Nitrogen cycling in Sandusky Bay, Lake Erie: Oscillations between strong and weak export and implications for harmful algal blooms

Published

Journal Article

© 2018 Author(s). Recent global water quality crises point to an urgent need for greater understanding of cyanobacterial harmful algal blooms (cHABs) and their drivers. Nearshore areas of Lake Erie such as Sandusky Bay may become seasonally limited by nitrogen (N) and are characterized by distinct cHAB compositions (i.e., Planktothrix over Microcystis). This study investigated phytoplankton N uptake pathways, determined drivers of N depletion, and characterized the N budget in Sandusky Bay. Nitrate (NO 3- ) and ammonium (NH 4+ ) uptake, N fixation, and N removal processes were quantified by stable isotopic approaches. Dissimilatory N reduction was a relatively modest N sink, with denitrification, anammox, and N 2 O production accounting for 84, 14, and 2% of sediment N removal, respectively. Phytoplankton assimilation was the dominant N uptake mechanism, and NO 3- uptake rates were higher than NH 4+ uptake rates. Riverine N loading was sometimes insufficient to meet assimilatory and dissimilatory demands, but N fixation alleviated this deficit. N fixation made up 23.7-85.4% of total phytoplankton N acquisition and indirectly supports Planktothrix blooms. However, N fixation rates were surprisingly uncorrelated with NO 3- or NH 4+ concentrations. Owing to temporal separation in sources and sinks of N to Lake Erie, Sandusky Bay oscillates between a conduit and a filter of downstream N loading to Lake Erie, delivering extensively recycled forms of N during periods of low export. Drowned river mouths such as Sandusky Bay are mediators of downstream N loading, but climate-change-induced increases in precipitation and N loading will likely intensify N export from these systems.

Full Text

Duke Authors

Cited Authors

  • Salk, KR; Bullerjahn, GS; McKay, RML; Chaffin, JD; Ostrom, NE

Published Date

  • May 16, 2018

Published In

Volume / Issue

  • 15 / 9

Start / End Page

  • 2891 - 2907

Electronic International Standard Serial Number (EISSN)

  • 1726-4189

International Standard Serial Number (ISSN)

  • 1726-4170

Digital Object Identifier (DOI)

  • 10.5194/bg-15-2891-2018

Citation Source

  • Scopus