Warren et al 2018.pdf (4.12 MB)
Download fileEstimation of the width of the nearshore zone in Lake Michigan using eleven years of MODIS satellite imagery
journal contribution
posted on 2018-10-18, 00:00 authored by Glenn J. Warren, Barry M. Lesht, Richard P. BarbieroThe nearshore zone, that region of water directly influenced by its proximity to the coast, has
received increasing attention in recent years. The extent of the nearshore zone has been defined
by some constant descriptive feature: e.g., a specific depth or a particular distance offshore. This
type of definition does not allow for the dynamic nature of the relationship between the land and
water and how it may be influenced by local, seasonal, or transient effects. Here satellite
observations examined evaluate how the width of the nearshore zone in Lake Michigan varies
with position along the coastline and with time. Satellite-derived estimates of chlorophyll
concentration along seventy-one shore-normal transects spaced approximately 10 km apart
around the lake were used to determine the width of the nearshore zone, defined as the point at
which the estimated chlorophyll concentration close to the shore approaches the more-uniform
offshore concentration. Of a total of 23,807 transects extracted from MODIS observations made
between 2003 and 2013, we successfully fit a bi-linear model relating chlorophyll concentration
to distance offshore to 15,996. We found that the width of the nearshore zone is variable, both
seasonally and spatially. Although the overall median width of 4.5 km (mean width 5.3 km)
closely corresponds to the 5 km value used in a number of Great Lakes studies including Lake
Michigan, ten percent of the estimates are greater than 8.9 km, likely representing times of
enhanced mixing and transport of nearshore waters into the offshore.