CORRELATING HABITAT QUALITY TO DOCK FREQUENCY: A MEASURE OF HUMAN IMPACT ON GLACIAL LAKES

The hypothesis of this study is that docks/piers cause a littoral and adjacent area impact whether through shading or, direct and indirect human actions on the flora and fauna within a 25-foot buffer zone of the structures and along the associated shoreline. We used a combination of ArcGIS and Google Earth Pro to study100 lakes of glacial origin (greater than 25 acres) in Iowa, 38 of which have one or more peers or docks. Research methodology consisted of visually inspecting subject lakes using Google Earth Pro to identify, enumerate and categorize structures; random sample ground truthing for verification of correct dock categorization from satellite/areal overhead views; random sample ground truthing to measure turbidity of the lakes; use of various data sources views to determine surface area of structures and their associated shoreline impact areas. We used data from the Midwest Glacial Lakes Partnership to generate a Cumulative Anthropogenic Stress Index (CASI), and predictors of natural origin (e.g., bedrock geology) to generate a Cumulative Natural Quality Index (CNQI). We found no correlation between dock frequency and either index (CASI or CNQI). We did find that high natural quality indicators were associated with growth of sport fish in lakes studied; high anthropogenic stress indices were associated with smaller growth rates of sport fish. We compared these growth factors with dock frequency and found a negative correlation. When dock frequency is high, growth indices (fish sizes) are lower. Initial comparisons of turbidity to dock frequency are inconclusive at this time. Total pier/dock surface area comparisons, with or without a buffer zone, as well as the shoreline impact area is not complete at this time. The next step will be to compare dock frequencies to a Shoreline Development Index. Turbidity measurements, taken using a standard secchi disk, are highly variable. Secchi depths range from 42.5cm (two separate lakes) to 85 cm (Five Island Lake). Using ArcGIS to identify the number and areal coverage of docks and piers on glacial lakes appears to provide some insight into habitat quality. It is possible that the technique could be used as a first pass filter to identify those lakes that are the best candidates for habitat restoration.