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Mn biogeochemistry was studied from 1994 to 2003 in a small forested catchment in the central Czech Republic using the watershed mass balance approach together with measurements of internal stores and fluxes. Mn inputs in bulk deposition were relatively constant during a period of sharply decreasing acidic deposition, suggesting that the Mn source was terrestrial, and not from fossil fuel combustion. Mn inputs in bulk deposition and Mn supplied by weathering each averaged 13 mg m −2 year −1 (26 mg m −2 year −1 total input), whereas Mn export in streamwater and groundwater averaged 43 mg m −2 year −1 . Thus an additional Mn source is needed to account for 17 mg m −2 year −1 . Internal fluxes and pools of Mn were significantly greater than annual inputs and outputs. Throughfall Mn flux was 70 mg m −2 year −1 , litterfall Mn flux was 103 mg m −2 year −1 , and Mn net uptake by vegetation was 62 mg m −2 year −1 . Large pools of labile or potentially labile Mn were present in biomass and surficial soil horizons. Small leakages from these large pools likely supply the additional Mn needed to close the watershed mass balance. This leakage may reflect an adjustment of the ecosystem to recent changes in atmospheric acidity.

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