Graduate Thesis Or Dissertation
 

Fine organic debris and dissolved oxygen in streamed gravels in the Oregon Coast Range

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  • Intragravel organic loading and intragravel dissolved oxygen were studied to determine the relationship between timber harvesting adjacent to first-, second-, and third-order streams and intragravel water quality. Twenty watersheds in the central Coast Range of western Oregon were studied of which five were undisturbed, nine were partially harvested, and six were completely harvested. Intragravel dissolved oxygen was sampled by accessing intragravel water with a small, steel probe and dissolved oxygen was determined with a membrane electrode and dissolved oxygen meter. Streambed gravels were sampled with a liquid nitrogen freeze-core technique and the organics were separated from the inorganics by elutriation. Intragravel organic loading averaged 6.6 gms/ℓ core volume and ranged from 0.2 to 79.5. Intragravel dissolved oxygen averaged 6.5 mg/ℓ and ranged from 2.2 to 10.8 while iritragravel dissolved oxygen depression averaged 34% and ranged from 0% to 74%. Partially harvested watersheds had significantly ([alpha] = .01) lower intragravel organic loading than the undisturbed or completely harvested Gravels in the Oregon Coast Range. watersheds which were not significantly different. A reduction of large organic debris was observed in the partially harvested watersheds. This could have modified the stream's retention capacity for fine organic debris and in turn reduced intragravel organic loading. The most significant variables associated with intragravel organic loading in the multiple linear regression equations were: sample depth, streambed porosity, percent inorganic fines, and large organic debris loading. An increase in any of these variables indicated increased intragravel organic loading. When percent area harvested and length of streambank with harvesting adjacent were included in a regression equation, they explained a small, but significant amount of the variation in intragravel organic loading. Increased harvesting activities as indicated by these variables were associated with decreased intragravel organic loading. There was no significant difference in intragravel dissolved oxygen depression between the undisturbed, partially harvested, and completely harvested watersheds. Percent inorganic fines was the single most significant variable correlated with intragravel dissolved oxygen depression in the multiple linear regression equations. An increase in inorganic fines was associated with decreased intragravel dissolved oxygen. Another group of variables which were indicators of watershed size was correlated with intragravel dissolved oxygen depression. The relationship indicated that larger watersheds were associated with higher intragravel dissolved oxygen. The general conclusion drawn from this study is that timber harvesting in the Oregon Coast Range has not had an adverse impact upon intragravel dissolved oxygen by increasing intragravel organic loading.
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