(Nearly) A Decade of Directly Measured Sediment N2 Fluxes: What Can Narragansett Bay Tell Us About the Global Ocean Nitrogen Budget?

Fulweiller, Robinson; Heiss, Elise M.

doi:10.5670/oceanog.2014.22

Cited by 34 publications

(41 citation statements)

References 35 publications

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“…When Sandusky River discharge and N loading are low, sediment N removal and N recycling by phytoplankton result in a smaller pulse of N delivery to Lake Erie that has been extensively processed into organic forms. Sandusky Bay thus oscillates between acting as a conduit and a filter of N. Discharge-driven oscillations in N cycling and downstream delivery may be a common feature in river-lake mixing zones and estuaries, most notably Narragansett Bay (Fulweiler et al, 2007;Fulweiler and Heiss, 2014).…”

Section: N Budgetmentioning

confidence: 99%

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

Salk¹,

Bullerjahn²,

McKay³

et al. 2018

Biogeosciences

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Abstract. 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.

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Section: N Budgetmentioning

confidence: 99%

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

Salk¹,

Bullerjahn²,

McKay³

et al. 2018

Biogeosciences

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“…Both N-fixation and denitrification can occur at a given site and the net N 2 flux depends on the balance between the two (Brown, 2013;Fulweiler et al, 2013;Ehrlich, 2014;Fulweiler and Heiss, 2014). In measurements from 2005 to 2013 in Narragansett Bay, Fulweiler and Heiss (2014) found a net positive flux of N 2 gas out of the sediments in both hypoxic and normoxic areas. Denitrification rates were significantly higher in the hypoxic areas, while Nfixation rates were not significantly different.…”

Section: Nutrient Cyclingmentioning

confidence: 99%

“…That the higher net flux of N 2 gas from the hypoxic sediments of Narragansett Bay was not statistically different is not surprising (Fulweiler and Heiss, 2014). Both N-fixation and denitrification can occur at a given site and the net N 2 flux depends on the balance between the two (Brown, 2013;Fulweiler et al, 2013;Ehrlich, 2014;Fulweiler and Heiss, 2014). In measurements from 2005 to 2013 in Narragansett Bay, Fulweiler and Heiss (2014) found a net positive flux of N 2 gas out of the sediments in both hypoxic and normoxic areas.…”

Section: Nutrient Cyclingmentioning

confidence: 99%

“…The sediment nitrogen cycle is complex and several processes are particularly sensitive to the sediment DO gradient. That the higher net flux of N 2 gas from the hypoxic sediments of Narragansett Bay was not statistically different is not surprising (Fulweiler and Heiss, 2014). Both N-fixation and denitrification can occur at a given site and the net N 2 flux depends on the balance between the two (Brown, 2013;Fulweiler et al, 2013;Ehrlich, 2014;Fulweiler and Heiss, 2014).…”

Section: Nutrient Cyclingmentioning

confidence: 99%

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Eutrophication and Hypoxia Diminish Ecosystem Functions of Benthic Communities in a New England Estuary

2016

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Excessive input of nitrogen to estuaries and coastal waters leads to eutrophication; the resulting organic matter over-enrichment of sediments and seasonal hypoxia of bottom water have significant deleterious effects on benthic community biodiversity, abundance, and biomass. Our goal was to better understand how these losses carry through to impairment of key ecosystem functions of benthic communities. Recent management efforts to address eutrophication have reduced nitrogen loading to several estuaries of the Virginian Biogeographic Province (northeast United States). How the ecosystems will respond remains to be seen. Using Narragansett Bay as an example estuary within this Province, we compared measures of community structure and function from stations in seasonally hypoxic areas with stations in normoxic areas. We analyzed a benthic data set spanning 20 years and 155 stations, along with ancillary data from other sources. Hypoxic areas had half the species richness, many fewer rare species, lower biomass, and lower secondary production. Benthic communities in the hypoxic areas had a significantly different abundance structure, were at an earlier successional stage, and bioturbated the sediments to a depth about one-fifth that of the normoxic areas. On average, sediments in the hypoxic areas took up more oxygen-used for aerobic metabolism and oxidation of reduced compounds from anaerobic metabolism. Sediments in hypoxic areas released into the overlying water two to three times more ammonium and phosphate. Mean flux of dissolved oxygen into the sediments of hypoxic areas and mean net flux of nitrogen gas (from sediment denitrification) out were slightly higher. Eutrophication-driven over-enrichment of organic matter, along with seasonal hypoxia in the northern part of the Bay have led to degradation of benthic community structure and function, which have serious implications for sustainable provision of ecosystem services. We quantified fifteen stressor-response relationships that can help understand how, following a reduction in nitrogen inputs, a recovery of benthic ecosystem functions in hypoxic areas could proceed.

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“…In this manner, Sandusky Bay oscillates between acting as a strong N source and a weak N source, creating a N pendulum. This N pendulum may be a common feature of other estuarine systems, most notably Narragansett Bay (Fulweiler et al, 2007;Fulweiler and Heiss, 2014). The pendulum action of N cycling in Sandusky Bay indicates that the system may be oscillating between alternate states, and the capacity for the bay to act as a net N sink has been overwhelmed by riverine 25 N loading.…”

Section: N Budget and The N Pendulummentioning

confidence: 99%

The nitrogen pendulum in Sandusky Bay, Lake Erie: Oscillations between strong and weak export and implications for harmful algal blooms

Salk¹,

Bullerjahn²,

McKay³

et al. 2018

Preprint

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Abstract.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 (NO3 -) and ammonium (NH4 + ) uptake, N fixation, and N removal processes were quantified by stable 15 isotopic approaches. Dissimilatory N uptake was a relatively modest N sink, with denitrification, anammox, and N2O production accounting for 84, 14, and 2 % of N removal, respectively. Phytoplankton assimilation was the dominant N uptake mechanism, and NO3 -uptake rates were higher than NH4 + uptake rates. Riverine DIN 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 20 surprisingly uncorrelated with NO3 -or NH4 + concentrations. Owing to temporal separation in sources and sinks of N to Lake Erie, Sandusky Bay pendulums between acting as a strong and weak source of downstream N loading to Lake Erie.Estuarine systems such as Sandusky Bay are mediators of downstream N loading, but climate change-induced increases in precipitation and N loading will likely intensify the swings of the N pendulum in favor of N export.

show abstract

(Nearly) A Decade of Directly Measured Sediment N2 Fluxes: What Can Narragansett Bay Tell Us About the Global Ocean Nitrogen Budget?

Cited by 34 publications

References 35 publications

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

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

Eutrophication and Hypoxia Diminish Ecosystem Functions of Benthic Communities in a New England Estuary

The nitrogen pendulum in Sandusky Bay, Lake Erie: Oscillations between strong and weak export and implications for harmful algal blooms

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