Depressional wetlands are those that are associated with natural depressional landform features such as ox bows, meander scars, karst depressions, sinkholes, sag ponds, and natural ponds. Deeper depressions filled with water for prlonged periods form either open-water ponds or marshes with emergent vegetation. Some depressions exhibit rapid and frequent fluctuation of water levels tied to precipitation events and they may range from holding 1-2 feet of water after rain events to being very dry during dry spells. Such vernal ponds were often embedded in treeless prairie but were themselves likely dominated by small, annual grasses, sedges, and herbs. Saturated portions of karst depressions that rarely flood for prolonged periods but remain saturated year-round and likely supported wet prairie. These would sometimes have been positioned along the gradient between depression marsh and upland prairie.