Floodplain Ecosystem Productivity on a Large Restricted River: Warm Season Flooding on the Mississippi

The Middle Mississippi River (MMR) has been disconnected from 80% of its historic floodplain by an extensive levee system. This loss has likely had impacts on native fishes that evolved to use the floodplain for feeding, refuge, and reproduction. The MMR experienced a large flood during the summer of 2015 which inundated most of the available floodplain. Oxygen and temperature data were collected from locations at varying distance from the main channel in order to examine gross primary productivity (GPP) and net ecosystem productivity (NEP) on the floodplain. Sites were additionally selected outside of the levee in a minimally connected floodplain (disconnected floodplain). Data was also collected from the thalweg of the main channel. Temperature and oxygen values were similar between the main channel and most floodplain sites. GPP was close to zero and NEP was negative at main channel and floodplain sites. GPP at the disconnected floodplain was variable but always greater than at other sites. Sites on the disconnected floodplain experienced both positive and negative NEP throughout the flood. Productivity during floods appears to be restricted by velocity and proximity to the main channel. Levees both reduce the area available for flooding and restrict floodwaters, increasing velocity.