Problems with using chlorophyll a to predict primary production in the Western Basin of Lake Erie

Session: Great Lakes Primary Production: Methods, Results, and Management Implications (1)

Erin Hillis, University of Windsor- GLIER, [email protected]
Christina Fasching, Trent University, [email protected]
Marguerite Xenopoulos, Trent University, [email protected]
Gordon Douglas Haffner, Great Lakes Institute for Environmental Research, Univ. of Windsor, [email protected]

Abstract

One of the greatest threats to aquatic systems is accelerated eutrophication, which is an unnatural increase in primary production resulting in high phytoplankton biomass.  In response to eutrophication in Lake Erie in the 1960s, TP loadings were reduced by the mid-1980s, corresponding with a decline in phytoplankton biomass and chlorophyll a.  However, primary production was not measured during this time, despite evidence that the ratio of primary production to chlorophyll a, known as the assimilation efficiency, can vary if phytoplankton pigmentation adapts to changes in light and nutrient availability.  Since nutrient concentrations and light penetration have changed dramatically in Lake Erie, particularly in the Western Basin, the relationship of chlorophyll a with primary production warrants further study. In 2014 and 2015, monthly (May-October) measurements of chlorophyll a and primary production were taken at a nearshore and offshore site in the Western Basin.  Combined with historical measurements, chlorophyll a only predicted 28% of the variation in primary production, despite a significant (p < 0.05) relationship between the two variables.  There was also considerable seasonal and long-term variation in the assimilation efficiency.  This questions whether chlorophyll a should be used as a proxy measurement for primary production in the Western Basin.  

Twitter handle of presenter
@ErinHillis7