Sources, bioavailability, and photoreactivity of dissolved organic carbon in the Sacramento-San Joaquin River Delta
RAMUNAS STEPANAUSKAS1*, MARY ANN MORAN1,
BRIAN A. BERGAMASCHI2 and JAMES T. HOLLIBAUGH1
1Department of Marine Sciences, University of
Georgia, Athens, GA 30602-3636, USA;
2US Geological Survey, Placer Hall M/S 6129,6000 J Street,
Sacramento, CA 95819-6129, USA;
*Author for crrespondence: Present address: Savannah River
Ecology Laboratory, Drawer E, Aiken, SC 29802, USA (e-mail: ramunas@uga.edu;
phone: + 18037252752; fax: +18037253309)
Received 2 February 2004; accepted in revised form 16 September 2004
Key words: Bacterioplankton, Dissolved organic carbon,
DOC bioavailability, Photodegradation, Sacramento-San Joaquin River Delta,
San Francisco Bay, Solar radiation
Abstract. We analyzed bioavailability, photoreactivity,
fluorescence, and isotopic composition of dissolved organic carbon (DOC)
collected at 13 stations in the Sacramento-San Joaquin River Delta during
various seasons to estimate the persistence of DOC from diverse shallow
water habitat sources. Prospective large-scale wetland restorations in
the Delta may change the amount of DOC available to the food web as well
as change the quality of Delta water exported for municipal use.Our study
indicates that DOC contributed by Delta sources is relatively refractory
and likely mostly the dissolved remnants of vascular plant material from
degrading soils and tidal marshes rather than phytoplankton production.
Therefore, the prospective conversion of agricultural land into submerged,
phytoplankton-dominated habitats may reduce the undesired export of DOC
from the Delta to municipal users.A median of 10% of Delta DOC was rapidly
utilizable by bacterioplankton. A moderate dose of simulated solar radiation
(286 W m-2 for 4 h) decreased the DOC bioavailability by an
average of 40%, with a larger relative decrease in samples with higher
initial DOC hioavailability. Potentially, a DOC-based microbial food web
could support ‹ 0.6 x 109 g C of protist production in
the Delta annually, compared to ~17 x 109 g C phytoplankton
primary production. Thus, DOC utilization via the microbial food web is
unlikely to play an important role in the nutrition of Delta zooplankton
and fish, and the possible decrease in DOC concentration due to wetland
restoration is unlikely to have a direct effect on Delta fish productivity.
SREL Reprint #2874
Stepanauskas, R., M. A. Moran, B. A. Bergamaschi and J. T. Hollibaugh. 2005. Sources, bioavailability, and photoreactivity of dissolved organic carbon in the Sacramento?San Joaquin River Delta. Biogeochemistry 74:131-149.
