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biodiversity, making them feasible candidates for comprehensive stoichiometric analysis, (3)
differences in plant and invertebrate community composition are associated with variation in
hydrologic characteristics, and (4) streams in this region are likely to experience altered
precipitation patterns-and therefore altered hydrologic regime-due to climate change (Hauer
et al. 1997, Inouye et al. 2000). It is therefore imperative to increase our ability to predict
consequences of climate change-mediated impacts to these benthic systems.
I will examine patterns of hydrologic disturbance and biotic stoichiometry across the East
River watershed. I will work in 10 streams previously detennined to be phosphorus limited
(Moslemi, unpublished data), and that reflect a gradient of hydrologic variability (Peckarsky,
unpublished data).
Characterization of disturbance regime
Together with collaborators at the RMBL, I will characterize the hydrologic regime of the
10 study streams using three indices: (1) discharge variability, (2) potential substrate movement,
and (3) actual substrate movement. Discharge variability will continue to be calculated from
information provided by TruTrack stage height data loggers. Year-round data from loggers will
enable a comparative analysis of magnitude, frequency, duration, timing, and predictability of
high and low flow events among streams (Lytle and Poff 2004), and subsequent classification of
streams on a continuum of stable to highly variable using a principle components analysis (sensu
Taylor and Warren 2001). Actual substrate movement will be measured using a technique
combining photography of stream beds and GIS technology to determine particle movement into
and out of established transects (Peckarsky, unpublished data). Potential substrate movement
will be estimated from tractive force and particle size distributions (sensu Giberson and Caissie
1998, Parker and Huryn 2006).
By using three indices to characterize hydrologic regime I will generate a robust estimate
of relative impacts experienced by benthic communities. If water flow variability were the sole
estimate of disturbance, for example, I may not adequately capture stability of the benthos if
particle size varies between streams. This comprehensive approach and use of novel techniques
will move closer to solving the inherently difficult problem of defining disturbance in streams.
Collection of food web components
Basal resources (algae and detritus) will be collected biweekly for a total of 8 weeks in each
study stream for analysis of stoichiometric composition. I will collect samples at three randomly
chosen transects within each 5Om study reach. Periphyton will be removed from 5 rocks and
algal and detrital fractions separated at each transect. Within the algal fraction, filamentous
algae will be separated from diatoms by creating a density gradient with colloidal silica
following Hamilton et al. (2005). Biomass of primary producers and detritus will be estimated
by measurements of ash-free dry mass, obtained by combusting samples in a muffle furnace at
5000 C (sensu Wallace et al. 2006). I will identify benthic macro invertebrates to species and
estimate densities biweekly using a modified box sampler (D. Hoffman, U. of Wisconsin).
Classifying organisms by species allows for finer detection of stoichiometric differences that
may be lost if lumped into broader categories. I will use established length to mass ratios to
estimate biomass of consumers (Benke et al. 1999). Six samples of each food web component
will be collected for transport to Cornell University where C:N:P ratios will be analyzed using
J. Moslemi; Andrew W. Mellon Research Grant
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