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A 400-m2 beaver pond on Cabbage Gulch (Deer Lodge County, MT) was investigated for its retention of total recoverable (TR) and dissolved arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), zinc (Zn), and total suspended solids (TSS) during three storm water runoff events in the summer of 2013. Water samples were collected and flow rates were measured at monitoring stations above and below the pond. Decreases in TR metals concentrations were -17 percent for As (that is, As concentrations increased), 10 percent for Cu, 7 percent for Pb, and 27 percent for Zn. Total recoverable metals retained in the pond, on a mass basis, were 24 .percent for As, 47 percent for Cu, 45 percent for Pb, and 55 percent for Zn. The average retention was 49 percent (by mass) for TR Cu, Pb, and Zn. Twenty-four percent of the influent TR Cu and TR Zn loads were retained because the metals were suspended in the pond with stored storm water. An additional 27 percent of the influent TR Cu and TR Zn loads settled out of the water during the sampling periods. Arsenic retention was low because all of the As was in the dissolved phase and no As could settle out. Total suspended solids concentrations decreased by 2 percent and TSS mass retention was 41 percent.


Originally published in Intermountain Journal of Sciences, Vol. 21, No. 1-4, December 2015, pp. 38-46.