The main objective of this
research project is to
understand how stream network position influences spatial patterns in
the
feedbacks between multiple nutrient cycles, stream metabolism, and
consumer-resource interactions. This
research is a natural extension of previous work on food web controls
on algal
productivity and pathways of energy flow in the South Fork Eel
watershed (see the Angelo Coast
Range Reserve and the Power
Lab for more information) to
include feedbacks between these interactions and downstream propagation
of
their effects on biogeochemical cycling.
In essence, we ask where and when are biotic interactions and
biological
stoichiometry important determinants of nutrient transport and
retention in
river networks, and what are the consequences for downstream
communities? Recent
theory
addressing consumer-driven nutrient recycling suggests that shifts in
elemental
content of consumers are driven in part by resource availability and in
part by
the emergence of specific life history traits in response to changing
environmental conditions along gradients of physical variables. The effects of shifts in stoichiometric
imbalance between consumers and resources on nutrient spiraling have
yet to be
studied. We believe this to be an
exciting frontier in the study of stream ecosystems.
The proposed work will contribute to the development of these
ideas by establishing 1) empirical relationships between stoichiometric
imbalances and changing environmental conditions along a drainage area
gradient
in a river network; and 2) experimental determination of the effects of
stoichiometric imbalance in consumer-resource interactions on nutrient
spiraling.
We
will use spiraling as a tool to examine feedbacks between stream
metabolism,
consumer-resource interactions and biogeochemical cycling at plot and
reach
scales at several network positions and during algal succession. We will measure uptake length and net
retention of nitrogen (N) and phosphorus (P) over reach scales at
different
channel network positions. These
measurements will reveal changes in nutrient uptake and regeneration
with
changes in network position, light and temperature.
On smaller (1-10 m) scales, we will manipulate algal and
detrital
biomass, consumer densities, and stoichiometric imbalances to determine
their
individual and interactive effects on uptake rate.
We will ultimately use these measurements to estimate
whole-system effects of changes in algal and detrital biomass and
consumer-resource interactions on spiraling of multiple nutrients by
exploring
their specific effects on nutrient uptake and regeneration.
For more information
on Biological Stoichiometry, including many references click here