Acute physicochemical effects from Hurricane Gustav in a large river-floodplain system

On 1 September 2008, Hurricane Gustav passed over the Atchafalaya River Basin (ARB) in southcentral Louisiana as a strong category 2 hurricane.  Anticipating physicochemical shifts attributable to the combination of concentrated precipitation and wind stress generated by a storm of this magnitude, we deployed a continuous recording multiparameter water quality sonde in a southern ARB bayou.  Quarter-hourly measurements taken over a two-week period indicated that daily mean dissolved oxygen (DO) concentration dropped to hypoxic level (DO < 2 mg/L) three days post-Gustav landfall and to near anoxic conditions within five days, resulting in extensive system wide fish kills.  A comparison of physicochemistry at multiple sites (n = 16) in the lower ARB throughout 2008 indicated that mean DO, pH, and specific conductance all reached annual lows immediately following storm passage.  Within six weeks, however, physicochemical parameters returned to pre-storm levels.  To assess the impact of the hurricane on ARB physicochemistry, we contrasted several physicochemical parameters (i.e., temperature, DO, pH, and specific conductance) collected at multiple microhabitats prior to and following the arrival of the storm.  Multivariate analysis of variance indicated that physicochemistry between pre and post-Gustav sample dates was dissimilar (Wilks’ Lambda = 0.10, F_4,91 = 209.29, P < 0.0001).