Low dissolved oxygen can be caused by several conditions.
Stratification is typically a summertime problem in ponds deeper than 8 ft (solar heating of the top layer of water). But with high turbidity and/or phytoplankton blooms it can happen in ponds 4-6 ft deep. Adding a large organic load under these conditions can significantly magnify the oxygen problem.
"Turnover" occurs with sudden water mixing and/or a sudden large temperature drop.
Adding a big organic load to a shallow pond can cause oxygen levels to drop because of the bacterial decomposition process. Some ponds are fertilized with organics like alfalfa meal, hay, cottonseed meal etc. -- we used alffalfa meal for ponds at the redfish hatchery in TX. Oxygen levels will drop for several days after organics are added. Low oxygen levels due to high organic loads are more likely in warm weather months.
Low oxygen levels during cold weather are less likely. But I cannot say with any certainty that a high "leaf load" will not cause low oxygen in the winter. In this situation, my inclination would be to exercise caution.
Low Oxygen and Pond Aeration:
https://wkrec.ca.uky.edu/files/lowox...ndaeration.pdf