Dissolved Organic Nitrogen Release Research Articles

Impact of drying and re-wetting on N, P and K dynamics in a wetland soil

As increased nutrient availability due to drainage is considered a major cause of eutrophication in wetlands rewetting of drained wetlands is recommended as a restoration measure. The effect of soil drying and rewetting on the contribution of various nutrient release or transformation processes to changed nutrient availability for plants is however weakly understood. We measured effects of soil drying and re-wetting on N mineralization, and denitrification, as well as on release of dissolved organic nitrogen (DON), phosphorus, and potassium in incubated soil cores from a wet meadow in southern Sweden. Additionally, the impact of re-wetting with sulphate-enriched water was studied. Soil drying stimulated N mineralization (3 times higher) and reduced denitrification (5 times lower) compared to continuously wet soil. In the wet cores, denitrification increased to 20 mg N m(-2) d(-1), which was much higher than denitrification measured in the field. In the field, increased inorganic-N availability for plants due to drainage seemed primarily to be caused by increased N mineralization, and less by decreased denitrification. Soil drying also stimulated the release of DON and K, but P release was not affected. Re-wetting of dried soil cores strongly stimulated denitrification (up to 160 mg N m(-2) d(-1)), but N mineralization was not significantly decreased, neither were DON or K release. In contrast, the extractable P pool increased upon soil wetting. Re-wetting with sulphate-enriched water had no effect on any of the nutrient release or transformation rates. We conclude that caution is required in re-wetting of drained wetlands, because it may unintendently cause internal eutrophication through an increased P availability for plants.

Release of dissolved organic nitrogen by a planktonic community in Akkeshi Bay

We applied conventional incubation experiments combined with a 15 N-tracer technique to evaluate the relative contributions of phytoplankton, micrograzers and copepods to the release of dissolved organic nitrogen (DON) or dissolved nitrogen (DN) in coastal waters from Akkeshi Bay, eastern Hokkaido, Japan. From March to November, water temperature ranged from -1 to 17°C, and chl a concentrations showed about 5-fold change (from 2.6 to 12 µg l -1 ). The calculated rates of DON release by phytoplankton (18 to 28 nmol l -1 d -1 ) were comparable to those of DN release by copepods (18 to 67 nmol l -1 d -1 ). However, the DON release rates by micrograzers (140 to 350 nmol l -1 d -1 ) greatly exceeded those of the other planktonic assemblages. DON release by micrograzers was well coupled to DON uptake by bacteria, indicating that there was a significant nitrogen flux from phyto- plankton to bacteria via micrograzers. DON supply in the upper layer would activate microbial food webs and consequently relieve the short supply of dissolved inorganic nitrogen for phytoplankton during the stratified season.

Dissolved and particulate organic nitrogen in shelf waters of northern Spain during spring

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 214:25-41 (2001) - doi:10.3354/meps214025 Dissolved and particulate organic nitrogen in shelf waters of northern Spain during spring A. Bode*, M. Varela, M. Canle**, N. González Instituto Español de Oceanografía, Apdo. 130, 15080 A Coruña, Spain *E-mail: antonio.bode@co.ieo.es **Present address: Departamento de Química Fundamental e Industrial, Universidade da Coruña, A Zapateira, 15071 A Coruña, Spain ABSTRACT: An extensive survey of nitrogen forms and phytoplankton of the euphotic zone on the northern Spanish shelf was made in March 1992. Dissolved inorganic nitrogen (DIN) included nitrate, nitrite and ammonium, which were determined by colorimetric analysis. Dissolved organic nitrogen (DON) was determined by persulfate oxidation of filtered seawater. In addition, particulate nitrogen, chlorophyll a, sestonic proteins and primary production measurements were carried out at selected stations. Surface waters in the western region (Galicia) were characterized by the presence of Eastern North Atlantic Central Water of subtropical origin (ENACWt). This water mass extended over the southern Bay of Biscay (Mar Cantábrico) where large phytoplankton accumulations occurred. Chlorophyll a concentration and primary production rates measured in the Mar Cantábrico were significantly higher than in Galicia. DON reached concentrations of up to 10 mmol m–3 in phytoplankton rich areas, particularly in the eastern part of the southern Bay of Biscay, where primary production was also high. Positive correlations were found between DON and particulate nitrogen, and between chlorophyll and primary production, while a negative correlation was found between DON and DIN. On average, dissolved nitrogen was ca 95% of total nitrogen, and DON formed from 52% (Galicia) to 61% of total nitrogen (Mar Cantábrico). The average concentration of DON in the Mar Cantábrico (7.82 mmol N m–3) was almost double that of Galicia. Using salinity as a conservative tracer, DON was partitioned and the excess DON (DONexcess) compared to the expected concentration resulting from mixing between continental water and ENACWt at each depth was computed. We found lower correlation values between DONexcess and phytoplankton biomass and production than between total DON and these variables, which suggests an uncoupling between phytoplankton and DON production and the participation of microplanktonic grazers in the release of DON in surface waters. However, considering nitrogen stocks integrated in the euphotic zone in each region, DONexcess accounted on average for only 7% of total nitrogen in Galicia, while in the phytoplanktonrich Mar Cantábrico it accounted for 26%. This suggests that phytoplankton spring blooms are one of the main sources of organic matter in this pelagic ecosystem. KEY WORDS: Nitrogen speciation · Dissolved organic matter · Phytoplankton · Primary production · Northern Spain Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 214. Online publication date: April 26, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Release of dissolved organic nitrogen by size-fractionated natural planktonic assemblages in coastal waters

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 198:43-49 (2000) - doi:10.3354/meps198043 Release of dissolved organic nitrogen by size-fractionated natural planktonic assemblages in coastal waters Toru Hasegawa1,*, Isao Koike1, Hiroshi Mukai2 1Ocean Research Institute, University of Tokyo, 1-15-1, Minamidai, Nakano, Tokyo 164-8639, Japan 2Akkeshi Marine Biological Station, Hokkaido University Akkeshi, Hokkaido 088-1113, Japan *E-mail: thasegaw@ori.u-tokyo.ac.jp ABSTRACT: To evaluate the effect of differences in community structure on the process of dissolved organic nitrogen (DON) release in natural planktonic assemblages, DO15N release from size-fractionated (<20 and <94 µm) waters of Akkeshi Bay, eastern Hokkaido, Japan, was measured after the addition of 15NH4+. Calculations of percent extracellular release (PER) based on particulate organic 15N nitrogen (PO15N) and DO15N accumulation were higher in the <20 µm fraction than in the <94 µm fractions in 2 out of 3 experiments; though the absolute magnitude of the release was higher in the larger size-fraction. Phytoplankton was primarily responsible for the DO15N release in the <20 µm fraction, which suggested more efficient DON release by smaller phytoplankton compared to larger ones. A passive permeation through the cell membrane is a likely explanation for the DON release observed in our study. PER (<94 µm) fell within the range of 2.7 to 4.9%, which is almost equal to, or somewhat lower than, the PER reported for carbon. In addition, the occurrence of tight coupling between DON release and its consumption by bacteria was suggested in a time-course experiment, showing efficient use of released nitrogenous compounds within the natural community. KEY WORDS: DON · Phytoplankton · Size-fraction · 15N tracer Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 198. Publication date: June 05, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

Gross and net nitrogen uptake and DON release in the euphotic zone of Monterey Bay, California

15N tracer techniques were used to measure rates of NH4+ and NO3− uptake, dissolved organic nitrogen (DON) release resulting from both ammonium (NH4+) and nitrate (NO3−) uptake, and NH4+ regeneration at discrete depths throughout the euphotic zone in Monterey Bay, California, at a site, H3, outside the plume of direct upwelling influence. In March 1993, 94% of the inorganic nitrogen taken up was NH4+, and the primary fate of nitrogen uptake was particle production. In September 1993, NH4+ and NO3− uptake were more in balance, and the primary fate of nitrogen uptake was DON. We suggest that grazing was an important mechanism resulting in DON release in March and that a combination of grazing and a more physiologically stressed phytoplankton population produced the higher observed rates of DON release in September. During both cruises, the percentage of nitrogen released as DON increased with depth, suggesting that deeper in the water column, a smaller percentage of the nitrogen taken up is incorporated into sinking particles. Based on these data, we suggest that the DON pool acts as an intermediate between DIN assimilation and the net formation of particles for export and will thus affect carbon flow in Monterey Bay.

The effects of irradiance on nitrate uptake and dissolved organic nitrogen release by phytoplankton in the Ross Sea

The effects of irradiance on nitrate uptake and subsequent dissolved organic nitrogen (DON) release were investigated using laboratory cultures of Phaeocystis sp. and phytoplankton assemblages dominated by Phaeocystis antarctica in the Ross Sea during cruises in November–December, 1994 and December 1995–January, 1996. 15N-labeled nitrate was used to determine nitrate uptake rates, and an ion retardation column (IRC) method was used to determine 15N-DON release rates (both the total as well as the low molecular weight (LMW) fraction). Nitrate uptake was strongly dependent on irradiance. The maximum specific nitrate uptake rate achieved by Phaeocystis cultures in short (<8 h) incubations was 0.0069 h -1, and maximum specific nitrate uptake rates by phytoplankton assemblages dominated by Phaeocystis antarctica in the Ross Sea were 0.0089 and 0.0033 h -1, respectively, for the two cruises. Photoinhibition of nitrate uptake was observed during both cruises, but was greatest during late December and January, although the mean daily irradiances for the two cruises were similar (49.9 vs. 49.5 mol m -2 d -1). From 8 to 19% of the nitrate assimilated by Phaeocystis cultures and natural phytoplankton assemblages was released as dissolved organic nitrogen. Total DON release rates increased with irradiance in the laboratory and the Ross Sea; however, LMW DON release rates were extremely low and appeared independent of irradiance in the Ross Sea. DON release was also highly correlated with nitrate uptake and phytoplankton growth rate. Release of dissolved organic nitrogen from Phaeocystis-dominated assemblages in general does not appear to play a substantial role in the nitrogen flux in the Ross Sea.

Inorganic and organic nitrogen cycling in Chesapeake Bay: autotrophic versus heterotrophic processes and relationships to carbon flux

To define the role of dissolved organic nitrogen (DON) in Chesapeake Bay (USA) nitrogen cycling, we performed experiments in the mesohaline Chesapeake Bay dunng 3 seasons: May, during the mid to late spring bloom, August, when patchy summer blooms often develop, and October, after the fall overturn. Every 3 h for 30 h we measured ambient nitrogen concentrations and used tracers to determine uptake and regeneration rates of NH,' and urea, uptake rates of NO,(NO; was measured in October only), and rates of DON release due to NH,' uptake. Autotrophic production and dissolved organic carbon (DOC) release were determined sunultaneously using 'v tracer techniques to compare with nitrogen flux rates We found that first, the water column nitrogen demand exceeded nitrogen regeneration in May but n~ t rogen regeneration was over 3 times greater than the nitrogen demand in October. Second, mean rates of autotrophic DON release were highest in May but heterotrophic release was more important in summer and fall. Third, dunng all 3 studies, the C N ratio of DOC to DON release rates was 3.4 to 4.5, indicating release of nitrogen-rich compounds. Release of dissolved organic matter (DOM) \nth a low C:N ratio was corroborated by an observed increase in DON concentrations from 7 to 4 2 pg-at. N I-' from May to August and a concomitant decrease in the C . N ratio of the ambient DOM pool from 36.6 to 8.8. These data suggest that Chesapeake Bay IS primarily autotrophic In the spring, but becomes progressively more heterotrophic later in the year. These data also suggest that DON is an Important intermediate in this transition and serves as a link between the allochthonous nitrogen-based autotrophic production In the spring and the autochthonous nitrogen-based heterotrophic system in the summer and fall.

Stable isotope dynamics of nitrogen recycled during interactions among marine bacteria and protists

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 132:229-239 (1996) - doi:10.3354/meps132229 Stable isotope dynamics of nitrogen recycled during interactions among marine bacteria and protists Hoch MP, Snyder RA, Cifuentes LA, Coffin RB Variation in the distribution of stable nitrogen isotopes among different size classes of particulate organic nitrogen (PON) in aquatic environments may be partly explained by isotope effects associated with regeneration of NH4+ by the microbial food web. Protists fed the marine bacterium Vibrio natriegens were grown in batch and continuous culture to define the isotope discrimination between NH4+, microbial biomass, and dissolved organic nitrogen (DON) for culture systems closed or open to exogenous nutrient inputs. In batch cultures of a flagellate Pseudobodo sp. and a scuticociliate Uronema sp., the nitrogen isotope discrimination between biomass and NH4+ was 3 to 5 o/oo during exponential growth of protists corresponding to the highest rates of biomass-specific NH4+ release. The delta15N of DON, calculated by mass balance, was very depleted in 15N relative to NH4+ and biomass during exponential and early stationary growth when DON and dissolved free amino acid (DFAA) concentrations increased. In contrast to batch culture results, for continuous culture of the flagellate the isotope discrimination between biomass and NH4+ and the change in the calculated delta15N of DON were small: 1 to 2 o/oo. Based on rates of thymidine incorporation and turnover of DFAA, protist excretion and bacterial uptake of DON were less coupled for exponentially growing protists fed starved bacteria in batch cultures than for the flagellate fed active bacteria growing in a 2-stage continuous culture. Coupling between release and utilization of DON, as well as isotope effects associated with protist metabolism, are proposed to constrain the nitrogen isotope dynamics of NH4+ suspended PON, and DON within marine ecosystems, especially those environments dominated by regenerated primary production. Stable nitrogen isotopes . Protist grazing . Marine bacteria . Ammonium regeneration . Dissolved organic nitrogen Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 132. Publication date: February 29, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Release of Dissolved Organic Nitrogen by Marine Diazotrophic Cyanobacteria, Trichodesmium spp

Trichodesmium sp. is a filamentous, colonial cyanobacterium which contributes substantially to the input of nitrogen in tropical and subtropical oceanic waters through nitrogen fixation (N(2) fixation). We applied a N tracer technique to assess the rate of release of dissolved organic nitrogen (DON) from this cyanobacterium and compared those rates with rates of N(2) fixation determined for the same assemblages at the same times of day. Rates of release of DON showed considerable variation within replicate experiments and were variable depending on time of day and duration of time course experiments. On average, rates of DON release were ca. 50% the rates of N(2) fixation. We also fractionated the DON released by using ultrafiltration and found that 60 to 80% of the total organic release was of the size class <10,000 Da. The release of these organic compounds by Trichodesmium spp. is likely a significant source of new nitrogen for the associated bacteria or the non-nitrogen-fixing filaments of the Trichodesmium colonies.

Nitrogen Uptake, Dissolved Organic Nitrogen Release, and New Production

In oceanic, coastal, and estuarine environments, an average of 25 to 41 percent of the dissolved inorganic nitrogen (NH(4) (+) and NO(3) (-)) taken up by phytoplankton is released as dissolved organic nitrogen (DON). Release rates for DON in oceanic systems range from 4 to 26 nanogram-atoms of nitrogen per liter per hour. Failure to account for the production of DON during nitrogen-15 uptake experiments results in an underestimate of gross nitrogen uptake rates and thus an underestimate of new and regenerated production. In these studies, traditional nitrogen-15 techniques were found to underestimate new and regenerated production by up to 74 and 50 percent, respectively. Total DON turnover times, estimated from DON release resulting from both NH(4) (+) and NO(3) (-) uptake, were 10 +/- 1, 18 +/- 14, and 4 days for oceanic, coastal, and estuarine sites, respectively.