suggested it correlated with a loess under "Kansan" till. Stratigraphy indicates the Marianna is the older of the five loesses. Researchers identified loess on both the east and west side of the LMV as well as on higher terraces within the valley. Many researchers assumed unaltered loesses were commonly yellowish brown, and silts or silt loams (West et al., 1980; Miller et al., 1986). The nonclay fraction of unweathered LMV loesses was dominated by quartz followed by carbonates, mainly dolomites, followed by feldspars, and micas. Clays were dominated by montmorillonite followed by micaceous minerals, kaolinite and vermiculite (Miller et al., 1986). Soils in the Crowley's Ridge loess are most developed, followed by the soils in the Loveland/Sicily Island which are more developed than the modern soils in the Peoria Loess. Soils in the Roxana and Marianna loesses are least developed and the Farmdale Soil of the Roxana is the weaker of the two (Miller et al., 1986). There is certainly overlapping range in the degree of soil development in the various loesses.

Engineering Geology↗
USGS2019

Manipulating wild and tamed phytobiomes: Challenges and opportunities

This white paper presents a series of perspectives on current and future phytobiome management, discussed at the Wild and Tamed Phytobiomes Symposium in University Park, PA, USA, in June 2018. To enhance plant productivity and health, and to translate lab- and greenhouse-based phytobiome research to field applications, the academic community and end-users need to address a variety of scientific, practical, and social challenges. Prior discussion of phytobiomes has focused heavily on plant-associated bacterial and fungal assemblages, but the phytobiomes concept covers all factors that influence plant function. Here we discuss various management considerations, including abiotic conditions (e.g. soil, nutrient applications), microorganisms (e.g. bacterial and fungal assemblages, bacterial and fungal inoculants, viruses), macroorganisms (e.g. arthropods, plant genetics), and societal factors (e.g. communication approaches, technology diffusion). An important near-term goal for this field should be to estimate the potential relative contribution of different components of the phytobiome to plant health, as well as the potential and risk of modifying each in the near-future.

Phytobiomes Journal↗
USGS2026

Vegetation cover and composition in environments surrounding uranium mines in the Grand Canyon ecosystem, Northern Arizona

Mining uranium from breccia-pipe deposits in the greater Grand Canyon region has occurred since the mid-1900s. However, possible ecosystem contamination with harmful levels of radionuclides may have occurred due to mining activities in the 21st century. In response, a 20-year Federal moratorium on new mining claims in the Grand Canyon watershed was initiated in 2012, to allow time to evaluate the potential effects of uranium exploration and mining on human health, wildlife, and water resources. This moratorium, nor the 2023 designation of the “Baaj Nwaavjo I’tah Kukveni–Ancestral Footprints of the Grand Canyon National Monument,” precludes operation or development of mining claims predating 2012. Vegetation is a core ecosystem component that may be affected by uranium mining (for instance, through uptake and storage of radionuclides from the air or soil) or may act as a vector of exposure to wildlife, livestock, and humans (for instance, via their consumption of contaminated plant tissues). To provide baseline information about the plant communities associated with uranium mines in the Grand Canyon region, the U.S. Geological Survey surveyed an approximately 200-meter-wide buffer surrounding four breccia-pipe deposits, each in a unique stage of mine development, and at one reference area (a livestock water tank) that underwent ground disturbance but contains no mineral deposits. We sectioned the buffer zones into 0.65–4.52 hectare plots, within which we (1) inventoried all plant species, (2) measured percent cover of plant species, plant functional groups, and ground surface types (dark cyanobacteria, lichen, moss, bedrock, rock, embedded litter, duff, plant bases, and bare soil) using line-point intercept, and (3) measured length and frequency of gaps between perennial plant canopies using canopy gap intercept. We found that plant composition at the mines and the reference area differed from one another but were all characteristic of expected regional vegetation patterns. We provide this data summary as potential baseline information for future research and management efforts.

Arizona↗
USGS2024

Intercomparison of same-day remote sensing data for measuring winter cover crop biophysical traits

Winter cover crops are planted during the fall to reduce nitrogen losses and soil erosion and improve soil health. Accurate estimations of winter cover crop performance and biophysical traits including biomass and fractional vegetative groundcover support accurate assessment of environmental benefits. We examined the comparability of measurements between ground-based and spaceborne sensors as well as between processing levels (e.g., surface vs. top-of-atmosphere reflectance) in estimating cover crop biophysical traits. This research examined the relationships between SPOT 5, Landsat 7, and WorldView-2 same-day paired satellite imagery and handheld multispectral proximal sensors on two days during the 2012–2013 winter cover crop season. We compared two processing levels from three satellites with spatially aggregated proximal data for red and green spectral bands as well as the normalized difference vegetation index (NDVI). We then compared NDVI estimated fractional green cover to in-situ photographs, and we derived cover crop biomass estimates from NDVI using existing calibration equations. We used slope and intercept contrasts to test whether estimates of biomass and fractional green cover differed statistically between sensors and processing levels. Compared to top-of-atmosphere imagery, surface reflectance imagery were more closely correlated with proximal sensors, with intercepts closer to zero, regression slopes nearer to the 1:1 line, and less variance between measured values. Additionally, surface reflectance NDVI derived from satellites showed strong agreement with passive handheld multispectral proximal sensor-sensor estimated fractional green cover and biomass (adj. R 2 = 0.96 and 0.95; RMSE = 4.76% and 259 kg ha−1, respectively). Although active handheld multispectral proximal sensor-sensor derived fractional green cover and biomass estimates showed high accuracies (R 2 = 0.96 and 0.96, respectively), they also demonstrated large intercept offsets (−25.5 and 4.51, respectively). Our results suggest that many passive multispectral remote sensing platforms may be used interchangeably to assess cover crop biophysical traits whereas SPOT 5 required an adjustment in NDVI intercept. Active sensors may require separate calibrations or intercept correction prior to combination with passive sensor data. Although surface reflectance products were highly correlated with proximal sensors, the standardized cloud mask failed to completely capture cloud shadows in Landsat 7, which dampened the signal of NIR and red bands in shadowed pixels.

Maryland↗
USGS2016

Illuminating wildfire erosion and deposition patterns with repeat terrestrial lidar

Erosion following a wildfire is much greater than background erosion in forests because of wildfire-induced changes to soil erodibility and water infiltration. While many previous studies have documented post-wildfire erosion with point and small plot-scale measurements, the spatial distribution of post-fire erosion patterns at the watershed scale remains largely unexplored. In this study lidar surveys were collected periodically in a small, first-order drainage basin over a period of 2 years following a wildfire. The study site was relatively steep with slopes ranging from 17° to > 30°. During the study period, several different types of rain storms occurred on the site including low-intensity frontal storms (2.4 mm h −1 ) and high-intensity convective thunderstorms (79 mm h −1 ). These storms were the dominant drivers of erosion. Erosion resulting from dry ravel and debris flows was notably absent at the site. Successive lidar surveys were subtracted from one another to obtain digital maps of topographic change between surveys. The results show an evolution in geomorphic response, such that the erosional response after rain storms was strongly influenced by the previous erosional events and pre-fire site morphology. Hillslope and channel roughness increased over time, and the watershed armored as coarse cobbles and boulders were exposed. The erosional response was spatially nonuniform; shallow erosion from hillslopes (87% of the study area) contributed 3 times more sediment volume than erosion from convergent areas (13% of the study area). However, the total normalized erosion depth (volume/area) was highest in convergent areas. From a detailed understanding of the spatial locations of erosion, we made inferences regarding the processes driving erosion. It appears that hillslope erosion is controlled by rain splash (for detachment) and overland flow (for transport and quasi-channelized erosion), with the sites of highest erosion corresponding to locations with the lowest roughness. By contrast, in convergent areas we found erosion caused by overland flow. Soil erosion was locally interrupted by immobile objects such as boulders, bedrock, or tree trunks, resulting in a patchy erosion network with increasing roughness over time.

Colorado↗
USGS2004

Relative effect of temperature and pH on diel cycling of dissolved trace elements in Prickly Pear Creek, Montana

Diel (24 hr) cycles in dissolved metal and As concentrations have been documented in many northern Rocky Mountain streams in the U.S.A. The cause(s) of the cycles are unknown, although temperature- and pH-dependent sorption reactions have been cited as likely causes. A light/dark experiment was conducted to isolate temperature and pH as variables affecting diel metal cycles in Prickly Pear Creek, Montana. Light and dark chambers containing sediment and a strand of macrophyte were placed in the stream to simulate instream temperature oscillations. Photosynthesis-induced pH changes were allowed to proceed in the light chambers while photosynthesis was prevented in the dark chambers. Water samples were collected periodically for 22 hr in late July 2001 from all chambers and the stream. In the stream, dissolved Zn concentrations increased by 300% from late afternoon to early morning, while dissolved As concentrations exhibited the opposite pattern, increasing 33% between early morning and late afternoon. Zn and As concentrations in the light chambers showed similar, though less pronounced, diel variations. Conversely, Zn and As concentrations in the dark chambers had no obvious diel variation, indicating that light, or light-induced reactions, caused the variation. Temperature oscillations were nearly identical between light and dark chambers, strongly suggesting that temperature was not controlling the diel variations. As expected, pH was negatively correlated ( P < 0.01) with dissolved Zn concentrations and positively correlated with dissolved As concentrations in both the light and dark chambers. From these experiments, photosynthesis-induced pH changes were determined to be the major cause of the diel dissolved Zn and As cycles in Prickly Pear Creek. Further research is necessary in other streams to verify that this finding is consistent among streams having large differences in trace-element concentrations and mineralogy of channel substrate.

Montana↗
USGS2006

Detection of water quality trends at high, median, and low flow in a Catskill Mountain stream, New York, through a new statistical method

The effects of changes in acid deposition rates resulting from the Clean Air Act Amendments of 1990 should first appear in stream waters during rainstorms and snowmelt, when the surface of the watershed is most hydrologically connected to the stream. Early detection of improved stream water quality is possible if trends at high flow could be separately determined. Trends in concentrations of sulfate (SO 4 2− ), nitrate (NO 3 − ), calcium plus magnesium (Ca 2+ +Mg 2+ ), and acid‐neutralizing capacity (ANC) in Biscuit Brook, Catskill Mountains, New York, were assessed through segmented regression analysis (SRA). The method uses annual concentration‐to‐discharge relations to predict concentrations for specific discharges, then compares those annual values to determine trends at specific discharge levels. Median‐flow trends using SRA were comparable to those predicted by the seasonal Kendall tau test and a multiple regression residual analysis. All of these methods show that stream water SO 4 2− concentrations have decreased significantly since 1983; Ca 2+ +Mg 2+ concentrations have decreased at a steady but slower rate than SO 4 2− ; and ANC shows no trend. The new SRA method, however, reveals trends that differ at specified flow levels. ANC has increased, and NO 3 − concentrations have decreased at high flows, but neither has changed as significantly at low flows. The general downward trend in SO 4 2− flattened at median flow and reversed at high flow between 1997 and 2002. The reversal of the high‐flow SO 4 2− trend is consistent with increases in SO 4 2− concentrations in both precipitation and soil solutions at Biscuit Brook. Separate calculation of high‐flow trends provides resource managers with an early detection system for assessing changes in water quality resulting from changes in acidic deposition.

Water Resources Research↗
USGS2010

Mercury dynamics in relation to dissolved organic carbon concentration and quality during high flow events in three northeastern U.S. streams

Mercury (Hg) contamination is widespread in remote areas of the northeastern United States. Forested uplands have accumulated a large reservoir of Hg in soil from decades of elevated anthropogenic deposition that can be released episodically to stream water during high flows. The objective of this study was to evaluate spatial and temporal variations in stream water Hg species and organic matter fractions over a range of hydrologic conditions in three forested upland watersheds (United States). Mercury and organic matter concentrations increased with discharge at all three sites; however, the partitioning of Hg fractions (dissolved versus particulate) differed among sites and seasons. Associated with increased discharge, flow paths shifted from mineral soil under base flow to upper soil horizons. As flow paths shifted, greater concentrations of dissolved organic carbon (DOC) richer in aromatic substances were flushed from upper soil horizons to stream water. The hydrophobic organic matter associated with humic material from upper soils appears to have had a greater capacity to bind Hg. Because of the strong correlation between Hg and DOC, we hypothesize that there was a concurrent shift in the source of Hg with DOC from lower mineral soil to upper soil horizons. Our study suggests that stream discharge is an effective predictor of dissolved total Hg flux.

Water Resources Research↗