David M. Vandergucht

A comparison of phosphorus deficiency indicators with steady state phosphate in lakes

A fundamental step in the management of nutrient impacted water bodies is the determination of the type and degree of nutrient limitation. However, nutrient deficiency indicators often provide inconsistent results. Recent advances in the measurement of phosphate concentrations may provide a better means to understand results from P deficiency indicators. With regards to phosphorus, deficiency indicators should predict P-limitation when phosphate concentrations are consistently low. We use this new understanding to examine the relationships between phosphate concentration and P deficiency. Patterns of steady state phosphate (ssPO(4)(3-)) concentrations and P deficiency were evaluated in 109 lakes located across Canada. Lakes encompassed a broad range in TP concentration (1.79-139.7 μg L(-1)). The relationships between ssPO(4)(3-) concentrations and simultaneously measured total P (TP), total dissolved P (TDP) and soluble reactive P (SRP) concentrations, particulate C:P and N:P ratios, alkaline phosphatase activities (APA) and phosphate turnover times (TT) were analyzed. ssPO(4)(3-) was positively correlated with TP and TDP. The ssPO(4)(3-) concentrations were 2-3 orders of magnitude lower than SRP concentrations. These two measures were only weakly correlated, suggesting that SRP is a major overestimate of PO(4)(3-). The ssPO(4)(3-) concentrations were negatively correlated with C:P and N:P ratios, and with APA, consistent with expectations. When only lakes with TT < 15 min were considered, TT was negatively correlated with TP, challenging the idea that nutrients become less limiting in more eutrophic systems. Overall, P deficiency indicators related to ssPO(4)(3-) in the expected manner. However, variability in relationships with APA and particulate stoichiometry emphasize the need for cautious interpretation of P deficiency measurements. We recommend simultaneous use of multiple techniques to confidently assess P deficiency.

Do human activities affect phytoplankton biomass and composition in embayments on Lake Diefenbaker

ABSTRACT Lake Diefenbaker (LD) is an important source of water for southern Saskatchewan. LD is characterized by numerous embayments containing anthropogenic activities (e.g., housing, marinas, cattle watering). Many of these activities are increasing on this important reservoir in association with the rapidly developing economy of Saskatchewan. These activities may reduce water quality directly or indirectly by encouraging the growth of nuisance algae (i.e. cyanobacteria). Here, we examined phytoplankton biomass and composition in eight embayments exposed to anthropogenic activities, four unexposed embayments with no perceived human activities and six main channel sites adjacent to the embayments from June to October (2011 and 2012). Phytoplankton biomass and composition was not significantly different in exposed, unexposed embayments and main channel sites (p > 0.05), with the diatoms and cryptomonads constituting 87%–91% of the total phytoplankton biomass in both years. High flows from the South Saskatchewan River (SSR) in both years may have resulted in the rapid flushing of the embayments and dampened any localized impacts that could have resulted from anthropogenic activities as found in other studies. Hence, future study on LD should be conducted during years with low flow from the SSR when the rate of flushing of embayments will be reduced.