Daily, biweekly, and seasonal temporal scales ofpCO₂variability in two stratified Mediterranean reservoirs

Abstract

Temporal scales of variability for the partial pressure of CO 2 (pCO 2 ) in the surface waters of two stratified Mediterranean reservoirs were examined through the temporal decomposition of 5 month time series with hourly sampling frequency. pCO 2 time series included similar patterns of variability at daily, biweekly, and seasonal scales regardless of the difference in amplitude of the pCO 2 variation in the two reservoirs studied. Daily variability was strongly related to the day-night cycles of metabolic activity, accounting for about one third of the total amplitude in pCO 2 variation. At a biweekly scale, wind forcing led to higher rates of air-water CO 2 exchange and subsequently temporary partial mixing events associated to relevant increase of CO 2 concentration in surface waters. Seasonal variability accounted for one third of the amplitude of the pCO 2 variability and was coupled to the seasonal dynamics of water temperature and thermal stratification of the water column. Our results provide evidence that CO 2 emission from stratified water bodies shows significant variability at daily, biweekly, and seasonal scales; all of which should be taken into consideration in the analyses of the carbon fluxes. The wind-induced mixing events, operating at temporal scales between daily and seasonal cycles, may become a major factor controlling the pCO 2 dynamics. Hence, some of the most common models for computing CO 2 fluxes from pCO 2 were not able to reproduce the biweekly response patterns of CO 2 emissions to wind forcing.

Evaluations of Climate and Land Management Effects on Lake Carbon Cycling Need to Account for Temporal Variability in CO2 Concentrations

“…Such data are widely used in the evaluation of lake contributions to landscape‐ and global‐scale carbon budgets (Figure and Table S1). While it is well known that CO 2 concentration and budget estimates depend on the temporal coverage of sampling (Morales‐Pineda et al, ; Natchimuthu et al, ), we here show that this is also true for evaluations of environmental drivers of lake CO 2 . Our data confirms recent insights from terrestrial carbon flux studies (Chu et al, ; Montagnani et al, ) and highlights a general problem in empirical sciences: The scale of observed patterns and underlying mechanisms must match if observations are used to understand and predict patterns and processes (Levin, ).…”

CO2 evasion from boreal lakes: Revised estimate, drivers of spatial variability, and future projections

“…Wind speed has previously been shown to exert a strong negative control on p CO 2 in reservoirs (Morales‐Pineda, Cózar, Laiz, Úbeda, & Gálvez, ), the likely mechanism being higher wind speeds leading to higher F CO 2 (Cole & Caraco, ; Read et al., ; Vachon & Prairie, ) and in turn a decrease in p CO 2 . In contrast, our study revealed a strong positive correlation between wind speed and lake p CO 2 .…”

Carbon Dioxide Emissions from the Littoral Zone of a Chinese Reservoir

“…Most researchers have focused on the water body itself (see [26][27][28], disregarding the green zone at the water's edge. For lakes especially, and for reservoirs to a lesser extent, there are many investigations of the CO2 flux from the open water surface, sometimes measured directly using chambers or (rarely) obtained from micrometeorological techniques; but more often, fluxes are estimated from a knowledge of the dissolved CO2 concentration in the water samples [29][30][31][32]. Our study helps to redress the balance by providing new observational data from the margins of a reservoir which may be compared to values obtained from open water.…”