How many Carolina bays? An analysis of Carolina bays from USGS topographic maps at different scales

Carolina bays are elliptical or oval geomorphologic depressions often characterized by the presence of shallow ponds or swamps that occur in the Atlantic Coastal Plain of the US from Delaware to Florida. Explanations of their origin include meteor impacts, subsidence from subsurface karst, and thermokarst or thaw lakes. Quantification of the number of Carolina bays, which may help in forming theoretical explanations for their origin, is also elusive ranging from 10,000 to 500,000. This research demonstrates the large variations in numbers of Carolina bays as a function of mapping scale, the most important factor in enumerating topographic features. The systematic skills from analysts and cartographers in the USGS who mapped Carolina bays on two different scale map series in the national mapping program was exploited. The results indicate the number of Carolina bays is twenty times greater when enumerated at a 1:24,000 scale as compared to a 1:100,000 scale. An empirical model of the frequency of Carolina bays using different minimum mapping units (MMUs) was developed and applied to estimate bay frequency at any MMU. A more reliable estimate of the number of Carolina bays in the U.S. using an MMU of 0.1 ha is between 40,000 and 50,000.