Volk, Carol. 2004. Nutrient and biological responses to red alder (Alnus rubra) presence along headwater streams: Olympic Peninsula, Washington. Ph.D.
Ecological concern for riparian environments has increased in recent years as human population growth, water rights, and land use practices have reduced aquatic habitat and pressured biological communities. My study of streams dominated by nitrogen-fixing red alder (Alnus rubra Bong.) and old-growth conifer forests have suggested nutrient resources, productivity, and diversity as defined by water chemistry, suspended particulate matter, periphyton, invertebrates, and trout to be influenced by local forest cover. Algae and invertebrate communities had increased production (biomass) and quality (essential fatty acid and elemental nutrient content) in the presence of alder. Higher production of invertebrate biomass in alder than conifer streams was also transferred to downstream (drift) and adjacent terrestrial environments (emergence). High quality body composition was defined as high quantities of omega 3 and omega 6 fatty acids, %N, and %P. Additionally, within stream variation of periphyton fatty acid content was low compared to variation among streams, suggesting periphyton communities were unique to streams. Fatty acid profiles were also specific to invertebrate families. Periphyton, invertebrates, and trout from streams influenced by salmon had increased omega 3 fatty acid content. High trophic connectivity was suggested through omega 3 and omega 6 fatty acid content correlations between periphyton and grazers, and grazers and trout, indicating these markers might be effectively used in tracing food quality in stream ecosystems. The influence of red alder on aquatic ecosystems shows its importance as a keystone species in the Pacific Northwest. Riparian and upland forest composition can be an important influence on nutrient and organic input to small streams, affecting the nutrient dynamics, productivity, and diversity of aquatic ecosystems.
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