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Sampling Along Human Pressure Gradients in the Coastal Great Lakes

Nicholas P. Danz 1, Gerald J. Niemi 1,2, Ronald R. Regal 3, Lucinda B. Johnson 1, Tom Hollenhorst 1, Terry Brown 1, and Valerie Brady 1

1 Center for Water and the Environment, Natural Resources Research Institute, University of Minnesota Duluth, 5013 Miller Trunk Highway, Duluth, MN, 55811, USA
2 Department of Biology, University of Minnesota Duluth, 10 University Drive, Duluth, MN, 55811, USA
3 Department of Mathematics and Statistics, University of Minnesota Duluth, 10 University Drive, Duluth, MN, 55811, USA

The goal of our work is to develop indicators that both estimate ecological condition and suggest plausible causes of ecosystem degradation for Great Lakes coastal ecosystems. Understanding the relationship between human disturbance and ecological response is essential to the process of indicator development. Sampling designs for large-scale observational studies to develop indicators should explicitly consider how to select sites across important pressure gradients. In the Great Lakes, the major types of human pressures include nutrient inputs, exotic species, contaminants, sedimentation, atmospheric deposition, land use, and human population growth. An impediment for distributing sampling effort across such gradients is that the gradients are not quantified prior to site selection. We used over 200 publicly available variables to partially characterize six types of human pressures for the U.S. Great Lakes basin. To reflect the influence of upstream human activities on coastal ecosystem condition, we used a watershed-based approach to divide the coastline into 762 units, each consisting of a coastline reach and a drainage area. The pressure variables were categorized into six types of human pressure and summarized for each coastal unit using a geographic information system (GIS). Redundancy within the six pressure categories was reduced with principal components analysis, and the principal components (PCs) were interpreted as integrated measures of human pressure. The PCs were used to assess relative risks to coastal ecosystems and to distribute sampling effort in the Great Lakes.

Keywords: human pressure gradients, Great Lakes, sample design, GIS

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