A flow-through flume technique for quantifying nutrient and materials fluxes in microtidal estuaries

The marsh flume methodology has been modified for use in northern Gulf Coast esturies, where tidal ranges are small and irregular and where wetlands are flat and expansive. In this technique, two key changes have been made: (i) flumes are open to water exchange at both ends, and; (ii) samples are taken simultaneously at both ends throughout a tidal cycle. Thus, the flumes are conceptually through-flow systems. Nutrient fluxes are calculated volumetrically, from the microtopography of the marsh and changes in water height over a tidal cycle. Instantaneous fluxes across each end of the flume are pooled for flooding or ebbing flow, then subtracted to give total net flux. Data from three flumes built in fresh, brackish, and saline marshes of the Barataria Basin estuary, LA, show that significant concentration differences (and hence significant fluxes) are detectable using our modified flume technique. Net areal flux values measured using the modified technique are in close agreement with values reported from past studies using flumes where concentrations are sampled only at the mouth end. The similarities indicate that our modifications to the flume methodology allowed us to quantify adequately the nutrient and material fluxes between Gulf Coast marshes and their inundating water column. This technique hhas application in any estuary where marshes are microtidal, expansive, or irregularly flooded.