Importance of wind and river discharge in influencing nutrient dynamics and phytoplankton production in summer in the central Strait of Georgia

A cruise was conducted during August 6-14, 3 991 to investigate the dynam~cs of nutrients and phytoplankton pi-oduction in the central Strait of Georgld, British Columbia, Canada, dunng a period when strong stratification resulted In nitrogen-l~mited primary productivity. High resolution vertical profiles of salinity, temperature, fluorescence and nutrients (nitrate and phosphate) were taken daily along a transect. A wind event occurred on August 7 and a rapid increase in the Fraser River discharge took place from August 8 to 14 . The wind event mixed the water column and nutrients increased at the same time. Phytoplankton responded to the incrcdscb in nutrients and a bloom occurred soon after the wind event. The rapid increase in river discharge caused the entrainment of nltrate in the estuanne plume and, a s a result, a subsurface maxlmum of chl a was developed. Our results clearly demonstrated that summer phytoplankton productivity in the central Strait of Georgia is fueled by a supply of nutrients from the nitracline through vertical mixing induced by the interaction of winds, rlver discharge and tidal cycles. Of these 3 factors, winds are the most variable and therefore a summer with frequent wind events could result in higher than normal productivity. The mechanism for t h ~ s is that part of the nitracline was maintained above the euphotic zone due to various physical processes in spite of the strong stratification, and therefore, nutrients were frequently available for phytoplankton uptake caused by across-pycnocline mixing due to w ~ n d , rlver dischdrge and tides.

[1]  P. Harrison,et al.  Effects of a fluctuation in Fraser River discharge of primary production in the central Strait of Georgia, British Columbia, Canada , 1997 .

[2]  P. Harrison,et al.  Spring bloom in the central Strait of Georgia: interactions of river discharge, winds and grazing , 1996 .

[3]  J. Cloern.  PHYTOPLANKTON BLOOM DYNAMICS IN COASTAL ECOSYSTEMS' A REVIEW WITH SOME GENERAL LESSONS FROM SUSTAINED INVESTIGATION OF SAN FRANCISCO , 1996 .

[4]  P. Harrison,et al.  Entrainment of Nitrate in the Fraser River Estuary and its Biological Implications. II. Effects of Springvs.Neap Tides and River Discharge , 1995 .

[5]  P. Harrison,et al.  Entrainment of Nitrate in the Fraser River Estuary and its Biological Implications. I. Effects of the Salt Wedge , 1995 .

[6]  H. Kuosa,et al.  Late summer trophic conditions in the north-east Gulf of Finland and the River Neva Estuary, Baltic Sea. , 1993 .

[7]  S. G. Marinone,et al.  A Horizontally Resolving Physical–Biological Model of Nitrate Concentration and Primary Productivity in the Strait of Georgia , 1993 .

[8]  P. Clifford,et al.  A computer-based system for the acquisition and display of continuous vertical profiles of temperature, salinity, fluorescence and nutrients , 1991 .

[9]  F. Colijn,et al.  Evaluation of measurements and calculation of primary production in the Dogger Bank area (North Sea) in summer 1988 , 1991 .

[10]  P. Clifford,et al.  Nutrient and plankton dynamics in the Fraser River plume, Strait of Georgia, British Columbia , 1991 .

[11]  F. Colijn,et al.  Primary production of phytoplankton at a frontal zone located at the northern slope of the Dogger Bank (North Sea) , 1990 .

[12]  H. Ducklow,et al.  Nitrogenous nutrient transformations in the spring and fall in the Chesapeake Bay , 1990 .

[13]  T. Malone,et al.  Influences of river flow on the dynamics of phytoplankton production in a partially stratified estuary , 1988 .

[14]  C. Langdon,et al.  Short-term changes in the biology of a gulf stream warm-core ring: phytoplankton biomass and productivity , 1987 .

[15]  B. Cole,et al.  An empirical model for estimating phytoplankton productivity in estuaries , 1987 .

[16]  L. Legendre,et al.  Phytoplankton Responses To Vertical Tidal Mixing , 1986 .

[17]  M. Bowman,et al.  Tidal Mixing and Plankton Dynamics , 1986, Lecture Notes on Coastal and Estuarine Studies.

[18]  B. Cole,et al.  Significance of biomass and light availability to phytoplankton productivity in San Francisco Bay , 1984 .

[19]  L. Albright.  Heterotrophic Bacterial Biomasses, Activities, and Productivities Within The Fraser River Plume , 1983 .

[20]  Paul J. Harrison,et al.  Review of the Biological Oceanography of the Strait of Georgia: Pelagic Environment , 1983 .

[21]  P. Leblond.  The Strait of Georgia: functional anatomy of a coastal sea , 1983 .

[22]  W. Boynton,et al.  A COMPARATIVE ANALYSIS OF NUTRIENTS AND OTHER FACTORS INFLUENCING ESTUARINE PHYTOPLANKTON PRODUCTION , 1982 .

[23]  J. Stronach.  The Fraser River plume, Strait of Georgia , 1981 .

[24]  J. Stockner,et al.  Phytoplankton Ecology of the Strait of Georgia, British Columbia , 1979 .

[25]  J. Sévigny,et al.  Summer Plankton Distributions Associated with the Physical and Nutrient Properties of the Northwestern Gulf of St. Lawrence , 1979 .

[26]  R. Allyn Clarke,et al.  Introductory Dynamic Oceanography. , 1979 .

[27]  M. Sinclair.  Summer Phytoplankton Variability in the Lower St. Lawrence Estuary , 1978 .

[28]  R. Iverson,et al.  Summer phytoplankton blooms in Auke Bay, Alaska, driven by wind mixing of the water column1 , 1974 .

[29]  T. Parsons,et al.  Levels of Production in the Pelagic Environment of the Strait of Georgia, British Columbia: A Review , 1970 .

[30]  F. A. Richards,et al.  Determination of nitrate in sea water by cadmium-copper reduction to nitrite , 1967, Journal of the Marine Biological Association of the United Kingdom.

[31]  M. Waldichuk.  Physical Oceanography of the Strait of Georgia, British Columbia , 1957 .