SPATIAL AND TEMPORAL CHARACTERIZATION OF LIGHT AND NUTRIENT LIMITATION IN LAKE DIEFENBAKER: INFLUENCE OF ANTHROPOGENIC ACTIVITIES AND UPSTREAM FLOW
Hunter, Kristine Rachelle 1982-
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Management of water quality in lakes and reservoirs often requires an understanding of the factors that control algal biomass. Primary production in freshwater systems may be limited by nutrients such as phosphorus (P) and nitrogen (N), or by physical conditions such as availability of light. Lake Diefenbaker (LD) is a multi-purpose reservoir located on the South Saskatchewan River (SSR). Its uses include, but are not limited to, power generation, flood control, irrigation, and drinking water supply. Prior to beginning this study little was known about the factors that controlled algal populations in this reservoir. To determine if algae and bacteria were nutrient limited or light limited, I measured various biological and environmental conditions and conducted a series of nutrient status assays. Sampling sites were located in the main channel along the length of the reservoir and in a set of embayments. Embayments were of three types, those containing cattle operations, marinas, or no observed anthropogenic activity (reference embayment). Temporal patterns were assessed from monthly samples collected from June to October in 2011 and 2012. I found that P was the primary limiting nutrient in LD; N deficiency was less prevalent but was associated with high flows and consequent low light. Nutrient and light dynamics in the reservoir followed the expectations of the longitudinal zonation concept (LZC) of Kimmel and Groeger (1984) in most instances. The upstream riverine region was characterized by high flows, high nutrient concentrations and low light penetration. The transition region experienced a reduction in flow (the basin was wider and deeper) that resulted in the settling of particulate matter and an increase in light penetration. Finally, in the lacustrine region, light penetration increased, and P concentrations declined. However, N concentrations either increased or were consistent along the length of the reservoir and light limitation was widespread due to deep mixing depths, neither expected under the LZC. Light limitation was more prevalent in 2011 than 2012 due to higher flows and associated turbidity, with higher indications of deficiency in the main channel than the embayments in both years. We did not detect differences in nutrient or light limitation indicators in the embayments exposed to cattle or recreational activities when compared to reference embayments. The lack of an effect may be attributed to greater than normal inflow from the SSR that may have increased flushing of the embayments during the two years of study. The high flows entering Lake Diefenbaker were associated with greater nutrients and turbidity, both of which affected light and nutrient limitation throughout the reservoir. Overall, the results of this study could suggest that light is the primary limiting factor in LD, with P limitation being secondary. However, long-term constraints on algal biomass will still be controlled by P levels. During these two years of study, light and nutrient limitation was sufficient to limit significant algal blooms. Regardless of whether light or P is considered the ultimate limiting factor, only P can be feasibly controlled. With the anticipated changes to flow and stratification patterns associated with climate change, and the potential for legacy P loading in LD, P reduction strategies need to be considered to protect this important resource for the province of Saskatchewan.
DegreeMaster of Science (M.Sc.)
CommitteeDavies, John-Mark; Sereda, Jeff; Sheard, John; Wei, Yangdou; Finlay, Kerri
Copyright DateDecember 2018