Intragravel Characteristics In Some Western North Carolina Trout Streams

Characteristics of the intragravel environment of Southern Appalachian trout streams have not been studied. It was the purpose of this study to measure intragravel ~ermeability,apparent velocity, temperature, dissolved oxygen, and bottom composition in areas that visually appeared suitable for trout spawning in 8 relatively undisturbed streams in the Pisgah National Forest of western North Carolina. Comparisons were made between these measurements and the development requirements of salmonid embryos. Two types of standpipes were used, the Mark VI groundwater standpipe and polyvinyl chloride (PVC) standpipes. The lowest mean intragravel dissolved oxygen was 3.2 mg/l. Dissolved oxygen measured by the Mark VI was consistently higher than when measured by the PVC standpipes which indicates that the Mark VI gives a better measure of the true intragravel dissolved oxygen than does the PVC standpipes. Between I November and 30 April, the period when trout embryos are in the gravel, none of the intragravel dissolved oxygen measurements taken with the Mark VI were below 6 mg/l. The data indicate that during the development period the dissolved oxygen was adequate for normal embryo survival. Between I November and 30 April the intragravel temperature varied from 0.5 to II C, temperatures considered to be adequate for trout spawning and embryo development. On a given sampling day the temperature varied no more than 0.5 C from one site to another and the mean intragravel temperature was about the same as the mean surface temperature. This indicates that most of the intragravel water is from surface origin rather than from ground sources. Mean apparent velocity varied from 3.5 to 42.7 cm! hour and mean permeability from 838 to J,967 cm! hour. The mean percentage of the bottom sample between 0.84 and 3.36 mm varied from 8.8 to 28.2% When the measurements are compared with requirements of salmonid embryos and alevins, the areas sampled are adequate for embryo survival. There is a possibility that the embryos are smaller than if intragravel dissolved oxygen and apparent velocity were higher. With the exception of 1creek, it is probable that the amount of sand does not affect fry emergence.

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