Summary

Description

Biologists from the U.S. Fish and Wildlife Service surveyed environmental quality at a backwater system of the Upper Mississippi River between 1994 and 1996. The backwater system is the Keithsburg Division management unit of the Mark Twain National Wildlife Refuge located in the floodplain of Navigation Pool 18. The surface water and groundwater sources for this backwater are agricultural drainage water and streams impacted by rural nonpoint source pollution. The environmental quality parameters that were studied included water quality, sediment quality and toxicity testing, organism health and ecological diversity. The chemistry data indicated nutrient rich surface water, groundwater and aquatic sediment resources in the refuge unit. The concentrations of toxic contaminants detected in the water and aquatic sediment resources were below lethal benchmark values for aquatic life. The concentrations of herbicide chemicals detected in surface water and aquatic sediments were above levels that may stress aquatic plants. Poor aquatic macroinvertebrate and plant diversity was observed in many areas around the refuge unit. We suggest that the loading of nutrients in these areas was sufficient to cause changes to the structure and composition of refuge plant communities and related shifts in invertebrate populations. The altered ecological communities in the polluted areas function to treat nitrogen inputs, providing less diverse wildlife habitats. Several lake and watershed management strategies are discussed to help increase habitat diversity and benefits to migratory birds. It is important to note that an increment of improvement in the watershed will not necessarily result in an increment of improvement in habitat quality in the backwater system. It is possible that little or no ecological change may occur or be observed at Keithsburg Division until a critical level is reached in the watershed resulting in a noticeable shift in refuge habitat quality.