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Joop Nieuwenhuize - One of the best experts on this subject based on the ideXlab platform.
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Nitrogen Isotope Tracing of Dissolved Inorganic Nitrogen Behaviour in Tidal Estuaries
Estuarine Coastal and Shelf Science, 2001Co-Authors: Jack J. Middelburg, Joop NieuwenhuizeAbstract:Concentration versus salinity diagrams are the most widely used method to derive estuarine sources and sinks of Nitrogen. This method can not distinguish conservative mixing due to a lack of activity, from that due to an approximate balance of sources and sinks. The combined study of concentration and Nitrogen isotopic signatures may provide this information because balanced sources and sinks do affect the isotopic composition of Dissolved Inorganic Nitrogen. This is illustrated with three cases of European tidal estuaries: the Scheldt (Belgium/The Netherlands), the Thames (U.K.) and the Loire Estuary (France). Concentration versus salinity diagrams for nitrate showed conservative mixing for the Thames and Loire estuaries and nitrate generation in the Scheldt Estuary. The delta N-15 of nitrate versus salinity diagram confirmed the conservative behaviour for the Thames Estuary and the non-conservative behaviour for the Scheldt Estuary, but revealed active nitrate turnover in the Loire Estuary. Concentration and delta N-15 of ammonium versus salinity diagrams consistently showed non- conservative mixing as a result of ammonium consumption. [KEYWORDS: Thames; Scheldt; Loire; Nitrogen; nitrate; ammonium; Nitrogen isotopes Coastal marine ecosystems; ammonia diffusion method; organic-matter; delaware estuary; scheldt estuary; thames estuary; nitrate; denitrification; dynamics; france]
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uptake of Dissolved Inorganic Nitrogen in turbid tidal estuaries
Marine Ecology Progress Series, 2000Co-Authors: Jack J. Middelburg, Joop NieuwenhuizeAbstract:Ammonium and nitrate uptake was measured in 6 European tidal estuaries (Ems, Rhine, Scheldt, Loire, Gironde and Douro) using N-15-tracer techniques. Uptake rates of ammonium and nitrate ranged from 0.005 to 1.56 mu mol N l(-1) h(-1) and 0.00025 to 0.25 mu mol N l(-1) h(-1), respectively, and differed significantly between and within estuaries. Analysis of Nitrogen uptake using the relative preferential index (RPI) indicated ammonium to be the preferred substrate. The turnover times of particulate Nitrogen (0.7 to 31 d) and Dissolved ammonium (0.1 to 27 d) were similar to or shorter than estuarine-water residence times, whereas turnover times of Dissolved nitrate (19 to 2160 d) were longer than residence times. Assimilation of nitrate in the water column of estuaries consequently does not influence its distribution, and most nitrate entering or produced in estuaries flushes through unless significant denitrification and/or burial in the sediment occur. As ammonium and particulate Nitrogen are efficiently recycled, most allochthonous organic matter is extensively microbially modified before export, burial, or consumption by higher trophic levels. [KEYWORDS: Nitrogen uptake; Nitrogen turnover; ammonium; nitrate; estuary; heterotrophy Ecosystem model moses; north-atlantic ocean; schelde estuary; sw netherlands; river estuary; heterotrophic bacteria; westerschelde estuary; organic Nitrogen; delaware estuary; nitrate uptake]
Kon-kee Liu - One of the best experts on this subject based on the ideXlab platform.
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inverse isolation of Dissolved Inorganic Nitrogen yield for individual land uses from mosaic land use patterns within a watershed
Hydrology and Earth System Sciences Discussions, 2015Co-Authors: Yu Ting Shih, Shuh-ji Kao, Tsung-yu Lee, J.c. Huang, Kon-kee Liu, Fijohn ChangAbstract:Abstract. This study combines the observed riverine DIN (Dissolved Inorganic Nitrogen) export and the controlling factors (land-use, population and discharge) to inversely estimate the effective DIN yield factors for individual land-use and DIN per capita loading. A total of 16 sub-catchments, with different land-use compositions on the Danshui River of Taiwan, were used in this study. Observed riverine DIN concentrations and yields varied from 20–450 μM and 400–10 000 kg N km −2 yr −1 corresponding to the increase of urbanization gradient (e.g. building and population). Meanwhile, the transport behaviors changed from hydrological enhancement to dilution with increasing urbanization as well. Our method shows that the DIN yield factors, independent of discharge, are 12.7, 63.9, and 1381.0 μM, for forest, agriculture, and building, respectively, which equals to 444.5, 2236.5, 48 335 kg N km −2 yr −1 at the given annual runoff of 2500 mm. The agriculture DIN yield only accounts for 10% of fertilizer application indicating the complicated N cascade and possible over fertilization. The DIN per capita loading (~0.49 kg N capita −1 yr −1 ) which is lower than the documented human N emission (1.6–5.5 kg N capita −1 yr −1 ) can be regarded as an effective export coefficient after treatment or retention. A conducted scenario experiment supports the observations demonstrating the capability for assessment. We therefore, can extrapolate all possible combinations of land-use, discharge, and population density for evaluation. This can provide a strong basis for watershed management and supplementary estimation for regional to global study.
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impacts of increasing Dissolved Inorganic Nitrogen discharged from changjiang on primary production and seafloor oxygen demand in the east china sea from 1970 to 2002
Journal of Marine Systems, 2015Co-Authors: Kon-kee Liu, Weijin Yan, Hungjen Lee, Shennyu Chao, Gwoching Gong, Tzuying YehAbstract:Abstract In recent years, benthic hypoxia has been observed in the outflow region of the Changjiang River in the East China Sea. Because the Nitrogen input to the Changjiang watershed, mainly from human activities, has increased by 3 fold in the last four decades and the Nitrogen load had grown exponentially, it is speculated that anthropogenic nutrients may be responsible for the hypoxia in the East China Sea shelf. We employ a coupled 3-D physical–biogeochemical model of the East China Sea to investigate how the changing Changjiang nutrient loads from 1970 to the end of 2002 may have impacted on primary production in the water column and the seafloor oxygen demand (SOD) on the seafloor. The model predicts an average value of 437 mgC m − 2 d − 1 for primary production and 10.0 mmol O 2 m − 2 d − 1 for SOD for the ECS shelf over the entire modeling period. The model results compare reasonably with observations during the period from December 1997 to October 1998. Responding to the increase of the Changjiang DIN loading by a factor of ~ 2.4, the modeled primary production in the East China Sea shelf has increased by 17%, and the modeled SOD by 22%. In the inner shelf, where the impact is the strongest, the SOD increases by 30%. We are able to identify areas of potential hypoxia using two criteria: SOD > 30 mmol O 2 m − 2 d − 1 and water depth > 25 m. The maximum area of potential hypoxic region in any month of a year has increased dramatically after 1991; the change appears related to the Changjiang DIN loads from May to July that showed a sudden increase after 1990. The responses in potential hypoxic area are more pronounced than the increases in DIN (Dissolved Inorganic Nitrogen) loads, suggesting strong nonlinear effect in the development of hypoxia, which warrants further investigation. It is cautioned that the SOD calculation was based on the Redfield C/N ratio, but the actual C/N ratio may deviate from it. Direct observations of the sediment oxygen consumption are needed to validate our modeling approach. We also assessed the potential impacts of particulate organic matter from Changjiang by introducing a load of reactive particulate Nitrogen (PN), which was assumed proportional to DIN based on estimated yields in the watershed. The modeled impacts on primary productivity and SOD are significant, but more accurate quantification of the monthly PN load and better characterization of its reactivity are required for better assessment.
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Speciation and dynamics of Dissolved Inorganic Nitrogen export in the Danshui River, Taiwan
Biogeosciences, 2014Co-Authors: Tsung-yu Lee, Shuh-ji Kao, Fuh-kwo Shiah, Yu Ting Shih, J.c. Huang, Kon-kee LiuAbstract:Human-induced excess Nitrogen outflowing from land through rivers to oceans has resulted in serious impacts on terrestrial and coastal ecosystems. Oceania, which occu- pies < 2.5 % of the global land surface, delivers 12 % of the freshwater and Dissolved materials to the ocean on a global scale. However, there are few empirical data sets on river- ine Dissolved Inorganic Nitrogen (DIN) fluxes in the region, and their dynamics are poorly understood. In this study, a river monitoring network covering different types of land uses and population densities was implemented to investi- gate the mechanism of DIN export. The results show that DIN concentration/yield varied from 20 µM/ 300 kg- N km 2 yr 1 to 378 µM/ 10 000 kg-N km 2 yr 1 from the relatively pristine headwaters to the populous estuary. Agriculture and population density control DIN export in less densely populated regions and urban areas, respectively, and runoff controls DIN at the watershed scale. Compared to doc- umented estimates from global models, the observed DIN ex- port from the Danshui River is 2.3 times larger, which results from the region-specific response of DIN yield to dense pop- ulation and abundant runoff. The dominating DIN species change gradually from NO 3 in the headwaters ( 97 %) to NH + in the estuary ( 60 %) following the urbanization gra- dient. The prominent existence of NH + is probably the result of the anaerobic water body and short residence time, unlike in large river basins. Given the analogous watershed charac- teristics of the Danshui River to the rivers in Oceania, our study could serve as a first example to examine riverine DIN fluxes in Oceania.
Jack J. Middelburg - One of the best experts on this subject based on the ideXlab platform.
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Nitrogen Isotope Tracing of Dissolved Inorganic Nitrogen Behaviour in Tidal Estuaries
Estuarine Coastal and Shelf Science, 2001Co-Authors: Jack J. Middelburg, Joop NieuwenhuizeAbstract:Concentration versus salinity diagrams are the most widely used method to derive estuarine sources and sinks of Nitrogen. This method can not distinguish conservative mixing due to a lack of activity, from that due to an approximate balance of sources and sinks. The combined study of concentration and Nitrogen isotopic signatures may provide this information because balanced sources and sinks do affect the isotopic composition of Dissolved Inorganic Nitrogen. This is illustrated with three cases of European tidal estuaries: the Scheldt (Belgium/The Netherlands), the Thames (U.K.) and the Loire Estuary (France). Concentration versus salinity diagrams for nitrate showed conservative mixing for the Thames and Loire estuaries and nitrate generation in the Scheldt Estuary. The delta N-15 of nitrate versus salinity diagram confirmed the conservative behaviour for the Thames Estuary and the non-conservative behaviour for the Scheldt Estuary, but revealed active nitrate turnover in the Loire Estuary. Concentration and delta N-15 of ammonium versus salinity diagrams consistently showed non- conservative mixing as a result of ammonium consumption. [KEYWORDS: Thames; Scheldt; Loire; Nitrogen; nitrate; ammonium; Nitrogen isotopes Coastal marine ecosystems; ammonia diffusion method; organic-matter; delaware estuary; scheldt estuary; thames estuary; nitrate; denitrification; dynamics; france]
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uptake of Dissolved Inorganic Nitrogen in turbid tidal estuaries
Marine Ecology Progress Series, 2000Co-Authors: Jack J. Middelburg, Joop NieuwenhuizeAbstract:Ammonium and nitrate uptake was measured in 6 European tidal estuaries (Ems, Rhine, Scheldt, Loire, Gironde and Douro) using N-15-tracer techniques. Uptake rates of ammonium and nitrate ranged from 0.005 to 1.56 mu mol N l(-1) h(-1) and 0.00025 to 0.25 mu mol N l(-1) h(-1), respectively, and differed significantly between and within estuaries. Analysis of Nitrogen uptake using the relative preferential index (RPI) indicated ammonium to be the preferred substrate. The turnover times of particulate Nitrogen (0.7 to 31 d) and Dissolved ammonium (0.1 to 27 d) were similar to or shorter than estuarine-water residence times, whereas turnover times of Dissolved nitrate (19 to 2160 d) were longer than residence times. Assimilation of nitrate in the water column of estuaries consequently does not influence its distribution, and most nitrate entering or produced in estuaries flushes through unless significant denitrification and/or burial in the sediment occur. As ammonium and particulate Nitrogen are efficiently recycled, most allochthonous organic matter is extensively microbially modified before export, burial, or consumption by higher trophic levels. [KEYWORDS: Nitrogen uptake; Nitrogen turnover; ammonium; nitrate; estuary; heterotrophy Ecosystem model moses; north-atlantic ocean; schelde estuary; sw netherlands; river estuary; heterotrophic bacteria; westerschelde estuary; organic Nitrogen; delaware estuary; nitrate uptake]
Akihide Kasai - One of the best experts on this subject based on the ideXlab platform.
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Key biogeochemical processes evaluated by the stable Nitrogen isotopes of Dissolved Inorganic Nitrogen in the Yodo River estuary, Japan: significance of estuarine nutrient recycling as a possible source for coastal production
Biogeochemistry, 2016Co-Authors: Ryo Sugimoto, Akihide KasaiAbstract:Isotope analysis of Dissolved Inorganic Nitrogen (DIN) and a mixing model along the salinity gradient were used to clarify the dominant biogeochemical processes controlling nutrient dynamics within a shallow eutrophic estuary in Japan. Although delivery of riverine DIN into the estuary is largely dominated by mixing with seawater during most months, internal biogeochemical processes of DIN assimilation by phytoplankton and DIN production by remineralization and subsequent nitrification within the estuary offer the most reasonable explanation for observed deviations in the isotopic compositions of $$ {\text{NO}}_{3}^{ - } $$ NO 3 - from mixing behavior. However, the balance of each process changed over time. During phytoplankton blooming in summer, co-occurrence of $$ {\text{NO}}_{3}^{ - } $$ NO 3 - assimilation and $$ {\text{NO}}_{3}^{ - } $$ NO 3 - regeneration inhibited the accumulation of $$ {\text{NO}}_{3}^{ - } $$ NO 3 - within the estuary. Moreover, assimilation of $$ {\text{NH}}_{4}^{ + } $$ NH 4 + as well as $$ {\text{NO}}_{3}^{ - } $$ NO 3 - by phytoplankton complicates the nutrient dynamics within the estuary. However, mostly conservative or productive behavior of DIN as well as $$ {\text{PO}}_{4}^{3 - } $$ PO 4 3 - showed that recycled nutrients are significant net source within the estuary. These results suggest recycled nutrients within the estuary could have a non-negligible impact on eutrophication in Osaka Bay.
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Modeling phytoplankton production in Ise Bay, Japan: Use of Nitrogen isotopes to identify Dissolved Inorganic Nitrogen sources
Estuarine Coastal and Shelf Science, 2010Co-Authors: Ryo Sugimoto, Akihide Kasai, Toshihiro Miyajima, Kouichi FujitaAbstract:Abstract An important aspect of the Nitrogen cycle in coastal environments concerns the source of the Nitrogen used in primary production. Phytoplankton production in Ise Bay, one of the most eutrophic embayments in Japan, is supported by external Nitrogen derived from rivers and the ocean, and regenerated Nitrogen formed in hypoxic water within the bay. We evaluated the contribution of each source of Dissolved Inorganic Nitrogen (DIN) to phytoplankton production in Ise Bay. A unique three-dimensional ecosystem model including Nitrogen isotopes ( δ 15 N) was developed based on precise observations. Model results revealed that DIN (=ammonium + nitrate) consumption by phytoplankton exceeds the DIN supply from the rivers and ocean, indicating that a large amount of phytoplankton production in Ise Bay depends on regenerated DIN within the bay rather than on newly supplied DIN. However, the ratio of consumption to external supply differs seasonally. Distributions of simulated δ 15 N clearly showed the source of Nitrogen incorporated by phytoplankton in each source. The intrusion depth of oceanic water changes from the bottom to the middle layer in spring. Oceanic nitrate is transported into the euphotic layer by the middle layer intrusion and stimulates phytoplankton production at the bay mouth. The subsurface chlorophyll maximum layer then develops. In autumn, however, the intrusion depth of oceanic water changes from the middle layer to the bottom layer. Regenerated NO 3 − , which is accumulated in the hypoxic water mass, is uplifted and continuously supplied to the euphotic layer. These results imply that phytoplankton production in Ise Bay is mainly dominated by the internal cycle rather than the external supply.
Michelle L. Mccrackin - One of the best experts on this subject based on the ideXlab platform.
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factors influencing export of Dissolved Inorganic Nitrogen by major rivers a new seasonal spatially explicit global model
Global Biogeochemical Cycles, 2014Co-Authors: Michelle L. Mccrackin, John A. Harrison, Jana E. ComptonAbstract:Substantial effort has focused on understanding spatial variation in Dissolved Inorganic Nitrogen (DIN) export to the coastal zone and specific basins have been studied in depth. Much less is known, however, about seasonal patterns and controls of coastal DIN delivery across large spatial scales. Understanding seasonal patterns of DIN export is critical to efforts to predict impacts of coastal eutrophication, such as algal blooms and hypoxic areas, which are often seasonal phenomena. Here we describe, test, and apply a global model that predicts seasonal DIN export to coastal regions for >6000 rivers using the Nutrient Export from Watersheds (NEWS2) model. NEWS2-DIN-S used spatially explicit, seasonal N inputs and was calibrated with measured DIN yield (kg N km−2 season−1) for 77 rivers, distributed globally. Of the characteristics considered, DIN-transport efficiency was positively related to runoff and negatively related to temperature (r2 = 0.34–0.60, depending on season p < 0.0001), likely due to flushing effects and increased retention by plants and soils, respectively. NEWS2-DIN-S incorporated these insights and performed well in predicting DIN yield (Nash-Sutcliffe Efficiency = 0.54–0.65, depending on season). Catchments were effective in retaining DIN and average export rates were lower during the growing season (3–5% of total Nitrogen inputs) compared to other seasons (6–10%) for major latitude bands. Model output was insensitive to changes in the magnitude of N inputs, suggesting that refinement of seasonal N input budgets will not substantially improve model performance. Rather, better representation of land-to-river N transfers could improve future models because of strong landscape N attenuation.