Predicting logging debris accumulation in natural streambeds : a method for forest managers Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3t945t088

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  • This study has analyzed factors which affect the accumulation of terrestrial organic debris within natural gravel streambeds. In addition, the amounts, sizes, and physical conditions of intruded material were measured, along with the effect of the detritus on intragravel dissolved oxygen levels. Measurements indicate that aged intragravel detritus had no significant impact on subsurface dissolved oxygen levels. The organic material extracted from the streambeds was composed primarily of highly conditioned woody material, which is characterized by a very low B.O.D. These measurements support the hypothesis that decomposing organic material produces only a temporary demand on intragravel dissolved oxygen supplies. Previous work has indicated that this demand has generally been met after only 60 days. One hundred and forty-four frozen core samples of ten streambeds were taken as a means of analyzing subsurface organic debris concentrations. These cores provided the data needed to calculate streambed porosity, median cobble size, and average detritus size. In addition, stream gradient and surface debris loading were measured. Subsurface organic debris concentrations were found, to be extremely variable. The range of values observed, in grams of detritus per liter of pore volume, was 1.4 to 439.9. The mean value was 29.3 grams per liter of pore volume, with a standard. deviation of 52.9. These values indicate that organic material may provide a severe threat to subsurface dissolved oxygen levels, especially if high concentrations of fresh, finely divided material, such as leaves or needles, are present. Although the impacts exerted by organic material are only temporary, there may be a detrimental impact on the fisheries resource, if a large B.O.D. is produced at the time alevins are dependent on intragravel dissolved oxygen. Regression equations for predicting subsurface debris concentrations were developed. It was observed That subsurface debris accumulations can generally be expected to increase with increases in streambed porosity, surface debris loading, and median cobble size. Concentrations can be expected to decrease with increases in stream gradient. Estimates developed with these models cannot be expected to yield accurate values under all conditions, and the possibility of high variability must be anticipated. However, the models developed in this study do provide a means of predicting subsurface debris accumulations in natural gravel streambeds under a variety of conditions. In addition, the measurement and analysis techniques described will encourage future research which will further develop an understanding of the small stream ecosystem.
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  • Master files scanned at 600 ppi (256 Grayscale) using Capture Perfect 3.0 on a Canon DR-9080C in TIF format. PDF derivative scanned at 300 ppi (256 B+W), using Capture Perfect 3.0, on a Canon DR-9080C. CVista PdfCompressor 3.1 was used for pdf compression and textual OCR.
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