Comparing watershed soil erosion of Taiwan and Thailand

Tropical watersheds in Taiwan and Thailand face the same severe soil erosion problem that is increasing at an alarming rate. In order to evaluate the severity of soil erosion, we quantitatively investigate the issue using a common soil erosion model (Universal Soil Loss Equation, USLE) on the Shihmen reservoir watershed of Taiwan and the Lam Phra Ploeng basin of Thailand, and compare their respective erosion factors. The results show an interesting contrast between the two watersheds. Some of the factors (rainfall factor, slope-steepness factor) are higher in the Shihmen reservoir watershed, while others (soil erodibility factor, cover and management factor) are higher in the Lam Phra Ploeng basin. The net result is that these factors cancel each other out, and the amount of soil erosion of the two watersheds are very similar at 68.03 t/ha/yr and 67.57 t/ha/yr, respectively.

Preparation of Erosion Susceptibility Map of Dhaman Khadi Sub-Watershed in Eastern Gujarat Using ArcGIS Interface

An attempt has been made to model land degradation in term of water erosion of selected Dhaman Khadi sub-watershed (7710.64 ha.) in Eastern Gujarat, India through Revised Universal Soil Loss Equation using ArcGIS interface. The average erosivity of 30 years (1986-2015) annual rainfall using standard formula was estimated to be 480.63 MJ mm ha−1 hr−1 per year. The erodibility factor K was computed as 0.236 and 0.177 mt∙hr MJ−1 mm−1 per unit R respectively for clay loam and clay soils using modified formula.. 20 m Digital Elevation Model was prepared from Toposheet No. F43N10 by using ‘Topo to Raster’ interpolation method. The slope length factor L was derived from DEM using Unit Stream Power Erosion and Deposition (USPED) Model. The raster layers of slope steepness factor for slope having < 9 % and ≥ 9 % was prepared separately to form final slope steepness factor map. Cover management factor map was derived based on cropping pattern for the various land cover categories of the study area. The standard conservation practice factor values for cross-sloped agricultural lands were assigned to the attribute table of the intersected map of LU/LC and slope maps to prepare the P factor map. Average gross soil erosion was minimum for evergreen forest while maximum for wasteland without scrub. Highest area covered by agricultural land (i. e. 41.54) of Dhaman Khadi sub-watershed having 33.28 tons/ha/yr gross soil erosion needs immediatetreatment to prevent land degradation. Soil loss tolerance limit of study area was used to derive erosion susceptibility map in order to identify the priority of conservation programs. As all the factors of RUSLE was estimated precisely at sub-watershed level, the study could help for rapid and reliable planning of watershed development programs in combination with the use of RS and GIS technology.

An Equation for Estimating the (R) Use Slope Steepness Factor, s

Currently three equations are used for calculating slope steepness factor for the revised universal soil lossequation (RUSLE); one for slopes less than nine percent, the second for slopes equal or greater than ninepercent, and the third equation that has been proposed for use in China for slopes equal or greater than 17%. The three equations have linear relationships between slope steepness factor, S and the sine of the slopeangle, q. The three equations under predict the factor, S when used on slope steepness beyond the data setsused to develop them. In addressing this problem several alternative forms of equations (linear, power, andpolynomial) were tested using field plot soil loss data gathered by several researchers in different countriesfor slopes ranging from three percent to 55 %. A single power function relating the sine of the slope angle, qto the slope steepness factor, S has been identified to be more suitable and accurate for estimating the RUSLEslope steepness factor, S.

Effects of depolarization and low intracellular pH on charge movement currents of frog skeletal muscle fibers

The low intracellular pH and membrane depolarization associated with repeated skeletal muscle stimulation could impair the function of the transverse tubular (t tubule) voltage sensor and result in a decreased sarcoplasmic reticulum Ca2+ release and muscle fatigue. We therefore examined the effects of membrane depolarization and low intracellular pH on the t-tubular charge movement. Fibers were voltage clamped in a double Vaseline gap, at holding potential (HP) of −90 or −60 mV, and studied at an internal pH of 7.0 and 6.2. Decreasing intracellular pH did not significantly alter the maximum amount of charge moved, transition voltage, or steepness factor at either HP. Depolarizing HP significantly decreased steepness factor and maximum charge moved and shifted the transition voltage to more positive potentials. Elevated extracellular Ca2+ decreased the depolarization-induced reduction in the charge movement. These results indicate that, although the decrease in intracellular pH seen in fatigued muscle does not impair the t-tubular charge movement, the membrane depolarization associated with muscle fatigue may be sufficient to inactivate a significant fraction of the t-tubular charge. However, if t-tubular Ca2+ increases, some of the charge may be stabilized in the active state and remain available to initiate sarcoplasmic reticulum Ca2+ release.

Potassium currents in the inner segment of single retinal cone photoreceptors

1. The K+ currents of cone inner segments isolated from the retina of a lizard were studied with the use of tight-seal electrodes in the whole cell configuration. To conduct these studies other identified currents in the cell were blocked. Co2+ blocked a voltage-dependent Ca2+ current and a Ca2(+)-dependent Cl- current, and Cs+ blocked an inward-rectifying current partially carried by K+. 2. The cells sustained a voltage-dependent K+ current that was blocked by tetraethylammonium (TEA)+ and had characteristics typical of the delayed rectifier. However, we found no evidence for the existence of “A”-type K+ currents or Ca2(+)-dependent K+ currents. 3. The delayed-rectifier current was nearly ideally selective for K+. Increasing external K+ concentration 10-fold shifted the reversal potential by 55 mV. 4. Analysis of the voltage dependence of the activation of the delayed-rectifier current revealed the existence of two distinct subclasses of this current. We referred to them as IdrL and IdrH for low and high threshold of voltage activation. 5. IdrL activated at voltages above -70 mV. Its dependence on voltage was described by Boltzmann's function with average half-maximum activation at -51 mV and steepness factor k = 7.5 mV. IdrH activated at voltages above -50 mV. Its dependence on voltage was described by Boltzmann's function with average half-maximum activation at -4.6 mV and steepness factor k = 17.1 mV. 6. Of nine cells analyzed in detail, one demonstrated IdrH alone, whereas the remaining had a variable mixture of the two current subtypes. At maximum activation the current through IdrL ranged between 0.3 and 0.5 of the total delayed-rectifier current. 7. The kinetics of activation of the total delayed-rectifier current were described by the sum of two exponentials the amplitudes and time constants of which were voltage dependent. However, the kinetics of the current subtypes were not resolved individually. The current inactivated slowly with a single-exponential time course that was voltage dependent. 8. The voltage dependence of the delayed-rectifier current indicates the current is active in a cone photoreceptor in the dark. The current is 20-30 pA in amplitude at the dark-membrane potential and outwardly directed. 9. IdrL may generate a rapid relaxation of photovoltages activated by dim lights--those that hyperpolarize the membrane by only a few millivolts. The delayed-rectifier currents help shape the action potentials that can be generated in isolated cone photoreceptors