In this study, we quantified the contribution of mineral tunneling by fungi to weathering of feldspars and ecosystem influx of K and Ca. We studied the surface soils of 11 podzols across a Lake Michigan sand dune chronosequence with soil ages between 450 and 5000 years. Weathering by tunneling was quantified in thin sections by image analysis. Total mineral weathering was quantified by comparing the mineralogy of the surface soil with the underlying parent material was characterized using X-ray fluorescence spectroscopy (XRFS), followed by a non-native mineralogical calculation. Tunnels were observed only in soils older than 1650 years. Throughout the chronosequence the contribution of tunneling to mineral weathering in the upper mineral soil, expressed as tunnel volume divided by volume of weathered feldspars was less then 1%. Contribution of tunneling to Na/Ca-feldspar weathering was higher than the contribution of tunneling to K-feldspar weathering. Feldspar tunneling equals an average ecosystem influx of 0.4 g ha(-1) year(-1) for K and 0.2 g ha(-1) year(-1) for Ca over 5000 years of soil development. Intensity of mineral tunneling, determined as fraction weathered feldspars, was higher than in a previously described North Swedish podzol chronosequence. The presented data suggest that the contribution of tunneling to weathering becomes more important in older soils, but remains low. (C) 2004 Elsevier B.V. All rights reserved.