Using stable isotopes to determine sources of fog drip in a tropical seasonal rain forest of Xishuangbanna, SW China

To identify the possible sources of fog drip, samples of rainfall, fog drip, throughfall, stemflow, stream water, river water, pond water and soil water were collected for 3 years (2002–2004) for stable isotopic analysis, at a tropical seasonal rain forest site in Xishuangbanna, Southwest China. We found that radiation fog is produced mainly through evaporation from pond, river, and soil, and through forest evapotranspiration. The analyses suggest that evaporation from the stream is limited. In addition, radiation fog produced during the dry season (low absolute humidity) contained more terrestrially recycled water than fog produced during the rainy season (high absolute humidity). Forest evapotranspiration appears to be the largest fraction, but a more intense sampling scheme will be needed to assign the relative contribution of the different sources of fog.