Nutrient Transport in a Riverine-Influenced, Tidal Freshwater Bayou in Louisiana

Abstract

Transport of ammonium (NH4+), nitrate + nitrite (NO3−), total Kjeldahl nitrogen (TKN), soluble reactive phosphate (SRP), and total suspended solids (TSS) was measured in a freshwater tidal bayou located in a marsh system near the mouth of the Atchafalaya River in Louisiana. Sampling was conducted six times over one year and was timed to assess effects of seasonal variation in river flow and mean sea level of the Gulf of Mexico on material fluxes. Net fluxes of all materials were large and ebb directed in all seasons except fall, when net transport was 2 to 3 orders-of-magnitude smaller than in any other season. These results demonstrate that riverine forcing was the primary influence on materials transport in all seasons except fall when tidal forcing was most important. The range of net fluxes (g s−1) for each nutrient was as follows (a negative sign indicates a net export toward the Gulf): NO3−, −0.006 to −6.69; TKN, 0.09 to −10.41; NH4+, −0.02 to −1.36; SRP, −0.001 to −0.53; TSS, −2 to −81. Analysis of nutrient concentrations indicated the marsh/aquatic system removed NO3−, SRP, and TSS from the water column from late spring through early fall and released NH4+ and TKN in summer. The results of this study show that net materials export per unit cross section channel area increased as riverine influence increased.