12 acres means 3 to 4 times more snow removal compared to 3 acres. Using an ATV, small tractor or old pickup could work okay on thick ice that forms in Manitoba. Most of your ice should freeze clear so adequate amounts of sunlight should penetrate thick clear ice up to 2-3ft thick. Your aquifer could supply some needed oxygen? See it you can get the DO checked in aquifer water.
Working on getting both the gravel pit water and the aquifer water tested.
You are right clearing the ice will be more time consuming than just shoveling off a pond. However, with a body of water that big, it would also mean that the water should retain more oxygen throughout the winter?
What keeps a big lake like Lake Winnipeg from losing so much oxygen in the water that the fish all die? The lake is completely frozen all winter long.
