Journal
ECOLOGY
Volume 85, Issue 10, Pages 2818-2827Publisher
WILEY
DOI: 10.1890/04-0171
Keywords
ammonium retention; Brazil; channel morphology; hydraulic characteristics; surface transient storage; tropical streams; uptake potential
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Ammonium retention was studied in 12 tropical headwater streams differing in channel morphology and hydraulic characteristics. Results from NaCl and NH4Cl injections combining a one-dimensional transport model with the nutrient spiraling concept were evaluated. Transient solute storage was large in swamp reaches, with ratios of storage zone and main channel cross-sectional area (A(s)/A) of up to 18, and fractions of residence time due to transient storage ((200)(med)) of up to 94%. Moreover, transient storage was at an inter mediate level in step-pool and meandering reaches and low in run reaches. Maximum ammonium uptake potentials (U-MAX) varied by a factor of 15 due to differing stream morphologies, and ammonium retention was high in swamp and step-pool reaches, with U-max values as high as 1.8 mg N (.) m(-2). min(-1). Between 52% and 85% of ecosystem retention occurred in storage zones. Additionally, differences in ammonium uptake efficiency in the storage zones of contrasting stream morphotypes were negligible; hence, ecosystem ammonium uptake potential was determined by storage zone size. Interestingly, surface transient storage, which is usually neglected in stream tracer studies, was both an important transient storage mechanism and a strong determinant of ammonium uptake potentials. Here, we demonstrated that channel morphology controlled transient storage and ammonium retention potentials in these tropical ecosystems.
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