Effects of sediment removal techniques on avian communities and vegetational attributes in restored prairie pothole wetlands
Authors:   , Galt Alexander 
Published: February 2023

With the loss and degradation of wetlands in some areas of the Prairie Pothole Region (PPR) reaching 80-90%, it is critical that resource managers ensure that the habitat that is put back on the landscape is as high quality as possible. Resource managers have been excavating sediment and topsoil, to promote the “hemi-marsh” condition, during the wetland restoration process in the PPR for over 20 years. I refer to the commonly held perception that the hemi-marsh condition supports the most diverse avian communities in small prairie pothole wetlands as the hemi-marsh condition hypothesis. The literature currently does not address the effects of excavation on the proportion of vegetative zones (i.e., sedge meadow, emergent vegetation, and open water) or avian communities in semi-permanent wetlands that are less than 0.6 ha, yet there are thousands of these wetlands throughout the PPR. Understanding the effects of excavation and testing the hemi-marsh condition hypothesis in small prairie wetlands is important to resource managers because these small wetlands are critical for maintaining the integrity of prairie wetland complexes. I conducted vegetation surveys, avian surveys, and estimated nest success on 40 small ( &lt; 0.6 ha), semi-permanent wetlands in the PPR of Minnesota to assess the influence of excavation on vegetation and avian communities. My data indicated a significant difference in the proportion of all vegetative zones between wetlands that were excavated until topsoil was exposed (topsoil excavations) and wetlands that were excavated until subsoil was exposed (subsoil excavations) (F3, 148 = 21.533, P &lt; 0.001, ηp2 = 0.304). The subsoil excavation technique increased the proportion of the open water zone (subsoil excavations: = 20.5%, SD = 18.1 and topsoil excavations: = 15.7%, SD = 14.8) by inhibiting plant growth in exposed subsoil. Altering the topography within basins decreased the proportion of the sedge meadow zone when the subsoil excavation technique was used (subsoil excavations: = 46.8%, SD = 20.7 and topsoil excavations: = 69.9%, SD = 13.6). This technique resulted in an increase in the proportion of the emergent vegetation zone (subsoil excavations: = 32.7%, SD = 23.4 and topsoil excavations: = 14.6%, SD = 12.5) by replacing sedge meadow with deeper water habitat. My analyses did not show a significant difference in Shannon-Weiner Diversity Index (F2, 70 = 0.770, P = 0.467, ηp2 = 0.022), Simpson’s Index of Diversity (F1.844 = 0.016, P = 0.979, ηp2 &lt; 0.001), or daily survival probability (F1 = 1.334, P = 0.254, ηp2 = 0.029) between topsoil and subsoil excavations. However, avian density (F1.688 = 3.497, P = 0.041, ηp2 = 0.047) and nest density (F1 = 9.863, P = 0.003, ηp2 = 0.180) were significantly higher in subsoil excavations. With red-winged blackbird (Agelaius phoeniceus) and sora (Porzana Carolina) accounting for over 83.5% of the nests in my study, I expected to see greater avian densities and nest densities in subsoil excavations since these species required emergent vegetation for nesting substrate. My statistical models indicated that avian diversity is best predicted by a combination of the proportion of emergent vegetation spring, proportion of emergent vegetation summer, and wetland area more so than by the proportion of emergent vegetation alone which is the basis of the hemi-marsh condition hypothesis. Clearly, small, less than 0.6 ha, prairie pothole wetlands function differently than their larger counterparts. Resource managers need to recognize the limitations in small wetlands; therefore, promoting the hemi-marsh condition in small wetlands is not the most efficient use of management dollars. My recommendations are to restore small prairie wetlands to their historical topography by using the topsoil excavation technique because resource managers do not currently know the potential negative impacts that exposing subsoil could have on plant and macroinvertebrate communities.