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RESEARCH ARTICLE
Contents Vol 61(9)

Sorption and desorption dynamics of bulk dissolved organic matter and amino acids in the Mississippi River plume – a microcosm study

Bryan L. Grace A C and Thomas S. Bianchi B
+ Author Affiliations
- Author Affiliations

A Earth and Environmental Sciences, Tulane University, New Orleans, LA 70118, USA. Present address: CH2M Hill, Metairie, LA 70112-1746, USA.

B Department of Oceanography, Texas A&M University, College Station, TX 77843-3146, USA.

C Corresponding author. Email: bryan.grace@ch2 m.com

Marine and Freshwater Research 61(9) 1067-1081 https://doi.org/10.1071/MF09181
Submitted: 15 July 2009  Accepted: 22 December 2009   Published: 23 September 2010

Abstract

Particulate and dissolved carbon, nitrogen and amino acids were analysed in a microcosm experiment where particulate material from the Mississippi River was mixed with surface waters of different salinities (2.0, 20.4 and 28.9) collected from the Mississippi River plume. There was evidence for the partitioning of amino acids in different salinity treatments during a 24-h period. Dissolved amino acids in the productive mid-salinity region of the plume had higher binding efficiencies than did amino acids from non-productive waters, indicative of the relative importance of phytoplankton sources of reactive amino acids. Basic amino acids were adsorbed more readily to particles, whereas acidic amino acids remained in the dissolved pool, indicating that electrostatic mechanisms affected amino-acid partitioning. Neutral amino-acid enrichment onto the particles was proportional to their respective hydrophobicity. Because riverine particles enter the higher salinity-shelf waters of the Mississippi River plume, changing ionic strength is a key in controlling amino-acid sorption and desorption kinetics. We propose that the short-term partitioning of amino acids between dissolved and particulate amino-acid pools across salinity gradients in the plume were affected by (1) electrostatic characteristics of suspended riverine sediment surfaces, (2) the availability of ‘freshly’ produced amino acids from phytoplankton and (3) the functional groups of amino acids.

Additional keywords: amino acids, desorption, dissolved organic matter, microcosm experiment, Mississippi River plume, particulate organic matter, sorption.


Acknowledgements

Funding for this research came primarily from Tulane University’s Center for Bioenvironmental Research via NOAA Grant Number NA16OA2672. We thank Katherine Rinker and Troy Sampere for their invaluable assistance in collecting samples. We also thank Larry Mayer and his laboratory for performing BET analyses and Pierre Burnside for XRD and XRF analyses. We also thank the captain and crew of the Research Vessel Pelican for their invaluable help in the field. Finally, we thank the anonymous reviewers for their comments to this manuscript and editorial assistance from Elizabeth Grace.


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