The influence of dissolved humic material (humic, fulvic and hydrophilic acids) on marine phytoplankton

Cynthia Ann Heil, University of Rhode Island


Blooms of nuisance phytoplankton species often occur after periods of extensive rainfall and river runoff which introduce large quantities of dissolved humic material into coastal waters. The influence of hydrophobic (humic and fulvic acids) and hydrophilic acids (extracted from river runoff by XAD-8 resin) on eight nuisance marine phytoplankton was investigated. Quantitative effects with hydrophobic and hydrophilic acid additions of 5-50 $\mu$g ml$\sp{-1}$ included stimulation of cell yield and growth rates in Asterionellopsis glacialis, Gymnodinium sanguineum, Heterosigma carterae, Prorocentrum micans, Prorocentrum minimum and Skeletonema costatum and decreased cell yield in Gyrodinium aureolum. Organic additions also influenced chain length of A. glacialis. Chain length increased from 5.51 ($\pm$1.05) cells chain$\sp{-1}$ in controls to 16.54 ($\pm$0.06) cells chain$\sp{-1}$ with 15 $\mu$g ml$\sp{-1}$ humic acid. Although growth rates of A. glacialis were correlated (r$\sp2$ = 0.73) with chain length, ANOVA analyses showed that approximately one-third of the variance in chain length was explained by growth rate while two-thirds of the variance in chain length was directly attributable to organic treatment. Oxygen-based respiration and production rates of P. minimum were increased by additions of $\ge$10 $\mu$g ml$\sp{-1}$ of fulvic and hydrophilic acids, suggesting that these compounds were actively respired. Humic acid additions had no significant effect upon respiration rates, but decreased oxygen evolution by 30% at concentrations $\ge$25 $\mu$g ml$\sp{-1}$ due to attenuation of PAR. A molecular fractionation experiment suggested that responses can be attributed to particular molecular weight fractions: responses to hydrophilic acids to the $<$500 molecular weight fraction, responses to fulvic acid to the $<$1,000 and $>$10,000 molecular weight fractions and responses to humic acid to a $>$500 to $>$10,000 range of molecular weights. Qualitative responses to organic additions included the induction of meiosis in four of five dinoflagellates, alternate vegetative cell forms in G. aureolum and G. sanguineum and aberrant cells in P. minimum, S. costatum and A. glacialis. Gamete production, fusion and planozygote development were documented for G. aureolum and tetrad cells and cysts of P. minimum were reported for the first time. ^

Subject Area

Biology, Oceanography|Biogeochemistry

Recommended Citation

Cynthia Ann Heil, "The influence of dissolved humic material (humic, fulvic and hydrophilic acids) on marine phytoplankton" (1996). Dissertations and Master's Theses (Campus Access). Paper AAI9723559.