The effects of fluid flow and epiphytes on submerged aquatic vegetation

Abstract

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.