Seasonality of Nearshore and Offshore Size Fractionated Primary Productivity in Western Lake Ontario

Session: State of Lake Ontario: 2003-2018 CSMI Overview (1)

Heather Niblock, GLLFAS, DFO, [email protected]
Mohiuddin Munawar, Fisheries & Oceans Canada, [email protected]
Mark Fitzpatrick, Fisheries & Oceans Canada, [email protected]

Abstract

Primary production sets the maximum carrying capacity of a large aquatic systems like Lake Ontario.  Using a size fractionated ¹⁴C tracer technique, rates of primary productivity were determined at two stations in western Lake Ontario.  Estimates were made either monthly or biweekly from early May to late October.  Individual rates measured between 0.4 and 21 mg C m^-3 hr^-1 and the May to October annual averages ranged from 4.8 (2013) to 6.6 mg C m^-3 hr^-1 (2017) at the offshore station (60m) and from 5.5 (2016) to 8.6 mg C m^-3 hr^-1 (2017) at the nearshore station (7m). At both stations and in all years except 2017, the productivity was mainly nanoplankton (2-20 µm) followed by picoplankton (<2µm)  and netplankton (>20µm).  In addition to variability between sites and years, there are also differences within the water column related to light penetration, thermal structure and community composition. Additional sampling was undertaken in 2015 to measure productivity in the deep chlorophyll layer.  Seasonal differences in productivity will be related to differences in community structure and compared to lakewide CSMI results.