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- Title
Nitrous oxide and methane seasonal variability in the epilimnion of a large tropical meromictic lake (Lake Kivu, East-Africa).
- Authors
Roland, Fleur; Darchambeau, François; Morana, Cédric; Borges, Alberto
- Abstract
We report a data-set of monthly vertical profiles obtained from January 2012 to October 2013, from the surface to 70 m depth of nitrous oxide (NO) and dissolved methane (CH) in Lake Kivu, a large and deep meromictic tropical lake (East Africa). Vertical variations of NO were modest, with ranges of 6-9 and 0-16 nmol L in surface and bottom waters, respectively, and occasionally peaks of NO (up to 58 nmol L) were observed at the oxic-anoxic interface. On the contrary, steep vertical gradients of CH were observed with values changing several orders of magnitude from surface (19-103 nmol L) to 70 m (~113,000-520,000 nmol L). Seasonal variations of CH were caused by annual cycles of mixing and stratification, during the dry and rainy seasons, respectively. This mixing allowed the establishment of a thick oxic layer (maximum 65 m deep), leading to decreased CH concentrations (minimum of 8 nmol L), presumably due to bacterial CH oxidation. During the stratification period, the oxic mixed layer was thinner (minimum 25 m deep), and an increase of CH concentrations in surface waters was observed (maximum of 103 nmol L), probably due to a lower integrated CH oxidation on the water column. Lake Kivu seasonally alternated between a source and a sink for atmospheric NO, but on an annual scale was a small source of NO to the atmosphere (on average 0.43 µmol m day), while it was a small source of CH to the atmosphere throughout the year (on average 86 µmol m day). Vertical and seasonal variations of NO are discussed in terms of nitrification and denitrification, although from the present data-set it is not possible to unambiguously identify the main drivers of NO production.
- Subjects
LAKE Kivu (Congo &; Rwanda); NITROUS oxide &; the environment; METHANE in water; NITRIFICATION; SEASONAL physiological variations
- Publication
Aquatic Sciences, 2017, Vol 79, Issue 2, p209
- ISSN
1015-1621
- Publication type
Article
- DOI
10.1007/s00027-016-0491-2