Effects of micro-nutrients and major nutrients on the growth and species composition of natural phytoplankton populations

Graduation date: 1977Large-volume (20-liter) bioassays were carried out in order to\ud assess the effects of major nutrients and micro-nutrients on\ud natural phytoplankton populations in water collected from a site\ud close to the mouth of Yaquina Bay, Oregon. Seven long-term\ud experiments were conducted during the years 1975-1976. A stripping\ud technique employing activated carbon was used to reduce the trace\ud metal and dissolved organic load of a portion of the water. Various\ud combinations of major nutrients (nitrate, phosphate, and silicate)\ud and micro-nutrients (trace metals and vitamins) were added to both\ud the carbon-stripped and the non-carbon-stripped water in order to\ud assess the effects of various nutrient substances on the growth\ud rate, biomass yield, and species composition of the phytoplankton\ud populations which developed from small natural inocula.\ud The major nutrients and the micro-nutrients appear to have\ud fundamentally different effects on the species composition and\ud population growth characteristics of the phytoplankton. The\ud micro-nutrients had marked systematic effects on the species composition\ud of the phytoplankton populations which developed in the\ud experimental vessels, while the major nutrients had minimal effects\ud on species composition. The micro-nutrients appeared essential for\ud the achievement of maximal population growth rates and minimal lags,\ud while the major nutrients had no effect on growth rates or lags.\ud Both the major nutrients and micro-nutrients had significant\ud effects on the final biomass yields. There were seasonal variations\ud in the control of final biomass yields by major nutrients and micro-nutrients