The importance of fog-drip water to vegetation: Point Reyes Peninsula, California

Fog and rain were collected for stable isotopic analysis for nearly 4 years at three locations on the Point Reyes Peninsula in California. In addition, in 1990, soil water and tree water were collected at the end of the rainy season, and again at the end of the foggy season to determine the importance of fog-drip water to arboreal vegetation. The stable isotopic compositions of the collected fog water range from −15.6 to −9‰ in δD and −2.9 to −2.0‰ in δ 18O, and are consistently more enriched than the compositions of the rain, which range from −43 to −30‰ in δD and from −7.6 to −5.8‰ in δ 18O. Ground water collected from the Peninsula plots between the fog and rain was about 5‰ more enriched in D than the rain and 15‰ more depleted than the fog. The stable isotopic composition of this ground water may reflect the addition of fog-drip water. The isotopic composition of the tree core water indicates varying degrees of fog water use by the arboreal vegetation. At the most coastal location, the vegetation appears to use fog-drip water year-round. At another location, the use is seasonal, occurring at least during the end of the summer foggy season. At the third location the vegetation appears to use solely ground water, which may or may not contain fog water.