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

[摘要] This study was designed to determine the causes for decreasedmigrant waterfowl use in the Weaver Bottoms of Mississippi River poolfive. Spring Slough, in pool seven, was selected as a control.Vegetation was sampled on square foot plots. The species presentand their respective abundances were determined. These were related todepth, clarity and substrate type. Chemical parameters of the wateralso were determined.Vegetation type maps and waterfowl censuses made during this studywere compared to those made at intervals since impoundment created thishabitat in the late 1930;;s.Lessened waterfowl use was due to a pronounced decrease in theabundance of aquatic macrophytes which supplied food for waterfowl.The amount and variety of vegetation declined as a result of greatlyaccelerated successional changes. The depth, size and openess of theWeaver Bottoms allowed winds to uproot vegetation and increase turbidity.Water flow patterns through the area were altered by the deposition ofdredge spoil by the u.s. Army Corps of Engineers since 1940.Much of the vegetation was dislodged by severe wind action by lateJuly during this study. Exclosures designed to test the effects ofcarp on vegetation showed no significant difference between areas withand without carp.Measures for rehabilitating the Weaver Bottoms were suggested. Thebest methods would be complete or partial filling of selected areascombined with construction of islands to decrease wave action and apartial closing dam at the downstream end to increase sedimentation andraise the river bottom. Water flow could be reduced by closing openingsto the main channel. Most of the remedial measures would use largequantities of previously unwanted dredge spoil. Spoil would be cappedwith silt or topsoil to insure rapid vegetation growth.

[发布机构] University of Wisconsin-Stevens Point, College of Natural Resources