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Results for “Soil Research”

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At least 1,063 records · Page 59Linked to original sources
USGS2013

Epifluorescent direct counts of bacteria and viruses from topsoil of various desert dust storm regions

Topsoil from arid regions is the main source of dust clouds that move through the earth's atmosphere, and microbial communities within these soils can survive long-range dispersion. Microbial abundance and chemical composition were analyzed in topsoil from various desert regions. Statistical analyses showed that microbial direct counts were strongly positively correlated with calcium concentrations and negatively correlated with silicon concentrations. While variance between deserts was expected, it was interesting to note differences between sample sites within a given desert region, illustrating the 'patchy' nature of microbial communities in desert environments.

Research in Microbiology↗
USGS2012

Landscape controls on total and methyl Hg in the Upper Hudson River basin, New York, USA

Approaches are needed to better predict spatial variation in riverine Hg concentrations across heterogeneous landscapes that include mountains, wetlands, and open waters. We applied multivariate linear regression to determine the landscape factors and chemical variables that best account for the spatial variation of total Hg (THg) and methyl Hg (MeHg) concentrations in 27 sub-basins across the 493 km 2 upper Hudson River basin in the Adirondack Mountains of New York. THg concentrations varied by sixfold, and those of MeHg by 40-fold in synoptic samples collected at low-to-moderate flow, during spring and summer of 2006 and 2008. Bivariate linear regression relations of THg and MeHg concentrations with either percent wetland area or DOC concentrations were significant but could account for only about 1/3 of the variation in these Hg forms in summer. In contrast, multivariate linear regression relations that included metrics of (1) hydrogeomorphology, (2) riparian/wetland area, and (3) open water, explained about 66% to >90% of spatial variation in each Hg form in spring and summer samples. These metrics reflect the influence of basin morphometry and riparian soils on Hg source and transport, and the role of open water as a Hg sink. Multivariate models based solely on these landscape metrics generally accounted for as much or more of the variation in Hg concentrations than models based on chemical and physical metrics, and show great promise for identifying waters with expected high Hg concentrations in the Adirondack region and similar glaciated riverine ecosystems.

New York↗
USGS2021

Storm-scale and seasonal dynamics of carbon export from a nested subarctic watershed underlain by permafrost

Subarctic catchments underlain by permafrost sequester a major stock of frozen organic carbon (C), which may be mobilized as the Arctic warms. Warming can impact C export from thawing soils by altering the depth and timing of runoff related to changing storm and fire regimes and altered soil thaw depths. We investigated C export in a first order headwater stream (West Twin Creek) and its receiving third order river (Beaver Creek) in interior Alaska using discrete sampling of dissolved organic and inorganic C (DOC and DIC) and 15-min collection of specific conductance (SC), fluorescent dissolved organic matter (fDOM) and water discharge (Q). Storm SC-Q relationships displayed negative slopes, indicating solute limitation and limited influence of seasonal soil thaw on storm runoff chemistry. Concurrently, fDOM-Q displayed positive slopes that decreased over the summer, indicating flushing of a limited fDOM pool. Baseflow DIC increased over the season concurrent with soil thaw, with higher DIC at the larger scale indicating greater influence of deeper, mineral-rich flow paths. Storm and seasonal trends were generally similar at both scales. The biggest difference was in fDOM, which displayed higher concentrations and slower depletion in the first order stream. Improved process understanding from this study can be used to better predict carbon export and cycling by stream networks as northern forests and arctic regions continue to warm.

Alaska↗
USGS2024

A conceptual framework to assess post-wildfire water quality: State of the science and knowledge gaps

Wildfire substantially alters aquatic ecosystems by inducing moderate to catastrophic physical and chemical changes. However, the relations of environmental and watershed variables that drive those effects are complex. We present a Driver-Factor-Stressor-Effect (DFSE) conceptual framework to assess the current state of the science related to post-wildfire water-quality. We reviewed 64 peer-reviewed papers using the DFSE framework to identify drivers, factors, stressors, and effects associated with each study. A total of five drivers were identified and ranked according to their frequency of occurrence in the literature: atmospheric processes > fire characteristics > ecologic processes and characteristics > land surface characteristics > soil characteristics. Commonly reported stressors include increased nutrients, runoff, and sediment transport. Furthermore, although several different factors have been used at least once to explain water-quality effects, relatively few factors outside of precipitation and fire characteristics are frequently studied. We identified several gaps indicating the need for long-term monitoring, multi-factor studies, consideration of organic contaminants, consideration of groundwater, and inclusion of soil characteristics. This assessment expands on other reviews and meta-analyses by exploring causal linkages between influential variables and overall effects in post-wildfire watersheds. Information gathered from our assessment and the framework itself can be used to inform future monitoring plans and as a guide for modeling efforts focused on better understanding specific processes or to mitigate potential risks of post-wildfire water quality.

Water Resources Research↗
USGS2010

An analytic solution of the stochastic storage problem applicable to soil water

The accumulation of soil water during rainfall events and the subsequent depletion of soil water by evaporation between storms can be described, to first order, by simple accounting models. When the alternating supplies (precipitation) and demands (potential evaporation) are viewed as random variables, it follows that soil-water storage, evaporation, and runoff are also random variables. If the forcing (supply and demand) processes are stationary for a sufficiently long period of time, an asymptotic regime should eventually be reached where the probability distribution functions of storage, evaporation, and runoff are stationary and uniquely determined by the distribution functions of the forcing. Under the assumptions that the potential evaporation rate is constant, storm arrivals are Poisson-distributed, rainfall is instantaneous, and storm depth follows an exponential distribution, it is possible to derive the asymptotic distributions of storage, evaporation, and runoff analytically for a simple balance model. A particular result is that the fraction of rainfall converted to runoff is given by (1 - R −1 )/( e α(1− R −1) − R −1 ), in which R is the ratio of mean potential evaporation to mean rainfall and a is the ratio of soil water-holding capacity to mean storm depth. The problem considered here is analogous to the well-known problem of storage in a reservoir behind a dam, for which the present work offers a new solution for reservoirs of finite capacity. A simple application of the results of this analysis suggests that random, intraseasonal fluctuations of precipitation cannot by themselves explain the observed dependence of the annual water balance on annual totals of precipitation and potential evaporation.

Water Resources Research↗
USGS1991

Spatial variability and collector requirements for sampling throughfall volume and chemistry under a mixed-hardwood canopy

Ion concentrations were generally less variable within storms compared with net ion input data. Concentrations and net inputs of some ions were consistently less variable than others; for example, Ca2+, NO3-, and SO42- were less variable than NH4 + and K+. These patterns of variability were consistent in comparisons both within and among storms. The relatively low variability of NO3- and SO42- is probably due to dry deposition of these ions as anthropogenic pollutants, while the low variability of Ca2+ is the result of deposition in windblown soil particles. The high variability of NH4+ and K+ is probably the result of biological processes. Ammonium is strongly retained by the canopy, and K+ is readily leached from it. Retention by, and leaching from, the canopy can induce spatial variability as a result of spatial heterogeneity in the biota. Throughfall volume also displayed low variability within and among events, requiring an average of 11 collectors to estimate the mean within 10% at the 95% confidence level. -from Author

Canadian Journal of Forest Research↗
USGS2012

Physical setting and natural sources of exposure to carcinogenic trace elements and radionuclides in Lahontan Valley, Nevada

In Lahontan Valley, Nevada, arsenic, cobalt, tungsten, uranium, radon, and polonium-210 are carcinogens that occur naturally in sediments and groundwater. Arsenic and cobalt are principally derived from erosion of volcanic rocks in the local mountains and tungsten and uranium are derived from erosion of granitic rocks in headwater reaches of the Carson River. Radon and 210Po originate from radioactive decay of uranium in the sediments. Arsenic, aluminum, cobalt, iron, and manganese concentrations in household dust suggest it is derived from the local soils. Excess zinc and chromium in the dust are probably derived from the vacuum cleaner used to collect the dust, or household sources such as the furnace. Some samples have more than 5 times more cobalt in the dust than in the local soil, but whether the source of the excess cobalt is anthropogenic or natural cannot be determined with the available data. Cobalt concentrations are low in groundwater, but arsenic, uranium, radon, and 210 Po concentrations often exceed human-health standards, and sometime greatly exceed them. Exposure to radon and its decay products in drinking water can vary significantly depending on when during the day that the water is consumed. Although the data suggests there have been no long term changes in groundwater chemistry that corresponds to the Lahontan Valley leukemia cluster, the occurrence of the very unusual leukemia cluster in an area with numerous 210 Po and arsenic contaminated wells is striking, particularly in conjunction with the exceptionally high levels of urinary tungsten in Lahontan Valley residents. Additional research is needed on potential exposure pathways involving food or inhalation, and on synergistic effects of mixtures of these natural contaminants on susceptibility to development of leukemia.

Nevada↗
USGS2015

Habitats of North American sea ducks.

Breeding, molting, fall and spring staging, and wintering habitats of the sea duck tribe Mergini are described based on geographic locations and distribution in North America, geomorphology, vegetation and soil types, and fresh water and marine characteristics. The dynamics of habitats are discussed in light of natural and anthropogenic events that shape areas important to sea ducks. Strategies for sea duck habitat management are outlined and recommendations for international collaboration to preserve key terrestrial and aquatic habitats are advanced. We follow the definition of habitat advanced by Odum (1971), which is the place or space where an organism lives. Weller (1999) emphasized that habitats for waterbirds required presence of sufficient resources (i.e., food, water, cover, space) for maintenance during a portion of their annual cycle. Habitats exploited by North American sea ducks are diverse, widespread across the continent and adjacent marine waters and until recently, most were only superficially known. A 15-year-long effort funded research on sea duck habitats through the Sea Duck Joint Venture and the Endangered or Threatened Species programs of the United States and Canada. Nevertheless, important gaps remain in our understanding of key elements required by some species during various life stages. Many significant habitats, especially staging and wintering sites, have been and continue to be destroyed or altered by anthropogenic activities. The goal of this chapter is to develop a comprehensive summary of marine, freshwater, and terrestrial habitats and their characteristics by considering sea duck species with similar needs as groups within the tribe Mergini. Additionally, we examine threats and changes to sea duck habitats from human-caused and natural events. Last, we evaluate conservation and management programs underway or available for maintenance and enhancement of habitats critical for sea ducks.

Book chapter↗
USGS2006

A landscape perspective of the stream corridor invasion and habitat characteristics of an exotic (Dioscorea oppositifolia) in a pristine watershed in Illinois

The spatial distribution of exotics across riparian landscapes is not uniform, and research elaborating the environmental constraints and dispersal behavior that underlie these patterns of distribution is warranted. This study examined the spatial distribution, growth patterns, and habitat constraints of populations of the invasive Dioscorea oppositifolia in a forested stream corridor of a tributary of Drury Creek in Giant City State Park, IL. The distribution of D. oppositifolia was determined at the watershed scale mainly by floodplain structure and connectivity. Populations of D. oppositifolia were confined to the floodplain, with overbank flooding from the stream. Dioscorea oppositifolia probably originates in disturbed areas upstream of natural corridors, and subsequently, the species disperses downstream into pristine canyons or ravines via bulbils dispersing in the water. In Giant City State Park, populations of D. oppositifolia were distributed on the floodplain across broad gradients of soil texture, light, slope, and potential radiation. The study also examined the longevity of bulbils in various micro-environments to illuminate strategies for the management of the species in invaded watersheds. After 1 year, the highest percentages of bulbils were viable under leaves, and much lower percentages were viable over leaves, in soil, and in the creek (76.0±6.8, 21.2±9.6, 21.6±3.6, and 5.2±5.2%), respectively. This study suggests that management procedures that reduce leaf litter on the forest floor (e.g., prescribed burning) could reduce the number of bulbils of D. oppositifolia stored in the watershed.

Illinois↗
USGS2007

Identifying spatial variability of groundwater discharge in a wetland stream using a distributed temperature sensor

Discrete zones of groundwater discharge in a stream within a peat‐dominated wetland were identified on the basis of variations in streambed temperature using a distributed temperature sensor (DTS). The DTS gives measurements of the spatial (±1 m) and temporal (15 min) variation of streambed temperature over a much larger reach of stream (>800 m) than previous methods. Isolated temperature anomalies observed along the stream correspond to focused groundwater discharge zones likely caused by soil pipes within the peat. The DTS also recorded variations in the number of temperature anomalies, where higher numbers correlated well with a gaining reach identified by stream gauging. Focused zones of groundwater discharge showed essentially no change in position over successive measurement periods. Results suggest DTS measurements will complement other techniques (e.g., seepage meters and stream gauging) and help further improve our understanding of groundwater–surface water dynamics in wetland streams.

Water Resources Research↗
USGS1998

Three-year decline of magmatic CO2 emissions from soils of a Mammoth Mountain tree kill: Horseshoe Lake, CA, 1995-1997

We used the closed chamber method to measure soil CO 2 efflux over a three-year period at the Horseshoe Lake tree kill (HLTK)—the largest tree kill on Mammoth Mountain in central eastern California. Efflux contour maps show a significant decline in the areas and rates of CO 2 emission from 1995 to 1997. The emission rate fell from 350 t d −1 (metric tons per day) in 1995 to 130 t d −1 in 1997. The trend suggests a return to background soil CO 2 efflux levels by early to mid 1999 and may reflect exhaustion of CO 2 in a deep reservoir of accumulated gas and/or mechanical closure or sealing of fault conduits transmitting gas to the surface. However, emissions rose to 220 t d −1 on 23 September 1997 at the onset of a degassing event that lasted until 5 December 1997. Recent reservoir recharge and/or extension-enhanced gas flow may have caused the degassing event.

Geophysical Research Letters↗
USGS2010

Theoretical analysis of the transient pressure response from a constant flow rate hydraulic conductivity test

Incorporating a flow pump into a conventional triaxial laboratory system allows fluid to be supplied to or withdrawn from the base of a sediment sample at small and constant rates. An initial transient record of hydraulic head versus time is observed which eventually stabilizes to a constant steady state gradient across the sample; values of hydraulic conductivity can subsequently be determined from Darcy's law. In this paper, analytical methods are presented for determining values of specific storage and hydraulic conductivity from the initial transient phase of such a constant flow rate test. These methods are based on a diffusion equation involving pore pressure and are analogous to those used to describe the soil consolidation process and also to interpret aquifer properties from pumping tests. Examination of the effective stress distributions within the test specimen induced during this type of measurement shows that values of specific storage corresponding to both compression and rebound conditions can be deduced and differentiated simply by reversing the direction of fluid flow. Applicability and limitations of the methods are illustrated with analyses of recently reported flow pump test measurements conducted on a silty-clay specimen.

Water Resources Research↗
USGS2022

Radial growth decline of white spruce (Picea glauca) during hot summers without drought: Preliminary results from a study site south of a boreal forest border

If the modern climate trend continues for an additional 20–40 years, forests along the southern border of Canadian taiga may shift into new ranges of annual temperature and precipitation that are similar to the modern climate of central New York State, United States. Here we investigate the possible future response of white spruce ( Picea glauca (Moench) Voss) to a warmer climate by studying trees planted 90 years ago near the southern limit of their climate tolerance in central New York, 300 km south of the boreal forest where this species is prevalent. We employed high-frequency recording dendrometers to determine radial growth phenology of six mature white spruce trees during 2013–2017. The results demonstrate significant reductions in the length of radial growth periods inversely proportional to the number of hot days with air temperature exceeding 30 °C. During years with very hot summers, the start of radial growth began about 3 days earlier than the 2013–2017 average. However, in those same years, the end of radial growth was also about 17 days earlier resulting in a shorter (70 days versus 100 days) radial growth season. Abundant (350–500 mm) summer precipitation, which resulted in soil moisture values of 20%–30%, allowed us to dismiss drought as a factor. Instead, a likely cause of reduced radial growth was mean temperature that exceeded optimal growth ranges, exacerbated by temperature extremes in ranges that lead to photoinhibition. The latter case was evident in the two warmest growing seasons (2013 and 2017), marked by extended periods of high daytime temperature (>30 °C) followed by early cessation of radial growth independent of seasonal precipitation.

New York↗
USGS2024

Advancing water security in Africa with new high-resolution discharge data

VegDischarge v1 is a comprehensive river discharge across Africa (2000–2021), produced by coupling the agro-hydrologic VegET model and the mizuRoute routing framework. Using remote sensing data and hydrological modeling, the 1-km runoff field simulated by VegET, and routed with mizuRoute, covers over 64,000 river segments in Africa. The VegET model simulates runoff based on vegetation and soil moisture dynamics, while mizuRoute processes this runoff through a detailed river network. Performance metrics show strong model reliability, with R² ranging from 0.5 to 0.9, NSE between 0.6 and 0.9, and KGE from 0.5 to 0.8. The total annual average discharge for Africa is quantified at 3238.1 km³ . year-1, with contributions to various oceanic basins: 989.9 km³ . year-1 to the North Atlantic, primarily from West African rivers like the Senegal, Gambia, Volta, and Niger; 1313.7 km³ . year-1 to the South Atlantic, largely from the Congo River; 212.5 km³ . year-1 to the Mediterranean Sea, predominantly from the Nile River; and 722.0 km³ . year-1 to the Indian Ocean, with substantial inputs from rivers such as the Zambezi. This VegDischarge v1 is valuable for policymakers, stakeholders, and researchers to better understand water availability, its temporal and spatial variations, that impact water-related infrastructure planning, sustainable resource allocation, and the development of climate resilience mitigation strategies.

Scientific Data↗
USGS2007

Physiological Ecology and Ecohydrology of Coastal Forested Wetlands

The form, function, and productivity of wetland communities are influenced strongly by the hydrologic regime of an area. Wetland ecosystems persist by depending upon surpluses of rainfall, evapotranspiration, soil moisture, and frequency and amplitude of water-level fluctuations. Yet, wetland vegetation can also influence ecosystem water economy through conservative water- and carbon-use strategies at several organizational scales. Scientists have described leaf-level water-use efficiency in coastal mangrove forests as being among the highest of any ecosystem. These forested wetlands occur in intertidal areas and often persist under flooded saline conditions. Are these same strategies used by other types of coastal forested wetlands? Do conservative water-use strategies reflect a consequence of salt balance more than efficiency in water use per se? At what organizational scales do these strategies manifest? These are just a few of the questions being answered by physiological and landscape ecologists at the U.S. Geological Survey National Wetlands Research Center (NWRC).

Fact Sheet↗
USGS2013

Nitrate in watersheds: straight from soils to streams?

Human activities are rapidly increasing the global supply of reactive N and substantially altering the structure and hydrologic connectivity of managed ecosystems. There is long-standing recognition that N must be removed along hydrologic flowpaths from uplands to streams, yet it has proven difficult to assess the generality of this removal across ecosystem types, and whether these patterns are influenced by land-use change. To assess how well upland nitrate (NO 3 - ) loss is reflected in stream export, we gathered information from >50 watershed biogeochemical studies that reported nitrate concentrations ([NO 3 - ]) for stream water and for either upslope soil solution or groundwater NO 3 - to examine whether stream export of NO3- accurately reflects upland NO 3 - losses. In this dataset, soil solution and streamwater [NO 3 - ] were correlated across 40 undisturbed forest watersheds, with streamwater [NO 3 - ] typically half (median = 50%) soil solution [NO 3 - ]. A similar relationship was seen in 10 disturbed forest watersheds. However, for 12 watersheds with significant agricultural or urban development, the intercept and slope were both significantly higher than the relationship seen in forest watersheds. Differences in concentration between soil solution or groundwater and stream water may be attributed to biological uptake, microbial processes including denitrification, and/or preferential flow routing. The results of this synthesis are consistent with the hypotheses that undisturbed watersheds have a significant capacity to remove nitrate after it passes below the rooting zone and that land use changes tend to alter the efficiency or the length of watershed flowpaths, leading to reductions in nitrate removal and increased stream nitrate concentrations.

Journal of Geophysical Research G: Biogeosciences↗
USGS2020

Vegetation affects timing and location of wetland methane emissions

Common assumptions about how vegetation affects wetland methane (CH) flux include acting as conduits for CH release, providing carbon substrates for growth and activity of methanogenic organisms, and supplying oxygen to support CH oxidation. However, these effects may change through time, especially in seasonal wetlands that experience drying and re-wetting, or change across space, dependent on proximity to vegetation. In a mesocosm study, we assessed the impacts of on CH flux using clear flux-chamber measurements directly over plants (‘whole-plant’), adjacent to plants (where roots were present but no stems; ‘plant-adjacent’), and plant-free soils (‘control’). During the establishment phase of the study (first 30-days), the whole-plant treatment had ~5-times higher CH flux rates (51.78±8.16 mg-C md) than plant-adjacent or control treatments, which was primarily due to plant-mediated transport, with little contribution from diffusive-only flux. However, high fluxes from whole-plants depleted porewater CH concentrations both directly below whole-plant and in neighboring plant-adjacent treatments, while controls accumulated a highly concentrated reservoir of porewater CH. When the water table was drawn down to simulate seasonal drying, reserve porewater CH from control soil was released as a pulse, equaling the earlier higher CH emissions from whole-plants. Plant-adjacent treatments, which had neither plant-mediated CH transport nor a concentrated reservoir of porewater CH, had low CH flux throughout the study. Our findings indicate that in seasonal wetlands, vegetation affects the timing and location of CH emissions. These results have important mechanistic and methodological implications for understanding the role of vegetation on wetland CH flux.

Journal of Geophysical Research: Biogeosciences↗
USGS2016

Land uses, fire, and invasion: Exotic annual Bromus and human dimensions

Human land uses are the primary cause of the introduction and spread of exotic annual Bromus species. Initial introductions were likely linked to contaminated seeds used by homesteading farmers in the late 1880s and early 1900s. Transportation routes aided their spread. Unrestricted livestock grazing from the 1800s through the mid-1900s reduced native plant competitors leaving large areas vulnerable to Bromus dominance. Ecosystems with cooler and moister soils tend to have greater potential to recover from disturbances (resilience) and to be more resistant to Bromus invasion and dominance. Warmer and drier ecosystems are less resistant to Bromus and are threatened by altered fire regimes which can lead to Bromus dominance, impacts to wildlife, and alternative stable states. Native Americans used fire for manipulating plant communities and may have contributed to the early dominance of Bromus in portions of California. Fire as a tool is now limited to site preparation for revegetation in most ecosystems where Bromus is a significant problem. Once Bromus dominates, breaking annual grass/fire cycles requires restoring fire-tolerant perennial grasses and forbs, which can compete with Bromus and resist its dominance. Current weed management policies often lack regulations to prevent further expansion of Bromus . Research is needed on how and where livestock grazing might help increase perennial grass and forb cover and density to create ecosystems that are more resistant to Bromus . Also, studies are needed to ascertain the role, if any, of oil and gas development in contributing to the spread of Bromus .

Book chapter↗