SREL Reprint #2162
Spatial and temporal response of stream bacteria to sources of dissolved organic carbon in a blackwater stream system
PETER KOETSIER III,1 J. VAUN McARTHUR2 AND LAURA G. LEFF3
Savannah River Ecology Laboratory, Division of Wetland Ecology, P.O. Drawer E,
Aiken, SC 29802, U.S.A.
1Present address: Biology Department, 1910 University Drive, Boise State University,
Boise, ID 83725, U.S.A.
2present address: Department of Biological Sciences, PO Box 5190, Kent State
University, Kent, OH 44242, U.S.A.
3author to whom correspondence should be sent
SUMMARY
1. We hypothesized that changes in bacterial colony growth would be correlated
to shifts in riparian vegetation (via leachate quality) along a river continuum of a
south-eastern, blackwater stream (U.S.A.). Spatially, we expected bacterial
assemblages from downstream reaches to utilize more sources of leachate and at
higher concentrations than bacteria collected from headwater reaches.
Temporally, we predicted higher colony growth on leachate from autumn-shed
(senescent) leaves compared with leachate from fresh, green leaves.
2. We examined spatial differences in assemblage growth by culturing bacteria
sampled along the stream continuum on gradient plates using leachates from four
common riparian species (Taxodium distichum, Carya spp., Acer rubrum and
Decumaria barbara). Bacteria from the lowest site were able to use all sources
provided and at all concentrations, whereas bacteria from upper reaches could
not. Colony density was correlated to relative leachate concentration at all sites
along the continuum.
3. Leachates from fresh and senescent A. rubrum leaves were used to
determine temporal differences. Winter assemblages of bacteria could not grow
on fresh leaf leachate at any concentration but grew well on autumn leaf leachate
at higher concentrations. Differential response of bacterial assemblages indicated
local adaptation to potential sources of dissolved organic matter.
4. Growth response of stream bacterial colonies appeared to be dependent on
the timing and source of leachate as well as on sources of dissolved organic
carbon from further upstream. Growth of bacterial assemblages exhibited
'generalist' characteristics in headwater reaches and 'specialist' characteristics at
the mouth of our study stream drainage. Thus, our findings lend support to the
argument that variable resource habitats favour a small, generalist assemblage,
while environments with stable resource supplies allow for highly diverse
assemblages dominated by specialists.
SREL Reprint #2162
Koetsier, P., J.V. McArthur, and L. Leff. 1997. Spatial and temporal response
of stream bacteria to sources of dissolved organic carbon in a blackwater stream
system. Freshwater Biology 37:79-89.
