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. I n addition, in 1990, soil water and tree water were collected at the e nd of the rainy season, and again at the end of the foggy season to de termine the importance of fog-drip water to arboreal vegetation. The s table isotopic compositions of the collected fog water range from -15. 6 to -9 parts per thousand in delta D and -2.9 to -2.0 parts per thous and in delta(18)O, and are consistently more enriched than the composi tions of the rain, which range from -43 to -30 parts per thousand in d elta D and from -7.6 to -5.8 parts per thousand in delta(18)O. Ground water collected from the Peninsula plots between the fog and rain was about 5 parts per thousand more enriched in D than the rain and 15 par ts per thousand more depleted than the fog. The stable isotopic compos ition of this ground water may reflect the addition of fog-drip water. The isotopic composition of the tree core water indicates varying deg rees 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 e nd of the summer foggy season. At the third location the vegetation ap pears to use solely ground water, which may or may not contain fog wat er.