SS3.10 Ecological Implications of Terrestrial Inputs into Lakes and Ponds
Date: Tuesday, June 11, 2002
Time: 11:00:00 AM
Location: Esquimalt
 
LennonJT, Dartmouth College, Hanover, NH, 03755, USA, Jay.T.Lennon@Dartmouth.EDU
 
EXPERIMENTAL EVIDENCE THAT TERRESTRIAL ORGANIC MATTER MODIFIES PLANKTON METABOLISM
image
Terrestrial-derived dissolved organic matter (DOM) is one of the largest C pools in freshwater ecosystems, typically exceeding the total living biomass. As such, DOM may play a major role in the functioning of pond ecosystems. In particular, terrestrial DOM inputs may determine whether a pond system is a CO2 source (net-heterotrophic) or sink (net-autotrophic). I will discuss how plankton metabolism responded to a terrestrial DOM gradient in two New England ponds. Along the DOM gradient, CO2 flux and bacterial production increased (200% and 600%, respectively), while O2 concentrations declined (20%). Physical and chemical changes associated with DOM could have influenced these responses; DOM enrichment increased light attenuation and N and P concentrations. However, experimental results showed that these factors alone could not explain the observed shifts in plankton metabolism. Experimental light reduction (without DOM) increased CO2-flux only slightly (10%), while inorganic N and P additions (without DOM) made plankton systems net-autotrophic. This study supports the hypothesis that inputs of terrestrial DOM cause net-heterotrophy in freshwater plankton ecosystems.