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| Titel |
Study of the lacustrine phytoplankton productivity dependence on solar radiation, on the basis of direct high-frequency measurements |
| VerfasserIn |
Maria Provenzale, Anne Ojala, Jouni Heiskanen, Kukka-Maaria Erkkilä, Ivan Mammarella, Pertti Hari, Timo Vesala |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131272
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| Publikation (Nr.) |
 EGU/EGU2016-11663.pdf |
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| Zusammenfassung |
| One of the main components of the carbon cycle in lakes is phytoplankton. Its in situ
photosynthesis and respiration are usually studied with traditional methods (dark and light
bottle method, 14C labelling technique). These methods, relying on sampling and incubation,
may lead to unrealistic results. They also have a poor temporal resolution, which does not
allow the non-linear relationship between photosynthetically active solar radiation (PAR)
and photosynthesis to be properly investigated. As a consequence, the phytoplankton net
primary productivity (NPP ) cannot be parameterised as a function of ambient
variables.
In 2008 an innovative free-water approach was proposed. It is based on non-dispersive
infrared air CO2 probes that, by building an appropriate system, can be used to measure the
CO2 concentration in the water at a high-frequency. At that time, the method was tested
only on 3 days of data. Here, we deployed it on a boreal lake in Finland for four
summers, in order to calculate the NPP and verify its dependence on PAR. The set-up
was completed by an eddy-covariance system and water PAR and temperature
sensors.
In analogy with the procedure typically used in terrestrial ecology, we obtained the
phytoplankton NPP computing the mass balance of CO2 in the mixed layer of the lake, i.e.
the superficial layer where the conditions are homogeneous and most of the photosynthetic
activity takes place.
After calculating the NPP , we verified its dependence on PAR. The theoretical model we
used was a saturating Michaelis-Menten curve, in which the variables are water temperature
and PAR. The equation also contains parameters typical of the phytoplankton communities,
which represent their maximum potential photosynthetic rate, their half-saturation constant
and their basal respiration. These parameters allow the NPP to be parameterised as a
function of T and PAR.
For all the analysed year, we found a very good agreement between theory and data (R2
ranged from 0.80 to 0.88) and we were able to estimate the phytoplankton communities
parameters.
In conclusion, the approach used proved to be suitable for productivity studies
in aquatic ecosystems. In our opinion, it represents a great improvement over the
traditional methods and should be widely adopted. This would reduce the gap in the
CO2 exchange measurements between aquatic and terrestrial ecology, where high
frequency measurements are very common. It would also help us achieve a better
understanding of the biological processes behind the CO2 exchange and would
expand our knowledge on the carbon cycle in aquatic ecosystems, which is still
limited. |
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