Variability in ice cover does not affect annual metabolism estimates in
a small eutrophic reservoir
Abstract
Temperate reservoirs and lakes worldwide are experiencing decreases in
ice cover, which will likely alter the net balance of gross primary
production (GPP) and respiration (R) in these ecosystems. However, most
metabolism studies to date have focused on summer dynamics, thereby
excluding winter dynamics from annual metabolism budgets. To address
this gap, we analyzed six years of year-round high-frequency dissolved
oxygen data to estimate daily rates of net ecosystem production (NEP),
GPP, and R in a eutrophic, dimictic reservoir that has intermittent ice
cover. Over six years, the reservoir exhibited slight heterotrophy
during both summer and winter. We found winter and summer metabolism
rates to be similar: summer NEP had a median rate of -0.06 mg O2 L-1
day-1 (range: -15.86 to 3.20 mg O2 L-1 day-1), while median winter NEP
was -0.02 mg O2 L-1 day-1 (range: -8.19 to 0.53 mg O2 L-1 day-1).
Despite large differences in the duration of ice cover among years,
there were minimal differences in NEP among winters. Overall, the
inclusion of winter data had a limited effect on annual metabolism
estimates, likely due to short winter periods in this reservoir (ice
durations 0–35 days) relative to higher-latitude lakes. Our work
reveals a smaller difference between winter and summer NEP than in lakes
with continuous ice cover. Ultimately, our work underscores the
importance of studying full-year metabolism dynamics in a range of
aquatic ecosystems to help anticipate the effects of declining ice cover
across lakes worldwide.