Flow regulates biological NO3 -and N2O production in a turbid sub-tropical stream

AbstractThe ocean is a net source of N2O, a potent greenhouse gas and ozone-depleting agent. However, the removal of N2O via microbial N2O consumption is poorly constrained and rate measurements have been restricted to anoxic waters. Here we expand N2O consumption measurements from anoxic zones to the sharp oxygen gradient above them, and experimentally determine kinetic parameters in both oxic and anoxic seawater for the first time. We find that the substrate affinity, O2 tolerance, and community composition of N2O-consuming microbes in oxic waters differ from those in the underlying anoxic layers. Kinetic parameters determined here are used to model in situ N2O production and consumption rates. Estimated in situ rates differ from measured rates, confirming the necessity to consider kinetics when predicting N2O cycling. Microbes from the oxic layer consume N2O under anoxic conditions at a much faster rate than microbes from anoxic zones. These experimental results are in keeping with model results which indicate that N2O consumption likely takes place above the oxygen deficient zone (ODZ). Thus, the dynamic layer with steep O2 and N2O gradients right above the ODZ is a previously ignored potential gatekeeper of N2O and should be accounted for in the marine N2O budget.

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Saline mine-water alters the structure and function of prokaryote communities in shallow groundwater below a tropical stream

Environmental Pollution ◽

10.1016/j.envpol.2021.117318 ◽

2021 ◽

pp. 117318

Author(s):

Lisa Chandler ◽

Andrew J. Harford ◽

Grant C. Hose ◽

Chris L. Humphrey ◽

Anthony Chariton ◽

...

Keyword(s):

Mine Water ◽

Shallow Groundwater ◽

Structure And Function ◽

Tropical Stream ◽

And Function

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Post-fire consequences for leaf breakdown in a tropical stream

Acta Limnologica Brasiliensia ◽

10.1590/s2179-975x4118 ◽

2019 ◽

Vol 31 ◽

Author(s):

Renan de Souza Rezende ◽

Cristiano Queiroz de Albuquerque ◽

Andrezza Sayuri Victoriano Hirota ◽

Paulo Fernandes Roges Souza Silva ◽

Ricardo Keichi Umetsu ◽

...

Keyword(s):

Leaf Litter ◽

Fungal Biomass ◽

Mesh Size ◽

Fire Effects ◽

Dry Mass ◽

Tropical Stream ◽

Fire Event ◽

Litter Bags ◽

Fine Mesh ◽

Post Fire Effects

Abstract Aim Wildfire is a natural pulsed disturbance in landscapes of the Savannah Biome. This study evaluates short-term post-fire effects on leaf litter breakdown, the invertebrate community and fungal biomass of litter from three different vegetal species in a tropical stream. Methods Senescent leaves of Inga laurina, Protium spruceanum and Rircheria grandis (2 ± 0.1 g dry mass) were individually placed in litter bags (30 × 30 cm: 10 mm coarse mesh and 0.5 mm fine mesh) and submerged in the study stream before and after fire. Replicate bags (n = 4; individually for each species, sampling time, fire event and mesh size) were then retrieved after 20 and 40 days and washed to separate the invertebrates before fire event and again immediately after fire. Disks were cut from leaves to determine ash-free dry mass, while the remaining material was oven-dried to determine dry mass. Results The pre-fire mean decomposition coefficient (k = -0.012 day-1) was intermediate compared to that reported for other savannah streams, but post-fire it was lower (k = -0.007 day-1), due to decreased allochthonous litter input and increased autochthones production. Intermediate k values for all qualities of litter post-fire may indicate that fire is equalizing litter quality in the stream ecosystem. The abundance of scrapers was found to be more important than fungal biomass or shredder abundance, probably due to their functioning in leaf fragmentation while consuming periphyton growing on leaf litter. Conclusions Theses results indicate that fire can modify the relationships within decomposer communities in tropical stream ecosystems.

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N2O production by heterotrophic N transformations in a semiarid soil

Applied Soil Ecology ◽

10.1016/j.apsoil.2005.06.005 ◽

2006 ◽

Vol 32 (2) ◽

pp. 253-263 ◽

Cited By ~ 67

Author(s):

Jean E.T. McLain ◽

Dean A. Martens

Keyword(s):

N2o Production ◽

N Transformations

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

Biogeosciences ◽

10.5194/bg-15-2891-2018 ◽

2018 ◽

Vol 15 (9) ◽

pp. 2891-2907 ◽

Cited By ~ 14

Author(s):

Kateri R. Salk ◽

George S. Bullerjahn ◽

Robert Michael L. McKay ◽

Justin D. Chaffin ◽

Nathaniel E. Ostrom

Keyword(s):

Harmful Algal Blooms ◽

Algal Blooms ◽

Lake Erie ◽

N Uptake ◽

N Fixation ◽

N Budget ◽

N2o Production ◽

N Removal ◽

Uptake Rates ◽

N Loading

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 isotopic approaches. Dissimilatory N reduction was a relatively modest N sink, with denitrification, anammox, and N2O production accounting for 84, 14, and 2 % of sediment N removal, respectively. Phytoplankton assimilation was the dominant N uptake mechanism, and NO3- uptake rates were higher than NH4+ 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 NO3- or NH4+ 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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