Temporal and spatial variations in the discharge and dissolved organic carbon of drip waters in Beijing Shihua Cave, China

To detect the causal relationship between cave drip waters and stalagmite laminae, which have been Used as a climate chan-c proxy, three drip sites in Beijing Shihua Cave were monitored for discharge and dissolved organic carbon (DOC). Drip discharges and DOC were determined at 0 to 14-day intervals over the period 2004-2006. Drip discharges show two types of response to surface precipitation variations: (1) a rapid response; and (2) a time-lagged response. Intra-annual variability in drip discharge is significantly higher than inter-annual variability. The content of DOC in all drip waters varies inter- and intra-annually and has good correlation with drip water discharge at the rapid response sites. High DOC was observed in July and August in the three years observed. The flusing of soil organic matter is dependent upon the intensity of rain events. The DOC content of drip water increases sharply above a threshold rainfall intensity (>50 mm d(-1)) and shows several pulses correspondim, with intense rain events (>25 mm d(-1)). The DOC content was lower and less variable during the dry Period than during the rainy period. The shape of DOC peak also varies front year to year as it is influenced by the intensity and frequency of rainfall. The different drip sites show marked differences in DOC response, which are dominated by hydrological behaviour linked to the recharge of the soil and karst micro-fissure/porosity network. The results explain why not all stalagmite laminae are consistent with climate changes and suggest that the structure of the rainy season events could be preserved in speleothems. Copyright (C) 2008 John Wiley & Sons, Ltd.