"Defining The Atchafalaya River Basin Hydrograph/Hypoxia Relationship"

The annual flood pulse (January-July) in the lower Atchafalaya River Basin (ARB) flushes the floodplain but often results in extensive hypoxia, which stresses resident organisms and can result in periodic fish kills.  We were interested in the characteristics of flooding and their relationship to the development of hypoxic conditions in the ARB, particularly in light of continuing state and federal efforts to improve water quality in this dynamic floodplain swamp ecosystem.  Because the relationship between flooding and hypoxia is non-linear and spatially explicit, we developed several discrete metrics to quantify the timing and magnitude of annual flooding.  We then described ARB hydrographs from 2001-2009 with a principal components analysis based on these metrics and investigated the relationships of flood types with basin-wide and management-unit water quality measurements.   Results indicate that long, high magnitude floods tended to result in extensive hypoxia during and after flooding that sometimes lasted well into fall, although patterns differed among the hydrologically-distinct management units.  Results emphasize the overriding effect of environmental changes on water quality characteristics during the annual flood pulse, and provide a unique insight into future management strategies that alter the timing and magnitude of flooding within the ARB.