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

The Missouri River floodplain historically contained numerous wetlands; how ever, alterations to the corridor have resulted in the loss of flood-pulse processes. The annual contributions of small wetlands (<15 ha) perched on t he Missouri River floodplain have not been viewed as important; however, co nsequences of draining or filling perched wetlands in the upper Missouri Ri ver 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 secti on of the Missouri River. Fishes, macroinvertebrates, zooplankton, and habi tat parameters were sampled during May, July, and September 1997. No signif icant differences (P > 0.05; F < 4.2; df = 2,9) in densities or catch-per-u nit-effort among sample periods were detected for macroinvertebrates. Copep oda nauplii, calanoid Copepoda, and Bosmina spp. densities showed significa nt changes (P < 0.03; F > 6.1; df = 2,9) and collectively surpassed 3,200 o rganisms/L. These densities exceeded other regional means by as much as 900 %. Twenty-four fish species were documented in the wetland; however, the bl ack bullhead, Ameiurus melas Rafinesque, dominated the fish community. Wetl and depth and surface area increased during the connection period and inund ated terrestrial grasses and woody debris. Decay of submerged organic matte r, combined with the lack of rooted macrophytes, loss of algal productivity to flushing, and higher turbidity, may have all contributed to reduced sum mer dissolved oxygen levels. Avian feeding activity suggested that fishes w ere using the upper water column when nearly anoxic lower water column cond itions existed. Although the wetland habitat may be harsh, presence of juve nile fishes and dense zooplankton populations establishes the potential imp ortance of these water bodies to the Missouri River ecosystem.