APPLICABILITY OF THE OXYGEN STABLE ISOTOPE METHOD FOR ESTIMATING METABOLISM IN SMALL ARCTIC LAKES

Metabolism is a key property of lake ecosystem functioning, but in remote systems such as Arctic-alpine lakes, metabolism is difficult to estimate due to logistical challenges associated with fieldwork. A method that requires minimal field sampling efforts is the dissolved oxygen (DO) stable isotope (δ¹⁸O) approach. However, this method relies on debated assumptions on the dynamics of δ¹⁸O relative to DO and lacks evaluation in Arctic-alpine lakes. We evaluated the δ¹⁸O method by comparing it to the state-of-the-art free-water diel DO method in 39 small Arctic-alpine lakes during the open water season. We found that whether methods agreed depended on the sampling conditions and lake depth. The methods agreed well in autumn when water temperatures were relatively stable, especially in lakes with fast gas exchange relative to their depth. In these conditions, the impact of metabolism on DO saturation and δ¹⁸O is more pronounced relative to temperature-driven changes in DO solubility and the lakes readapt to new steady state conditions faster following changes in mixed layer depth. In contrast, we found low agreement between methods and a frequent occurrence of unrealistic estimates by the isotope method in spring and summer, likely due to solubility decreases that affect DO saturation independent from δ¹⁸O. We conclude that the δ¹⁸O method can be used in Arctic-alpine lakes if lake characteristics and seasonal climatic conditions are carefully considered.

Primary Presenter: Fredrik Sundberg, Umeå University (fredrik.sundberg@umu.se)

Authors:

Fredrik Sundberg, Umeå Universitet  (fredrik.sundberg@umu.se)

Marcus Klaus, Swedish University of Agricultural Sciences  (marcus.klaus@slu.se)

Cristian Gudasz, Umeå University  (cristian.gudasz@umu.se)

Gerard Rocher-Ros, Swedish University of Agricultural Sciences  (gerard.rocher.ros@slu.se)

Dominic Vachon, Environnement Québec  (domvachon@gmail.com)

Jan Karlsson, Umeå University  (jan.p.karlsson@umu.se)