Mean Water Intake Research Articles

Water balance and maximum concentrating capacity in the primitive rodent, Aplodontia rufa

1. 1. Water balance and maximum urine concentrating capacity were studied in twenty-one specimens of Aplodontia rufa, the Mountain Beaver. 2. 2. Anatomical findings are consistent with the hypothesis of countercurrent gradient and countercurrent multiplication. 3. 3. Water balance studies demonstrated a mean water intake of 32·7 percent ± S. E. 2·4 per cent of body weight; urinary output accounts for most of the water loss. 4. 4. Water deprivation studies with and without oral solute loading demonstrated a maximum U/ P ratio of 2·46 for osmotic concentration in this species. Data are consistent with the countercurrent hypothesis. 5. 5. Physiological data are consistent with the origin of countercurrent gradient either in the loop of Henle or the collecting ducts of the kidneys in the medullary region. 6. 6. Inability to concentrate urine and the necessity of a large daily water intake may account for the limited distribution of these animals in wet, western slopes of the Pacific Coast areas. Before the uplift of the Sierra, these animals ranged through the Great Basin area.

Evaluation of a Radioactive Tracer Method for Measuring Water Intake of Soils

AbstractA tracer method of measuring water intake by application of radioactive gold in the irrigation water was evaluated. When irrigation water containing a constant known amount of isotope is applied to the soil, the amount of isotope adsorbed is proportional to the amount of water entering the soil. To calculate water intake the amount of isotope adsorbed is determined by measuring the activity of soil samples taken in the field. Two factors, vertical distribution of the tracer in the soil, and magnitude of adsorption on the soil surface from flowing irrigation water, were studied. The radioactive tracer was not measurably lost by adsorption from the tagged water as it flowed over the soil surface. It was adsorbed near the soil surface and sampling to a depth of 6 cm. recovered 95% of the gold in Holtville clay loam. The method was used to determine water intake variability. Samples within a plot had an average coefficient of variability of 9%. This would require 7 samples to determine the mean water intake within 10% at the 1% level.