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Lake Michigan: Nearshore variability and a nearshore-offshore distinction in water quality
Citation:
Yurista, P., J. Kelly, A. Cotter, S. Miller, AND J. Van Alstine. Lake Michigan: Nearshore variability and a nearshore-offshore distinction in water quality. JOURNAL OF GREAT LAKES RESEARCH. International Association for Great Lakes Research, Ann Arbor, MI, 41(1):111-122, (2015).
Impact/Purpose:
This paper uses comprehensive data to provide a holistic view of Lake Michigan nearshore-offshore waters. The designation of distinct regions serves as a tool for efficiently compartmentalizing regions of the lake to improve our monitoring (targeted sample sites), assessment (confidence levels), and knowledge base in the functioning of the Great Lakes.
Description:
We conducted a high-resolution survey of the Lake Michigan nearshore using towed electronic instrumentation and fixed station sampling (1049 km at the approximate 20-m depth contour and grab samples at 15 sites). The principal variability in the alongshore reach was generally represented across large reaches (over 100s km) with local variability (5-10 km) much smaller. We found that the spatial patterns in some water quality parameters were strongly correlated with adjacent landscape characterization. The stressors most frequently retained in step-wise regression models for each water quality parameter were population density factors, followed by agricultural-chemical factors, then land cover attributes. Specific conductivity had the greatest amount of variability explained by landscape character (83%) with chlorophyll next (46%), and followed by beam attenuation (30%). We combined our chemistry samples with the recent National Coastal Condition Assessment (2010 NCCA) and compared the nearshore chemistry data with the Great Lakes National Program Office (GLNPO) offshore fixed monitoring sites. There was a significant distinction in both mean values and variability between the nearshore (<30 m) and offshore waters. We also used historical data to compare patterns over time in a nearshore-offshore relationship. The nearshore waters were generally higher in concentrations (exception NO2/3) than the offshore and have changed over the years with the same pattern of declining concentrations observed in the offshore.
