Reconnaissance of Trace-Metal Loadings in Mahanoy Creek -- a Tributary to the Lower Susquehanna River, Pennsylvania, Affected by Acidic Mine Drainage

Reconnaissance sampling of a 7-mile-long reach above the mouth of Mahanoy Creek was conducted by the U.S. Geological Survey's National Water-Quality Assessment during base-flow conditions in September 1994. Metal-hydroxide precipitates coat rock surfaces in the reach. Samples of the coatings and water were collected at the upstream and downstream points of the reach and analyzed for the concentration of metals. Liver tissue from white sucker (Catostomus commersoni) collected at mid-reach also was analyzed.

Of 11 transition metals, 6 were present in detectable concentrations in water, sediment, and tissue. Transport of metals was dominated by suspended particulates or colloids in water. The particulates dissolved when a suspension was acidified, and thus were not sediment but suspended metal-hydroxide precipitates. Transport for the six detectable metals, estimated from total concentration in water and instantaneous discharge, from Mahanoy Creek to the Susquehanna River, ranged from 2,000 kilograms per day for Fe to 0.7 kilograms per day for Cu. Fe and Cu were transported primarily as suspended particulates greater than or equal to 0.45 µm in size. However, Mn transport of 1,400 kilograms per day was primarily as colloidal or dissolved Mn (less than 0.45 µm in size). A ranking of loadings was Fe > Mn > Zn > Ni > Co > Cu. Concentrations of metals in precipitate coatings in measured areas on rock surfaces and the total reach area were used to estimate a potential total storm loading to the Susquehanna River caused by scouring of the stream channel. Potential total storm loads from rock coatings, in kilograms, were calculated to be 9,100 (Fe), 1,700 (Mn), 100 (Zn), 35 (Co), 30 (Ni), and 7 (Cu). The potential total storm load of metals from rock coatings was small compared to the daily load from suspended particulates and solutes in water. Metals concentration in fish liver did not correlate with metal occurrence in coatings. A ranking of concentrations in fish liver was Fe > Zn > Cu > Mn > Cd > Co > Ni.

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