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Communication at the NABS Annual meeting, Keystone, 2000
(196) BOTTOM-UP HYDRAULIC CONTROL OF STREAM ECOSYSTEMS.
D.D. Hart1,2, B.J.F. Biggs2, and V.I. Nikora2. 1Patrick Center for Environmental Research, Academy of Natural Sciences, Philadelphia, PA 19103, 2National Institute of Water and Atmospheric Research, Christchurch, New Zealand
Environmental factors that affect the species composition and productivity of benthic algae can potentially shape many different facets of ecosystem structure and function. In theory, hydraulic conditions can influence benthic algae via at least three different mechanisms: (1) modification of mass transfer rates of limiting nutrients; (2) delivery of algal propagules to the bed; and (3) removal of algae from the bed. We present the results of studies conducted in the Waipara River (northern Canterbury, NZ) that examined how flow affects interactions between two macroscopically-distinct algal assemblages (i.e., blue-green algal mats dominated by Phormidium, and filamentous green algae, especially Mougeotia). The abundances of these two algal assemblages were inversely related along a velocity gradient, with Phormidium most abundant at high near-bed velocities (> 40 cm/s) and Mougeotia dominant at low near-bed velocities (< 20 cm/s). Moreover, when velocities above Phormidium mats were experimentally reduced, the mats were rapidly replaced by the Mougeotia-dominated assemblage. Subsequent studies indicated that hydraulically-controlled delivery and removal processes play an important role in mediating the inverse distribution of these two algal types along observed velocity gradients. We conclude by examining how the hydraulic control of benthic algae can propagate to higher trophic levels in this system.
Presented at 8:15 AM on Wednesday, May 31, 2000 in Context Dependency: Role of the environment in shaping species interactions and organizing communities in streams
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