Effekten av kvävegödsling på gasproduktionen vintertid i boreala sjöar | Effects of nitrogen fertilization on the production of CO2 and CH4 during winter in boreal lakes
2013
Robygd, Joakim
To investigate effects of nitrogen on in-lake CO2 and CH4 production during winter, three pair of lakes was subject for a fertilizing experiment in which one lake in each pair was fertilized with nitric acid (HNO3) directly into the water column in the summer of 2012. The lakes in each pair are assumed to be morphologically, hydrologically and biologically similar, that is, the non-fertilized lakes are considered references. The pairs do differ in one major way by being progressively less humic, going from around 25 mg/l to 10 mg/l DOC. Sampling and analysis was carried out at the end of the frozen period in 2013. Results show a significantly higher concentration of both CO2 (p<0,001) and CH4 (α=0,1, p=0,053) between impact and reference sites in the two less humic pairs. The very humic pair generated lower concentrations of CO2 and CH4 after fertilization in the impact site compared to the reference site. The lakes with low and intermediate humic content are assumed to have increased their biomass production during the ice-free season which contributed to elevated amount of available organic carbon to be mineralized to gas during winter. The absence of a fertilization effect in the very high humic lake is most likely due to light-limitation being the key limitator in that lake, thus preventing an elevated biomass production during the ice-free season. Northern boreal lakes can be expected to react differently to elevated N-deposition and runoff depending on the amount of catchment derived terrestrial carbon transported to the lake.
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