Bio-optical properties and primary production of Lake Michigan: Insights from 13-years of SeaWiFS imagery

Thirteen years of SeaWiFS data (1998-2010) from the early spring isothermal period (March-April) were used to determine trends of water attenuation coefficient (K-dPAR), chlorophyll a (Chl a), Photosynthetic Available Radiation (PAR), and modeled primary production in southern Lake Michigan. Surface PAR values remained unchanged between 1998 and 2010, but there was an 18-22% drop in K-dPAR during the March/April isothermal period as water clarity increased. This transparency increase was accompanied by a 41-53% decline in Chl a concentration (pg . L-1) and a 42-46% decline in modeled primary production (Great Lakes Primary Production Model). These changes were most pronounced in 2001-2003 which coincided with the period of initial colonization of the quagga mussels. Statistically significant spatial differences were noted in Chl a (mu g . L-1) concentrations between mid-depth (z = 30-90 m deep), and offshore (z > 90 m deep) waters. Chi a concentrations in the mid-depth region (30-90 m) decreased at a higher rate compared to offshore waters (>90 m) likely as a result of filtration activities of quagga mussel. (C) 2014 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.