Spatial-temporal variability of methane fluxes in lakes varying in latitude, area, and depth.

Many previous studies have found spatial and seasonal variabilities in CH fluxes, which could significantly affect lake-wide CH budgets. However, the ways in which the spatial and seasonal patterns of CH fluxes vary among lakes on a global scale is largely unknown. We compiled literature on CH flux data from global lakes and analyzed the spatial and seasonal variabilities for lakes varying in latitude, maximum depth, and area. Spatially, we found a significant linear relationship between the ratio of littoral to profundal fluxes and lake morphology (more related to area than depth), while globally, half of the lakes would have within 5% error of CH emission estimation under single-zone sampling. Seasonally, mid-latitude lakes showed higher CH fluxes in the summer and autumn, indicating the influence of temperature and autumn overturn, and the latter being largely related to maximum depth. Globally, due to abundant shallow lakes in the mid-latitude zone, approximately 99% of lakes had higher fluxes in the summer, while 75% of lakes showed errors in CH emission estimation within 20% when only the summer flux was investigated. In the high-latitude lakes, CH evasion during the spring ice-off period was significantly correlated with lake maximum depth, while lake area was also important when analyzing the CH diffusive flux. Our study yields preliminary conclusions about spatial and seasonal patterns of CH flux in different lake types, which are fundamental to building an effective sampling strategy and to determining an accurate CH budget from global lakes.