Causes of Decreased Migrant Waterfowl use in Part of the Upper Mississippi River Wildlife and Fish Refuge

Abstract

This study was designed to determine the causes for decreased migrant waterfowl use in the Weaver Bottoms of Mississippi River pool five. Spring Slough, in pool seven, was selected as a control. Vegetation was sampled on square foot plots. The species present and their respective abundances were determined. These were related to depth, clarity and substrate type. Chemical parameters of the water also were determined. Vegetation type maps and waterfowl censuses made during this study were compared to those made at intervals since impoundment created this habitat in the late 1930's. Lessened waterfowl use was due to a pronounced decrease in the abundance of aquatic macrophytes which supplied food for waterfowl. The amount and variety of vegetation declined as a result of greatly accelerated successional changes. The depth, size and openess of the Weaver Bottoms allowed winds to uproot vegetation and increase turbidity. Water flow patterns through the area were altered by the deposition of dredge spoil by the u.s. Army Corps of Engineers since 1940. Much of the vegetation was dislodged by severe wind action by late July during this study. Exclosures designed to test the effects of carp on vegetation showed no significant difference between areas with and without carp. Measures for rehabilitating the Weaver Bottoms were suggested. The best methods would be complete or partial filling of selected areas combined with construction of islands to decrease wave action and a partial closing dam at the downstream end to increase sedimentation and raise the river bottom. Water flow could be reduced by closing openings to the main channel. Most of the remedial measures would use large quantities of previously unwanted dredge spoil. Spoil would be capped with silt or topsoil to insure rapid vegetation growth.