Simultaneous observations revealed the non-steady state effects of a tropical storm on the export of particles and inorganic nitrogen through a river-estuary continuum

Abstract. Photochemistry of dissolved organic matter (DOM) plays an important role in marine biogeochemical cycles, including the regeneration of inorganic nutrients. DOM photochemistry affects nitrogen cycling by converting bio-refractory dissolved organic nitrogen to labile inorganic nitrogen, mainly ammonium (NH4+). During the August 2009 Mackenzie Light and Carbon (MALINA) Program, the absorbed photon-based efficiency spectra of NH4+ photoproduction (i.e. photoammonification) were determined using water samples from the SE Beaufort Sea, including the Mackenzie River estuary, shelf, and Canada Basin. The photoammonification efficiency decreased with increasing wavelength across the ultraviolet and visible regimes and was higher in offshore waters than in shelf and estuarine waters. The efficiency was positively correlated with the molar nitrogen : carbon ratio of DOM and negatively correlated with the absorption coefficient of chromophoric DOM (CDOM). Combined with collateral measurements of CO2 and CO photoproduction, this study revealed a stoichiometry of DOM photochemistry with a CO2:CO:NH4+ molar ratio of 165:11:1 in the estuary, 60:3:1 on the shelf, and 18:2:1 in the Canada Basin. The NH4+ efficiency spectra, along with solar photon fluxes, CDOM absorption coefficients and sea ice concentrations, were used to model the monthly surface and depth-integrated photoammonification rates in 2009. The summertime (June–August) rates at the surface reached 6.6 nmol l−1 d−1 on the Mackenzie Shelf and 3.7 nmol l−1 d−1 further offshore; the depth-integrated rates were correspondingly 8.8 μmol m−2 d−1 and 11.3 μmol m−2 d−1. The offshore depth-integrated rate in August (8.0 μmol m−2 d−1) was comparable to the missing dissolved inorganic nitrogen (DIN) source required to support the observed primary production in the upper 10-m layer of that area. The yearly NH4+ photoproduction in the entire study area was estimated to be 1.4 × 108 moles, with 85 % of it being generated in summer when riverine DIN input is low. Photoammonification could mineralize 4 % of the annual dissolved organic nitrogen (DON) exported from the Mackenzie River and provide a~DIN source corresponding to 7 % of the riverine DIN discharge and 1400 times the riverine NH4+ flux. Under a climate warming-induced ice-free scenario, these quantities would increase correspondingly to 6 %, 11 %, and 2100 times. Photoammonification is thus a significant nitrogen cycling term and may fuel previously unrecognized autotrophic and heterotrophic production pathways in the surface SE Beaufort Sea.

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Seasonal and spatial controls on N2O concentrations and emissions in low-nitrogen estuaries: Evidence from three tropical systems

10.1101/650705 ◽

2019 ◽

Author(s):

Rachel Murray ◽

Dirk Erler ◽

Judith Rosentreter ◽

Naomi Wells ◽

Bradley Eyre

Keyword(s):

Inorganic Nitrogen ◽

River Estuary ◽

The Other ◽

Dissolved Inorganic Nitrogen ◽

Wet Season ◽

Tropical Estuaries ◽

Dry Seasons ◽

Low Nitrogen ◽

Fitzroy River ◽

Wet And Dry Seasons

AbstractEstuarine N2O emissions contribute to the atmospheric N2O budget, but little is known about estuary N2O fluxes under low dissolved inorganic nitrogen (DIN) conditions. We present high-resolution spatial surveys of N2O concentrations and water-air fluxes in three low-DIN (NO3−< 30µmol L−1) tropical estuaries in Queensland, Australia (Johnstone River, Fitzroy River, Constant Creek) during consecutive wet and dry seasons. Constant Creek had the lowest concentrations of dissolved inorganic nitrogen (DIN; 0.01 to 5.4µmol L−1of NO3−and 0.09 to 13.6µmol L−1of NH4+) and N2O (93–132% saturation), and associated lowest N2O emissions (– 1.4 to 8.4µmol m−2d−1) in both seasons. The other two estuaries exhibited higher DIN inputs and higher N2O emissions. The Johnstone River Estuary had the highest N2O concentrations (97–245% saturation) and emissions (– 0.03 to 25.7µmol m−2d−1), driven by groundwater inputs from upstream sources, with increased N2O input in the wet season. In the Fitzroy River Estuary, N2O concentrations (100–204% saturation) and emissions (0.03–19.5µmol m−2d−1) were associated with wastewater inputs, which had a larger effect during the dry season and were diluted during the wet season. Overall N2O emissions from the three tropical estuaries were low compared to previous studies, and at times water-air N2O fluxes were actually negative, indicating that N2O consumption occurred. Low water column NO3−concentration (i.e. < 5µmol L−1) appears to promote negative water-air N2O fluxes in estuary environments; considering the number of estuaries and mangrove creeks where DIN falls below this threshold, negative water-air N2O fluxes are likely common.

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Temperature Dependence of Inorganic Nitrogen Uptake: Reduced Affinity for Nitrate at Suboptimal Temperatures in Both Algae and Bacteria

Applied and Environmental Microbiology ◽

10.1128/aem.65.6.2577-2584.1999 ◽

1999 ◽

Vol 65 (6) ◽

pp. 2577-2584 ◽

Cited By ~ 115

Author(s):

David S. Reay ◽

David B. Nedwell ◽

Julian Priddle ◽

J. Cynan Ellis-Evans

Keyword(s):

Steady State ◽

Temperature Dependence ◽

Thermophilic Bacteria ◽

Inorganic Nitrogen ◽

Maximum Growth ◽

Maximum Growth Rate ◽

Ammonium Uptake ◽

Inorganic Nitrogen Source ◽

Batch Cultures ◽

Specific Affinity

ABSTRACT Nitrate utilization and ammonium utilization were studied by using three algal isolates, six bacterial isolates, and a range of temperatures in chemostat and batch cultures. We quantified affinities for both substrates by determining specific affinities (specific affinity = maximum growth rate/half-saturation constant) based on estimates of kinetic parameters obtained from chemostat experiments. At suboptimal temperatures, the residual concentrations of nitrate in batch cultures and the steady-state concentrations of nitrate in chemostat cultures both increased. The specific affinity for nitrate was strongly dependent on temperature (Q10 ≈ 3, where Q10 is the proportional change with a 10°C temperature increase) and consistently decreased at temperatures below the optimum temperature. In contrast, the steady-state concentrations of ammonium remained relatively constant over the same temperature range, and the specific affinity for ammonium exhibited no clear temperature dependence. This is the first time that a consistent effect of low temperature on affinity for nitrate has been identified for psychrophilic, mesophilic, and thermophilic bacteria and algae. The different responses of nitrate uptake and ammonium uptake to temperature imply that there is increasing dependence on ammonium as an inorganic nitrogen source at low temperatures.

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Understanding how estuarine hydrology controls ammonium and other inorganic nitrogen concentrations and fluxes through the subtropical Jiulong River Estuary, S.E. China under baseflow and flood-affected conditions

Biogeochemistry ◽

10.1007/s10533-019-00546-9 ◽

2019 ◽

Vol 142 (3) ◽

pp. 443-466 ◽

Cited By ~ 4

Author(s):

Dan Yu ◽

Nengwang Chen ◽

Michael D. Krom ◽

Jingjie Lin ◽

Peng Cheng ◽

...

Keyword(s):

Inorganic Nitrogen ◽

River Estuary ◽

Jiulong River Estuary ◽

Jiulong River ◽

Nitrogen Concentrations

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Seasonal dissolved inorganic nitrogen and phosphorus budgets for two sub-tropical estuaries in south Florida, USA

Biogeosciences ◽

10.5194/bg-10-6721-2013 ◽

2013 ◽

Vol 10 (10) ◽

pp. 6721-6736 ◽

Cited By ~ 10

Author(s):

C. Buzzelli ◽

Y. Wan ◽

P. H. Doering ◽

J. N. Boyer

Keyword(s):

Nutrient Loading ◽

Inorganic Nitrogen ◽

River Estuary ◽

South Florida ◽

External Loading ◽

Dissolved Inorganic Nitrogen ◽

Nutrient Inputs ◽

Wet Season ◽

Nitrogen And Phosphorus ◽

Annual Variations

Abstract. Interactions among geomorphology, circulation, and biogeochemical cycling determine estuary responses to external nutrient loading. In order to better manage watershed nutrient inputs, the goal of this study was to develop seasonal dissolved inorganic nitrogen (DIN) and phosphorus (DIP) budgets for the two estuaries in south Florida, the Caloosahatchee River estuary (CRE) and the St. Lucie Estuary (SLE), from 2002 to 2008. The Land–Ocean Interactions in the Coastal Zone (LOICZ) approach was used to generate water, salt, and DIN and DIP budgets. Results suggested that internal DIN production increases with increased DIN loading to the CRE in the wet season. There were hydrodynamic effects as water column concentrations and ecosystem nutrient processing stabilized in both estuaries as flushing time increased to >10 d. The CRE demonstrated heterotrophy (net ecosystem metabolism or NEM < 0.0) across all wet and dry season budgets. While the SLE was sensitive to DIN loading, system autotrophy (NEM > 0.0) increased significantly with external DIP loading. This included DIP consumption and a bloom of a cyanobacterium (Microcystis aeruginosa) following hurricane-induced discharge to the SLE in 2005. Additionally, while denitrification provided a microbially-mediated N loss pathway for the CRE, this potential was not evident for the SLE where N2 fixation was favored. Disparities between total and inorganic loading ratios suggested that the role of dissolved organic nitrogen (DON) should be assessed for both estuaries. Nutrient budgets indicated that net internal production or consumption of DIN and DIP fluctuated with inter- and intra-annual variations in freshwater inflow, hydrodynamic flushing, and primary production. The results of this study should be included in watershed management plans in order to maintain favorable conditions of external loading relative to internal material cycling in both dry and wet seasons.

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Dissolved inorganic nitrogen in a tropical estuary in Malaysia: transport and transformation

Biogeosciences ◽

10.5194/bg-16-2821-2019 ◽

2019 ◽

Vol 16 (14) ◽

pp. 2821-2836 ◽

Cited By ~ 11

Author(s):

Shan Jiang ◽

Moritz Müller ◽

Jie Jin ◽

Ying Wu ◽

Kun Zhu ◽

...

Keyword(s):

Primary Productivity ◽

Inorganic Nitrogen ◽

River Estuary ◽

Dry Season ◽

Similar Distribution ◽

Tropical Estuary ◽

Dissolved Inorganic Nitrogen ◽

Wet Season ◽

Terrestrial Organic Matter ◽

Transport And Transformation

Abstract. Dissolved inorganic nitrogen (DIN), including nitrate, nitrite and ammonium, frequently acts as the limitation for primary productivity. Our study focused on the transport and transformation of DIN in a tropical estuary, i.e., the Rajang River estuary, in Borneo, Malaysia. Three cruises were conducted in August 2016 and February–March and September 2017, covering both dry and wet seasons. Before entering the coastal delta, decomposition of the terrestrial organic matter and the subsequent soil leaching was assumed to be the main source of DIN in the river water. In the estuary, decomposition of dissolved organic nitrogen was an additional DIN source, which markedly increased DIN concentrations in August 2016 (dry season). In the wet season (February 2017), ammonium concentrations showed a relatively conservative distribution during the mixing, and the nitrate addition was weak. La Niña events induced high precipitations and discharge rates, decreased reaction intensities of ammonification and nitrification. Hence similar distribution patterns of DIN species in the estuary were found in September 2017 (end of the dry season). The magnitude of riverine DIN flux varied between 77.2 and 101.5 t N d−1, which might be an important support for the coastal primary productivity.

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Summer flow event induces a cyanobacterial bloom in a seasonal Western Australian estuary

Marine and Freshwater Research ◽

10.1071/mf02090 ◽

2003 ◽

Vol 54 (2) ◽

pp. 139 ◽

Cited By ~ 99

Author(s):

Barbara J. Robson ◽

David P. Hamilton

Keyword(s):

Inorganic Nitrogen ◽

Cyanobacterial Bloom ◽

River Estuary ◽

Summer Rainfall ◽

High Water ◽

Surface Mixed Layer ◽

Cell Counts ◽

High Concentrations ◽

Reactive Phosphorus ◽

Australian Estuary

In January 2000, record rainfall led to the first recorded bloom of Microcystis aeruginosa in the Swan River estuary. A simple model is used to examine the bloom dynamics and the unusual conditions that produced it. Laboratory trials were conducted to determine the response to salinity of M. aeruginosa, while other parameters for the model were obtained from the literature. Growth was found to be optimal at salinities up to 4, and declined to zero at 25. The unseasonable summer rainfall flushed brackish and marine water from the estuary and produced a surface mixed layer with low salinity. The model simulations show that the hydrological conditions, in combination with high concentrations of inorganic nutrients (dissolved inorganic nitrogen >1.2 mg L–1, filterable reactive phosphorus >0.02 mg L–1) in river inflows, high water temperature and high daily insolation, promoted rapid phytoplankton growth, favouring dominance by M. aeruginosa. Doubling rates during the bloom were around 0.35 day–1 and cell counts exceeded 105 cells mL–1 within three weeks of the inflow event. Although this doubling rate ultimately determined the total bloom biomass, local concentrations were strongly influenced by physical processes that concentrated M. aeruginosa cells both vertically and horizontally, and advected a seed population from the upper estuary into the lower basin.

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SPATIAL AND TEMPORALVARIATION OF DISSOLVED INORGANIC NUTRIENTS, AND CHLOROPHYLL-α IN A TROPICAL ESTUARY IN NORTHEASTERN BRAZIL: DYNAMICS OF NUTRIENT REMOVAL

Brazilian Journal of Oceanography ◽

10.1590/s1679-87592015064506301 ◽

2015 ◽

Vol 63 (1) ◽

pp. 1-15 ◽

Cited By ~ 13

Author(s):

Maria Aparecida Macedo Silva ◽

Marcelo F. L. Souza ◽

Paulo C. Abreu

Keyword(s):

Nutrient Removal ◽

Organic Phosphorus ◽

Inorganic Nitrogen ◽

Salinity Gradient ◽

Sewage Treatment Plant ◽

Treatment Plant ◽

River Estuary ◽

Temporal Distribution ◽

Northeastern Brazil ◽

Nutrient Concentrations

Monthly sampling campaigns were carried out between February 2010 and January 2011 to evaluate the spatial and temporal distribution of nutrients (ammonium, nitrite, nitrate, dissolved organic nitrogen, phosphate, dissolved organic phosphorus and silicate) and chlorophyll-α along a salinity gradient in the tropical Cachoeira River estuary, subject to the untreated effluents of a sewage treatment plant (STP). During the study period the lowest and highest river discharge occurred in February and April 2010, respectively. High river outflow promoted increased concentrations of inorganic nitrogen and silicate but did not affect the concentration of phosphate. Based on the chlorophyll-α concentration the estuary may be classified as eutrophic / hypereutrophic in its inner portion and mesotrophic in the lower region. The inner portion is more affected by the nutrient load carried out by the river and STP, while dilution by seawater contributed to the reduction of the nutrient concentrations in the lower reaches of the estuary. The results indicate that nutrient uptake by the phytoplankton is the most effective dissolved inorganic nutrient removal processes, especially for phosphate. Mixing diagrams suggest that the coupling of nitrification and denitrification processes is also responsible for the elimination of nitrogen from this ecosystem.

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