Acute Physicochemical Effects in a Large River-Floodplain System Associated with the Passage of Hurricane Gustav

On 1 September 2008, Hurricane Gustav passed over the Atchafalaya River Basin (ARB) in south-central Louisiana. Anticipating physicochemical shifts due to concentrated precipitation and wind stress generated by this strong category 2 storm, we deployed a continuous recording multiparameter water quality sonde in a southern ARB bayou 3 days prior to storm arrival to document conditions before, during, and after hurricane landfall. Quarter-hourly physicochemical measurements taken over a 2-week period indicated that dissolved oxygen (DO), pH, and specific conductance all reached annual lows immediately following storm passage. The most pronounced post-storm fluctuation involved DO. Daily mean DO concentration dropped to hypoxic level (DO <= 2 mg/L) within 3 days of landfall, followed by near anoxic conditions within 5 days that resulted in extensive system-wide fish kills. Within 6 weeks, however, DO returned to, and pH was near pre-storm levels. To evaluate the impact of Hurricane Gustav on ARB physicochemistry, we contrasted data on DO, pH, temperature, and specific conductance collected from 16 lower ARB sampling sites over a 54-day interval prior to storm landfall with data collected during a 45-day post-storm period. Results indicated that water quality was highly dissimilar (P<0.0001) between the two periods.