Periphyton Ecology in Great Basin Rivers: Winter Blooms, Hyporheic Exchange Effects, and Reservoir-tailwater Productivity
AuthorDavis, Clinton John
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Recent surveys have revealed a preponderance of evidence that strong periphyton-nutrient interactions occur in Great Basin rivers. These initial field efforts have, to some extent, determined the occurrence, coverage and magnitude of these periphyton blooms. Localized studies are warranted that focus on quantifying ecologically relevant rates (e.g. accrual, primary production, growth rates) and environmental conditions related to bloom events. Three observational studies were conducted in Great Basin rivers focusing on various spatial and temporal dynamics of periphyton blooms. The first study provides a detailed description of a recurring winter bloom in the Truckee River, CA-NV. Results show that despite near-freezing temperatures and low light, the bloom appears as a result of slow but steady growth that experiences minimal losses for an extended period (>100 days). Further, net ecosystem production during the winter bloom can account for approximately a third of the annual net ecosystem production. The second study is an investigation of the potential influence of vertical hyporheic exchange on periphyton assemblages in the main channel of a montane reach and a desert reach in the Truckee River. No convincing evidence was found that periphyton assemblages were affected by exchange processes at the riffle-pool scale in either reach. A sufficient flux of nutrients from other sources (e.g. water column, N2 fixation, internal cycling within mats) supports balanced periphyton growth.Third, a reservoir-tailwater system in eastern Nevada appears to provide the optimal conditions for periphyton that maximizes areal rates of primary production. Periphyton-nutrient interactions were exceptionally strong due to a combination of reservoir operations and a favorable environmental setting in the semi-arid landscape. Estimated primary production rates ranked among the highest reported for streams worldwide and appeared to be constrained to maximum rates by self-regulating mechanisms.