Rainfall possibly disturbs the diurnal pattern of CO_2 degassing in the Lijiang River, SW China

摘要

Estimates of CO_2 flux from rivers are uncertain due to limited measurements at high-resolution. In addition,precipitation may impact diurnal variation of riverine CO_2 flux but the processes controlling those impacts are unknown. Here, we examine the diurnal characteristics of some physicochemical parameters, meteorological parameters, water level, δ~(13)C_(DIC) values, and the CO_2 emission flux at two transects (DM and PY) of a typical karst river (Lijiang River, LJR), southwest China, during May 13-16, 2017. Our results show significant correlations between CO_2 flux, DO, pCO_2, and δ~(13)C_(DIC) and reflect control of CO_2 flux diel pattern (decreasing during daytime and increasing at night) by metabolic processes of aquatic plants. The amplitude of CO_2 flux diel pattern is weakened at DM. In contrast, diurnal pattern are interrupted at PY by the precipitation, and afterwards controlled by water level due to the significant positive correlation between water level and CO_2 flux. Certainly, this amplitude will return to prestorm values as the water level recovered. We suggest that effects of precipitation on regional CO_2 efflux estimate require scaling water level and CO_2 flux with a linear relationship, and converting hourly flux to daily flux (α values) to improve the estimate of CO_2 flux diel cycle. These methods will optimize sampling monitoring strategies and provide more reliable estimates of regional riverine CO_2 emissions.