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Communication at the NABS Annual meeting, Keystone, 2000
(28) PRONOUNCED GRADIENT IN ALGAL ACCUMULATION RATES AMONG RIFFLES OF THE SOUTH FORK EEL RIVER, CALIFORNIA, USA.
C. McNeely and M.E. Power. Dept. of Integrative Biology, Univ. of California, Berkeley, CA 94709
Downstream changes in river ecosystems can be driven by changes in energy sources, physical factors, species distributions, or interactions of such factors. We documented a pronounced gradient in algal accumulation rates among riffles of the South Fork Eel River, Mendocino Co., California, USA. We measured chlorophyll accumulation over 32 days on tiles protected from herbivores in seven riffles along a 6km stream reach. Chlorophyll accumulations reached an asymptote in all riffles during the study. We fit transformed chlorophyll densities to a Michaelis-Menten function. Asymptotic chlorophyll densities did not vary significantly. Half saturation values varied from less than 2 days to 14 days, indicating faster accrual rates over the initial phase of growth downstream. Both accrual rates and asymptotic accumulations of algae vary among productive and unproductive sites in other streams. In our study, higher accumulation rates downstream may be balanced by higher export rates. In this reach, aquatic consumers are supported mainly by algae, and higher renewal rates of this resource are likely to have consequences for trophic and competitive interactions among them. Benthic invertebrate samples collected concurrently with the algal accumulation data will show whether invertebrate grazer biomass and diversity correlate with renewal rates of this resource.
Presented at 1:45 PM on Monday, May 29, 2000 in Spatial and Temporal Variation in Aquatic Communities I
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