Download abstract

Title: H OW I MPORTANT A RE R ESUSPENDED PARTICLES TO NITROGEN DYNAMICS I N T HE N ORTHERN G ULF O F M EXICO?
Authors: W. S. Gardner, X. Lin, M. J. McCarthy, G. Cartwright, K. Fall, Z. Liu, K. Briggs, and C. Friedrichs
Abstract: The paradigm for coastal, nutrient-­‐induced hypoxia formaTon is that oxygen demand is derived from seVling biogenic parTcles via high biological producTvity in surface waters. The hypothesis that freshly seVled parTcles in sediments parTcipate acTvely in biogeochemical processes and lead to hypoxia was examined in the Northern Gulf of Mexico by measuring nitrogen transformaTon rates ( /h) of near-­‐boVom water in the absence and presence of parTcles resuspended at different levels of shear stress with a “GUST chamber.” Rates of ammonium regeneraTon (0.01 – 0.03) and potenTal uptake (0.06 – 0.12), nitrificaTon (< 0.01 – 0.14), and ammonium producTon from added amino acids (0.13– 0.17) were not enhanced significantly by resuspended parTcles. Ammonium demand (0.04 – 0.11), defined as the difference between potenTal and actual uptake (esTmated from regeneraTon) rates, and ¹⁵N-­‐amino acid addiTon experiments suggested that bacterial acTvity is limited by substrate availability. These results, and the observaTon that depth-­‐averaged, areal water column respiraTon exceeds that at the sediment-­‐water interface, suggest that the effects of seVled organic parTcles on ammonium regeneraTon and oxygen demand are minimal.