Streamflow strongly influences river ecosystem structure, function, and the services theyprovide. River biota are adapted to regional flow regimes in unmanaged systems, and changes in
land use, climate, and water management alter hydrology in ways that impact ecosystem
function. While prior research has established a strong understanding of river ecosystem
structure and large-scale processes, we know considerably less about the mechanisms through
which river biota affect ecosystem function or how such understanding can inform river
management. This dissertation addresses that knowledge gap using a mid-sized temperate river
in Athens, Georgia, the Middle Oconee River, to evaluate producer-mediated effects of
antecedent flow conditions on stream primary productivity and assessing how modeling
decisions influence ecological inference.
I first examined how antecedent flow affected the biomass and distribution of primary
producer groups, including the foundation species Podostemum ceratophyllum, which is of
conservation concern, in the Middle Oconee River over a three-year period. High and low flows
drove producer biomass and distribution, and sustained drought and floods produced distinct,
producer-specific effects. I then conducted laboratory incubations using producers collected from
the same reach to quantify gross primary productivity and combined these rates with biomass
data to assess each producer’s potential contribution to overall stream productivity. Producers
differed in their mass-specific productivity rates, reflecting variation in their responses to light
availability, and their potential contributions to total productivity varied with biomass dynamics
driven by antecedent flow conditions.
Lastly, I evaluated how key decisions in hydraulic model design and hydrologic
representation influenced ecological inference about habitat provisioning. Higher resolution
models consistently outperformed simpler models, and a complementary approach using time-
weighted and targeted discharge statistics provided the most accurate and comprehensive
depiction of how streamflow variability affects habitat provisioning. The value of increased
modeling investment depended on the risks of uncertainty for a given ecological outcome,
demonstrating the importance of evaluating modeling trade-offs in light of project objectives and
risk tolerance. Collectively, this dissertation establishes producer-mediated effects of antecedent
flow as a mechanism driving variation in stream function and underscores the importance of
incorporating ecological mechanisms into modeling efforts to better inform river management.
