Uptake Of NO3 Research Articles

Gas chromatograph analysis on closed nitrous oxide and air atmospheres of recalcitrant Quercus alba seeds

Storage of recalcitrant seeds remains an unsolved problem. The study of gaseous atmospheres could provide insights in understanding the metabolism of recalcitrant seeds and their potential in being used as means for storage. This study investigated the metabolism of the recalcitrant Quercus alba seeds when subjected under nitrous oxide (N2O) and air atmospheres. Seeds were placed in sealed atmospheric flasks of 98/2% N2O/O2. Three experiments were conducted to determine N2O uptake in relation to oxygen (O2) and carbon dioxide (CO2) levels. For the first experiment, “non-renewed” closed atmospheric systems with 98/2% N2O/O2 and air were used. Two more experiments were also conducted for the 98/2% N2O/O2 atmosphere to determine how rate of gas renewal (two and seven days) affects the N2O, O2, and CO2 gases quantitatively. Cumulative results on non-renewed flasks with 98/2% N2O/O2 showed that as time progressed, N2O uptake increased with variation in the magnitude of N2O utilization throughout the 37 experimental days, while seeds ceased O2 utilization by the 11th day. However, CO2 levels did not decrease, suggesting a shift toward fermentation processes. Finally, the two experiments for the 98/2% N2O/O2 indicated that the O2 levels did not deplete under a two-day gas renewal, suggesting a frequent gas renewal under low O2 storage conditions.

Disruption of the mitochondrial alternative oxidase (AOX) and uncoupling protein (UCP) alters rates of foliar nitrate and carbon assimilation in Arabidopsis thaliana.

Under high light, the rates of photosynthetic CO2 assimilation can be influenced by reductant consumed by both foliar nitrate assimilation and mitochondrial alternative electron transport (mAET). Additionally, nitrate assimilation is dependent on reductant and carbon skeletons generated from both the chloroplast and mitochondria. However, it remains unclear how nitrate assimilation and mAET coordinate and contribute to photosynthesis. Here, hydroponically grown Arabidopsis thaliana T-DNA insertional mutants for alternative oxidase (AOX1A) and uncoupling protein (UCP1) fed either NO3 (-) or NH4 (+) were used to determine (i) the response of NO3 (-) uptake and assimilation to the disruption of mAET, and (ii) the interaction of N source (NO3 (-) versus NH4 (+)) and mAET on photosynthetic CO2 assimilation and electron transport. The results showed that foliar NO3 (-) assimilation was enhanced in both aox1a and ucp1 compared with the wild-type, suggesting that foliar NO3 (-) assimilation is probably driven by a decreased capacity of mAET and an increase in reductant within the cytosol. Wild-type plants had also higher rates of net CO2 assimilation (A net) and quantum yield of PSII (ϕPSII) under NO3 (-) feeding compared with NH4 (+) feeding. Additionally, under NO3 (-) feeding, A net and ϕPSII were decreased in aox1a and ucp1 compared with the wild type; however, under NH4 (+) they were not significantly different between genotypes. This indicates that NO3 (-) assimilation and mAET are both important to maintain optimal rates of photosynthesis, probably in regulating reductant accumulation and over-reduction of the chloroplastic electron transport chain. These results highlight the importance of mAET in partitioning energy between foliar nitrogen and carbon assimilation.

Contrasts in growth and nitrogen nutrition of species in the Cupressaceae and Pinaceae in response to calcium

Background and aims Cupressaceae species thrive on calcareous soils and accumulate calcium (Ca) in their tissues. High nitrification rates occur in soils under these species, and many prefer nitrate (NO3) as a nitrogen (N) source. We tested the hypothesis that high levels of available Ca enhance NO3 uptake to a greater degree in Cupressaceae than Pinaceae using seedlings of Thuja plicata and Callitropsis (Chamaecyparis) nootkatensis compared with Pseudotsgua menziesii and Tsuga heterophylla.

Time-dependent uptake of NO3 by sea salt

Using a coated-insert flow tube reactor coupled to a low-energy electron-impact mass spectrometer with molecular beam sampling, we studied uptake of NO3 by sea salt at room temperature and [NO3] = 8⋅1011 − 4⋅1013 molecule cm−3. The radical uptake coefficient γ(t) is time dependent: its initial value (γ ini) decreases exponentially with the characteristic time (τ) to its steady-state value (γ ss) at given [NO3]. The parameters γ ini, γ ss and τ depend on [NO3], whereas γ ss is water vapor independent at [H2O] = 8⋅1012 − 1.6⋅1015 molecule cm−3 and RH ≤ 0.5 %. HCl and NO2 are uptake products detected in the gas phase. We used these findings to estimate γ values under tropospheric conditions for urban coastal and remote marine environments: at high NO3 (~90 ppt), the time dependence becomes important, and the γ value averaged over the aerosol lifetime is 4⋅10−3; at low NO3 (~1 ppt), the radical uptake is time independent and proceeds faster with γ ini = 8⋅10−3

Seasonal shifts in the contributions of the Changjiang River and the Kuroshio Current to nitrate dynamics in the continental shelf of the northern East China Sea based on a nitrate dual isotopic composition approach

Abstract. The northern East China Sea (ECS) serves as a spawning and nursery ground for many species of fish and squid. To clarify the basis of the food web in the northern ECS, we examined the nitrate (NO3) dynamics along four latitudinal transects based on stable nitrogen and oxygen isotopes of NO3 (δ15NNO3 and δ18ONO3) and temperature–salinity dynamics in both winter (February 2009) and summer (July 2009 and July 2011). The δ15NNO3 and δ18ONO3, which were distinctly different among the potential NO3 sources, were useful for clarifying NO3 sources and its actual usage by phytoplankton. In winter, Kuroshio Subsurface Water (KSSW) and the Yellow Sea Mixed Water (YSMW) predominantly contributed to NO3 distributed in the shelf water. In the surface water of the Okinawa Trough, NO3 from the KSSW, along with a temperature increase caused by an intrusion of Kuroshio Surface Water (KSW), seemed to stimulate phytoplankton growth. In summer, Changjiang Diluted Water (CDW), Yellow Sea Cold Water Mass (YSCWM), and KSSW affected the distribution and abundance of NO3 in the northern ECS, depending on precipitation in the Changjiang drainage basin and the development of the YSCWM in the shelf bottom water. Although isotopic fractionation during NO3 uptake by phytoplankton seemed to drastically increase δ15NNO3 and δ18ONO3 in summer, relatively light nitrate with δ15NNO3 lower than expected from this fractionation effect might be explained by contribution of atmospheric nitrogen and/or nitrification to NO3 dynamics in the surface and subsurface layers. If the latter were a dominant process, this would imply a tightly coupled nitrogen cycle in the shelf water of the northern ECS.

Inorganic nitrogen transformations within permeable carbonate sands

A combination of in-situ push pull tests and a flow through reactor trial were used to quantify the inorganic nitrogen sinks in the permeable carbonate sands of a tropical coral cay (Heron Island – Great Barrier Reef). Addition of dissolved inorganic nitrogen (DIN in the form of nitrate – NO3−, and ammonium – NH4+) directly into sediment porewater resulted in uptake of up to 97% and 60% of added DIN respectively. The initial push pull experiment qualitatively showed that dissimilatory nitrate reduction to ammonia (DNRA), denitrification and nitrification were all active in the sediments. A flow through reactor experiment provided a more detailed approach to quantify these processes and showed that both denitrification and DNRA occurred within the sands at rates of 7.3 and 5.5µmolNcm−3d−1, respectively. Unexpectedly the addition of labile organic material (fresh coral spawn) to the permeable sands did not result in the release of DIN from the reactors, on the contrary it resulted in the increased uptake of both NO3− and NH4+. This was most likely because of the stimulated N uptake associated with the addition of high C:N coral spawn material. The bulk of NH4+ produced via DNRA was found to be adsorbed to sediments within the reactor and was not released with the outlet water. A mass balance over the entire experimental period showed that more inorganic N was retained within the sediments than lost as gaseous products. Our results point to permeable carbonate sands acting as reservoirs of N under the influence of advective flow, even during sudden enrichment periods such as those following coral mass spawning. This implies that permeable carbonate sands may help to buffer coral reefs during periods of extreme oligotrophy.

CH4 and N2O dynamics of a Larix gmelinii forest in a continuous permafrost region of central Siberia during the growing season

Forest soils are generally sinks of CH4 and sources of N2O. To characterize the dynamics of these major greenhouse gases in central Siberia during the growing season, we measured fluxes from forest soil and assessed the relationships between CH4 and N2O fluxes and forest floor vegetation types, soil temperature, and moisture conditions. At the soil surface, both CH4 uptake and emission (−6.6 to 3.1 μg CH4–C m−2 h−1) were observed, and CH4 fluxes did not differ among vegetation types. CH4 flux was positively correlated with soil moisture, but not with soil temperature. The small CH4 uptake compared with previous reports was due to CH4 production in response to high precipitation. N2O was also emitted and taken up by soil (−0.2 to 0.4 μg N2O–N m−2 h−1), and N2O fluxes did not differ among vegetation types. N2O flux was negatively correlated with soil moisture and not correlated with soil temperature. Our findings suggest that high soil moisture and low availability of mineral nitrogen resulted in N2O uptake due to denitrification. Furthermore, both CH4 and N2O were emitted from a river at the site; these were produced in the basin of the riverbank rather than deep in the soil.

Plant nitrogen status and co-occurrence of organic and inorganic nitrogen sources influence root uptake by Scots pine seedlings

Insights into how the simultaneous presence of organic and inorganic nitrogen (N) forms influences root absorption will help elucidate the relative importance of these N forms for plant nutrition in the field as well as for nursery cultivation of seedlings. Uptake of the individual N forms arginine, ammonium (NH4(+)) and nitrate (NO3(-)) was studied in Scots pine (Pinus sylvestris (L.)) seedlings supplied as single N sources and additionally in mixtures of NO3(-) and NH4(+) or NO3(-) and arginine. Scots pine seedlings displayed a strong preference for NH4(+)-N and arginine-N as compared with NO3(-)-N. Thus, NO3(-) uptake was generally low and decreased in the presence of NH4(+) in the high-concentration range (500 µM N), but not in the presence of arginine. Moreover, uptake of NO3(-) and NH4(+) was lower in seedlings displaying a high internal N status as a result of high N pre-treatment, while arginine uptake was high in seedlings with a high internal N status when previously exposed to organic N. These findings may have practical implications for commercial cultivation of conifers.

Mineral Oxides Change the Atmospheric Reactivity of Soot: NO2 Uptake under Dark and UV Irradiation Conditions

The heterogeneous reactions between trace gases and aerosol surfaces have been widely studied over the past decades, revealing the crucial role of these reactions in atmospheric chemistry. However, existing knowledge on the reactivity of mixed aerosols is limited, even though they have been observed in field measurements. In the current study, the heterogeneous interaction of NO2 with solid surfaces of Al2O3 covered with kerosene soot was investigated under dark conditions and in the presence of UV light. Experiments were performed at 293 K using a low-pressure flow-tube reactor coupled with a quadrupole mass spectrometer. The steady-state uptake coefficient, γ(ss), and the distribution of the gas-phase products were determined as functions of the Al2O3 mass; soot mass; NO2 concentration, varied in the range of (0.2-10) × 10(12) molecules cm(-3); photon flux; and relative humidity, ranging from 0.0032% to 32%. On Al2O3/soot surfaces, the reaction rate was substantially increased, and the formation of HONO was favored compared with that on individual pure soot and pure Al2O3 surfaces. Uptake of NO2 was enhanced in the presence of H2O under both dark and UV irradiation conditions, and the following empirical expressions were obtained: γ(ss,BET,dark) = (7.3 ± 0.9) × 10(-7) + (3.2 ± 0.5) × 10(-8) × RH and γ(ss,BET,UV) = (1.4 ± 0.2) × 10(-6) + (4.0 ± 0.9) × 10(-8) × RH. Specific experiments, with solid sample preheating and doping with polycyclic aromatic hydrocarbons (PAHs), showed that UV-absorbing organic compounds significantly affect the chemical reactivity of the mixed mineral/soot surfaces. A mechanistic scheme is proposed, in which Al2O3 can either collect electrons, initiating a sequence of redox reactions, or prevent the charge-recombination process, extending the lifetime of the excited state and enhancing the reactivity of the organics. Finally, the atmospheric implications of the observed results are briefly discussed.

ChemInform Abstract: Understanding Automotive Exhaust Catalysts Using a Surface Science Approach: Model NOx Storage Materials

AbstractReview: 56 refs.

Heterogeneous uptake of NO2 on Arizona Test Dust under UV-A irradiation: An aerosol flow tube study

Abstract The uptake rate of NO 2 on Arizona Test Dust aerosols was measured using an aerosol flow tube (AFT). While the uptake rate in the dark could not be measured, the uptake under UV-A irradiation was enhanced, with values in the range from (0.6 ± 0.3) × 10 −8 , (2.4 ± 0.4) × 10 −8 . The observed gas phase products were HONO and NO, with yields of at 30% and 9.6%, respectively. The difference between these measurements and those previously reported on macroscopic films are discussed and differences highlighted. Interestingly, a reasonable agreement is observed between the uptake kinetics of NO 2 on Arizona Test Dust macroscopic films and aerosols, despite the different experimental approaches. The simplest approach i.e. thin films having a significant porosity, provides similar uptake kinetics to the more complex and realistic AFT approach.

Development of novel inexpensive adsorbents from waste concrete to mitigate NOx emissions

Mitigating NOx (NO + NO2) pollution can have result in notable improvement of public health and environmental conditions, especially in urban environments. This work is the first demonstration of applications of both fresh and aged concrete as inexpensive adsorbents for NO2 removal. The gas phase uptake experiments with fresh and aged concrete demonstrated the feasibility of this approach, while infrared spectroscopy identified a potential mechanism of NO2 adsorption on concrete surfaces. A decrease in surface basicity due to carbonation appears to be the main factor for observed decrease in NO2 uptake as a function of concrete age.

Nitrous oxide fluxes in undisturbed riparian wetlands located in agricultural catchments: Emission, uptake and controlling factors

Riparian wetlands can mitigate nutrient pollution to the aquatic environment when they serve as biogeochemically active buffer zones between arable land and water bodies. Nevertheless, as a result of the extensive nutrient transformation, wetlands hold a potential of atmospheric emission of greenhouse gases such as nitrous oxide (N2O). To quantify this potential, fluxes of N2O were measured over a year at 48 sub-plots located in four Danish riparian wetlands with contrasting characteristics of soil parameters and groundwater dynamics. The wetlands were hydrologically and physically relatively undisturbed, but they were all located in catchments dominated by agriculture. Individual fluxes of N2O measured using the static chamber technique ranged from −44 to 122 μg N2O–N m−2 h−1 (n = 800) while cumulative fluxes ranged from −0.25 to 0.50 g N2O–N m−2 yr−1 (n = 48), i.e., showing both uptake and emission of N2O. Modeling of the fluxes using linear mixed models revealed that ammonium in the groundwater was the only tested variable having a significant effect on N2O fluxes. Tentative maximum estimates showed that only about 2.2% of the total Danish N2O emissions could be related to freshwater wetlands (representing about 1.3% of the land area). Further, the low and frequently negative N2O fluxes (n = 294) indicated that riparian wetlands, at least under some conditions, may actually reduce atmospheric N2O pollution, although the measured N2O uptake was weak. In conclusion, riparian ecosystems with only minor disturbances are not generally to be considered as hotspots of N2O emissions in the landscape.

Variations in nitrogen-15 natural abundance of plant and soil systems in four remote tropical rainforests, southern China

The foliar stable N isotope ratio (δ(15)N) can provide integrated information on ecosystem N cycling. Here we present the δ(15)N of plant and soil in four remote typical tropical rainforests (one primary and three secondary) of southern China. We aimed to examine if (1) foliar δ(15)N in the study forests is negative, as observed in other tropical and subtropical sites in eastern Asia; (2) variation in δ(15)N among different species is smaller compared to that in many N-limited temperate and boreal ecosystems; and (3) the primary forest is more N rich than the younger secondary forests and therefore is more (15)N enriched. Our results show that foliar δ(15)N ranged from -5.1 to 1.3‰ for 39 collected plant species with different growth strategies and mycorrhizal types, and that for 35 species it was negative. Soil NO3 (-) had low δ(15)N (-11.4 to -3.2‰) and plant NO3 (-) uptake could not explain the negative foliar δ(15)N values (NH4 (+) was dominant in the soil inorganic-N fraction). We suggest that negative values might be caused by isotope fractionation during soil NH4 (+) uptake and mycorrhizal N transfer, and by direct uptake of atmospheric NH3/NH4 (+). The variation in foliar δ(15)N among species (by about 6‰) was smaller than in many N-limited ecosystems, which is typically about or over 10‰. The primary forest had a larger N capital in plants than the secondary forests. Foliar δ(15)N and the enrichment factor (foliar δ(15)N minus soil δ(15)N) were higher in the primary forest than in the secondary forests, albeit differences were small, while there was no consistent pattern in soil δ(15)N between primary and secondary forests.

Microbial transformation of nitrogen compounds in middle taiga soils

The intensity of mineralization, nitrogen fixation, and denitrification in forest soils of the Karelian middle taiga ecosystems has been evaluated. Podzol-gleyish soil underlying a birch forest with gramineous plants and miscellaneous herbs was shown to have the highest nitrogen-fixing activity. The loss of gaseous nitrogen during denitrification was insignificant due to the low nitrifying activity of the soils named above. N2O uptake by microorganisms was rather intensive in all the soils analyzed, and in illuvial-humo-ferric podzols underlying pine and spruce forests this process predominated. Podzolic sandy loam gley-like soil of a birch forest with gramineous plants and miscellaneous herbs had the highest potential for the mineralization of organic nitrogen; the rate of ammonification and nitrification in this soil was maximal.

Influence of emergent vegetation on nitrate cycling in sediments of a groundwater-fed river

Emergent vegetation in river beds can play a significant role in nutrient cycling in riverine sediments. We analysed and compared pore water NO3 − concentration gradients in the sediments of the River Leith, Cumbria, UK, in the presence and absence of emergent vegetation (dominated by Sparganium spp.). High resolution (1 cm interval), in situ, vertical profiles of NO3 − to 30 cm depth were measured using deployment of diffusive equilibrium in thin films probes on four occasions from July to September 2010. We found significantly (p < 0.05) lower NO3 − concentration under vegetated sediments (VS) compared to those under adjacent un-vegetated sediments (UVS). Concentrations of dissolved oxygen, measured in pore water collected from multi-level piezometers at 10, 20, 25, 30 and 35 cm depths at the VS and UVS sties, were generally lower under VS (median concentration = 28 μM) than under UVS (median = 132 μM) and correlated significantly with NO3 − concentration (Spearman’s r = 0.74, p < 0.05). Similarly, pore water dissolved organic carbon (DOC) concentration was 2.8 times higher under VS compared to UVS, and correlated negatively with NO3 − concentration (Spearman’s r = −0.39, p < 0.05). Specific ultra-violet absorption at 254 nm (SUVA) and per cent aromaticity values of DOC were significantly higher under VS (p < 0.05), suggesting that the DOC contained more complex (aromatic) compounds than DOC recorded under UVS. We suggest that, the higher quantity of DOC and its distinct SUVA and percentage aromaticity under VS may have supported faster dissolved oxygen consumption, with the creation of anoxic zones conducive for NO3 − reduction mainly through denitrification. Metabolic uptake and immobilization of NO3 − by plants and microbes may have further contributed to lower NO3 − concentrations under VS. As Sparganium spp. is a common plant growing in river beds in the UK, its role in NO3 − cycling should be considered in attempts to accurately budget N cycling in river beds.

IMPACT OF CHANGING HYDROLOGY ON NUTRIENT UPTAKE IN HIGH ARCTIC RIVERS

ABSTRACTDespite the importance of river nutrient retention in regulating downstream water quality and the potential alterations to nutrient fluxes associated with climate‐induced changes in Arctic hydrology, current understanding of nutrient cycling in Arctic river systems is limited. This study adopted an experimental approach to quantify conceptual water source contributions (meltwater, groundwater), environmental conditions and uptake of NO3−, NH4+, PO43− and acetate at 12 headwater rivers in Svalbard and so determine the role of changing hydrology on nutrient uptake in these Arctic river systems. Most rivers exhibited low demand for NO3− and PO43−, but demand for NH4+ and acetate was more variable and in several rivers comparable with that measured in sub‐Arctic regions. The proportion of meltwater contributing to river flow was not significantly related to nutrient uptake. However, NH4+ uptake was associated positively with algal biomass, water temperature and transient storage area, whereas acetate uptake was associated positively with more stable river channels. Mean demand for NH4+ increased when added with acetate, suggesting NH4+ retention may be facilitated by labile dissolved organic carbon availability in these rivers. Consequently, nutrient export from Arctic river systems could be influenced in future by changes in hydrological and environmental process interactions associated with forecasted climate warming. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Heterogeneous photochemistry of gaseous NO2 on solid fluoranthene films: A source of gaseous nitrous acid (HONO) in the urban environment

Abstract Using a coated flow tube equipped with several near-ultraviolet emitting lamps, (range 300–420 nm), we examined the effect of actinic radiation on the heterogeneous loss kinetics of gaseous nitrogen dioxide on solid Polycyclic Aromatic Hydrocarbon (PAH) films deposited on a Pyrex substrate. The PAH studied was mainly fluoranthene, with additional tests on phenanthrene and pyrene. No dependence of the uptake coefficient (γ) was observed either with temperature, or with relative humidity. In the dark, the reaction was very slow but was greatly enhanced by increasing the UV-A light intensity. A linear dependency of the reaction kinetics with the photonic flux was observed. Under atmospherically-relevant NO2 concentrations (20 ppbv), the uptake coefficient was about 1 × 10−6. The uptake coefficient variation as a function of the NO2 concentration suggests a Langmuir–Hinshelwood (L–H) type mechanism. This is characterized by the adsorption of NO2 on the solid surface followed by a chemical reaction. The corresponding equilibrium constant (K′) and the surface reaction rate constant ( k s 1 ) were found to be 3 × 10−2 ppbv−1 and 5 × 10−5 s−1 respectively for the photo-enhanced uptake of NO2 on the fluoranthene substrate. Particular attention was given to the detection of the gas-phase products showing the photo-enhanced reduction of NO2 to HONO and NO via a photosensitized reaction involving excited states of the PAH. Additionally we investigated the reactivity of PAH in the presence of nitrates in order to better understand if HONO generation mechanism could be explained by a first deposition of nitrates (generated via NO2 hydrolysis) on the solid surface.

Understanding the role of the ground surface in HONO vertical structure: High resolution vertical profiles during NACHTT‐11

A negative‐ion proton‐transfer chemical ionization mass spectrometer was deployed on a mobile tower‐mounted platform during Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) to measure nitrous acid (HONO) in the winter of 2011. High resolution vertical profiles revealed (i) HONO gradients in nocturnal boundary layers, (ii) ground surface dominates HONO production by heterogeneous uptake of NO2, (iii) significant quantities of HONO may be deposited to the ground surface at night, (iv) daytime gradients indicative of ground HONO production or emission, and (v) an estimated surface HONO reservoir comparable or larger than integrated daytime HONO surface production. Nocturnal integrated column observations of HONO and NO2 allowed direct evaluation of nocturnal ground surface uptake coefficients for these species (γNO2, surf = 2 × 10−6 to 1.6 × 10−5 and γHONO, surf = 2 × 10−5 to 2 × 10−4). A chemical model showed that the unknown source of HONO was highest in the morning, 4 × 106 molecules cm−3 s−1 (600 pptv h−1), declined throughout the day, and minimized near 1 × 106 molecules cm−3 s−1 (165 pptv h−1). The quantity of surface‐deposited HONO was also modeled, showing that HONO deposited to the surface at night was at least 25%, and likely in excess of 100%, of the calculated unknown daytime HONO source. These results suggest that if nocturnally deposited HONO forms a conservative surface reservoir, which can be released the following day, a significant fraction of the daytime HONO source can be explained for the NACHTT observations.

Summer nitrogenous nutrient transport and its fate in the Taiwan Strait: A coupled physical‐biological modeling approach

In order to understand the fate of nutrients in the Taiwan Strait during summer, we built a coupled physical‐biological numerical ocean model, which can capture the basic hydrographic and biological features within the strait. The nutrient that we chose to model is dissolved inorganic nitrogen (DIN). The model includes individual reservoirs for nitrate (NO3) and ammonium (NH4). Both the observational evidence and model results show that NO3 in the strait originates primarily from the upwelling subsurface water in the northern South China Sea (SCS) that enters the strait via the eastern and western routes separated by the Taiwan Bank. The coupled physical and biological effects on the NO3 transport at these two routes are highlighted in the study. For the western route, the shallow topography and the coastal upwelling intensify the biological uptake of NO3 in the whole water column. Consequently, the nitrogenous contribution by this route is mainly in form of the particulate organic nitrogen (PON). In contrast, NO3 is transported conservatively below the nitricline at the deep eastern route, contributing the whole NO3 supply in the TWS. The model estimates the fluxes of DIN and PON into the TWS, from the northern SCS, are 1.8 and 4 kmol s−1, respectively. Over half (∼1 kmol s−1) of the DIN is synthesized into PON by the phytoplankton in the strait. Overall, this study estimates the physical and biological effects on the nutrient transport in the TWS during summer.