American Beauty

Aristegi, I. (2000). American Beauty. Banda aparte. (18):66-67. http://hdl.handle.net/10251/42442.Importación Masiva66671

Metabolism of Basque streams measured with incubation chambers

The metabolism (gross primary production, GPP; respiration, R; and net metabolism, NM) of epilithon was measured by incubating randomly selected cobbles in recirculatory chambers in 21 Basque streams running to the Atlantic coast. The studied streams spanned a broad range of environmental conditions and ranged in ecological status from excellent to poor. The GPP ranged from negligible to 35 g 02m-2d-1 , and the R ranged from 1 to 17 g 02m-2d-1. The NM showed that the epilithon was autotrophic in 15 sites and heterotrophic in the rest. None of the measured environmenta1 variables was significant1y correlated with R. Stepwise analyses showed that both the GPP and the NM were related to the epilithic chlorophyll a and phosphate concentrations. The metabolism values obtained were lower than those previously published from open-channel method, the number of autotrophic sites higher, and the controlling environmenta1 variables different. The difference between open-channel and chamber methods was not related to the area covered with cobbles in the study sites. Although chamber measurements yield results in sites where open-channel methods do not work, they seem to overestimate the importance of autotrophy.Se midió el metabolismo (producción primaria bruta, PPB; respiración, R; y metabolismo neto, MN) del epiliton en 21 ríos vascos que drenan a la costa atlántica, incubando cantos en cámaras recirculatorias. Los ríos estudiados comprendían un amplio abanico de condiciones ambientales y su estado ecológico iba desde excelente hasta pésimo. Los valores de PPB iban desde cercanos a O hasta 35 g 02m-2d-J, los de R desde 1 hasta 17 g 02m-2d-J. El MN indicaba que el epiliton de 15 ríos era autótrofo, el resto heterótrofo. Ninguna de las variables ambientales medidas estaba correlacionada de forma significativa con la R. Regresiones paso a paso indicaban que tanto la PPB como el MN estaban relacionados con la clorofila epilítica y con la concentración de fosfato. Los valores de metabolismo obtenidos fueron más bajos que los publicados previamente en base a métodos de cauce abierto, el número de tramos autotróficos era mayor, y las variables ambientales responsables diferentes. Las diferencias entre ambos métodos no eran proporcionales a la abundancia de cantos en el lecho. Auque las medidas en cámara pemüten obtener resultados en tramos en los que no funcionan los métodos en cauce abierto, aparentemente sobreestiman la importancia de la autotrofia

Grip Force Measurement as a Complement to High-Resolution Ultrasound in the Diagnosis and Follow-Up of A2 and A4 Finger Pulley Injuries

The ability of finger flexors to generate force has been studied in relation to climbing performance. However, not much attention has been paid to the decrease in finger grip force in relation to annular pulley injuries. The purpose of the present study was to determine if an injured annular pulley implies a finger flexor force decrease, as well as its relation to clinical and sonographic changes. We performed an observational study in 39 rock climbers with A2 or A4 pulley injuries to the 3rd or 4th fingers. The variables considered were pain upon palpation, ultrasound tendon–bone distance, and finger grip strength decrease. Three rock climbing grip types were considered: the one finger crimp, open crimp, and close crimp. Injured rock climbers presented a decrease in finger grip strength compared to non-injured controls when performing a one finger crimp (p < 0.001). There exists a significant correlation between a tendon–bone distance at the level of the injured pulley and a decreased finger grip strength measured by performing a one finger crimp (p = 0.006). A decrease in finger grip strength could be considered in the diagnostic and follow-up process of A2 and A4 pulley injuries to the 3rd and 4th fingers

Habitat-specific benthic metabolism in a Mediterranean-type intermittent stream

A modified flow-through chamber method was used to measure gross primary production (GPP), net primary production (NPP), community respiration (CR) and associated environmental variables in an intermittent Mediterranean-type stream in Southern Portugal. Three common types of in stream habitats were targeted: cobble (C), cobble covered with filamentous algae (C+A) and leaf litter (LL). NPP, GPP and CR differed significantly among all three habitats. GPP increased with chlorophyll a and, less strongly, with photosynthetic active radiation and, therefore, was highest in C+A habitat. The highest CR was in LL and its variation was best determined by ash-free dry mass (AFDM) of plant litter. Higher respiration in LL was related to heterotrophic activity and, to a lesser extent, to autotrophic respiration associated with periphyton. We observed a decrease of production efficiency of primary producers with AFDM in C+A and C habitats. Our results demonstrate that each habitat type should be considered as a discrete metabolic entity and that particular sets of environmental factors are responsible for habitat specific metabolic responses. Scaling up measurements from discrete habitat patches to the entire reach or stream should not be done by extrapolating the results of a single habitat type and will require quantification of habitat coverage, at the appropriate scale

Headwater gas exchange quantified from O-2 mass balances at the reach scale

Headwater streams are important in the carbon cycle and there is a need to better parametrize and quantify exchange of carbon-relevant gases. Thus, we characterized variability in the re-aeration coefficient (k2) and dissolved oxygen (O2) gas transfer velocity (k) in two lowland headwaters of the River Avon (UK). The traditional one-station open-water method was complemented by in situ quantification of riverine sources and sinks of O2 (i.e., groundwater inflow, photosynthesis and respiration in both the water column and benthic compartments - sediments) enabling direct hourly estimates of k2 at the reach–scale (~150 m) without relying on the nighttime regression method. Obtained k2 values ranged from 0.001 – 0.600 h-1. Average daytime k2 were a factor two higher than values at night, likely due to diel changes in water temperature and wind. Temperature contributed up to 46% of the variability in k on an hourly scale, but clustering temperature incrementally strengthened the statistical relationship. Our analysis suggested that k variability is aligned with dominant temperature trends rather than with short-term changes. Similarly, wind correlation with k increased when clustering wind speeds in increments correspondent with dominant variations (1 m s-1). Time scale is thus an important consideration when resolving physical drivers of re-aeration. Mean estimates of k from recent parametrizations proposed for upscaling, when applied to the settings of this study, were found to be in agreement with our independent O2 budget assessment (within <15%), adding further support to the validity of upscaling efforts aiming at quantifying large-scale riverine gas emissions

Climate-Induced Changes in Spring Snowmelt Impact Ecosystem Metabolism and Carbon Fluxes in an Alpine Stream Network

Although stream ecosystems are recognized as an important component of the global carbon cycle, the impacts of climate-induced hydrological extremes on carbon fluxes in stream networks remain unclear. Using continuous measurements of ecosystem metabolism, we report on the effects of changes in snowmelt hydrology during the anomalously warm winter 2013/2014 on gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production (NEP) in an Alpine stream network. We estimated ecosystem metabolism across 12 study reaches of the 254 km2 subalpine Ybbs River Network (YRN), Austria, for 18 months. During spring snowmelt, GPP peaked in 10 of our 12 study reaches, which appeared to be driven by PAR and catchment area. In contrast, the winter precipitation shift from snow to rain following the low-snow winter in 2013/2014 increased spring ER in upper elevation catchments, causing spring NEP to shift from autotrophy to heterotrophy. Our findings suggest that the YRN transitioned from a transient sink to a source of carbon dioxide (CO2) in spring as snowmelt hydrology differed following the high-snow versus low-snow winter. This shift toward increased heterotrophy during spring snowmelt following a warm winter has potential consequences for annual ecosystem metabolism, as spring GPP contributed on average 33% to annual GPP fluxes compared to spring ER, which averaged 21% of annual ER fluxes. We propose that Alpine headwaters will emit more within-stream respiratory CO2 to the atmosphere while providing less autochthonous organic energy to downstream ecosystems as the climate gets warmer