Seasonal dynamics of aquatic fauna and habitat parameters in a perched upper Missouri River wetland

Abstract

The Missouri River floodplain historically contained numerous wetlands; however, alterations to the corridor have resulted in the loss of flood-pulse processes. The annual contributions of small wetlands (<15 ha) perched on the Missouri River floodplain have not been viewed as important; however, consequences of draining or filling perched wetlands in the upper Missouri River basin remain unclear. The objective of this study was to survey aquatic fauna and basic habitat characteristics in a small perched wetland before, during, and after a connection period within a naturally functioning section of the Missouri River. Fishes, macroinvertebrates, zooplankton, and habitat parameters were sampled during May, July, and September 1997. No significant differences (P>0.05; F<4.2; df=2,9) in densities or catch-per-uniteffort among sample periods were detected for macroinvertebrates. Copepoda nauplii, calanoid Copepoda, and Bosmina spp. densities showed significant changes (P < 0.03; F > 6.1; df=2,9) and collectively surpassed 3,200 organisms/L. These densities exceeded other regional means by as much as 900%. Twentyfour fish species were documented in the wetland; however, the black bullhead, Ameiurus melas Rafinesque, dominated the fish community. Wetland depth and surface area increased during the connection period and inundated terrestrial grasses and woody debris. Decay of submerged organic matter, combined with the lack of rooted macrophytes, loss of algal productivity to flushing, and higher turbidity, may have all contributed to reduced summer dissolved oxygen levels. Avian feeding activity suggested that fishes were using the upper water column when nearly anoxic lower water column conditions existed. Although the wetland habitat may be harsh, presence of juvenile fishes and dense zooplankton populations establishes the potential importance of these water bodies to the Missouri River ecosystem.