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TECHNICAL REPORTS

Wetlands and Aquatic Processes

Effects of Static vs. Tidal Hydrology on Pollutant Transformation in Wetland Sediments

^a Lab. for Ecological Chemistry, CBS Dep., School of Veterinary Medicine, Louisiana State Univ., Baton Rouge, LA 70803
^b Dep. of Chemistry, Univ. of Louisiana-Monroe, Monroe, LA

^* Corresponding author (jcatallo{at}mail.vetmed.lsu.edu).

Received for publication May 7, 2002. This work addressed effects of hydrology on biogeochemical processes relevant to pollutant chemical transformation in wetland sediments. Microcosms were designed to impose three hydrologic conditions on salt marsh sediments: (i) drained–oxidized redox potenial (Eh); (ii) flooded–reduced Eh and, (iii) diurnal tide–oscillating Eh. The test chemicals were N- and/or S-heterocycles (NSHs) including quinoxaline (1,4-benzodiazine), 2-methylquinoxaline(2-methyl-1,4-benzodiazine), 2,3-dimethylquinoxalinen (2,3-dimethyl-1,4,benzodiazine), phenazine (2,3,5,6-dibenzo-1,4-diazine), acridine (2,3,5,6-dibenzopyridine), dibenzothiophene (2,3,5-dibenzothiophene), phenothiazine (dibenzo-1,4-thiazine), and phenanthridine (2,3-benzoisoquinoline). Biogeochemical processes reflected the hydrologic conditions in ways analogous to field settings, e.g., Eh characteristics were drastically different: static (flooded and drained) systems had reduced (µ = -428 mV ± 57) and oxidized (µ = +73 mV ± 32) values, respectively, with no evidence of periodic variation while the tidal systems exhibited regularly oscillating Eh (amplitudes 40–250 mV). Sediment trace gases also corresponded to the Eh, with the major species detected being CO₂ and H₂O (drained, tidal) vs. CO₂ + H₂O + sulfides + methane (flooded). The NSH transformation rates were different in each hydrologic regime and decreased as follows: tidal drained >> flooded. These results indicated that there were subtle differences in NSH processing in drained and tidal systems, but both of these systems transformed NSHs faster and to lower levels than flooded sediments. These data suggest that in situ remediation options that preserve wetland integrity and tidal hydrology can be as or more effective than static conditions that obtain in approaches such as impoundment and excavation–upland placement.

Abbreviations: Ahs, aromatic hydrocarbons • DCM, dichloromethane (methylene chloride) • Eh, redox potential • FTIR, fourier transform infrared spectrometry • GC-MS, gas chromatography–mass spectrometry • NSHs, N- and S- heterocycles • SCE, saturated calomel–KCl reference electrode

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JEQ 2003 32: 1931-1938. [Full Text]  

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