ABSTRACT: Ten topographic analysis methods were employed to estimate watershed mean slopes for 13 small forested watersheds (32 to 131 mi2) in East Texas. Of the ten methods employed, the mean slope curve is the most accurate but also the most tedious and laborious one. The method can be simplified by measuring only the lengths of five contours and the areas between these contours within the watershed with little loss of its accuracy. Watershed slopes estimated by the contour length method, the grid contour method, the systematic slope sampling method, and the simplified contour length method are satisfactory for general purposes and relatively simple. The watershed circumference-stream length method, the length-width axis method, the Justin method, and the regression plane method are not suitable for estimating watershed slopes in East Texas without modification. 相似文献
Effects of proportion of watersheds in forest and watershed physiographic factors on mean annual streamflow (1965-76), median flow, and 12 flood flow characteristics were regionally analyzed for 19 unregulated streams in East Texas. Annual streamflow increased with decreasing proportion of forest area. Differences in annual streamflow between full forest cover and bare watersheds could be as much as 200 mm. Other things being equal, the minimum watershed area required to generate 0.142 cm (5 cfs), a criterion used by the U.S. Corps of Engineering in regulating dredge and fill activity for water pollution abatement in East Texas streams, is 70 km2 (27 mi2). Of the 31 physio-climatic parameters analyzed, watershed area, percent forest area, shape index, spring precipitation, and annual temperature were the most significant in affecting streamflow characteristics in East Texas. Using 2-3 of these five variables, all of the 14 streamflow characteristics can be estimated with accuracy ranging from acceptable to excellent levels. 相似文献
The flagellae of the unicellular marine algae Dunaliella bioculata and the freshwater Chlamydomonas resemble very much the cilia lining the bronchial tubes in human lungs. Lindane the commercial product containing 99% of the isomer of hexachlorocyclohexane was tested at various concentrations on the two algae.The concentrations of Lindane tested (5ppm - 30ppm) proved to be cytotoxic and also had a remarkable effect on the motility of both Dunaliella bioculata and Chlamydomonas. The , and isomers of lindane showed similar efects on Dunaliella bioculata.Cytoxicity was measured by growth curves and motility was quantified by microcinematography and Doppler laser velocimetry methods.At low concentrations of all the isomers (5-10 ppm), there was an acceleration of movement which lasted for 5 minutes followed by rapid deceleration of movement.Dunaliella was tested with the ionophore (mobile ion carrier) A23187 for calcium at concentration of (10-5M). The results were compared with that of Dunaliella with lindane at 15ppm and a combination of lindane (15ppm) and Ionophore A23187 (10-5M).The results show that the ionophore A23187 (10-5M) enhances the effect of lindane on the motility of Dunaliella. This could suggest that lindane induced effects may be due to interferences with the intracellular calcium flux. 相似文献
This study assessed the daily exposure to dioxin using comparable approach methods in order to predict the human health risks of dioxin on the general adult population and incinerator workers in Korea. The health risk assessment of dioxin involved four scenarios (General-Direct, General-Breast Milk, General-Blood, and Worker-Blood). The risks were described in terms of the excess cancer risk and the MOEs (Margin-Of-Exposure) for cancer, reproductive dysfunctions, endometriosis, and neurobehavioral effects. The adult daily intake (General-Direct) of dioxin was estimated to be 0.50 pg-TEQ/kg-day based on the dioxin concentrations in the environmental media and foods in Korea. The average dioxin concentrations in General-Breast Milk, General-Blood, and Worker-Blood were 15.13 pg-TEQ/g fat, 14.57 pg-TEQ/g lipid, and 22.90 pg-TEQ/g lipid, respectively. The lifetime average daily doses (LADDs) of dioxin for General-Breast Milk, General-Blood, and Worker-Blood were estimated to be 1.35 pg-TEQ/kg day, 0.99 pg-TEQ/kg day, and 1.15 pg-TEQ/kg day, respectively. Although the estimated risks of cancer and reproductive dysfunctions were not unusually high in any of the four scenarios, the MOE values for the neurobehavioral effects on infants were not sufficiently high to guarantee the safety against this endpoint. 相似文献