This study examined the regulation of throughfall flux by six factors: precipitation amount, dry deposition, precipitation acidity, precipitation ion concentrations, forest type, and leaf area index. The influences of these factors were determined by analyzing the spatial and temporal variance in net throughfall flux (throughfall minus precipitation) in the forested landscape of the Hubbard Brook Experimental Forest (White Mountains, New Hampshire, U.S.A.). Throughfall was collected during the growing seasons of 1989–1992 in eight sites encompassing differences in elevation, forest type (including mature northern hardwood, young northern hardwood, and spruce–fir–birch types), and canopy surface area. Regression analysis of single-event data showed that within a forest type, the most important factor regulating the event-to-event variation in net throughfall flux was the amount of precipitation, suggesting that canopy exchange (leaching and uptake) regulated the net throughfall flux for most solutes. The l...