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Mississippi and Atchafalaya River Influence on Sediment Porewater Chemistry
Citation:
Beddick, D., R. Devereux, B. Jarvis, J. Lehrter, AND D. Yates. Mississippi and Atchafalaya River Influence on Sediment Porewater Chemistry. Presented at ASLO 2013 Aquatic Sciences Meeting, February 17 - 22, 2013.
Impact/Purpose:
To demonstrate spatial patterns observed from porewater concentrations as they relate to distance from freshwater input from the Mississippi and Atchafalaya River.
Description:
The Louisiana continental shelf (LCS) receives 380 km3 of freshwater per year from the Mississippi and Atchafalaya Rivers. Sources and transport of nutrients and organic matter (OM) delivered to the LCS may result in spatial variation in sediment biogeochemistry important for understanding seasonal hypoxia. Twelve stations were sampled during the fall of 2010 along four north-south transects spaced between the Mississippi River delta and southwest of Vermillion Bay. Triplicate sediment cores were collected at each station near the 10, 30, and 50 m isobaths. The stations at the 10 m isobath had higher average porewater dissolved inorganic carbon and NH4+ (end members of OM decomposition) and dissolved inorganic phosphorus. A similar pattern was observed in nitrate and silicate concentrations. In addition, porewater Mn and Fe2+ concentrations were highest in stations closest to the delta and sulfate reduction rates were lowest at the offshore stations. These results indicate a gradient in nearshore to offshore sediment biogeochemical rates likely due to differences in the deposition of organic matter.