Particulate organic carbon export from a subtropical mountainous river (Lanyang Hsi) in Taiwan

Abstract

Small mountainous rivers have received increasing attention in recent years because of their high yield of sediments and particulate organic matter. A one‐year (1993–1994) study of the fluxes of the total suspended matter (TSM) and particulate organic carbon (POC) in different parts of Lanyang Hsi, a typical small mountainous river in subtropical northeastern Taiwan indicated that the mean TSM and POC yields of the whole drainage area were high (3,600 and 23 g m‒2 yr‒1, respectively) but that the yields of less disturbed (control) tributaries were only 1/30 of the mean yields of the whole area. Radiocarbon analysis by accelerator mass spectrometry gave very old apparent ages (>10,000 yr) to the POC in the main channel, indicating that >70% of the POC produced in the drainage basin was probably derived from kerogen in the bedrock. TSM yields for 1970–1991, calculated from historical records of runoffs and TSM concentrations, showed large fluctuations from year to year; however, the average yield after 1976 (8,335 g m‒2 yr‒1) was higher than that before 1976 (3,127 g m‒2 yr‒1) by a factor of 2.7, suggesting a significant increase in sediment production related to massive road construction in 1975–1980. The average POC yield for 1977–1994 was calculated to be 53 g m‒2 yr‒1. The very high yields of TSM and POC in recent years are attributable to human disturbances.