Running Waters of the Alaskan Boreal Forest

Abstract

Running waters reflect the character of their landscape. Landscapes influence their streams by supplying dissolved ions to the water, determining the organic matter supply to stream foodwebs, and influencing water temperature and water flows (Gregory et al. 1991, Hynes 1975). The water that feeds streams has passed over and through the vegetation, soils, and rocks of the valley. Just as urine carries the chemical imprint of metabolic activities (such as diabetes), the kinds and amounts of dissolved matter delivered to stream channels carry the signature of the valley’s parent materials and biota. Riparian (streamside) vegetation similarly regulates the balance of carbon sources to stream consumers. In valleys with sparse riparian vegetation, abundant light at the streambed allows in-stream primary production by protists and plants to dominate. Where riparian vegetation forms a canopy over the stream, leaves and needles from shrubs and trees dominate carbon supplies to consumers because low light limits contributions from in-stream primary producers (Vannote et al. 1980). Water temperature and flow are complexly determined by climatic controls (e.g., air and soil temperatures, patterns of precipitation), landscape physiography (e.g., shading of streams by valley walls), and the filter of lightabsorbing and water-transpiring riparian vegetation. Thus, streams in the desert biome of the American Southwest, with intermittent droughts and floods, high water temperatures, and abundant light, are very different habitats from the cool, dark waters of perennial streams in the temperate rain forest of the Pacific Northwest coast (Fisher 1995). Likewise, streams in the boreal forest of Alaska (and in the cold circumboreal forests of the world) take their cues from the landscape. Cold permeates the ecology of the boreal landscape and the running waters therein. The consequences of high-latitude climate on running waters are at least three: creation of ice in both terrestrial and running water systems; limited inputs of organic matter and nutrients to foodwebs; and thermal effects of low water temperatures on biological processes (Oswood 1997). For forested streams, a good case can be made for autumn as the beginning of the stream’s “fiscal” year. Autumnal leaf fall from riparian vegetation provides a major proportion of the annual energy budget to stream foodwebs.