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Abstract Assessments of riverine ecosystem health and water quality require knowledge of how headwater streams transport and transform nutrients. Estimates of nutrient demand at the watershed scale are commonly inferred from reach‐scale solute injections, which are typically reported as uptake velocities (vf). Multiple interacting processes controlvf, making it challenging to predict howvfresponds to physical changes in the stream. In this study, we linkvfto a continuous time random walk model to quantify howvfis controlled by in‐stream (velocity, dispersion, and benthic reaction) and hyporheic processes (exchange rate, residence times, and hyporheic reaction). We fit the model to conservative (NaCl) and nitrate (NO3−‐N) pulse tracer injections in unshaded replicate streams at the Notre Dame Linked Experimental Ecosystem Facility, which differed only in substrate size and distribution. Experiments were conducted over the first 25 days of biofilm colonization to examine how the interaction between substrate type and biofilm growth influenced modeled processes andvf. Model fits of benthic reaction rates were ∼8× greater than hyporheic reaction rates for all experiments and did not vary with substrate type or over time. High benthic reactivity was associated with filamentous green algae coverage on the streambed, which dominated total algal biomass. Finally,vfwas most sensitive to benthic reaction rate and stream velocity, and sensitivity varied with stream conditions due to its nonlinear dependence on all modeled processes. Together, these results demonstrate how reach‐scale nutrient demand reflects the relative contributions of biotic and abiotic processes in the benthic layer and the hyporheic zone.
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Biofilm disturbance and tracer particle experiment from Mill Creek in Cleveland, OH
Clay tiles and tracer particles were deployed in Mill Creek in Cleveland, OH to investigate how biofilm and streambed materials respond to high flow events. Ten cross-sectional transects were established evenly across a 100-meter reach where cinderblocks with 16 unglazed clay tiles were buried in the streambed near the deepest part of the channel to promote biofilm growth. Particles of sizes corresponding to the 50th, 75th, and 90th percentile of the substrate size classes at each transect were painted and numbered for use as tracer particles. Samples from the tiles were collected after each high-flow event and measured their biomass using chlorophyll a (chla) and ash-free dry mass (AFDM). Movement of tracer particles (yes/no) was recorded to estimate how much of the streambed moved.
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- Award ID(s):
- 1805319
- PAR ID:
- 10629621
- Publisher / Repository:
- HydroShare
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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