Graduate Thesis Or Dissertation
 

The effects of logging on periphyton communities of coastal streams

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  • The purpose of this study was to investigate the effects of logging on the productivity, structure and biomass of a periphyton community developed in mountain streams. The three streams used in this investigation were located in the coast range of Lincoln County, Oregon. They were selected for similarity of habitat, terrestrial canopy, and benthic community, one dominated by diatoms (Bacillarophyceae). In 1966, Deer Creek watershed was subjected to a selective pattern of logging with a buffer strip of canopy left standing along the stream. Needle Branch watershed was subjected to clearcut logging resulting in the removal of all the canopy, and the watershed of Flynn Creek was left in its natural condition and used as a control. Clearcut logging had a profound impact on the aquatic environment of Needle Branch. As indicated by light reading taken during primary productivity runs, the stream received a mean value of seven times more light in 1967, July-September, as compared to similar months in 1964, prior to logging. This resulted in a high of 50 langleys/hr as compared to 13 langleys/hr recorded prior to logging. Concurrently, the mean temperature of the stream, as measured during productivity runs, increased 6 C, with a high of 26 C recorded as compared to 14. 8 C prior to logging. The impact of these environmental changes resulted in a periphyton community quite different from that existing in the stream prior to logging. As indicated by the communities developed on glass artificial substrates, this stream, which supported a periphyton community of diatoms prior to logging, was changed to a habitat supporting a mixed community of filamentous algae and diatoms with the filamentous algae becoming dominant. The diatom flora of the stream changed in species composition and became more uniform throughout, after logging. Samples of the communities taken from the natural substrate and glass artificial substrates were similar, but dissimilarities arose in the relative abundance of the species. Artificial substrates cut from native rock supported a community of greater similarity to that on the natural substrate, than existed between the communities developed on glass artificial substrates and the natural substrate. The index of the autotrophic organisms in Needle Branch (mg chlorophyll a/m²) was lower after logging, as compared to that found in the stream prior to logging. Mean concentrations,for cornparable months, of 51.3 mg chlorophyll a/m² were recorded before logging, compared to 9.10 mg chlorophyll a/m² recorded after logging. The index of the autotrophic organisms obtained from the organic matter collected on glass artificial substrates showed little relationship to that obtained from the substrate of the stream. Respiration of the community after logging was higher than during the equivalent period prior to logging. Mean respiration for July-September, 1964,was 1.08 g 0₂/m²/day while after logging the reduced biomass had a respiration rate of 1.28 g 0₂ /m²/day. After logging, gross primary production was higher in Needle Branch than in Flynn Creek (control watershed),, but slightly less than recorded for Needle Branch prior to logging. Needle Branch maintained gross primary production comparable to the prelogging period, with a smaller biomass, by increased efficiency of photosynthesis per mg chlorophyll a. The photosynthesis-respiration ratio (P/R ratio) indicated that prior to logging, Needle Branch was autotrophic for all seasons except the fall. After logging, the stream became progressively more heterotrophic from spring to summer.
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