Diel variations in inorganic carbon and nitrogen uptake by phytoplankton in an arctic lake

• Published in: Journal of Plankton Research
• Main Authors: Whalen, S.C., Alexander, V.
• Format: Text
• Language: English
• Published: Oxford University Press 1984
• Subjects: Articles; Arctic; Arctic Lake; Phytoplankton
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/6/4/571; https://doi.org/10.1093/plankt/6.4.571

Time—depth variations in inorganic carbon and nitrogen uptake by phytoplankton in Toolik Lake were examined over 36 h using isotope tracer techniques. Rates of dissolved inorganic carbon (DIC = CO 2 + <f>$${\hbox{ HCO }}_{3}^{-}$$</f> + <f>$${\hbox{ CO }}_{3}^{2-}$$</f>) and maximum <f>$${\hbox{ NO }}_{3}^{-}$$</f> uptake were phased with the did high light/low light regime characteristic of the brief arctic summer with the amplitude of oscillation greater for DIC than for <f>$${\hbox{ NO }}_{3}^{-}$$</f>. Ammonium uptake was continuous at uptake-saturating concentrations. No conclusive evidence was found for a diel periodicity in nitrogenous nutrient levels or uptake of <f>$${\hbox{ NO }}_{3}^{-}$$</f> and <f>$${\hbox{ NH }}_{4}^{+}$$</f> ambient concentrations. A pronounced light—temperature effect on dissolved inorganic nitrogen (DIN = <f>$${\hbox{ NO }}_{3}^{-}$$</f> + <f>$${\hbox{ NH }}_{4}^{+}$$</f>) uptake was evident at depth when rates of uptake were maximum. Depth-integrated daily C/N uptake ratios (mol) estimated as the mean of four consecutive 6 h incubations ranged from 1.8–6.4 under conditions of substrate saturation and from 6.0–16.1 at ambient levels of DIN. The efficacy of 24 h incubations to estimate accurately day-rates of DIC and substrate-saturated DIN uptake was assessed by comparing estimates obtained from 24 h exposures to those approximated by summing results from serial short-term incubations. Experiments of 24 h duration accurately predicted day-rates of maximum <f>$${\hbox{ NO }}_{3}^{-}$$</f> uptake but underestimated daily DIC uptake by 13 � 7% (<f>$$\stackrel{\¯}{\hbox{ X }}$$</f> � SD). Day-length incubations introduced serious errors in the estimation of day-rates of maximum <f>$${\hbox{ NH }}_{4}^{+}$$</f> uptake, effecting an underestimation of 29 � 5% (<f>$$\stackrel{\¯}{\hbox{ X }}$$</f> � SD).