Science Serving Maryland's Coasts

Audrey Barnett, Millersville University of Pennsylvania

Class Year: 

Project Title: 

The Effect of Humic Substances on Heterotrophic Dinoflagellate Population Growth


The hypothesis that humic substances stimulate the growth of dinoflagellate populations was tested in natural assemblages from the Chicamacomaco and Choptank Rivers. All humic additions were from a stock solution of Aldrich Humic Acid. Experiment 1 used samples from both rivers to see the effect of adding humics (HS), at a concentration of 5mg/L on heterotrophic and phototrophic dinoflagellate populations as well as on other parameters such as absorbance, pH, nutrient concentration, and Chl a concentration. Both trophic types of dinoflagellates decreased in density throughout the experiment, however, this decline was up to 50% lower in the HS treatments. This result was not consistent when the experiment was repeated. Nutrient Experiment 1 repeated this procedure for a Choptank sample, but added two treatments: one with nitrogen at 44μM and phosphorus at 1.8μM (NP), and one to which both nutrients and HS were added (HSNP). Heterotrophic dinoflagellates showed positive growth rates, however, they were 50% lower in the HSNP treatment then in the NP treatment. Phototrophs again showed a decline, however, the rate of decrease was slowed by 300% lower in the HSNP treatment than the NP treatment. Data, such as Chl a, indicate other parts of the community may be affected differently by the addition of HS.