Reprint Series No. 28

SEASONAL CONTROL OF PHYTOPLANKTON GROWTH BY ANTHROPOGENIC NUTRIENT LOADING IN PADILLA BAY NATIONAL ESTUARINE RESEARCH RESERVE

Gisele Muller-Parker and Emily R. Peele

 

December 1998

Bibliographic Citation
Muller-Parker, Gisele and Emily R. Peele. 1998. Seasonal control of phytoplankton growth by anthropogenic nutrient loading in Padilla Bay National Estuarine Research Reserve. Western Washington University, Bellingham, Washington and Shannon Point Marine Center, Anacortes, Washington. Final Report OCRM Project #NA470R088. Washington State Department of Ecology (Publication No. 00-06-018), Padilla Bay National Estuarine Research Reserve Reprint Series No. 28.

Abstract
The effects of nutrient (N,P) availability on phytoplankton growth, abundance and productivity were assessed seasonally from stations representing a freshwater slough, mid-bay, and outside Padilla Bay, WA in 1994 and 1995. We used a growth bioassay method with surface water samples containing phytoplankton (<153 um) incubated under natural light with three different inorganic nutrient additions (nitrogen, phosphate, nitrogen plus phosphate, and an ambient control). Under ambient nutrient levels, summer phytoplankton biomass approached 8 ug chlorophyll a L -1 growth rate was 1.3 d-1; during winter phytoplankton biomass averaged 0.5 ug chlorophyll a L -1 and growth rate was 0.5 d-1. Significant increases in phytoplankton growth and biomass occurred only in response to nitrogen enrichment, and only during spring and summer seasons. Phytoplankton from the mid-bay station showed the greatest response to nitrogen additions. Phosphorus stimulated the growth rate and final biomass yield of phytoplankton from the slough station once, in February 1995. Nutrients had no effect on phytoplankton growth and biomass yields during fall and winter. Light is likely to limit phytoplankton growth during these seasons.