PARENT SESSION
Oral Session # 61: Biogeochemistry IV: Al, Ca, P, and DOC.
Presiding: R Fitzhugh
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 205.
Relative effects of dissolved organic matter derived from Spartina alterniflora and Phragmites australis on secondary production.
Bushaw-Newton, Karen*,1, Kreeger, Danielle2, Doaty, Sarah1, Velinsky, David2, 1 American University, Washington, DC, USA2 Academy of Natural Sciences, Philadelphia, PA, USA
ABSTRACT- Historically, salt marshes along the mid-Atlantic US have been dominated by Spartina alterniflora, but presently, many of these marshes have been invaded by Phragmites australis. Although, P. australis has high rates of primary production, it is not known whether this species supports a marsh food web in the same manner as S. alterniflora. Using several related photochemical and biological assays, we compared patterns of organic matter flow of plant primary production through a key salt marsh metazoan (Geukensia demissa) using a bacteria intermediate. Whole plants were collected from Delaware Bay salt marshes and grown in the laboratory with either [14C]-CO2 (14C) or [15N]-inorganic N (15N). Bacterial utilization of plant-derived dissolved organic matter (DOM) measured as carbon mineralization (14C), or bacterial production (15N) over time revealed that both types of DOM were available to the natural bacterioplankton, but utilization of Spartina-derived DOM was consistently higher than utilization of Phragmites-derived DOM. For the 14C bioassays, total carbon mineralization after 19 days measured 35 % (+3 S.D.) for the Spartina-treatments compared with 29% (+2, S.D.) for the Phragmites-treatments. When bacteria were fed to mussels, both plant source and sunlight regime yielded significant effects on clearance rates. Mussels cleared Spartina-derived products at 0.38 L h-1 [g dry tissue weight] -1, more than twice that for Phragmites-derived products 0.15 L h-1 [g dry tissue weight]-1. As with the bacterial bioassays, no clear patterns were attributable to sunlight exposure with light positively affecting clearance rates for Phragmites-products but negatively positively affecting clearance rates for Spartina-products. Results from 15N analyses indicate that the level of [15N]-enrichment may not have been high enough to supply mussels with enough isotope to resolve their N budget. Overall, these results suggest the importance of understanding the linkages between primary and secondary production in marsh systems.
Key words: dissolved organic matter, mussels, salt marshes, bacteria