| The aim of this work was to investigate and quantify the effects of ultraviolet radiation (UVR) in L. Erie phytoplankton communities. Briefly, primary production, measured as 14C incorporation over time, was determined during the late spring and summer months of 1997 and 1998. While all three basins of L. Erie were sampled, the East basin was under represented relative to both the Central and West basins. In all experiments, determination of the effects of UVR on primary production was carried out using natural solar radiation which was selectively screened by various optical filters or modified using ultraviolet B (UVB) lamps.; In L. Erie, UVB inhibited primary production severely (58%) but only in very severe exposures, as would be experienced at the surface. The kinetics of inhibition were, however, rapid suggesting that short exposures, as would occur under mixing, could result in significant inhibition. No simple and strong relationships could be identified between the efficiency of UVB in inducing photoinhibition and measures of phytoplankton light history or micro- and nanoplankton dominant genera. However, UVB inhibition efficiency was higher for phosphorus (P) deficient than P-replete algal assemblages.; A new model (the R model) for the response of photosynthetic carbon fixation to UVR was formulated, allowing finite rates of recovery and the incorporation of wavelength interactions, and was tested against observations on phytoplankton communities in L. Erie. Additionally, biological weighting functions (BWFs), the first for freshwater phytoplankton assemblages, were determined. The application of both the R model and the BWFs successfully described the kinetics of UVR- and PAR-dependent photoinhibition in L. Erie.; Possessing both measures of spectral sensitivity and recovery rates, losses of daily production were calculated under mixing and water transparency scenarios that span the common range of conditions in L. Erie. Predictions of daily integrated photoinhibition (PIint) were insensitive to variations in mixing rates, although, simulated mixed conditions always resulted in higher daily losses of production than simulated motionless water column. The contribution of each spectral waveband to PIint also varied little with mixing scenarios.; Overall, UVA, rather than UVB or PAR, appears to be the major waveband responsible for photoinhibition of primary production in L. Erie. (Abstract shortened by UMI.)... |
