Assessing the effects of climate change driven decreases in Great Lakes water levels on the distribution of three-square bulrush (Schoenoplectus pungens) in Cecil Bay, Michigan.

Abstract

Since the year 2000, Great Lakes water levels have been abnormally low, and they are projected to continue decreasing. Great Lakes coastal wetlands are particularly vulnerable ecosystems to water level decline because wetland plants that typically grow in standing water become subject to dry conditions. Three-square bulrush (Schoenoplectus pungens) is one of the few emergent wetland plants that can tolerate deep water, and it plays important roles in attenuating wave energy, retaining sediment, and providing habitat for many fish and bird species. The ability of three-square bulrush to remain an emergent plant with water level decline was evaluated by analyzing the relationship between rhizome growth and water level, and by comparing annual growth rate to projected future water level decreases in the Great Lakes. Rhizomes appear to grow more when they are dry than when they are submerged, and rhizome growth appears to be particularly strongly suppressed by high water levels in May. Assuming maximum rhizome growth rate, three-square bulrush will very likely not be able to keep up with projected water level decline in the future. This can result in ecosystem-wide consequences and predominantly threaten organisms that are exclusively dependent on emergent wetland vegetation.