 |
| Titel |
Interactive effects of vertical mixing, nutrients and ultraviolet radiation: in situ photosynthetic responses of phytoplankton from high mountain lakes in Southern Europe |
| VerfasserIn |
E. W. Helbling, P. Carrillo, J. M. Medina-Sánchez, C. Durán, G. Herrera, M. Villar-Argaiz, V. E. Villafañe |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 2 ; Nr. 10, no. 2 (2013-02-14), S.1037-1050 |
| Datensatznummer |
250017517
|
| Publikation (Nr.) |
 copernicus.org/bg-10-1037-2013.pdf |
|
|
|
|
|
| Zusammenfassung |
| Global change, together with human activities, has resulted in increasing
amounts of organic material (including nutrients) that water bodies receive.
This input further attenuates the penetration of solar radiation, leading to
the view that opaque lakes are more "protected" from solar ultraviolet
radiation (UVR) than clear ones. Vertical mixing, however, complicates this
view as cells are exposed to fluctuating radiation regimes, for which the effects
have, in general, been neglected. Furthermore, the combined impacts of mixing,
together with those of UVR and nutrient inputs are virtually unknown. In this
study, we carried out complex in situ experiments in three high mountain
lakes of Spain (Lake Enol in the National Park Picos de Europa, Asturias, and
lakes Las Yeguas and La Caldera in the National Park Sierra Nevada, Granada),
used as model ecosystems to evaluate the joint impact of these climate change
variables. The main goal of this study was to address the question of how
short-term pulses of nutrient inputs, together with vertical mixing and
increased UVR fluxes modify the photosynthetic responses of phytoplankton.
The experimentation consisted in all possible combinations of the following
treatments: (a) solar radiation: UVR + PAR (280–700 nm) versus PAR (photosynthetically active radiation)
alone (400–700 nm); (b) nutrient addition (phosphorus (P) and nitrogen
(N)): ambient versus addition (P to reach to a final concentration of
30 μg P L−1, and N to reach N:P molar ratio of 31); and (c)
mixing: mixed (one rotation from surface to 3 m depth (speed of
1 m 4 min−1, total of 10 cycles)) versus static. Our findings suggest
that under ambient nutrient conditions there is a synergistic effect between
vertical mixing and UVR, increasing phytoplankton photosynthetic inhibition
and excretion of organic carbon (EOC) from opaque lakes as compared to algae
that received constant mean irradiance within the epilimnion. The opposite
occurs in clear lakes where antagonistic effects were determined, with mixing
partially counteracting the negative effects of UVR. Nutrient input, mimicking
atmospheric pulses from Saharan dust, reversed this effect and clear lakes
became more inhibited during mixing, while opaque lakes benefited from the
fluctuating irradiance regime. These climate change related scenarios of
nutrient input and increased mixing, would not only affect photosynthesis and
production in lakes, but might also further influence the microbial loop and
trophic interactions via enhanced EOC under fluctuating UVR exposure. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|