Benthic algal response to pulsed versus distributed inputs of sediments and nutrients in a Mackenzie Delta lake

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Authors: Squires, MM; Lesack, LFW
Year: 2001
Journal: Journal of the North American Benthological Society 20: 369-384
Title: Benthic algal response to pulsed versus distributed inputs of sediments and nutrients in a Mackenzie Delta lake
Abstract: The Mackenzie Delta is a lake-rich region where the distribution and abundance of phytoplankton, macrophytes, and benthic algae among lakes may be controlled by an interaction between nutrient supply and sediment in the water column, and episodic reduction in light availability associated with river flooding. To simulate the effects of episodic river inflow on benthic algae, limnocorrals (depth = 3 m) were either not manipulated (control), or received high or low weekly additions of nutrients (N and P) and sediments, delivered as a pulse (1/wk: high-pulsed, low-pulsed) or distributed incrementally through each week (1/3 of high or low load x 3 d/wk: high-distributed, low-distributed) in a balanced triplicated design (15 limnocorrals). Artificial substrates, enriched to mimic the supply of nutrients at the sediment/water interface, were suspended in the limnocorrals at 2 rn depth for 6 wk beginning in mid-July 1995. Maximum average levels of phytoplankton biomass (inferred from chlorophyll) occurred in the treatment where light attenuation was highest (high-distributed), and lowest levels occurred where light attenuation was lowest (control). By contrast, maximum average accrual of benthic algal biomass on the artificial substrates occurred in the control, whereas lowest accrual occurred in the high-distributed treatment. Chlorophyll content per unit biovolume of benthic algae increased modestly in treatments experiencing low light relative to treatments with higher light, but was insufficient to explain the 3-fold difference in inferred biomass between the control and high-distributed treatment in the case of benthic algae, or the 4-fold difference in the case of phytoplankton. Under equivalent in situ light conditions, areal net photosynthesis of benthic algae was highest in the control and lowest in the high-pulsed treatment. Net photosynthetic rate per unit benthic algal chlorophyll was not significantly different among the control and treatments. Last, biomass accrual rates among treatments showed a strong inverse relation with average light attenuation among the limnocorrals over the duration of the experiment. These results indicate that light availability was primarily responsible for maximum biomass accrual in the control and was the dominant factor affecting accrual rates among treatments. Overall, this study suggests that the abundance of benthic algae among Mackenzie Delta lakes may progressively increase as flood frequency decreases and light availability becomes greater, whereas phytoplankton abundance may peak in lakes with intermediate transparencies by responding to nutrient additions despite interruption of the light environment by suspended sediments.
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