MISSISSIPPI RIVER ISLANDS AND THEIR POTENTIAL TO AFFECT NITROGEN CYCLING NEAR MEMPHIS, TN, USA
Wells were installed at several sites on each island to assess stratigraphy and hydrology. Soil samples were characterized in the field and then later classified using sieve analysis. Representative soil samples from each 1-ft borehole increment were subjected to Loss on Ignition (LOI) analysis to assess their relative organic content and potential to promote nitrogen cycling. The non-vegetated island was found to be mostly sand with minor lenses of fine material. The vegetated island displayed alternating layers of fine sands and silt/clay representing deposits from seasonal flood events. Historical observations of the islands indicate that the vegetated island is more susceptible to vertical accretion, whereas the non-vegetated island is more susceptible to broader morphological changes. Data suggest the non-vegetated island behaves similarly to an unconfined system with potential perched zones, whereas the vegetated island may act as a series of confined to semi-confined aquifer units. The non-vegetated island samples showed ranges of LOI360 between 0% and 1%, and LOI550 below 0.3%. For the vegetated island samples, LOI360 ranged from 0.3% to 5.1% and LOI550 ranged from 0% to 2% indicating a higher organic content in the sediment of the vegetated island. These findings suggest that islands could potentially play a significant role in cycling and the overall nitrogen budget of the LMR.