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ET Measurements (et + measurement)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Menstruation does not cause anemia: Endometrial thickness correlates positively with erythrocyte count and hemoglobin concentration in premenopausal women

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2006
Kathryn B.H. Clancy
Menstruation has often been cited as a risk factor for iron-deficiency anemia. This study tested whether normal, premenopausal women's luteal endometrial thickness (ET) was associated with their red blood cell count (RBC) and hemoglobin concentrations (Hg), and therefore whether a high ET put women at risk for anemia. Endometrial thickness can be considered a reasonable proxy for menstrual blood loss in normal women. Twenty-six healthy women from the Mogielica Human Ecology Study Site in Poland, aged 20,40 years (29 ± 5.3 years, mean ± SD), were selected. Subjects' ET was measured by transvaginal ultrasound in the luteal phase of the menstrual cycle, and their red blood cell count and hemoglobin concentrations were measured by fasting morning blood samples. Controlling for day of ET measurement, RBC and Hg were positively correlated with ET (r2 = 0.24, P = 0.05; r2 = 0.25, P = 0.04, respectively). We propose that, contrary to popular understanding, a thicker endometrium suggests greater iron reserves, rather than greater risk for anemia, in healthy women. Am. J. Hum. Biol. 18:710,713, 2006. © 2006 Wiley-Liss, Inc. [source]

Connecting Atmosphere and Wetland: Energy and Water Vapour Exchange

GEOGRAPHY COMPASS (ELECTRONIC), Issue 4 2008
Peter M. Lafleur
Wetlands are ubiquitous over the globe, comprise a vast array of ecosystem types and are of great ecological and social importance. Their functioning is intimately tied to the atmosphere by the energy and mass exchanges that take place across the wetland,atmosphere boundary. This article examines recent research into these exchanges, with an emphasis on the water vapour exchange. Although broad classes of wetland type, such as fen, bog and marsh, can be defined using ecological or hydrologic metrics, distinct difference in energy exchanges between the classes cannot be found. This arises because there are many factors that control the energy exchanges and interplay of these factors is unique to every wetland ecosystem. Wetlands are more similar in their radiation balances than in the partitioning of this energy into conductive and turbulent heat fluxes. This is especially true of evapotranspiration (ET) rates, which vary considerably among and within wetland classes. A global survey of wetland ET studies shows that location has little to do with ET rates and that variation in rates is largely determined by local climate and wetland characteristics. Recent modelling studies suggest that although wetlands occupy a small portion of the global land surface, their water and energy exchanges may be important in regional and global climates. Although the number of studies of wetland,atmosphere interactions has increased in recent years more research is needed. Five key areas of study are identified: (i) the importance of moss covers, (ii) lack of study in tropical systems, (iii) inclusion of wetlands in global climate models, (iv) importance of microforms in wetlands and their scaling to the whole ecosystem, and (v) the paucity of annual ET measurements. [source]

Evapotranspiration rates and crop coefficients for a restored marsh in the Sacramento,San Joaquin Delta, California, USA,

HYDROLOGICAL PROCESSES, Issue 6 2008
Judy Z. Drexler
Abstract The surface renewal method was used to estimate evapotranspiration (ET) for a restored marsh on Twitchell Island in the Sacramento,San Joaquin Delta, California, USA. ET estimates for the marsh, together with reference ET measurements from a nearby climate station, were used to determine crop coefficients over a 3-year period during the growing season. The mean ET rate for the study period was 6 mm day,1, which is high compared with other marshes with similar vegetation. High ET rates at the marsh may be due to the windy, semi-arid Mediterranean climate of the region, and the permanently flooded nature of the marsh, which results in very low surface resistance of the vegetation. Crop coefficient (Kc) values for the marsh ranged from 0·73 to 1·18. The mean Kc value over the entire study period was 0·95. The daily Kc values for any given month varied from year to year, and the standard deviation of daily Kc values varied between months. Although several climate variables were undoubtedly responsible for this variation, our analysis revealed that wind direction and the temperature of standing water in the wetland were of particular importance in determining ET rates and Kc values. Published in 2007 by John Wiley & Sons, Ltd. [source]

,18O of water vapour, evapotranspiration and the sites of leaf water evaporation in a soybean canopy

PLANT CELL & ENVIRONMENT, Issue 9 2008
LISA R. WELP
ABSTRACT Stable isotopes in water have the potential to diagnose changes in the earth's hydrological budget in response to climate change and land use change. However, there have been few measurements in the vapour phase. Here, we present high-frequency measurements of oxygen isotopic compositions of water vapour (,v) and evapotranspiration (,ET) above a soybean canopy using the tunable diode laser (TDL) technique for the entire 2006 growing season in Minnesota, USA. We observed a large variability in surface ,v from the daily to the seasonal timescales, largely explained by Rayleigh processes, but also influenced by vertical atmospheric mixing, local evapotranspiration (ET) and dew formation. We used ,ET measurements to calculate the isotopic composition at the sites of evaporative enrichment in leaves (,L,e) and compared that with the commonly used steady-state prediction (,L,s). There was generally a good agreement averaged over the season, but larger differences on individual days. We also found that vertical variability in relative humidity and temperature associated with canopy structure must be addressed in canopy-scale leaf water models. Finally, we explored this data set for direct evidence of the Péclet effect. [source]