Periphyton response to increased light and salmon carcass enhancement in six northern California streams

Ambrose, Heather

A Masters of Science thesis in Natural Resources: Fisheries Biology from Humboldt State University, California. From the Abstract: "Concern that declining returns of Pacific salmon have resulted in a loss of nutrients that historically enriched nutrient-poor streams of the Pacific Northwest has prompted recent efforts to introduce salmon carcasses as a recovery technique. While some studies have reported increased periphyton response to nutrient enrichment from carcasses or other sources, other evidence suggests that light may serve as a primary limitation on stream productivity. This study examined periphyton response to simultaneous manipulations of light and salmon carcass enrichment. Chlorophyll a, biofilm ash-free dry mass (AFDM), gross primary production (GPP), and periphyton taxonomic structure were measured in 6 tributary streams in the Smith and Klamath River basins in northern California that received varying treatments of increased light and salmon carcass introductions. In each stream, red alder (Alnus rubra) and other hardwoods were felled from the riparian zone to increase light along a 100 m stretch of stream. In each stream another 100 m reach was established that had an intact ripariancanopy. In 3 streams, salmon carcasses were introduced in both open and canopy-closed sections. Carcass enrichment provided a significant influx of phosphorus, but not nitrogen, into study streams. Results of an experiment using nutrient diffusing clay saucers to evaluate nutrient limitation, conducted in open and closed sections of a carcass-fertilized and a non-fertilized stream, implicated nitrogen as a limiting nutrient, and established a strong canopy effect on periphyton accrual, measured as AFDM. Canopy and carcass treatments did not detectably affect biomass of periphyton on natural substrates. Taxonomic composition of the periphyton assemblage was dominated by diatoms in all stream reaches on all dates, but diatom coverage was significantly reduced in open stream sections in August 2002 with a concomitant increase in green algae. Gross primary production, which was estimated by measuring changes in oxygen concentration in light and dark respiration chambers in early summer, did not differ among treatments. Collectively, results suggest that stream productivity, as indexed by attributes of the periphyton assemblage, may be enhanced to a greater extent by opening of the riparian canopy than by salmon carcass enrichment."

Periphyton response to increased light and salmon carcass enhancement in six northern California streams

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