Predicting Floodplain Hypoxia in the Atchafalaya River, Louisiana, USA, a Large, Regulated Southern Floodplain River System

The Atchafalaya River Basin Floodway (ARBF), a regulated river/floodplain distributary of the Mississippi River, experiences an annual flood pulse that strongly influences floodplain physicochemistry. We developed several metrics to investigate the relationship between the timing and magnitude of the flood pulse and floodplain hypoxia, which in most years is a spatially extensive and temporally prolonged problem in the lower ARBF. Principal components analysis of flood metrics from 2001 to 2009 revealed contrasting flood types (early cool and late warm), but component-based general linear models were unable to predict the magnitude of hypoxia in ARBF water management areas (WMAs). Further analyses based on temperature and geographic information system-determined WMA inundation with generalized additive models (GAMs) revealed WMA-specific patterns of hypoxia, but the likelihood of hypoxia consistently increased when temperatures approached 20 degrees C and inundation rose above 20-30%. Validation with held-out data based on logistic regression indicated that the models constructed with the 2001-2009 temperature and inundation data were able to accurately predict the probabilities of hypoxia in two WMAs based on data collected from 2010 to 2013. The GAMs were an effective tool for visualizing and predicting the probability of hypoxia based on two easily generated parameters. Our analyses indicate that modification of the Atchafalaya River flood pulse could reduce the magnitude of hypoxia within the lower ARBF, subject to engineering (control structure operation) and economic (commercial fisheries production) constraints, by minimizing floodplain inundation after water temperatures reach 20 degrees C. Copyright (c) 2015 John Wiley & Sons, Ltd.