Great Lakes nearshore-offshore: Distinct water quality regions

We compared water quality of nearshore regions in the Laurentian Great Lakes to water quality in offshore regions. Sample sites for the nearshore region were from the US EPA National Coastal Condition Assessment and based on a criteria or sample-frame of within the 30-m depth contour or 5-km distance from the shoreline, whichever occurred first. The offshore sites were composed of US EPA Great Lakes National Program Office (GLNPO) annual monitoring sites. There was a contrast in both variability and mean values of water quality values between the nearshore and the offshore regions. Lake-by-lake the nearshore was more variable and had higher average parameter values than the offshore, except for NO2/3 which was lower in mean value. A subset of all sites was re-visited in supplemental years to explore temporal effects (57 nearshore sites in Lake Erie 2009 and for 67 nearshore sites in Lake Huron 2012). The operational sample-frame for nearshore water provided a reliable means for separating the lakes into two distinct and persistent water quality regions across years.