Overcoming Barriers to Coastal Wetland Ecosystem Rehabilitation: Strategies for the Great Lakes.

Abstract

Great Lakes coastal wetlands provide many important ecological functions and values, but most of these highly productive systems have been degraded or destroyed by anthropogenic stressors. The multidimensional nature of wetland degradation presents challenges for habitat rehabilitation, but rehabilitation efforts designed to mimic natural processes could yield positive results. In this dissertation, I explored two hydrology-related habitat rehabilitation strategies (i.e., short-term management-induced dewatering to mimic cyclic low water levels and reducing hydrologic isolation typically associated with diked wetland units) applied to the riverine and diked wetlands at Crane Creek, a small western Lake Erie tributary. Initially, I studied the effectiveness of using portable, water-filled cofferdams as a management tool to promote the natural growth of emergent vegetation from the seed bank. A short dewatering stimulated a rapid seed-bank-driven response by 45 plant taxa, but submersed aquatic species reestablished after subsequent flooding. Although long- term habitat rehabilitation using this technology may be difficult, it could be an important tool for resource managers.

Fishes, plants, and water quality in the wetland complex were sampled to describe spatial and seasonal patterns of fish assemblages and explore habitat rehabilitation through hydrologic reconnection of diked wetlands and Lake Erie. Pronounced differences were found in hydrology (water-level fluctuation), fish assemblages (composition and abundance), and wetland vegetation (composition) between the diked and coastal wetlands, suggesting that a fish-passage structure and periodic management actions could improve habitat and restore seasonal access to Lake Erie fishes. Finally, I quantified wetland use (abundance and movement) by Lake Erie fishes using a high-resolution sonar (DIDSON). Despite very dynamic environmental conditions, the degraded Crane Creek wetlands supported an abundance of fishes that moved extensively through the channel connecting to Lake Erie. Longnose gar, shoals of small fish, and other unidentifiable large fish used the channel as a temporary habitat and to escape diurnally poor water quality. Results of my research suggest that rehabilitation strategies that account for ecosystem complexity and mimic natural hydrologic processes (e.g., water-level variability, habitat connectivity) can benefit wetland ecosystems on multiple dimensions. Finally, numerous management objectives could be met through function-based rotation of wetlands in the landscape.