The Hydrographic Setting for Mercury Sampling

U.S. Geological Survey

Fish mercury concentrations from the U.S. Geological Survey Report 2009-5109, "Mercury in Fish, Bed Sediment, and Water from Streams Across the United States, 1998-2005" are portrayed using graduated symbols overlaid on a detailed view of the high resolution National Hydrography Dataset.

The upstream drainage area is displayed as well as the hydrography within the drainage area and the calculated summation of the upstream network (arbolate sum). The downstream path is shown for a distance equal to the maximum upstream single-path distance. The mean annual flow of the surrounding hydrography calculated using the Unit Runoff Method (UROM) from the U.S. Environmental Protection Agency's NHDPlus is portrayed using line width related to cubic feet per second. This geographic portrayal of the upstream/downstream areas near the sample sites provides a good understanding of the hydrographic environment in which the samples were collected.

Courtesy of U.S. Geological Survey.

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