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At least 1,261 records · Page 70Linked to original sources

USGS2001

Soil efflux and total emission rates of magmatic CO2 at the horseshoe lake tree kill, mammoth mountain, California, 1995-1999

We report the results of eight soil CO2 efflux surveys by the closed circulation chamber method at the Horseshoe Lake tree kill (HLTK) - the largest tree kill on Mammoth Mountain. The surveys were undertaken from 1995 to 1999 to constrain total HLTK CO2 emissions and to evaluate occasional efflux surveys as a surveillance tool for the tree kills. HLTK effluxes range from 1 to > 10,000 g m -2 day -1 (grams CO2 per square meter per day); they are not normally distributed. Station efflux rates can vary by 7-35% during the course of the 8- to 16-h surveys. Disturbance of the upper 2 cm of ground surface causes effluxes to almost double. Semivariograms of efflux spatial covariance fit exponential or spherical models; they lack nugget effects. Efflux contour maps and total CO2 emission rates based on exponential, spherical, and linear kriging models of survey data are nearly identical; similar results are also obtained with triangulation models, suggesting that the kriging models are not seriously distorted by the lack of normal efflux distributions. In addition, model estimates of total CO2 emission rates are relatively insensitive to the measurement precision of the efflux rates and to the efflux value used to separate magmatic from forest soil sources of CO2. Surveys since 1997 indicate that, contrary to earlier speculations, a termination of elevated CO2 emissions at the HLTK is unlikely anytime soon. The HLTK CO2 efflux anomaly fluctuated greatly in size and intensity throughout the 1995-1999 surveys but maintained a N-S elongation, presumably reflecting fault control of CO2 transport from depth. Total CO2 emission rates also fluctuated greatly, ranging from 46 to 136 t day-1 (metric tons CO2 per day) and averaging 93 t day-1. The large inter-survey variations are caused primarily by external (meteorological) processes operating on time scales of hours to days. The externally caused variations can mask significant changes occurring at depth; a striking example is the masking of a degassing event generated at depth and detected by a soil gas sensor network in September 1997 while an efflux survey was in progress. Thus, occasional efflux surveys are not an altogether effective surveillance tool for the HLTK, and making them effective by greatly increasing their frequency may not be practical. Published by Elsevier Science B.V.

Chemical Geology↗

USGS2003

Lithologic mapping in the Mountain Pass, California area using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data

Evaluation of an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image of the Mountain Pass, California area indicates that several important lithologic groups can be mapped in areas with good exposure by using spectral-matching techniques. The three visible and six near-infrared bands, which have 15-m and 30-m resolution, respectively, were calibrated by using in situ measurements of spectral reflectance. Calcitic rocks were distinguished from dolomitic rocks by using matched-filter processing in which image spectra were used as references for selected spectral categories. Skarn deposits and associated bright coarse marble were mapped in contact metamorphic zones related to intrusion of Mesozoic and Tertiary granodioritic rocks. Fe-muscovite, which is common in these intrusive rocks, was distinguished from Al-muscovite present in granitic gneisses and Mesozoic granite. Quartzose rocks were readily discriminated, and carbonate rocks were mapped as a single broad unit through analysis of the 90-m resolution, five-band surface emissivity data, which is produced as a standard product at the EROS Data Center. Three additional classes resulting from spectral-angle mapper processing ranged from (1) a broad granitic rock class (2) to predominately granodioritic rocks and (3) a more mafic class consisting mainly of mafic gneiss, amphibolite and variable mixtures of carbonate rocks and silicate rocks. ?? 2002 Elsevier Science Inc. All rights reserved.

Remote Sensing of Environment↗

USGS1998

Controls on denitrification in riparian soils in headwater catchments of a hardwood forest in the Catskill Mountains, U.S.A.

Denitrification in riparian soils is thought to be an important factor that reduces hydrologic export of nitrate from forested and agricultural catchments. A 2-y study to identify the soil factors most closely associated with denitrification in riparian soils in headwater catchments within the Catskill Mountains of New York, included field surveys of surface and subsurface denitrification rates, and an amendment experiment to assess the relative effects of increases in available carbon and substrate NO-/3 on denitrification rates. Denitrification rates were measured by acetylene inhibition during incubation of intact soil cores from eight soil types representing a range of drainage classes. Soil cores were analyzed for organic matter, total P, extractable NO-/3-N and NH+/4-N, organic N, pH, moisture, porosity, and water-filled pore space, to determine which of these factors were most closely associated with denitrification. The distribution of denitrification rates found during the field surveys was highly skewed, with many low or zero values and few high values. Denitrification rates were positively associated with high soil organic matter, total P, and water-filled pore space, and were highest in seep (poorly-drained) soils, toeslope (seasonally-drained) soils, and stream-edge (poorly- to moderately well-drained) soils in which these three soil characteristics were typically high. Denitrification rates in these wet locations were also positively associated with soil NH+/4-N concentration and pH, but not with NO-/3-N concentration, suggesting that the rate of NO-/3 supply (via nitrification or hydrologic transport) was more important than the instantaneous concentration of NO-/3-N in the soils. The amendment experiment indicated that denitrification in soil types studied was most responsive to added glucose alone or with NO-/3. Thus, in these soils, a combination of slow rates of NO-/3 supply and low available carbon appears to limit denitrification. Annual denitrification rates in spring-fed soils (0.74 to 1.43 kg N ha-1 y-1) were up to 5 times greater than in other surface soils, yet these soils accounted for only 1.8% of the catchment's N loss through denitrification because they represent less than 3% of the catchment area. Dry upland soils constituted 71% of the catchment area and accounted for 91% of the catchment's N loss through denitrification. Annual denitrification in the catchment equaled about 65% of stream NO-/3-N and NH+/4-N export and 14% of precipitation NO-/3-N and NH+/4-N inputs. Denitrification appears to be important relative to N input and export in these Catskill catchments.

Soil Biology and Biochemistry↗

USGS1997

Dual-porosity analysis of conservative tracer testing in saturated volcanic rocks at Yucca Mountain in Nye County, Nevada

A radially convergent conservative tracer injection test was conducted between boreholes UE-25 #2 and UE-25 c #3 of the C-hole complex at Yucca Mountain to determine effective porosity and longitudinal dispersivity. Approximately 47% of the tracer mass was recovered and a dual-porosity analytical model replicates the breakthrough curve. Fractured-rock analyses focus on the fracture-porosity and geometry as the controlling factors in transport.

International Journal of Rock Mechanics and Mining↗

USGS1996

Application of reflectance micro-Fourier Transform infrared analysis to the study of coal macerals: An example from the Late Jurassic to Early Cretaceous coals of the Mist Mountain Formation, British Columbia, Canada

The applicability of the reflectance micro-Fourier Transform infra-red spectroscopy (FTIR) technique for analyzing the distribution of functional groups in coal macerals is discussed. High quality of spectra, comparable to those obtained using other FTIR techniques (KBr pellet and transmission micro-FTIR), indicate this technique can be applied to characterizing functional groups under most conditions. The ease of sample preparation, the potential to analyze large intact samples, and ability to characterize organic matter in areas as small as 20 ??m are the main advantages of reflectance micro-FTIR. The quantitative aspects of reflectance micro-FTIR require further study. The examples from the coal seams of the Mist Mountain Formation, British Columbia show that at high volatile bituminous rank, reflectance micro-FTIR provides valuable information on the character of aliphatic chains of vitrinite and liptinite macerals. Because the character of aliphatic chains influences bond disassociation energies, such information is useful from a hydrocarbon generation viewpoint. In medium volatile bituminous coal liptinite macerals are usually not detectable but this technique can be used to study the degree of oxidation and reactivity of vitrinite and semifusinite.

International Journal of Coal Geology↗

USGS2003

Airflows and turbulent flux measurements in mountainous terrain: Part 1. Canopy and local effects

We have studied the effects of local topography and canopy structure on turbulent flux measurements at a site located in mountainous terrain within a subalpine, coniferous forest. Our primary aim was to determine whether the complex terrain of the site affects the accuracy of eddy flux measurements from a practical perspective. We observed displacement heights, roughness lengths, spectral peaks, turbulent length scales, and profiles of turbulent intensities that were comparable in magnitude and pattern to those reported for forest canopies in simpler terrain. We conclude that in many of these statistical measures, the local canopy exerts considerably more influence than does topographical complexity. Lack of vertical flux divergence and modeling suggests that the flux footprints for the site are within the standards acceptable for the application of flux statistics. We investigated three different methods of coordinate rotation: double rotation (DR), triple rotation (TR), and planar-fit rotation (PF). Significant variability in rotation angles at low wind speeds was encountered with the commonly used DR and TR methods, as opposed to the PF method, causing some overestimation of the fluxes. However, these differences in fluxes were small when applied to large datasets involving sensible heat and CO 2 fluxes. We observed evidence of frequent drainage flows near the ground during stable, stratified conditions at night. Concurrent with the appearance of these flows, we observed a positive bias in the mean vertical wind speed, presumably due to subtle topographic variations inducing a flow convergence below the measurement sensors. In the presence of such drainage flows, advection of scalars and non-zero bias in the mean vertical wind speed can complicate closure of the mass conservation budget at the site.

Agricultural and Forest Meteorology↗

USGS2003

Lithogeochemistry of Carlin-type gold mineralization in the Gold Bar district, Battle Mountain-Eureka trend, Nevada

The Gold Bar district contains five Carlin-type gold deposits and four resources for a combined gold endowment of 1.6 M oz [50 t]. The gold deposits are hosted in Devonian carbonate rocks below parautochthonous and allochthonous Paleozoic siliciclastic rocks emplaced during the Early Mississippian Antler orogeny. The district is in the Battle Mountain-Eureka trend, a long-lived structural feature that localized intrusions and ore deposits of different types and ages. The whole-rock geochemistry of four different mineralized and unmineralized Devonian carbonate rock units (two favorable and two unfavorable) were determined and interpreted in the context of the regional geology. A combination of basic statistics, R-mode factor analysis, isocon plots, and alteration diagrams were utilized to (1) identify favorable geochemical attributes of the host rocks, (2) characterize alteration and associated element enrichments and depletions, and (3) identify the mechanism of gold precipitation. This approach also led to the recognition of other types of alteration and mineralization in host rocks previously thought to be solely affected by Carlin-type mineralization. Unit 2 of the Upper Member of the Denay Formation, with the highest Al2O3, Fe2O3 and SiO2 contents and the lowest CaO content, is the most favorable host rock. Based on the high regression coefficients of data arrays on X-Y plots that project toward the origin, Al2O3 and TiO2 were immobile and K2O and Fe2O3 were relatively immobile during alteration and mineralization. Specific element associations identified by factor analysis are also prominent on isocon diagrams that compare the composition of fresh and altered equivalents of the same rock units. The most prominent associations are: Au, As, Sb, SiO2, TI, -CaO and -LOI, the main gold mineralizing event and related silicification and decalcification; Cd, Zn, Ag, P, Ni and Tl, an early base metal event; and MgO, early dolomitization. Alteration diagrams, consisting of X-Y plots of SiO2/Al2O3, K2O/Al2O3, CO2/Al2O3, that documented in classic Carlin-type gold deposits in the region, but the size of the deposits and the intensity of alteration and mineralization are less. The presence of other types of mineralization in the Gold Bar district is also common to most of the other Carlin-type districts located in major mineral belts. The approach used in this study is well suited to the interpretation of multi-element geochemical data from other study areas with superimposed alteration and mineralization. ?? 2002 Elsevier Science B.V. All rights reserved.

Ore Geology Reviews↗

USGS2003

Chemical analyses of pore water from boreholes USW SD-6 and USW WT-24, Yucca Mountain, Nevada

Analyses of pore water extracted from cores of boreholes USW SD-6 in the central part and USW WT-24 in the northern part of Yucca Mountain, Nevada, show significant vertical and lateral variations in dissolved-ion concentrations. Analyses of samples of only a few milliliters of pore water extracted by uniaxial or triaxial compression and by ultracentrifugation methods from adjacent core samples are generally in agreement, within the analytical error of 10% to 15%. However, the values of silica for water obtained by ultracentrifugation are consistently lower than values for water obtained by compression. The larger concentrations probably are due to localized pressure solution of silicate minerals during compression. The shallower water from core in borehole USW SD-6 was extracted from nonwelded units collectively referred to as the Paintbrush Tuff nonwelded (PTn). The deeper water was from core in both boreholes USW SD-6 and USW WT-24 in the nonwelded units referred to as the Calico Hills nonwelded (CHn). Significant differences in mean dissolved-ion concentrations in pore water between the PTn and CHn are (1) decreases in Ca, Mg, SO4, and NO3 and (2) increases in HCO3 and (Na+K)/(Ca+Mg) ratios. The decrease in NO3 and the increase in HCO3 could be the result of denitrification through the oxidation of organic matter. The decrease in Ca and associated increase in (Na+K)/(Ca+Mg) is the result of ion exchange with zeolites in the CHn in borehole USW WT-24. This effect is not nearly as pronounced in borehole USW SD-6, probably reflecting a smaller amount of zeolitization of the CHn in USW SD-6. Geochemical calculations using the PHREEQC code indicate that the pore water from both boreholes USW SD-6 and USW WT-24 is uniformly undersaturated in anhydrite, gypsum, and amorphous silica, but supersaturated in quartz and chalcedony. The saturation of calcite, aragonite, sepiolite, and dolomite is more variable from sample to sample. ?? 2002 Elsevier Science B.V. All rights reserved.

Journal of Contaminant Hydrology↗

USGS2003

Estimation of past seepage volumes from calcite distribution in the Topopah Spring Tuff, Yucca Mountain, Nevada

Low-temperature calcite and opal record the past seepage of water into open fractures and lithophysal cavities in the unsaturated zone at Yucca Mountain, Nevada, site of a proposed high-level radioactive waste repository. Systematic measurements of calcite and opal coatings in the Exploratory Studies Facility (ESF) tunnel at the proposed repository horizon are used to estimate the volume of calcite at each site of calcite and/or opal deposition. By estimating the volume of water required to precipitate the measured volumes of calcite in the unsaturated zone, seepage rates of 0.005 to 5 liters/year (l/year) are calculated at the median and 95th percentile of the measured volumes, respectively. These seepage rates are at the low end of the range of seepage rates from recent performance assessment (PA) calculations, confirming the conservative nature of the performance assessment. However, the distribution of the calcite and opal coatings indicate that a much larger fraction of the potential waste packages would be contacted by this seepage than is calculated in the performance assessment.

Journal of Contaminant Hydrology↗

USGS2003

Chlorine-36 data at Yucca Mountain: Statistical tests of conceptual models for unsaturated-zone flow

An extensive set of chlorine-36 (36Cl) data has been collected in the Exploratory Studies Facility (ESF), an 8-km-long tunnel at Yucca Mountain, Nevada, for the purpose of developing and testing conceptual models of flow and transport in the unsaturated zone (UZ) at this site. At several locations, the measured values of 36Cl/Cl ratios for salts leached from rock samples are high enough to provide strong evidence that at least a small component of bomb-pulse 36Cl, fallout from atmospheric testing of nuclear devices in the 1950s and 1960s, was measured, implying that some fraction of the water traveled from the ground surface through 200-300 m of unsaturated rock to the level of the ESF during the last 50 years. These data are analyzed here using a formal statistical approach based on log-linear models to evaluate alternative conceptual models for the distribution of such fast flow paths. The most significant determinant of the presence of bomb-pulse 36Cl in a sample from the welded Topopah Spring unit (TSw) is the structural setting from which the sample was collected. Our analysis generally supports the conceptual model that a fault that cuts through the nonwelded Paintbrush tuff unit (PTn) that overlies the TSw is required in order for bomb-pulse 36Cl to be transmitted to the sample depth in less than 50 years. Away from PTn-cutting faults, the ages of water samples at the ESF appear to be a strong function of the thickness of the nonwelded tuff between the ground surface and the ESF, due to slow matrix flow in that unit. ?? 2002 Elsevier Science B.V. All rights reserved.

Journal of Contaminant Hydrology↗

USGS2000

Transient calcite fracture fillings in a welded tuff, Snowshoe Mountain, Colorado

The core from two boreholes (13.1 and 19.2 m depth) drilled 500 m apart in the fractured, welded tuff near the summit of the Snowshoe Mountain, Colorado (47??30'N, 106??55'W) had unique petrographic and hydrodynamic properties. Borehole SM-4 had highly variable annual water levels, in contrast to SM-1a, whose water level remained near the land surface. Core samples from both boreholes (n = 10 and 11) were examined petrographically in thin sections impregnated with epoxy containing rhodamine to mark the pore system features, and were analyzed for matrix porosity and permeability. Core from the borehole sampling the vadose zone was characterized by open fractures with enhanced porosity around phenocrysts due to chemical weathering. Fractures within the borehole sampling the phreatic zone were mineralized with calcite and had porosity characteristics similar to Unweathered and unfractured rock. At the top of the phreatic zone petrography indicates that calcite is dissolving, thereby changing the hydrogeochemical character of the rock (i.e. permeability, porosity, reactive surface area, and mineralogy). Radiocarbon ages and C and O stable isotopes indicate that calcite mineralization occurred about 30 to 40 ka ago and that there was more than one mineralization event. Results of this study also provide some relationships between primary porosity development from 3 types of fracture in a welded tuff. (C) 2000 Elsevier Science Ltd.

Applied Geochemistry↗

USGS2002

Geochemistry of rock units at the potential repository level, Yucca Mountain, Nevada

The compositional variability of the phenocryst-poor member of the 12.8 Ma Topopah Spring Tuff at the potential repository level was assessed by duplicate analysis of 20 core samples from the cross drift at Yucca Mountain, Nevada. Previous analyses of outcrop and core samples of the Topopah Spring Tuff showed that the phenocryst-poor rhyolite, which includes both lithophysal and nonlithophysal zones, is relatively uniform in composition. Analyses of rock samples from the cross drift, the first from the actual potential repository block, also indicate the chemical homogeneity of this unit excluding localized deposits of vapor-phase minerals and low-temperature calcite and opal in fractures, cavities, and faults. The possible influence of vapor-phase minerals and calcite and opal coatings on rock composition at a scale sufficiently large to incorporate these heterogeneously distributed deposits was evaluated and is considered to be relatively minor. Therefore, the composition of the phenocryst-poor member of the Topopah Spring Tuff is considered to be adequately represented by the analyses of samples from the cross drift. The mean composition as represented by the 10 most abundant oxides in wt. % or g/100 g is: SiO2, 76.29; Al2O3, 12.55; FeO, 0.14; Fe2O3, 0.97; MgO, 0.13; CaO, 0.50; Na2O, 3.52; K2O, 4.83; TiO2, 0.11; and MnO, 0.07. ?? 2002 Published by Elsevier Science Ltd.

Applied Geochemistry↗

USGS2002

Uranium-series disequilibrium in tuffs from Yucca Mountain, Nevada, as evidence of pore-fluid flow over the last million years

Samples of tuff from boreholes drilled into fault zones in the Exploratory Studies Facility (ESF) and relatively unfractured rock of the Cross Drift tunnels, at Yucca Mountain, Nevada, have been analysed by U-series methods. This work is part of a project to verify the finding of fast flow-paths through the tuff to ESF level, indicated by the presence of 'bomb' 36Cl in pore fluids. Secular radioactive equilibrium in the U decay series, (i.e. when the radioactivity ratios 234U/238U, 230Th/234U and 226Ra/230Th all equal 1.00) might be expected if the tuff samples have not experienced radionuclide loss due to rock-water interaction occurring within the last million years. However, most fractured and unfractured samples were found to have a small deficiency of 234U (weighted mean 234U/238U=0.95??0.01) and a small excess of 230Th (weighted mean 230Th/234U 1.10??0.02). The 226Ra/230Th ratios are close to secular equilibrium (weighted mean = 0.94??0.07). These data indicate that 234U has been removed from the rock samples in the last ???350 ka, probably by pore fluids. Within the precision of the measurement, it would appear that 226Ra has not been mobilized and removed from the tuff, although there may be some localised 226Ra redistribution as suggested by a few ratio values that are significantly different from 1.0. Because both fractured and unfractured tuffs show approximately the same deficiency of 234U, this indicates that pore fluids are moving equally through fractured and unfractured rock, More importantly, fractured rock appears not to be a dominant pathway for groundwater flow (otherwise the ratio would be more strongly affected and the Th and Ra isotopic ratios would likely also show disequilibrium). Application of a simple mass-balance model suggests that surface infiltration rate is over an order of magnitude greater than the rate indicated by other infiltration models and that residence time of pore fluids at ESF level is about 400 a. Processes of U sorption, precipitation and re-solution are believed to be occurring and would account for these anomalous results but have not been included in the model. Despite the difficulties, the U-series data suggest that fractured rock, specifically the Sundance and Drill Hole Wash faults, are not preferred flow paths for groundwater flowing through the Topopah Spring tuff and, by implication, rapid-flow, within 50 a, from the surface to the level of the ESF is improbable. ?? 2002 Elsevier Science Ltd. All rights reserved.

Applied Geochemistry↗

USGS1998

Spatial patterns of tropospheric ozone in the Mount Rainier region of the Cascade Mountains, USA

Few data exist on tropospheric ozone concentrations in rural and wildland areas of western Washington, U.S.A. We measured tropospheric ozone in Mount Rainier National Park and the Puget Sound region of Washington using electronic analyzers and passive samplers during the summers of 1994 and 1995. Electronic analyzers recorded hourly ozone concentrations from five locations between Seattle and Mount Rainier. Ozone concentrations generally increased with distance from Seattle, with maximum hourly concentrations recorded at Enumclaw (319 m elevation, 50 km SE of Seattle). Paradise (1650 m elevation, 100 km SE of Seattle) had the highest monthly mean concentration of all sites measured with analyzers. Diurnal patterns on high-ozone days indicate that concentrations at Paradise remain near 60 ppbv throughout the day, whereas ozone concentrations closer to Seattle had higher peaks during the afternoon but dropped to near zero at night. Passive ozone samplers were used to measure weekly average ozone exposures in four river drainages within Mount Rainier National Park, across an elevation gradient (420 a??2100 m). In most drainages, ozone levels increased with elevation, with highest average weekly ozone exposure (47 ppbv) recorded at 2100 m. Ozone concentrations are significantly higher in the western portion of the park, indicating that ozone exposure varies considerably over short distances. These data provide a reference point for air quality in western Washington and indicate that intensive sampling is necessary to quantify spatial patterns of tropospheric ozone in mountainous regions.

Washington↗

USGS2000

Comparison of precipitation chemistry in the Central Rocky Mountains, Colorado, USA

Volume-weighted mean concentrations of nitrate (NO3-), ammonium (NH4+), and sulfate (SO42-) in precipitation were compared at high-elevation sites in Colorado from 1992 to 1997 to evaluate emission source areas to the east and west of the Rocky Mountains. Precipitation chemistry was measured by two sampling methods, the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) and snowpack surveys at maximum accumulation. Concentrations of NO3- and SO42- in winter precipitation were greater on the western slope of the Rockies, and concentrations of NO3- and NH4+ in summer precipitation were greater on the eastern slope. Summer concentrations in general were almost twice as high as winter concentrations. Seasonal weather patterns in combination with emission source areas help to explain these differences. This comparison shows that high-elevation ecosystems in Colorado are influenced by air pollution emission sources located on both sides of the Continental Divide. It also suggests that sources of nitrogen and sulfur located east of the Divide have a greater influence on precipitation chemistry in the Colorado Rockies. Copyright (C) 2000.

Atmospheric Environment↗

USGS2026

Geochronologic data reveal Late Pleistocene to Holocene debris-flow history and wildfire association within Whiskeytown National Recreation Area, Klamath Mountains, northern California

Understanding the local to regional history of extreme events such as debris flows and floods provides context to plan for and mitigate these hazards to life, property, and infrastructure. The Klamath Mountains of northwestern California have experienced both debris flows and devastating wildfires. Whiskeytown National Recreation Area (WHIS) is at the heart of this range and has a wealth of debris flow–related landforms. Gaining an understanding of prehistoric flows and their relationship with fire or other potential triggers can help mitigate future problems. Optically stimulated luminescence and radiocarbon analyses from sediment and entrained organics in undisturbed facies, including beneath partially buried boulders, establishes a chronology of paleo-events in WHIS. The levee deposits indicate a repetition of debris flows during the latest Holocene, every 125–150 years, since 850 yr. Larger flows occurred, with a record elucidated from debris-flow deposits along Clear Creek, with Middle Holocene ages, ca. 2600 to 5500 yr, most of which have sufficient concentrations of charcoal to indicate origins as postfire debris flows. Deposits at higher elevations show events from the latest Pleistocene ca. 13,000 yr. This geochronology indicates that these are not singular events but are relatively common and inherent to the geomorphic processes shaping this landscape.

California↗

USGS2000

Non-indigenous bamboo along headwater streams of the Luquillo Mountains, Puerto Rico: Leaf fall, aquatic leaf decay and patterns of invasion

The introduction of bamboo to montane rain forests of the Luquillo Mountains, Puerto Rico in the 1930s and 1940s has led to present-day bamboo monocultures in numerous riparian areas. When a non-native species invades a riparian ecosystem, in-stream detritivores can be affected. Bamboo dynamics expected to influence stream communities in the Luquillo Experimental Forest (LEF) were examined. Based on current distributions, bamboo has spread down-stream at a rate of 8 m y-1. Mean growth rate of bamboo culms was 15.3 cm d-1. Leaf fall from bamboo stands exceeded that of native mixed-species forest by c. 30% over a 10-mo study. Bamboo leaves (k = -0.021), and leaves from another abundant riparian exotic, Syzygium jambos (Myrtaceae) (k = -0.018), decayed at relatively slow rates when submerged in streams in fine-mesh bags which excluded macro-invertebrate leaf processors. In a second study, with leaf processors present, bamboo decay rates remained unchanged (k = -0.021), while decay rates of S. jambos increased (k = -0.037). Elemental losses from bamboo leaves in streams were rapid, further suggesting a change in riparian zone/stream dynamics following bamboo invasion. As non-indigenous bamboos spread along Puerto Rico streams, they are likely to alter aquatic communities dependent on leaf input.

Journal of Tropical Ecology↗

USGS2002

Assessing trail conditions in protected areas: Application of a problem-assessment method in Great Smoky Mountains National Park, USA

The degradation of trail resources associated with expanding recreation and tourism visitation is a growing management problem in protected areas worldwide. In order to make judicious trail and visitor management decisions, protected area managers need objective and timely information on trail resource conditions. This paper introduces a trail survey method that efficiently characterizes the location and lineal extent of common trail problems. The method was applied to a large sample of trails within Great Smoky Mountains National Park, a high-use protected area in the USA. The Trail Problem-Assessment Method (TPAM) employs a continuous search for multiple indicators of pre-defined tread problems, yielding census data documenting the location, occurrence and extent of each problem. The present application employed 23 different indicators in three categories to gather inventory, resource condition, and design and maintenance data of each surveyed trail. Seventy-two backcountry hiking trails (528 km), or 35% of the Park's total trail length, were surveyed. Soil erosion and wet soil were found to be the two most common impacts on a lineal extent basis. Trails with serious tread problems were well distributed throughout the Park, although trails with wet muddy treads tended to be concentrated in areas where horse use was high. The effectiveness of maintenance features installed to divert water from trail treads was also evaluated. Water bars were found to be more effective than drainage dips. The TPAM was able to provide Park managers with objective and quantitative information for use in trail planning, management and maintenance decisions, and is applicable to other protected areas elsewhere with different environmental and impact characteristics.

North Carolina, Tennessee↗