Understanding patterns of expansion, contraction, and disconnection of headwater stream length in diverse settings is invaluable for the effective management of water resources as well as for ...informing research in the hydrology, ecology, and biogeochemistry of temporary streams. More accurate mapping of the stream network and quantitative measures of flow duration in the vast headwater regions facilitate implementation of water quality regulation and other policies to protect waterways. We determined the length and connectivity of the wet stream and geomorphic channel network in 3 forested catchments (<75 ha) in each of 4 physiographic provinces of the Appalachian Highlands: the New England, Appalachian Plateau, Valley and Ridge, and Blue Ridge. We mapped wet stream length 7 times at each catchment to characterize flow conditions between exceedance probabilities of <5% and >90% of the mean daily discharge. Stream network dynamics reflected geologic controls at both regional and local scales. Wet stream length was most variable at two Valley and Ridge catchments on a shale scarp slope and changed the least in the Blue Ridge. The density and source area of flow origins differed between the crystalline and sedimentary physiographic provinces, as the Appalachian Plateau and Valley and Ridge had fewer origins with much larger contributing areas than New England and the Blue Ridge. However, the length and surface connectivity of the wet stream depended on local lithology, geologic structure, and the distribution of surficial deposits such as boulders, glacially derived material, and colluival debris or sediment valley fills. Several proxies indicate the magnitude of stream length dynamics, including bankfull channel width, network connectivity, the base flow index, and the ratio of geomorphic channel to wet stream length. Consideration of geologic characteristics at multiple spatial scales is imperative for future investigations of flow intermittency in headwaters.
The effect of rapid erosion on kinematic partitioning along transpressional plate margins is not well understood, particularly in highly erosive climates. The Blue Mountains restraining bend (BMRB) ...of eastern Jamaica, bound to the south by the left-lateral Enriquillo-Plantain Garden fault (EPGF), offers an opportunity to test the effects of highly erosive climatic conditions on a 30-km-wide restraining bend system. No previous thermochronometric data exists in Jamaica to describe the spatial or temporal pattern of rock uplift and how oblique (>20°) plate motion is partitioned into vertical strain. To define the exhumation history, we measured apatite (n=10) and zircon (n=6) (U-Th)/He ages, 40Ar/39Ar (n=2; amphibole and K-spar) ages, and U/Pb zircon (n=2) crystallization ages. Late Cretaceous U/Pb and 40Ar/39Ar ages (74–68Ma) indicate rapid cooling following shallow emplacement of plutons during north-south subduction along the Great Caribbean Arc. Early to middle Miocene zircon helium ages (19–14Ma) along a vertical transect suggest exhumation and island emergence at ~0.2mm/yr. Older zircon ages 10–15km to the north (44–35Ma) imply less rock uplift. Apatite helium ages are young (6–1Ma) across the entire orogen, suggesting rapid exhumation of the BMRB since the late Miocene. These constraints are consistent with previous reports of restraining bend formation and early emergence of eastern Jamaica. An age-elevation relationship from a vertical transect implies an exhumation rate of 0.8mm/yr, while calculated closure depths and thermal modeling suggests exhumation as rapid as 2mm/yr. The rapid rock uplift rates in Jamaica are comparable to the most intense transpressive zones worldwide, despite the relatively slow (5–7mm/yr) strike-slip rate. We hypothesize highly erosive conditions in Jamaica enable a higher fraction of plate motion to be accommodated by vertical deformation. Thus, strike-slip restraining bends may evolve differently depending on erosivity and local climate.
•Jamaica offers a unique opportunity to study the effect of climate on tectonics.•The Blue Mountains restraining bend is a zone of rapid transpressive rock uplift.•Two phases of Miocene exhumation occurred from 20–5Ma and 5Ma-Present.•Rates of exhumation since 5Ma are ~1–2mm/yr across the entire BMRB.•Highly erosive tropical climates partition vertical deformation efficiently.
We have investigated the geologic controls on hydraulic geometry of bedrock rivers using a single large catchment, the New River, from a stable tectonic setting with variable, resistant lithology but ...spatially stable climate. Our survey of channel width at 0.5km spacing along 572km of the river shows major variation that only roughly fits the expected scaling relationships between width, drainage area, and slope. Considerable variations in width, including steps in trends and large spikes, relate to physiogeologic boundaries that the river passes through. A large fraction (15%) of the river's length classifies as bedrock reach, showing that it behaves more like a bedrock river than an alluvial river. Unlike established trends, the channel is wider in bedrock than in alluvium. Field observations show that aspect ratio (width to depth) is not constant, but fluctuates systematically with width from wide, shallow reaches to narrower, deeper reaches. Our observations of bedrock properties suggest that susceptibility to fluvial plucking versus abrasion may control this anomalous channel morphology. One end member form with aspect ratio as high as 500, which we term the incision plain, is associated with very closely spaced discontinuities (~10cm) in otherwise hard rock. We propose that the closely spaced discontinuities enable efficient plucking that leads to widening by lateral erosion. This morphology locally occurs in other passive margin rivers and may be a fundamental fluvial form that is similar to, but the inverse of, slot canyons. The other end member, which we term channel neck, is narrower and deeper with complex flow paths through blocky bedrock. This form occurs where discontinuity spacing is longer (>0.5m) and erosion is abrasion dominated. These results imply that changes in channel width do not necessarily reflect variations in uplift rate, but instead may result from complex response to bedrock properties.
•Bedrock channel width can be extremely variable along large passive margin rivers.•High aspect ratio (width/depth) occurs in bedrock with closely spaced joints.•Narrower channels occur where erosion is dominated by abrasion.•Morphology reflects local properties, not necessarily variation in uplift rate.
The Blue Ridge escarpment of the southern Appalachian Mountains is a striking and rugged topographic feature of the ancient passive margin of eastern North America. The crest of the escarpment ...generally coincides with an asymmetric regional drainage divide, separating steep streams of the escarpment face from low-gradient streams of the Blue Ridge Upland. Recent exhumation and erosion rate studies suggest that the escarpment has evolved by inland erosional retreat, but the mechanism, timing, and magnitude of retreat remain poorly understood. Longitudinal stream profiles and slope–drainage area relationships of several upland basins draining the divide have led to the identification of 14 previously unknown fluvial terrace deposits preserved at the escarpment crest. These relict terraces and the associated beheaded drainages indicate the role of large stream capture events in producing ongoing escarpment retreat through landward divide migration and subsequent topographic adjustment. Terrace location and preservation suggest that rectilinear drainage patterns and divide asymmetry generate discrete high order captures and episodes of rapid localized retreat that collectively produce slower evolution of the escarpment at large. While overall retreat magnitude and rate remain unknown, roundness of terrace alluvium suggests that the most recent captures have locally produced tens of kilometers of retreat within the limited preservation lifetime of the deposits. In contrast with recent numerical modeling and cosmogenic studies, these data show the potential for stream capture and divide migration to sustain passive margin escarpment evolution long after the cessation of rifting. The fluvial record of divide retreat preserved atop the Blue Ridge escarpment suggests the potential for using field methods to better constrain the histories of younger, taller, and potentially more dynamic passive margin escarpments.
Spotila, J.A.; Marshall, J.; DePew, K.; Prince, P.S., and Kennedy, L., 2016. Potential for geologic records of coseismic uplift and megathrust rupture along the Nicoya Peninsula, Costa Rica. This ...study presents the first paleoseismic investigation of the Middle America subduction zone at the Nicoya Peninsula, Costa Rica. This megathrust has been intensely studied over the past decade using a range of geologic and geophysical techniques, and it experienced interplate rupture in 2012 (moment magnitude 7.6). Despite many factors that could hinder preservation of a paleoseismic record in this coastal environment, including complex deposition in a tropical mangrove setting, this reconnaissance identifies two sites where stratigraphic evidence may record relative sea-level changes associated with Holocene earthquakes. Although more work is required to better constrain the timing and nature of these events, this study suggests that the Tamarindo and Playa Carrillo estuaries contain possible paleoseismic records. At the main study site of Tamarindo, alternations between mud and peat below 1 m in depth may record relative sea-level change associated with multiple earthquakes between ∼5 and 8 ka. However, this site offers no paleoseismic evidence of late-Holocene earthquakes. Much younger stratigraphy occurs at a Playa Carrillo, where mud-peat alternations from 200 to 500 years ago could represent recent coseismic ground motions. The work presented here is limited to litho- and chronostratigraphy, however, and full interpretation of the relative sea-level histories of both sites will require quantitative, high-resolution biostratigraphic analysis. Although the results suggest paleoseismic records exist along the Nicoya Peninsula, they appear fragmentary and complex and ultimately may not provide a continuous, high-resolution paleoseismic record like those obtained at other subduction zones worldwide.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Patient surveys suggest that fatigue is a common problem in primary biliary cirrhosis (PBC). The actual extent of the problems caused by fatigue in PBC has yet to be determined as previous studies ...addressing this question have tended to use selected patient subgroups and subjective or non-quantitative fatigue assessment tools. Here, we have attempted to more accurately assess the extent of fatigue in PBC, and the specificity of the symptom for this disease, by the application of an objective measure of fatigue impact (the fatigue impact score FIS) to a geographically based patient cohort, age- and sexmatched normal controls, and chronic liver disease controls.
Postal completion of the FIS and linked symptom assessment tools.
Median FIS was significantly higher in patients (n = 136) than community controls (40 0–138 vs. 28 0–156; P < 0.0001) and chronic liver disease controls (n = 38) (20.5 0-145; P < 0.05). Fatigue scores in the 11 patients who had undergone liver transplantation (median 3.5 years previously) were the same as those in non-transplanted patients with advanced disease.
Fatigue is a significant and specific problem in PBC. It is not, however, universal and affects fewer patients than has previously been thought to be the case based on data from selected patient cohorts. This definition of the “normal range” for fatigue in PBC will assist in future studies of etiology and therapy.
Abstract Understanding patterns of expansion, contraction, and disconnection of headwater stream length in diverse settings is invaluable for the effective management of water resources as well as ...for informing research in the hydrology, ecology, and biogeochemistry of temporary streams. More accurate mapping of the stream network and quantitative measures of flow duration in the vast headwater regions facilitate implementation of water quality regulation and other policies to protect waterways. We determined the length and connectivity of the wet stream and geomorphic channel network in 3 forested catchments (<75 ha) in each of 4 physiographic provinces of the Appalachian Highlands: the New England, Appalachian Plateau, Valley and Ridge, and Blue Ridge. We mapped wet stream length 7 times at each catchment to characterize flow conditions between exceedance probabilities of <5% and >90% of the mean daily discharge. Stream network dynamics reflected geologic controls at both regional and local scales. Wet stream length was most variable at two Valley and Ridge catchments on a shale scarp slope and changed the least in the Blue Ridge. The density and source area of flow origins differed between the crystalline and sedimentary physiographic provinces, as the Appalachian Plateau and Valley and Ridge had fewer origins with much larger contributing areas than New England and the Blue Ridge. However, the length and surface connectivity of the wet stream depended on local lithology, geologic structure, and the distribution of surficial deposits such as boulders, glacially derived material, and colluival debris or sediment valley fills. Several proxies indicate the magnitude of stream length dynamics, including bankfull channel width, network connectivity, the base flow index, and the ratio of geomorphic channel to wet stream length. Consideration of geologic characteristics at multiple spatial scales is imperative for future investigations of flow intermittency in headwaters.
Abstract Objectives This systematic review was to compare the effects of interventions for the management of fear and anxiety for dental treatments. Methods This research project was applied to ...PubMed, CENTRAL, Web of Science, Cochrane library databases. The last search was run on March 31st, 2021. A list of references of relevant articles and previous reviews were checked. Qualitative and quantitative analyses were performed. Results A total of 20 eligible randomized controlled trials were included, and 969 participations in experimental group and 892 participations in the control group were involved. Anxiety levels decreased more in intervention groups than in control groups (Z=3.47, P=0.0005, SMD=-0.62, 95% CI -0.98 to -0.27). For adults, there was statistical difference between experimental and control groups Z=2.14, P=0.03, 95% CI -0.54 (-1.03, -0.04), while there was not no such statistical difference in children and adolescents Z=1.62, P=0.11, 95% CI -0.60 (-1.32, 0.13). Patients experienced a significant decrease in anxiety level using sedation drugs Z=2.44, P=0.01, 95% CI -0.61 (-1.10, -0.12) and audio-visual distractions Z=3.1, P=0.002, 95% CI -0.86 (-1.40, -0.32). For the informative intervention groups, patients did not show significant difference than control groups Z=1.22, P=0.22, 95% CI -0.55 (-1.43, 0.33). There was no statistical difference in vital signs Z=1.39, P=0.16, 95% CI -0.25 (-0.61, 0.10) and pain levels Z=0.69, P=0.49; SMD=-0.06, 95% CI (0.27, 0.11) between intervention and control groups. Conclusions Interventions should be used in managing anxiety and fear for dental treatment. It might be effective for anxiety alleviating for adults, but there was a low certainty of evidence that interventions could reduce anxiety level in children and adolescents. Sedation drugs and audio-visual distractions might be useful for managing dental fear and anxiety. Pain levels and vital signs could not be improved form our study. High-quality randomized clinical trials are required for further study.
PDF
