CS26 Organic Carbon Dynamics
Date: Thursday, June 13, 2002
Time: 10:30:00 AM
Location: Carson C
 
VähätaloAV,  University of North Carolina, Chapel Hill, USA, anssi_vahatalo@hotmail.com
Salonen, K, , University of Jyväskylä, Jyväskylä, Finland, arisalon@jyu.fi
Münster, U, , Tampere University of Technology, Tampere, Finland,  uwe.munster@tut.fi
Järvinen, M, , University of Helsinki, Helsinki, Finland, mujarvin@mappi.helsinki.fi
Wetzel, R, G, Univeristy of North Carolina, Chapel Hill, USA, rwetzel@unc.edu
 
PHOTOCHEMICAL TRANSFORMATION OF DISSOLVED ORGANIC MATTER PROVIDES BIOAVAILABLE NUTRIENTS IN A HUMIC LAKE
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The role of solar radiation on the transformation of DOM into inorganic and bioavailable forms was investigated in a humic boreal Lake Valkea-Kotinen. The concentration of nitrate + nitrite, inorganic phosphorus and carbon increased, but that of ammonium decreased in <0.2-µm filtered hypolimnetic water during 1-d exposures to solar radiation. Solar radiation increased the concentration of ammonium in epilimnetic water at the rate corresponding to atmospheric deposition of inorganic nitrogen. When indigenous bacteria of Lake Valkea-Kotinen were inoculated into exposed waters, bacteria achieved higher biovolume and productivity, and incorporated carbon, nitrogen and phosphorus at greater rates than those grown in non-exposed waters. Bacteria mineralized dissolved organic carbon 92-375% more in exposed than in non-exposed waters. Results showed that solar radiation transformed dissolved organic nitrogen, phosphorus and carbon during summer into forms readily available to phyto- and bacterioplankton. The photochemical supply of nutrients increased the production of bacterioplankton and can be expected also to increase production of phytoplankton. Therefore, transformation of allochthonous DOM by solar radiation contributes to the productivity of planktonic ecosystems.