| Summary: | Nutrients are pivotal in the structure and function of river ecosystems. As essential resources they control primary production and decomposition processes, and influence metabolic pathways in the riparian, parafluvial and hyporheic zones (e.g. Duff & Triska, 2000; Wetzel, 2001). Surprisingly few year-round studies, however, have quantified concentrations and fluxes of all major nutrient fractions; this is particularly true for remote alpine and arctic areas (Tockner et al., 2002, and references therein). The fractionation of nutrients into dissolved and particulate forms, and into inorganic and organic components, is essential for a comprehensive understanding of nutrient dynamics. Alpine and arctic streams appear resource limited in terms of both nutrients and organic matter. For example, Lock et al. (1990) showed that the addition of phosphorous to an arctic river resulted in a substantial stimulation of both heterotrophic and autotrophic processes. Peterson et al. (1993) documented bottom-up control of tundra rivers subjected to long-term phosphorous addition. Robinson and Gessner (2000) demonstrated that nutrient addition accelerated leaf breakdown in a glacial stream. Further, there is strong evidence that zoobenthic communities in glacial streams are not solely structured by temperature and channel stability (cf. Milner & Petts, 1994), but are strongly influenced by seasonal shifts in water sources and corresponding availability of nutrient and organic matter resources (Ward, 1994; Füreder, 1999). [.]
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