「Typhoon effects on the variation of DOC inventory
in a P-limited reservoir」
Fuh-Kwo Shiah (
To explore the effects of
typhoon on dissolved organic carbon (DOC) dynamics, field investigations
(tributary and dam-site) and laboratory experiments (bioassay and DOC
degradation) were conducted in a subtropical reservoir. The tributary study (5
stations; monthly sampling, Mar 2004-Jul 2005) indicated that after typhoon
disruption, upstream areas were the sources of phosphate (P) but not DOC for
the dam-site located at downstream. The bioassay experiments verified
P-limitation on bacteria and phytoplankton during the stratified summer and
that bacteria showed faster response than algae to added P. The DOC degradation
experiments indicated that DOC degradation was determined by the availability
of P. The 4-yearsf typhoon period (Jun-Sep) data of the dam-site (depth `100m;
weekly sampling; May 2004`Nov 2007) denoted that DOC stock (27-270μMC) and its changing rates (-13 to 24μMC/d) varied more dramatically in the weak (2006 and
2007) than the strong (2004 and 2005) typhoon years. The negative correlation
of DOC with the ratio of bacterial production (BP) to primary production (PP)
in the euphotic zone (0-10m) signified the
interactive effects of auto- and hetero-trophic
processes on DOC variation. In the aphotic zone, the
variation of DOC could be ascribed to the change of BP, which showed a positive
correlation with P concentrations. This study documents that DOC stock in the
studied system varied at multiple time scales. And such variation can be
explained by the decoupling between BP and PP, which is believed to be a
function of limiting nutrients availability. More importantly, our study
suggests that the P supply introduced by strong typhoons might substantiate a
tighter coupling between BP and PP, so that the amplitude of DOC oscillation
during summer period was effectively reduced.