Resumé
We investigated the influence of light, nutrients, and organic matter on
gross primary production (GPP), ecosystem respiration (R), and net
ecosystem production (NEP = GPP - R) in a dystrophic forest lake
and an open eutrophic lake. Forest vegetation reduced incoming
irradiance (20%) and wind speed (34%) in dystrophic Gribsø, having
thermal stratification 1 month longer than in eutrophic Slotssø. While
Gribsø had nutrient-limited phytoplankton during most of the year,
Slotssø only experienced nutrient depletion during algal blooms. Colored
dissolved organic matter (CDOM) absorbed most light (average 82%) in
dystrophic Gribsø, while phytoplankton and other particles absorbed most
light (45%) in eutrophic Slotssø. GPP and NEP were positively related
to irradiance in both lakes. However, because of higher CDOM absorbance,
three times more light was needed to attain autotrophy in Gribsø, being
net heterotrophic (NEP < 0) for 79% of all days, compared to 59% in
Slotssø. This difference vanished when NEP was scaled to light
absorption by pigments, although the eutrophic lake maintained a higher
photon yield. Metabolic rates varied much more in Slotssø, where higher
light and nutrient availability facilitated occasional phytoplankton
blooms, while low light and nutrient availability in Gribsø dampened
temporal variability. Both lakes were annually net heterotrophic with
similar annual areal rates (NEP, -14 mol C m−2). Net
heterotrophy in dystrophic Gribsø derives from high import of organic
carbon-rich water, while heterotrophy in eutrophic Slotssø is fueled by
degradation of sediment pools of organic matter accumulated under
previous hypereutrophic conditions, emphasizing the importance of lake
history on the contemporary metabolic state.
Originalsprog | Engelsk |
---|---|
Sider (fra-til) | 817-830 |
Antal sider | 14 |
Tidsskrift | Limnology and Oceanography |
Vol/bind | 55 |
Udgave nummer | 2 |
DOI | |
Status | Udgivet - mar. 2010 |
Emneord
- metabolism
- heterotrophy
- Lakes
Programområde
- Programområde 2: Vandressourcer