The intent of this research was to investigate the effects of fluid flow
characteristics and epiphyte colonization on submerged aquatic vegetation (SAV)
photosynthesis and dissolved material uptake. SAV, with its stems and leaves completely
submerged in the water column, is strongly affected by both the physical characteristics
of the water, such as dissolved material concentrations and fluid motion, and by factors
that alter its interaction with the water, such as epiphyte colonization of SAV surfaces.
The nature of these interactions was investigated through a series of four separate studies.
First, through a laboratory mesocosm experiment, epiphyte uptake and SAV uptake of a
dissolved contaminant (nickel) were shown to occur at different rates and due to different
mechanisms. Second, a model of photosynthetic rates, based on mass transfer theory,
was developed requiring only three parameters that accounted for the effect of water
motion on photosynthetic rates. This model was experimentally validated with dissolved
oxygen and velocity profiles over blades of giant kelp, Macrocystis pyrifera. Third,
using two separate microscale velocity imaging methods, photosynthesis was shown to
alter fluid motion near the surface of a Cladophora spp. filament by more than doubling
velocity gradients and thus surface shear stress. In this investigation, bacterial epiphytes
had no effect on shear stresses but assemblages consisting primarily of diatom epiphytes
strongly decreased the surface shear stress from what would have been experienced
during photosynthesis without epiphytes present; indicating a harmful interaction with epiphytes. Fourth, in agreement with the microscale results in the third study, epiphyte
removal was shown to increase local dissolved oxygen concentrations throughout the
water column as well as decrease water column soluble reactive phosphorus
concentrations due to higher photosynthetic rates in field research in a constructed
wetland. In a related laboratory study, epiphyte detachment rates were functionally
related to water velocity. Overall, I have shown through laboratory and field experiments
that SAV photosynthesis is closely linked to fluid flow characteristics, SAV and epiphyte
uptake are not equally affected by flow conditions, and epiphyte colonization decreases
SAV photosynthetic rates.
University of Minnesota Ph.D. dissertation. May 2012. Major: Civil Engineering. Advisors:Dr. Miki Hondzo, Dr. Jacques Finlay. 1 computer file (PDF); x, 118 pages.
Hansen, Amy Therese.
The effects of fluid flow and epiphytes on submerged aquatic vegetation.
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