Lake Superior: Nearshore variability and a landscape driver concept

Spatial variation is well known to exist in water quality parameters of the Great Lakes nearshore; however, strong patterns for extended reaches also have been observed and found to be robust across seasonal time frames. Less is known about robustness of inter-annual variation within parameters for water quality in the nearshore. We have conducted high-resolution surveys with towed electronic instrumentation in nearshore areas of Lake Superior and have combined several seasons (2001-2005) of measurements from multiple research efforts to investigate how spatial variation compares across years. The combined survey tows ranged across approximately 1200 km of Lake Superior's south shore. In addition to the survey tracks, we also sampled fixed stations to collect calibration data and other parameters not observed by the in situ electronic sensors. The towed sensor data provided information on the spatial and temporal variability of water quality parameters along the nearshore. We found a consistent spatial pattern over time along the south shore of Lake Superior. Nearshore water quality parameters were analyzed with respect to landscape characteristics of the adjacent watersheds (US only) using multivariate stepwise regressions and found to correlate to landscape characterization. The stressor categories of landscape character that best described the nearshore parameters were agriculture-chemical usage and land-cover attributes. Peak nearshore values corresponded with landscape position that had the most altered landuse character (e.g. Duluth/Superior region). The landscape character appears to drive and maintain the spatial pattern in nearshore water quality parameters.