Changes in the Optical Properties of Lake Michigan by the Invasive Species Dressina bugensis (Quagga Mussel)

Sara Schaal, Yang Xie, Timothy Zeidler, Francis Yankey

Abstract


The non-indigenous species Dressena bugensis (quagga mussel) became the dominant benthic bivalve in Lake Michigan by 2004 due to its rapid proliferation and extreme filtering abilities (Fahnenstiel, Nalepa, & Pothoven, 2010). Their takeover is re-engineering the physical and biogeochemical processes of Lake Michigan on an ecosystem scale. This study focused on their impact on the optical properties of the water column throughout the lake. Analyses were done using CTD data that was collected from 1993 – 2012 from three sampling stations. Based on photosynthetically active radiation (PAR) measurements in the water column, the extinction coefficient (ke) for every quarter meter depth interval was estimated, along with the depth of 1% light penetration for each CTD data set in the 19-year time span. A Student’s t-test was applied to test for a significant increase in the depth of 1% light penetration before and after the quagga mussel invasion, which found significance at the deep mid-lake station, and less pronounced changes at the near-shore stations. Analyses were also done to compare seasonal variation in the optical properties before and after the quagga mussel invasion, which further indicated significant changes at the deep mid-lake station, but less pronounced changes at near-shore sampling stations. Comparative analysis of the extinction coefficient, percent transmission, and fluorescence measurements suggests that detection of the presence of thin layers in the water column may be possible.


Keywords


Lake Michigan, light attenuation, 1% depth, quagga mussel

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