Methodology and Interpretation

Percent wetland within 120 meters of streams
The affects of runoff from areas adjacent on streams is strongly influenced by land cover type within approximately 120 meters of the streambank. Thus, the percentage of wetland cover within 120 meters of a stream is calculated by summing the total number of wetland land cover cells underneath stream segments in the reporting unit and within a four cell buffer (120 meters) and dividing by the stream corridor's total land area (i.e., all cells within 120 meters of streams minus those classified as water). Cells inside the cell buffer zone but outside of the reporting unit boundary are ignored. Wetlands may remove or reduce the amount of pollutants entering streams and lakes. Wetlands also provide habitat for a wide variety of plant and animal species. Other distances may be more appropriate, depending on the runoff chemical constituent(s), flow dynamics, soil conditions, stream channel morphology, and other landscape characteristics.

Quantile: Each class contains an approximately equal number (count) of features. A quantile classification is well-suited to linearly distributed data. Because features are grouped by the number within each class, the resulting map can be misleading, in that similar features can be separated into adjacent classes, or features with widely different values can be lumped into the same class. This distortion can be minimized by increasing the number of classes.

Metric input GIS data:

• United States Hydrologic Units (8-digit HUCs) - Metadata

• United States Coastal Change Analysis Program (CCAP) - Metadata

• United States National Elevation Dataset (NED) - Metadata