Fog and Soil Weathering as Sources of Nutrients in a California Redwood Forest Holly A. Ewing, Bates College, [email protected]; Kathleen C. Weathers, Cary Institute of Ecosystem Studies, [email protected]; Amanda Lindsey, Cary Institute of Ecosystem Studies, [email protected]; Pamela H. Templer, Boston University, [email protected]; Todd E. Dawson, University of California, Berkeley, [email protected]; Damon Bradbury, University of California, Berkeley, [email protected]; Mary K. Firestone, University of California, Berkeley, [email protected]; Vanessa K.S. Boukili; University of Connecticut, [email protected]. Abstract Fog water deposition is thought to influence the ecological function of many coastal ecosystems, including coastal redwood forests. In California, as in many coastal ecosystems, fog presence is distinctly seasonal and its distribution within and among ecosystems is patchy. As a horizontally driven vector, fog interacts with the structure of the landscape and the ecosystem to create spatial patterns of deposition not seen in the more even distribution of vertically delivered rainwater. We examined spatial and temporal patterns of cation and anion inputs from fog and rain, as well as the fate of these inputs, within a Sonoma County, California, coastal redwood forest to elucidate the availability of these ions and some of the biotic and abiotic processes that may influence their relative abundance. At this site, the spatial patterns of water, chemical inputs and the their movement through the soil-plant ecosystem differed between the summer fog and winter rain seasons. Most (98%) of the annual water and approximately 82% of the total ionic load was delivered to the forest during the rain season. While water inputs were relatively uniform across the forest, the mean daily ionic load was nearly two-fold greater at the edge than in the interior of the forest. During the fog season, the spatial pattern of inputs was markedly asymmetrical across the site: the forest edge received approximately five times more water and more than three times the daily ionic load than the forest interior. Spatial variation was driven both by differences in water inputs (fog season) and in ionic concentration of throughfall (both seasons): the interior of the forest received the most concentrated throughfall in the fog season while the edge throughfall was more concentrated in the rain season. Soil water patterns followed those of throughfall. Water for plant use was most available in the rain season, however, after large fog events (fog season) plant-available soil water was also collected at the forest edge. Differences between soil water and throughfall chemistry were likely to be a function of the mobility of each ion, whether or not an ion was a soil weathering product, and the likely biological demand for the ion. The impact of redwoods as fog catchers, transformers, and redistributors of both water and chemistry may extend all the way into the soil profile: in our plots, soil organic matter content was higher and organic-rich horizons thicker at the forest edge than in the forest interior. Thus, our data suggest that although total fog water inputs were small compared to inputs from rain, fog carried nearly one fifth of the total ionic inputs—inputs that, presumably, continued to be biologically available until their loss during the rain season. Cross-seasonal, functional coupling of above (canopy)- and belowground (soil) processes are likely to be prevalent in this and other fog-inundated redwood forests. .