1412. Earth
Walker was one of the few that could feel the change in the earth elemental mana. It wasn't that he was looking for it, however, he felt it as soon as he had moved to fix the earth he had manipulated over the last hour.
Only seven people had issues with their potions which was a fairly low number. That didn't mean that Walker was responsible and would help clean up the mess he had made to prevent anyone from being harmed. This was the same for the other mages working in pairs to protect the participants.
That being said, there were a handful of earth mages that had used the same technique as Walker had. They had moved the earth elemental mana to cover the cauldrons and partnered with water mages to douse the fires used. But the earth mages with higher affinity for the earth elemental mana suddenly stopped.