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| Titel |
Effects of nitrate fertilization on CO2 and CH4 concentrations in small boreal lakes |
| VerfasserIn |
Marcus Klaus, Ann-Kristin Bergström, Jan Karlsson |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250075342
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| Zusammenfassung |
| Ecosystem functioning in boreal lakes is largely affected by atmospheric nitrogen loading
enhanced by anthropogenic activities. Additional deposition of nitrate entering these systems
affects pelagic metabolic processes and thus the production and consumption of
aquatic greenhouse gases. This study assesses the effect of nitrate fertilization on
concentrations of dissolved carbon dioxide (CO2) and methane (CH4) in six small lakes
in northern Sweden (area: 1.0-4.8 ha, max. depth: 4.5-8.5 m) with three different
levels of dissolved organic carbon (DOC) concentrations (clear lakes: 7 mg l-1,
medium brown lakes: 13 mg l-1, dark brown lakes: 18 mg l-1). A whole lake
fertilization experiment was carried out utilizing a Before-After-Control-Impact (BACI)
design with one reference year (2011) and one impact year (2012); including one
control lake and one impact lake for each DOC level. During 2012, the impact lakes
were fertilized with potassium nitrate once in March and biweekly from June to
September. Fertilization caused epilimnion total nitrogen concentration to increase by
around 10% in the impact lakes relative to the reference year while it decreased
by around 20% in the control lakes. From June to September, epilimnion water
was sampled biweekly by grab sampling and analyzed in the field by an infrared
gas analyzer or in the laboratory using a gas chromatographer. Three additional
samples were taken along a depth profile on three occasions. In the reference year,
concentrations of CO2 and CH4 did not differ significantly between control and impact lakes
(p>0.05). In the impact year, epilimnion CO2 concentrations were significantly higher
compared to the reference year in all medium and dark brown lakes. Fertilization
mostly caused a slight reduction in CO2 and CH4 concentrations in the impact lakes
relative to the control lakes. This effect was not significant but most pronounced and
coherent across the whole water column in clear lakes. In clear lakes, CO2 and CH4
concentrations may have been more sensitive to internal primary production affected by
fertilization rather than by external inputs of CO2 and CH4. In turn, external gas
inputs not affected by fertilization may have been relatively more important for
pelagic gas concentrations in brown lakes. The results suggest that increased nitrogen
loading may have only a minor effect on CO2 and CH4 concentrations in boreal
lakes relative to natural interannual variation. Our experiment also shows that the
effect of nitrogen addition may depend on the trophic state of small boreal lakes. |
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