Carbon and nitrogen content of suspended matter in a Hong Kong drainage basin

Abstract

A sampling programme was undertaken to monitor the total carbon (C) and total nitrogen (N) content of suspended matter in a small undisturbed upland drainage basin in the New Territories of Hong Kong. Mean C and N contents were 12.9% and 1.0%, respectively, for 132 samples. Samples collected under stable flow conditions had mean C and N contents of 12.8% and 1.1%, respectively. Stormflow samples had mean C and N values of 12.9% and 1.0%, respectively, which were very similar to the levels observed under stable flow conditions. The mean C:N ratios of 12.5 and 13.4 for stable flow and stormflow also reveal little variation with hydrologic conditions. When all the data is considered, little seasonal variation was observed in C and N. However, in winter there is a significant difference in C and N content between stable and stormflow samples. When C and N are plotted against water level, the scattergraphs suggest that as stage increases the percentage of C and N in the suspended matter declines. Scattergraphs of C and N against suspended sediment concentration reveal a negative association. This may reflect the dominance of inorganic sediments produced by erosion processes during rainfall.