46 results on '"Hietanen, Susanna"'
Search Results
2. Legacy Effects of Eutrophication on Modern Methane Dynamics in a Boreal Estuary
- Author
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Myllykangas, Jukka-Pekka, Hietanen, Susanna, and Jilbert, Tom
- Published
- 2020
3. Denitrification in an oligotrophic estuary : a delayed sink for riverine nitrate
- Author
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Hellemann, Dana, Tallberg, Petra, Bartl, Ines, Voss, Maren, and Hietanen, Susanna
- Published
- 2017
4. Nitrification and the ammonia-oxidizing communities in the central Baltic Sea water column
- Author
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Jäntti, Helena, Ward, Bess B., Dippner, Joachim W., and Hietanen, Susanna
- Published
- 2018
- Full Text
- View/download PDF
5. Denitrification in the River Estuaries of the Northern Baltic Sea
- Author
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Hietanen, Susanna, Liikanen, Anu, Kuparinen, Jorma, and Martikainen, Pertti J.
- Published
- 2007
- Full Text
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6. Diffusion and Advection within and around Sinking, Porous Diatom Aggregates
- Author
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Ploug, Helle, Hietanen, Susanna, and Kuparinen, Jorma
- Published
- 2002
7. Spatial and temporal dynamics of ammonia oxidizers in the sediments of the Gulf of Finland, Baltic Sea
- Author
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Vetterli, Adrien, Hietanen, Susanna, and Leskinen, Elina
- Published
- 2016
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- View/download PDF
8. Seasonal patterns of bacterial communities in the coastal brackish sediments of the Gulf of Finland, Baltic Sea
- Author
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Vetterli, Adrien, Hyytiäinen, Kirsi, Ahjos, Minttu, Auvinen, Petri, Paulin, Lars, Hietanen, Susanna, and Leskinen, Elina
- Published
- 2015
- Full Text
- View/download PDF
9. Hypoxia in the Baltic Sea: Biogeochemical Cycles, Benthic Fauna, and Management
- Author
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Carstensen, Jacob, Conley, Daniel J., Bonsdorff, Erik, Gustafsson, Bo G., Hietanen, Susanna, Janas, Urzsula, Jilbert, Tom, Maximov, Alexey, Norkko, Alf, Norkko, Joanna, Reed, Daniel C., Slomp, Caroline P., Timmermann, Karen, and Voss, Maren
- Published
- 2014
10. The role of recurrent disturbances for ecosystem multifunctionality
- Author
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Villnäs, Anna, Norkko, Joanna, Hietanen, Susanna, Josefson, Alf B., Lukkari, Kaarina, and Norkko, Alf
- Published
- 2013
11. Dynamics of dissolved nutrients among different macrophyte stands in a shallow lake
- Author
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Holmroos, Heidi, Horppila, Jukka, Niemistö, Juha, Nurminen, Leena, and Hietanen, Susanna
- Published
- 2015
- Full Text
- View/download PDF
12. The Effects of Hypoxia on Sediment Nitrogen Cycling in the Baltic Sea
- Author
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Jäntti, Helena and Hietanen, Susanna
- Published
- 2012
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13. Hypoxia and nitrogen processing in the Baltic Sea water column
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Hietanen, Susanna, Jäntti, Helena, Buizert, Christo, Jürgens, Klaus, Labrenz, Matthias, Voss, Maren, and Kuparinen, Jorma
- Published
- 2012
14. Community Structure of the Bacteria Associated with Nodularia sp. (Cyanobacteria) Aggregates in the Baltic Sea
- Author
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Tuomainen, Jaana, Hietanen, Susanna, Kuparinen, Jorma, Martikainen, Pertti J., and Servomaa, Kristina
- Published
- 2006
- Full Text
- View/download PDF
15. Microbial dynamics on diatom aggregates in Øresund, Denmark
- Author
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Grossart, Hans Peter, Hietanen, Susanna, and Ploug, Helle
- Published
- 2003
16. No sign of denitrification in a Baltic Sea cyanobacterial bloom
- Author
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Hietanen, Susanna, Moisander, Pia H., Kuparinen, Jorma, and Tuominen, Liisa
- Published
- 2002
17. Silicate Release from Sand-Manipulated Sediment Cores: Biogenic or Adsorbed Si?
- Author
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Tallberg, Petra, Lehtoranta, Jouni, and Hietanen, Susanna
- Published
- 2013
- Full Text
- View/download PDF
18. Seasonal and short-term variation in denitrification and anammox at a coastal station on the Gulf of Finland, Baltic Sea
- Author
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Hietanen, Susanna and Kuparinen, Jorma
- Published
- 2008
- Full Text
- View/download PDF
19. Denitrification in the river estuaries of the Northern Baltic Sea
- Author
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Silvennolnen, Hanna, Hietanen, Susanna, Lilkanen, Anu, Stange, C. Florian, Russow, Rolf, Kuparinen, Jorma, and Martlkalnen, Perttl J.
- Subjects
Baltic Sea -- Environmental aspects ,Denitrification -- Research ,Estuaries -- Environmental aspects ,Marine pollution -- Research ,Environmental issues - Abstract
A study to measure the denitrification rates in six different estuaries of the Northern Baltic Sea is conducted. The results demonstrate that the nitrogen load on the Baltic Sea cannot be satisfactorily reduced by the sediments of the fast-flowing rivers and the estuary areas with short residence times.
- Published
- 2007
20. BIOGEOCHEMISTRY: The depths of nitrogen cycling
- Author
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Voss, Maren and Hietanen, Susanna
- Published
- 2013
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21. A simple sediment process description suitable for 3D-ecosystem modelling — Development and testing in the Gulf of Finland
- Author
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Kiirikki, Mikko, Lehtoranta, Jouni, Inkala, Arto, Pitkänen, Heikki, Hietanen, Susanna, Hall, Per O.J., Tengberg, Anders, Koponen, Jorma, and Sarkkula, Juha
- Published
- 2006
- Full Text
- View/download PDF
22. Application of the isotope pairing technique in sediments : Use, challenges, and new directions
- Author
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Robertson, Elizabeth K., Bartoli, Marco, Bruechert, Volker, Dalsgaard, Tage, Hall, Per O. J., Hellemann, Dana, Hietanen, Susanna, Zilius, Mindaugas, Conley, Daniel J., Marine Ecosystems Research Group, Aquatic Biogeochemistry Research Unit (ABRU), and Ecosystems and Environment Research Programme
- Subjects
MEASURING BENTHIC DENITRIFICATION ,COUPLED NITRIFICATION-DENITRIFICATION ,ORGANIC-MATTER ,CONTINENTAL-SHELF ,FRESH-WATER ,116 Chemical sciences ,1181 Ecology, evolutionary biology ,BALTIC SEA ,DISSIMILATORY NITRATE REDUCTION ,SHALLOW-WATER SEDIMENTS ,NITROGEN-FIXATION ,ANAEROBIC AMMONIUM OXIDATION - Abstract
Determining accurate rates of benthic nitrogen (N) removal and retention pathways from diverse environments is critical to our understanding of process distribution and constructing reliable N budgets and models. The whole-core N-15 isotope pairing technique (IPT) is one of the most widely used methods to determine rates of benthic nitrate-reducing processes and has provided valuable information on processes and factors controlling N removal and retention in aquatic systems. While the whole core IPT has been employed in a range of environments, a number of methodological and environmental factors may lead to the generation of inaccurate data and are important to acknowledge for those applying the method. In this review, we summarize the current state of the whole core IPT and highlight some of the important steps and considerations when employing the technique. We discuss environmental parameters which can pose issues to the application of the IPT and may lead to experimental artifacts, several of which are of particular importance in environments heavily impacted by eutrophication. Finally, we highlight the advances in the use of the whole-core IPT in combination with other methods, discuss new potential areas of consideration and encourage careful and considered use of the whole-core IPT. With the recognition of potential issues and proper use, the whole-core IPT will undoubtedly continue to develop, improve our understanding of benthic N cycling and allow more reliable budgets and predictions to be made.
- Published
- 2019
23. Baltic Sea cyanobacterial bloom contains denitrification and nitrification genes, but has negligible denitrification activity
- Author
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Tuomainen, Jaana M., Hietanen, Susanna, Kuparinen, Jorma, Martikainen, Pertti J., and Servomaa, Kristina
- Published
- 2003
- Full Text
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24. Linking process rates with modelling data and ecosystem characteristics:Report Oceanography no. 61
- Author
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Eilola, Kari, Lindqvist, Stina, Edman, Moa, Wåhlström, Iréne, Bartoli, Marco, Burska, Dorota, Carstensen, Jacob, Hellemann, Dana, Hietanen, Susanna, Hulth, Stefan, Janas, Urszula, Kendzierska, Halina, Pryputniewicz-Flis, Dorota, Voss, Maren, and Zilius, Mindaugas
- Subjects
eutrophication ,biogeochemistry ,nutrient retention ,coastal zone - Published
- 2017
25. Linking process rates with modellingdata and ecosystem characteristics
- Author
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Eilola, Kari, Lindqvist, Stina, Almroth-Rosell, Elin, Edman, Moa, Wåhlstrom, Irene, Bartoli, Marco, Burska, Dorota, Carstensen, Jacob, Hellemann, Dana, Hietanen, Susanna, Hulth, Stefan, Janas, Urszula, Kendzierska, Halina, Pryputniewicz-Flis, Dorota, Voss, Maren, and Zilius, Mindaugas
- Subjects
Oceanography, Hydrology and Water Resources ,Nutrient retention ,Oceanografi, hydrologi och vattenresurser ,Eutrophication ,Biogeochemistry ,Coastal zone - Abstract
This report is related to the BONUS project “Nutrient Cocktails in COAstal zones of the Baltic Sea” alias COCOA. The aim of BONUS COCOA is to investigate physical, biogeochemical and biological processes in a combined and coordinated fashion to improve the understanding of the interaction of these processes on the removal of nutrients along the land-sea interface. The report is especially related to BONUS COCOA WP 6 in which the main objective is extrapolation of results from the BONUS COCOA learning sites to coastal sites around the Baltic Sea in general. Specific objectives of this deliverable (D6.4) were to connect observed process rates with modelling data and ecosystem characteristics. In the report we made statistical analyses of observations from BONUS COCOA study sites together with results from the Swedish Coastal zone Model (SCM). Eight structural variables (water depth, temperature, salinity, bottom water concentrations of oxygen, ammonium, nitrate and phosphate, as well as nitrogen content in sediment) were found common to both the experimentally determined and the model data sets. The observed process rate evaluated in this report was denitrification. In addition regressions were tested between observed denitrification rates and several structural variables (latitude, longitude, depth, light, temperature, salinity, grain class, porosity, loss of ignition, sediment organic carbon, total nitrogen content in the sediment, sediment carbon/nitrogen-ratio, sediment chlorphyll-a as well as bottom water concentrations of oxygen, ammonium, nitrate, and dissolved inorganic phosphorus and silicate) for pooled data from all learning sites. The statistical results showed that experimentally determined multivariate data set from the shallow, illuminated stations was mainly found to be similar to the multivariate data set produced by the SCM model. Generally, no strong correlations of simple relations between observed denitrification and available structural variables were found for data collected from all the learning sites. We found some non-significant correlation between denitrification rates and bottom water dissolved inorganic phosphorous and dissolved silica but the reason behind the correlations is not clear. We also developed and evaluated a theory to relate process rates to monitoring data and nutrient retention. The theoretical analysis included nutrient retention due to denitrification as well as burial of phosphorus and nitrogen. The theory of nutrient retention showed good correlations with model results. It was found that area-specific nitrogen and phosphorus retention capacity in a sub-basin depend much on mean water depth, water residence time, basin area and the mean nutrient concentrations in the active sediment layer and in the water column.
- Published
- 2017
26. A bioreactor approach to investigate the linkage between methane oxidation and nitrate/nitrite reduction in the pelagic oxic-anoxic transition zone of the central Baltic Sea
- Author
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Jakobs, Gunnar, Labrenz, Matthias, Rehder, Gregor, Hietanen, Susanna, Kießlich, Katrin, Blumenberg, Martin, Schmale, Oliver, Vogts, Angela, Environmental Sciences, Susanna Hietanen / Principal Investigator, Aquatic Biogeochemistry Research Unit (ABRU), and Marine Ecosystems Research Group
- Subjects
Global and Planetary Change ,denitrification ,methanotrophs ,Baltic Sea ,methane oxidation ,enrichment cultures ,education ,Ocean Engineering ,Aquatic Science ,Oceanography ,Marine Science ,1172 Environmental sciences ,Water Science and Technology - Abstract
Evidence of aerobic methane oxidation coupled to denitrification has been provided for different freshwater environments, whereas the significance of this process for the marine realm has not been adequately investigated. The goal of this study was to investigate the methane-related reduction of nitrate/nitrite in a marine environment (salinity 8.5). A water sample was collected from the oxic-anoxic transition zone of the Gotland Deep (central Baltic Sea) and the microorganisms contained therein were cultivated in a bioreactor under hypoxic conditions (0.5 μM O2). To enrich the microorganisms involved in the coupled process the bioreactor was continuously sparged with methane as the sole energy and carbon source and simultaneously supplied with a nutrient solution rich in nitrate and nitrite. The bioreactor experiment showed a relationship between the turnover of methane and the concomitant concentration decrease of nitrite and nitrate at the early stage of the experiment. This relationship indicates the role of methanotrophs, which may support heterotrophic denitrifiers by the release of organic compounds as an energy source. Besides, a mixture of uncultured microorganisms, aerobic methanotrophic and heterotrophic denitrifying bacteria were identified in the enrichment culture. Microbial incorporation of nitrite and methane was proven on the cellular and gene levels via 15NO−22-/13CH4 incubation experiments and subsequent analyses with nano secondary ion mass spectrometry (NanoSIMS) and stable isotope probing (SIP). The NanoSIMS showed the incorporation of 15N in almost all the bacteria and in 9% of those there was a concomitant enrichment in 13C. The relatively low abundance of methane-consuming bacteria in the bioreactor was further reflected in specific fatty acids indicative for type I methanotrophic bacteria. Based on pmoA gene analyses, this bacterium is different from the one that was identified as the only key player of methane oxidation in previous studies in the Gotland Deep, indicating the existence of other subordinate methanotrophic bacteria at that site. The results provide the first indications for the predisposition of a methane-related reduction of nitrate/nitrite under hypoxic conditions in the marine realm, supporting the assumption of an interaction between methanotrophic and denitrifying bacteria which hitherto has only been described for fresh water environments.
- Published
- 2016
27. Particulate organic matter controls benthic microbial N retention and N removal in contrasting estuaries of the Baltic Sea.
- Author
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Bartl, Ines, Hellemann, Dana, Rabouille, Christophe, Schulz, Kirstin, Tallberg, Petra, Hietanen, Susanna, and Voss, Maren
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PARTICULATE matter ,ORGANIC compounds ,GEOMORPHOLOGY ,ESTUARIES ,GREEN'S functions ,BOUNDARY layer (Aerodynamics) ,NITRIFICATION - Abstract
Estuaries worldwide act as "filters" of land-derived nitrogen (N) loads, yet differences in coastal environmental settings can affect the N filter function. We investigated microbial N retention (nitrification, ammonium assimilation) and N removal (denitrification, anammox) processes in the aphotic benthic system (bottom boundary layer (BBL) and sediment) of two Baltic Sea estuaries differing in riverine N loads, trophic state, geomorphology, and sediment type. In the BBL, rates of nitrification (5–227 nmol N L -1 d -1) and ammonium assimilation (9–704 nmol N L -1 d -1) were not enhanced in the eutrophied Vistula Estuary compared to the oligotrophic Öre Estuary. No anammox was detected in the sediment of either estuary, while denitrification rates were twice as high in the eutrophied (352±123 µ mol N m -2 d -1) as in the oligotrophic estuary. Particulate organic matter (POM) was mainly of phytoplankton origin in the benthic systems of both estuaries. It seemed to control heterotrophic denitrification and ammonium assimilation as well as autotrophic nitrification by functioning as a substrate source of N and organic carbon. Our data suggest that in stratified estuaries, POM is an essential link between riverine N loads and benthic N turnover and may furthermore function as a temporary N reservoir. During long particle residence times or alongshore transport pathways, increased time is available for the recycling of N until its eventual removal, allowing effective coastal filtering even at low process rates. Understanding the key controls and microbial N processes in the coastal N filter therefore requires to also consider the effects of geomorphological and hydrological features. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
28. Particulate organic matter controls benthic microbial N retention and N removal in contrasting estuaries of the Baltic Sea.
- Author
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Bartl, Ines, Hellemann, Dana, Rabouille, Christophe, Schulz, Kirstin, Tallberg, Petra, Hietanen, Susanna, and Voss, Maren
- Subjects
ORGANIC compounds ,ESTUARIES ,APHOTIC zone ,RELIEF models ,EUTROPHICATION - Abstract
Estuaries worldwide are known to act as
filters
of land-derived N loads, yet their variable environmental settings can affect microbial nitrogen (N) retention and removal and thus the coastal filter function. We investigated microbial N-retention (nitrification, ammonium assimilation) and N-removal (denitrification, anammox) in the aphotic benthic systems (here defined as: bottom boundary layer [BBL] and sediment) of two Baltic Sea estuaries that differ in riverine N loads, trophic state, bottom topography, and sediment type. Contrary to our expectations, nitrification rates (5-227 nmol L-1 d-1 ) in the BBL neither differed between the eutrophied Vistula estuary and the oligotrophic Öre estuary, nor between seasons. Ammonium assimilation rates were slightly higher in the oligotrophic Öre estuary in spring but did not differ between estuaries in summer (9-704 nmol L-1 d-1 ). In the sediment, no anammox was found in either estuary and denitrification rates were higher in the eutrophied (349 ± 117 µmol N m-2 d-1 ) than in the oligotrophic estuary (138 ± 47 µmol N m-2 d-1 ). Irrespective of their differences, in both estuaries the quality of the mainly phytoplankton-derived particulate organic matter (POM) - evaluated by means of C : N and POC : Chl.a ratios - seemed to control N-cycling processes through the availability of particulate organic N and C as substrate sources. Our data suggest, that in stratified estuaries, phytoplankton-derived POM is an essential link between riverine N loads and benthic N cycling and may function as a temporary N reservoir via long particle residence time or coastal parallel transport. Even at low process rates, effective coastal filtering would thus be achieved by the increased time available for the recycling of N via microbial retention processes until its permanent removal via denitrification. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
29. The depths of nitrogen cycling: breakdown of dissolved organic nitrogen in the ocean had been thought to be the preserve of microbes at the surface. The discovery that these microbes are not up to the task calls for a reassessment of the biogeochemistry of this nitrogen pool
- Author
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Voss, Maren and Hietanen, Susanna
- Subjects
Nitrogen cycle -- Research ,Microorganisms -- Research ,Ocean -- Statistics -- Chemical properties ,Biogeochemistry -- Research ,Environmental issues ,Science and technology ,Zoology and wildlife conservation - Abstract
The largest pool of fixed nitrogen on Earth is dissolved organic nitrogen in the oceans, but its dynamics and transport between ocean zones are largely unknown. Writing in Global Biogeochemical [...]
- Published
- 2013
30. Impacts of flocculation on the distribution and diagenesis of iron in boreal estuarine sediments.
- Author
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Jilbert, Tom, Asmala, Eero, Schröder, Christian, Tiihonen, Rosa, Myllykangas, Jukka-Pekka, Virtasalo, Joonas J., Kotilainen, Aarno, Peltola, Pasi, Ekholm, Päivi, and Hietanen, Susanna
- Subjects
OXIDATION-reduction reaction ,DISSOLVED organic matter ,IRON ,CARBON ,FLOCCULATION ,SEDIMENTS - Abstract
Iron (Fe) plays a key role in sedimentary diagenetic processes in coastal systems, participating in various redox reactions and influencing the burial of organic carbon. Large amounts of Fe enter the marine environment from boreal river catchments associated with dissolved organic matter (DOM) and as colloidal Fe oxyhydroxides, principally ferrihydrite. However, the fate of this Fe pool in estuarine sediments has not been extensively studied. Here we show that flocculation processes along a salinity gradient in an estuary of the northern Baltic Sea efficiently transfer Fe and OM from the dissolved phase into particulate material that accumulates in the sediments. Flocculation of Fe and OM is partially decoupled. This is likely due to the presence of discrete colloidal ferrihydrite in the freshwater Fe pool, which responds differently from DOM to estuarine mixing. Further decoupling of Fe from OM occurs during sedimentation. While we observe a clear decline with distance offshore in the proportion of terrestrial material in the sedimentary particulate organic matter (POM) pool, the distribution of flocculated Fe in sediments is modulated by focusing effects. Labile Fe phases are most abundant at a deep site in the inner basin of the estuary, consistent with input from flocculation and subsequent focusing. The majority of the labile Fe pool is present as Fe (II), including both acid-volatile sulfur (AVS)-bound Fe and unsulfidized phases. The ubiquitous presence of unsulfidized Fe (II) throughout the sediment column suggests Fe (II)-OM complexes derived from reduction of flocculated Fe (III)-OM, while other Fe (II) phases are likely derived from the reduction of flocculated ferrihydrite. Depth-integrated rates of Fe (II) accumulation (AVS-Fe + unsulfidized Fe (II) + pyrite) for the period 1970-2015 are greater in the inner basin of the estuary with respect to a site further offshore, confirming higher rates of Fe reduction in near-shore areas. Mössbauer 57Fe spectroscopy shows that refractory Fe is composed largely of superparamagnetic Fe (III), high-spin Fe (II) in silicates, and, at one station, also oxide minerals derived from past industrial activities. Our results highlight that the cycling of Fe in boreal estuarine environments is complex, and that the partial decoupling of Fe from OM during flocculation and sedimentation is key to understanding the role of Fe in sedimentary diagenetic processes in coastal areas. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
31. Flocculation of dissolved organic matter controls the distribution of iron in boreal estuarine sediments.
- Author
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Jilbert, Tom, Asmala, Eero, Schröder, Christian, Tiihonen, Rosa, Myllykangas, Jukka-Pekka, Virtasalo, Joonas J., Kotilainen, Aarno, Peltola, Pasi, Ekholm, Päivi, and Hietanen, Susanna
- Subjects
ESTUARINE sediments ,IRON ,DISSOLVED organic matter - Abstract
Iron (Fe) plays a key role in sedimentary diagenetic processes in coastal systems, participating in various redox reactions and influencing the burial of organic carbon. Large amounts of Fe enter the marine environment from boreal river catchments associated with dissolved organic matter (DOM). However, the fate of this Fe pool in estuarine sediments has not been extensively studied. Here we show that flocculation of DOM along salinity gradients in an estuary of the northern Baltic Sea efficiently transfers Fe from the dissolved phase into particulate material that accumulates in the sediments. Consequently, we observe a decline with distance offshore in both the Fe content of the sediments and proportion of terrestrial material in the sedimentary organic matter pool. Mössbauer spectroscopy and sequential extractions suggest that large amounts of Fe in sediments of the upper estuarine zone are associated with organic matter as unsulfidized Fe (II) complexes, or present in the form of ferrihydrite, implying a direct transfer of flocculated material to the sediments. Accordingly, the contribution of these components to the total sedimentary Fe declines with distance offshore while other Fe phases become proportionally more important. Sediment core records show that the observed lateral distribution of Fe minerals has remained similar over recent decades, despite variable Fe inputs from anthropogenic sources and eutrophication of the coastal zone. Pore water data suggest that the vertical zonation of diagenetic processes in the sediments is influenced by both the availability of Fe and by bottom water salinity, which controls the availability of sulfate (SO
4 2 - ). [ABSTRACT FROM AUTHOR]- Published
- 2017
- Full Text
- View/download PDF
32. On the role of bacterial production and denitrification in some less-studied Baltic Sea habitats
- Author
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Hietanen, Susanna, University of Helsinki, Faculty of Agriculture and Forestry, Department of Limnology and Environmental Protection, Helsingin yliopisto, maatalous-metsätieteellinen tiedekunta, limnologian ja ympäristönsuojelun laitos, and Helsingfors universitet, agrikultur forstvetenskapliga fakulteten, institutionen för limnologi och miljövård
- Published
- 2002
33. Benthic bacterial production in the northern Baltic Sea measured using a modified 14C-leucine uptake method
- Author
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Hietanen, Susanna, Tuominen, Liisa, Kuparinen, Jorma, and Environmental Sciences
- Subjects
education - Published
- 1999
34. Aeration-Induced Changes in Temperature and Nitrogen Dynamics in a Dimictic Lake.
- Author
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Holmroos, Heidi, Horppila, Jukka, Laakso, Sanna, Niemistö, Juha, and Hietanen, Susanna
- Subjects
OXYGEN in water ,NUTRIENT cycles ,NITROGEN cycle ,DENITRIFICATION ,AERATION of lakes ,WATER quality management - Abstract
Low levels of oxygen (O
2 ) in the hypolimnion layer of lakes are harmful to benthic animals and fish; they may also adversely affect nutrient cycles. Artificial aeration is often used in lake management to counteract these problems, but the effects of aeration on nitrogen (N) cycling are not known. We studied the effects of hypolimnetic aeration on N dynamics and temperature in a eutrophic lake by comparing continuous and pulsed aeration with a nonaerated station. Aeration decreased the accumulation of NH4 + -N deep in the lake (20-33 m) by supplying O2 for nitrification, which in turn provided substrate for denitrification and promoted N removal. Aeration also increased the temperature in the hypolimnion. Denitrification rate was highest in the nonaerated deep areas (average, 7.62 mg N m-2 d-1 ) due to very high rates during spring turnover of the water column, demonstrating that natural turnover provides O2 for nitrification. During stratification, denitrification was highest at the continuously aerated station (4.06 mg N m-2 d-1 ) and lowest at the nonaerated station (3.02 mg N m-2 d-1 ). At the periodically aerated station, aeration pauses did not restrict the increase in temperature but resulted in accumulation of NH4 + -N and decreased the contribution of denitrification as a nitrate reduction process. Our findings demonstrate that hypolimnetic aeration can substantially affect N cycling in lakes and that the effect depends on the aeration strategy. Because N is one of the main nutrients controlling eutrophication, the effects of aeration methods on N removal should be considered as part of strategies to manage water quality in lakes. [ABSTRACT FROM AUTHOR]- Published
- 2016
- Full Text
- View/download PDF
35. Oxygen flux and penetration depth in the sediments of aerated and non-aerated lake basins.
- Author
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Horppila, Jukka, Köngäs, Petrina, Niemistö, Juha, and Hietanen, Susanna
- Subjects
AERATION of lakes ,OXYGEN in water ,HYPOXEMIA ,STRATIGRAPHIC geology ,OXYGEN consumption ,OXIDATION-reduction reaction ,PREVENTION - Abstract
The effects of hypolimnetic aeration on oxygen penetration depth and oxygen flux into the sediment (DOU) were studied during two successive years. The study was conducted by comparing data from the aerated Enonselkä basin with the non-aerated Kajaanselkä basin of Lake Vesijärvi (southern Finland). Aeration increased the average O
2 concentration in near-bottom layers. This was mainly due to shortened stratification period in the aerated basin, which was again attributed to the positive effect of aeration on hypolimnetic water temperature. Aeration did not prevent hypoxia during summer stratification and oxygen penetration depth in the sediment and DOU did not increase. During summer stratification DOU was even lower at the aerated than at the non-aerated basin. The weak effect of aeration on DOU and oxygen penetration was mostly due to the minor effect on hypolimnetic oxygen concentrations. The positive effect of aeration on hypolimnetic O2 concentration was negated by the positive effects of aeration on hypolimnetic temperature and turbulence that increase oxygen consumption in the water column. Due to the generally low effect on DOU, the present aeration effort in Enonselkä does not have positive effects on sediment quality. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
36. N and O Isotope Fractionation in Nitrate during Chemolithoautotrophic Denitrification by Sulfurimonas gotlandica.
- Author
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Frey, Claudia, Hietanen, Susanna, Jürgens, Klaus, Labrenz, Matthias, and Voss, Maren
- Subjects
- *
ISOTOPIC fractionation , *NITRATES , *DENITRIFICATION , *NITROGEN reduction , *OXYGEN , *NITRATE reductase - Abstract
Chemolithoautotrophic denitrification is an important mechanism of nitrogen loss in the water column of euxinic basins, but its isotope fractionation factor is not known. Sulfurimonas gotlandica GD1T, a recently isolated bacterial key player in Baltic Sea pelagic redoxcline processes, was used to determine the isotope fractionation of nitrogen and oxygen in nitrate during denitrification. Under anoxic conditions, nitrate reduction was accompanied by nitrogen and oxygen isotope fractionation of 23.8 ± 2.5° and 11.7 ± 1.1°, respectively. The isotope effect for nitrogen was in the range determined for heterotrophic denitrification, with only the absence of stirring resulting in a significant decrease of the fractionation factor. The relative increase in δ18ONO3 to δ15NNO3 did not follow the 1:1 relationship characteristic of heterotrophic, marine denitrification. Instead, δ18ONO3 increased slower than δ15NNO3, with a conserved ratio of 0.5:1. This result suggests that the periplasmic nitrate reductase (Nap) of S. gotlandica strain GD1T fractionates the N and O in nitrate differently than the membrane-bound nitrate reductase (Nar), which is generally prevalent among heterotrophic denitrifiers and is considered as the dominant driver for the observed isotope fractionation. Hence in the Baltic Sea redoxcline, other, as yet-unidentified factors likely explain the low apparent fractionation. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
37. Measuring nitrification in sediments – comparison of two techniques and three NO measurement methods.
- Author
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Jäntti, Helena, Leskinen, Elina, Stange, Claus Florian, and Hietanen, Susanna
- Subjects
NITRIFICATION ,SEDIMENTS ,NITROGEN cycle ,NITROGEN isotopes ,NITRATE content of water - Abstract
Nitrification is a crucial process in sediment nitrogen cycling. We compared two 15N tracer-based nitrification measurement techniques (isotope pairing technique (IPT) combined with 15N nitrate pool dilution and 15N ammonium oxidation) and three different 15N analyses from bottom water nitrate (ammonia diffusion, denitrifier and SPINMAS) in a sediment mesocosm. The 15N nitrate pool dilution technique combined with IPT can be used to quantify the in situ nitrification, but the minimum detection limit for the total nitrification is higher than that in the 15N ammonium oxidation technique. The 15N ammonium oxidation technique, however, is not applicable for sediments that have high ammonium content. If nitrate concentration and the amount of 15N label in the sample are low, the 15N nitrate analysis should be done with the denitrifier method. In higher 15N concentrations, the less sensitive SPINMAS method can also be applied. The ammonia diffusion method is not suitable for bottom water 15N nitrate analyses. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
38. Hypoxia-Related Processes in the Baltic Sea.
- Author
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CONLEY, DANIEL J., BJÖRCK, SVANTE, BONSDORFF, ERIK, CARSTENSEN, JACOB, DESTOUNI, GEORGIA, GUSTAFSSON, BO G., HIETANEN, SUSANNA, KORTEKAAS, MARLOES, KUOSA, HARRI, METER, H. E. MARKUS, MÜLLER-KARULIS, BAERBEL, NORDBERG, KJELL, NORKKO, ALF, NÜRNBERG, GERTRUD, PITKÄNEN, HEIKKI, RABALAIS, NANCY N., ROSENBERG, RUTGER, SAVCHUK, OLEG P., SLOMP, CAROLINE P., and VOSS, MAREN
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- 2009
- Full Text
- View/download PDF
39. The complex effects of the invasive polychaetes Marenzelleria spp. on benthic nutrient dynamics
- Author
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Hietanen, Susanna, Laine, Ari O., and Lukkari, Kaarina
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- *
DENITRIFICATION , *DENITRIFYING bacteria , *PORE fluids , *WATER - Abstract
Abstract: The effects of the polychaetes Marenzelleria sp. (Polychaeta, Spionidae), nonindigenous, rapidly increasing species in the Baltic Sea, on benthic nutrient fluxes, denitrification and sediment pore water nutrient concentration were studied in laboratory experiments using a flow-through setup with muddy sediment from coastal regions of the Gulf of Finland. In addition, different forms of sediment phosphorus (P), separated by chemical fractionation, were studied in three sediment layers. At a population density corresponding to about half the highest measured in the northern Baltic Sea, Marenzelleria sp. increased the fluxes of P and ammonium to the water column. No effect could be recorded for denitrification. Since the previously dominant species of the area, Monoporeia affinis, can enhance denitrification and lower the amount of dissolved P in the pore water, the replacement of M. affinis with Marenzelleria spp. may lead to increased P flux to the water column and decreased denitrification, further increasing the ammonium flux to the water column. However, sediment reworking by Marenzelleria spp. also oxidizes the surface sediment in the long run, improving its ability to retain P and support nitrification. Therefore, the impact of Marenzelleria spp. on sediment nutrient release may not be as drastic as the initial reactions seen in our experiments suggest. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
40. Seasonal and short-term variation in denitrification and anammox at a coastal station on the Gulf of Finland, Baltic Sea.
- Author
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Hietanen, Susanna and Kuparinen, Jorma
- Subjects
- *
NITRIFYING bacteria , *AMMONIUM compounds , *OXYGEN consumption , *DENITRIFICATION , *NITROGEN removal (Water purification) , *NITROGEN cycle , *MARINE sediments - Abstract
Benthic processes were measured at a coastal deposition area in the northern Baltic Sea, covering all seasons. The N2 production rates, 90–400 μmol N m−2 d−1, were highest in autumn-early winter and lowest in spring. Heterotrophic bacterial production peaked unexpectedly late in the year, indicating that in addition to the temperature, the availability of carbon compounds suitable for the heterotrophic bacteria also plays a major role in regulating the denitrification rate. Anaerobic ammonium oxidation (anammox) was measured in spring and autumn and contributed 10% and 15%, respectively, to the total N2 production. The low percentage did, however, result in a significant error in the total N2 production rate estimate, calculated using the isotope pairing technique. Anammox must be taken into account in the Gulf of Finland in future sediment nitrogen cycling research. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
41. Denitrification in the River Estuaries of the Northern Baltic Sea.
- Author
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Silvennoinen, Hanna, Hietanen, Susanna, Liikanen, Anu, Stange, C. Florian, Russow, Rolf, Kuparinen, Jorma, and Martikainen, Pertti J.
- Subjects
- *
ESTUARIES , *TOTAL maximum daily load for water pollutants , *NITROGEN , *DENITRIFICATION , *DENITRIFYING bacteria , *NITRATES & the environment - Abstract
Estuaries have been suggested to have an important role in reducing the nitrogen load transported to the sea. We measured denitrification rates in six estuaries of the northern Baltic Sea. Four of them were river mouths in the Bothnian Bay (northern Gulf of Bothnia), and two were estuary bays, one in the Archipelago Sea (southern Gulf of Bothnia) and the other in the Gulf of Finland. Denitrification rates in the four river mouths varied between 330 and 905 µmol N m-2 d-1. The estuary bays at the Archipelago Sea and the Gulf of Bothnia had denitrification rates from 90 µmol N m-2 d-1 to 910 µmol N m-2 d-1 and from 230 µmol N m-2 d-1 to 320 µmol N m-2 d-1, respectively. Denitrification removed 3.6-9.0% of the total nitrogen loading in the river mouths and in the estuary bay in the Gulf of Finland, where the residence times were short. In the estuary bay with a long residence time, in the Archipelago Sea, up to 4.5% of nitrate loading and 19% of nitrogen loading were removed before entering the sea. According to our results, the sediments of the fast-flowing rivers and the estuary areas with short residence times have a limited capacity to reduce the nitrogen load to the Baltic Sea. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
42. Methane processes in the coastal sediments and water column of the Baltic Sea
- Author
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Jukka-Pekka Myllykangas, University of Helsinki, Faculty of Biological and Environmental Sciences, Doctoral Programme in Interdisciplinary Environmental Sciences, Helsingin yliopisto, bio- ja ympäristötieteellinen tiedekunta, Ympäristöalan tieteidenvälinen tohtoriohjelma, Helsingfors universitet, bio- och miljövetenskapliga fakulteten, Doktorandprogrammet i tvärvetenskaplig miljöforskning, Lehtoranta, Jouni, Jilbert, Tom, and Hietanen, Susanna
- Subjects
akvaattiset tieteet - Abstract
Methane is a powerful greenhouse gas that contributes significantly to global warming. In aquatic systems, microbes in anoxic sediments are the main methane producers. However, due to effective oxidative filters in the sediments and the water column, most of the methane produced does not end up in the atmosphere. This study explores methane dynamics in the Baltic Sea from the open sea, to estuaries and specific microbial processes. Major inflow cycles control methane dynamics in the open Baltic by bringing oxygen to the deep basins, where methane typically accumulates in large amounts during stagnation. The introduction of oxygen during a major inflow in 2014–2015 caused the disappearance of methane from the deep basins due to a combination of oxidation and displacement. However, the effects of the inflow were short-lived and methane started accumulating again in less than a year after the inflow. The coastal areas were more dynamic, and the primary source of methane varied with distance offshore. Near the river mouth of the studied estuarine system, methane brought in by the river was the most important source, whereas further offshore sedimentary methanogenesis fuelled by a legacy of eutrophication was the primary source. Atmospheric fluxes of methane were highest near the river mouth and decreased seawards, while bathymetry was the main control of sedimentary fluxes. Seasonality had a strong effect on methane dynamics, with methane concentrations generally increasing towards winter. However, as in the open Baltic, displacement also played a role at times, removing large amounts of methane at a time. While aerobic methane oxidation in the water column was the primary sink offshore, in the coastal areas anaerobic oxidation of methane (AOM) was by far the most important sink. Offshore, sulphate mediated AOM is expected to be the most important type of AOM. However in this study, metal mediated AOM was an equally important sink in the sediments. Both rates of AOM, and microbial community abundances, were highest below the main sulfidic zone in the sediment, pointing towards non-sulphate AOM pathways. Overall, eutrophication has had a large impact on methane dynam ics in the Baltic Sea. The legacy of past eutrophication fuels methanogenesis in the coastal areas to this day, despite reductions in nutrient and organic matter input from land, leading to enhanced atmospheric flux of methane. In the future, climate change will likely exacerbate methane emissions from the Baltic Sea. Metaani on voimakas kasvihuonekaasu, jolla on merkittävä vaikutus ilmaston lämpenemiseen. Vesiekosysteemeissä sitä muodostuu pääosin hapettomissa sedimenteissä, joista muodostuva kaasu pyrkii kohoamaan vesipatsaan läpi ilmakehään. Tehokkaat hapetusprosessit sedimentissä ja vesipatsaassa kuitenkin estävät suurinta osaa muodostuvasta kaasusta saavuttamasta ilmakehää. Tämä tutkimus tarkastelee Itämeren metaaniprosessien dynamiikkaa avomerellä, rannikkosedimenteissä ja metaania hapettavien mikrobiprosessien kannalta. Suolavesipulssit säätelevät metaanin esiintymistä Itämeren syvänteissä. Vuoden 2014 lopun suuri suolavesipulssi poisti tehokkaasti Gotlannin syvänteeseen aiemmin kertyneen metaanin, osin hapettumisen ja osin vesimassojen syrjäyttämisen kautta. Tämä vaikutus jäi kuitenkin lyhytaikaiseksi ja metaania havaittiin kertyvän jälleen syvänteisiin alle vuoden sisällä suolapulssista. Itämeren rannikkoalueet olivat metaaniprosesseiltaan avomerta dynaamisempia. Metaanin pääasiallinen lähde muuttui etäisyyden rannasta kasvaessa. Jokisuun lähistöllä jokiveden mukaan tuoma metaani oli tärkein metaanin lähde rannikkovesissä, siinä missä kauempana rannasta sedimenteissä tapahtuva metaanituotanto oli tärkein tekijä. Aiempien vuosikymmenten aikana tapahtuneen rehevöitymisen katsottiin vaikuttavan sedimentissä muodostuvia metaanimääriä lisäävästi. Eniten ilmakehään päätyi metaania jokisuun lähettyviltä ja määrät vähenivät kauempana rannasta. Sedimentistä vesipatsaaseen päätyvän metaanin määrään vaikuttivat eniten rannikon pohjatyyppi. Vuodenaikaisvaihtelu metaanin pitoisuuksissa niin vesipatsaassa kuin ilmakehäpäästöissäkin oli suurta, mutta yleisesti ottaen molemmat kasvoivat talvea kohti. Toisaalta kuten avomerelläkin, myös vesimassojen liikkeillä oli voimakas vaikutus veden metaanipitoisuuksiin. Siinä missä vesipatsaassa tapahtuva hapettuminen oli avomerellä tärkein metaanin nielu, rannikkoalueilla sedimenteissä tapahtuva hapetus olivat selvästi tärkein prosessi. Meriveden sulfaattipitoisuuden takia sulfaattipohjaisen metaanihapetuksen odotetaan yleensä voimistuvan korkeammissa suolapitoisuuksissa, mikä piti paikkansa tässäkin tutkimuksessa. Tämän lisäksi kuitenkin havaittiin myös, että syvemmällä sedimenteissä tapahtuvat metallipohjaiset metaanin hapetusreaktiot olivat vähintään yhtä tärkeitä tutkitulla alueella. Kaiken kaikkiaan rehevöitymisellä on suuri vaikutus Itämeren metaaniprosesseihin. Vaikka ravinnekuormitus valuma-alueilta onkin nykyisin vähäisempää, menneiden vuosikymmenten rehevöityminen vaikuttaa edelleen metaanin tuotantoa ja ilmakehäpäästöjä lisäävästi. Tämän lisäksi ilmastonmuutoksen aiheuttaman yhteisvaikutuksen voidaan odottaa lisäävän Itämeren metaanipäästöjä entisestään tulevaisuudessa.
- Published
- 2020
43. Autochthonous organic matter promotes DNRA and suppresses N2O production in sediments of the coastal Baltic Sea.
- Author
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Aalto, Sanni L., Asmala, Eero, Jilbert, Tom, and Hietanen, Susanna
- Subjects
- *
COASTAL sediments , *ORGANIC compounds , *NITROUS oxide , *DENITRIFICATION , *ESTUARIES - Abstract
Coastal environments are nitrogen (N) removal hot spots, which regulate the amount of land-derived N reaching the open sea. However, mixing between freshwater and seawater creates gradients of inorganic N and bioavailable organic matter, which affect N cycling. In this study, we compare nitrate reduction processes between estuary and offshore archipelago environments in the coastal Baltic Sea. Denitrification rates were similar in both environments, despite lower nitrate and carbon concentrations in the offshore archipelago. However, DNRA (dissimilatory nitrate reduction to ammonium) rates were higher at the offshore archipelago stations, with a higher proportion of autochthonous carbon. The production rate and concentrations of the greenhouse gas nitrous oxide (N 2 O) were higher in the estuary, where nitrate concentrations and allochthonous carbon inputs are higher. These results indicate that the ratio between nitrate and autochthonous organic carbon governs the balance between N-removing denitrification and N-recycling DNRA, as well as the end-product of denitrification. As a result, a significant amount of the N removed in the estuary is released as N 2 O, while the offshore archipelago areas are characterized by efficient internal recycling of N. Our results challenge the current understanding of the role of these regions as filters of land-to-sea transfer of N. • The availability of bioavailable carbon defines nitrate reduction end-product. • Estuaries with low bioavailable organic carbon can release high amounts of N2O. • Nitrogen is recycled through DNRA in the archipelago areas. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
44. Nutrient dynamics in eutrophic lakes : Effects of resuspension, macrophytes and oxygen
- Author
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Holmroos, Heidi, University of Helsinki, Faculty of Biological and Environmental Sciences, Department of Environmental Sciences, Helsingin yliopisto, bio- ja ympäristötieteellinen tiedekunta, ympäristötieteiden laitos, Helsingfors universitet, bio- och miljövetenskapliga fakulteten, miljövetenskapliga institutionen, Nõges, Peeter, Hietanen, Susanna, and Horppila, Jukka
- Subjects
akvaattiset tieteet - Abstract
The dynamics of phosphorus (P) and nitrogen (N) were examined in two (shallow and deep) eutrophic lakes. The effects of resuspension and macrophytes as well as oxygen availability were determined, as was the role of natural nitrogen (N) removal (denitrification). The effect of resuspension on the availability of N and P was examined in experimental columns in a shallow eutrophic lake. The release of soluble reactive P (SRP) from resuspended matter varied both seasonally and interannually, depending on the conditions in the lake. SRP release was most significant during periods of high primary production, probably due to pH-induced ligand-exchange reactions. The effect of resuspension on dissolved N was less clear, although resuspension also increased the concentrations of ammonium, nitrite and nitrate during some of the experiments. The studies also showed that strong resuspension decreases the total N to total P ratio in the water independently of the phase of the growing season. The nutrient dynamics were further studied among two different macrophyte stands (submerged and floating-leaved macrophytes) and in the open water. The concentration of combined nitrate and nitrite N (NOx N) decreased to the detection limit (PIENEMPI 2 µg l 1) at all of the stations during summer. Among the submerged macrophytes, the NOx N was depleted almost 2 months earlier than at the other stations, which restricted denitrification. The rate of denitrification was measured with the isotope-pairing technique in both lakes. In the shallow lake, denitrification was measured at the location of the resuspension experiments as well as at the macrophyte stations and adjacent open-water area. Denitrification was mainly dependent on the availability of NOx N and temperature, and also contributed to the changes observed in the total N to total P ratio in water during summer by removing substantial amounts of NOx N from the water. The effects of oxygen (O2) availability were studied in a deeper, stratifying lake, where the deeps were treated with continuous or pulsed aeration, or with no aeration. The SRP release in the deeps was linked with the O2 in the sediment and the SRP accumulated in the hypolimnion during the periods of anoxia. During the aeration pauses and pulses, the concentration of NOx N decreased and increased respectively and the concentration of ammonium varied contrastingly. Continuous aeration prevented the ammonium from accumulating and provided NOx N for denitrification to occur. Accordingly, denitrification showed higher rates during aeration. However, aeration also increased the temperature of the hypolimnion and thereby also the O2 consumption. Väitöskirjassa tutkittiin typen ja fosforin kiertoa kahdessa rehevässä järvessä. Matalassa Hiidenveden Kirkkojärvessä tehdyissä tutkimuksissa selvitettiin leville käyttökelpoisen fosforin ja typen saatavuutta tilanteessa, jossa järven pohjasedimenttiä sekoittuu vesipatsaaseen virtausten vaikutuksesta. Tutkimuksissa havaittiin, että vuodenajasta riippumatta sekoittuminen nosti ravinteiden kokonaispitoisuuksia vedessä, mutta kasveille sellaisenaan käyttökelpoisten liukoisten ravinteiden vapautumiseen vaikuttivat vedessä vallitsevat olosuhteet. Liukoisen fosforin vapautuminen oli merkittävintä loppukesällä, kun voimakkaat leväkukinnat olivat nostaneet veden pH-tasoa. Samalla järvellä tutkittiin myös vesikasvien (ulpukka ja kiehkuraärviä) vaikutusta ravinteiden kiertoon. Ravinnepitoisuudet olivat hyvin samankaltaisia ulpukkakasvustossa ja avovedessä, mutta ärviäkasvustossa veden ravinnepitoisuudet olivat huomattavasti muita pienempiä. Tulokset selittyvät kasvien erilaisilla ravinteidenoton mekanismeilla; ärviät voivat ottaa ravinteita myös lehdillään suoraan vedestä, kun taas ulpukat ottavat ravinteita pääsääntöisesti juuriensa avulla järven sedimentistä. Hapen vaikutuksia typen ja fosforin saatavuuteen tutkittiin Lahden Vesijärvessä, jonka syvänteitä hapetetaan Mixox-ilmastimilla. Tutkimuksessa havaittiin, että vaikka ilmastimet toimivat maksimiteholla, ei syvänteiden veteen alkanut kertyä happea. Ilmastuksen vaikutuksesta kuitenkin liukoinen typpi pysyi hapettuneessa nitraatti-muodossa. Yhdessä tutkimussyvänteessä tutkittiin myös pulssimaisen hapetuksen vaikutuksia. Pulssimaisesti käytettynä ilmastimet nostivat alusveden lämpötilaa vähemmän kuin jatkuva ilmastus, mutta ilmastustaukojen aikana veden nitraattityppi pelkistyi ammoniumtypeksi. Ammoniumtyppi jää veteen ja on näin ollen myöhemmin kasvien käytettävissä, kun taas nitraattimuotoinen typpi voi poistua vedestä luontaisen typenpoistoprosessin (denitrifikaatio) seurauksena. Luontaista typenpoiston nopeutta tutkittiin kummassakin järvessä. Tutkimusten perusteella typenpoistoon käytettävän nitraattimuotoisen typen saatavuus määräsi kesän aikana typenpoistonopeuden. Keväällä ja myöhään syksyllä kylmyys nousi nitraatin saatavuutta tärkeämmäksi rajoittavaksi tekijäksi.
- Published
- 2014
45. The roles of nitrification and nitrate reduction pathways in nitrogen cycling of Baltic Sea
- Author
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Jäntti, Helena, University of Helsinki, Faculty of Biological and Environmental Sciences, Department of Environmental Sciences, Aquatic Sciences, Helsingin yliopisto, bio- ja ympäristötieteellinen tiedekunta, ympäristötieteiden laitos, Helsingfors universitet, bio- och miljövetenskapliga fakulteten, miljövetenskapliga institutionen, Voss, Maren, Hietanen, Susanna, and Leskinen, Elina
- Subjects
akvaattinen biogeokemia - Abstract
The Baltic Sea is one of the largest brackish water bodies in the world. Primary production in the Baltic Sea is limited by nitrogen (N) availability with the exception of river outlets and the northernmost phosphorus limited basin. The excess human induced N load from the drainage basin has caused severe eutrophication of the sea. The excess N loads can be mitigated by microbe mediated natural N removal processes that are found in the oxic-anoxic interfaces in sediments and water column redoxclines. Such interfaces allow the close coupling between the oxic nitrification process, and anoxic denitrification and anaerobic ammonium oxidation (anammox) processes that lead to the formation of molecular nitrogen gas. These processes are governed by various environmental parameters. The effects of these parameters on N processes were investigated in the northern Baltic Sea sediments. During summer months when the sediment organic content is at its highest, nitrification and denitrification reach their maximum rates. However, nitrification had no excess potential, which was probably because of high competition for molecular oxygen (O2) between heterotrophic and nitrification microbes. Subsequently, the limited nitrate (NO3-) availability inhibited denitrification. In fall, winter and spring, nitrification was limited by ammonium availability and denitrification limited by the availability of organic carbon and occasionally by NO3-. Anaerobic ammonium oxidation (anammox) was not an important N removal process in the northern Baltic Sea. Modeling studies suggest that when hypoxia expands in the Baltic Sea, N removal intensifies. However, the results of this study suggest the opposite because bottom water hypoxia (O2< 2 ml l-1) decreased the denitrification rates in sediments. Moreover, N was recycled by the dissimilatory nitrate reduction to ammonium (DNRA) process instead of being removed from the water ecosystem. High N removal potentials were found in the anoxic water column in the deep basins of the Baltic Proper. However, the N removal in the water column appeared to be limited by low substrate availability, because the water at the depths at which the substrate producing nitrification process occurred, rarely mix with the water at the depths at which N removal processes were found. Overall, the natural N removal capacity of the northern Baltic Sea decreased compared to values measured in mid 1990s and early 2000. The reason for this appears to be increasing hypoxia. Rehevöitynyt Itämeri- Typpiravinteiden poistokyky Suomenlahdella on heikentynyt Itämeri on yksi maailman rehevöityneimmistä meristä. Rehevöityminen ilmenee vuotuisina laajoina sinileväkukintoina ja pohjan happikatona. Yksi tärkeimmistä rehevöitymistä aiheuttavista tekijöistä on valuma-alueelta tuleva liiallinen typpiravinteiden määrä. Typpiravinteiden rehevöittävän vaikutuksen on ajateltu vähenevän luonnollisesti meren mikrobiprosesseissa. Julkaistavan väitöstutkimuksen tulokset kuitenkin osoittavat, että Suomenlahdella luonnollisen typenpoiston merkitys on vähäinen. Lisäksi tulokset vahvistavat typpikuormituksen vähentämisen tarpeellisuutta rehevöitymisen ehkäisyssä. Väitöstutkimuksessa selvitettiin typpeä poistavien mikrobiprosesseiden merkitystä ja niitä sääteleviä tekijöitä Suomenlahdella ja eteläisellä Itämerellä. Tutkimuksen tulokset osoittivat, että pohjasedimentin luonnollinen typenpoistokyky Suomenlahdella vaihtelee huomattavasti vuodenajoittain ja on pienimmillään keväällä, jolloin typpikuormitus valuma-alueelta on suurinta. Yhdeksänkymmentäluvun puolivälissä, jolloin Suomenlahden pohjan happitilanne oli nykyistä parempi, luonnollinen typenpoisto vähensi noin kolmanneksen maalta tulevasta typpikuormasta. Tällä hetkellä typpikuormasta poistuu luonnollisesti vain noin kymmenesosa. Tutkimuksessa osoitettiin rehevöitymisestä aiheutuvan pohjan happikadon pienentävän luonnollista typenpoistokykyä ja kiihdyttävän typen varastoitumista pohjasedimentteihin. Tämä johtaa rehevöitymisen noidankehään, jossa rehevöitymisestä aiheutunut hapettomuus lisää typen saatavuutta kasviplanktonille kiihdyttäen niiden kasvua. Hajotessaan lisääntynyt kasviplankton taas kuluttaa happea lisäten pohjien hapettomuutta. Vastaava mekanismi fosforiravinteen suhteen osoitettiin jo 40-luvun alkupuolella. Luonnollista typenpoistoa tutkittiin myös eteläisen Itämeren hapettomissa syvänteissä. Mittaukset osoittivat, että Itämeren syvänteiden hapettomassa vedessä on huomattava typenpoistopotentiaali, mutta potentiaali toteutuu vain kun syvänteiden hapelliset ja hapettomat vesimassat sekoittuvat keskenään. Jotta typenpoiston merkitys vedessä pystyttäisiin selvittämään tarkasti, vesimassojen sekoittumista säätelevät fysikaaliset prosessit pitäisi tuntea paremmin.
- Published
- 2012
46. Measuring nitrification in sediments--comparison of two techniques and three 15NO(-)3 measurement methods.
- Author
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Jäntti H, Leskinen E, Stange CF, and Hietanen S
- Subjects
- Data Interpretation, Statistical, Denitrification, Finland, Nitrogen Isotopes analysis, Oxidation-Reduction, Environmental Monitoring methods, Geologic Sediments chemistry, Nitrates analysis, Nitrification
- Abstract
Nitrification is a crucial process in sediment nitrogen cycling. We compared two (15)N tracer-based nitrification measurement techniques (isotope pairing technique (IPT) combined with (15)N nitrate pool dilution and (15)N ammonium oxidation) and three different (15)N analyses from bottom water nitrate (ammonia diffusion, denitrifier and SPINMAS) in a sediment mesocosm. The (15)N nitrate pool dilution technique combined with IPT can be used to quantify the in situ nitrification, but the minimum detection limit for the total nitrification is higher than that in the (15)N ammonium oxidation technique. The (15)N ammonium oxidation technique, however, is not applicable for sediments that have high ammonium content. If nitrate concentration and the amount of (15)N label in the sample are low, the (15)N nitrate analysis should be done with the denitrifier method. In higher (15)N concentrations, the less sensitive SPINMAS method can also be applied. The ammonia diffusion method is not suitable for bottom water (15)N nitrate analyses.
- Published
- 2012
- Full Text
- View/download PDF
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